COMPETITIVE DEGRADATION BETWEEN THE FUMIGANTS CHLOROPICRIN AND 1,3-DICHLOROPROPENE IN UNAMENDED AND AMENDED SOILS

Authors: ZHENG, WEI - UC RIVERSIDE, CA; Schneider, Sharon; GUO, MINXING - UC RIVERSIDE, CA; Yates, Scott

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2003
Publication Date: 9/20/2003
Citation: Zheng, W., Papiernik, S.K., Guo, M., Yates, S.R. 2003. Competitive degradation between the fumigants chloropicrin and 1,3-dichloropropene in unamended and amended soils. Journal of Environmental Quality. 32:1735-1742.

Interpretive Summary: Methyl bromide (MeBr) is widely used to control soilborne pests in many high cash value crops such as strawberry and tomato. Since MeBr contributes to the depletion of stratospheric ozone, its production and importation are being phased out. Excessive emissions of their vapor into the atmosphere may contribute to air pollution and cause adverse effects on human and environmental health. To minimize these negative impacts of the fumigant on the environment, it is necessary to develop efficient management strategies to control fumigant emission and possible leaching. Ideally, a fumigant will be destroyed by degradation in the soil after adequate pest control is achieved. However, in general, the fumigant degradation rate is relatively slow in comparison with its rapid vapor diffusion. Therefore, it is necessary modify fumigant degradation to decrease harmful effects such as emission and leaching. The objectives of this study were to investigate the rate of degradation of 1,3-D and CP when applied separately to soil, and in a mixture, and to determine the transformation rate of 1,3-D, CP and their mixture in soils amended with compounds that degrade these fumigants.

Technical Abstract: The mixture of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) is used as a pre-plant soil fumigant. In comparison with individual fumigants, application of a mixture may affect the environmental dissipation and fate of each chemical, such as emission and degradation. We investigated the degradation of CP, 1,3-D and their mixture in fresh soils and sterile soils, and evaluated the competitive characteristic of fumigants in the mixture. The degradation of low concentrations of CP in fresh soil was accelerated at early times in the presence of 1,3-D, whereas the addition of CP reduced the degradation rate of trans-1,3-D, possibly by inhibiting the activity of trans-1,3-D degrading microorganisms. The potential of applying amendments to the soil to increase the rate of CP and 1,3-D degradation was also illustrated. The degradation of both fumigants was significantly enhanced in soils amended with ammonium thiosulfate and sodium diethyldithiocarbamate compared to unamended soil. Competitive degradation was observed for CP in amended soils in the presence of 1,3-D. The degradation of cis-1,3-D in amended soils spiked as a mixture of 1,3-D and CP was repressed compared to the rate of degradation in samples spiked with 1,3-D only. No significant influence of fumigant mixtures was observed for trans-1,3-D in amended soil. Overall, the application of a mixture of CP and 1,3-D had little influence on the degradation rate of either of the individual fumigants at the concentrations studied in fresh soil. Therefore, in applications of mixtures of 1,3-D and CP, the fumigant compounds appear to behave relatively independently in terms of their degradation, indicating that the strategy of application of fumigant mixtures may have little effect on the efficacy and environmental fate of these compounds.