Dicrotophos

CAS RN:141-66-2

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values of 16-188(2), indicate that dicrotophos is expected to have very high to moderate mobility in soil(SRC). Volatilization of dicrotophos from moist soil surfaces is not expected to be an important fate process(SRC) given a Henry's Law constant of 5.03X10-11 atm-cu m/mole(2). Dicrotophos is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 1.6X10-4 mm Hg at 25 deg C(2). Photolysis on soil surfaces is not expected to be an important fate process(3). In a laboratory persistence study using 14-C labeled dicrotophos in sandy loam soil, half-lives of 3 and 7 days were observed under aerobic and anaerobic conditions, respectively(3). Dicrotophos has been classified as a non-persistent pesticide with an estimated soil half-life of less than 0.5 month(4).
AQUATIC FATE: Based on a classification scheme(1), Koc values of 16-188(2), indicate that dicrotophos is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(3) based upon a Henry's Law constant of 5.03X10-11 atm-cu m/mole(2). According to a classification scheme(4), an estimated BCF of 3(SRC), from its log Kow of 0.00(5) and a regression-derived equation(6), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Dicrotophos' decomposition in aqueous environments is primarily by hydrolysis(7). Half-lives for the hydrolysis of dicrotophos were 117, 72, and 28 days at pH 5, 7, and 9 at 25 deg C, respectively(7). Aqueous photolysis studies showed the degradation rate was not affected by exposure of an aqueous solution of dicrotophos (pH 7) to UV light(7).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), dicrotophos, which has a vapor pressure of 1.6X10-4 mm Hg at 25 deg C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase dicrotophos 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 7.4 hours(SRC), calculated from its rate constant of 5.2X10-11 cu cm/molecule-sec at 25 deg C(SRC) that was derived using a structure estimation method(3). Vapor-phase dicrotophos is also degraded in the atmosphere by reaction with ozone(SRC); the half-life for this reaction in air is estimated to be 24 hours(SRC), calculated from its rate constant of 1.1X10-17 cu cm/molecule-sec at 25 deg C(SRC) that was derived using a structure estimation method(3). Particulate-phase dicrotophos may be removed from the air by wet or dry deposition(SRC). Dicrotophos contains chromophores that absorb at wavelengths >290 nm(4) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).
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