Chemical characterization of size-fractionated humic and fulvic materials in aqueous samples

Abstract

Humic and fulvic acids have been shown to be potentially important transport agents for inorganic and organic contaminants, including radionuclides, in surface and groundwaters. In this work, the possibility of characterizing humic and fulvic materials in the colloidal and macromolecular size ranges (i.e., between 3000 molecular weight (1 nm) and 0.45 μm) after size fractionation and collection with hollow-fiber ultrafilters has been investigated. Three surface waters have been examined as test cases. Using ultrafiltration, sized samples of humic and fulvic acids were chemically characterized with 13C-nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) using diffuse reflectance, and pyrolysis/gas chromatography (GC). These test cases demonstrate that sufficient material can be obtained by ultrafiltration with minimal or no alteration to the materials. In addition, inorganic analyses performed on the size fractions show that ultrafiltration can also allow the binding capacity of the humic materials in each fraction to be measured. Substantial variability among the different humic and fulvic fractions demonstrates the importance of sizing submicron materials in attempts to understand the mechanisms of pollutant transport by natural humic materials.