Aquatic Ecological Risk Assessment of Thiamethoxam Single Agent Regis-tered in Rice Fields in China
To assess the potential risks of the second-generation neonicotinoid insecticide thiamethoxam to aquatic environments,this study utilized the TOP-RICE model to predict exposure concentrations for two application methods on rice,namely high concentration/short interval and low concentration/long interval,among the various thiamethoxam formulations registered in China for rice,applied by spraying.Risk quotient(RQ)method was employed to evaluate the aquatic ecological risks of thiamethoxam.The results showed that as of October 2023,a total of 383 effective thiamethoxam formulations for single application on rice were registered in China over the past three years,mainly including water dispersible granules,wettable powders,suspensions,seed treatment suspen-sions,suspension seed coatings,and granules,among which water dispersible granules accounted for the largest proportion at 28.72％.The TOP-RICE model predicted environmental concentrations ranging from 0.2300 to 29.2464 μg·L-1 for thiamethoxam formulations of water dispersible granules,wettable powders,and suspensions after application on rice.The species sensitivity distribution(SSD)curve showed that the acute HC5 of thiamethoxam to aquatic organisms was 16.09 μg·L-1,and the chronic HC5 was 2.096 μg·L-1,and most invertebrates represented by Chironomus dilutus were sensitive to the insecticide.Calculations based on RQ values indicated that three for-mulations of thiamethoxam pose a certain threat to the aquatic ecological environment.According to the current registered application conditions,the predicted environmental concentration of thiamethoxam wettable powder was relatively high,indicating greater risks to aquatic ecosystems compared to other formulation types.Due to reliance on modeling and limited availability of metabolite data,coupled with conservative experimental data,there is some degree of uncertainty in the results of this study.
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