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Environmental fate & pathways

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Terrestrial fate: dibromomethaneis expected to have very high mobility based upon an estimated Koc of 29.86. Volatilization from moist soil surfaces is expected to be an important fate process based upon a Henry's Law constant of 8.22X10-4atm m3/mole. Dibromomethanemay volatilize from dry soil surfaces based upon its vapor pressure 35.3mmHg.

Aquatic fate: estimated Koc value of 29.86 and Level III Fugacity Model, indicates that dibromomethaneis not expected to adsorb to suspended solids and sediment in water. Volatilization from water surfaces is expected based upon a Henry's Law constant of 8.22X10-4atm m3/mole. Using this Henry's Law constant and an estimation method, volatilization half-lives for a model river and model lake are 2 hours and 6 days, respectively. On the other hand, dibromomethane can be available to biotic and abiotic degradations processes in water based on its high solubility and Level III Fugacity Model which predicts that 84% of the substance remains in water.

Dibromomethane is readily biodegradable. Biodegradation of dibromomethane occur in different natural water sources and salinity (fresh water, marine and hypersaline water) almost at the same rate with half-life value of 2 days. Dibromomethane can be hydrolyzed under environmental conditions and the hydrolysis half-life is 143 days at pH 7 and 25° C. An estimated BCF of 5.963, suggests the potential for bioconcentration in aquatic organisms is low.

Atmospheric fate: a vapor pressure of 35.3 mm Hg at 25oC, indicates dibromomethaneis expected to exist solely as a vapor in the ambient atmosphere. Direct photolysis should have only a minor effect on the atmospheric lifetime of dibromomethane due to its very low UV absorption at wavelengths > 290 nm. The tropospheric lifetime of dibromomethane by reaction of hydroxyl radicals has been estimated to be 0.29 years (105.9 days). These results are further supported by calculation of the rate constant for the atmospheric reaction between photochemically produced hydroxyl radicals and dibromomethane in the vapor phase estimating half-life of 146.1 days.