While some pollutants are restricted in their range and in the size and number of the population they affect, mercury is not one of them. Wherever it is mined, used or discarded, it is liable – in the absence of effective disposal methods – to finish up thousands of kilometers away because of its propensity to travel through air and water. Beyond that, it reaches the environment more often after being unintentionally emitted than through negligence in its disposal. The prime example of this is the role played by the burning of fossil fuels and biomass in adding to mercury emissions. Once released, mercury can travel long distances, and persists in environments where it circulates between air, water, sediments, soil, and living organisms. Mercury is concentrated as it rises up the food chain, reaching its highest level in predator fish such as swordfish and shark that may be consumed by humans. There can also be serious impacts on ecosystems, including reproductive effects on birds and predatory mammals. High exposure to mercury is a serious risk to human health and to the environment. Air emissions of mercury are highly mobile globally, while aquatic releases of mercury are more localised. Mercury in water becomes more biologically dangerous and eventually some mercury evaporates into the atmosphere. Once deposited in soils and sediments, the mercury changes its chemical form, largely through metabolism by bacteria or other microbes, and becomes methylmercury, the most dangerous form for human health and the environment. Methylmercury normally accounts for at least 90 per cent of the mercury in fish. Mercury can enter the food chain either from agricultural products or from seafood.
From collection: Mercury - Time to act