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3. What are the impacts of mercury on the environment?

  • 3.1 How does mercury accumulate in organisms?
  • 3.2 How is wildlife affected?
  • 3.3 How may certain ecosystems be affected?

3.1 How does mercury accumulate in organisms?

Methylmercury can accumulate along the food chain
Methylmercury can accumulate along the food chain © Aurileide Alves

The harmful effects that different forms of mercury can have on living things are greatly influenced by bioaccumulation (build up inside an organism) and biomagnification (build up along the food chain).

All forms of mercury can accumulate in organisms. However, methylmercury is taken up at a faster rate than other forms and bioaccumulates to a greater extent.

In fish, methylmercury becomes so tightly bound in the tissues that, if exposure ceases, it takes a very long time for it to be removed.

This tighter binding leads methylmercury to build up (biomagnify) much more than other forms of mercury along the food chain, e.g. from smaller fish to larger predatory fish. As a result, nearly 100% of the mercury that accumulates in predator fish is methylmercury. Another consequence is that older fish typically have higher mercury concentrations in their tissue than younger fish of the same species, partly because older fish eat more fish and larger fish as they age.

The extent to which mercury will bioaccumulate in any given situation depends on several factors. One important factor is how much mercury is converted to methylmercury, and vice-versa, particularly by some bacteria in the aquatic environment. Consequently, the extent of bioaccumulation and biomagnification of mercury in fish remain difficult to predict in specific situations.

The mercury in fish is passed on to the predators at the top of the food chain (e.g. humans, seabirds, seals, otters, eagles and ospreys) and how much they accumulate depends on the type and size of fish they eat. More...

3.2 How is wildlife affected?

Methylmercury is a poison for the central nervous system. During the Minamata poisoning incident in Japan (see 2.1.1), birds had trouble flying and behaved abnormally in other ways.

Mercury can also affect reproduction. Methylmercury poses a particular risk to the developing foetus because it readily moves into the placenta and can damage the developing nervous system. Mercury may be present in eggs and harm bird reproduction even when concentrations in eggs are low.

The kidneys are the organs most vulnerable to damage from inorganic mercury.

Rising levels of mercury are a concern for some seals and whales in the Arctic and for predatory marine mammals in warmer waters. More...

3.3 How may certain ecosystems be affected?

Recent evidence suggests that mercury is reducing microbiological activity, vital to the terrestrial food chain. This may already be affecting forest3 soils over large parts of Europe and potentially in many other places in the world with similar soil characteristics.

Impacts from long-range transport of mercury in the Arctic region have been the focus of recent discussion, but the effects are by no means restricted to this region of the world. The same food web characteristics are found in specific ecosystems and human communities in many countries, particularly in places where a fish diet is predominant.

There are indications that climate change might also increase the levels of methylmercury in water in some areas, and its accumulation in fish. More...

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