Testing single-species predictions for a cationic surfactant in a stream mesocosm

Abstract

Assessment of single-species bioassays of aquatic toxicity is a standard approach to predict the potential for effects of a test chemical in the environment. To reach a prediction, however, the assessment process takes into consideration both the results of the bioassays and the uncertainty associated with extrapolating results to the environment. Application of higher uncertainty factors to these bioassays implies that single-species are less sensitive to test chemicals than the environment. This assumption has not been validated. In studies reviewed here, the ability of bioassay results to predict ecosystem effects of surfactant chemicals was investigated by conducting concurrent studies of the aquatic toxicity potential of the cationic surfactant dodecyl trimethyl ammonium chloride (TMAC) in single-species bioassays and a stream mesocosm. The bioassay results compare favorably with the range of previously reported bioassay results with TMAC (125–1250 ppb No Effect Concentration, NOEC). When an assessment was done for the stream mesocosm results, negligible ecosystem-level effects were seen at 250 ppb TMAC. The predictions of both the concurrent and previously reported bioassay studies were comparable to stream mesocosm results without the use of uncertainty or extrapolation factors. Therefore, results to date demonstrate that assessments with standard single-species bioassays conducted with a cationic surfactant predict ecosystem-level effects without the application of uncertainty factors.