Comparison of a partial life-cycle bioassay in artificial streams to a standard beaker bioassay to assess effects of metal mine effluent on Chironomus tentans.

A novel, partial life-cycle bioassay using Chironomus tentans in artificial streams was developed for evaluating the effects of metal mine effluent. The utility of this bioassay was compared to an existing beaker life-cycle bioassay under laboratory conditions. Chironomus tentans larvae were exposed to 45% (v/v) treated metal mine effluent from day 11 through hatching of the second generation. Response patterns were consistent between the two bioassays for hatching success and time to emergence but inconsistent for other endpoints. Significant effects of effluent were obtained for growth, survival, number of adults emerged, and number of eggs per egg case in the artificial stream bioassay but not in the beaker bioassay. Conversely, significant effects on sex ratio and number of egg cases per female were observed in the beaker bioassay but not in the artificial stream bioassay. These differences are believed to be a consequence of the number of organisms per replicate used in each bioassay, which results in a difference in statistical power. As a result, higher coefficients of variation and effects sizes were observed in the beaker bioassay relative to the artificial stream bioassay for almost all endpoints. These results provide evidence that the bioassay in artificial streams can be an effective tool for evaluating the effects of metal mine effluent on life-cycle endpoints in C. tentans.