Volatilisation of aromatic hydrocarbons from soil: Part I, fluxes from coal tar contaminated surface soils

Abstract

The non-steady-state fluxes of aromatic hydrocarbons were measured in the laboratory from the surface of soils contaminated with coal tar. Four soil samples from a former gasworks site were used for the experiments. The fluxes were quantified for 11 selected compounds, 4 mono- and 7 polycyclic aromatic hydrocarbons, for a period of up to 8 or 16 days. The concentrations of the selected compounds in the soils were between 0.2 and 3,100 µg/g. The study included the experimental determination of the distribution coefficient of the aromatic hydrocarbons between the sorbed phase and the water under saturated conditions. The determined distribution coefficients showed that the aromatic hydrocarbons were more strongly sorbed to the total organic carbon including the coal tar pitch — by a factor of 8 to 25 — than expected for natural organic matter. The fluxes were also estimated using an analytical solution of the Fick's diffusion equation and assuming that the compounds diffused independently of each other and that instant equilibrium existed between the air, water and sorbed phases. A relatively good agreement was found between the predicted and the measured flux. The predicted fluxes were between 0.11 and 7.5 time the measured fluxes. The fluxes were overestimated for the monocyclic aromatic hydrocarbons and underestimated for 3-rings-PAHs.