Summary

This memorandum supercedes an earlier memorandum evaluating the ground water contamination potential of fumigants (Dias and Clayton, 2007). Additional fumigants are analyzed in this memorandum and the irrigation amounts were increased from 0.25 inches to 0.4 inches. The Department of Pesticide Regulation (DPR) fumigant use regulations require post-application water treatments to reduce volatilization of the fumigants to the atmosphere (Title 3, California Code of Regulations [3 CCR], section 6447.3, et seq.). An empirical model was developed to assess whether or not the proposed mitigation measures shifted potential contamination from the air to the ground water environment. The fate and transport of four registered fumigants–methyl bromide, chloropicrin, methyl isothiocyanate (MITC), and 1,3-dichloropropene (1,3-D)–and three proposed fumigants–iodomethane, dimethyl disulfide (DMDS), and furfural–were evaluated in a leaching-vulnerable Fresno, California soil. To provide a worst-case scenario for potential ground water contamination, the model did not explicitly account for fumigant losses from sorption of the residues to the soil or by volatilization even though volatilization, especially, is well-known to be one of the primary routes of fumigan