(Toxic) Metals in the Environment

Toxic metals have accompanied mankind throughout its existence. However, through industrial activity, they now enter the environment to an unprecedented extent. For most people, dietary sources are the main way of exposure to metals. Some of them are beneficial (e.g. Cr(III), Fe, Cu), while others do not have any biological functions (e.g. Cd, Pb and Hg).

Part 1: Pollution in a historical context

Two hundreds of lead in Czechia

source: Novák et al. (2004), doi:10.1021/es0200387

We have illustrated the tendency of the burden reduction for the population of the Czech Republic on the example of lead emissions development from transport and industry. However, since the metals are non-degradable (they cannot decompose to anything else, only change compounds or be deposited), once mined and mobilized elements do not dissapear from the environment completely.

Part 2: What does it mean to be a toxic metal? What metals are the most dangerous?

According to vague definition of "heavy metals", their typical representative is such a useful metal as iron. At the same time, iron is the most frequently deficient element in the world. (It is followed by zinc.) Saturation of the body with iron is an ideal protective factor against the action of toxic elements, as the body does not show an excessive tendency to absorb metal cations from the diet when saturated with Fe. 

After absorption into the body, metals behave differently and they also have different target organs. They may also pronounce an allergenic effect by mere touch (nickel is a typical contact allergen). In the treatment of acute posioning (which is rather rare today), chelating therapy is used, whilst chelating agents such as EDTA od dimercaprol are administered. 

Cadmium

Cadmium in its elemental, metallic, form. Cadmium compounds are all toxic and classified as carcinogens. Cd is consumed mostly with plant foods, but smokers have a different source of cadmium – tobacco as a very well-accumulating plant.

Hg thermometer

The use of mercury thermometers is being phased out, but they are still popular in homes and hospitals. However, when they break, you need to know what to do. It is best to collect the mercury in a glass container and take it to a pharmacy, to a collection yard or to a fire station. Vapors released from residues are dangerous, so it is necessary to clean up really thoroughly.

As, Cd, Hg, Pb

Four elements that are carefully monitored and have strict limits for occurrence in foodstuffs.

Part 3: Typical toxic metals

The most risky elements, such as Cd, Hg and Pb, do not have a useful function in the body. We would like their concentration in food, the environment and the body to be zero, but in reality this is not achievable. They are natural part of the environment. However, human has mobilized a substantial amount of them into the environment – the higher amount than natural sources!

Let's now focus on Mercury, which is a very illustrative element. Its forms (compounds) behave very differently. While methylmercury (MeHg), found in fish, is a very toxic matter, metallic mercury – unless we consider its vapors! – is not that available for the body. I will also explain benefits of hair and nails analysis as a useful materials for biological monitoring. 

In the video, I refer to a three-minute documentary about the tragedy in Minamata, Japan, where dozens of people died of methylmercury poisoning from fish consumption. The video contains rough footage of poisoned people and cats (as they often got the guts from the fish). Therefore, it has long been thought that the disease is transmitted from cats, which has been fatal for many of them.

Learning resources

The test questions, as well as one of the state questions, are based on presentations and comments.

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