Octanol–water partitioning of chemical constituents in river water and treated sewage effluent

A shake-flask approach has been employed to determine the n-octanol–water partitioning of chemical constituents in various river waters and in treated sewage effluent. The bulk inorganic composition of the water samples (conductivity, pH and the concentrations of major solutes: Ca, K, Mg, Na) was unaffected by the presence of solvent. Boron, however, exhibited increasing partition with decreasing sample pH, because its dominant form in freshwaters, B(OH)3, is neutral, covalent and acidic. Constituents having significant association with dissolved organic matter (DOM), including components of DOM itself (C, S) and trace metals that form complexes with organic ligands (Al, Cu, Fe, Pb, Zn), exhibited measurable partition into the solvent in most cases, with conditional partition coefficients, Dow, in the region 0.03–2.5. Significant differences in the partitioning among these constituents and among the environments studied did not appear to be related to bulk sample characteristics or the degree of association of the constituent with DOM. These observations suggest that partition is sensitive to the nature of the organic matter (C, S) and the availability of specific binding ligands (trace metals). Thus, although Dow is critical for defining the biogeochemical behaviour and potential impacts of chemical constituents in the environment, it appears to be a difficult parameter to model or predict.