Mercury

Abstract

Exposure to environmental mercury is an important potential cause of morbidity in human populations, the chief sources of exposure being ingestion of contaminated fish, dental amalgams and vaccines.1 The burning of coal and of mercury amalgams used in gold and silver mining releases mercury vapour into the environment. This mercury then returns to the earth’s surface in rainwater entering waterways, where it is converted by microorganisms to highly toxic methyl mercury which can contaminate fish, becoming further concentrated with each successive step up the food chain. A study by the United States Geological Survey in 2009 revealed mercury in all fish sampled, with concentrations exceeding the US Environmental Protection Agency human health criterion of 0.3 µg per gram wet weight in over a quarter of fish.2 The main route of environmental mercury exposure is ingestion, but inhalation and transdermal uptake also occur. Dental amalgams release mercury vapour, which is inhaled and absorbed into the bloodstream. Ethyl mercury, the active ingredient of thiomersal, is a preservative used in many vaccines.