Sampling and analysis of the soil fumigants 1,3-dichloropropene and methyl isothiocyanate in the air

Methods of sampling and analysis have been developed to measure concentrations of the soil fumigants 1,3-dichloropropene and methyl isothiocyanate (formed from metham-sodium) in air. We tested these methods under laboratory and field conditions. Air samples were taken with glass tubes containing charcoal as adsorbent. The charcoal was extracted with acetone and subsamples of the extracts were injected into a gas Chromatograph with a capillary column. 1,3-dichloropropene was determined by an electron capture (EC) detector and methyl isothiocyanate by a nitrogen-phosphorus (NP) detector. Concentrations of these fumigants in 40 L of air as low as 0.2 μg m−3 and 1.0 μg m−3, respectively, could be determined. A study on the influence of storage temperature and time on the recovery from charcoal showed that charcoal tubes can be stored for up to 4 d at −20 °C. A test program on the breakthrough of the charcoal tubes when sampling at different flow rates and air humidity revealed no significant breakthrough from the first to the second (check) tube. Similar results were obtained from sampling the air during fumigation of the soil in a greenhouse and in two fields.