R8 PM Pesticide Mixtures
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 331-332

(TRI-1117-727128) Effects of triazine herbicides on organophosphate insecticide toxicity in Chironomus tentans and Hyalella azteca.

Trimble, A¹, Schuler, L¹, Belden, J¹, Lydy, M¹, ¹ Southern Illinois University, Carbondale, Illinois, USA

ABSTRACT- The purpose of this research was to examine the effects of select triazine herbicides on organophosphate insecticide toxicity. The acute toxicities of two organophosphate insecticides, chlorpyrifos and diazinon, were measured separately and in binary mixtures with 10 different triazine herbicides using 4^th instar larvae of the aquatic midge, Chironomus tentans, and the juvenile aquatic amphipod, Hyalella azteca. Preliminary studies with the triazine herbicides indicated no significant toxicity effects to either organism when dosed alone. However, with nearly every triazine, binary mixture studies showed greater than additive effects relative to the toxicity of the insecticides alone. These effects were greater overall to C. tentans compared to H. azteca, with some of the triazines causing a doubling in the toxicities of the organophosphates. In addition to the acute analyses, chronic toxicity effects to chlorpyrifos toxicity were examined using three of the most commonly detected active-use triazine herbicides. Results of these chronic tests will be presented and compared to the acute effects obtained previously. These results should be of interest to water managers responsible for policy decisions because it provides important information on acceptable concentrations of commonly occurring pesticides that do not follow the concentration addition model.

Key words: triazine, organophosphate, herbicide, insecticide