High exposure of Chinese mercury mine workers to elemental mercury vapor and their increased hair methylmercury levels: A preliminary report

Abstract

Environmental impact resulting from mining activities is serious and ubiquitous all over the world, and it has become one of the important aspects in environmental geochemistry. The environment was seriously damaged by wastes from historical zinc smelting in Northwest Guizhou. The geochemical distributions of Pb and Zn in the different grain-size fractions of wastes indicate that the coarser particles show similar or even higher heavy metal concentrations than finer ones in the samples, although the concentrations of heavy metals tend generally to increase as the size fractions get finer. The heavy metal contents are very high, with maximum values of 31631, 57178, 2367 and 311.5 mg/kg for Pb, Zn, Cu and Cd, respectively. It is also shown that the residual fraction of Pb is less than that of Zn, accounting for 0.39%--15.75% and 14.3%--46.2%, respectively, of the total, and this is likely relative to Zn-silicate minerals formed from smelting. Although the relative partitioning of Pb and Zn is very low (0.03%-1.3.% for Pb; 0.03% --3.3% for Zn), the exchangeable fraction of the waste contains large amounts of heavy metals (1.5%--385 p,g/g for Pb; 3--590 ~tg/g for Zn). Heavy metals in exchangeable forms have the highest solubility to give the highest potential bioavailability in contrast to other chemical forms. Mineralogical study indicates that the wastes were found to be highly heterogeneous materials, dominated by quartz, feldspar, carbonatite, iron or/and aluminum vitric compounds and a few secondary mineral phases, and their contents vary with the type of smelting wastes. The secondary minerals formed from smelting and sequentially weathering are the major chemical phase for heavy metals. Complex composition of many phases and substitution of elements suggested that many of the phases were found to be non-stoichiometric compounds. Pb was found to be the main Pb phase in the wastes by precipitation or/and adsorption. The species Zn is more complex in the form of occurrence than Pb, and Zn-bearing minerals include willemite, tephrowillemite and zinalsite, and occasionally Zn can be found in the wastes, and this is a possible reason why the relative partitioning of Zn in residue fraction is higher than that of Pb. The natural releasing processes of Pb, Zn and Cd in the wastes can be primely described with minus-exponent equation and with prolongation of piling time, the contents of these heavy metals in the wastes decrease gradually. They are hazardous to environment because of their high total contents and long-time release.