[Comparative study on water desorption and thermal desorption of aromatic hydrocarbons in soils]

In order to develop a new method to study the mobility and bioavailability of organic contaminants in soils, a set of thermal desorption device was established. Water desorption and thermal desorption of toluene and pyrene in three types of soils were investigated. The two desorption occurred as bi-phase, which indicates that the combination states of the aromatic hydrocarbons in soils are different. The desorption was described by the first-order two compartment model and an exponential decay equation. Parameters, such as fast desorption fraction F(rap), water and thermal desorption rate constants, b(w) and b(t) were derived. For toluene, values of F(rap) in three soils were 27.9%, 12.5%, 16.0%, respectively, and 2.4%, 22.0%, and 19.1% for pyrene. Values of b(w) were 0.241, 0.018, 0.038 for toluene and 0.008, 0.013, 0.012 for pyrene. There is a significantly positive correlation relationship between F (rap) and b(w) (toluene: R2 = 0.982; pyrene: R2 = 0.991). At 250 degrees C, values of b(t) in three soils were 0.167, 0.064, 0.141 for toluene, and 0.036, 0.062, 0.047 for pyrene. At 400 degrees C, the corresponding values were 0.429, 0.084, 0.398 for toluene and 0.066, 0.162, 0.153 for pyrene. Meanwhile, the water b(w) shows a good correlation with b(t) at selected temperatures (250 degrees C: R2 = 0.985; 400 degrees C: R2 = 0.848). Moreover, F(rap) is positively correlated with b(t). As F(rap) has been used to predict bioavailability, thermal desorption can therefore be used to predict bioavailability.