Mercury (Hg), also known as quicksilver, is a naturally occurring chemical element. It is a heavy, silvery-white metal which is liquid at room temperature and evaporates easily. Mercury exists in several forms: elemental (metallic) mercury; methylmercury and other organic compounds; and inorganic mercury compounds. In the earth’s crust, mercury is usually found in the form of cinnabar, used in the past as a red pigment. While all humans are exposed to some level of mercury, high exposure is a serious risk to human health and to the environment.
Mercury has been recognized as a chemical of global concern owing to its long-range atmospheric transportation, its persistence in the environment, its ability to bioaccumulate in ecosystems and its significant negative effects on human health and the environment.
Emissions of Mercury
Mercury is released into the atmosphere or into global waters from natural sources, such as volcanoes and forest fires, and through anthropogenic processes.
Human activities that release mercury include coal burning, mining and smelting of iron and non-ferrous metals, cement production, oil refining, artisanal and small-scale gold mining, incineration of consumer products or slow degradation in landfills, use of dental amalgam, chlor-alkali production, and vinyl-chloride monomer production.
Air emissions of mercury are highly mobile globally, while aquatic releases are more localized. In soils and sediments, on in the water column, mercury can change its chemical form, largely through metabolism by bacteria or other microbes, and become methylmercury, a particularly toxic form of mercury. Methylmercury normally accounts for at least 90 per cent of the mercury in fish.
Hazardous effects of Mercury
Once released, mercury can travel long distances, and persists in the environment 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 in swordfish and sharks that may be consumed by humans. There are also serious impacts on ecosystems, including reproductive effects on birds and predatory mammals.
Elemental and methylmercury are toxic to the central and peripheral nervous systems. The inhalation of mercury vapour can produce harmful effects on the nervous, digestive and immune systems, as well as on lungs and kidneys, and may be fatal. The inorganic salts of mercury are corrosive to the skin, eyes and gastrointestinal tract, and may induce kidney toxicity if ingested. Neurological and behavioural disorders may be observed after inhalation, ingestion or dermal exposure of different mercury compounds. Symptoms include tremors, insomnia, memory loss, neuromuscular effects, headaches and cognitive and motor dysfunction.
The tragic health consequences from industrial mercury pollution in the 1950-60s in the Minamata Bay in Japan raised the world’s awareness of the dangers of mercury pollution. Global efforts to tackle mercury pollution resulted in the adoption in 2013 of the Minamata Convention, a global treaty to protect human health and the environment from the adverse effect of mercury.
