Sorption of chlorinated phenols by natural sediments and aquifer materials

Laboratory experiments have been conducted to study the sorption of chlorinated phenols by sediments and aquifer materials. It is shown that sorption not only of the nondissociated phenols but also of their conjugate bases (phenolates) can occur. At typical ambient concentrations, sorption equilibrium can be described by the equation <I>S</I> = <I>DC</I>, where <I>S</I> = concentration in the solid phase, <I>D</I> = overall distribution ratio, and <I>C</I> = concentration in the liquid phase. In natural waters of low ionic strength (i.e., <I>I</I> ≤ ~10<sup>-3</sup> M) and of pH not exceeding the p<I>K</I><sub>a</sub> of the phenol by more than one log unit, phenolate sorption can be neglected and the overall distribution coefficient may be expressed by <I>D</I> = <I>K</I><sub>p</sub><I>Q</I>, where <I>K</I><sub>p</sub>= partition coefficient of the nonionized phenol and <I>Q</I> = degree of protonation. <I>K</I><sub>p</sub> may be estimated from the octanol/water partition coefficient of the compound and from the organic carbon content of the sorbent. In the case of tetra-and pentachlorophenol, phenolate sorption usually has to be considered. It is strongly influenced by the organic carbon content of the sorbent and by the ionic strength of the aqueous medium.