Ecotoxicological effects and ecological risk assessment of azoxystrobin on Chironomus kiiensis

Azoxystrobin, a strobilurin fungicide, has been widely used in the control of plant pathogens for a long time, and its residues are widely distributed in surface water in many countries and regions, which has potential ecological security risks to aquatic organisms. In this study, the ecological risk of 50% azoxystrobin water dispersing granules (WDG) to Chironomus kiiensis was evaluated by acute and chronic toxicity tests combined with TOP-RICE model. The results showed that the 48 h median lethal concentration (LC₅₀) value of azoxystrobin was 1.52 mg/L, indicating moderate acute toxicity. The chronic toxicity test showed that high concentrations of azoxystrobin (1.6 and 3.2 mg/L) significantly inhibited the growth and development of larva, leading to significant decreases in emergence rate, growth rate, body length, wet weight and dry weight (P < 0.05), among which the dry weight and emergence rate of larva were most sensitive to azoxystrobin, and the median effective concentration (EC₅₀) values were 0.13 and 0.12 mg/L, respectively. It is speculated that azoxystrobin can potentially affect the relevant factors of Chironomus kiiensis emergence, and then affect the growth, development and reproduction of chironomid. Further studies at the cellular and gene levels need to be carried out. Azoxystrobin posed a relatively high risk to the larvae of chironomid in aquatic ecosystem of rice fields. The acute risk quotients of overlying water and the chronic risk quotients of spiked sediments were both greater than 1, but the chronic risk quotients of spiked sediments were significantly lower than the acute risk quotients of overlying water. In conclusion, the 50% azoxystrobin water dispersible granule has a relatively high aquatic ecological risk for the bottom-dwelling chironomid. In the future, special attention should be paid to the toxic effects of azoxystrobin on benthic organisms in the registration, risk prevention and re-evaluation processes.