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Title: Reactive films for mitigating methyl bromide emissions from fumigated soil

Author
item XUAN, RICHENG - University Of California
item Ashworth, Daniel
item LUO, LIFANG - University Of California
item Yates, Scott

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2011
Publication Date: 2/22/2011
Citation: Xuan, R., Ashworth, D.J., Luo, L., Yates, S.R. 2011. Reactive films for mitigating methyl bromide emissions from fumigated soil. Environmental Science and Technology. 45(6):2317-2322.

Interpretive Summary: Methyl bromide (MeBr) has been used for several decades to control plant pests prior to production of many food crops. MeBr has also been identified as an ozone depleting compound and was scheduled for phase out during 2005 in developed countries, and 2015 elsewhere. MeBr use continues in the United States due to the submission and approval of Critical Use Exemptions (CUE). To obtain a CUE, an emission mitigation methodology must be used; therefore, a great need exists for low-cost and effective methods to reduce MeBr emissions, which in turn, will protect stratospheric ozone. Designing a gas-tight film that degrades MeBr once it leaves the soil could provide an effective method to reduce MeBr emissions. Furthermore, the same strategy could be used to develop films for other fumigant compounds. This paper reports on a laboratory experiment to test the feasibility of using a film to degrade MeBr in the airspace below the film. This approach to reduce MeBr emissions will help to protect stratospheric ozone from depletion during the phase-out period. This research would be of interest to scientists, regulators and film manufacturers.

Technical Abstract: Emissions of methyl bromide (MeBr) from agricultural fumigation can lead to depletion of the stratospheric ozone layer, and so its use is being phased out. However, as MeBr is still widely used under Critical Use Exemptions, strategies are still required to control such emissions. In this work, novel reactive films (RFs) were designed and their efficacy in limiting loss of MeBr from soil was tested. A reactive layer, containing dry ammonium thiosulfate (ATS), was sandwiched between two layers of plastic film, the lower layer being HDPE (high-density polyethylene film, which is permeable to MeBr) and the upper layer HDPE or VIF (virtually impermeable film). MeBr diffusion through, and transformation by, the RFs were tested in a stainless-steel permeability cell. Although ineffective when dry, the RFs substantially depleted MeBr when activated with water to produce ATS solution. MeBr half-life (t1/2) was around 9.0 h at 20 _C in the presence of activated RF, and was sensitive to temperature (t1/2 15.7 and 2.9 h at 10 and 40 _C, respectively). When the upper film layer was VIF, less than 0.15% of the added MeBr diffused through the film, with the remainder being transformed within the reactive layer. These findings indicate that such films have good potential to reduce MeBr loss from fumigated soils to the atmosphere.