Mercury (Hg) also known as quicksilver is a naturally occurring element found in rocks in the earth’s crust. It is a heavy, silvery-white metal which is liquid at room temperature and evaporates easily. It exist in several forms: elemental (metallic) mercury; methylmercury and organic compounds; and inorganic mercury compounds. In nature it is usually found in the form of cinnabar, used in the past as a red pigment.
Emissions of Mercury?
It is released into the atmosphere or into global waters from natural sources, such as volcanoes and forest fires, and through anthropogenic processes. These human activities include: coal burning, mining and smelting of iron and non-ferrous metals, cement production, oil refining, artisanal and small-scale gold mining, burning of consumer products or slow degradation in landfills, use of dental amalgam, chlor-alkali production, and vinyl-chloride monomer production. Once released, mercury persists in the environment, cycling through air, water, land, sediments, animals and plants.
Why is Mercury a problem?
Mercury has been recognized as a “chemical of global concern owing to its long-range atmospheric transportation, its persistence in the environment once anthropogenically introduced, its ability to bioaccumulate in ecosystems and its significant negative effects on human health and the environment”.
Hazardous effects of Mercury to ecosystems and human health
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 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 are more localized. Mercury in water becomes more biologically dangerous. Once deposited in soils and sediments, mercury changes its chemical form, largely through metabolism by bacteria or other microbes, and becomes methylmercury, the most dangerous form for health. Methylmercury normally accounts for at least 90 per cent of the mercury in fish.
All humans are exposed to some level of mercury. 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.
Minamata Convention on Mercury
The Minamata Convention on Mercury is a global treaty to protect human health and the environment from the adverse effects of mercury. It was adopted in 2013 and entered into force in August 2017.
The Knowledge and Risk Unit of the UN Environment Chemicals and Health Branch supports monitoring and waste-related projects and activities to assist countries in the environmentally sound management of POPs and mercury waste. It is also participating in the Small Intersessional Working Group established by the Basel Convention.
- Global mercury monitoring project
- Development of the Mercury laboratory databank
- Mercury waste management project (2008-2010)
- Technical and economic assessment of mercury-containing tailings (2009)
- Chlor-Alkali Project in Uruguay