Triclosan: environmental exposure, toxicity
and mechanisms of action
Andrea B. Dann and Alice Hontela*
ABSTRACT: Triclosan [5‐chloro‐2‐(2,4‐dichlorophenoxy)phenol; TCS] is a broad spectrum antibacterial agent used in personal
care, veterinary, industrial and household products. TCS is commonly detected in aquatic ecosystems, as it is only partially
removed during the wastewater treatment process. Sorption, biodegradation and photolytic degradation mitigate the
availability of TCS to aquatic biota; however the by‐products such as methyltriclosan and other chlorinated phenols may be
more resistant to degradation and have higher toxicity than the parent compound. The continuous exposure of aquatic
organisms to TCS, coupled with its bioaccumulation potential, have led to detectable levels of the antimicrobial in a number of
aquatic species. TCS has been also detected in breast milk, urine and plasma, with levels of TCS in the blood correlating with
consumer use patterns of the antimicrobial. Mammalian systemic toxicity studies indicate that TCS is neither acutely toxic,
mutagenic, carcinogenic, nor a developmental toxicant. Recently, however, concern has been raised over TCS’s potential for
endocrine disruption, as the antimicrobial has been shown to disrupt thyroid hormone homeostasis and possibly the
reproductive axis. Moreover, there is strong evidence that aquatic species such as algae, invertebrates and certain types of
fish are much more sensitive to TCS than mammals. TCS is highly toxic to algae and exerts reproductive and developmental
effects in some fish. The potential for endocrine disruption and antibiotic cross‐resistance highlights the importance of the
judicious use of TCS, whereby the use of TCS should be limited to applications where it has been shown to be effective.
Copyright © 2011 John Wiley & Sons, Ltd.
Keywords: triclosan; irgasan; review; levels; exposure; effects; toxicity; aquatic species; mammals; human; endocrine disruption;
reproduction
BACKGROUND
Triclosan [5‐chloro‐2‐(2,4‐dichlorophenoxy)phenol: TCS], a
halogenated phenol, is a nonionic, broad spectrum antimicrobial
used throughout North America, Europe and Asia,
as an ingredient in disinfectants, soap, detergent, tooth‐
paste, mouthwash, fabric, deodorant, shampoo and plastic
additives, in addition to innumerable other personal care,
veterinary, industrial and household products. TCS is effective
against many types of bacteria and certain types of fungi,
preventing bacterial propagation and/or eventually resulting
in cell death. It permeates the bacterial cell wall and targets
multiple cytoplasmic and membrane sites, including RNA
synthesis and the production of marcomolecules (Russell,
2004). TCS also blocks synthesis of fatty acids through
inhibition of enoyl reductase, but has no effect on bacterial
spores (McMurry et al., 1998; Levy et al., 1999; Russell, 2004).
TCS may be classified as a halogenated aromatic hydrocarbon,
containing phenol, diphenyl ether and polychlorinated
biphenyl functional groups (Ahn et al., 2008). The chemical
structure of TCS (Fig. 1), a halogenated biphenyl ether, is
similar to polychlorinated biphenyls (PCBs), polybrominated
diphenyl ethers (PBDEs), bispenol A, dioxins and thyroid
hormones (Veldhoen et al., 2006; Crofton et al., 2007; Allmyr
et al., 2008), molecules with two aromatic rings.
TCS was invented over 40 years ago and has been used
increasingly over the past 25 years (Jones et al., 2000; Russell,
2004). In the period from 1992 to 1999, a majority of the 700
antibacterial products on the market contained TCS as an
active ingredient (Schweizer, 2001). TCS is the generic name
for the chemical, with brand names including Irgasan DP300,
Aquasept, Sapoderm and Ster‐Zac. Fibres and other materials
that have TCS incorporated into them may be referred to as
Ultra‐Fresh, Amicor, Microban, Monolith, Bactonix and Sanitized
(Adolfsson‐Erici et al., 2002). The antimicrobial has the
capability to migrate from treated surfaces into foodstuffs.
Notwithstanding, the addition of TCS to food coverings and
surfaces that are in contact with food during processing is
currently being considered (Canosa et al., 2008). However, in
March 2010, TCS was removed from the EU list of provisional
additives for use in plastic food‐contact materials.
Unlike some other organochlorine compounds, the use of TCS
is not highly regulated, as the antimicrobial has a low acute
toxicity and is generally accepted as well tolerated and safe
(Jones et al., 2000; Rodricks et al., 2010). Concentrations of TCS in
personal care products are typically in the range of 0.1–0.3% of
product weight (Sabaliunas et al., 2003), with significant
amounts of the antimicrobial entering wastewater treatment
facilities (Table 1). The prevalence of TCS in waterways is likely to
increase as consumer demand for antimicrobial products is
anticipated to grow. TCS is being increasingly scrutinized after
*Correspondence to: A. Hontela, Department of Biological Sciences, Alberta
Water and Environmental Science Bldg, 4401 University Dr. W., University of
Lethbridge, Lethbridge, Alberta, Canada T1K 3M4.
E‐mail: alice.hontela@uleth.ca
Department of Biological Sciences, Alberta Water and Environmental Science
Bldg, 4401 University Dr. W., University of Lethbridge, Lethbridge, Alberta,
Canada T1K 3M4
J. Appl. Toxicol. 2011; 31: 285–311 Copyright © 2011 John Wiley & Sons, Ltd.
Review
Received: 23 September 2010, Revised: 25 December 2010, Accepted: 25 December 2010 Published online in Wiley Online Library: 1 April 2011
(wileyonlinelibrary.com) DOI 10.1002/jat.1660
285
concerns emerged that the product might be harmful to human
health and the environment. TCS has been detected in surface
water, sediment, biosolids, soils, aquatic species and humans
(Chu and Metcalfe, 2007; Chalew and Halden, 2009; Reiss et al.,
2009). Potential health issues surrounding the use of TCS include
antibiotic resistance, skin irritations, endocrine disruption,
increasing rates of allergies and the formation of carcinogenic
by‐products (Schweizer, 2001; Adolfsson‐Erici et al., 2002; Latch
et al., 2003), yet a recent review by Rodricks et al. (2010)
concluded that exposure to TCS in consumer products is not
expected to cause adverse health effects in children or adults
who use the products as intended.
Despite the widespread use of TCS, few independently
published studies have investigated the emerging health concerns
surrounding the use of this antimicrobial and the environmental
impact it may have. Previous reviews of TCS have focused primarily
on its toxicity in laboratory animals and humans, its fate in the
environment, or its link to antibiotic cross‐resistance. The objective
of this review is to provide a comprehensive review of the literature
on TCS, its occurrence in aquatic and terrestrial environments,
exposure levels in humans and wildlife, including aquatic species,
its toxicity and endocrine disrupting potential.
IDENTITY, PHYSICAL AND CHEMICAL
PROPERTIES, MANUFACTURE AND USE
Identity, Physical and Chemical Properties
Triclosan (CAS registration number 3380‐34‐5), is a diphenyl ether
and may be referred to as 5‐chloro‐2‐(2,4‐dichlorophenoxy)
phenol or 2,4,4′‐trichloro‐2′‐hydroxydiphenyl ether. The molecular
formula for TCS is C12H7Cl3O2 and the chemical has a
molecular weight of 289.55. Most commercially obtained grades
of TCS are over 99% pure and are available in the solid form as a
white to off‐white crystalline powder with a barely detectable
aromatic odor. TCS is a stable compound with a boiling point
between 280‐290 °C, and a melting point between 54 and 57 °C.
The thermal stability of TCS is why certain manufacturers have
chosen the antimicrobial for the incorporation into plastics and
fibers. The octanol–water partition coefficient (log Kow) of TCS is
4.76; it is not readily soluble in water (10 mg l−1
at 20 °C),
although solubility increases as the pH becomes more alkaline.
TCS is, however, easily dissolved in a wide array of organic
solvents (Bhargava and Leonard, 1996).
In aquatic ecosystems, the majority of TCS exists in the ionized
form (Orvos et al., 2002) and it is primarily the un‐ionized form
that is responsible for the majority of TCS’s toxic effects. The
half‐life of TCS in surface water is approximately 41 min, with
most of the parent compound converting to 2,4‐dichlorophenol,
although degradation rates vary considerably across aquatic
ecosystems (Reiss et al., 2002; Lyndall et al., 2010).
Manufacture and Use
During the synthesis of TCS, a chlorinated phenoxyphenol,
the potential for contamination with toxic impurities exists. Beck
et al. (1989) reported trace amounts of lower chlorinated
dibenzodioxins and furans in Irgasan DP300, but not in excess
of the μg kg−1
range, leading to the conclusion that presence of
these compounds in TCS is of little concern. Low levels of dioxins
and dibenzofurans may be present as unwanted by‐products,
depending on the quality of the initial materials used to synthesize
TCS, as well as manufacturing conditions such as temperature
and pressure (Ni et al., 2005). The US EPA considers that TCS may
be potentially contaminated with dioxins, with the EU, Canada
and the USA having taken initiatives to set standards for
maximum permissible levels of impurities in this compound.
Between 1992 and 1999, over 700 antibacterial products, the
majority of which contained TCS, entered the consumer market.
Personal care products are the most common form of exposure
to the antimicrobial, typically at concentrations of 0.1–0.3%,
levels which are regulated by the European Community
Cosmetic Directive or the US Food and Drug Agency (USFDA)
in Europe and the USA, respectively (Sabaliunas et al., 2003;
Rodricks et al., 2010). In Sweden, 25% of toothpaste brands
contain TCS, which translates into 2 tons of TCS consumption
per year. Soaps, deodorants and other personal care products
account for another 300 kg of the chemical in Sweden alone
(Adolfsson‐Erici et al., 2002). On the global front, the production
of TCS has now exceeded 1500 tons per year, with Europe
being responsible for 350 tons of total production (Singer
et al., 2002). As public concern over the transmission of disease
is heightened, the use of antimicrobials is anticipated to
increase. TCS will continue to be an environmental pollutant
that warrants monitoring, especially since its transformation
products are not yet fully understood.
ENVIRONMENTAL EXPOSURE
Occurrence in the Aquatic Environment
Triclosan
The antimicrobial TCS is commonly detected in aquatic
ecosystems (Table 1; Capdevielle et al., 2008; Chalew and
Triclosan Bisphenol-A
Diethylstilbestrol
Thyroxine
Figure 1. The structural similarity of TCS to Bisphenol A, Diethylstilbestrol, and the thyroid hormone thyroxine.
A. B. Dann and A. Hontela
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Halden, 2009; Lyndall et al., 2010). The majority (96%) of
consumer products containing TCS are eventually rinsed down
the drain (Reiss et al., 2002) and discharged with wastewater
effluent. Although wastewater treatment plants (WWTP) are
generally highly effective in removing TCS, a small percentage of
the antimicrobial is usually discharged with effluent into
receiving waters, usually a river system (Morrall et al., 2004;
Nakada et al. 2008). The efficiency of TCS removal can be highly
variable, with elimination rates ranging from complete removal
to 100% ineffective (Kanda et al., 2003; Heidler and Halden, 2007).
Table 1. Concentrations of triclosan (TCS) in the aquatic environment
Medium Sample description Location Concentration of TCS Reference
Surface water Natural streams/rivers USA NDa
to 2.3 μg l−1
Kolpin et al. (2002);
Morrall et al. (2004)
Switzerland ND to 0.074 μg l−1
Lindström et al. (2002)
Germany ND to 0.01 μg l−1
Bester (2005)
Sweden ND Bendz et al. (2005)
Australia 0.075 μg l−1
Ying et al. (2007)
Japan <0.0006–0.059 μg l−1
Nakada et al. (2008)
Streams with inputs
of raw wastewater
Switzerland 0.011–0.098 μg l−1
Singer et al. (2002)
USA 1.6 μg l−1
Halden and Paull (2005)
Estuarine waters USA 0.0075 μg l−1
Fair et al. (2009)
Sediment Freshwater Switzerland 53 μg kg−1
Singer et al. (2002)
Spain ND to 35.7 μg kg−1
Morales et al. (2005)
Estuarine USA ND to 800 μg kg−1
Miller et al. (2008)
Marine Spain 0.27–130.7 μg kg−1
Agüera et al. (2003)
Sewage sludge Activated sludge USA 0.5–15.6 μg g−1
McAvoy et al. (2002)
Spain 0.4–5.4 μg g−1
Morales et al. (2005)
Germany 1.2 μg g−1
Bester (2003)
Canada 0.62–1.45 μg g−1
Chu and Metcalfe (2007)
Biosolids Australia 90–16 790 μg kg−1
Ying and Kookana (2007)
USA 10 500–30 000 μg kg−1
Kinney et al. (2008);
Heidler and Halden (2007)
Spain 1508 μg kg−1
Morales et al. (2005)
Canada 680–12 500 μg kg−1
Lee and Peart (2002);
Chu and Metcalfe (2007)
WWTP influent In‐flowing waste water USA 2.70–26.80 μg l−1
McAvoy et al. (2002);
Halden and Paull (2005);
Heidler and Halden (2007);
Fair et al. (2009)
Canada 0.01–4.01 μg l−1
Lishman et al. (2006)
Germany 1.2 μg l−1
Bester (2003)
Sweden 0.38 μg l−1
Bendz et al. (2005)
Japan 2.7–11.9 μg l−1
Nakada et al. (2010)
WWTP effluent Treated water Switzerland 0.042–0.213 μg l−1
Singer et al. (2002)
Germany 0.01–0.6 μg l−1
Bester (2003, 2005)
Canada 0.01–0.324 μg l−1
Lishman et al. (2006)
USA 0.03–2.7 μg l−1
McAvoy et al. (2002);
Heidler and Halden (2007);
Halden and Paull (2005);
Fair et al. (2009)
UK 0.34–3.1 μg l−1
Kanda et al. (2003);
Sabaliunas et al. (2003)
Australia 0.023–0.434 μg l−1
Ying and Kookana (2007)
Sweden 0.16 μg l−1
Bendz et al. (2005)
Japan 0.26–0.27 μg l−1
Nakada et al. (2010)
a
ND, not detectable.
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The variability in removal rates for TCS is due in part to
different treatment processes, as the antimicrobial is readily
degraded in aerobic conditions but not under anaerobic
conditions (McAvoy et al., 2002). Field measurements from a
Swiss WWTP have detailed the elimination process of TCS: 79%
was biologically degraded, 15% was sorbed to sludge and 6%
left the plant in the final effluent at a concentration of 42 ng l−1
(Singer et al., 2002; Table 1). These results are consistent with
tests conducted at several WWTPs in Germany, where 4–10% of
TCS remained dissolved in out‐flowing water (Bester, 2003).
Generally, WWTP influent concentrations of the antimicrobial
range from 1.86 to 26.8 μg l−1
, with effluent concentrations
ranging from 0.027 to 2.7 μg l−1
(Morrall et al., 2004; Chalew and
Halden, 2009; Nakada et al. 2010). In the period from 1999 to
2000, the US Geological Survey detected TCS in 57.6% of
streams and rivers sampled, at concentrations ranging from
below the detection limit up to 2.3 μg l−1
(Kolpin et al., 2002). In
addition to the incomplete removal from WWTP effluent, the
antimicrobial exhibits a tendency to accumulate and persist in
biosolids; it is estimated that up to 50% of TCS in WWTP
influent will remain in biosolids in WWTPs which utilize
activated sludge treatments in combination with anaerobic
biosolid digestion (Heidler and Halden, 2007; Chalew and
Halden, 2009; Lozano et al., 2010). The TCS removal capacities
of various sorbents, including activated charcoal and kaolinite,
and the effects of pH, ionic strength and humic acid on the
sorptive interactions have been investigated (Behera et al.
2010). Organic matter content was a major factor controlling
the sorption of TCS. The occurence of TCS and other organic
contaminants has been reported in Canadian municipal
sewage sludge and biosolids samples (Lee and Peart, 2002;
Chu and Metcalfe, 2007; Mackay and Barnthouse, 2010;
Table 1). Thus the two main sources of TCS release into the
environment are: (1) discharge of WWTP effluent into receiving
waters; and (2) land application of biosolids containing
residues of the antimicrobial.
A multitude of factors influence TCS concentrations in aquatic
systems, including the TCS load in effluent, physical and
chemical properties of TCS, characteristics of the aquatic
ecosystem (pH, sediment density and organic matter content,
water flow and velocity, depth), and even season and intensity
of sunlight (Reiss et al., 2002; Trixier et al., 2002; Lyndall et al.,
2010). TCS has been measured not only in surface waters, but
also in freshwater and estuarine sediment, at concentrations up
to 800 μg kg−1
(Miller et al., 2008; Chalew and Halden, 2009;
Table 1). Monitoring TCS concentrations in surface water is
important, as the antimicrobial has demonstrated a propensity
for bioaccumulation in aquatic species (Balmer et al., 2004) and
can persist in aquatic ecosystems for extended periods of time.
The antimicrobial has been measured in 30‐year‐old sediment
from lake Greifensee in Switzerland (Singer et al., 2002). This
study provided evidence of the persistence of TCS in sediment
and detailed the pattern of use of TCS. TCS concentrations in
sediment increased between the early 1960s until the mid‐
1970s, reflecting steadily increasing patterns of use, then a
reverse in this trend was observed from the mid‐1970s until the
early 1980s, when a new process of wastewater treatment was
introduced into most WWTPs. Increases in TCS concentrations
occurred again from the early 1980s until the present time.
Similar depth–time profiles for TCS spanning last 40 years were
reported by Miller et al. (2008) for estuarine sediments in the
USA. The environmental persistence of TCS in sediment is
indicative of the antimicrobial’s potential to partition into
sediment and resist degradation processes under anaerobic
conditions. Buth et al. (2009) chronicled the historical pattern of
dioxin photoproducts of TCS and its chlorinated derivatives in
sediment cores from the Mississippi river. Between 1963 and
2008, TCS levels markedly increased, corresponding to increases
in the concentration of several chlorinated derivatives of TCS
(CTDs), including dichlorodibenzo‐p‐dioxin (2,8‐DCDD), a direct
transformation product of the photolysis of TCS. A further
source of TCS derived dioxins comes from the solar irradiation
of CTDs, leading to the formation of higher level chlorinated
dioxins.
Degradation Products of TCS
Methyltriclosan
During the wastewater treatment process, TCS is transformed
by biological methylation into methyltriclosan [MTCS; 5‐
chloro‐2‐(2,4 dichloropheoxy)anisole; CAS no. 4640‐01‐1]
(Boehmer et al., 2004; Bester, 2005), a more lipophilic
compound (Kow 5.2), which is then released into receiving
waters. The presence of MTCS in fish has in fact been
proposed for use as marker of exposure to WWTP effluent,
specifically to lipophilic WWTP contaminants (Balmer et al.,
2004). The lipophilicity of MTCS and its resistance to
biodegradation processes and photolysis (Lindström et al.,
2002) makes this metabolite exhibit a higher degree of
environmental persistence than its parent compound.
Dioxins
Over the last decade there has been increasing concern
regarding the degradation products of TCS, most notably
dioxins, and consequently, the transformation of TCS during
manufacturing, incineration and in the aquatic environment.
The photolysis of TCS constitutes the principal removal
pathway of the antimicrobial in the aquatic environment, with
some studies having documented the formation of 2,8‐
dichlorodibenzodioxin (DCDD) and other dioxin derivatives
during the photodegradation of TCS in aqueous solutions
(Latch et al., 2003; Mezcua et al., 2004; Lores et al., 2005;
Sanchez‐Prado et al., 2006; Aranami and Readman, 2007).
There is evidence that the pH of aqueous solutions spiked with
TCS influences the formation of dioxin by‐products. Latch et al.
(2003) reported that 1–12% of TCS is converted to DCDD in
aqueous solutions buffered at a pH 8 or higher. Considering that
the pKa of TCS is 7.9, it is probable that the dissociated form of TCS
is the photoreactive species, potentially explaining why DCDD
was not observed in experiments using methanol solutions
spiked with TCS (Latch et al., 2003). From this study, it is apparent
that, in sunlight‐irradiated waters, the conversion of TCS into
dioxin by‐products is dependent on both the pH and the
irradiation wavelength. The findings of Latch et al. (2003) were
confirmed by Mezcua et al. (2004), who were the first to
investigate the photodegradation of TCS to dioxins in
wastewater samples. The study indicated that 2,7/2,
8‐dibenzodichloro‐p‐dioxin is indeed a by‐product of the
photolysis of TCS, in both water and wastewater samples
spiked with 8 μg ml−1
of the antimicrobial. The degree of
photolytic conversion was dependent upon pH and the organic
matter content in the sample. Sanchez‐Prado et al. (2006) were
the first to use a solar simulator photoreactor, in conjunction
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with actual contaminated wastewater samples, identifying the
formation of 2,8‐DCDD and a possible DCDD isomer or
dichlorohydroxydibenzofuran independently of sample pH.
Aranami and Readman (2007) irradiated freshwater and
seawater samples with a low‐intensity artificial white light
source for a 12 day period. Similar to previous studies, the
photodegradation of TCS produced DCDD, in both freshwater
and seawater samples, after 3 days of irradiation.
The photochemical conversion of TCS in natural water
samples, specifically Mississippi River and Lake Josephine
waters, was investigated by Buth et al. (2009). The photolysis
of the antimicrobial was dependent on speciation, with the
phenolate form of TCS being degraded 44–586 times faster than
the phenol form. The conversion of chlorinated TCS derivatives
into dioxins was substantiated in natural and buffered pure
water, with yields of 0.5–2.5%, respectively. The majority of TCS’s
photolytic transformation products and their kinetics, along with
the environmental factors influencing their degradation, have
yet to be identified (Aranami and Readman, 2007). Of great
importance in quantifying the level of risk to both aquatic
environments and humans is determining to what extent and
under which environmental conditions the conversion of TCS
into toxic by‐products occurs.
Chlorophenols
Dioxins are not the only toxic transformation product of TCS
that warrants further study. The photochemical transformation
of TCS has also been shown to produce 2,4‐dichlorophenol and
2,4,6‐trichlorophenol, chemicals which the US EPA has flagged
as priority pollutants. The generation of chlorophenols from TCS
was originally demonstrated by Kanetoshi et al. (1987); however,
the study used high concentrations of chlorine and TCS, calling
into question the environmental relevance of the findings. Later
studies validated the finding that chlorophenols are transformation
products of TCS, even in the presence of low levels of
chlorine or chloramines (Rule et al., 2005; Canosa et al., 2005;
Greyshock and Vikesland, 2006). TCS reacted with free chlorine
under drinking water conditions and 2,4‐dichlorophenol was
formed via the ether cleavage of TCS, which then underwent
electrophilic substitution to form 2,4,6‐trichlorophenol. Consistent
with other studies, based on the effect of pH on the
formation of TCS by‐products, Rule et al. (2005) concluded that
it was primarily the ionized phenolate form of TCS that reacts
with hypochlorous acid. Canosa et al. (2005) tested low
concentrations of both TCS (ng ml−1
) and chlorine (mg l−1
and less), and consistently detected 2,4‐dichlorophenol and
2,4,6‐trichlorophenol in all of the samples analyzed. Even though
the molar yields of TCS conversion were <10%, these findings
are significant, as it has been demonstrated that these two
phenolic by‐products are relatively stable over time and
potentially toxic (Canosa et al., 2005). The formation of chlorophenols
from the degradation of TCS has been confirmed by others
(Sanchez‐Prado et al., 2006; Latch et al., 2005; Fiss et al., 2007).
Chloroform
There is evidence that, like other phenols, TCS in water or in
various consumer products will react with free chlorine or
chloramine to produce chloroform and other chlorinated
products over a range of pHs (Rule et al., 2005; Greyshock and
Vikesland, 2006; Fiss et al., 2007). Rule et al. (2005) also assessed
the propensity of a dish soap containing TCS to form chloroform
when added to chlorinated water. After 5 min, 15 μg l−1
of
chloroform was produced, with chloroform levels attaining 49 μg
l−1
after 120 min. Based on the results of this study, while it is
unlikely that significant amounts of chloroform are generated
from TCS in surface waters, chloroform may be formed during the
daily use of household products containing the antimicrobial.
The conversion of TCS to chlorinated derivatives is also
dependent on temperature, with higher temperatures resulting
in increased chloroform yields (Fiss et al., 2007). An exposure
model completed by the authors indicated that, under certain
conditions, the amount of chloroform produced could be
significant, and where chloroform formation is inconsequential,
other chlorinated by‐products are produced, which may place
consumers at an increased risk for adverse health effects.
Exposure to Triclosan and its Degradation Products in
Aquatic Organisms
Algae and invertebrates
The incomplete removal of TCS during the wastewater treatment
process leads to the continual exposure of aquatic biota in
receiving waters, and the accumulation of the antimicrobial and
its degradation products in tissues of aquatic organisms
(Table 2). Algae, a primary food source for many aquatic species,
constitute an important pathway for the accumulation of
lipophilic water‐borne contaminants, such as TCS (Capdevielle
et al., 2008). Coogan et al. (2007) sampled the filamentous algae
(Cladophora spp.) in a receiving stream for the city of Denton
(Texas) for TCS and MTCS, measuring 100–150 and 50–89 μg
kg−1
, respectively. From these measurements, bioaccumulation
factors of 1600 and 1100 were estimated for the parent
compound and its methylated by‐product. The bioaccumulation
potential of TCS and MTCS was also determined in freshwater
snails (Helisoma trivolvis) and again in algae (Cladophora spp.),
using isotope dilution GC‐MS (Coogan and La Point, 2008).
Bioaccumulation factors for snail tissue were 500 and 1200 for
TCS and MTCS, respectively. The algal bioaccumulation factors
were also high, 1400 and 1200, respectively. The occurrence and
formation of TCS metabolites was also investigated in estuarine
systems. In a study by DeLorenzo et al. (2008), adult grass shrimp
(Palaemonetes pugio) were exposed to 100 μg l−1
of TCS and,
even though TCS was not measured, they were found to
accumulate MTCS after a 14‐day exposure period. This finding
provides evidence for both the conversion of TCS to MTCS in
seawater, and of the bioaccumulation potential of the metabolite
in aquatic organisms. Yet, even though MTCS is resistant to
biodegradation processes and has demonstrated the ability to
persist in the environment for longer periods of time than the
parent compound, it has received considerably less attention in
the literature. As snails and other aquatic invertebrates depend
on algae as a source of nutrients, and considering the ubiquity of
TCS in the aquatic environment, it is probable that grazed algal
compartments will contain TCS and MTCS, potentially making
these compounds available to higher aquatic organisms.
Fish
In addition to invertebrates, TCS and its transformation products
have been detected in higher level aquatic organisms, most
notably fish (Table 2). Miyazaki et al. (1984) was the first to
report the presence of MTCS in aquatic biota. Fish and shellfish
were collected from the Tama River and Tokyo Bay, and MCTS
was identified by GC/MS in all of the freshwater fish samples
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(1–38 μg kg−1
whole body) and three of the four shellfish
samples (3–20 μg kg−1
). A well‐cited study by Adolfsson‐Erici et al.
(2002) measured TCS levels in rainbow trout (Oncorhynchus
mykiss) caged in the receiving waters of a WWTP in Sweden, in
wild fish living downstream from the plant and in rainbow
trout exposed to treated water in tanks. Bile fluid from
the fish contained TCS at concentrations ranging from
<0.01–0.08 mg kg−1
fresh weight in controls and fish sampled
at reference sites, and 0.44–120 mg kg−1
in fish exposed to
sewage water. Houtman et al. (2004) also used GC/MS to
identify a multitude of xenobiotic compounds, including TCS,
in the bile of male bream (Abramis brama) living in Dutch
surface waters. TCS was detected in two of the three
locations sampled, at relatively high concentrations of 14
and 80 μg ml−1
of bile. The results of these two studies
provide evidence for the accumulation of TCS in the bile of
fish. Other European studies have reported TCS and its
derivatives in fish tissues. Buser et al. (2006) analyzed levels of
MTCS in juvenile (1–2 year old) brown trout (Salmo trutta
fario) from rivers in Northern Switzerland receiving effluent
from WWTPs. Concentrations of MTCS in fish were reported
between 130 and 2100 ng g−1
of lipid weight. Balmer et al.
(2004) detected MTCS in lake fish in the range 4–370 ng g−1
,
lower levels compared with those previously measured in fish
samples from rivers. This difference is to be expected as
concentrations of MTCS should typically be higher in river
systems that receive inputs from WWTPs. A large monitoring
study on TCS and MTCS was conducted by Boehmer et al.
(2004) using fish tissues from the German Environmental
Specimen Bank. Samples of muscle tissue from breams
(Abramis brama) from the period 1994–2003 were analyzed
for TCS and MTCS. While TCS was only detected in a small
number of samples, MTCS was present in all of the muscle
samples analyzed. A pattern of increasing MTCS concentrations
was observed in bream muscle tissue from the mid
1990s until after 2000, with levels of MTCS increasing from 10
to 14–26 ng g−1
of wet weight. TCS concentrations ranged
from below the limit of quantification up to 3.4 ng g−1
. From
their retrospective monitoring data, the authors of the study
concluded that MTCS is a persistent pollutant with the
potential to accumulate in the muscle tissue of fish.
To date, only a few North American studies have monitored
TCS and MTCS levels in freshwater fish (Table 2). Valters et al.
(2005) detected TCS in the plasma samples of 13 species of fish
sampled from the Detroit River, in the range of 750 to >10 000 pg
g−1
of wet weight. MTCS was also detected in the plasma samples,
albeit in much lower concentrations, ranging from 0.4 to 13.4 pg
g−1
of wet weight. Based on these plasma samples, the authors
estimated the body burden of TCS to be 2–67 ng. Leiker et al.
(2009) identified MTCS in male common carp (Cyprinus carpio)
from the Las Vegas Bay and in the Las Vegas Wash, Nevada; MTCS
was detected in all carp sampled (n = 29), with a mean
concentration of 520–596 μg kg−1
per wet weight basis. The
concentrations of MTCS detected in this study were much higher
than those documented in previous studies, with the authors,
indicating that this might be due to the sediment foraging
behavior of carp, which exposes them to higher levels of
lipophilic water‐borne chemicals than other fish species. TCS
and its metabolites have been detected in sediments, both
freshwater and marine (Agüera et al., 2003; Miller et al., 2008;
Chalew and Halden, 2009). A national pilot study in the USA
surveyed the presence of pharmaceuticals and personal care
products, including TCS, in fish sampled from five effluent‐
dominated rivers receiving discharge from WWTPs in large urban
centers and a reference river (Ramirez et al., 2009). Although
several products, including carbamazepine and norfluoxetine,
were detected at ng g−1
concentrations in fish tissues, GC/MS
analysis revealed only trace amounts of TCS in fillets.
Marine mammals
Fair et al. (2009) characterized the occurrence of TCS in the
plasma of wild Atlantic bottlenose dolphins (Tursiops truncates),
a top level predator, and then correlated biological levels with
environmental concentrations. This study was the first to
document the bioaccumulation of TCS in a marine mammal.
Plasma samples were collected from the dolphins in Charleston,
South Carolina and Indian River Lagoon, Florida, two southeast
USA estuarine sites. TCS measured in estuarine water samples
Table 2. Concentrations of triclosan (TCS) in aquatic organisms
Organisms Type of sample Site description TCS (μg kg−1
) Reference
Algae and invertebrates
Filamentous algae
(Cladophora spp.)
Whole organism Receiving stream for the city of Denton
(TX, USA) WWTP
100–150 Coogan et al. (2007)
Whole organism 50–400 Coogan and La Point
(2008)
Freshwater snails
(Helisoma trivolvis)
Muscle 50–300 Coogan and La Point
(2008)
Vertebrates
Rainbow trout
(Oncorhynchus mykiss)
Bile Upstream from WWTP, Sweden (caged);
downstream 2 km from WWTP (caged)
710 Adolfsson‐Erici et al.
(2002)17 000
Breams, male
(Abramis brama)
Bile River sites (Netherlands) 14 000–80 000 Houtman et al. (2004)
Muscle River sites (Germany) 0.25–3.4 Boehmer et al. (2004)
Pelagic fish Plasma Detroit River (USA) 0.75–10 Valters et al. (2005)
Atlantic bottlenose dolphins
(Tursiops truncates)
Plasma Estuary, South Carolina 0.12–0.27 Fair et al. (2009)
Estuary, Florida 0.025–0.11
Killer whale
(Orcinus orca)
Plasma Vancouver Aquarium 9.0
Marine Science Centre
Bennett et al. (2009)
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ranged from 4.9 to 13.7 ng l−1
, averaging 7.5 ng l−1
. Plasma
concentrations were 0.12–0.27 and 0.025–0.11 ng g−1
wet
weight, at the two estuaries, respectively. Subsequently, TCS has
also been detected at a concentration of 9.0 ng g−1
of wet
weight in the plasma of a captive killer whale (Orcinus orca) fed
a diet of herring harvested from the coast of British Columbia
(Bennett et al., 2009). These studies further highlight the need to
monitor TCS and assess its effects in wild species.
Occurrence of TCS and its Derivatives in the
Terrestrial Environment
Although TCS is considered to be primarily a water‐borne
contaminant, the antimicrobial can, and does, enter the terrestrial
environment during the application of sewage sludge to
agricultural and/or industrial land (Lozano et al., 2010; Fuchsman
et al. 2010). Activated sludge concentrations of TCS are typically
measured between 580 and 14 700 μg kg−1
of dry weight,
whereas concentrations in biosolids have been documented in
the range of 90–32 900 μg kg−1
(Chalew and Halden, 2009;
Lozano et al., 2010; Table 1). Studies across three continents
examined TCS levels in sewage WWTP sludge and reported
similar concentrations of the antimicrobial, with a median
concentration of 5000 μg kg−1
of dry weight (Reiss et al., 2009).
In WWTPs that use activated sludge treatment in combination with
anaerobic biosolid digestion, 50± 19 of the influent mass of TCS
will accumulate and persist in sewage sludge (Chalew and Halden,
2009). Although it is clear that the amendment of agricultural lands
with biosolids produced from WWTPs represents a significant
pathway for the release of TCS into the terrestrial environment, the
environmental impact of land amendment practices that use
biosolids from WWTPs has not been assessed.
To predict the effects of TCS in biosolids on the terrestrial
environment, it is necessary to understand its fate in soil. Ying
et al. (2007) investigated the biological degradation of TCS in
soil under aerobic and anaerobic conditions. Quantitative
structure–activity relationship analyses confirmed findings from
previous studies, demonstrating TCS’s propensity to sequester in
soil and sediment. Laboratory experiments under aerobic
conditions showed that TCS had a half‐life of 18 days. However,
the antimicrobial persisted in anaerobic soil for the entire
duration of the 70 day experiment. These findings agree with
McAvoy et al. (2002), who reported that the bulk of TCS in
WWTPs was removed during aerobic sludge digestion, with
anaerobic sludge digestion accounting for a very small portion
of TCS removal. Thus in both terrestrial and aquatic environments,
the biodegradation of TCS occurs primarily under
aerobic conditions as the antimicrobial is resistant to anaerobic
degradation. Owing to TCS’s lipophilic nature, the antimicrobial
partitions into sediment and soil, but its transport potential from
biosolids into surface runoff has been characterized as low
(Sabourin et al., 2009).
Although TCS may not be physically mobile between soil
compartments, other processes may transfer TCS from soil to
biota. Kinney et al. (2008) assessed the potential for organic
biosolid‐ or manure‐derived soil contaminants in amended
agriculture land to accumulate in biota. Tissue concentrations of
TCS in earthworms inhabiting the amended soil reached
2610 μg kg−1
, translating into a bioaccumulation factor of 27.
Based on the findings of this study, the predation of earthworms
by birds and other animals could result in the transfer of TCS up
the food chain, although this has not yet been documented.
HUMAN EXPOSURE AND LEVELS
The presence of TCS in human tissues has been documented
by a number of studies from populations in Europe, the USA
and Australia, which would be expected considering the
number of personal care products containing the antimicrobial
and the ability of TCS to be absorbed dermally (Queckenberg
et al., 2010).
Urine
Measuring the levels of environmental chemicals, such as TCS,
in urine represents an important biomonitoring tool for
exposure assessment, especially considering that TCS and its
metabolites are excreted primarily in urine (Queckenberg et al.,
2010). One of the earlier characterizations of the baseline
excretion of TCS in urine, along with plasma levels, was
published by Sandborgh‐Englund et al. (2006). Five male and
five female subjects with a median age of 28 years were
exposed to a single oral dose of TCS, and urine and blood
samples were collected before and up to 8 days after exposure.
The baseline excretion of TCS was in the range of 0.1–743 μg
day−1
, and although maximal plasma levels were reached within
1–3 h in all subjects, plasma levels varied considerably, ranging
between 0.1 and 8.1 μg l−1
. Neither baseline urinary excretion of
TCS nor plasma levels were correlated with the use of TCS
containing personal care products. The authors provided three
possible explanations for these unexpected results: (1) the
monitoring of personal hygiene products was not exhaustive;
(2) labeling of product contents was not complete; (3) other
sources of exposure explain the variable baseline levels. Indeed,
other sources of TCS exposure may include sportswear items,
shoes, socks and impregnated household items (Adolfsson‐Erici
et al., 2002). The full range of consumer, industrial and
pharmaceutical products that contain TCS needs to be included
in future exposure assessment studies in humans.
To further assess the exposure to TCS in a representative
sample of the US population, the National Health and Nutrition
Examination Survey collected 2517 urine samples and detected
TCS in 74.6% of the samples at concentrations of 2.4–3790 μg l−1
(Calafat et al., 2008). TCS concentrations varied with age and
socio‐economic status, but not race/ethnicity or sex. Concentrations
were the highest amongst people in their thirties and
those with higher household incomes. The high frequency of
detection resulting from this study is not surprising, since a
significant proportion of personal care products on the market
today contain TCS, with personal care products considered the
primary route of exposure.
As with other toxicants, including potential endocrine
disruptors, childhood exposures are a concern, as it is
uncertain how these chemicals may alter growth and
development processes. In light of the high potential for
exposure to TCS, a better understanding of TCS exposure and
levels in children is urgently needed. A pilot study by Wolff et
al. (2007) collected urine samples from 90 girls between the
ages of 6 and 8. Sampling was conducted in a manner that
ensured that participants represented four racial groups (Asian,
African American, White and Hispanic) and three regional
locations (New York City, Cincinnati and the San Francisco
Bay area of California). Urinary concentrations of TCS for all
sites were 1.6–956.0 μg l−1
, with a median concentration of
7.2 μg l−1
.
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Plasma
TCS was detected in human plasma in a study investigating the
body burden of phenolic halogenated compounds (PHC)
(Hovander et al., 2002). Ten samples of blood plasma were
randomly selected from male donors between the ages of 30
and 40, donated from a blood donor central at a hospital in
Stockholm, Sweden. The authors identified TCS as one of more
than 100 PHCs present in the plasma of Swedish males. Building
on the work of Hovander et al. (2002), later studies, including the
study of baseline plasma levels and urine excretion of TCS
(Sandborgh‐Englund et al., 2006, see above), have detected the
antimicrobial in humans.
The ubiquitous presence of TCS in the plasma of nursing
mothers in Sweden has been documented by Allmyr et al. (2006).
Plasma concentrations of TCS ranged from 0.010 to 38 ng g−1
, and
in contrast to the study by Sandborgh‐Englund et al. (2006),
median TCS concentrations in subjects classified as users of
products containing TCS were significantly higher than those in
the control group, although the antimicrobial was detected in
plasma samples from both the exposed and the control group. Of
interest is the presence of TCS in the entire study population,
indicating that other routes of exposure than personal care
products influence plasma concentrations of TCS. Determining
the various potential sources of TCS in human tissues warrants
further research. As it currently stands, not all countries require
TCS to be listed on a product’s label, making it difficult to ascertain
all the potential sources of exposure to the antimicrobial.
The influence of age, gender and place of residence on
plasma concentrations of TCS in the Australian population has
been examined by Allmyr et al. (2008). In this particular study,
place of residence had no effect on serum concentrations of
TCS, while age and gender exerted minimal yet significant
influence. TCS concentrations were more elevated in males than
females, and reached peak concentrations in the group of
31–45‐year‐old males and females. Owing to the lack of marked
differences in plasma concentrations observed in the study, the
authors concluded that the exposure of the Australian population
to TCS is relatively homogenous. In comparison to data from
the Swedish population, serum levels of TCS were 2 times higher
in the Australian population, a phenomenon which is most likely
due to the fact that the Swedish government strongly
discourages consumers from using antibacterial products
(Swedish Chemical Agency, 2001).
Dirtu et al. (2008) tested the sensitivity of solid‐phase
extraction and gas chromatography coupled to electron‐capture
negative‐ionization mass spectrometry to detect phenolic
compounds, including TCS, in human serum. The method used
in the study yielded results that were comparable to previous
data collected on the levels of TCS in human fluids. In this study,
the median concentration of TCS in Belgian human serum
samples (n = 21) was 0.52 ng ml−1
. As in earlier studies, TCS
exhibited a high detection frequency as was evidenced by its
presence in all the samples.
Breast Milk
The lipophilicity of TCS (Kow = 4.76) coupled with its relative
stability in human tissues makes it probable that the
antimicrobial will be present in breast milk, with concentrations
relating to maternal serum levels and the fat content of the milk
(Ito and Lee, 2003). The presence of TCS in the breast milk of
Swedish women was first reported by Adolfsson‐Erici et al.
(2002). A second study measuring TCS in breast milk was carried
out by Allmyr et al. (2006), confirming the findings that were
initially reported by Adolfsson‐Erici et al. (2002). Concentrations
of TCS in milk samples were higher in women who used
personal care products containing TCS, compared with women
who did not, although TCS and/or its metabolites were detected
in all the milk samples. Concentrations of TCS ranged from
<0.018 to 0.95 ng g−1
, which is comparable to the concentrations
measured by Adolfsson‐Erici et al. (2002). The universal
presence of TCS in both groups indicates that personal care
products are not the only source of human exposure to the
antimicrobial. The levels of TCS in the subject’s milk were
significantly lower than levels measured in their plasma,
indicating that infants receive a smaller dose of TCS than what
is present in maternal systemic circulation.
Building on the landmark study conducted by Adolfsson‐Erici
et al. (2002) a risk assessment for TCS in human breast milk was
conducted by Dayan (2007). The study obtained 62 samples of
breast milk from The Mothers Milk Banks in California and Texas.
A GC/MS method was used to measure TCS levels in the milk
samples, expressing the results as TCS per lipid basis. The results
of the study were as follows: no TCS detected in two of the
samples, trace amounts present in nine of the samples, with the
remaining 51 samples ranging in TCS concentrations from 100
to 2100 μg kg−1
lipid. Based on the finding that a 6500‐fold
margin of safety exists between the levels of human exposure
and the highest concentration of TCS that would elicit any
adverse effects in human systems, the author concluded that
the levels of TCS measured in breast milk do not pose a risk to
breastfeeding infants. Interestingly, a recent review on TCS and
development of margins of safety for consumer products by
Rodricks et al. (2010) did not assess the exposure of infants to
TCS through breast milk and the associated risks. The
prevalence of TCS in human systems warrants further investigation
into the bioaccumulation potential and toxicological
effects of the antimicrobial, especially during sensitive periods
of fetal and neonatal development.
KINETICS AND METABOLISM
Dermal
The percutaneous absorption of TCS from personal care product
preparations was first investigated by Black et al. (1975). Rat skin
was treated with shampoo or aerosol deodorant containing
0.05% (w/v) and 0.1% (w/v) [3
H] TCS, respectively. The degree
of TCS penetration was calculated from the amount of
radioactivity excreted from the animals. Of the total amount
of shampoo and aerosol deodorant applied, the bulk of TCS
was removed by rinsing, with only small amounts penetrating
the skin. Kanetoshi et al. (1992) confirmed that, in mice, TCS is
absorbed through the skin and is widely distributed throughout
the various compartments in the body. Tissue concentrations
of TCS peaked at 12 or 18 h and were present in
decreasing order in the following tissues: gall bladder, liver,
lung, adipose tissue and blood. Moss et al. (2000) used a
similar approach to characterize the metabolism and kinetics
of TCS. Following a dermal application of 3
H‐labeled TCS to the
backs of female rats, the antimicrobial penetrated the dermis
within the first hour of the experiment and was subsequently
removed from the bloodstream. The primary elimination route
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of radioactivity was through fecal matter, with urinary
excretion constituting a secondary removal pathway. In both
urine and feces, TCS glucuronide and sulfate were detected,
indicating that phase II biotransformation reactions play an
essential role in the metabolism of the antimicrobial. Moreover,
TCS glucuronide and sulfate were extracted from rat skin
in vivo, suggesting that the antimicrobial is locally metabolized
in skin cells. The amount of TCS that entered systemic circulation
over the 24 h period was 21%; 12% of radioactivity was in the
feces, 8% in the carcass, 1% in the urine, 30% in the stratum
corneum, with 26% remaining on the surface of the skin.
Queckenberg et al. (2010) characterized the absorption and
pharmacokinetics of TCS after a dermal administration in human
subjects. A hydrophobic cream containing 2% TCS was applied
to the skin of six Caucasian volunteers. The 12 h exposure period
culminated by the subjects taking a shower to eliminate any
cream that remained on their skin. Urinary excretion of free and
conjugated TCS was measured in intervals up to 168 h post‐
application. Of the TCS absorbed, the majority of the
antimicrobial was excreted within 24 h. The half‐life of TCS
was calculated to be 10.8 h. This value is consistent with the
previous study by Sandborgh‐Englund et al. (2006), which
determined the median half‐life of TCS based on urinary
excretion to be 11 h, following an oral administration. The total
amount of TCS excreted is reflective of the amount absorbed,
indicating a limited potential for accumulation in the body, and
further reinforcing previous findings that, in humans, urinary
excretion is a major elimination route for the antimicrobial.
Subcutaneous
To investigate the kinetics of subcutaneous exposure, female
rats were injected with 0.5 ml of [3
H] TCS solution in aqueous
polyethylene glycol (Black et al., 1975). The animals were housed
in individual metabolic cages, and urine and feces were
collected for the analysis of radioactivity. Within 4 days of the
injection, 89.2% of the dose was recovered, with 33% of TCS
recovered in urine. In agreement with other animal studies on
the pharmacokinetics of TCS, a greater proportion of radioactivity
was eliminated in feces than urine. TCS levels in the blood
peaked at 6 h after the administration of the dose, decreasing
steadily after this time, and the biological half‐life was calculated
as 14 h.
Oral
The earliest published kinetic study of orally administered TCS is
the study by Tulp et al. (1979). A single oral dose of 500 mg kg−1
TCS was given to male albino Wistar rats housed in metabolic
cages for 7 days. Fecal matter and urine was collected daily and
upon termination of the experiment, liver and abdominal fat
were collected for analysis. TCS was metabolized primarily
through hydroxylation, with scission of the ether bond
representing a minor biotransformation pathway. Five hydroxylated
metabolites were detected in urine, whereas only three
of these metabolites were present in feces. The metabolite
2,4‐dichlorophenol was detected in both urine and feces, with
4‐chlorocatechol occurring in urine only, both of these
metabolites being the product of the scission of the ether bond.
In feces, TCS and its metabolites were excreted primarily
unconjugated, with significant amounts of the parent compound
present in both urine and feces. On completion of the
experiment (7 days), TCS was present in both liver and
abdominal fat samples, but because the dose of the TCS was
so high (500 mg kg−1
), no conclusions could be made about its
bioaccumulation potential. The authors concluded that the
metabolism of TCS is unlikely to yield chlorodibenzo‐p‐dioxins or
chlorodibenzofurans.
A later study by Kanetoshi et al. (1988) examined the
disposition and excretion of TCS and its three chlorinated
derivatives in mice. [3
H]‐TCS and 2′,3,4,4′‐tetrachloro‐2‐
hydroxydiphenyl ether, 2′,4,4′,5‐tetrachloro‐2 hydroxydiphenyl
ether and 2′,3,4,4′,5‐pentachloro‐2‐hydroxydiphenyl ether were
orally administered to male mice. Radioactivity was primarily
distributed in the gall bladder, liver, lung, heart and kidneys. Of
the five tissues, TCS was most concentrated in the gall
bladder which the authors attributed to biliary excretion via
enterohepatic circulation. These results are consistent with other
studies that have determined that, in animals, radiolabeled TCS
is excreted primarily in feces and secondarily in urine (Siddiqui
and Buttar, 1979; Moss et al., 2000). The 3
H‐labeled TCS was
rapidly absorbed and excreted, with calculated half‐life of 8 h.
At the 24 h mark, the radioactivities of TCS and its three
chlorinated derivatives were nearly completely eliminated from
all tissues, indicating that TCS and/or its metabolites do not
accumulate in the body. Gilbert and Williams (1987) investigated
the oral retention and pharmacokinetics of [3
H]‐TCS in an
antimicrobial toothpaste. Twelve healthy male volunteers
between the ages of 19 and 37 were recruited for the study
and brushed their teeth with 1 g of toothpaste containing
0.02% of [3
H]‐TCS. The oral retention of TCS was found to be
36.3 ± 1.4%. TCS remained in bacterial plaque for at least 8 h
after dosage and in oral mucosa for 3 h. A review of the safety of
TCS was conducted by DeSalva et al. (1989), evaluating data
from multiple sources including pre‐clinical and clinical studies,
data submitted to the Antimicrobial I OTC Review Panel and
unpublished work from the Pharmacology and Toxicology
Department of the Colgate‐Palmolive company. Humans, dogs,
rabbits and rats were used to study the pharmacokinetics of
TCS. Routes of administration included oral, dermal and
intravenous; pharmacokinetic data on the antimicrobial indicated
that, in humans, the kidneys are the main excretory organ
responsible for the elimination of TCS, as is evidenced by the
proportion of TCS and its conjugates that are concentrated in
urine.
The buccal absorption of TCS from 0.03% mouthwash was
calculated by Lin (2000). Subjects were given 15 ml of TCS
oral mouthrinse or a placebo oral rinse to be used twice daily.
Blood and dental plaque samples were collected 4 and 1 h
after rinsing, respectively. The average daily retention dose of
TCS was 0.660 mg, which translates into 7.33% of the original
dose. On average, TCS concentrations in plaque were in the
range of 20.5–46.4 μg per gram of plaque collected. The
average concentration of TCS in plasma ranged from 74.5
to 94.2 μg ml−1
, with peak concentrations attained 2 days
following exposure. Plasma levels of TCS returned to baseline
concentrations 8 days after the last treatment. More recently,
Sandborgh‐Englund et al. (2006) examined the pharmacokinetic
pattern of TCS in humans after a single dose oral administration.
Subjects were required to fast overnight and the following
morning they were given 13 ml of a 0.03% mouthwash solution,
equivalent to a 4 mg oral dose of TCS. Blood and urine levels
were monitored prior to exposure and up to 8 days after
exposure, and baseline levels of TCS in plasma and urine were
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determined for each subject. Plasma concentrations of
TCS increased rapidly after dosing, attaining peak levels within
1–3 h, resulting in a terminal plasma half‐life of 21 h. In plasma,
30–35% of TCS was present in the unconjugated form. These
results are different from those of DeSalva et al. (1989), who
reported that the entirety of TCS measured in plasma was in the
conjugated form (either glucuronide or sulfonate). Unfortunately,
the basis for these differences is unknown. Lastly, the cumulative
urinary excretion of TCS was 54%, occurring 4 days after
exposure, and the calculated urinary excretion half‐life was
11 h. The results of this study confirmed again that TCS is rapidly
absorbed from the gastrointestinal tract and swiftly eliminated
from the body, usually within a 24 h period.
Intravenous
Siddiqui and Buttar (1979) investigated the pharmacokinetics of
intravenous and intravaginal injections of TCS in sexually mature
virgin Wistar rats. 14
C‐Triclosan was injected into the femoral
vein (5 mg kg−1
in polyethylene glycol‐400) or the vaginal orifice
(5 mg kg−1
in corn oil) and liquid scintillation spectrophotometry
was used to determine radioactivity. In both treatments, the
rate of transfer from plasma to tissues was rapid, probably
attributable to the lipophilicity of TCS. The half‐life of TCS in the
β phase was 8.8 ± 0.6 h and the blood clearance rate was
77.5 ± 11.3 ml kg−1
h−1
after intravenous injection or intravaginal
administration. In the intravenous administration, after 24 h,
18% of TCS was excreted in feces and 9% was eliminated in
urine. In contrast, the intravaginal injections resulted in
excretions of 26% in feces and 14% in urine.
Phase I and II Enzymes
There is evidence for the ability of TCS to interact with
cytochrome P450 enzymes in liver microsomes, although the
effects may be dose‐ and species‐dependent. The antimicrobial
inhibited in vitro methylcholanthrene (MC)‐ and phenobarbital
(PB)‐inducible P450‐dependent monoxygenases, specifically
pentoxyresorufin O‐depentylase (PROD) and ethoxyresorufin
O‐deethylase (EROD) activity, competitively or noncompetitively
(Hanioka et al., 1996). These results are important since
induction of P450 isoforms of the CYP1A or CYP2B subfamily
closely relates to toxicity of the antimicrobial. A later study
(Hanioka et al., 1997) reported that TCS (Irgasan DP300) induces
the P450 isoforms of the CYP2B subfamily. Similar results
suggesting that TCS is a phenobarbital‐type inducer were
reported by Jinno et al. (1997), in cultured rat hepatocytes and
by Kanetoshi et al. (1992), in mice liver microsomes. In contrast,
Ishibashi et al. (2004) found no evidence that TCS induces EROD
and PROD activity in the hepatic microsomes of female medaka,
Oryzias latipes. This discrepancy may be due to physiological
differences between mammals and fish, and/or differences in
exposure. Jacobs et al. (2005) presented in vitro evidence for TCS
acting as a ligand, with a moderate affinity for the human
pregnane X receptor (hPXR). The hPXR regulates the expression
of phase I enzymes such as cytochrome P450 3A4 (CYP3A4),
which play an integral role in the biotransformation of
approximately 50% of pharmaceuticals (Luo et al., 2002; Jacobs
et al., 2005). Compounds that are capable of upregulating the
transcription of CYP3A4 enzymes can alter the rate at which
pharmaceuticals are metabolized, creating the potential for
adverse effects.
TCS, structurally similar to hydroxylated polychlorinated
biphenyls, also interacts with phase II enzymes. TCS is both a
substrate and inhibitor of sulfonation and glucoronidation in
human liver cytosol and microsomes (Wang et al., 2004). The
inhibition of sulfonation was noncompetitive, while the
inhibition of glucuronidation was competitive. These results
confirm earlier evidence of the inhibition of sulfation, specifically
that of thyroid hormones, by TCS and other hydroxylated
halogenated chemicals (Schuur et al., 1998). TCS sulfonation in
polar bear liver, similar to human liver in respect to enzyme
affinity, was characterized by Sacco and James (2005). In
addition to effects on phase I and phase II enzymes, TCS may
have direct effects on mitochondria, impairing function through
an uncoupler effect and disrupting mitochondrial membrane
fluidity (Newton et al., 2005).
The available evidence indicates that the two most probable
routes of exposure to TCS in humans are ingestion and/or
percutaneous absorption. Low but detectable levels of TCS have
been reported in drinking water (Loraine and Pettigrove, 2006;
Servos et al. 2007). Blanset et al. (2007) estimated the ADI
(acceptable daily intake) for TCS at 0.05 mg kg−1
per day, and
concluded that, based on TCS levels typically measured in
drinking water, the risk to human health is minimal. Concentrations
of TCS in the blood are directly related to consumer use
patterns of the antimicrobial. In humans, after an oral dose of
TCS, the antimicrobial is eliminated primarily as conjugated
metabolites in urine. In the study by Sandborgh‐Englund et al.
(2006), approximately 70% of the total amount of TCS measured
in plasma existed as either sulfate or glucuronide conjugates.
TCS interacts with phase I and II enzymes, contributing to its
toxicity and endocrine disrupting properties.
TOXICITY
Numerous studies have evaluated the toxicity of TCS in various
organisms, including algae, invertebrates, amphibians, fish, birds
and mammals. Data from mammalian studies, including humans,
has recently been reviewed by Rodricks et al. (2010). The
following section briefly summarizes those studies and provides
a more detailed review of toxicity data from nonmammalian
species.
Acute Toxicity
Terrestrial organisms
Several recent studies investigated the terrestrial ecotoxicological
effects of TCS. TCS inhibited plant growth (EC50 57–108 mg kg−1
)
and soil respiration, with some evidence for recovery after 2 days,
possibly linked to degradation of TCS (Liu et al., 2009). Waller and
Kookana (2009) reported that TCS, at concentrations below
10 mg kg−1
, disturbs the nitrogen cycle in some soils. An
ecological risk assessment for TCS in the terrestrial environment
has been published by Reiss et al. (2009). The assessment
reviewed available data and found satisfactory margins of safety
for terrestrial organisms, including earthworms, plants, and soil
microorganisms exposed to TCS in soils amended with sewage
sludge, and to birds and mammals exposed indirectly through
the consumption of earthworms and fish. However, the number
of studies available for the risk assessment was relatively small
(n = 31), indicating that further investigations of the potential
impact of TCS on the terrestrial ecosystems are needed.
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Table3.Effectsoftriclosan(TCS)onfreshwater(FW)andmarine(SW)organisms
TestspeciesLifestageSystemtypeRouteofexposureTestdurationTCSexposureEndpointReference
Algae
Phytoplankton
(Dunaliellatertiolecta)
SWWater(static)Acute(96h)3.5μgl−1
EC50(populationdensity)DeLorenzoand
Fleming(2008)
Greenalga
(Selenastrumcapricornutum)
FWWater(static)Acute(72h)4.7μgl−1
EC50(growth)Tatarazakoetal.(2004)
Greenalga
(Scenedesmussubspicatus)
FWWater(static)Acute(96h)1.4μgl−1
EC50(biomass)Orvosetal.(2002)
Alga(Closteriumehrenbergii)FWWater(static)Acute(48h)620μgl−1
;250μgl−1
EC50genotoxicityCinigliaetal.(2005)
Blue‐greenalga
(Anabaenaflos‐aquae)
FWWater(static)Acute(96h)1.6μgl−1
EC50(biomass)Orvosetal.(2002)
Invertebrates
DaphniamagnaFWWater(renewal)Acute(48h)390μgl−1
EC50NOECreproductionOrvosetal.(2002)
21days40μgl−1
CeriodaphniadubiaFWWater(renewal)Acute(48h)240μgl−1
EC50NOECreproductionOrvosetal.(2002)
7days182μgl−1
FWWater(renewal)6–7days220μgl−1
IC50(growth)Tatarazakoetal.(2004)
Chironomustentans
Hyalellaazteca
FWWater(renewal)10days400μgl−1
LC50Dussauetal.(2008)
200μgl−1
Grassshrimp
(Palaemonetespugio)
EmbryoSWWater(renewal)Acute(96h)651μgl−1
LC50DeLorenzoetal.(2008)
Larvae154μgl−1
LC50
Adult305μgl−1
LC50
Crustacean
(Thamnocephalusplatyurus)
FWWater(static)Acute(24h)470μgl−1
LC50Kimetal.(2009)
Bivalve
(Mytilusgalloprovincialis)
HemocytesSWInvitroAcute(30min)1μM↓lysosomalmembrane
stability
Canesietal.(2007)
WholeanimalSWInjectionAcute(24h)2.9ngg−1
Alteredhemocyteand
digestiveglandfunction
Canesietal.(2007)
Zebramussel
(Dreisenapolymorpha)
HemocytesFWInvitroAcute(60min)0.1μMGenotoxicityBinellietal.(2009a,2009b)
InvivoAcute(96h)1MGenotoxicity
Fish
Rainbowtrout
(Oncorhynchusmykiss)
AdultFWWater
(flow‐through)
Acute(96h)390μgl−1
LC50CIBA(1998)
EmbryoFW61days71.3μgl−1
Delayedswim‐up;
↓35dphsurvival;
erraticswimming,lockedjaw
Orvosetal.(2002)
35days
Medaka(Oryziaslatipes)FertilizedeggsFWWater(renewal)14days313μgl−1
↓hatching;delayedhatchingIshibashietal.(2004)
Larvae(24hold)Acute(96h)602μgl−1
LC50
Malefish21days20μgl−1
↑liverVtg
FryFWAcute(48h)350μgl−1
LC50Foranetal.(2000)
EggsFW14days400μgl−1
IC50(hatching)Tatarazakoetal.(2004)
SWInovoinjection1daypost‐
fertilization
4.2ngegg−1
EC50(survival)Nassefetal.(2010)
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Table3.(Continued)
TestspeciesLifestageSystemtypeRouteofexposureTestdurationTCSexposureEndpointReference
LarvaeFWWater(static)Acute(96h)600μgl−1
LC50Kimetal.(2009)
AdultSWWater(renewal)Acute(96h)1700μgl−1
LC50Nassefetal.(2009)
Bluegillsunfish
(Lepomismacrochirus)
FWWater(renewal)Acute(96h)370μgl−1
LC50Orvosetal.(2002)
Fatheadminnow
(Pimephalespromelas)
AdultFWWater(renewal)Acute(96h)260μgl−1
LC50(atpH7.5)Orvosetal.(2002)
FulllifecycleFWWater
(TCSinmixture)
0.1and0.3μgl−1
mixtureofproducts
NoeffectsFo;
↑larvaldeformitiesinF1
ParrottandBennie(2009)
Zebrafish(Daniorerio)EggsFWWater(renewal)9Days220μgl−1
IC50(hatching)Tatarazakoetal.(2004)
EmbryoFW24‐WellmicroplatesAcute(96h)420μgl−1
LC50;teratogeniceffectsOliveiraetal.(2009)
AdultFWSemi‐staticAcute(96h)340μgl−1
LC50Oliveiraetal.(2009)
Amphibians
Bullfrog
(Ranacatesbeiana)
TadpolesFWWaterAcute(96h)0.15μgl−1
↑hindlimbdevelopment,
↓bodyweight,disruption
ofthyroidhormone‐
associatedgeneexpression
Veldhoenetal.(2006)
XenopusleavisXTC‐2cellsFWInvitroAcute(24h)0.03μgl−1
Alteredthyroidhormone
receptormRNAexpression
Veldhoenetal.(2006)
Acriscrepitans
blanchardii
LarvaeFWWaterAcute(96h)367μgl−1
LC50PalenskeandDzialowski
(2010)
Bufowoodhousii
woodhousii
Stage30152μgl−1
Ranasphenocephala562μgl−1
XenopuslaevisStage41343μgl−1
Leopardfrog
(Ranapipiens)
TadpolesFWStatic
(weeklyrenewal)
24days0.23μgl−1
↓activity,lossofstartle
response,↓survivorship
FrakerandSmith(2004)
230μgl−1
Americantoad
(Bufoamericanus)
TadpolesFWStatic
(weeklyrenewal)
14days230μgl−1
↑activitySmithandBurgett(2005)
EC50,effectiveconcentration;LC50,lethalconcentration;NOEC,noobservedeffectconcentration.
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Aquatic organisms
Microorganisms and algae. TCS is primarily a water‐borne
pollutant, with numerous studies having investigated its toxicity
in aquatic organisms (Table 3). The toxicity of TCS to WWTP
sludge organisms, algae, daphnids and fish was assessed by
Orvos et al. (2002). While sludge microorganisms were
unaffected by TCS, the aquatic species that appeared most
vulnerable to the toxic effects of TCS were algal species such
as Scenedesmus subspicatus, with a 96 h biomass EC50
(median effective concentration) of 1.4 μg l−1
and a 96 h no‐
observed‐effect concentration (NOEC) of 0.69 μg l−1
(Orvos
et al., 2002). Similar evidence regarding algal sensitivity was
provided by Tatarazako et al. (2004) for Selenastrum
capricornutum, and by DeLorenzo and Fleming (2008) for a
marine phytoplankton, Dunaliella tertiolecta (Table 3). The
toxic effects of TCS were primarily due to the neutral form
of TCS, where sorption and ionization could potentially
temper these effects in the aquatic ecosystems. The lowest
NOEC for algae, integral components of aquatic food webs,
is less than 1 μg l−1
, with TCS being measured in the range
of 0.2–2.7 μg l−1
in US wastewater effluent (Reiss et al.,
2002). It is then possible that current levels of TCS in rivers
and streams (PEC, predicted environmental concentration)
may surpass the NOEC for algae, as indicated by HQ value
(Hazard Quotient, PEC divided by NOEC) greater than 1.
Coogan et al. (2007) measured TCS levels in the algal
species, Cladophora spp., located downstream from a WWTP.
Although TCS concentrations in the water column decreased
downstream from the effluent output (0.12–0.06 μg l−1
),
concentrations of the antimicrobial in algae demonstrated the
reverse pattern (100–150 μg l−1
), indicating bioaccumulation. It
is unclear how the propensity of algae to accumulate TCS affects
the species vulnerability to the toxicity of the antimicrobial.
Invertebrates. Aquatic invertebrates also exhibit vulnerability
to TCS (Table 3). Short‐term (30 min) exposure of hemocytes,
the immune cells of bivalve Mytilus galloprovincialis, to TCS
reduced lysosomal stability and induced the release of
lysosomal hydrolytic enzymes (Canesi et al., 2007). Moreover,
in vivo exposures of the bivalve affected glycolytic enzymes and
redox balance in different systems/organs. For Daphnia magna,
a key invertebrate aquatic species, the 48 h median effective
concentration was 390 μg l−1
(Orvos et al., 2002). The toxicity of
TCS to the midge, Chironomus tentans, and the freshwater
amphipod, Hyalella azteca, was evaluated in a 10‐day exposure
test (LC50 0.4 and 0.2 mg l−1
, respectively). TCS was more toxic
than carbamazepine, an anticonvulsant, and atorvastatin, a lipid
regulator (Dussault et al., 2008).
Fish. Kim et al. (2009) assessed the acute toxicity of TCS in two
test species, a freshwater crustacean (Thamnocephalus platyurus)
and a fish (Oryzias latipes). The organisms were exposed to a
range of TCS concentrations and the 24 h LC50 values were
determined by probit analysis. The LC50 values of TCS for
T. Platyurus and O. Latipes were 0.47 and 0.60 mg l−1
,
respectively. The LC50 (96 h) value for O. Latipes calculated in
this study confirms the previous findings of Tatarazako et al.
(2004), in which an LC50 value of 0.40 mg l−1
was ascertained for
the antimicrobial.
Nassef et al. (2010) applied in ovo nanoinjection of TCS to
medaka embryos and determined 4.2 ng per egg as the EC50
value based on survival and embryonic development. Foran
et al. (2000) examined the acute toxicity of TCS in medaka fry
(Table 3). Concentrations of 1 and 500 μg l−1
resulted in fry
death within 24 h and 3 days, respectively. The LC50 (48 h) for
medaka fry was calculated to be 352 μg l−1
. A 96 h median lethal
concentration of 602 μg l−1
for medaka fry was reported by
Ishibashi et al. (2004). Although this value is higher than the LC50
(48 h) of 352 μg l−1
previously determined by Foran et al. (2000),
it appears that, during early development, fish are especially
vulnerable to the toxic effects of TCS. Nassef et al. (2009) used
adult Japanese medaka as the test organism in an acute toxicity
study and observed concentration‐ and time‐dependent
mortality. Test solutions of TCS were 1, 2, 2.4 and 3 mg l−1
and the adult fish were exposed to TCS for a period of 96 h.
Reported 96 h survival rates were 100% (1 mg l−1
), 16.7% (2 mg
l−1
), 3.3% (2.4 mg l−1
) and 0% (3 mg l−1
). At higher exposure
levels (2.4 and 3 mg l−1
), fish displayed abnormal behaviors and
experienced a loss of equilibrium. The LC50 (96 h) of TCS for
adult medaka was 1.7 mg l−1
, while the NOEC was estimated at
1.7 μg l−1
, which is 12 times higher than the PEC for the
antimicrobial. The authors of this study are in agreement with
Ishibashi et al. (2004), in their conclusion that TCS is highly toxic
to fish.
Oliveira et al. (2009), in an experiment similar to the one by
Nassef et al. (2009), studied the acute toxicity of TCS in different
life stages of zebrafish (Danio rerio). The effect of TCS on
mortality and developmental, genetic and enzymatic biomarkers
were determined in adult fish and embryo/larvae using
the OECD guidelines on Fish Embryo Toxicity. At concentrations
above 0.7 mg l−1
, TCS exhibited teratogenic effects, delaying
embryo development and resulting in mortality within 48 h. The
LC50 (96 h) of TCS for embryo/larvae was 0.42 mg l−1
. The results
of the biomarker analysis indicated that TCS increased the activity
of cholinesterase (ChE; 0.25 mg l−1
), lactate dehydrogenase
(LDH; 0.25 mg l−1
) and glutathione S‐transferase (GST; 0.25 and
0.35 mg l−1
). Based on the results, concentrations of TCS equal
to, or above 0.3 mg l−1
, were estimated to constitute a hazard
for aquatic ecosystems. Using the OECD Guideline TG 203 in
semi‐static conditions, the LC50 (96 h) value for adult zebrafish
was determined as 0.34 mg l−1
, a value similar to the LC50 (96 h)
of 0.42 mg l−1
for zebrafish larvae. The acute toxicity of TCS was
primarily limited to behavioral effects, none of which were
studied in detail. Abnormal behavioral patterns observed during
the study included irregular swimming, loss of equilibrium, and
anomalous gill movement. In contrast to the embryo/larvae
stage, there was no evidence of genotoxicity or changes in
enzyme levels of ChE, GST and LDH in adult zebrafish. Although
there were differences in species sensitivity to TCS, the range of
LC50 (96 h) was relatively small (Table 3); the 96 h median lethal
concentration values for Pimephales promelas and Lepomis
macrochirus were 260 and 370 μg l−1
, respectively (Orvos et al.,
2002), while the value for adult zebrafish was 340 μg l−1
. During
early development, juvenile fish are more sensitive to TCS than
adults. In an early life‐stage toxicity test with Oncorhynchus
mykiss, the NOEC and the lowest‐observed‐effect concentration
(LOEC) were 34.1 and 71.3 μg l−1
, respectively (Orvos et al., 2002).
Amphibians. The effects of TCS were also investigated in
amphibians. There is evidence to indicate that TCS affects
behavior and survivorship in tadpoles; however, the effects
seem to be species‐specific. TCS increased activity levels in
American toad tadpoles, Bufo americanus, although the effects
on survivorship were not concentration‐dependent (Smith and
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Burgett, 2005). In tadpoles of the northern leopard frog, Rana
pipiens, ecologically relevant concentrations of TCS decreased
activity and survivorship (Fraker and Smith, 2004), indicating
that the HQ for this specific endpoint is >1.0. In the latter study,
no evidence of an interaction between TCS and caffeine or
acetaminophen, pharmaceuticals often co‐occuring in WWTP
effluents, was detected. Palenske and Dzialowski (2010)
assessed the species specific and developmental toxicity of
TCS in amphibian larvae for Acris crepitans blanchardii, Bufo
woodhousii woodhousii, Rana sphenocephala and Xenopus laevis.
Bioconcentration factors for X. laevis, B. woodhousii woodhousii
and R. sphenocephala were also determined. As is the case with
other aquatic species, TCS toxicity was dependent upon larval
maturity and amphibian species. X. laevis larvae were most
vulnerable to TCS during the first two developmental stages.
Larval LC50 values were reported as follows: 259–664 μg l−1
(X. laevis), 367 μg l−1
(A. crepitans blanchardii), 152 μg l−1
(B. woodhousii woodhousii) and 562 μg l−1
(R. sphenocephala),
with significant differences observed for all three amphibian
species (Table 3). In this study, TCS tissue uptake was related to
larval species, stage of development and mean mass. Bioconcentration
factors ranged from 44 in X. laevis up to 740 in
B. woodhousii woodhousii.
Mammals. The toxicity of TCS has been tested in laboratory
rodents, and other mammalian models. An early study by
Lyman and Furia (1969), sanctioned by the Geigy Chemical
Corporation, provided toxicological data on TCS in rats,
concluding that TCS was neither acutely toxic (LD50 oral > 1000
mg kg−1
) nor carcinogenic. Later, nephrotoxic effects of orally
administered TCS in rats were reported by Chow et al. (1977), in
a study where the accumulation of p‐aminohippurate (PAH) was
estimated both in vivo and in vitro, using kidney slices to detect
dose‐related inhibition. A 1989 review on the safety of TCS was
published by DeSalva et al. (1989). The majority of data in this
review cited unpublished results from reports submitted by
Ciba‐Geigy Company to the Antimicrobial I OTC Review Panel.
Ciba‐Geigy Company tested the acute toxicity of TCS on four
different species of animals; mouse, rat, rabbit and dog. Based on
these studies, TCS was deemed not to be an acute oral toxicant.
One of the more recent studies detailing the acute toxicity of
TCS in mammals was conducted by Kanetoshi et al. (1992). The
study evaluated the acute toxicity and percutaneous absorption
of TCS and its chlorinated derivatives in male mice. The results
indicated that TCS has a low acute toxicity (LD50 > 1 g kg−1
), a
value which is in agreement with the previous findings of
Lyman and Furia (1969). The authors previously reported that
Irgasan DP300 is commonly detected in commercial textile
products and that an exposure to sodium hypochlorite
(domestic bleach) leads to the formation of three different
chlorinated derivatives. It is worth noting that the chlorinated
derivatives of TCS are significantly more toxic than TCS itself,
and as the number of chlorine substitutions in the TCS
derivatives increases, their LD50 values decrease (Kanetoshi
et al., 1992). Dermal contact with textiles that have TCS
incorporated into their fibers may expose consumers to
chlorinated TCS derivatives. However, Rodricks et al. (2010)
provided a recent critical review of the current mammalian
literature and developed margins of safety for consumer
products, concluding that the exposure to TCS in consumer
products is not expected to cause adverse health effects in
humans.
Current literature suggests that, while TCS is not acutely toxic
to mammals, aquatic species such as algae and certain types of
fish are highly sensitive to the antimicrobial. The NOEC for fish is
in the range of 34.1–200 μg l−1
(Orvos et al., 2002; Ishibashi et al.,
2004; Capdevielle et al., 2008), a concentration range which
exceeds the PECs (0.01–0.14 μg l−1
, Table 1) for TCS. The toxicity
of TCS is also dependent on the life stage of the organism, with
juveniles having a tendency to be more vulnerable to the toxic
effects of the antimicrobial.
Subacute/subchronic and Chronic Toxicity
Toxicity data from prolonged exposure studies of aquatic
organisms to TCS are relatively scarce (Table 3). Algae were
determined to be the most sensitive aquatic organisms in
experiments lasting up to 21 days, as has been shown in the
acute toxicity studies (Orvos et al., 2002). Significant adverse
effects on survival and reproduction were also detected in the
invertebrate, Daphnia magna. While juvenile rainbow trout were
adversely affected by chronic exposures to TCS, fathead
minnows were not. Parrott and Bennie (2009) used fathead
minnow life‐cycle tests to study the sub‐lethal effects of
environmentally relevant mixtures (ng l−1
range) of a personal
care product (TCS, up to 115 ng l−1
) and six common
pharmaceuticals. In comparison to controls, no significant
differences in survival, growth, development or reproduction
were observed in any of the treatment groups. The only
significant effect of the PPCP mixture was observed in the F1
generation; the 100 and 300 ng l−1
PPCP mixture but not
1000 ng l−1
, produced significant increases in the rates of
deformities, including cardiac edema, spinal deformities and
yolk‐sac edema. The magnitude of the effect was, however, low
since only doubling or tripling of the deformity rate compared
with controls was observed. The results of the study are
noteworthy, as they indicate that the chronic exposure of fathead
minnows to an environmentally relevant mixture of seven PPCPs
did not affect any of the parameters tested, with the exception of
F1 larval deformities, where the impact was relatively minor.
Subacute and chronic toxicity data from mammalian species,
including mice, rats, hamsters and baboons, are extensive, and
have been reviewed by Rodricks et al. (2010). For systemic
toxicity, excluding endocrine disruption, the effects of TCS were
primarily limited to changes in the liver and kidneys. TCS
induced changes in liver weight, liver enzymes and liver
hypertrophy, and increased peroxisome size and numbers. In
rodent species, renal toxicity was evidenced by inflammation
and tubular regeneration.
Genotoxicity
Genotoxicity and mutagenicity studies using classical prokaryotic
and eukaryotic systems were reviewed by Rodricks et al. (2010).
The available evidence led the authors to conclude that TCS is
neither genotoxic nor mutagenic. However, there is some
evidence to suggest that TCS may be genotoxic in certain types
of organisms and/or cell types.
Acute toxicity experiments (96 h exposure) using hemocytes
from zebra mussels (Dreissena polymorpha) that were exposed to
environmentally relevant concentrations of TCS (1, 2 and 3 nM)
provided evidence of genotoxicity after only 24 h of exposure
(Binelli et al., 2009a). The genotoxicity of TCS in hemocytes was
evaluated with the single cell gel electrophoresis (SCGE) assay
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(also known as the comet assay), the micronucleus assay, and
the halo test, a measure of the apoptotic frequencies, while
cytotoxicity was assessed with the neutral red retention assay.
The genetic damage accrued in the hemocytes was significant
at all three concentrations of TCS, following a concentration‐
dependent and time‐dependent pattern. The authors of this
study concluded that the genotoxicity of TCS in zebra mussels
was probably due to a combination of oxidative stress and/or
a direct effect on DNA. In a follow‐up study (Binelli et al.,
2009b), hemolymph from zebra mussels was extracted and
then used to investigate TCS’s potential for both cytotoxicity
and genotoxicity. In this experiment, antimicrobial concentrations
of 0.1, 0.15, 0.2 and 0.3 μM caused extensive DNA
damage in hemocytes, as indicated by the SCGE assay and
the apoptotic frequency. Although the range of concentrations
used in this study was very narrow, the results clearly
indicated that TCS’s genotoxicity increased in a dose‐
dependent fashion. Based on these two studies, there is
compelling evidence to suggest that TCS has genotoxic
effects in zebra mussels, both in vivo and in vitro, although
future studies are needed to confirm these findings.
The genotoxicity of TCS has also been evaluated using the
comet assay in the algal species Closterium ehrenbergii (Ciniglia
et al., 2005). Algal cells were exposed to TCS for 96 h, at
concentrations in the range 0.125‐1 mg l−1
. At concentrations of
0.25 mg l−1
and greater, the genetic toxicity of TCS was apparent,
with the antimicrobial exerting its toxicity in a dose‐dependent
manner. Complete dissolution of the nucleus was observed at
concentrations of 0.5 and 1 mg l−1
. Although the results of this
study indicate that TCS has genotoxic effects on C. ehrenbergii,
the concentrations used in the experiment were much higher
than those typically observed in surface water (HQ < 1.0), and as
such, the results should be interpreted with caution.
The genotoxicity and cytotoxicity of TCS have been tested in
animal cell lines. Zuckerbraun et al. (1998) demonstrated that TCS
is cytotoxic to Smulow–Glickman cells (S‐G cells), which are
derived from a human gingival epithelial cell line. TCS damaged
the integrity of the plasma membrane and induced apoptotic cell
death. The effects of TCS on gingival cells are important, as TCS is
a common ingredient in a number of oral hygiene products.
Jirasripongpun et al. (2008) used the comet assay and the
apoptosis assay to test the genotoxicity of TCS on two animal cell
lines. KB and Vero cell lines were treated with two concentrations
of TCS, the 50% inhibition concentration (IC50, 0.034 and
0.036 mM respectively) and the maximum concentration of TCS
in personal care products (0.023 mM). In both cell lines, the
number of comet cells increased as the concentration and
exposure time to TCS increased. Most notably, genetic damage
accrued from the exposure to TCS was observed at concentrations
in the IC20–30 range, following a 5 day exposure period. At
levels of TCS that are normally in personal care products, the
antimicrobial failed to produce any signs of genotoxicity. TCS is a
lipophilic chemical and as such, could potentially accumulate in
the body. However, exposure to TCS levels that cause genetic
damage is unlikely, considering that pharmacokinetic studies
have demonstrated that the antimicrobial is rapidly metabolized
and readily eliminated from the body.
Mutagenicity and Carcinogenicity
Reviews of data on TCS’s safety by DeSalva et al. (1989),
Bhargava and Leonard (1996), and more recently by Rodricks
et al. (2010), included extensive data from mutagenicity assays,
many completed by Ciba‐Geigy Co. The overwhelming majority
of these assays indicated that TCS did not exhibit any
mutagenic potential, with the exception of the mammalian
spot test. The mammalian spot test was first performed by
Fahrig (1978) and resulted in a positive response, but later
yielded negative results when repeated by Russell and
Montgomery (1980). The study published by Fahrig was
criticized, and it has been suggested that the effective dose
of TCS used by Fahrig would result in maternal toxicity, thus
precluding evaluation in the offspring. It is not clear why these
two studies, using the same method, yielded such very different
results. Fahrig (1978) used a higher dose of TCS dissolved in
HBSS, whereas Russell and Montgomery deemed TCS to be
insoluble in HBSS, opting to dissolve the antimicrobial in
methanol instead. Montgomery and Russell conjectured that,
owing to the limited solubility of TCS in HBSS, the experiment
by Fahrig (1978) probably failed to inject any of the dams with
TCS, which would explain the limited toxicity observed at the
50 mg kg−1
dose, a dose which proved to be highly toxic to
embryos in the study by Russell and Montgomery. The majority
of researchers seem to accept the findings of the experiment by
Russell and Montgomery, as reviews on TCS safety (DeSalva
et al., 1989; Bhargava and Leonard, 1996; Rodricks et al., 2010)
consistently conclude that TCS is not a mutagen and that
personal care products containing the antimicrobial do not
pose a risk to human health.
The mutagenic potential of TCS and its photodegradation
products were later examined by Onodera et al. (1995), in two
Salmonella strains tested with and without S9 fractions. Any
mutagenic effects of TCS went undetected, owing to the high
toxicity of the antimicrobial to the test species. Following
treatment with photo‐irradiation and chlorine, TCS in aqueous
solution failed to elicit a mutagenic effect in either of the
Salmonella strains tested. However, it would seem that the
selection of bacteria to test the mutagenicity of TCS is somewhat
questionable, considering that TCS is a potent antimicrobial and
would be highly toxic to the bacterial test species.
Currently available evidence from studies using classical assay
systems indicates that TCS is not genotoxic, mutagenic or
carcinogenic. However, there is some evidence that TCS is able
to exert genotoxicity in nonmammalian systems, including algae
and bivalves. Owing to the limited number of studies addressing
the genotoxicity, mutagenicity and carcinogenicity of TCS in
nonmammalian systems, it is difficult to conclude with certainty
that the antimicrobial does not display a potential for harm.
Reproductive and Developmental Effects
The reproductive and developmental toxicity of TCS was
assessed in several aquatic species, under controlled laboratory
exposures. Orvos et al. (2002) investigated the early life‐stage
toxicity of TCS to rainbow trout. No statistical differences were
observed in mean time to egg hatch among groups exposed
to different concentrations of TCS in water, although swim‐up
behavior was delayed in the 71.3 μg l−1
treatment (Table 3).
Decreased rates of fry survival were observed in this treatment
group. Sublethal effects were also observed during the course
of the study, and included a loss of equilibrium, locked jaw,
erratic swimming, spinal deformities and reduced activity.
The effects of TCS on early development and reproduction in
medaka were studied by Ishibashi et al. (2004). In fertilized eggs
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Table4.Endocrine‐disruptingeffectsoftriclosan(TCS)
Testspecies/systemLifestageAquaticsystemRouteofexposureTestdurationTCSexposureEffectsReference
FishMedaka
(Oryziaslatipes)
EmbryosFWWater14days100μgl−1
Weakandrogenic
(oranti‐estrogenic)
effect(↑malefinsize,
slightmalebiassexratio)
Foranetal.(2000)
MalefishFWWater14days20μgl−1
Weakestrogenicactivity;
↑Vtginmalefish;activity
inyeastassay
Ishibashietal.(2004)
Mosquitofish
(Gambusiaaffinis)
MalefishFWWater35days101.3μgl−1
↑vitellogenin,↓spermcountRautandAngus(2010)
Bream
(Abramisbrama)
Bileof
malefish
FWFieldsites,
Netherlands
Noactivity
upto0.1mM
Noestrogenicactivity
detectedinER‐CALUXassay
Houtmanetal.(2004)
Amphibians
NorthAmerican
bullfrog
(Ranacatesbeiana)
TadpolesFWInvivo18days0.15μgl−1
DisruptionofT3‐dependent
developmental
metamorphosisprocesses
Veldhoenetal.(2006)
SouthAfrican
clawedfrog
(Xenopuslaevis)
TadpolesFWInvivo21days1.5μgl−1
↓larvalgrowth;noeffect
onmetamorphosis
Fortetal.(2010)
0.6–32.4μgl−1
MalesFWWater;
i.p.injection
14days20–200μgl−1
;
inject4‐400μgg−1
bodyweight
NoeffectonVtginmales;
noeffectsonCYP1Aand
EROD;↓Vtgini.p.injected
males
Matsumuraetal.(2005)
Mammals
SheepPlacentaInvitro0.6nM↓Estrogensulfonation(IC50)Jamesetal.(2010)
Rats(Wistar)Pre‐pubescent
males
Oral(gavage)31days200mgkg−1
Noeffectontimingofpuberty;
↓levelsofplasma
testosteroneandT4
Zorrillaetal.(2009)
30mgkg−1
Males;
isolated
Leydigcells
Invivo
(dailyintubation)
60days5–20mgkg−1
DisruptionofLH,FSH,
pregnenoloneand
testosteronesynthesis;
↓mRNAexpressionofStAR
andsteroidogenicenzymes
Kumaretal.(2008,2009)
Invitro2h0.01–10μM
Rats(Long–Evans)AdultfemaleOral(gavage)4days100mgkg−1
day−1
↓PlasmaT4Croftonetal.(2007)
Female
weanlings
Oral(gavage)4days300mgkg−1
day−1
↓PlasmaT4andT3Pauletal.(2010)
HumanAdultsbrush2/day
withTCStootpaste
14days0.3%w/wTCSNoeffectonthyroidstatusAllmyretal.(2009)
A. B. Dann and A. Hontela
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300
exposed to 313 μg l−1
of TCS, hatchability and time to hatching
were significantly decreased and postponed, respectively. A
21 day exposure period to the antimicrobial failed to have any
observable effect in the number of eggs produced and fertility,
when comparing the control group with the 20, 100, 200 μg l−1
TCS treatments. TCS appears to be quite toxic during the early
life stages of medaka, and although the metabolite of TCS had
weak estrogenic activity, the antimicrobial did not negatively
impact the reproductive success of paired medaka or the
survivability, growth and sex ratios of the offspring.
In addition to the acute toxicity of TCS in adult fish, Oliveira
et al. (2009) investigated the teratogenic effects of TCS on
zebrafish larvae. The experiment was designed according to the
OECD guideline on Fish Embryo Toxicity Test. Zebrafish embryos
were exposed to five different concentrations of TCS – 0.1, 0.3,
0.5, 0.7 and 0.9 mg l−1
for a 6 day period. The embryos were
monitored daily for mortality, developmental parameters, and
hatching. Additional larvae were collected for ChE, GST and LDH
biomarker analyses. TCS exhibited acute toxicity for embryo/
larvae (96 h LC50 of 0.42 mg l−1
), resulting in delayed hatching,
and mortality at 48 h. The teratogenic effects of TCS were
observed at concentrations above 0.7 mg l−1
. The developmental
effects of TCS included delayed otolith formation and eye
and body pigmentation, spinal malformations, pericardial
edema and undersized larvae. In addition to embryo malformations,
biomarker levels were also affected: ChE activity increased
in the 25 mg l−1
treatment, GST activity increased in both the
0.25 and 0.35 mg l−1
treatments, and LDH activity increased in
the 0.25 mg l−1
treatment. The results of this study indicate that
TCS is toxic to zebrafish embryo/larva and negatively impacts
hatching, embryonic development, enzyme activities and
survival. Based on the sensitivity of the biomarkers analyzed
(GST, ChE and LDH), the authors concluded that concentrations
of TCS equal to or greater than 0.3 mg l−1
constitutes a
significant environmental hazard.
Reproductive and teratological studies in rats, mice and rabits
carried out by Ciba‐Geigy were reviewed by DeSalva et al.
(1989), Bhargava and Leonard (1996), and Rodricks et al. (2010).
In the rat study, TCS was administered in the diet. There were no
effects on reproductive performance at any of the doses,
including the highest dose of 3000 mg kg−1
. Effects in the
offspring were detected only in pups from mothers fed the
highest dose of TCS. In rabbits, TCS was administered by oral
intubation to mothers, but no teratogenic effects were observed
in the offspring. The reviews concluded that at doses of 150 mg
kg−1
and higher, TCS is toxic to pregnant rats, but is not an overt
teratogen. Similar conclusions regarding reproductive and
developmental toxicity of TCS to mammalian species were
reached by Rodricks et al. (2010). However, a study by Russell
and Montgmory (1980), cited mostly for the failure to confirm
mutagenicity of TCS in the mouse spot test, did provide some
reproductive data for TCS. A single intraperitoneal dose of
25 mg kg−1
TCS affected the survival of embryos, significantly
reducing litter size. In addition to reduced prenatal survival, an
average dose of 3.2 mg kg−1
TCS resulted in significant
decreases in postnatal survival. Despite the pronounced effects
of TCS on survivability, very few externally identifiable
abnormalities were observed in newborn mice in the higher
dose groups. The study by Russell and Montgomery is one of
the few studies to have examined the effects of TCS on
mammalian development, as more recent studies have focused
primarily on aquatic species.
Table4.(Continued)
Testspecies/systemLifestageAquaticsystemRouteofexposureTestdurationTCSexposureEffectsReference
Cell‐basedassays
MCF37breast
cancercells
Invitro10μMEstrogenicandandrogenic
effects
Geeetal.(2008)
2933Ycells(human)Invitro1.0and10μM↓Testosterone‐induced
transcriptionalactivity
Chenetal.(2007)
Cell‐based
nuclear‐receptor‐
responsiveand
calciumsignaling
bioassays(AhR,ER,
AR,RyR)
Invitro1–10μM(forER‐
andAR‐responsive
geneexpression;
0.1–10μM(for
RyRresponse)
WeakAhRactivity;
antagonisticactivityin
ER‐andAR‐dependent
geneexpression;
interactionwithRyR1,
↑Ca2+
mobilizationin
skeletalmyotubes
Ahnetal.(2008)
HuH7cells(human
hepatomacellline)
transfectedwith
humanpregnane
Xreceptor(hPXR)
Invitro>10μMActivationofhPXRJacobsetal.(2005)
Inducedratliver
microsomes
Invitro3.1μM(IC50)↓Diiodothyronine(T2)
sulfotransferaseactivity
Schuuretal.(1998)
Triclosan: exposure, toxicity and mechanisms of action
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Endocrine Disruption
The structural similarity of TCS to known estrogenic and
androgenic EDCs, including polychlorinated biphenyls (PCBs),
polybrominated diphenyl ethers (PBDEs), and bisphenol A, and
to thyroid hormones (Norris and Carr, 2006; Veldhoen et al.,
2006; Allmyr et al., 2008) would be predictive, using the
structure–activity relationship, of endocrine disruption. Several
studies have shown that the antimicrobial has the ability to
influence endocrine function in a variety of species (Table 4).
This represents a considerable concern, as large amounts of TCS
are used on a regular basis, with the antimicrobial having been
detected in human plasma (Hovander et al., 2002), breast milk
(Adolfsson‐Erici et al., 2002), urine (Calafat et al., 2008), and the
aquatic environment (Chalew and Halden, 2009).
Thyroid hormones
Investigations of the propensity of TCS to disrupt thyroid
homeostasis are based on the structural similarity of the
antimicrobial to thyroid hormones. If TCS is indeed capable of
perturbing the thyroid axis, the implications for developmental
processes could be profound.
The first study to investigate the effects of polyhalogenated
aromatic hydrocarbons (PHAHs), including TCS, on the metabolism
of thyroid hormones was conducted, to the authors’
knowledge, by Schuur et al. (1998). The in vitro inhibition of
diiodothyronine (T2) sulfotransferase activity was measured
using rat liver cytosol (Table 4). After an incubation of the
PHAHs with induced liver microsomes, T2 sulfotransferase
inhibiting metabolites were formed. Specifically, the IC50 for
TCS was 3.1 ± 0.7 μM. The results of this study were the first to
indicate that TCS and its metabolites, like other hydroxylated
halogenated compounds, are capable of inhibiting in vitro
sulfation of thyroid hormones. Thyroid hormones are inactivated
by sulfation, with sulfation playing a pivotal role in
controlling thyroid metabolism during the developmental
period (Norris and Carr, 2006). Schuur et al. (1998) postulate
that fetal exposure to hydroxylated compounds such as TCS
could result in the inhibition of thyroid hormone inactivation,
with potential consequences to thyroid‐mediated developmental
processes. Future studies are needed to address the in vivo
potential of TCS to alter T2 sulfotransferase activity, and what, if
any, effect that would have on the embryo and developing
fetus.
To further assess the endocrine disrupting potential of TCS,
Veldhoen et al. (2006) conducted a study to assess the potential
of TCS to alter thyroid‐mediated developmental processes in
premetamorphic North American bullfrog (Rana catesbeiana)
tadpoles (Table 4). Tadpoles were immersed in low concentrations
of TCS for 4 days, and on day 4 were injected with 3,5,3′‐
triidothyronine (T3) or a vehicle control. TCS exposure continued
after the injection of T3, ending on day 6, day 11 or day 18, with
tissue samples collected and morphometric measurements
made. Pretreatment with TCS concentrations as low as 0.15 μg
l−1
accelerated metamorphological changes following the
administration of T3. Within 48 h of T3 treatment, T3 mediated
TRβ mRNA expression in the tadpole tail decreased and levels of
PCNA (proliferating nuclear cell antigen) transcript in the brain
increased. In the absence of T3, TCS alone affected thyroid
hormone receptor α transcript levels in the brain and resulted in
transitory weight loss. The results of this study indicate that
environmentally relevant levels of TCS are capable of disrupting
developmental processes that are contingent on thyroid
hormones in the bullfrog. Fort et al. (2010), exposed Xenopus
laevis (South African clawed frog) larvae to TCS (0.6–32.3 μg l−1
)
over a 21‐day exposure period. Although the authors concluded
that TCS did not have an effect on larval development, thyroid
histology, plasma thyroxine levels and/or survivorship, the
reported data suggest that TCS did have an effect on the
postembryonic development of the tadpoles. Moreover, there
was a significant difference between the exposed group and the
control in the expression of TRβ, which was induced by a
magnitude of 1.5 in the 1.5 and 7.2 μg l−1
TCS treatments. A
reduction in larval growth in the 1.5 μg l−1
treatment was also
observed. The evidence available from amphibian studies
suggests that metamorphosis of amphibians is highly sensitive
to TCS and that the HQ value (PEC divided by NOAEC) may be
greater than 1.0.
Following the study by Veldhoen et al. (2006), Crofton et al.
(2007) tested the hypothesis that, in vivo, TCS exposure
influences serum levels of thyroxine (T4) in rats. Long–Evans
females were given TCS (0, 10, 30, 100, 300 or 1000 mg kg−1
day−1
) via oral gavage for a short‐term 4‐day dosing schedule.
Rats were sacrificed 24 h after the final TCS treatment and serum
obtained. TCS doses of 100 mg kg−1
day−1
and higher decreased
serum levels of T4, with the 30 mg kg−1
day−1
dose as the NOEL.
This study was the first to demonstrate that TCS decreases
serum levels of T4 in female rats. The effects of TCS on pubertal
development and thyroid function in the male Wistar rat were
investigated by Zorrilla et al. (2009). Prepubescent male rats
were administered daily doses of 0, 3, 30, 100, 200 or 300 mg
kg−1
TCS via oral gavage for 31 days. At TCS doses of 30 to
300 mg kg−1
, serum levels of T4 decreased in a dose‐dependent
fashion. However, observed decreases in serum levels of T4 only
corresponded to decreases in T3 levels at the 200 mg kg−1
dose,
and colloid depletion was only observed in thyroid sections of
the 300 mg kg−1
treatment group. Compared with the controls,
no significant differences in serum levels of thyroid‐stimulating
hormone (TSH) were noted in any of the treatments. To test the
hypothesis that TCS decreases circulating T4 levels by upregulating
hepatic metabolism of thyroid hormones, Paul et al.
(2010) used a 4‐day exposure protocol in rats to analyze levels of
hepatic enzyme induction (phase I and II enzymes), serum T4,
serum T3, and TSH. Exposure to TCS caused a decrease in total T3
and T4, an upregulation of mRNA expression and an increase in
the activity of a number of phase I and phase II enzymes. The
results of the study support earlier work, which has demonstrated
that TCS‐induced hypothyroxinemia is probably due to the
induction of hepatic enzymes, which augment the catabolism
of T4. Although it is possible that TCS may have direct effects
on the thyroid gland and the production of thyroid hormones,
previous studies have found no evidence to indicate this is
occurring.
A study by Allmyr et al. (2009) is the first to have examined
the effect of TCS on thyroid homeostasis in humans. Participants
of the study brushed their teeth twice a day, for a period of
14 days, with a commercially available brand of dentifrice,
Colgate total, containing 0.3% (w/w) TCS. Blood samples were
collected from the participants prior to TCS exposure and the
day following the termination of the exposure period. Concentrations
of TCS in plasma were significantly higher at the end
of the exposure period. However, despite a significant difference
between pre‐ and post‐exposure levels of plasma TCS,
the increase in TCS had no effect on circulating levels of
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4β‐hydroxycholesterol, a cholesterol metabolite used as an
indicator of CYP3A4 activity, TSH, free T4, and free T3. The study
concluded that the regular use of TCS containing toothpaste
does not induce CYP3A4 activity or disrupt thyroid homeostasis.
Unfortunately, the small study population coupled with the
short‐term exposure period limits the validity of these findings.
Future studies should aim to address the effects of long‐term
exposure to TCS in human subjects, from multiple exposure
pathways, for prolonged periods of time.
Thus far, there has only been one human study (Allmyr et al.,
2009) chronicling the effect of TCS on thyroid homeostasis. In
this study, TCS did not alter circulating levels of thyroid
hormones. In contrast, animal studies have shown that TCS
decreases blood levels of T4, without concomitant changes in
TSH concentrations. Environmentally relevant levels of TCS have
also been shown to disrupt thyroid‐mediated developmental
processes in premetamorphic North American bullfrog tadpoles
(Veldhoen et al., 2006), and possibly in prometamorphic South
African clawed frog tadpoles (Fort et al., 2010). TCS studies on
thyroid disruption suggest that the antimicrobial is capable of
acting on the thyroid receptor and altering the clearance of
thyroid hormones, although future studies are needed to
confirm this suspected mechanism of action and whether or
not these effects are limited to animals. Given that TCS has been
implicated in the disruption of thyroid hormone homeostasis
and has been detected in breast milk samples of nursing
mothers, the priority of future studies should be to ascertain
whether or not TCS exposure can negatively affect fetal and
postnatal development. A better understanding of the mechanisms
of TCS‐mediated thyroid disruption is warranted, in
addition to species‐specific differences.
Sex hormones
TCS is structurally similar to the anthropogenic estrogens,
diethylstilbestrol and bisphenol A, in addition to the anti‐
estrogen, 2,3,7,8 tetrachloro‐p‐dibenzo‐dioxin (Jacobs et al.,
2005). Despite these structural similarities, an in vivo fish study
by Foran et al. (2000) suggested that the antimicrobial was
weakly androgenic, not estrogenic. In this study, Japanese
medakas (Oryzias latipes) were exposed to TCS for 14 days, at
concentrations of 1, 10, 100 and 500 μg l−1
and 1 mg l−1
. The
effect of TCS on phenotypic sex ratios was determined by
inspecting fin size and shape. The antimicrobial had no effect on
the sex ratio of exposed fish, although a slight male bias in the
100 μg l−1
treatment, and an accompanied difference in fin
length between males of different exposure groups, indicated a
possible anti‐estrogen or a weakly androgenic effect (Table 4).
Ishibashi et al. (2004) further investigated the estrogenic
potential of TCS. The estrogenic activity of TCS was measured
using the induction of hepatic vitellogenin (Vtg) in male
medaka, and an in vitro yeast two‐hybrid assay. Hepatic Vtg
levels were increased significantly in males exposed to TCS at 20
and 100 μg l−1
, although this was not the case in the 200 μg l−1
treatment group. The estrogenic activity of TCS was measured in
the yeast two‐hybrid assay alone and in the presence of rat S9
liver fractions. Alone, TCS had a weak estrogenic activity, but
with the addition of the rat S9 liver treatment, the estrogenic
activity of the antimicrobial was increased 2‐fold. The results of
the study suggest that the metabolite of TCS is a weak estrogen,
with the potential of inducing Vtg in male medaka.
Houtman et al. (2004) identified TCS at relatively high
concentrations in the bile of male breams (Abramis brama)
collected at river sites in the Netherlands. The estrogenic
potencies of TCS and other compounds in the bile were
assessed using the ER‐CALUX (Estrogen Responsive Chemical
Activated Luciferase Gene Expression) assay (Houtman et al.,
2007). Estradiol and estrone were the major contributors to
estrogenic activity, where TCS concentrations of up to 0.1 mM
gave no indication of any estrogenic activity. The authors
concluded that the antimicrobial did not contribute significantly
to the estrogenic activity measured in the bile of male breams. It
is important to keep in mind that key differences between the
toxicity of compounds in vivo and in vitro exist.
The potential of TCS to induce Vtg production and decrease
sperm counts, both well‐established biomarkers of endocrine
disruption, was assessed in male mosquito fish (Gambusia
affinis) by Raut and Angus (2010). A 35‐day exposure period to
TCS induced Vtg production and decreased sperm production;
moreover, the hepatosomatic index of TCS exposed fish was
significantly elevated compared with controls. However, it is
important to note that, in this study, endocrine disruption was
observed at TCS concentrations approximately 100 times
greater than those typically detected in surface water, and as
such, it is not known if environmentally relevant concentrations
of TCS would produce similar results.
Matsumura et al. (2005) investigated the effects of TCS on
plasma Vtg levels, testosterone synthesis and hepatic CYP1A and
CYP2B activities in male Xenopus laevis. Waterborne TCS at
environmentally relevant concentrations did not have any
estrogenic effects, while male frogs treated with intraperitoneal
injections of TCS at 4–400 μg g−1
body weight had lower plasma
Vtg and testosterone levels than the control group. Hepatic CYP1A
and CYP2B activity, as measured by EROD or PROD, was not
significantly different from the controls. The authors hypothesized
that the observed decrease in plasma Vtg may be partially
explained by the (anti)estrogenic effects of TCS in male X. laevis.
The evidence provided by fish and amphibian models
suggests that TCS has endocrine disrupting activity, however
the number of studies with these species is limited. The research
efforts to assess endocrine disruption in mammalian models are
more extensive. A potential explanation for TCS’s ability to act as
an endocrine disruptor comes from evidence that the antimicrobial
activates the hPXR. This receptor is stimulated by a wide
array of environmental chemicals and is responsible for
inducing enzymes that metabolize steroids and detoxify
xenobiotics (Jacobs et al., 2005). In the study by Jacobs et al.
(2005), the human hepatoma cell line (HuH7) was used to
quantify PXR activity. Cells were exposed to concentrations of
TCS from 0.01 to 10 μM and the capacity of TCS to induce PXR
activity was expressed as the percentage of the positive control.
At 46.2%, TCS proved to be a moderate inducer of hPXR activity.
In contrast to the other compounds tested, TCS was the only
one to show concomitant increases in percentage maximum
induction, with doses above 10 μM.
Subsequently, Chen et al. (2007) tested the in vitro (anti)
androgenic effect of TCS on testosterone induced transcriptional
activity, in a cell line lacking essential steroid metabolizing
enzymes. These cells (2933Y) are highly sensitive to endogenous
steroids, in addition to anthropogenically sourced
endocrine disruptors. At TCS concentrations of 1.0 and
10 μM, testosterone‐induced transcriptional activity was
reduced by 38.8 and 92%, respectively. In the absence of
testosterone, TCS did not exhibit any androgenic activity, at
concentrations up to 10 μM. A second study to test the
Triclosan: exposure, toxicity and mechanisms of action
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in vitro endocrine disrupting effects of TCS was done by Gee
et al. (2008). This study examined both the estrogenic and
androgenic activity of TCS in breast cancer cells. At
environmentally relevant concentrations, TCS was capable of
producing both estrogenic and androgenic effects. TCS
displaced radiolabeled estradiol from estrogen receptors of
MCF7 human breast cancer cells, whilst also inhibiting
testosterone from binding to the rat androgen receptor.
The endocrine disrupting potential of TCS was further
investigated by Ahn et al. (2008) using in vitro cell‐based
and nuclear‐receptor–responsive bioassays for aryl hydrocarbon
(AhR), estrogen (ER), androgen (AR) and ryanodine
receptors. The results of the cell‐ based AhR‐mediated bioassay
demonstrated that TCS is an AhR inducer, a receptor which has
been implicated in various toxic and biological responses. In
both the cell‐based ER‐ and AR‐mediated bioassays, TCS acted
antagonistically, but was a powerful disruptor of Ca2+
regulation. The authors concluded that the results of their
study provided sufficient reason to be concerned about the
antimicrobial’s neurotoxic potential. These results are further
supported by previous studies that have shown that TCS alters
thyroid homeostasis (Veldhoen et al., 2006). Moreover, there is
evidence that TCS can also influence endocrine function
indirectly, through effects on the metabolism of key hormones,
including the thyroid hormones. The effects of TCS on EROD,
PROD, UDP‐GT and sulfotransferase enzymes, all of which play
a role in the metabolism and clearance of hormones from the
body, have been reported (Hanioka et al., 1997; Jinno et al.,
1997; Kanetoshi et al., 1992; Schuur et al., 1998). In addition,
several in vivo studies have shown that TCS has endocrine
disrupting effects.
Further evidence for the (anti)androgenic effect of TCS was
provided by Kumar and colleagues, who sought to describe
the targets of TCS endocrine disruption, in addition to the
mechanism(s) of action. An earlier study with Leydig cells
exposed to TCS in vitro (Kumar et al., 2008), was followed by a
whole animal study (Kumar et al., 2009). Male rats were dosed
with 5, 10 or 20 mg kg−1
of TCS per kg of body weight per
day. Rats were treated with TCS once a day for a period of
60 days. RT‐PCR analysis indicated that TCS decreased mRNA
levels for testicular steroidogenic acute regulatory (StAR) protein,
cytochrome P450scc, cytochrome P450C17, 3β‐hydroxysteroid
dehydrogenase (3β‐HSD), 17β‐hydroxysteroid dehydrogenase
(17β‐HSD) and AR. The translation of testicular StAR and AR
protein was also disrupted by the antimicrobial. Decreases in
serum levels of lutenizing hormone (LH), follicle stimulating
hormone (FSH), cholesterol, pregnenolone and testosterone were
observed. Histopathological analysis of the testes and sex
accessory glands were indicative of widespread malformations.
TCS‐induced decreases in testosterone and spermatogenesis
were likely the result of decreases in serum levels of LH and FSH,
thereby implicating the pituitary–gonadal axis, at various levels,
as a target for endocrine disruption.
The reproductive effects of TCS on testosterone‐dependent
endpoints in rats were not as clearly evident in a study by
Zorrilla et al. (2009), which sought to assess the effect of TCS on
puberty, as well as thyroid hormones (see section above) in male
Wistar rats. The antimicrobial had no effect on the growth or
onset of preputial separation. A significant difference in serum
testosterone levels was observed in the 200 mg kg−1
treatment,
but not in the 300 mg kg−1
treatment. In addition, the age of
pubertal onset and the development of androgen‐dependent
reproductive tissues did not differ significantly between the
experimental and control groups.
James et al. (2010) tested the vulnerability of the placenta to
the endocrine‐disrupting effects of TCS. TCS proved to be a
powerful inhibitor of estradiol sulfonation in the placental tissue
of sheep, with IC50 of 0.6 nM TCS. As the majority of estrogen
secreted by the placenta is sulfoconjugated and estrogen
sulfonation has been linked to pregnancy loss (Tong et al.,
2005), TCS could potentially have a negative impact on the fetal
environment and pregnancy maintenance. Environmental and/
or household exposure to TCS in humans can lead to blood
levels in the low nanomolar range (Allmyr et al. 2006, 2008). The
possibility then exists for placental levels of TCS to reach
concentrations high enough to interfere with placental estrogen
metabolism.
There is good evidence for the endocrine disrupting effects of
TCS, although it remains unclear as to whether TCS has (anti)
estrogenic effects, (anti)androgenic effects, or both. Foran et al.
(2000) concluded that, based on changes in fin length and
slightly skewed sex ratios in medaka fish, TCS is a weak
androgen. A later study by Ishibashi et al. (2004) reported that a
TCS metabolite induced Vtg production in male medaka,
suggesting estrogenic activity. Evidence from amphibian studies
supported the role of TCS as an anti‐estrogenic chemical.
Several in vitro studies have demonstrated the potential for TCS
to act as an anti‐estrogen and/or anti‐androgen (Chen et al.,
2007; Gee et al., 2008; Ahn et al., 2008). Studies with male rats
(Zorrilla et al., 2009; Kumar et al., 2009) have shown that TCS
decreases serum levels of testosterone and the activity of
several important steroidogenic enzymes. Lastly, TCS is a
powerful inhibitor of estrogen sulfonation in sheep placental
tissue, and as such, could have deleterious effects on the ability
of female mammals to maintain a full‐term pregnancy. Because
TCS has been shown to have estrogenic and androgenic activity
at environmentally relevant levels, there is sufficient reason to
be concerned about the impact of the antimicrobial on aquatic
ecosystems and human health.
EFFICACY AND ANTIBACTERIAL RESISTANCE
Efficacy
The efficacy of TCS‐containing consumer products has recently
been called into question, as several studies have reported that
the antimicrobial is no more effective than regular soap.
Health‐care settings
The efficacy and safety of TCS in health‐care settings was
reviewed by Jones et al. (2000). The popularity of TCS in health‐
care settings has long endured the test of time, as the
antimicrobial has proven its immediate, broad‐spectrum
antimicrobial effects, in addition to the fact that TCS elicits
neither dermal irritation nor photosensitization effects. Interestingly,
cell culture experiments have even shown that the
antimicrobial has anti‐inflammatory, anti‐allergic, anti‐asthmatic
activity and can even protect against cell damage. All of the
aforementioned characteristics are very important for ensuring
antimicrobial acceptance and compliance in health‐care
settings.
The antimicrobial effects of TCS have been established for
concentrations of 0.2–2.0%. TCS formulations of 1% have been
proven effective for managing antibiotic‐resistant Staphylococcus
A. B. Dann and A. Hontela
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aureus outbreaks in health‐care settings, in the form of either
handwash solutions or bathing antiseptics (Jones et al., 2000).
TCS is often favored over other antimicrobial products due to its
mild nature, helping to increase handwashing compliance in
health‐care workers. According to the authors, a 1% TCS
formulation is preferable for securing high rates of handwashing
compliance and reducing nosocomial infections in high‐risk,
high‐frequency handwashing health‐care settings (see Jones
et al., 2000). It is worth reinforcing that, while the use of TCS
formulations appears to be beneficial in high‐risk, high‐
frequency handwashing health‐care settings, these benefits do
not necessarily translate into the domestic domain.
Personal care products
As previously mentioned, a staggering number of personal care
products contain TCS, at varying concentrations. As TCS is not
subject to stringent government regulation, concentrations of
TCS in consumer products can vary substantially, although they
generally remain in the range of 0.1–0.45% (w/v) (Aiello et al.,
2007). A review on the efficacy of TCS‐containing hand soaps,
with efficacy defined as antibacterial activity above and beyond
that of plain hand soap, revealed that, at concentrations typically
present in antibacterial soaps, TCS was not superior for reducing
bacterial counts on the hands or decreasing the prevalence of
infectious diseases (Aiello et al., 2007). In studies that showed
TCS reduced bacterial populations on the hands (Bhargava and
Leonard, 1996), longer handwashes and/or high concentrations
of the antimicrobial were used, accounting for the higher
efficacies recorded. Owing to the lack of data supporting the
efficacy of TCS‐containing antimicrobial soaps, the use of these
products seems unnecessary in light of concerns about the
potential for the selection of antibiotic cross‐resistance and
impacts on the aquatic environment.
Despite a lack of data on the efficacy of TCS in antibacterial
soaps, there is a growing body of evidence to suggest that, in
oral care formulations, TCS and TCS/copolymers deliver effective
antibacterial protection by causing bacterial lysis. TCS is the
most commonly used antibacterial agent in oral care formulations
(van den Broek et al., 2008). According to a review on the
management of halitosis by van den Broek et al. (2008), a
dentifrice formulated with 0.3% TCS, 2.0% of a copolymer of
polyvinyl methyl ether maleic acid and 0.243% sodium fluoride
significantly reduced the incidence of organoleptic sores and
hydrogen sulfide‐releasing bacteria. Moreover, the antimicrobial
and anti‐inflammatory properties of TCS have been proven to
reduce plaque and gingivitis, in addition to slowing the
progression of periodontal disease (Rosling et al., 1997; Cullinan
et al., 2003; Gunsolley, 2006; Rautemaa et al., 2007). The long‐
term use of antimicrobials is, however, worrisome, as resistance
is always a lingering concern, although there is no data to
suggest that TCS‐resistant strains of pathogens have emerged
alongside the incorporation of the antimicrobial into oral care
formulations (Rosling et al., 1997; Cullinan et al., 2003; Rautemaa
et al., 2007). Based on the evidence from several review studies,
the weighing of the risks and benefits of TCS in oral care
formulations strongly favors the use of the antimicrobial in
dentifrice and mouthwashes (Sreenivasan and Gaffar, 2002;
Gilbert et al., 2007).
Plastics and other materials
The number of applications for TCS has expanded immensely
over the years, with the antimicrobial now being impregnated in
a number of different materials, ranging from medical devices to
athletic clothing to meat packaging, in the hopes of providing
the user with long‐lasting antibacterial protection. The extent to
which TCS is able to prevent the proliferation of bacterial
populations in many of these products has not been adequately
established. Ensuring that TCS is consistently released, at
concentrations that are high enough to limit bacterial growth,
remains a significant challenge for manufacturers.
The use of TCS in textiles has been banned in Europe, owing
to concerns of antibiotic resistance and the generation of toxic
by‐products, primarily 2,8‐dichlorodibenzo‐p‐dioxin. However,
manufacturers in North America continue this practice on a
widescale basis. The premise of this manufacturing process is
that TCS will migrate to the surface of the textile, providing
extended antimicrobial release throughout the lifespan of the
fiber (Gao and Cranston, 2008). Despite these claims of
antibacterial protection, experimental evidence to support the
practice of impregnating clothing fibers with TCS remains
limited.
There is no doubt that manufacturers are feeling increased
pressure from consumers to create products that provide
extended antibacterial protection. The development of Micro-
ban©
products, an innovative technology that enables TCS to be
incorporated into virtually any type of plastic material (either
directly into the plastic or as a coating with a second type of
film), while allowing the antimicrobial to accumulate on the
surface to inhibit bacterial growth, has garnered the attention of
the food packaging industry (Vermeiren et al., 2002). It has
been thought that, by incorporating antimicrobial agents such
as TCS, into food packaging, the shelf‐life and safety of the
product(s) would be ameliorated. Although this technology
seems very promising, several in vitro studies have demonstrated
that TCS‐incorporated products do little to prevent the
growth of bacteria in commercial applications, probably due
interactions between TCS and food particles (Cutter, 1999;
Vermeiren et al., 2002).
The effectiveness of TCS incorporated plastic has been
investigated by Cutter (1999). In plate overlay assays, TCS
demonstrated antibacterial activity, but when the plastic was
vacuum‐packaged and refrigerated, bacterial growth was not
sufficiently reduced. The authors attributed the failure of the
TCS polymer to inhibit bacterial growth to the interactions
between TCS and adipose deposits in meat. The antimicrobial
efficacy of a polymer coated in TCS, for the purpose of
packaging perishable foods, has also been evaluated in a study
by Chung et al. (2003). The applicability of the study is limited, in
that only one type of bacteria was used, Enterococcus faecalis, in
addition to the fact that incubations were carried out at one
temperature only, 30 °C. The results of the study specify that
only minute amounts of the antimicrobial are released from the
polymer, although one must consider that the minimum
inhibitory concentration for TCS is fairly low. Despite only small
amounts of TCS being released, bacterial inhibition by the TCS
coating was clearly seen in both the agar diffusion test and a
liquid culture test, although neither test was performed at
refrigeration temperature. Plate overlay assays at refrigeration
temperature, with different bacterial strains, are needed to
confirm the antimicrobial efficacy of TCS in food packaging.
More recently, Camilloto et al. (2009) evaluated the antimicrobial
efficacy of three different concentrations (0, 2000 and
4000 mg kg−1
) of a TCS active film in the preservation of sliced
ham. The activity of the film was tested both in vitro and in
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sliced ham inoculated with E. coli and S. aureus. In the in vitro
experiment, film efficiency was measured by the diameter of the
inhibition halos around the TCS containing film in agar plates
that had been inoculated with E. coli, S. aureus, L. innocua,
S. choleraesius or P. aureginosa. The film only showed inhibition
effects against E. coli and S. aureus. Correspondingly, in the
sliced ham packaged with the TCS‐containing film, a reduction
of 1.5 logarithmic cycles for E. coli and S. aureus was observed
after 12 days of storage at 7 ± 2 °C. The efficacy of TCS
containing films in this particular study are suggestive of a
potential for the use of the antimicrobial in food packaging, as
the film controlled the proliferation of certain types of bacteria
that cause food borne illnesses.
Studies on the efficacy of TCS‐incorporated film have been far
from conclusive, perhaps in part due to methodological
variations. The efficacy of these films is probably dependent
on the type of polymer material, the method of TCS
incorporation and production, the concentration of antimicrobial
used and also the bacterial strains and conditions used
(Camilloto et al., 2009). Testing antimicrobial films at refrigeration
temperatures, with a variety of meat products, is
paramount, since this type of packaging is generally used with
refrigerated foods and fatty acids from meat are thought to
decrease the efficacy of TCS containing films (Cutter, 1999).
Medical devices
Medical devices are often a site of bacterial proliferation, which
can cause debilitating infections and even death. Bacterial
adhesion to medical devices is a serious medical problem that
places a significant strain on the health‐care system. A proposed
solution to this problem has been the incorporation of
antibacterial agents into medical polymers. The antibacterial
potency of TCS incorporated into plasma‐modified medical
polyethylene (PE) and bulk PVC has been investigated (Zhang
et al., 2006; Ji and Zhang, 2009). The results of these two studies
demonstrated that TCS‐incorporated bulk PVC significantly
reduced bio‐film on polymer surfaces and that plasma‐modified
PE with TCS provided adequate antibacterial protection.
However, these studies were laboratory‐based, and it has been
previously shown in antibiotic cross‐resistance studies that the
effects observed in the laboratory setting often do not translate
to the ‘real world’. Further studies are needed to confirm that
TCS‐impregnated medical polymers are genuinely able to
reduce bacterial adhesion and proliferation.
The results of the studies by Zhang et al. (2006) and Ji and
Zhang (2009) do not agree with previous studies on the
antibacterial efficacy of TCS incorporated polymers. Junker and
Hay (2004) compared biofilm populations on ABS plastic
impregnated with or without TCS, after 1–3 weeks of exposure
to drinking water. A lack of measurable differences in bacterial
populations between TCS‐impregnated and control plastic was
observed, a phenomenon which can be explained by the fact
that only a minute amount of TCS actually migrated from the
plastic.
Previously, Kalyon and Olgun (2001) investigated the
antibacterial efficacy of TCS‐incorporated polymers, reporting
that TCS was only capable of inhibiting bacterial growth for a
limited period of time, after which bacterial growth flourished.
The authors suggested that the majority of TCS was not
available to bacteria, as was evidenced by the fact that the
amount of TCS incorporated into the polymer was much higher
than the minimum inhibitory concentration (MIC) for the
bacterial species. The findings of this study are in concordance
with those of Imazato et al. (1995), who studied the efficacy of
dental polymers containing TCS. The TCS incorporated polymer
composites reduced bacterial proliferation for 12 h, but once the
24 h mark had been reached, the number of bacteria on the
surface of the control and the TCS‐incorporated composite were
virtually the same.
Despite the fact that TCS‐impregnated polymers are commercially
available in a wide range of products, few studies have
been able to document their efficacy. With the noteworthy
exception of oral care products, the antimicrobial efficacy of
numerous TCS‐containing products has yet to be validated.
There is an urgent need to critically evaluate the false sense of
security that the mass marketing of antimicrobial products
creates, considering that the injudicious use of antimicrobials
may lead to antibiotic cross‐resistance and should be avoided.
Antibiotic Cross‐resistance
Traditionally, TCS was thought not to be implicated in
antimicrobial resistance because of its broad‐spectrum antibacterial
properties and multiple bacterial targets. However, this
understanding has been called into question, as several studies
have demonstrated the potential for TCS to target a specific
bacterial enzyme, enoyl‐acyl carrier protein reductase (McMurry
et al., 1998). Indeed, laboratory studies have shown that TCS‐
resistant bacteria can be cultured with relative ease, and it has
been suggested that TCS‐resistant bacteria may be the result of
mutations in and/or the over‐production of enoyl reductase,
changes in the membrane permeability, or efflux (Russell, 2004).
However, it is important to remember that at higher concentrations,
biocides, like TCS, have widespread targets. It is usually
only at lower concentrations, not typically in‐use concentrations,
that biocides become more selective in their targets (Russell,
2003, 2004).
The fact that TCS can target a specific enzyme could
potentially be a public health issue in the future, as
antimicrobials are not intended to target any particular cellular
constituents in bacteria (Jones et al., 2000). Instead, it is
antibiotics that exert their destructive powers by targeting
specific cellular components of bacteria. Unfortunately, it is the
case that these cellular targets regularly undergo mutations,
subsequently rendering the antibiotic ineffective. Once it was
discovered that TCS had the ability to target a specific enzyme
in bacteria, researchers began speculating that the antimicrobial
may have the potential to prime bacteria for antibiotic
cross‐resistance.
A review by Russell (2004) examined the link between TCS
and antibiotic resistance. Typical in‐use concentrations of TCS
generally far exceed MICs for most bacterial species, with the
exception of P. aeruginosa. A TCS‐susceptible mutant of
P. aeruginosa, when exposed to TCS, activates an efflux pump
that decreases the susceptibility of the bacterial strain to
ciprofloxacin (Russell, 2003). However, later studies have failed
to implicate TCS in ciprofloxacin resistance in the clinical setting.
Nor is there any evidence to suggest that TCS is linked to
antibiotic resistance in S. aureus. Moreover, comprehensive
surveys on the use of TCS in the home have failed to correlate
the antimicrobial with antibiotic resistance (Cole et al., 2003).
A later review by Yazdankhah et al. (2006) concluded that,
although cross‐resistance between TCS and other clinically
relevant antimicrobials has been documented for E. coli and
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Salmonella spp. in the laboratory setting, these findings have yet
to be confirmed in clinical environments. However, the authors
of the study draw attention to the fact that very few studies
have been done on clinical isolates, suggesting that future
studies on this topic may yet expose such a link. There is also a
large knowledge gap in the literature concerning the impact of
TCS use on commensal bacteria, which have the potential to
transfer resistance to bacterial strains that are known to be
human pathogens. Future studies should address the effect of
TCS on bacteria under typical conditions in community and
health‐care settings, and the relationship between TCS use and
microflora.
Interestingly, some researchers have suggested that, although
TCS resistance has been associated with antibiotic cross‐
resistance in the laboratory setting, these findings do not carry
over to clinical environments (Russell 2003, 2004; Gilbert et al.,
2007; Aiello et al., 2007). This discrepancy is not necessarily
surprising, as laboratory tests on TCS resistance have used
predominantly pure cultures, in nutrient rich environments,
both of which are not representative of real‐world conditions
(Gilbert et al., 2007). As it currently stands, there is a lack of
clinical evidence to suggest that the use of TCS has led to the
propagation of antibiotic resistant staphylococci, antibiotic‐
resistant Gram‐negative bacteria or isoniazid‐resistant
M. tuberculosis, although some researchers continue to speculate
that this type of cross‐resistance is just over the horizon
(Russell, 2003; Aiello et al., 2007).
Conclusions about TCS and a lack of antibiotic cross‐
resistance in a variety of environments must be drawn with a
considerable degree of trepidation, as studies examining the
issue have not provided enough evidence to assuage fears that
the use of the antimicrobial is devoid of risk. Based on the fact
that antibiotic cross‐resistance has been demonstrated in the
laboratory setting, further studies are needed to confirm that, in
clinical, household and community settings, the judicious use of
TCS does not, and will not, lead to antibiotic resistance. It would
then seem logical to suggest that gratuitous use of TCS should
be all but eliminated, whilst allowing for the continuation of its
important clinical functions. The use of TCS should be limited to
applications where it has been demonstrated to be effective,
which includes health‐care settings and in oral hygiene
formulations (Gilbert and McBain, 2002; Cozad and Jones,
2003; Russell, 2004). Currently, the Canadian Medical Association
is calling for a ban on antibacterial products because of
concerns that these products may actually promote bacterial
growth. Previously, many European countries, such as Sweden,
have actively discouraged consumers from using antimicrobial
products.
CONCLUSIONS AND FURTHER RESEARCH
Based on the existing literature, the judicious use of TCS should
be considered safe, and although antibacterial cross‐resistance
has been found in the laboratory setting, there is no evidence to
suggest that it is occurring in clinical and/or household
environments. However, there are a number of different issues
surrounding the use of TCS that warrant further research:
environmental by‐products, bioaccumulation potential, toxicity
to aquatic organisms, endocrine disrupting effects, and the
potential for TCS to prime bacteria for antibiotic resistance.
These issues are of importance for the safeguarding of human
health, aquatic ecosystems and the environment.
Acknowledgments
We would like to thank the anonymous reviewers, especially
reviewer #3, for their critical comments and suggestions about
this review.
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