Humic substances, hydrolysate

Piccolo, A., G. Celano, and C. DeSimone (1992). Interactions of atrazine with humic substances of different origins and their hydrolysed products. Sci. Total Environ., 117/118 403 -12. 

Alberts, J.J., Filip, Z., Price, M.T., Hedges, J.I., and Jacobsen, T.R. (1992) CuO-oxidation products, acid hydrolysable monosaccharides and amino acids of humic substances occurring in a salt marsh estuary. Qrg. Geochem. 18, 171-180. 

In the Arctic and Antarctic Ocean amino acids were also found in humic substances isolated from DOM by XAD-2 resins (Hubberten et ai, 1995). The concentration of THAA in humic substances was between 233—246 nM, with aU hydrolysable amino acids in the deep ocean and 60% of amino acids in the surface ocean residing in this fraction. Glycine was by far the most abundant amino acid detected in the humic fraction. These authors concluded that amino acids in the XAD-2 extracts represent a refractory protein background that is present throughout the ocean. The dominance of this refractory protein background in the surface and deep ocean could explain the relatively stable amino acid distribution observed by Yamashita and Tanoue (2003) at their open ocean sites. 

Dissolved amino acids are commonly divided into two pools that must be analyzed separately DFAA exist as individual monomers in solution, while DCAA are defined operationally as additional amino acids liberated by acid hydrolysis. DCAA are thus presumably present mostly as polypeptides, a supposition supported in at least the high molecular weight (HMW) fraction by N-nuclear magnetic resonance (NMR) spectroscopy data (discussed below). The operational nature of the DFAA versus DCAA definitions means that amino acids liberated from difficult matrixes (e.g., humic substances) also could make up a part of DCAA. Total hydrolysable amino acid (THAA) is another term commonly used to denote both pools together, when the sample is hydrolyzed but DFAA are not independently determined. Because the DFAA pool is typically much smaller than DCAA, THAA values are often assumed to be similar to DCAA. 

Hydrolysis is a mild degradation method for characterizing humic substances. It is believed that hydrolysis products may be closely related to the starting materials of humic substances, as mentioned later. Hydrolysis studies of lake humic substances were conducted by several authors (Ishiwatari, 1967a, 1970 Kemp and Mudrochova, 1973 Bourbonniere, 1979 Bourbon-niere and Meyers, unpublished) and many compounds were detected in their hydrolysates. 

At low concentrations, hundredths to tenths of mg 1 , iron is a common component of waters. Higher amounts of iron are found in the waters of peat moors where iron is bonded in complexes with humic substances and is kept in a stable colloid solution. In reservoirs and lakes the content of iron is stratified. On the bottom of reservoirs reduction processes take place to produce Fe(Il) (anaerobic conditions). During spring and autumn circulation, Fe(II) is dispersed in the whole water column and it oxidizes at the surface to Fe(III) due to the contact with dissolved oxygen and is hydrolysed. 

Table 2. Distribution of amino acid - and nucleic acid-N in 6M HCl hydrolysates of the fractions of alkali-soluble humic substances, isolated from a brown forest soil, and separated by "salt-boundary" gel chromatography.

---