Solubilization of phenanthrene by humic acids

Humic acids has a distinct solubilizing effect on phenanthrene. The rate constant for the dissolution of solid phenanthrene in synthetic groundwater is increased by ca. 50% in the presence of 50 mg/L humic acids. The phenanthrene - humic acid interactions was found to depend significantly on the actual humic acid concentration since a pronounced decrease in the interaction constant, as well as in the water - organic matter partitioning coefficient was observed with increasing humic acid concentration. The effects are discussed in terms of concentration dependent macromolecular structural changes in the humic acids, as are effects of varying pH and ionic strength conditions of the aqueous phase.