Effects of acute exposure to azoxystrobin on embryos and juveniles of the freshwater snail Lymnaea stagnalis

Azoxystrobin (AZ) is a systemic fungicide applied to soil to control a wide range of plant pathogenic fungi. AZ residues have been detected in surface waters due to excessive release, posing a risk to aquatic organisms. This study evaluated the toxic effects of short-term AZ exposure on embryos and juveniles of Lymnaea stagnalis. First, the 96-h LC₅₀ values of AZ were estimated as 7.98 (6.50–9.85) mg/L for embryos and 2.90 (2.30–3.86) mg/L for juveniles, indicating that juveniles are more sensitive to acute AZ toxicity. Additional experiments were conducted to assess the sublethal effects of AZ on embryos and juveniles. The highest sublethal exposure concentrations were set at approximately 20 % of the respective estimated LC₅₀ values for embryos and juveniles, while the lower concentrations were determined by successive ten-fold dilutions to include environmentally relevant AZ levels. Accordingly, embryos were exposed to 0, 15, 150, and 1500 μg/L, whereas juveniles were exposed to 0, 5, 50, and 500 μg/L over a 96-h period. In embryos, AZ exposure led to developmental delays, reduced growth, decreased hatching success and mortality at 1500 μg/L. Likewise, juvenile snails displayed marked biochemical and molecular alterations across all tested concentrations. AZ-induced ROS generation and elevated MDA levels were observed, alongside increased activities of SOD, CAT, GPx, and GR. Additionally, mRNA transcripts of HSP40, HSP70, SOD, CAT, GPx, and GR were upregulated in juveniles, even at the lowest exposure concentration. In conclusion, AZ contamination poses a significant ecological risk to the early life stages of freshwater gastropods.