Measured and computed concentrations of 1,3-dichloropropene and methyl isothiocyanate in air in a region with intensive use of soil fumigants

Abstract

A sampling programme was set up to measure 1,3-dichloropropene and methyl isothiocyanate in air in a region with intensive agricultural use of these soil fumigants. In two consecutive autumns, 6-hour air samples were taken at two locations in that region with charcoal tubes using automatic samplers. Most (81%) of the 6-hour concentrations of 1,3-dichloropropene measured in both years were below 3.2 μg m⁻³ and a few percent could not be measured with a detection limit of around 0.3 μg m⁻³. Only 4% of the 6-hour concentrations exceeded 10 μg m⁻³, almost all of which were measured at a location where a field just upwind of the measuring site had been treated. For methyl isothiocyanate, 73% of the 6-hour concentrations of both years could not be measured with a detection limit in the two years of 1 and 2 μg m⁻³, respectively. A small fraction (3%) of the concentrations were in the range of 3.2 to 10 μg m⁻³ and only 1% exceeded 10 μg m⁻³.

The rates of emission of 1,3-dichloropropene and methyl isothiocyanate into air were estimated for weeks with many applications in the region studied. Using the PAL model, the concentration of fumigant in air at a receptor site was computed for representative fumigations at different upwind positions. The computed concentrations in air ranged up to 9.9 μg m⁻³ for 1,3-dichloropropene and up to 2.5 μg m⁻³ for methyl isothiocyanate.