Quantum Yield for the Aqueous Photochemical Degradation of Chlorantraniliprole and Simulation of Its Environmental Fate in a Model California Rice Field

Abstract The photochemical degradation of chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)phenyl]-1-(3-chloro-2-pyridine-2-yl)-1H-pyrazole-5-carboxamide; CAP) was characterized under simulated solar light with 2-nitrobenzaldehyde (2NB) actinometry. Overall, aqueous CAP degraded quickly via direct photodegradation with no significant difference observed between high-purity water and filtered rice field water. The 24-h average half-life normalized to summer sunlight using 2NB was 34.5 ± 4.0 h (jCAP,env = 0.020 ± 0.0023 h−1, n = 3), and the calculated apparent quantum yield in simulated sunlight was 0.0099 ± 0.00060. These new values were used—alongside previously characterized data for air/and soil/water partitioning, degradation in soil, and hydrolysis—in the Pesticides in Flooded Applications Model to simulate CAP dissipation in a model California (USA) rice field. The model estimates an environmental half-life of 26 d in the aqueous phase, but the bulk of applied CAP remains in the benthic zone and degrades, with estimated half-lives of 29 and 92 d in flooded and drained fields, respectively. Environ Toxicol Chem 2020;39:1929–1935. © 2020 SETAC Abstract The photochemical quantum yield for chlorantraniliprole (CAP) was determined and direct photolysis was identified as a major dissipation pathway for the insecticide from aqueous environments.