Complexation-flocculation: A new method to determine binding coefficients of organic contaminants to dissolved humic substances

A complexation-flocculatin (CF) method was developed to determine binding (complexation) coefficients of organic contaminants to dissolved humic substances. The procedure is composed of two stages: first, the contaminant is allowed to interact with the humic material for the desired time period (complexation stage), and then a coagulant (aluminum sulfate) is added, resulting in precipitation of the dissolved humic and the bound contaminant associated with it (flocculation stage). Binding coefficients (K-b(oc)) are determined based on the fraction of the contaminant remaining in the clarified supernatant. The K-b(oc) values obtained with this method for four PAHs with humic and fulvic acid of several sources were within the range of values found in the literature and were well correlated with K-ow and the water solubility (S-w) of the respective compounds. The new method is relatively fast and simple, and compared to the frequently used fluorescence quenching technique, it is not limited to fluorescent compounds. The K-b(ow) values obtained by the CF method are somewhat lower than values obtained by quenching measurements, suggesting that fluorescence quenching tends to overestimate K-b(oc) values.