January, 2013

Abstract

In spite of its low abundance in the Earth's crust, mercury (Hg) has aroused substantial attention, first because of its numerous applications and more recently because of its toxicity. The extensive use of Hg has resulted in significant contamination of soils locally and regionally and sometimes to human and animal exposure at toxic levels. Human use of Hg started already in antiquity and reached a maximum around 1975. Since then the major applications have been strongly reduced in many countries. All chemical forms of Hg are toxic to humans and animals, methyl Hg in particular. In soils Hg may originate from Hg minerals, diffuse air pollution, and local pollution sources such as chlor-alkali factories and the use of sewage sludge and organic Hg compounds in agriculture. Elemental Hg from the atmosphere mainly due to previous human emissions is a dominant source of soil pollution worldwide. In soils, Hg occurs as various forms of Hg(II), generally strongly bound to organic matter and sulphides. The Hg content is generally higher in organic-rich soils than in mineral soils. Root uptake of Hg in plants is generally low, and Hg in above-ground plant material is mostly derived from atmospheric deposition. Under reducing conditions in soils methyl Hg may be formed and subsequentlytr ansportedt o lakes and rivers and accumulatedi n aquatic food chains.