In the Amazon River basin in Brazil, placer mining boomed at the end of
the 1970’s; many people began mining riverbeds and the ground of tropical
Since miners used metallic mercury for refining placer ores, released mercury
polluted the river and its basin.
Similar mercury pollution problems occurred in Tanzania, the Philippines,
Indonesia, China, and several other countries.
To date, studies of these pollution problems have revealed that mercury
released into rivers were converted to methylmercury, ] and accumulated
in fish living in the rivers concerned.
In addition to the inorganic mercury poisoning afflicting miners, therefore,
methylmercury poisoning is likely to affect the health of residents in
the relevant basins, particularly those living along the lower reaches
of the rivers.
To address such potential health problems, scientists of various nations
visited polluted areas to jointly survey the degrees of pollution and its
influence on the health of residents.
Metallic mercury (Hg0) used for refining placer ores is released from miners’ rafts into the
Of the amount, 55-60% evaporates, while the remaining 40-45% falls into
In the air, the evaporated Hg0 is oxidized by water (H2O) and ozone (O3), and becomes mercury ion (Hg2+), which then falls onto the ground with rain.
If it falls on ground of acid soil (around pH4), Hg2+ transforms to organic methylmercury (Hg(CH3)+), which is the immediately taken in by organisms living in the soil.
The methylmercury then undergoes bioaccumulation through the food web.