Evaluating the Effects of Pesticide Mixtures to Aquatic Organisms: Mechanisms of Synergistic ToxicityEPA Grant Number: R827589E04
Title: Evaluating the Effects of Pesticide Mixtures to Aquatic Organisms: Mechanisms of Synergistic Toxicity
Investigators: Lydy, Michael J. , Hendry, Bill , Siegfried, Blair , Zhu, Kun Yan
Institution: Wichita State University , Kansas State University , University of Nebraska at Lincoln
EPA Project Officer: Winner, Darrell
Project Period: June 1, 1999 through March 30, 2003
Project Amount: $107,011
RFA: EPSCoR (Experimental Program to Stimulate Competitive Research) (1998) RFA Text | Recipients Lists
Research Category: EPSCoR (The Experimental Program to Stimulate Competitive Research)
We propose a two-year, multicomponent investigation that will examine mechanisms by which we can explain the synergism between atrazine and various OP insecticides noted previously for C. tentans. Specific objectives include: determining biotransformation rates for C. tentans to selected OPs by determining the ratio of parent compound to metabolite in the body residues of midges exposed to either OP insecticides alone or animals treated with atrazine and OP insecticide; examining the effects a known inducer and inhibitor of the P450 system may have on OP toxicity; determining whether atrazine induces detoxification enzymes involved with OP insecticide metabolism in C. tentans and if so, quantify these induction levels; and examining the effects of atrazine exposure on the inhibition of acetylcholinesterase by OP insecticides.
Atrazine, a triazine herbicide, is a common pollutant in midwestern streams and lakes. Recent reviews of atrazine generally concluded that concentrations found in aquatic systems are not ecologically harmful. Although a large body of research was reviewed, the possibility of synergistic interactions between atrazine and other agricultural chemicals was not examined. Therefore, we began testing the hypothesis of whether atrazine may cause direct effects on invertebrate organisms when present in the environment in combination with other pesticides (organophosphate [OP] insecticides). To date, we have determined that midge larvae (Chironomus tentans) exposed to atrazine and several OP insecticides exhibit greater than additive toxicity. These studies suggest that the joint action seen between atrazine and the OPs may be due to increased biotransformation of the insecticides as a result of atrazine exposure and that the resulting body residue of the metabolite is responsible for the greater than additive toxicity. Based on these observations, a thorough investigation of the toxicodynamics of the insecticides in the presence and absence of atrazine, and its potential effects on insecticide metabolism, and target site interaction is necessary to explain the greater than additive toxicity.
Our lack of knowledge concerning the impacts of pesticides on aquatic communities is at least partially attributable to a general lack of understanding of the potential interactions of multiple contaminants on aquatic biota. Given our initial findings of synergism and the importance of benthic invertebrates to the integrity of aquatic ecosystems, obtaining more comprehensive information on the potential interaction of pesticides is clearly warranted and prerequisite to our assessment of pesticide impacts on aquatic systems. This information will improve risk assessments by providing risk managers responsible for policy decisions with important information on acceptable levels of pesticide contaminants and facilitate interpretation of the biological significance of existing mixture toxicity data.