Toxicity Evaluation of Urban Stormwater Runoff in Lincoln Creek, Milwaukee, Wisconsin

Abstract

Recent initiatives by the U.S. Environmental Protection Agency will bring stormwater runoff from large metropolitan areas under the purview of state water quality agencies. Yet, there is little information concerning the toxicological effects of stormwater runoff on aquatic biota on which to base new regulations. This study addressed acute and short-term chronic effects of stormwater runoff to aquatic biota in an urban stream, Lincoln Creek, in Milwaukee, Wisconsin. Samples of stormwater and baseflow for acute and short-term chronic tests were collected during runoff events and baseflow beginning with snowmelt March-October, 1 993. Stormwater samples were collected with a stream gauge-actuated automatic sampler programmed to collect up to eight sequential samples from the stream during each runoff event. Baseflow samples were a grab collected every other week from the drop structure located at 47th Street and Congress Avenue. A total of 24 runoff events and 1 2 biweekly baseflow samples were tested. A total of 316 laboratory toxicity tests were performed on serial dilutions of the stormwater runoff with Ceriodaphnia dubia, Daphnia magna and Pimephales promelas. In addition, 34 in-situ toxicity tests, fish and macroinvertebrate assemblages indigenous to Wisconsin were exposed in flow-through aquaria housed in a U.S. Geological Survey gauging station adjacent to Lincoln Creek. The short-term (less than 8 days) toxicity tests used in this study appear to have underestimated toxic effects of Lincoln Creek stormwater. The short term, acute or 7-day chronic toxic effects, which could be solely attributed to stormwater runoff, were identified with the three laboratory test species. In-situ acute tests with 23 families of macroinvertebrates (2- day) and 10 species of fish (7-day) detected only slight toxicity for some species. Significant mortality in Rhinichthyes atratulus, possible caused by stormwater or baseflow water quality, occurred in one of 26 tests with indigenous fish. Significant mortality in the caddisfly family Hydropsychidae occurred in one of 8 tests. It appears conventional short-term toxicity tests which include the 7-day Ceriodaphnia dubia reproductive test lack the sensitivity to detect the type of biological degradation seen in Lincoln Creek. Test organisms were exposed to a variety of metal contaminants in stormwater and baseflow samples at levels that exceeded Acute Toxicity Criteria and Chronic Toxicity Criteria values for metals established by Wisconsin Department of Natural Resources. Polycyclic aromatic hydrocarbon concentrations in stormwater runoff were much greater than at baseflow for samples collected from Lincoln Creek and were found at concentrations that are reported toxic to aquatic life. Although little acute mortality was recorded, there was evidence that longer exposure produced extensive mortality that could in part explain the paucity of aquatic biota in Lincoln Creek. Juvenile and adult Pimephales promelas exposed on-site to Lincoln Creek water for greater than 14 days suffered substantial mortality. Chronic (greater than 14 days) toxicity tests are more sensitive and appear better suited to identify biological impairment caused by stormwater runoff.