Sediment toxicity and stormwater runoff in a contaminated receiving system: Consideration of different bioassays in the laboratory and field

Several field and laboratory assays were employed below an urban storm sewe r outfall to define the relationship between stormwater runoff and contamin ant effects. Specifically, two bioassays that measure feeding rate as a tox icological endpoint were employed in the field and in the laboratory, along with bioassays measuring survival and growth of test organisms. In 7 to 10 d in situ exposures, amphipod leaf disc processing, growth and survival we re monitored. Different exposure scenarios were investigated by varying the mesh size (74 mu m or 250 mu m mesh) and method of deployment (water colum n, sediment surface, or containing sediment) of in situ exposure chambers. Hyalella azteca, Daphnia magna, and Pimephales promelas survival were monit ored in 48 h in situ exposures. Feeding inhibition was investigated via enz yme inhibition of H. azteca and D. magna and via leaf disc processing measu rements of the detritivore H. azteca. Additionally, we investigated the ext ent of phototoxicity at this site via field exposures in sun and shade and laboratory exposures with and without UV light. The measurement of detritiv ore leaf disc processing, and thus its usefulness as an endpoint, was hinde red by individual variability in the amount of leaf consumed and by leaf we ight gain during the summer field exposures. For D, magna, enzyme inhibitio n measured in a laboratory exposure did not reveal the toxicity observed in field exposures. For Ii. azteca, enzyme inhibition measured in the laborat ory indicated toxicity similar to that observed in short term chronic in si tu exposures. Enzyme inhibition also did not detect differences in toxicity due to variations in flow conditions. There were no statistically signific ant effects of any exposure on P. promelas survival or H, azteca growth, an d there were no statistically significant effects due to mesh size or sun e xposure. Survival of N. azteca was the most sensitive and the least variabl e endpoint. Effects on survival were noted in the same treatments over shor t-term chronic exposures in the laboratory and in situ. Significant differe nces in survival were noted due to the method of deployment under low flow conditions. In situ chambers containing sediment resulted in greater mortal ity in the 10 d low flow in situ experiments. Under high flow conditions, s ignificant reductions in survival and leaf disc processing were noted under all methods of deployment at the two impacted sites over a 7 d exposure. A lso under high flow conditions, significantly greater mortality of Ii. azte ca was reported at the downstream field site when sediment was included in the chamber at deployment. These results suggest that significant toxicity at this site is due to accumulation of contaminants in the sediment and the mobilization of these contaminants during a storm event. In situ( exposure s detected toxicity not observed in laboratory exposures. These results sug gest that a combination of laboratory and field bioassays is most useful in defining field effects. (C) 1999 Elsevier Science Ltd. All rights reserved .