Bis(2-Chloroethyl)sulfide

CAS RN: 505-60-2

Volatilization

The Henry's Law constant for bis(2-chloroethyl)sulfide is 2.45X10-5 atm-cu m/mole at 25 deg C(1). This Henry's Law constant indicates that bis(2-chloroethyl)sulfide is expected to volatilize from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as 49 hours(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as 19 days(SRC). Bis(2-chloroethyl)sulfide's Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). 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(3). Studies of the volatilization of bis(2-chloroethyl)sulfide applied to calcareous soil at a temperature of 21-25.5 deg C and relative humidity of 27-35%, showed that 7-32% of the applied chemical volatilizes within 6 hours and no additional bis(2-chloroethyl)sulfide volatilizes after 15 to 55 hours(4); at this time, 12-66% of the material was recovered. Both the rate of volatilization and the amount of gas ultimately recovered depend on the pH, moisture content, and soil type. Less bis(2-chloroethyl)sulfide is recovered from fine soils than from course sandy ones(4). Another study reported a half-life for the depletion of bis(2-chloroethyl)sulfide from the soil 'surface' has been estimated to be 20 minutes at 25 deg C(5). More sophisticated models estimate that 1.8 year is required for removal of bis(2-chloroethyl)sulfide applied uniformly at 71 ppm to the top 10 cm of soil (2% organic carbon content)(5). Bis(2-chloroethyl)sulfide evaporates from dry soil and sand surfaces(6); the rate of evaporation from one soil surface was similar to the rate of evaporation from glass where evaporation rates increase with the size of droplets applied to the surface(6); on glass surfaces, the rate of evaporation ranged from 2.746 to 7.336 ug/minutes at 30 deg C(6). A primary dissipation mechanism for bis(2-chloroethyl)sulfide from soil is evaporation(7).
Chemical agents, such as bis(2-chloroethyl)sulfide, are dispersed in the form of droplets(1). Bis(2-chloroethyl)sulfide was applied to a polyurethane surface at temperatures ranging from -40 deg C to 0 deg C; by extrapolating the experimental data, a 1.1 mm bis(2-chloroethyl)sulfide droplet took 8.2 days to evaporate at 0 deg C and a 1.5 mm droplet took 37 days to evaporate at -20 deg C(2). In the presence of a 2 m/sec wind speed, the drops were estimated to last for 13.5 days, 61 days, and 750 days at 0, -20, and -40 deg C, espectively(2). Persistence of these droplets will be a function of drop size, temperature, and air velocity(1,2). Viscosity will also impact the persistence of the drops. Viscosity increases at lower temperatures therefore increasing the persistence of the drops(1). The half-life of a 6.5 mg droplet of bis(2-chloroethyl)sulfide at 23.6 deg C, 99% relative humidity and an air flow of 0.63 cm/sec from an aluminum surface was 15 hr; 90% was volatilized in 32 hr(3). The estimated volatilization time for 1-mm bis(2-chloroethyl)sulfide drops on a hard surface with a 2 m/sec wind is (time (temperature in deg C)): 7.25 hr (10), 17.5 hr (0), 45.2 hr (-10), 5.25 days (-20), 16.0 days (-30), 53.3 days (-40)(1). Extrapolated vapor pressure data were used below -10 deg C. Humidity may affect evaporation since adsorption of atmospheric moisture causes dilution and concomitantly an increase in the drop size. Contact with permeable surfaces, snow, water, or ice will give rise to solubility phenomena, retarding evaporation(1). With porous surfaces, including soil and sand, leaching, surface flow, and adsorption would also lead to reduced volatilization. Since bis(2-chloroethyl)sulfide is so persistent at low temperatures, it is possible that hydrolysis, oxidation, or other processes may change the surface composition and therefore the volatilization(SRC). The volatilization rate of a pool of bis(2-chloroethyl)sulfide was measured; at a wind speed of 1 m/s, the volatilization flux was approximately 1.2, 3.0, and 7.5 ug/min-sq cm at 18.7, -10, and 0 deg C, respectively(2).
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