Mercury in nature/fish Print
Friday, 23 September 2011 16:01

There are several forms of mercury that exist naturally in the environment, with the most common being metallic mercury, mercuric chloride, mercuric sulphide, and methylmercury.

Mercury can be changed from one form to another by natural processes. A good example is where chemical reactions in the atmosphere can transform elemental mercury into inorganic mercury.

Some micro-organisms can produce organic mercury, particularly methylmercury, from other mercury forms. Methylmercury can accumulate in living organisms and reach high levels in fish and marine mammals via a process called biomagnification (i.e. concentrations increase in the food chain).

Because mercury is one of the basic chemical elements, of which all things are made, it cannot be broken down or degraded into something else. Once released into the biosphere through natural events or human activities, mercury readily moves and cycles through the environment. Mercury is believed to rest in soil, water bodies and the sediments underneath them until it is ultimately removed from the biosphere again.

Methymercury contamination of fish and fish-eating mammals is a global public health concern.

For that reason in 2009, and before going to the 25th session of the UNEP Governing Council (February 2009), ZMWG published a report after having carried out a study of fish tested in different locations around the world. The study shows that internationally accepted exposure levels for methylmercury are exceeded, often by wide margins, in each country and area covered. According to the report, “Mercury in Fish: An Urgent Global Health Concern”, the risk is greatest for populations whose per capita fish consumption is high, and in areas where pollution has elevated the average mercury content of fish. In cultures where fish-eating marine mammals are
part of the traditional diet, mercury in these animals can add substantially to total dietary exposure. In addition, the study shows that methylmercury hazards still exist where these dietary and local pollutant levels are less prevalent.

Executive summary in ENFR, ES, PT, CHI
[10 February 2009]