Distribution of mercury in the aquatic environment at Almadén, Spain.

The world's largest mercury mine is placed at Almadén, Spain. However, there is a lack of information about the environmental impact of these mining activities in the ecosystem that surrounds this area. The aim of this article is to document the concentration of mercury in waters, sediments and bivalves of the aquatic system impacted by historic mine wastes. Simultaneously, a comprehensive study has been undertaken to characterise this hydrosystem and to determine the influence of some major physico-chemical parameters on the fate of mercury. Samplings were carried out for the last few years. Concentration of mercury in waters ranged from not detectable to 20 microg/l. For the sediments study, samples have been taken both from contaminated and non-contaminated sites within the basin. The regional background mercury concentration is higher than values typically cited for natural backgrounds. At exposed sites the mercury concentrations between 5 and 1000 microg/g were measured. These values are one to four order of magnitude greater than regional background levels. In the comparison between the results obtained at the present moment and those available for the 1974-1977 period, a general diminution of mercury levels is observed. Mercury concentrations in fresh water bivalves ranged between 1 and 4 microg/g (d.w.), with around 30% as monomethylmercury. In the discussion of the implications for risk assessment data available for other areas affected both for mine activities and mercuriferous belt are included.