Effects of environmental variables on binding of a PCB congener by dissolved humic substances

The magnitude of the binding interaction of dissolved organic matter with 2,2′,5,5′-tetrachlorobiphenyl is affected by several environmental parameters: pH, ionic strength of the aqueous media, molecular weight and the source of the binding agent. Temperature has little effect. The binding constant for Aldrich humic acid is on the order of 1 × 105. Humic acids extracted from soil and water samples have lower binding capabilities than Aldrich humic acid (KDOC range: 0.24 × 105-0.64 × 105), whereas the fulvic acid and dissolved organic matter samples have KDOCs near the method detection limit (0.086 × 105 and 0.0076 × 105, respectively). Thermodynamic studies show the binding interaction to be entropy driven with ΔH° similar to that of van der Waals's interaction.