"Application of TIESin Studies of Urban Stormwater Impacts on Marine Organisms: ' Environmental Toxicoloev and Risk Assessment: Seventh Volume. ASTM

Urban stormwater runoff is a significant, yet poorly understood, source of wntaminants to the marine environment. One of the largest sources of stormwater inputs to Santa Monica Bay (California) is the Ballona Creek watershed. Receiving water and runoff water samples were collected during several storms in both the 1995-96 and 199697 wet seasons. Sea urchin f e r t w i o n tests indicated.toxicity inmost Ballona.Creek stormivater samples; ECso values were about 12-20%. Receiving water samples were also toxic, with the magnitude of effects generally corresponding to the concentration of runoffpresent. Selected phase I TL!2 (toxicity identification evaluation) manipulations were applied to samples showing toxicity. Ballona Creek samples had aconsistent response pattern; EDTA addition removed virtually all toxicity, implicating divalent trace metals as the probable toxic constituents. Santatapo@$&Bay surface water samples showed a similar response pattern but other marjpu~iri'dns also rem6ved some toxicity. Toxicity of receiving water samples tended to degrade &ith storage,, while mof f sample toxicity was more stable. Chemical analysis of runoff and comparison to spiking studies showed that concentrations of zinc and occasionally copper were sufficient to produce toxicity. Evaluation of the relative effectiveness of EDTA verSus sodium thiosulfate in toxicity removal also suggested zinc as a likely cause of toxicity.