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(467) Fluctuating Contaminant Exposures in Relation to Water Quality Criteria and NPDES Permit Limits.
Diamond, Jerome*,1, Butcher, Jonathan2, Bowersox, Marcus1, 1 Tetra Tech, Inc., Owings Mills, MD, USA2 Tetra Tech, Inc., Research Triangle Park, NC
ABSTRACT- Water quality criteria for protecting aquatic life are based primarily on laboratory testing that used constant exposure concentrations. However, typical effluent and nonpoint source exposure concentrations fluctuate in frequency, magnitude, and duration, which may result in different toxicological impacts than experienced in constant concentration tests. With funding sponsored by the Water Environment Research Foundation, we reviewed results of laboratory and field case studies and performed pulsed laboratory toxicity tests along with simulation modeling to improve our understanding of the links between real world exposures and effects. Our analyses demonstrate that pulsed or fluctuating exposures are generally more toxic than continuous exposures, when averaged over the applicable time period. However, the speed of chemical action, the duration of the pulse or exceedence episode relating to the averaging period, and the degree to which chronic toxicity mechanisms are as sensitive as acute mechanisms, will determine whether chronic effects are likely given fluctuating chemical patterns. Current models for dealing with acute exposures appear to be fairly robust under fluctuating exposures, and may be applicable for predicting chronic effects, particularly for fast-acting chemicals that are also depurated quickly, and for which the acute:chronic ratio is relatively low. Seven-day chronic tests, using fathead minnows and pulsed exposures of several chemicals (nitric acid, sodium chloride, copper, and cadmium), elicited fast-acting responses and small lag effects. In general, chronic or sublethal effects were not observed. Our results suggest that chronic effects of fluctuating exposures of many common effluent, permit constituents may be predicted based on current toxicological models.
Key words: water quality criteria, whole effluent toxicity, pulsed exposure, NPDES permit limits
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