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Environmental Fate and Exposure Potential

【Environmental Fate/Exposure Summary】

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 37(SRC), determined from a log Kow of 0.36(2) and a regression-derived equation(3), indicates that nicotinic acid is expected to have very high mobility in soil(SRC). The pKa of nicotinic acid is 4.75(4), indicating that this compound will primarily exist in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(5). Volatilization from moist soil is not expected as ions do not volatilize(SRC). Nicotinic acid is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 5.7X10-6 mm Hg(SRC), determined from a fragment constant method(6). In aqueous, aerobic soil suspensions, nicotinic acid was completely degraded after 2 to 4 days of incubation(7), suggesting that biodegradation may be an important environmental fate process in soil(SRC).
AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 37(SRC), determined from a log Kow of 0.36(2) and a regression-derived equation(3), indicates that nicotinic acid is not expected to adsorb to suspended solids and sediment(SRC). A pKa of 4.75(4) indicates nicotinic acid will exist almost entirely in the anion form at pH values of 5 to 9 and therefore volatilization from water surfaces is not expected to be an important fate process(5). According to a classification scheme(6), an estimated BCF of 3(SRC), from its log Kow(2) and a regression-derived equation(7), suggests the potential for bioconcentration in aquatic organisms is low(SRC). In aqueous, aerobic soil suspensions, nicotinic acid was completely degraded after 2 to 4 days of incubation(8), suggesting that biodegradation may be an important environmental fate process in water(SRC).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), nicotinic acid, which has an estimated vapor pressure of 5.7X10-6 mm Hg at 25 deg C(SRC), determined from a fragment constant method(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase nicotinic acid 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 24 days(SRC), calculated from its rate constant of 1.72X10-13 cu cm/molecule-sec at 25 deg C(3). Nicotinic acid does not absorb at wavelengths >290 nm(4) and therefore is not expected to be susceptible to direct photolysis by sunlight(SRC).

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