2-Xylene

CAS RN: 95-47-6

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values ranging from 24-251(2-5), indicate that 2-xylene is expected to have very high to moderate mobility in soil(SRC). Volatilization of 2-xylene from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 5.18X10-3 atm-cu m/mole(6). 2-Xylene is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 6.65 mm Hg at 25 deg C(7). 2-Xylene is expected to biodegrade in soil under both aerobic and anaerobic conditions(8). Biodegradation is an important process in subsurface soils and groundwater where volatilization is hindered(8). 2-Xylene has been observed to biodegrade in standard biodegradability tests using various inocula including sewage, activated sludge and sea water(9). For example, using aerobic OECD Guideline 301F (Ready Biodegradability: Manometric Respirometry Test) with a mixture of sewage, soil and natural water inoculum, 2-xylene reached 90-94% of its O2 consumption in 28 days which classified it as readily biodegradable in two separate studies(9). However, under anaerobic conditions, a long lag period may be required before degradation commences(10).
AQUATIC FATE: Based on a classification scheme(1), Koc values ranging from 24-251(2-5), indicates that 2-xylene is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(6) based upon a Henry's Law constant of 5.18X10-3 atm-cu m/mole(7). Using this Henry's Law constant and an estimation method(6), volatilization half-lives for a model river and model lake are 3.2 hours and 4.1 days, respectively(SRC). According to a classification scheme(8), a BCF of 14 measured in goldfish(9) indicates that bioconcentration in aquatic organisms is low(SRC). Biodegradation is an important process in groundwater where volatilization is hindered(10). 2-Xylene has been observed to biodegrade in standard biodegradability tests using various inocula including sewage, activated sludge and sea water(11). For example, using aerobic OECD Guideline 301F (Ready Biodegradability: Manometric Respirometry Test) with a mixture of sewage, soil and natural water inoculum, 2-xylene reached 90-94% of its O2 consumption in 28 days which classified it as readily biodegradable in two separate studies(11). Reported biodegradation half-lives in aerobic water range from days to weeks(12-15). However, under anaerobic conditions, a long lag period may be required before degradation commences(16). Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions(6).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), 2-xylene, which has a vapor pressure of 6.65 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase 2-xylene 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 1.2 days(SRC), calculated from its rate constant of 1.36X10-11 cu cm/molecule-sec at 25 deg C(3). Vapor-phase 2-xylene is also degraded in the atmosphere by reaction with night-time nitrate radicals(SRC); the half-life for this reaction in air is estimated to be 85 days(SRC), calculated from its rate constant of 3.77X10-16 cu cm/molecule-sec at 25 deg C(4). 2-Xylene has been detected in rainwater and snow(5,6), and therefore, it may be removed from the air by wet deposition(SRC). 2-Xylene does not absorb at wavelengths >290 nm(7) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC).
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