Environmental Fate of Pesticides 09

Environmental Fate of Rice Pesticides - 2009
Project Leader and Principal Investigators Ronald S. Tjeerdema, professor and chair, Dept. of Environmental Toxicology, UC Davis	The goal of this ongoing project is to study how pesticides important to rice culture dissipate under California rice field conditions. These compounds break down in the environment through interaction with soil, water, and air, as well as by degradation from sunlight and microbial activity. Studies in 2009 focused on the widely used herbicide CeranoŽ, an experimental insecticide etofenprox, and a newer experimental insecticide, clothianidin. CeranoŽ found safe CeranoŽ has become one of the most popular herbicides for control of watergrass, barnyardgrass, and sprangletop in California rice fields. This compound (clomazone) is used elsewhere in soybeans, cotton, and tobacco. It was registered for use in California in 2002. CeranoŽ is characterized as strongly water soluble, weakly soil adhering, and minimally volatile. These characteristics make it more likely to persist in water where microbial degradation may contribute to its environmental fate. California rice fields contain a mosaic of aerobic and anaerobic conditions and different microbial communities. Laboratory experiments showed that CeranoŽ degrades rapidly under anaerobic conditions. Under aerobic conditions, CeranoŽ degraded more slowly. A large experiment involving 10 commercial rice fields was conducted to observe CeranoŽ degradation under real-world conditions. Although water samples were taken from the fields over a 90-day period, CeranoŽ was not detected after day 14. The results confirm laboratory findings. Toxicologists conclude that CeranoŽ is a relatively safe herbicide for use in California rice fields and should dissipate rapidly in drainage water. Etofenprox fate Etofenprox is an experimental ether-based pyrethroid pesticide under consideration for rice water weevil control. Previous research showed that this compound has a strong tendency to partition out of water and adhere to soil particles. Laboratory experiments in 2009 simulated rice field conditions to determine microbial activity on etofenprox under unflooded (aerobic) and flooded (anaerobic) conditions. Etofenprox dissipated rapidly in the first three days under both aerobic and anaerobic conditions. The rate of dissipation slowed after that. As hypothesized, the insecticide degraded more efficiently when exposed to air in the unflooded test. The breakdown byproducts of etofenprox were also characterized. This experiment is being repeated at higher air temperatures to more closely simulate summer weather in the Sacramento Valley. Toxicologists believe the rate of dissipation will be faster at higher temperatures and thus etofenprox persistence should decrease. Clothianidin volatilization Clothianidin is a novel neonicotinoid insecticide that exhibits good systemic action and high insecticidal activity against a variety of sucking insect pests. It is registered for foliar-spray and seed-treatment applications in Europe and Asia. It is under consideration in California for rice water weevil control. In laboratory experiments, clothianidin was found to have very low volatility and high water solubility. Thus, dissipation into the air is unlikely for this compound under typical California rice field conditions.

Environmental Fate of
Rice Pesticides - 2009

Project Leader and Principal Investigators

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

The goal of this ongoing project is to study how pesticides important to rice culture dissipate under California rice field conditions. These compounds break down in the environment through interaction with soil, water, and air, as well as by degradation from sunlight and microbial activity. Studies in 2009 focused on the widely used herbicide CeranoŽ, an experimental insecticide etofenprox, and a newer experimental insecticide, clothianidin.

CeranoŽ found safe

CeranoŽ has become one of the most popular herbicides for control of watergrass, barnyardgrass, and sprangletop in California rice fields. This compound (clomazone) is used elsewhere in soybeans, cotton, and tobacco. It was registered for use in California
in 2002.

CeranoŽ is characterized as strongly water soluble, weakly soil adhering, and minimally volatile. These characteristics make it more likely to persist in water where microbial degradation may contribute to its environmental fate. California rice fields contain a mosaic of aerobic and anaerobic conditions and different microbial communities. Laboratory experiments showed that CeranoŽ degrades rapidly under anaerobic conditions. Under aerobic conditions, CeranoŽ degraded more slowly.

A large experiment involving 10 commercial rice fields was conducted to observe CeranoŽ degradation under real-world conditions. Although water samples were taken from the fields over a 90-day period, CeranoŽ was not detected after day 14. The results confirm laboratory findings. Toxicologists conclude that CeranoŽ is a relatively safe herbicide for use in California rice fields and should dissipate rapidly in drainage water.

Etofenprox fate

Etofenprox is an experimental ether-based pyrethroid pesticide under consideration for rice water weevil control. Previous research showed that this compound has a strong tendency to partition out of water and adhere to soil particles. Laboratory experiments in 2009 simulated rice field conditions to determine microbial activity on etofenprox under unflooded (aerobic) and flooded (anaerobic) conditions.

Etofenprox dissipated rapidly in the first three days under both aerobic and anaerobic conditions. The rate of dissipation slowed after that. As hypothesized, the insecticide degraded more efficiently when exposed to air in the unflooded test. The breakdown byproducts of etofenprox were also characterized.

This experiment is being repeated at higher air temperatures to more closely simulate summer weather in the Sacramento Valley. Toxicologists believe the rate of dissipation will be faster at higher temperatures and thus etofenprox persistence should decrease.

Clothianidin volatilization

Clothianidin is a novel neonicotinoid insecticide that exhibits good systemic action and high insecticidal activity against a variety of sucking insect pests. It is registered for foliar-spray and seed-treatment applications in Europe and Asia. It is under consideration in California for rice water weevil control. In laboratory experiments, clothianidin was found to have very low volatility and high water solubility. Thus, dissipation into the air is unlikely for this compound under typical California rice field conditions.