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

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 (j CAP,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 (PFAM) to simulate CAP dissipation in a model California rice field. The model estimates an environmental half-life of 26 days 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 days in flooded and drained fields, respectively. This article is protected by copyright. All rights reserved.