Aquatic ecological risk assessment of single-dose imidacloprid registered on rice of China

In order to evaluate the risk of the use of single-dose imidacloprid products to aquatic ecosystem, based on the conservative principles of risk assessment, different application rates of imidacloprid formulations registered on rice were evaluated and subsequently, the comprehensive risk assessment of these products to aquatic ecosystem was performed using the Top-Rice model and the risk quotient method. These results showed that a total of 375 imidacloprid formulations (single active component) had been registered on rice by June 2020, which could be separated into ten formulation groups. Among these formulations, the wettable powders (WP) accounted for the largest portion at 56.53%, followed by the soluble concentrate (SL) at 11.47%. And the emulsifiable concentrates (EC), suspension concentrate (SC), water dispersible granule (WG), microemulsion (ME), flowable concentrate for seed treatment (FS), effervescent tablet (EB), tablet (TA) and water dispersible powder for slurry seed treatment (WS) were 9.87%, 8.27%, 8.00%, 3.73%, 1.33%, 0.27%, 0.27% and 0.27%, respectively. These results showed that the predicted environmental concentration (PEC) of imidacloprid products ranged from 0.19 to 51.28 μg/L after applying different formulations of imidacloprid on rice in different scenes and seasons. In addition, the risk characterization results demonstrated that the risks of acute exposure to imidacloprid products to fish and invertebrates and that of chronic exposure to fish and primary producers were acceptable under existing registration conditions. However, there were potential chronic risks to Daphnia magna and Chironomus riparius as a result of only 13.58% of the simulated groups in which the risk quotient (RQ) was less than 1. These results suggested the currently imidacloprid products registered in China posed a certain risk to aquatic ecosystem according to the current registration application conditions. In the present study, it should be noted that the assessment method used to analyze the application model of all imidacloprid product formulations was relatively conservative, and the metabolite had not been analyzed because of its insufficient data. Therefore, these factors mentioned above made the evaluation results relatively conservative.