Effect of physical forms of soil organic matter on phenanthrene sorption Original Research Article

The sorption coefficient, KOC, of phenanthrene (PHE) has been reported to vary with different types of organic matter, leading to uncertainties in predicting the environmental behavior of PHE. Among the studies that relate organic matter properties to their sorption characteristics, physical conformation of organic matter is often neglected. In this work, organic matter samples of different physical forms were examined for their sorption characteristics. Dissolved humic acids (DHA) showed significantly higher KOC than the corresponding solid humic acids (SHA) from which the DHAs were made. The KOC of DHAs was found to be related to polarity, whereas KOC of SHAs increased with aliphatic carbon content. Soil particles were treated with H2O2 to remove organic matter, and humic acid was coated on H2O2-treated soil particles to make organo-mineral complexes at pH 4, 7 and 10. Although the nonlinear sorption was apparent for SHAs and H2O2-treated soil particles, the organo-mineral complexes formed using these two components at pH 4, 7 and 10 exhibited relatively linear sorption at organic carbon content, fOC > 0.5%. These results indicate that organic matter of the same composition may have different sorption properties due to different physical forms (or conformations). Nonlinear sorption for the complexes formed at pH 4 with lower fOC (< 0.5%) was also discussed.