Estimating dissolved organic carbon partition coefficients for nonionic organic chemicals

A literature search was performed for dissolved organic carbon/water partition coefficients for nonionic organic chemicals (K-DOC), and K-DOC data were taken from more than 70 references. The K-DOC data were evaluated as a function of the 1-octanol/water partition coefficients (K-OW). A predictive relationship of K-DOC = 0.08K(OW) with 95% confidence limits of a factor of 20 in either direction was developed using K-DOC data based upon naturally occurring dissolved organic carbon. Inclusion of K-DOC data for Aldrich humic acid, a reagent-grade organic carbon, resulted in a slightly different predictive relationship of K-DOC = 0.11K(OW) with 95% confidence limits of a factor of 14 in either direction. The large uncertainties in these relationships are, in part, caused by the variability in structure and composition of dissolved organic carbon (DOC) in sediments, soils, and surface waters. This variability is not accounted for by the hydrophobicity parameter. For individual chemicals, ranges in K-DOC values approaching 2 orders of magnitude were observed among investigations using Aldrich humic acid as the DOC. These large ranges of K-DOC values suggest that measurement techniques are also, in part, responsible for the large uncertainties in these relationships.