Pyrethroid insecticide transport into Monterey Bay through riverine suspended solids

Pyrethroid pesticides are used widely in both agricultural and urban landscapes. Toxicity has been recorded in creeks and rivers throughout California, confirming that pyrethroids move at least short distances from the areas of terrestrial application into downstream waterways. However, their further downstream transport into the marine ecosystem has received little study. The Monterey Bay was chosen as the study system in the current project due to the close proximity of both urban centers and intense agriculture. Suspended sediments were sampled from three major rivers during storm events and showed that pyrethroids were routinely discharged from these coastal rivers, with concentrations of bifenthrin and permethrin in suspended solids of 22 and 83 ng/g, respectively. These suspended solids were deposited in estuaries and downstream reaches of rivers as they approached the coast where concentrations of pyrethroids in the sediment were greater than those expected to be toxic. However, despite their transport onto the continental shelf, pyrethroid residues were not detected in bed sediments of the shelf or in the nearby deep sea canyon, presumably due to dilution and degradation.