Occurrence and toxicity of three classes of insecticides in water and sediment in two Southern California coastal watersheds.

The occurrence of chlorpyrifos, diazinon, pyrethroids, and fipronil was investigated in two watersheds along the southern California coast. Paired surface water and sediment samples were collected under dry and wet (after significant rain events) weather conditions. Insecticide concentrations in water and sediment were higher following rain events than during the dry season. Chlorpyrifos was the most frequently detected compound (>88%). Pyrethroids were detected in 74 and 100% of the water and sediment samples, respectively, with bifenthrin detected most frequently. Trans-permethrin was detected at the highest concentration followed by bifenthrin. Bifenthrin and trans-permethrin water concentrations were significantly correlated (P < 0.01) with the suspended solid level, suggesting transport facilitated by suspended particles. In 80% of the wet season samples with 100% of Ceriodaphnia dubia mortality, chlorpyrifos concentrations were >100 ng L(-1). Sediment pyrethroid levels (0.5-1100 ng g(-1)) were frequently higher than the respective Hyalella azteca LC(50) values, with bifenthrin as the primary contributor of H. azteca toxicity.