Diffusion and Sorption of Hexachlorobenzene in Sediments and Saturated Soils

In order to understand the transport and fate of hydrophobic organic chemicals (HOCs) in consolidated sediments and saturated soils, long-term (up to 512 d), one-dimensional, time-dependent diffusion experiments were done with a representative HOC, hexachlorobenzene (HCB), in three different sediments and soils. In addition, long-term HCB partitioning experiments in suspended sediments at high concentrations and tritiated water diffusion experiments in consolidated sediments were done in order to more accurately interpret the HCB diffusion experiments. Numerical models were used to analyze the results. Good agreement between the experimental data and calculated results was obtained. Despite the length of the experiments, the experimental results demonstrate that the HCB in the consolidated sediments was far from a steady-state chemical equilibrium. Experiments and theoretical results also indicate that the assumption of local chemical equilibrium was not valid, and sorption rates must therefore be considered for a valid analysis of transport.