Insecticides such
as pyrethroids and fipronil are used in large
amounts in both agricultural and urban settings and have the potential
to elicit toxicity to nontarget 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 levels
ranged from 1.8 to 5.6 μg/kg. Two pyrethroids were traced to
wastewater effluent discharge, while two others and fipronil sulfide
were traced to 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 of monitoring near-shore ocean environments
and developing mitigation strategies to reduce seaward movement.