Methyl isothiocyanate volatilization from fields treated with metam-sodium

Emission of methyl isothiocyanate (MITC) from fields treated with metam-sodium (sodium N-methyldithiocarbamate) is a potential environmental and human safety hazard. Concentrations of MITC at three heights above four arable fields were measured following the application of metam- sodium at a rate of 480 litre ha ˇ1 (166 kg AI ha ˇ1 ). Two of these fields were treated by injection into a center-pivot irrigation system (chemigation), while in the other two fields the fumigant was applied through injection directly into the soil. Generally, higher MITC air concentrations were observed above chemigated than above injected fields. Maximum MITC air concentrations were 11.2 and 7.4 mg m ˇ3 recorded 10cm above ground 6-8 h following application and the minimum concentrations were 0.7 and 0.2 m gm ˇ 3 observed at 200 cm 30-35h after application above chemigated and injected fields, respectively. The estimated MITC respiratory exposure a worker might encounter during the re-entry period ranged between 1.37 and 0.03 mg day ˇ1 in chemigated fields and between 0.35 and 0.02mg day ˇ1 in the injected fields. These results suggest that application of the fumigant through injection reduced MITC volatilization losses in comparison with the chemigation method, thus posing a relatively lower risk of exposure to MITC emissions. # 2000 Society of Chemical Industry