Chemical availability of mercury in stream sediments from the Almaden area, Spain

The chemical speciation, fractionation and availability of mercury in sedim ents from a cinnabar mining area (Almaden, Spain) was studied with differen t extraction and analytical procedures, in order to determine the degree to which the ecosystem is harmed by this pollutant. Three total extraction pr ocedures, a sequential extraction and the speciation of organo-mercury comp ounds were performed in nine sediment samples. In the study area, although concentrations of mercury can be extremely high (up to 1000 mg kg(-1)), no organo-mercury compounds were detected (< 2 mu g kg(-1)) and the availabili ty of this element seems restricted. One of the methods for total extractio n presented considerably lower recovery in Almaden's sediments, yet the res ults were controlled with certified reference materials. This disagreement was attributed to the fact that the mercury is in a refractory form. Sequen tial extraction was able to show that most of the mercury is associated wit h sulfides (probably as metacinnabar) or in the residual refractory phase ( probably as red cinnabar).