PARAMETERS AFFECTING THE ADSORPTION OF HEXACHLOROBENZENE TO NATURAL SEDIMENTS

Many of the toxic contaminants introduced into aquatic systems are hyd rophobic and, because of this, they are transported with the suspended sediments and eventually incorporated into the bottom sediments. Unde rstanding the dynamics of contaminant sorption to sediments is therefo re important in understanding and predicting the transport and fate of contaminants. In the present study, the adsorption and the partitioni ng of hexachlorobenzene (a hydrophobic organic chemical) to natural se diments from the Detroit River were investigated by means of batch mix ing experiments. Experiments were conducted over a long period (2 to 5 months) to reach a steady-state equilibrium and at different sediment concentrations (10, 100, 500, 2,000, and 10,000 mg/L). It was found t hat the adsorption rate was greatest for small time and decreased to z ero as time increased. For all concentrations, a steady-state equilibr ium was always attained. Experiments quantitatively demonstrate the ti me-dependent effects of hexachlorobenzene dissolution, of the floccula tion of colloidal matter in the water, and of the flocculation of the suspended sediments. Although a solids concentration effect on the par tition coefficient was observed, it is shown to be due to the above pr ocesses. From the data, a true equilibrium partition coefficient as we ll as the approximate times to equilibrium can be determined.