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 fumigant vapors and that the sorption is largely reversible. We tested three agricultural films (polyethylene and two highbarrier films) with four soil fumigants (methyl bromide, chloropicrin, 1,3-dichloropropene, and propargyl bromide, a potential alternative to methyl bromide). We observed significant sorption of all fumigants to all the films at fieldrelevant concentrations. Partition coefficients (sorbed/ vapor-phase concentration) ranged from <1 dm3/m2 film for methyl bromide to ∼200 dm3/m2 film for chloropicrin. Sorption isotherms were linear, indicating that the film may 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 minutes of contact. Desorption was also rapid, with most desorption occurring within minutes after the film samples were removed to fresh air. Firstorder rate constants for desorption were ∼0.5 to 1.5 min-1. Sorption/desorption may be important in reducing emissions and determining worker exposure and should be considered in measurements involving agricultural films.