pH-dependent sorption of chlorinated guaiacols on estuarine sediments: The effects of humic acids and TOC

Chlorinated guaiacols (o-methoxyphenols) are components of chlorine-bleached kraft pulp and paper mill effluents and have been detected in receiving water and sediment adjacent to paper milts. Their sorption is dependent on both solvent and sorbent characteristics. Sorption of four chlorinated guaiacols was investigated using four estuarine sediments from the York River, Va. Sites represented several types of estuarine environments, ranging from a well-scoured sandy point to a protected tidal mudflat Total organic carbon (TOC) contents ranged from 0.11 to 3.52% (dry weight). NaOH-extractable humic acids ranged from 0.03 to 1.2% (dry weight). Sorption coefficients, K-d, were measured at pH 6.6 and pH 7.8 by the batch isotherm method. Linear relationships were observed for K-d with both sediment TOC and humic acid contents. K-oc and K-humic, sorption coefficients normalized to % TOC and % humic acids, respectively, were calculated. Results indicated that the humic acid content of a sediment, along with TOC, is an important factor in controlling the sorption of chlorinated guaiacols. Due to differences in hydrophobicity, sorption of the protonated and deprotonated chlorinated guaiacol species is expected to differ. Using accurately measured pK(a) values, the K-d for each compound was resolved into values for the ionized and neutral species (K-d,K-i and K-d,K-n, respectively). The results indicated that sorption of highly chlorinated, ionized species is appreciable and cannot be discounted when assessing sorptive reactions.