Effect of environmental conditions on the permeability of low density polyethylene film and totally impermeable film to methyl isothiocyanate fumigant

Fumigant methyl isothiocyanate (MITC) is a very promising alternative to methyl bromide, providing effective control of soil borne disease. However, there is a significant volatilization of MITC following fumigation because of its high application rates and high vapor pressure. Covering the soil surface with plastic tarps is a common approach used for restricting fumigant emissions to the atmosphere. To minimize atmospheric emissions of MITC by tarping, we determined the effect of temperature, humidity, and fumigant mixtures on the permeability to MITC of low density polyethylene film (LDPE) and totally impermeable film (TIF), using static sealed chambers. The results showed that temperature had the largest impact on the mass transfer coefficient (MTC) of MITC across LDPE film; the permeability increased 8.8 times when temperature was raised from 5°C to 35°C. There was a small increase in tarp permeability with increasing relative humidity below 75%, but it was little difference in MTC values between 75% and 100% relative humidity. The permeability of TIF to MITC is much lower than that of LDPE. TIF is much more sensitive to the ambient conditions; both temperature and humidity can drastically alter the MTC of MITC across TIF. Fumigant mixtures of MITC did not have a significant impact on the MTC across the LDPE film. The results of this study will contribute to establishing guidance on the appropriate environmental conditions for using tarping films to reduce MITC emission and achieve adequate pest control. [Display omitted] •To determine the permeability of LDPE and TIF to MITC under different conditions.•Temperature and humidity had large impact on the permeability of plastic films to MITC.•The permeability increased with increasing temperature and humidity.•Fumigant mixtures did not have significant impact on the permeability of LDPE to MITC.