2,3,7,8-Tetrachlorodibenzo-p-dioxin

CAS RN: 1746-01-6

Volatilization

The Henry's Law constant for TCDD is estimated as 3.2X10-6 atm-cu m/mole(SRC) derived from its vapor pressure, 1.5X10-9 mm Hg(1), and water solubility, 2.0X10-4 mg/L(2). This Henry's Law constant indicates that TCDD is expected to volatilize from water surfaces(3). 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)(3) is estimated as 21 days(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(3) is estimated as 160 days(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 5.1X10+4 years if adsorption is considered(4). TCDD's estimated Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). However, adsorption to soil is expected to attenuate volatilization(SRC). TCDD is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(1). Volatilization of TCDD that has been mixed into soil depths beneath the upper surface boundary will volatilize extremely slowly(5).
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