Mercury enjoys very special physical-chemical properties. But this substance and its compounds are toxic, persistent in the environment and bio-accumulate in the food chain.

Properties and uses

Some properties of mercury explain its presence in several industrial products and processes. It is especially appreciated for its antiseptic values, its ability to amalgamate metals and even as metal that remain in liquid state at room temperature.

It is used under varied forms in measuring devices, vaccines, electronic components and even pesticides. It is also used in industrial processes (among other things for the production of chlorine and sodium) and large amounts are used in gold extraction activities in rivers.
Multiple uses of this substance and its compounds result in pollution at the global scale. It is necessary to prevent emissions for restricting exposure of mercury to man and the environment. This is what the States are tackling through the United Nations Environment Programme (UNEP).

Risks to the health and the environment

Mercury is a substance that is hazardous to health and environment, even in very tiny doses. Especially for the development of nervous system of young children, including through their mother's exposure during pregnancy. It is a persistent substance: it has unlimited lifespan and its various chemical compounds are toxic.

Mercury is naturally present in the environment, in various ores and in carbon. To this is added the mercury that human activities discharge in the air, water and soil.

In the environment, mercury undergoes changes leading to the formation of methylmercury, a form of highly toxic mercury. This methylmercury accumulates in the food chain. The human and animal population is therefore exposed to this compound, especially through eating fish.  
Mercury was measured in hair samples of 120 mother / child pairs in 17 countries under the LIFE + project DEMOCOPHES, coordinated by the FPS.
1.4% of the European children and 3.4% of the mothers have levels of mercury in their hair above the FAO/WHO health guidance value of 2.3 µg/g hair. In Belgium, that value is not exceeded, not even in a single mother or child.
Moreover, if we consider the European average as 100%, the average per country varies from about 10% to about 150% for Belgium, to 600% for countries around the Mediterranean Sea such as Spain, which consume significant amounts of large predatory fish.
The general recommendation is to not eat more than two portions of fish, including one portion of oily fish per week. This is especially true for pregnant women, lactating women and children. Condition is that predatory fish containing high levels of pollutants such as mercury, including shark, swordfish, marlin and, in a lesser extent, tuna are avoided.

Moreover, this substance travels long distances and a concentration has been identified at the poles.

The Minamata Bay, a martyr to mercury
In the 1950s and 60s, thousands of Japanese residing around the Minamata Bay were deeply affected by methylmercury. An industry discharged water in this Bay which was contaminated by mercury used in its industrial manufacturing process. This in turn contaminated the fish consumed by the local population. Medical authorities hesitated for a long time before identifying the reason for the symptoms seen in the population.
The international treaty aiming to reduce mercury emissions around the world is called the "Minamata Treaty" in reference to this health and environmental catastrophe.