T9 PM Pyrethroid Insecticides in Urban and Agricultural Environments
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 339-340

(WES-1117-831595) A tale of two creeks: An intensive study of pyrethroids and related toxicity in urban environments.

Weston, D¹, Holmes, R², English, T¹, ¹ University of California, Berkeley, CA, USA² Central Valley Regional Water Quality Control Board, Rancho Cordova, CA, USA

ABSTRACT- Pleasant Grove Creek and its tributaries drain an area of dense housing subdivisions in Roseville CA. The Kirker Creek watershed encompasses residential, commercial and industrial areas of Pittsburg, CA. Both systems were intensively studied with analysis of sediments for pesticides, sediment toxicity testing with Hyalella azteca, and in the case of Pleasant Grove Creek, sampling for resident H. azteca. Findings in both systems were very similar. From the point where the creeks enter developed areas, nearly all sediment samples contained pyrethroid insecticides at several times the acutely lethal level concentration for H. azteca. Total or near total mortality was observed in toxicity tests throughout both systems. Resident H. azteca were present in those portions of Pleasant Grove Creek with minimal development, but were absent from the most affected reaches. Toxicity Identification Evaluation procedures suggested pyrethroids were major contributors to the toxicity. Of the group, bifenthrin was the dominant contributor, though acutely toxic levels of cypermethrin, cyfluthrin and deltamethrin often occurred. Residential areas appeared to be the principal source for all these pyrethroids, and we were able to rule out significant inputs from agriculture or mosquito control. Use of outdoor pest control products by homeowners and structural pest control by professional applicators were the probable sources of pyrethroids to both creek systems.

Key words: Pyrethroids, Pesticides, Sediment toxicity, Bioassessment