ABSTRACT
Biogeochemical processes in sediments have an important role on the mobility and bioavailability of toxic trace metals in aquatic ecosystems, as well as on the cycling of other elements, including carbon, nitrogen and sulfur. The latter elements have in turn important implications for plant productivity and human health (Gadd, 2004). The state of metals in terms of mobility depends highly on the organisms involved and the oxidation state of the environment. The role of microorganisms in the metal speciation and mobility has received more attention recently. As examples of the effects microbial activities on the mobility of metals, it is possible to mention reduction of Fe(III) to Fe(II), Mn(IV) to Mn(II), Cr(VI) to Cr(III), U(VI) to U(IV) and biomethylation of Hg, As, Se, Sn, Te and Pb.
