Variation of 1-naphthol sorption with organic matter fractionation: the role of physical conformation

Nonionic, hydrophobic organic contaminant sorption to natural organic matter is of continual concern due to the strong association between the contaminant and organic matter. To better understand the underlying mechanisms in sorption interactions, humic acids (HAs) and humin from soils and geologic samples with varying diagenetic properties were isolated and used in sorption studies with 1-naphthol. The organic carbon-normalized sorption coefficient (Koc) values for the fractions differed from those of the source samples and, in most instances, increased. The Black, Brown, and Peat HA 1-naphthol Koc values are statistically similar (p < 0.01) but notable differences exist in their H/C ratios and cross polarization magic angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectra. The humin samples exhibited much higher 1-naphthol Koc values than their source samples, suggesting that the fractionation procedure reorganized the organic matter such that more, or more favorable sorption sites became available. A mass balance calculation revealed that the parts sorbed more than the whole and implies that accessible organic matter rather than total organic matter is a factor in the uptake of contaminants.