Water Solubility Enhancement of Some Organic Pollutants and Pesticides by Dissolved Humic and Fulvic Acids

Water solubility enhancements by dissolved humic and fulvic acids from soil and aquatic origins and by synthetic organic polymers have been determined for selected organic pollutants and pesticides (p,p'-DDT, 2,4,5,2',5'-PCB, 2,4,4'-PCB, 1,2,3-trichlorobenzene, and lindane). Significant solubility enhancements of relatively water-insoluble solutes by dissolved organic matter (DOM) of soil and aquatic origins may be described in terms of a partition-like interaction of the the solutes with the microscopic organic environment of the high-molecular-weight DOM species; the apparent solute solubilities increase linearly with DOM concentration and show no competitive effect between solutes. With a given DOM sample, the solute partition coefficient (K_dom) increases with a decrease of solute solubility (S_w) or with an increase of the solute's octanol-water partition coefficient (K_ow). The K_domvalues of solutes with soil-derived humic acid are approximately 4 times greater than with soil fulvic acid and 5-7 times greater than with aquatic humic and fulvic acids. The effectiveness of DOM in enhancing solute solubility appears to be largely controlled by the DOM molecular size and polarity. The relative inability of high-molecular-weight poly(acrylic acids) to enhance solute solubility is attributed to their high polarities and extended chain structures that do not permit the formation of a sizable intramolecular nonpolar environment.