Properties of Soil Fumigants and Their Fate in the Environment

Effects of CO2dissolution on phase distribution and degradation of dimethyl disulfide in soils under grape production

“…The half-life values of DMDS (26-143 days) in this study are much longer than those reported by Chellemi et al, 19 who observed DMDS half-lives of 1-6 days in a Dothan sandy loam. However, Ajwa et al 12 suggested that the half-life of DMDS in soil could be 2-3 times that of methyl isothiocyanate (1-13 days), which would be within the range of some half-life values observed in this study. 12 The stability of DMDS may explain its long nematode control efficacy (150 or 180 days) observed in a recent grape fumigation field study.…”

“…The K d values of other soil fumigants such as MeBr (0.04–0.10 L kg −1 ), methyl isothiocyanate (0.045 L kg −1 ), 1,3‐D (0.40–0.60 L kg −1 ) and chloropicrin (0.03–0.14 L kg −1 ) in loamy soils are 1–2 orders of magnitude lower than those found for DMDS in this study . This difference in sorption potential may partially be explained by the higher vapor pressures of the other fumigants (3.1–190 kPa at 20 °C), as compared with 2.9 kPa for DMDS . The higher sorption potential of DMDS could be advantageous over other fumigants as it may lead to longer compound retention in the soil that could increase efficacy when effectively dispersed in the soil.…”

“…12,20 -22 This difference in sorption potential may partially be explained by the higher vapor pressures of the other fumigants (3.1-190 kPa at 20 ∘ C), as compared with 2.9 kPa for DMDS. 12 The higher sorption potential of DMDS could be advantageous over other fumigants as it may lead to longer compound retention in the soil that could increase efficacy when effectively dispersed in the soil.…”

“…10,11 DMDS has a lower vapor pressure (2.9 kPa at 20 ∘ C) but higher octanol-water partition coefficient (K ow = 1.77) than MeBr (190 kPa at 20 ∘ C; K ow = 1.19), making it relatively less volatile, more sorptive and therefore less capable of spreading through the soil profile to make contact with and eliminate pests such as nematodes. 12,13 Therefore, to increase DMDS field fumigation efficacy, it must be applied in higher amounts, allowed to fumigate for longer periods or injected at a higher frequency. These options are either not allowed by the regulations (rates are currently capped at 455 lbs acre −1 ) or are not cost effective.…”

Fumigant emission reductions with TIF warrant regulatory changes

“…Only nominal benefits would be achieved by extending the tarping period from 10 to 16 days. Although TIF has the ability to retain 1,3-D in the soil for a few weeks, the degradation half-life of 1,3-D under field conditions is 5 to 7 days (Ajwa et al 2003(Ajwa et al , 2010, and a very small residual concentration, if any, is found in the soil when TIF is removed from the field after 10 days. Also, the final degradation products of 1,3-D are nontoxic (mainly carbon dioxide, 6 24 42 60 78 96 114 132 150 168 186 204 222 240 258 276 294 312 330 348 366 384 402 420 6 24 42 60 78 96 114 132 150 168 186 204 222 240 258 276 294 312 330 348 366 384 402 420 6 24 42 60 78 96 114 132 150 168 186 204 222 240 258 276 294 312 330 348 366 384 402 420 6 24 42 60 78 96 114 132 150 168 186 204 222 240 258 276 294 312 330 348 366 384 402 water and chlorine) and do not pose risk to humans and the environment (Dungan and Yates 2003).…”