Comparison of methods to measure acute metal and organometal toxicity to natural aquatic microbial communities

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Abstract
Microbial communities in water from Baltimore Harbor [Maryland, USA] and from the mainstem of Chesapeake Bay were examined for sensitivity to HgCl2, monomethyl mercury, SnCl4 and tributyltin chloride. Acute toxicity was determined by measuring the effects of [3H]thymidine incorporation, [14C]glutamate incorporation and respiration, and viability as compared with those of controls. Minimum inhibitory concentrations were low for all metals (monomethyl mercury, < 0.05 .mu.g l-1; HgCl2, < 1 .mu.g l-1; tributyltin chloride, < 5 .mu.g l-1) except SnCl4 (5 mg l-1). In some cases, HgCl2 and monomethyl mercury were equally toxic at comparable concentrations. The Chesapeake Bay community appeared to be slightly more sensitive to metal stress than the Baltimore Harbor community, but this was not true for all treatments or assays. For culturable bacteria, the opposite result was found. Thymidine incorporation and glutamate metabolism were much more sensitive indicators of metal toxicity than was viability. Evidently, this is the 1st use of the thymidine incorporation method for ecotoxicology studies. It is the easiest and fastest of the 3 methods, at least equal in sensitivity to metabolic measurements and likely measures the effects on the greater portion of the natural community.