Levels of total mercury and methylmercury compounds in sediments of the polluted Elbe River: influence of seasonally and spatially varying environmental factors

The Elbe River system in Germany is severely polluted with mercury, including methylmercury compounds. In the vicinity of the city of Hamburg, content of total mercury and methylmercury compounds in sediments of 12 mg/kg and 35 μg/kg (d.w.), respectively, are observed. Analyses of sediment samples from selected sites during different seasons indicate that levels of methylmercury compounds are dependent on microbial activity. CH3Hg+ content is high under conditions that stimulate Hg(II)-methylating microorganisms. Thus, levels are elevated where nutrient supplies and biological productivity are greatest. In addition, methylmercury content in the sediments increases with increasing abundance of acid volatile sulfide (AVS). Examination of seasonal effects shows larger amounts of methylmercury compounds under warm summer conditions than in cold winter and spring weather. Additional evidence indicates the importance of microbial activity for the production and occurrence of methylmercury compounds in sediments. A more detailed local cycle for mercury compounds is proposed, taking into account the data presented in this paper.