Fate of humic acids isolated from natural humic substances

Abstract

Composition of humic acids (HA) is a function of plant-derived inputs, degradation processes regulated by microorganisms, organo-mineral interactions and age. Characterization of different origin humic substances is important for evaluation of their contribution to stabile and labile carbon pool in the environment. The relative abundance of chemical components in HA isolated from soils, compost, commercial lignohumates, alginite, acadiane and lignite was studied with aim to quantify content of important biomarkers such as amino acid, lipids and polyphenols. HA were considered as a heterogeneous complex and high concentration of peptides, polyphenols and lipids was determined in acadian-HA to compare with soil-HA. Compost-HA contained much more amino acids to compare with soil-HA samples. Alginite-HA and lignite-HA were similar in biomarkers content to soil-HA. Fourier transform infrared spectroscopy confirmed that chemical composition and functional groups content differs with the origin, humification degree and the age of studied samples. Soil-HA are typically composed of a variety of −OH, COOH−, C–O, C–H2, (aliphatic and aromatic) groups, quinines, lignin fragments, polysaccharide, monosaccharide and proteins fragments, which are linked together by −O−, −NH−, −H=, >C=O, metal ions and –S− groups. 13C NMR spectroscopy showed that aromatic carbon content was the highest in lignite-HA and soil-HA.