Lead and Calcium Binding to Fulvic Acids: Salt Effect and Competition

Abstract

Knowledge of the speciation of Pb in natural aquatic systems is important if we want to understand the bioavailability and mobility of Pb in polluted and natural environments. The results given in this paper were obtained under conditions as close as possible to natural conditions. These new data show that Pb strongly binds to fulvic acids. We also show that the competitive effect of Pb on Ca binding to the same fulvic acid is smaller than the salt effect on Ca binding to fulvic acids as pH varies from 4 to 8. All the data were analyzed with the NICCA−Donnan model developed to describe metal ion binding to natural organic matter. The model predictions of competitive and salt effects are excellent. Comparison of our results with previously published data suggests that metal ion binding strength is similar for fulvics acids from different origins. Thus, all data sets could be interpreted within the framework of a unified modeling approach.