Impact of Atrazine on Chlorpyrifos Toxicity in Four Aquatic Vertebrates

Abstract. Atrazine has been shown previously to potentiate chlorpyrifos toxicity in selected invertebrates. This study examined interactions of atrazine and chlorpyrifos in four aquatic vertebrates. Organisms were exposed to binary mix-tures of atrazine and chlorpyrifos during toxicity bioassays. Inhibition of cholinesterase (ChE) enzyme activity and chlor-pyrifos uptake kinetics were also examined with and without atrazine exposure. Atrazine alone did not affect organisms at concentrations up to 5000 lg/L; however, the presence of atrazine at 1000 lg/L did result in a significant increase in the acute toxicity of chlorpyrifos in Xenopus laevis. Mixed results were encountered with Pimephales promelas; some bioassays showed greater than additive toxicity, while others showed an additive response. No effect of atrazine on chlorpyrifos tox-icity was observed for Lepomis macrochirus and Rana clam