The objective of this study was to determine the structural characteristics and sorption behavior of two soil-free and charcoal-free humic acids. The first, a synthetic humic acid, was made by spontaneous polymerization of various phenols, as well as a long chain fatty acid.The second humic acid was made from soil-free plant materials composted under isolated conditions. Structural characterization was performed using elemental analysis, FTIR and ¹³C solid state NMR. A batch equilibrium technique was used to determine the sorption of phenanthrene on both the synthetic and the compost humic acids. Preliminary sorption experiments produced non-linear sorption isotherms for the synthetic humic acid. Isotherm non-linearity for the greenhouse humic acid will be discussed. Charcoal-free humic acids could potentially contribute to sorption non-linearity.