Pimephales promelas and Laboratory Bioassay Responses to Cadmium in Effluent Dominated Systems
Bryan W. Brooks, Jacob K. Stanley, Jessica C. White, Philip K. Turner, Duane B. Huggett, Thomas W. La Point
Whole Effluent Toxicity tests predict individual responses, but do not measure natural population or community responses. Because southwestern U.S. rivers are often dominated by municipal effluents, more direct evaluations of ecosystem health are needed to properly evaluate fate and effects of metals in such aquatic systems. We designed lotic mesocosms to assess effluent and cadmium effects on stream biota and to determine relevance to regulatory criteria of standard laboratory tests. A municipal effluent served as source water for experimental streams, colonized by invertebrates from a nearby stream. Because of inherent temporal effluent variability, we characterized source water chemically (standard parameters hourly; alkalinity, hardness, TOC, total and dissolved metals at 0600, 1400, 2200) and biologically (C. dubia bioassays for 0600, 1400, and 2200 samples). Cadmium, a non-point contaminant in north Texas streams, was added to replicate units at 0, 0.22, and 2.22 mM during a 10-day study period. Cd concentrations were verified by GF-AAS. Adult fathead minnows were caged in stream pool sections on day -2 to acclimate. Stream riffles and pools were sampled on days 0 and 10 for macroinvertebrates, periphyton, system metabolism and fish biomarkers. Concurrent laboratory C. dubia and P. promelas bioassays were performed with stream water throughout this study. Compared to untreated streams, P. promelas vitellogenin, condition, hematocrit, GSI, and HSI were unaffected by 0.22 and 2.22 mM Cd treatments. Laboratory bioassays, benthic macroinvertebrates, periphyton and system metabolism were not affected by 0.22 mM Cd treatments. Our laboratory and field results indicate that municipal effluent constituents alter Cd bioavailability and effects. Current water quality criteria for metals based on hardness alone do not account for such constituents.