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Title: EFFECT OF COMBINED APPLICATION OF METHYL ISOTHIOCYANATE AND CHLOROPICRIN ON THEIR TRANSFORMATION

Author
item ZHENG, WEI - UC RIVERSIDE
item Yates, Scott
item Schneider, Sharon
item GUO, MINGXIN - UC RIVERSIDE

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2004
Publication Date: 10/20/2004
Citation: Zheng, W., Yates, S.R., Papiernik, S.K., Guo, M. 2004. Effect of combined application of methyl isothiocyanate and chloropicrin on their transformation. Journal of Environmental Quality. p. 2157-2164.

Interpretive Summary: For decades soil fumigants have been extensively used to control soil-borne pests. This trend will likely continue in the near future. Methyl bromide (MeBr), a popular and effective soil fumigant, will soon be phased out in the United States and other developed countries because its deletes stratospheric ozone. The few remaining chemicals currently registered for soil fumigation include chloropicrin, 1,3-dichloropropene (1,3-D), metam sodium and dazomet. These alternative fumigants are more specific to the target pest and lack the broad-spectrum activity compared to MeBr. Recent field research has focused on developing management practices for the existing soil fumigants to maintain crop yields and minimize environmental contamination. The simultaneous application of two or more fumigants is one approach to broaden the spectrum of pest control activity and to achieve pest control efficacy and crop yield responses similar to MeBr. However, we have found that chloropicrin and 1,3-D may react rapidly with metam sodium when combined in aqueous solution. This indicates that simultaneous application of metam sodium and chloropicrin or 1,3-D may not be a feasible application technology for soil fumigation. The objectives of our research are to characterize the interaction between methyl isothiocyanate (fumigant resulting from metam sodium) and chloropicrin in aqueous solution and soil, and to determine the influence of combined application on the environmental persistence of the individual chemicals.

Technical Abstract: Combining several soil fumigants to increase the broad-spectrum of pest control is a common fumigation practice in current production agriculture. In this study, we investigated the effect of combined application of chloropicrin and methyl isothiocyanate (MITC) on their transformations and persistence in the environment. In aqueous solution, no direct reaction between MITC and chloropicrin occurred and relatively slow rates of hydrolysis of these compounds were observed in aquatic environments free of suspended solids. The transformation of chloropicrin, however, was accelerated in aqueous solution with MITC because of a reduction reaction with bisulfide (HS-), which is a byproduct of MITC hydrolysis. In soil, when fumigants were applied simultaneously, the degradation of MITC was suppressed under bi-fumigant application due to the inhibition of soil microbial activity and an abiotic competition with chloropicrin for a limited number of reaction sites on the surface of soil particles. However, the dissipation rate of chloropicrin was significantly enhanced in the bi-fumigant soil system, which was primarily attributed to the reaction of chloropicrin and HS-. Two sequential application approaches were developed to investigate the feasibility of the combined application of metam sodium and chloropicrin in soil and assess their potential effects on environmental fate. For both application sequences, the degradation of chloropicrin was accelerated and that of MITC, as a major breakdown product of metam sodium, was inhibited in soil.