Characterization of humic acids extracted from the sediments of the various rivers and lakes in China

The humic acids (HAs) isolated from the sediments of the various rivers, lakes, and reservoirs in China were studied using elemental analyzer, fourier transform infrared (FT-IR), and CP/MAS 13C nuclear magnetic resonance (NMR) spectroscopy. The results showed that the HAs were characterized by some common chemical and physicochemical properties, but they also pose some differences in the C-containing functional groups. The C/N, C/H, O/C, and O/H ratios differ widely for the various HAs, showing that the elemental composition of the HAs from the various sediments was different due to the different environmental conditions. All HAs show similar spectra with different intense absorbance in the region of 4000–2000 cm−1, suggesting that they have very similar structures and functional groups. The absorbance region between 1900 and 400 cm−1 also showed similar spectra with different intense absorbance, different relative intensities, and some relevant differences for the various HAs. The total aromaticities for the six HAs varied from 23.1% to 41.8%. The differences in the elemental composition and functional groups for the various HAs were attributed to their different biogeochemical origins. The HAs in the sediments from Taihu Lake (one freshwater shallow lake with heavy eutrophication), the Pearl River (the tropical river), and the Liao River (located at the joint of the temperate zone and cold-temperate zone) showed different structural properties due to their different geographical and climate zones. These different properties for the six HAs were expected to affect the sorption, distributions, and fates of heavy metals and organic chemicals.