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(359) Evidence of pesticide impacts on benthic macroinvertebrate communities in the Salinas River.
Anderson, Brian*,1, Hunt, John1, Phillips, Bryn1, Nicely, Patricia1, de Vlaming, Victor1, Tjeerdema, Ron1, Richard, Nancy2, Connor, Valerie2, 1 Department of Environmental Toxicology, University of California, Davis, Davis, CA, US2 State Water Resources Control Board, Sacramento, CA, USA
ABSTRACT- The Salinas River is the largest of the three coastal rivers entering the Monterey Bay in central California. Agriculture in the Salinas Valley accounts for a significant portion of the fresh vegetables produced in the United States. Previous studies have demonstrated that Salinas River water and sediment samples downstream of agriculture drains are toxic in laboratory and in situ exposures. In the present study we used a combination of laboratory experiments, chemical analyses, TIEs and bioassessment surveys to investigate causes of impacts on two resident epibenthic macroinvertebrate genera: the amphipod Hyalella sp. and the baetid mayfly Procloeon sp. Bioassessments indicated that Hyalella sp. densities in field samples declined downstream of agriculture drainwater inputs, relative to an upstream reference station. Downstream sediments were acutely toxic to Hyalella, and TIE information combined with chemical analyses indicated that amphipod mortality was due to the pesticide chlorpyrifos and some other non-metabolically-activated chemical (possibly a pyrethroid). Bioassessments also demonstrated significant declines in aquatic insect species, in particular mayflies, downstream of agricultural drain inputs. Correlation analyses suggested that mayfly densities were negatively correlated with combined toxic units of diazinon and chlorpyrifos in Salinas River water. Experiments with the resident epibenthic baetid mayfly Procloeon sp. demonstrated that this species is acutely sensitive to chlorpyrifos at concentrations commonly measured in River water. The combined weight-of-evidence from these studies suggest that pesticides associated with agricultural drainwater are likely responsible for declines in resident sediment-associated macroinvertebrate populations.
Key words: Toxicity, bioassessments, organophosphates, sediments
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