Environmental Fate of
Rice Pesticides - 2008



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Project Leader and Principal  Investigators

Ronald S. Tjeerdema, professor and chair, Dept. of Environmental Toxicology, UC Davis


The goal of this project is to characterize what happens to rice pesticides under California rice field conditions. Compounds dissipate in the environment through four processes – volatilization through air, adherence to soil, degradation by sunlight, and degradation by soil microbes.  Studies in 2008 concentrated on etofenprox and clothianidin, experimental insecticides for control of rice water weevil (RWW), and clomazone, a popular grass

Etofenprox study continues

Etofenprox belongs to a new class of ether-based pyrethroid pesticides. It is not yet registered in California but is a promising insecticide for control of RWW.

Previous laboratory analysis showed that volatilization into the air will not be a major dissipation pathway for this compound. Etofenprox has shown a strong tendency to partition out of water and adhere to soil particles. Soil microbial decomposition is one of the most important degradation pathways for pesticides and can greatly reduce a compound’s persistence in a soil-water matrix.

Researchers suspect that etofenprox would undergo microbial degradation at a faster rate under aerobic conditions. A method for analyzing the insecticide and its metabolites was developed in 2008. It will be used to characterize dissipation rates through microbial and photochemical processes in California rice field conditions.

Experiments to characterize anaerobic microbial degradation of etofenprox in flooded soils are in progress.

Clomazone studies

Clomazone (Cerano®) is a popular and versatile herbicide used against barnyardgrass, sprangletop and water grasses. It is viewed as a potential replacement for herbicides such as Ordram® and/or Bolero®.

Researchers developed an advanced method for analyzing the herbicide in both soil and water samples. Preliminary experiments have been completed and indicate soil microbes under both aerobic and anaerobic conditions efficiently degrade clomazone.

Additional experiments are under way.

New insecticide examined

Clothianidin is a novel neonicotinoid insecticide that exhibits good systemic action and high insecticidal activity against various sucking insect pests. It has been registered for foliar spray and seed treatment applications for food crops in Japan and in Europe. It is being analyzed for potential RWW control in California. Because of their efficient mode of action, neonicotinoid insecticides show no cross-resistance to conventional insecticide classes and have begun replacing long-established insecticides such as pyrethroids, chlorinated hydrocarbons, and organophosphates.

Research into the potential volatility of the compound began in 2008. A soil- and water-extraction method and optimized conditions for instrumental analysis of the insecticide have been developed. Preliminary results indicate that clothianidin is not likely to dissipate from rice fields through volatilization. Analysis of the research data is continuing.


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