Mercury - the only metal that is liquid at ambient temperature - is an indestructible chemical element that is highly toxic to humans, animals and ecosystems. Exposure to large amounts of mercury can be fatal, but relatively low doses can also have serious health effects, affecting the nervous, cardiovascular, immune and reproductive systems in particular. In the presence of bacteria, mercury can convert to methylmercury, a more complex and harmful mercury compound, which passes both the placental barrier and the blood-brain barrier and can therefore inhibit children's mental development before and after birth. Exposure of women of child-bearing age and of children is therefore of greatest concern.
The main risk of exposure for human beings is through food as methylmercury accumulates in fish and seafood, in particular in large predatory fish. Other significant exposure risks result from human activities, including mercury mining, the use of mercury in products and industrial processes and artisanal and small-scale gold mining.
You can find a basic description of the mercury problem here. Mercury: Time to Act published in 2013 by the United Nations Environment Programme (UNEP) provides a good overview of the mercury problem on the global scale.
To address further mercury use and pollution, the Community Strategy concerning Mercury was adopted in 2005 and reviewed in 2010. It focuses, in particular, on mercury emissions to air, on banning export of mercury and of certain mercury compounds and on restrictions on mercury-added products and industrial processes using mercury.
As a long-range transboundary pollutant, mercury can affect areas located thousands of kilometers away from the sources of emissions. Accordingly, the EU has also endeavoured to address the global challenges posed by mercury, hence dedicating 7 of the actions foreseen in the Community Strategy concerning Mercury on measures to be implemented on the international level. Considerable progress has been made in this respect. Spearheaded by UNEP, the United Nations Environment Programme, an international negotiation process resulted in the signing by 127 countries and the Union of the Minamata Convention on Mercury, named after the Japanese town where the worst ever case of mercury pollution happened in the years 1950.
To allow the EU to implement and ratify the Minamata Convention, the European Commission adopted on 2 February 2016 a Minamata ratification package including proposed legislation to update EU law where needed to fully conform with the Convention.