Characterization of stormwater toxicants from an urban watershed to freshwater and marine organisms

Stormwater samples were collected from Chollas Creek, a highly urbanized watershed in San Diego, California, that discharges directly to San Diego Bay and tested using one freshwater species (Ceriodaphnia, water flea) and two marine species (Strongylocentrotus purpuratus, purple sea urchin; and Mysidopsis bahia, mysid shrimp). No two species responded similarly after exposure to urban wet weather discharges. Strongylocentrotus was extremely sensitive to stormwater, exhibiting responses during every storm at concentrations as low as 6–12% stormwater. In contrast, Mysidopsis, exhibited no response to stormwater for any of the storms sampled. Ceriodaphnia exhibited intermediate toxic responses; two of three samples were toxic at relatively high concentrations of 50–100% stormwater. Toxicity identification evaluations (TIEs) were conducted on each species to determine the toxic constituent(s). Organophosphate pesticides, most likely diazinon and chlorpyrifos, were responsible for the toxicity observed in Ceriodaphnia. Trace metals, most likely zinc and copper, were responsible for the toxicity observed to the sea urchin.