Sorption of fumigants to agricultural films

Plastic tarps are often used in soil fumigation to contain chemicals in the soil to increase efficacy and decrease emissions of fumigant vapors. This research has shown that plastic films have a significant capacity to sorb f umigant vapors and that the sorption is largely reversible. We tested three agricultural films (polyethylene and two high-barrier films) with four soi l fumigants (methyl bromide, chloropicrin, 1,3-dichloropropene, and proparg yl bromide, a potential alternative to methyl bromide). We observed signifi cant sorption of all fumigants to all the films at field-relevant concentra tions. Partition coefficients (sorbed/vapor-phase concentration) ranged fro m <1 dm(3)/m(2) film for methyl bromide to similar to 200 dm(3)/m(2) film f or chloropicrin. Sorption isotherms were linear, indicating that the film m ay be a large sink for fumigant vapors. Sorption of most fumigants was very rapid, with the bulk of the sorption occurring within the first few minute s of contact. Desorption was also rapid, with most desorption occurring wit hin minutes after the film samples we re removed to fresh a ir. First-order rate constants for desorption were similar to 0.5 to 1.5 min(-1). Sorption /desorption may be important in reducing emissions and determining worker e xposure and should be considered in measurements involving agricultural fil ms.