Metal Binding in Estuarine Humic and Fulvic Acids: FTIR Analysis of Humic Acid-Metal Complexes

Abstract

Humic and fulvic acids isolated from salt marsh estuaries of the southeastern United States had copper binding capacities (CuBC) of 0.16 to 0.26 µg atm Cu2+ mg−1 humic acid and 0.17 to 0.24 µg atm Cu2+ mg−1 fulvic acid. Competitive reactions of humic substances with alkaline earth elements Ca2+ and Mg2+ reduced the CuBC by only 11% for fulvic acids and by 17% for humic acids. Competition with the trivalent metal ions Al3+ and Fe3+ reduced the CuBC in humic substances by 30–40%. Fourier transform infrared (FTIR) spectral analyses of the humic-metal complexes suggest that Cu(II) may be bound preferentially by oxygen-containing functional groups in estuarine fulvic acids, but there is a much higher involvement of nitrogen-containing functional groups in binding Cu(II) to estuarine humic acids. FTIR spectra were also collected for humic acid-metal complexes of Ag, Au, Hg, Mn and Pb.