Z. Filip

Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.

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.