Effect Of Sulfur Biotransformation On Heavy Metal Bioavailability In Lake Sediment

Heavy metal pollution has become a major environmental problem around the world. Speciation, mobility and bioavailability of heavy metals are important for assessing potential toxicity risk potential of these metals. Sulfate reducing bacteria (SRB) is not only the main participator of sulphur cycle but also the one of the most important factors of decreasing heavy metal bioavailability. Studying physiological function of SRB which affects heavy metal transformation is important to heavy metal pollution remediation.Several heavy metals (Cr, Cu, Ni, Pb and Zn) contaminations were studied in surface sediment of Taihu Lake. Spatial variation were observed in total metal contents. Site S2 (Xiaomeikou estuary) maintained highest Cr and Pb contents, while site N5 (Zhushan Bay) maintained highest Cu, Ni and Zn contents. The spatial and temporal variation were observed in metals species determined by BCR extraction. The DGT-labile concentrations of Zn, Ni, Pb Cu and Cd in sediment of Taihu Lake were in the descending order, indicating the inconsistence of labile concentrations of different heavy metals with the total metal contents. According to DGT-measured concentrations, risks of Cd exposure in sediment of Taihu Lake should be paid attention to. AVS contents were positively correlated with the concentration of SO42- in porewater, indicating that SRB was important to transform substrate SO42- to AVS. However, correlations between AVS and CDGT were not significant. Heavy metal bioavailability in surface sediment of Taihu Lake may be influenced by exogenous inputs and wind-wave disturbance during certain seasons. According to the hakanson potential ecological risk index, the ecological risks of heavy metals were low in Taihu Lake sediment and Zhushan Bay was exposed to highest ecological risk that should be taken into consideration seriously.Two strains of SRB (Enterobacter sp.taihuN3 and Desulfotomaculum sp.taihuN5) were isolated from sediments of Taihu Lake in this study. Enterobacter sp.taihuN3 can utilize a variety of organic acids as carbon sourses and reduce 45% nitrate into nitrite, but sulfate-reducing activity was totally inhibited with the concentration of 1 g/L NaNO3. When the initial concentration of sulfate was 1.5-8 g/L, strain taihuN3 can remove the 75-42% sulfate and strain taihuN5 can remove the 8.2-79%. Removal rate decreased with increased initial sulfate concentration. When lactate was the sole carbon sourse and C/SO4-> 1, taihuN3 and taihuN5 can remove more than 90% and 95% sulfate respectively.Reduction and removel of As (V) by Enterobacter sp.taihuN3 and effects of adding other heavy metal were studied. Enterobacter sp.taihuN3 can utilize the SO4- in medium added with 200 mg/L As (V) and reduce 68.4% As (V) to As (â…¢) without the methylation process. The homologies of amino acid sequences of of arsenate reductase from arsC gene of strain taihuN3 and Enterobacter cloacae subsp. cloacae ATCC 13047 was 97%. Enterobacter sp.taihuN3 reduced As (V) to As (â…¢) and transported out of the cell to decrease the toxicity. Adding Zn2+ can enhance the arsenic removel by reducing S2- concentration to keep As2S3 precipitate from redissolving and adsorbing/wrapping arsenic during biogenic process of nano ZnS particles.