Occurrence and Probable Sources of Urban-Use Insecticides in Marine Sediments off the Coast of Los Angeles.

IInsecticides such as pyrethroids and fipronil are used in large amounts in both agricultural and urban settings, and have the potential to elicit toxicity to non-target aquatic organisms. In California, like in many other regions of the world, urban centers are located along the coast, and it is documented that urban-use insecticides enter the marine environment, where little is known about their occurrence and consequences. In this study, we measured the spatial distribution of pyrethroids and fipronil (and its metabolites) on the Palos Verdes Shelf off the coast of Los Angeles. Total pyrethroid levels ranged from nd to 170 µg/kg (dry weight), and fipronil sulfide from 1.8 to 5.6 µg/kg. Two pyrethroids were traced to wastewater effluent discharge, while two others and fipronil sulfide to surface runoff. Toxicity units (TUs) were estimated for benthic invertebrates, which ranged from no toxicity (nt) to 146 for total pyrethroids; and 0.09 to 1.6 and 4.2 to 75 for fipronil sulfide, depending on the indicator species. Therefore, near-shore deposition of urban-use insecticides due to wastewater discharge and surface runoff poses a significant risk to marine benthic invertebrates and highlights the importance to monitor near-shore ocean environments and develop mitigation strategies to reduce seaward movement.