Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2004
Publication Date: 11/20/2004
Citation: Guo, M., Zheng, W., Papiernik, S.K., Yates, S.R. 2004. Distribution and leaching of methyl iodide in soil following emulated shank and drip application. Journal of Environmental Quality 33:2149-2156. Interpretive Summary: Fumigants are biocides used to control weeds, pathogens, nematodes, and soil fungi. Fumigants have high vapor pressures at room temperature and quickly disperse in soils through gas phase diffusion. The environmental fate of field applied fumigants is of great concern because of their impacts on environmental quality and human health. Because of the high volatility, low sorptivity, and rapid degradation rate of fumigants in soils, persistent soil fumigant residues are usually considered insignificant, especially long after application. However, studies have shown that many fumigants remain in soils for a number of years following application. For instance, 1,3 dichloropropene, a methyl bromide replacement, has been detected in groundwater in many states and other fumigants such as ethylene dibromide, 1,2-dichloropropane, methyl bromide, and 1,2 dibromo 3 chloropropane have also been detected in groundwater. In this study, the distribution and leaching of MeI in soil after shank-injection and drip-application were investigated and significant leaching was observed. This suggests that MeI may pose a risk to surface and ground water.
Technical Abstract: Methyl iodide (MeI) is a promising alternative to methyl bromide in soil fumigation. The pest-control efficacy and groundwater contamination risks of MeI as a fumigant are highly related to its gas-phase distribution and leaching after soil application. In this study, the distribution and leaching of MeI in soil following shank-injection and drip-application were investigated. Arlington sandy loam (coarse-loamy, mixed, thermic Haplic Durixeralfs) was packed into stainless steel columns (12 cm i.d. by 70 cm height) with moisture content and topsoil bulk density adjusted. Methyl iodide was directly injected or drip-applied at 200 kg ha-1 into tarped columns at 20-cm depth, and concentration profiles of MeI in the soil air were monitored. Methyl iodide diffused rapidly after soil application, and reached 70 cm within 2 h. Relative to shank-injection, drip-application inhibited the diffusion, resulting in significantly lower concentration profiles in the soil air. Fumigated soil was aerated for 7 d prior to water leaching. Methyl iodide was measured in the leachate and as residues in leached soils. Leaching of MeI was significant from the soil columns under both application methods, with concentrations >10 µg L-1 in the early leachate. The leaching was greater following shank-injection than drip-application, with an overall extent of 33 g ha-1 for the former and 19 g ha-1 for the latter. Persistent residues of MeI remaining in soils after leaching were 50-240 ng kg-1, and the contents were slightly higher following shank-injection than drip-application. The results suggest that fumigation with MeI may pose a risk of groundwater contamination in vulnerable areas.