Irreversible binding of chlorophenols to soil and its impact on bioavailability

Experiments were conducted to quantify binding of phenol, 4-chlorophenol (4-CP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) to a sandy surface soil under aerobic and anoxic conditions, with and without autoclaving. Water and methylene chloride were used to extract the physisorbed contaminants. The chemically bound contaminant was characterized as biologically or abiotically coupled. A portion of the residual contamination on soil was attributed to the presence of a desorbable but mass transfer-rate limited component of the sorbate. Autoclaving the soil or eliminating O₂ from the system had no observable effect on the total sorption of chlorophenols. However, the amount of bound material that was resistant to extraction was at least twice as high in nonautoclaved soils under oxic conditions as compared to soil in systems from which O₂ or biochemical activity, or both had been eliminated. The initial aqueous concentration of the contaminant appeared to govern the amount of nonextractable material. A biodegradation study found that approximately 50% of the coupled contaminant was bioavailable.