Emission of methyl isothiocyanate to the air after application of metham-sodium to greenhouse soil

Greenhouse soils are regularly treated with metham-sodium, which in soil is quickly transformed to the fumigant methyl isothiocyanate. An experimental fumigation was carried out in a greenhouse with sandy soil. Data were collected on the behavior of methyl isothiocyanate in soil and its permeation through a film of low-density polyethene (LDPE) covering the soil. This cover was found to be highly permeable to methyl isothiocyanate. When the fumigation of greenhouse soil was simulated with a computation model, the use of LDPE film only appreciably reduced the rate of emission into the air in the first two days. The cumulative emission corresponded to about half of the dosage for some practical situations. It is concluded that dosages should be lower and applied more effectively, and less permeable soil covers should be used.