Aqueous Photolysis of Benzobicyclon Hydrolysate

Abstract

Benzobicyclon [3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one] is a pro-herbicide used against resistant weeds in California rice fields. Persistence of its active product, benzobicyclon hydrolysate, is of concern. As an acidic herbicide, the neutral species photolyzed faster than the more predominant anionic species ( t = 1 and 320 h, respectively; natural sunlight), from a >10-fold difference in the quantum yield. Dissolved organic matter in natural waters reduced direct photolysis and increased indirect photolysis compared to high-purity water. Light attenuation appears significant in rice field water and can slow photolysis. These results, used in the pesticides in flooded applications model with other experimental properties, indicate that a floodwater hold time of 20 days could be sufficient for dissipation of the majority of initial aqueous benzobicyclon hydrolysate prior to release. However, soil recalcitrance of both compounds will keep aqueous benzobicyclon hydrolysate levels constant months after benzobicyclon application.

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

“…The factor of 0.46 conservatively corrects for the approximate enhancement of photolysis resulting from the difference between light scattering in tubes versus a flat water body, and the factor of 0.283 converts the midday photolysis rate constant to the 24‐h–averaged rate constant (Leifer 1988; Williams et al 2018).…”