Discriminating the ecotoxicity due to metals and to low pH in acid mine drainage

Several techniques have been developed to assess the ecotoxicity of contami nated watercourses. Most of these techniques involve chemical alterations o f water samples, by diluting it or by adding chelating agents. These change s become particularly severe when assessing the toxicity of samples with ve ry low pH and with high quantities of contaminants. Trying to overcome this problem, a novel toxicity test, specific for acid waters, was previously d eveloped and field validated. The toxicity of acid samples is assessed usin g the survival time of Ceriodaphnia dubia. During this study, the novel tes t was applied to a field situation, where an aquatic system is seriously im pacted with acid mine drainage. Its efficiency was tested and compared with two classical toxicity tests: the Microtox and the median lethal dilution with C. dubia. The survival time test was performed without adjusting pH an d after adjusting pH to a fixed value (pH 2, 3, and 4). At pH 2 and 4 no ac ceptable results were obtained; at pH 3 it was possible to distinguish the toxicity due to pH from the toxicity due to other toxicants, The test condu cted at local pH was able to discriminate toxicity sources only for highly contaminated samples, The toxicity evaluation of acid mine drainage samples was possible neither with the median lethal dilution test nor with Microto x, (C) 1999 Academic Press.