Contaminants are suspected as culprits influencing the abundance of many aquatic species in the Sacramento-San Joaquin Delta. Organophosphates, effective insecticides that come with health risks, have been largely replaced by pyrethroids, which are safer humans. But large storm events can wash pyrethroids into waterways raising concerns about aquatic contamination; in fact they have been found at toxic levels in estuary waters close to urban areas after storm events. Our study focused on areas of Suisun Marsh area downstream from the city of Fairfield. Routine monitoring after a storm found pyrethroids in concentrations high enough to be of concern in few locations. The study found that pyrethroids caused paralysis in test species in urban creeks, but chemicals were readily diluted in the substantial water volumes in upper Suisun Marsh, reducing concentrations below known toxic levels.
Weston DP, Chen D, Lydy MJ. 2015. Stormwater-related transport of the insecticides bifenthrin, fipronil, imidacloprid, and chlorpyrifos into a tidal wetland, San Francisco Bay, California. Science of the Total Environment 528:18-25.