Azinphosmethyl

TERRESTRIAL FATE: Based on a classification scheme(1), Koc values of 298 to 4644(2-3), indicate that azinphosmethyl is expected to have moderate to slight mobility in soil(SRC). Volatilization of azinphosmethyl from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 2.9X10-9 atm-cu m/mole(SRC), based upon its vapor pressure, 2.0X10-7 mm Hg(4), and water solubility, 29 mg/L(4). Azinphosmethyl is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(4). Half-lives of 5.3 to 40 days have been reported under soil field conditions(2,5).

TERRESTRIAL FATE: Field tests with azinphosmethyl indicated that on treated apple trees the half-life of this pesticide was about 2.6 to 6.3 days.

TERRESTRIAL FATE: A half-life in soil of 194.15 days in the dark horizon was determined from a groundwater monitoring study conducted from October 1995 to March 1997 in the fruit production fields of the Neuquen River, Northern Patagonic, Argentina(1). Azinphosmethyl has reported field half-lives of 10 to 40 days(2). Using data from the 1993 UK database, half-lives for azinphosmethyl were 5.30 to 15 days in soil(3).

AQUATIC FATE: Based on a classification scheme(1), Koc values of 298 to 4644(2-3), indicate that azinphosmethyl is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(4) based upon an estimated Henry's Law constant of 2.9X10-9 atm-cu m/mole(SRC), derived from its vapor pressure, 2.0X10-7 mm Hg(5), and water solubility, 29 mg/L(5). According to a classification scheme(6), an estimated BCF of 30(SRC), from its log Kow of 2.75(7) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is moderate(SRC). Hydrolysis half-lives for azinphosmethyl in water at pH 8.6 were 36.4, 27.9, and 7.2 days at 6, 25, and 40 deg C, respectively(9). The half-life of azinphosmethyl in seawater was 11 days when exposed to natural sunlight, while the half-life in river water was 8 days when exposed to natural sunlight(10). A decrease from 99 mg/L to 49 mg/L after 4 days incubation in a stirred flask containing azinphosmethyl as the sole carbon source and a mixed culture indicates that biodegradation in water may be an important environmental fate process(11).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), azinphosmethyl, which has a vapor pressure of 2.0X10-7 mm Hg at 25 deg C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase azinphosmethyl 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 2.5 hours(SRC), calculated from its rate constant of 1.5X10-10 cu cm/molecule-sec at 25 deg C(SRC) that was derived using a structure estimation method(3). Particulate-phase azinphosmethyl may be removed from the air by wet or dry deposition(SRC). Azinphosmethyl contains chromophores that absorb at wavelengths >290 nm(4) and, therefore, may be susceptible to direct photolysis by sunlight(SRC).