Bis(2-Chloroethyl)sulfide

CAS RN: 505-60-2

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 240(SRC), determined from a structure estimation method(2), indicates that bis(2-chloroethyl)sulfide is expected to have moderate mobility in soil(SRC). Bis(2-chloroethyl)sulfide has been observed to bind to dry soil through a reversible interaction mechanism(3). Volatilization of bis(2-chloroethyl)sulfide from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 2.45X10-5 atm-cu m/mole(4). Bis(2-chloroethyl)sulfide evaporates from dry soil and sand surfaces(5). At moderate temperatures (25 deg C), bis(2-chloroethyl)sulfide deposited on the surface of soil has been reported to evaporate within 30 to 50 hours, depending on weather conditions(6). Evaporation rates can vary widely depending on temperature, surface type, wind and other factors(5-7); however, a primary dissipation mechanism for bis(2-chloroethyl)sulfide from soil is evaporation(8). Hydrolysis is an important process in moist soil environments; however, bis(2-chloroethyl)sulfide's low dissolution rate hinders the hydrolysis process(9). Bis(2-chloroethyl) hydrolyzes rapidly in distilled water with a half-life on the order of 4 to 8 minutes at 25 deg C(8); however, in addition to the very low rate of dissolution, intermediate hydrolysis products and/or water-insoluble thickners can coat or encapsulate bis(2-chloroethyl)sulfide droplets and retard hydrolysis(8). In the absence of water, bis(2-chloroethyl)sulfide can react at higher temperatures in soil to form adducts and polymers(10); it is possible that polymer formation may result in entrapment of bis(2-chloroethyl)sulfide droplets and protection from subsequent dissolution and degradation(SRC). Soil microorganisms capable of degrading bis(2-chloroethyl)sulfide have been isolated and identified(11). However, after application to soil, bis(2-chloroethyl)sulfide degradation occurs mainly through chemical hydrolysis with microbiological degradation being the important fate process for degradation of the hydrolysis products that include thiodiglycol(11). Although bis(2-chloroethyl)sulfide can hydrolyze rapidly and evaporate from soil surfaces, the compound may persist in the soil environment for many years, or even decades(12). Its persistence in soil was realized as French soil contaminated in 1917 was found to contain bis(2-chloroethyl)sulfide for a number of years after 1917(12). In another instance, soldiers allowed into an area deemed safe from bis(2-chloroethyl)sulfide contamination were burnt while digging the soil even though bis(2-chloroethyl)sulfide was not used in that area in 3 years(10).
TERRESTRIAL FATE: The persistence in five soils ranged from 27 to 68 hr, with sand having the longest persistence and gravelly soil the least(1). At 0 deg C the respective persistence times were 63.8, 72.6, 92.3, 49.7 days(2).
TERRESTRIAL FATE: The nature of the terrain has an important bearing on the behavior of the contaminant. Evaporation from grassland will be more rapid than from a permeable surface such as sand(1). In a field experiment designed to simulate a chemical attack, a small sample of bis(2-chloroethyl)sulfide was placed on top of the snow surface; another sample was immediately covered with 5 cm of snow in order to simulate a snowfall after an attack(2). Less than 0.1% of the bis(2-chloroethyl)sulfide was found after 14 days in both the uncovered and snow-covered samples. None of the agents studied, including bis(2-chloroethyl)sulfide, tended to migrate into the snow. Another investigator reported a persistence of 56 days in snow at -10 deg C(3). In view of the fact that snow samples are quite variable, this value is not necessarily in conflict with the first (14 day) result. It has been suggested that bis(2-chloroethyl)sulfide may react in warm, dry soil to form 1,2-bis(2-chloroethylthio)ethane and higher adducts(4); however, no experimental evidence of such reactions have been reported(SRC).
AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 240(SRC), determined from a structure estimation method(2), indicates that bis(2-chloroethyl)sulfide may adsorb moderately to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon a Henry's Law constant of 2.45X10-5 atm-cu m/mole(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 49 hours and 19 days, respectively(SRC). Hydrolysis is an important process in aquatic environments. Bis(2-chloroethyl)sulfide hydrolyzes rapidly in distilled water with a half-life on the order of 4 to 8 minutes at 25 deg C(5); however, hydrolytic destruction can be limited by a very low rate dissolution into the water(5,6). Experimental data measured hydrolysis in water, as a function of temperature; bis(2-chloroethyl)sulfide hydrolyzed in 1.5 to 158 mins at 40-0.6 deg C(7,8). Hydrolysis in seawater varies greatly with the temperature of the water and the depth of the chemical in the water(9). At the very bottom, bis(2-chloroethyl)sulfide will be found in the solid form; a one ton solid cylinder of bis(2-chloroethyl)sulfide would take about 5 yr to dissolve. In the water column of a body of seawater, dissolved bis(2-chloroethyl)sulfide will be lost by hydrolysis with its half-life ranging from 15 min at 25 deg C to 175 min at 5 deg C. According to a classification scheme(10), an estimated BCF of 12(SRC), from an estimated log Kow of 2.14(2), suggests the potential for bioconcentration in aquatic organisms is low.
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), bis(2-chloroethyl)sulfide, which has a vapor pressure of 0.11 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase bis(2-chloroethyl)sulfide 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 about 2 days(SRC), calculated from its rate constant of 7.8X10-12 cu cm/molecule-sec at 25 deg C(SRC) that was derived using a structure estimation method(3). The principal UV absorption band of bis(2-chloroethyl)sulfide in cyclohexane is at 205 nm; a very weak band occurs around 280 nm and has a tail that extends just beyond 300 nm(4). This indicates that direct photolysis, while possible, is not likely to be an important mode of degradation. Vapor-phase bis(2-chloroethyl)sulfide is relatively stable to hydrolysis in moist air, but the vapors can be adsorbed into liquid-phase water which results in hydrolysis(5).
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