Risk assessment of λ-cyhalothrin on aquatic organisms in paddy field in China

This study was carried out to assess the risk of λ-cyhalothrin to aquatic organisms used in paddy field, and to provide assistance in the ecological risk management of λ-cyhalothrin. The acute toxicities of five individual formulations of λ-cyhalothrin to four aquatic species were investigated in the laboratory, as well as in a simulated paddy field–pond ecosystem, and the results implicated that λ-cyhalothrin is highly toxic to fish, and to a greater extent to shrimp. There were differences in the toxicities to each aquatic organisms among different formulations. λ-Cyhalothrin degraded rapidly in the environment, with half-lives of different formulations in paddy field water (0.23–0.53 days), pond water (0.38–0.63 days), and paddy field soil (0.96–7.35 days), respectively. The water overflow from the paddy field following a simulated rainstorm 12 h after application of λ-cyhalothrin did not cause injury to fish, clam or crab, but was severely hazardous to shrimp. Additionally, no injury to shrimp was found when simulated overflow occurred 4 days after application. These results suggest that the environmental risk of λ-cyhalothrin to aquatic organisms can be reduced by (1) developing a relatively safe formulation such as a suspension concentrate, and/or (2) controlling the drainage time of the paddy field.