Sorption to dissolved macromolecules and colloidal particles may enhance the transport of environmental contaminants in subsurface environments. Some properties of sorbent and solute that may influence the adsorption behavior, especially in saturated soils with low organic C concentrations, were examined in a series of stirred reaction cell experiments, using acetophenone and ionizable 4‐chloroaniline and pentachlorophenol as solutes and substituted bio‐ and geopolymers and suspended clays as sorbents. The distribution coefficient was most variable, by a factor of 5500 from one sorbent to another, for the anionic pentachloropbenol and least variable, by a factor of 250, for acetophenone. These variations could be ascribed to differences in binding properties of the solute and sorbent functional groups. Sorption to clay minerals was generally low and approximated sorption to an aquifer soil suspension; the exception was a local clay with 12% organic C, which increased sorption of the phenolate ion more than 30 times compared with the low‐organic‐C clays. The most efficient sorbent was cells of bacteria isolated from aquifer material. The linear distribution coefficient for sorption on bacteria varied from 0.5 × 103 mL g−1 for acetophenone to 5 × 104 mL g−1 for neutral pentachlorophenol. The implications of sorption varying with solute and sorbent functional groups on movement of solutes through an aquifer were examined by a transport model, which divides the mobile system into an aqueous and a colloidal phase. The relative mobility of pentachlorophenol associated with colloidal sorbents can vary by as much as 90% as a result of variations of the distribution coefficient to the polymers and clays examined.
Dissolved organic macromolecules have been found to facilitate the transport of hydrophobic organic compounds in the soil. The facilitated transport increases the speed with which toxic and carcinogenic compounds reach the ground water drinking supply. The bacterial degradation of hydrophobic pollutants attached to the dissolved organic macromolecules is unknown. A better understanding is crucial for assessing the importance of the facilitated transport concept for drinking water quality. The degradation of C-14 labelled hexachlorobenzene (HCB) in a saturated soil, with and without 500 mg Blue Dextran/l (BD, model macromolecule) was measured by the amount of radioactive carbon dioxide produced. The soil was contained in stainless steel columns which were purged continuously with sterile air. The lag phase was much shorter in the columns with BD and at the end of the experiment all BD was consumed. In a current batch study with HCB-adapted bacteria the possibility of differentiating between degradation of HCB free in solution and HCB associated with the macromolecule is examined by evaluating three different mathematical models. Model 1 assumes only HCB free in solution is degraded, only by bacteria in solution. Model 2 assumes only HCB associated to BD is degraded, only by associated bacteria. Model 3 assumes associated HCB is degraded by associated bacteria and HCB free in solution is degraded in solution.
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