Methyl Bromide In Soil Research Articles

Status of Chemical Alternatives to Methyl Bromide for Pre-Plant Fumigation of Soil

ABSTRACT None of the chemical alternatives currently registered and available has the full spectrum of activity and versatility of methyl bromide as a pre-plant soil fumigant. Chloropicrin and 1,3-dichloropropene (Telone) can provide significant control of many plant pathogens in soil and growth stimulation in annual crops. These compounds, however, provide limited control of weeds or other residual plant materials in soil of concern in nursery production systems, and some perennial replant diseases. Methyl isothiocyanate generators such as metam sodium have broad biocidal activity in soil, but are more difficult to apply effectively. In most soil applications, the available alternatives are likely to be used in combinations, either as mixtures (e.g., 1,3-dichloropropene and chloropicrin) or sequentially (e.g., chloropicrin followed by metam sodium). They may also be supplemented with other more specific pesticides and cultural controls. Among the alternatives currently under active development but not yet available, methyl iodide and propargyl bromide probably have activity that most closely parallels that of methyl bromide in soil. However, all of the chemical alternatives to methyl bromide will be subject to continuing review and more regulation. Furthermore, we do not know the actual prospects for registration of the new fumigants currently under development and there is a risk that registered fumigants will not be available for large-scale use in soil indefinitely.

Stimulation of Microbial Degradation of Methyl Bromide in Soil during Oxidation of an Ammonia Fertilizer by Nitrifiers

To reduce volatilization of the fumigant methyl bromide (MeBr) from soil into the atmosphere, attempts were made to enhance microbial degradation of MeBr in soil by stimulating the activity of soil nitrifiers. Disappearance of MeBr in limed Arredondo soil (pH 7.70) treated with an ammonia-based nitrogen fertilizer, (NH4)2SO4, was initially more rapid than in unlimed Arredondo soil (pH 5.5−5.7). Disappearance of MeBr in limed soil with or without treatment of (NH4)2SO4 that received 20 μg/g MeBr was more rapid than in the corresponding soil samples that received a higher rate of MeBr (50 μg/g). Due to higher nitrification activity in limed surface soil (0−15 cm depth) than in limed subsurface soil (15−30 cm depth), disappearance of MeBr in the surface soil with or without (NH4)2SO4 treatment was also more rapid than in the corresponding subsurface soil. Both microbial and chemical degradation were involved in the MeBr degradation in soil, with chemical degradation possibly being the major factor. Contribut...

The influence of soil environmental variables on the degradation and volatility of methyl bromide in soil

Recent controversy over the potential role of methyl bromide (MeBr) in damaging the ozone layer has spurred interest in qualitatively increasing our understanding of the transformation and movement of this fumigant. In contrast to the extensive uses of this common agricultural fumigant, a paucity of data exits on the environmental fate of MeBr. Out research indicates that MeBr is rapidly volatilized from fumigated soil (within the first 24 h) and volatility significantly increases with temperature (35°C > 25°C > 15°C) and moisture (-3 kPa > -33 kPa > -300 kPa). Degradation of MeBr, measured by production of bromide ion (Br - ), was also positively related to temperature and moisture. Undisturbed soil column studies indicated that MeBr rapidly volatilized (>50% of the MeBr flux occurred in 48 h) and did not leach into subsurface soil. Residual MeBr was degraded in the soil column, as evident by the high concentrations of Br in the leachate water. These studies provide valuable information for assessing the fate of MeBr in soil, which should lead to more informed decisions for regulating its use.

Effect of soil properties on degradation and sorption of methyl bromide in soil

Methyl bromide (CH 3Br) is currently the most widely used soil fumigant, and its emission into the atmosphere after application reportedly contributes to ozone depletion in the stratosphere. Irreversible degradation and partially reversible sorption reactions affect the quantity of this furnigant reaching the soil surface and escaping into the atmosphere. Incubation studies in closed headspace vials under controlled conditions showed that degradation of CH 3Br was highly dependent on soil organic matter content, and to a lesser extent, on the moisture level in the soil. Methylation of CH 3Br on organic matter was suggested to be the major reaction that CH 3Br undergoes in the soil environment. Other soil constituents such as clay did not contribute to the degradation under moist or air-dried conditions, though enhanced degradation was observed on oven-dried montmorillonite and kaolinite clays. Within soil profiles, degradation of CH 3Br decreased with soil depth mainly due to the reduction of soil organic matter content with depth. In both Greenfield and Wasco sandy loams, the degradation rate of CH 3Br in soil layers from 0 to 270 cm could be estimated from soil organic matter content. Sorption of CH 3Br on moist soils was generally limited, and varied with soil depth. The degree of sorption could be predicted from soil moisture alone or soil moisture and organic matter content.

Diffusion of methyl bromide in soil

SUMMARYPhenomenological modelling is proposed for penetration by diffusion with aqueous dissolution of a gaseous constituent in non‐saturated soil when there is a thermodynamic imbalance between this gas phase constituent and the same constituent in solution. Non‐equilibrium experiments (Mignard & Benet, 1986) led to specifying the equation governing the kinetics of dissolution and measurement of the phenomenological coefficient for methyl bromide.The results of the model with dissolution imbalance are compared with those of models in the literature which assume immediate dissolution equilibrium in the treatment of soil with methyl bromide applied at the surface. The model developed gives profiles of concentration of substance in the soil in both liquid and gas phases, and makes it possible to judge the extent of the soil zone treated and to forecast what will be the behaviour of the substance.