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Title: Mitigating iodomethane emissions and iodide residues in fumigated soils

Author
item XUAN, RICHENG - University Of California
item ASHWORTH, DANIEL - University Of California
item WU, LAOSHENG - University Of California
item Yates, Scott

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2013
Publication Date: 10/23/2013
Citation: Xuan, R., Ashworth, D.J., Wu, L., Yates, S.R. 2013. Mitigating iodomethane emissions and iodide residues in fumigated soils. Environmental Science and Technology. 47(2):13047-13052. doi: 10.1021/es403954z.

Interpretive Summary: Fumigants are widely used in agriculture to control pests and soil-borne diseases in high-value crops. Among them, methyl bromide (MeBr) was very important and its consumption in 1991 reached 52,000 tons worldwide. However, because of its high emissions and its high potential to deplete stratospheric ozone, MeBr was scheduled for phase-out in the United States in 2005. A potential alternative, iodomethane (MeI), is a very effective fumigant for controlling soil pest organisms. Due to its high volatility and low boiling point, MeI can escape into the atmosphere and may pose a significant health risks to field workers and nearby residents. Furthermore, after being added in the soil, MeI degrades to iodide anion, which can also contaminate soils or leach to ground water. The purpose of this research was to continue investigating an approach to use ammonium hydroxide to accelerate MeI degradation in the soil to minimizing atmospheric MeI emissions while also reducing soil concentrations and leaching of iodide ion below the root zone. To date, there have been many efforts to reduce fumigant emissions to the atmosphere, but there have been few efforts to reduce or remove degradation products from fumigated soil. Completion of this research effort should provide a new technology to reduce atmospheric emissions, soil concentrations of iodide ion and leaching to ground water. This information should be of interest to the research community, regulators, policy makers and be of benefit to the public.

Technical Abstract: Although long-regarded as an excellent soil fumigant for killing plant pests, methyl bromide (MeBr) was phased out in 2005 in the USA, because it can deplete the stratospheric ozone layer. Iodomethane (MeI) has been identified as an effective alternative to MeBr and is used in a number of countries for pre-plant pest control. However, MeI is highly volatile and potentially carcinogenic to humans if inhaled. In addition, iodide anions, a breakdown product of MeI, can build up in fumigated soils, and potentially cause plant toxicity and contaminate groundwater via leaching. In order to overcome above two obstacles in MeI application, a method is proposed where ammonium hydroxide solution (NH4OH) is contained in reactive plastic bags placed on the soil surface underneath an impermeable plastic film which covers the entire fumigated area. This laboratory study has shown that using this approach, apart from < 0.04% remaining as a residue in the soil and < 0.4% being emitted through the VIF, the remainder of the applied MeI was quantitatively transferred to iodide. Of all the resulting iodide, only 2.7% remained in the fumigated soil, 97.3% was contained in the reactive bag and could potentially be removed after fumigation.