Dissipation of two neonicotinoid insecticides in soil and water under different conditions

The environmental fate of two widely used neonicotinoid insecticides, acetamiprid and imidacloprid, was investigated in soil and water under varying conditions to evaluate their dissipation behavior and half-life (DT50). Laboratory experiments were conducted using sterilized and non-sterilized clay and sandy soils, as well as water adjusted to pH 5, 7, and 9. Recovery studies demonstrated that acetonitrile: methanol (50:50) was the most effective solvent for extracting residues from soil, while dichloromethane efficiently recovered the insecticides from water. In soil, both insecticides degraded more rapidly under non-sterile than sterile conditions, confirming the significant role of microbial activity. Dissipation was faster in sandy soil compared to clay, likely due to lower adsorption capacity enhancing bioavailability. In non-sterile soils, the half-life of acetamiprid was 16.7 days in clay and 15.0 days in sandy soil, whereas the half-life of imidacloprid ranged from 29.2 days in clay to 6.9 days in sandy soil. In water, acetamiprid dissipated fastest under alkaline conditions (pH 9; DT50 = 19.7 days), whereas imidacloprid degraded more rapidly under acidic conditions (pH 5; DT50 = 17.9 days). These results indicate that both microbial activity and physicochemical factors, such as soil texture and water pH, critically influence neonicotinoid persistence. Understanding these parameters is essential for assessing their environmental fate and ecological risks.