Atmospheric mercury and fish contamination in the Amazon

RESUMO

Gold mining releases approximately 200 tons of mercury into the Amazon. Sixty-five to 83 percent of this input enters the atmosphere. Mercury emitted to the atmosphere is highly reactive and readily available for methylation and further bioaccumulation after beins washed out from the atmosphere. On the other hand, mercury lost to rivers and soils as liquid Hg(o) is practically unreactive and contributes little to the mercury burden of the biota. Atmospheric mercury returns to surface environments at a rate of 90 to 120 mug.m(-2).yr(-1), mostly as Hg(2+) and particulate-Hg. These forms are readily methylated in various Amazon environments, in particular flood plains, black-water rivers, lakes and reservoirs. The biology of many Amazon fish species, which migrate seasonaly to these flooded areas, favor the incorporation of methyl-Hg. Also, seasonal flooding contributes to exportation of methyl-Hg to large Amazon rivers.