RESPONSE OF PROTISTAN ASSEMBLAGES TO A MODEL TOXICANT, THE SURFACTANT C-12-TMAC (DODECYL TRIMETHYL AMMONIUM-CHLORIDE), IN LABORATORY STREAMS

Aquatic microbial communities contain many species performing several critical functions in aquatic ecosystems and, thus, may provide robust indicators of stress. Effects of the cationic surfactant dodecyl trimethyl ammonium chloride (C12-TMAC) on benthic microbial communities in experimental stream channels were assessed. Tests were performed with microbial communities: (1) developed in the stream channels for 14 days prior to exposure; (2) developed in the presence of the chemical; (3) developed in the relatively unimpacted headwaters of the stream providing water to the facility for 16 days prior to exposure. Gross indicators of community structure, such as the taxon richness and composition of the protozoan and diatom assemblages tended to be unaffected by the chemical. Effects on growth processes and trophic relationships were generally transitory and occurred at moderate concentrations (250-mu-g/l) of cationic surfactant. Most sensitive single species responses to this chemical in previous laboratory tests were more sensitive than overall community responses examined here and elsewhere. However, broad assessments of risk using these communities allow for: (1) validation of single species responses, and (2) predictions of potential long-term effects on natural ecosystems unavailable from single species tests. This should allow for increased precision in risk assessments.