Naphthalene

CAS RN: 91-20-3

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values of 112 to 9,333(2-4) indicate that naphthalene is expected to have high to no mobility in soil(SRC). Volatilization of naphthalene from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 4.4X10-4 atm-cu m/mole(5). The estimated volatilization half-life for naphthalene from soil is 1.1 days, and 14 days when incorporated at a depth of 1 cm and 10 cm, respectively(6). Naphthalene is not expected to volatilize from dry soil surfaces based upon a vapor pressure of 0.085 mm Hg at 25 deg C(7). In soils previously exposed to naphthalene or other PAHs, half-lives of 2-18 days have been reported(8).
AQUATIC FATE: Based on a classification scheme(1), Koc values of 112 to 9333(2-4) indicate that naphthalene is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(5) based upon a Henry's Law constant of 4.4X10-4 atm-cu m/mole(6). Using this Henry's Law constant and an estimation method(5), volatilization half-lives for a model river and model lake are 6 hours and 5 days, respectively(SRC). Naphthalene is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(5). According to a classification scheme(7), BCFs of 36.5-168 in carp(8) and 692-714 in minnows(9), suggest the potential for bioconcentration in aquatic organisms is moderate to high(SRC). Naphthalene has been shown to biodegrade in water with half-lives ranging from about 0.8 to 43 days(10-11).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), naphthalene, which has a vapor pressure of 0.085 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase naphthalene 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 14-16 hours(3), calculated from its rate constants of 2.73X10-11 to 2.16X10-11 cu cm/molecule-sec at 25 deg C(3-5). Vapor-phase naphthalene is also degraded in the atmosphere by reaction with nitrate radicals(SRC); the nighttime half-life for this reaction in air is estimated to be 60 hours(SRC), calculated from its rate constant of 6.4X10-15 cu cm/molecule-sec at 25 deg C(6). Naphthalene absorbs light in the environmental UV spectrum and, therefore, direct photolysis may occur(7).
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