Bromine

CAS RN: 7726-95-6

Environmental Fate

TERRESTRIAL FATE: Volatilization of bromine from moist soil surfaces is expected to be an important fate process(SRC) given a estimated Henry's Law constant of 1.32X10-3 atm-cu m/mole(1). Bromine is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 212 mm Hg at 25 deg C(2). Bromine is reportedly vaporized rapidly at room temperature(3). Bromine will slowly be reduced to bromide by natural oxidizable materials in water and soil(4).
AQUATIC FATE: Volatilization of bromine from water surfaces is expected(1) based upon a Henry's Law constant of 1.32X10-3 atm-cu m/mole(2). Using this Henry's Law constant and an estimation method(1), volatilization half-lives for a model river and model lake are 4.5 hours and 5 days, respectively(SRC). When bromine dissolves in water, it partially disproportionates into HOBr (hypobromous acid) and HBr(3). Above pH 3, the fraction present as Br2 decreases and HOBr is formed(4); between pH 6 and pH 8, most of the bromine is present as HOBr(4). Bromine will slowly be reduced to bromide by natural oxidizable materials in water and soil(4). Bromine absorbs at wavelengths >290 nm(5) and, therefore, may be susceptible to direct photolysis on water surfaces exposed to sunlight(SRC).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), bromine, which has a vapor pressure of 212 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase bromine is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 8.6 hours(SRC), calculated from its rate constant of 4.5X10-11 cu cm/molecule-sec at 25 deg C(3). The reaction of bromine with photochemically-produced hydroxyl radicals yields the bromide radical and HOBr(3). Bromine absorbs at wavelengths >290 nm(4) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).
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