ECOTOXICITY TESTING OF HEAVY-METALS USING METHODS OF SEDIMENT MICROBIOLOGY

Current measures of microbe-mediated biogeochemical processes in sedim ents were examined for their potential use as indicators of heavy meta l ecotoxicity in both river sediments and bacterial -cultures. Assays were carried out with HgCl2, CuSO4, and 3CdSO4 . 8H2O added to sedimen t samples and bacterial cell suspensions at concentrations ranging fro m 0.1 to 10 mM and 0.1 muM to 1 mM, respectively. Chemoautotrophic CO2 fixation by Elbe River sediment microbiota was most sensitive to Hg2 and Cd2+, but not to Cu2+. Among the estimates of heterotrophic produ ctivity, incorporation of leucine into cellular protein showed clearer dose responses than incorporation of thymidine into bacterial DNA. Th ymidine incorporation was highly resistant to and even stimulated by m etal ions, particularly in starved and anaerobic cultures of a test st rain of Vibrio anguillarum. Similar metal ion induced ''overshoot'' re sponses beyond the levels of untreated controls were noted for mineral ization of C-14-glucose by V. anguillarum and, in the case of Cd2+, al so in sediment. As a less complex measure of microbial respiratory act ivity, succinate dehydrogenase (SDH) showed normal dose responses with out stimulatory effects, as long as bacterial cell homogenates were as sayed. Despite this result, it is concluded that levels of SDH in natu ral sediment microbiota are inevitably affected by metal-induced proce sses of selection and enzyme synthesis, and would thus fail to provide an appropriate measure of metal ecotoxicity. The final conclusion is that current parameters of microbial production and activity often rev eal dose responses that do not fulfill basic requirements of ecotoxici ty testing in metal-polluted sediments. (C) 1993 John Wiley & Sons, In c.