Hexachlorocyclopentadiene

CAS RN:77-47-4

Volatilization

The Henry's Law constant for hexachlorocyclopentadiene is 0.027 atm-cu m/mole(1). This Henry's Law constant indicates that hexachlorocyclopentadiene is expected to volatilize rapidly from water surfaces; however, adsorption may attenuate this process(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 2 hours if adsorption is ignored(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 7 days if adsorption is ignored(SRC). The volatilization half-life from a model pond is about 37 days when adsorption is considered(3). Losses of hexachlorocyclopentadiene (initial conc 0.41 mg/L), from half-full glass-stoppered and unstoppered bottles shaken at room temperature over a 24 hour period were equivalent to 15-16% of the original amount(4). Loss was presumably due to volatilization(4). Volatilization losses of 5.3-9.9% were observed over a two hr period from a static aqueous solution of hexachlorocyclopentadiene at an initial concentration of 50 ng/L at 25 deg C(5). Hexachlorocyclopentadiene's Henry's Law constant indicates that volatilization from moist soil surfaces may occur; however, adsorption may attenuate volatilization(2). Hexachlorocyclopentadiene is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 0.060 mm Hg(6). Volatilization losses of 0.84-1.60% from moist sand, 0.35-0.67% from moist loam, and 0.15-0.285% from moist humus were observed over a two hour period in a laboratory study, carried out at 25 deg C, where the initial hexachlorocyclopentadiene concentration was 50 ug/kg soil on a dry weight basis(5). Following application of 100 mg of radiolabeled hexachlorocyclopentadiene to a moist Maury silt loam, the cumulative evaporative losses of this compound and its nonpolar metabolites (penta- and tetrachlorocylopentadiene) 1, 2, 3, 5, 7, and 14 days after application were 9.3, 10.2, 10.6, 10.8, 11.0, and 11.2%, respectively(4).
The ratio of the volatilization rate to the reaction rate constant for hexachlorocyclopentadiene in natural waters /was determined/ to be 0.58. ...Results indicated that on the order of 15% of the hexachlorcyclopentadiene load in a turbid river would be removed by volatilization, as compared to less than five percent for a pond or a eutrophic lake.
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