Environmental Fate of Rice Pesticides, 2019


Ronald S. Tjeerdema, distinguished professor and executive associate dean, Dept. of Environmental Toxicology, CAES, UC Davis

The overall goal of this project is to characterize how pesticides important to rice culture dissipate under California rice field conditions. These chemical compounds break down in the environment through interaction with soil, water, and air, as well as by degradation from sunlight and microbial activity. The research emphasis in 2019 was exclusively on the insecticide CoragenŽ (chlorantraniliprole).

Chemicals used in rice cultivation break down through many pathways. Information generated from this research project has helped protect the environment.
CoragenŽ was registered by the U.S. Environmental Protection Agency for agricultural use in 2008 and by the California Environmental Protection Agency in 2016 for use on California rice fields as a preflood treatment to control rice water weevil.

Chlorantraniliprole, the active ingredient in CoragenŽ, belongs to an emerging class of pesticides known as the anthranilic diamides. It has potent activity against rice water weevil larvae. Because of its specificity, chlorantraniliprole has lower toxicity than other currently used insecticides on nontarget species, including crayfish and pollinators.

However, it exhibits high toxicity toward some aquatic invertebrate species. Furthermore, other nontarget organisms have shown reduced activity, reproduction, and feeding after short-term exposure to chlorantraniliprole. This indicates the potential for ecological impacts at sublethal concentrations that could result from spray drift, weir leakage, or tailwater releases.

Previous research concluded that chlorantraniliprole is unlikely to volatilize and exhibits weak sorption to soil. Therefore, the photochemical degradation of chlorantraniliprole was characterized under simulated solar light. Overall, this compound degraded quickly. It is anticipated that that the majority of this insecticide will remain in soil, where it will degrade slowly through microbial actions. Thus, it may accumulate in the soil, leading to unintended chronic exposure to wildlife during overwintering flooding and/or the development of pest resistance. This research marks the completion of work on chlorantraniliprole under simulated California rice field conditions.