Dissipation patterns and characteristics of four pesticides in sandy and clay soil under controlled conditions

The dissipation of pesticides significantly influences their behaviour in soil, which is crucial for evaluating their stability and safety. This study investigated the dissipation patterns and half-lives of four pesticides—ametryn, bentazone, carbofuran, and oxamyl—in sandy and clay soils at two concentration levels (25 mg‧kg¹ and 100 mg‧kg¹). The experiment was conducted at 26°C with a 60% water-holding capacity. First-order kinetics effectively described the dissipation (R² > 0.92). After 60 days, pesticide dissipation exceeded 97% in sandy soil, while remaining residues were 80–86% for ametryn, 80– 89% for bentazone, and 85-88% for carbofuran and oxamyl. In clay soil, dissipation was initially slower (<8% for all pesticides), but subsequently accelerated. The quantity of pesticides declined sharply in the first month, followed by a gradual decrease in the second month. Ametryn exhibited the longest half-life, whereas bentazone had the shortest. Overall, pesticide loss correlated with decreased concentrations and organic matter content.