Binding of pyrene on lake aquatic humic matter: the role of structural descriptors

Partition coefficients for the binding affinities of pyrene to 28 different humic materials were determined by the solubility enhancement method. The humic materials used in the present study were isolated by different methods from different environmental sources, and characterized by various methods including spectroscopic and pyrolysis (Py) approaches. Several structural descriptors were derived for testing the binding affinity of pyrene. A significant correlation was observed, supporting the earlier literature results, between the pyrene binding coefficient and the molecular weights, molar absorptivities at 280nm, and aromaticity of the aquatic humic solutes. Also other structural descriptors, e.g. nitrogen and especially aliphatic moieties, have their own importance to the binding affinity of pyrene. The results confirm the fact that it is not meaningful to treat aquatic and terrestrial humic material as an integrated whole. The results also disclosed that the isolation and fractionation procedures of aquatic humic probes will strengthen, as a result of breaking hydrophobic bondings of aggregates between different humic solutes, the binding affinities of pyrene on different humic isolates compared with the original situation predominating in the water sample. One has to be very careful in the light of the forthcoming predictions what kind of humic probe has been adopted for representing aquatic humic matter (HM). A statistical approach for estimation of the most probable carbon distribution in a humus sample proved quite workable for the prediction of binding affinity of pyrene on aquatic humic materials.