Binding of organic pollutants to humic and fulvic acids: Influence of pH and the structure of humic material (original) (raw)

In order to compare their binding capacities, humic acids (HA) and fulvic acid8 (FA) were isolated from water and extracted from sediments, and used to measure partition coefficients (163 for the model compounds benxo(a)pyrene f&P) and pentachlorophenol (PCP). To study the effect of pH on the binding capacity of humic substances, k, values were measured at H 5.0, 6.5 and 8.0. An equilibrium dialysis method was used to detemline the Is, and elemental allalySis, P3C-NMRandFT-IR8pectrawerecarriedout on HA and FA to examine the relationship between the structure of humic material and the partition coefficients. The result8 show that HA have a greater affmity for binding hydrophobic compounds than FA. Change in pH only weakly affect8 k, values for the neutral chemical BaP while k values for PCP (about 102 times lower than values of BaP) decrease radically with an increasing pH from 5.0 to 8.0. This suggest that only the unionized form of a weak organic acid like PCP can interact with the humic material. Moreover, elemental analysis and spectra indicate that high 16, vahtes can be related to a large aromatic content and. to a rather low content of functional groups in the humic structures. This, at least partly, explain8 wiry the more hydrophobic HA bind the model chemical8 more than FA, and why the sedimentary humic substauces show a higher binding capacity in comparison with the largely ftmctionalised soluble humic compounds from the water phase. 8 1997 Elsevier Science Ltd. All rights reserved Key wordls: humic substances, humic acid, fulvic acid, organic pollutants, binding, structure of humic substances Illtroductian Dissolved organic material (DOM) and sedimentary organic material (SOM) in natural environments consist of a large variety of organic molecules. Most of these have no readily identifiable structure. This heterogeneous group of organic macromolecules is often referred to as humic substances. Humic substances are importaut in water chemistry and aquatic toxicology because they can bii both metals and hydrophobic organic pollutants [l-6]. At the same time, humic substances in sediments and particulate organic matter in water phase play an important role in the flocculation and in the accumulation of hydrophobic compounds such as PAID and PCBs, thus affecting the transport and fate of xenobiotics [7].