Attenuation Effect of Azolla spp. on Lambda-Cyhalothrin Toxicity to Aquatic Organisms

Wetlands play a crucial role in providing valuable ecosystem services, including the removal of various pollutants. In agricultural basins, wetlands are exposed to agrochemical loads. This study aims to assess the attenuation effect of the ubiquitous macrophyte Azolla spp. on the toxicity of lambda-cyhalothrin to sensitive aquatic organisms. An indoor mesocosm experiment was conducted to compare the concentration of lambda-cyhalothrin at different time points after pesticide application in vegetated and unvegetated treatments, including a control without pesticide addition. Toxicity tests were performed throughout the experiment on three organisms: a fish (Cnesterodon decemmaculatus), a macroinvertebrate (Hyalella curvispina), and an amphibian (Boana pulchella). The results demonstrated that lambda-cyhalothrin concentration and toxicity in water were significantly lower in the Azolla spp. treatment. Furthermore, the half-life of lambda-cyhalothrin decreased from 1.2 days in the unvegetated treatment to 0.4 days in the vegetated treatment. The vegetated treatment also resulted in a significantly lower mortality rate for both H. curvispina and C. decemmaculatus. However, no mortality was observed in B. pulchella for any of the treatments. Sublethal effects were observed in this organism, such as lateral bending of the tail and impairment of the ability to swim, which were attenuated in the vegetated treatment. We conclude that Azolla spp. can effectively reduce the concentration and toxicity of lambda-cyhalothrin, suggesting its potential use in farm-scale best management practices to mitigate the effects of pesticide loads from adjacent crops.