PARENT SESSION
WP6 - Agrochemicals
Chair: Giddings, Jeff¹, ¹ The Cadmus Group, Marion, MA
2:10 PM to 5:30 PM - Wednesday, 20 November 2002
Room Ballroom B

(620) Mixtures of Pesticides...Additive? More or Less.

Lydy, Michael¹, Parks, Kimberly^*,1, ¹ Southern Illinois University at Carbondale, Carbondale, IL, USA

ABSTRACT- The Sacramento-San Joaquin Delta of California contains a variety of orchards and crops, which require applications of different insecticides and herbicides. These pesticides are commonly applied before and during the rainy season (October-March) resulting in pulses of mixtures of pesticides entering surrounding surface waters. This study examined the effects of the 10 most commonly applied pesticides in the Sacramento-San Joaquin Delta on the aquatic midge, Chironomus tentans. These chemicals are from a variety of different classes of pesticides including organophosphate (OP), carbamate and pyrethroid insecticides, as well as triazine, triazinone and substituted urea herbicides. This study examined these compounds in both single toxicant and binary mixture bioassays. In addition, midges were pre-exposed to three organochlorines (OCs) currently detected in the Sacramento-San Joaquin Delta using sediment bioassays. Following the pre-exposures to the OCs, midges were then exposed to the other insecticides in single toxicant acute bioassays. Results indicate that most of the binary mixtures elicited additive responses in C. tentans, while OP insecticides in combination with triazine herbicides elicited greater than additive responses.

Key words: pesticides, binary mixtures, Chironomus tentans, Sacramento-San Joaquin Delta