Abstract:

1, 2Dichloroethane (1, 2DCA) and 1, 2dichloropropane (1, 2DCP) are two kinds of volatile organic compounds (VOCs) which are among the most frequently detected pollutants in groundwater at one contaminated site. In this paper the adsorption and desorption of 1, 2DCA and 1, 2DCP on three soil samples collected from the vadose zone are studied by batch experiments. The results showed that the adsorption isotherms of 1, 2DCA and 1, 2-DCP fit linear Henry isotherm equations well, and the partition coefficient (Kd) ranges  from 2049 to 2243 L·kg-1. The adsorption capacity of 1, 2-DCA and 1, 2-DCP on the three soils are very similar, suggesting that the contents of natural organic matter are responsible for adsorption. For the same soil, the adsorption capacity of 1, 2-DCA is slightly higher than that of 1, 2DCP. Meanwhile, the desorption isotherms of the two pollutants can be described with nonlinear Freundlich isotherm equations. Differences in desorption capacities among the soils are related to the clay contents; the higher clay contents, the lower desorption capacity. The soil within the deepest layer, which is about 4951 m below surface, has the lowest vulnerability to 1, 2-DCA and 1, 2-DCP. Desorption of both chemicals has significantly retarded and the hysteresis indices of 1, 2DCP are higher than those of 1, 2-DCA.

Key words:

unsaturated zone; 1, 2dichloroethane (1, 2DCA); 1, 2dichloropropane (1, 2DCP); adsorption; desorption; hysteresis