Fulvic acids decomposition

Since lignins are polymers of phenolics and are major plant constituents with resistance to microbial decomposition, they are the primary source of phenolic units for humic acid synthesis (178, 179). Once transformed, these humic acids become further resistant to microbial attack and can become bound to soils (180) form interactions with other high molecular weight phenolic compounds (ex. lignins, fulvic acids) and with clays (181) and influence the biodegradation of other organic substrates in soils (182, 183). 

NOM is common in sediments, soils, and near ambient (<50 °C) water. The materials result from the partial decomposition of organisms. They contain a wide variety of organic compounds, including carboxylic acids, carbohydrates, phenols, amino acids, and humic substances (Drever, 1997, 107-119 Wang and Mulligan, 2006, 202). Humic substances are especially important in interacting with arsenic. They result from the partial microbial decomposition of aquatic and terrestrial plants. The major components of humic substances are humin, humic acids, and fulvic acids. By definition, humin is insoluble in water. While fulvic acids are water-soluble under all pH conditions, humic acids are only soluble in water at pH >2 (Drever, 1997, 113-114). 

Thermal analysis of humic-mineral complexes has shown there is an overall reduction in the decomposition temperatures of humic acid that has been com-plexed to a mineral surface. Changes in the exothermic peak temperatures of humic substances in the free and complexed state are well-documented for synthetic mineral complexes with humic and fulvic acid (Schnitzer and Kodama, 1972 Tan, 1977 Schnitzer and Ghosh, 1982) as well as for authentic soil complexes. 

Tate, R. L. (1992). Ill Humic and fulvic acids Formation and decomposition. In Soil Organic Matter Biological and Ecological Effects, Tate, R. L., ed., Krieger, Melebar, FL, pp. 147-164. 

The photo decomposition of carbofuran (2,3-dihydro-2,2-dimethyl-7-ben-zofuranyl-AT-methylcarbamate) (III) was investigated in pure water and in the presence of various samples of organic matter (soil-extracted humic and fulvic acids) [66]. Irradiation of carbofuran (1.3 x 10 5 M) in pure water at 254 nm yielded several photoproducts however, only Ilia and Illb could be firmly identified. A step reaction was proposed first, formation of Ilia by cleavage of the O - CO bond, and second, formation of Illb by photohydrolysis of the furan ring (see Scheme 3). 

Specific organic matter or humic substances These are produced by the connection of decompositions products. Their structure is not exactly known, and depends on production conditions. On the basis of solubility, humic substances are classified as fulvic acid, humic acid, humin, and hymatomelanic acid (Stevenson 1982). 

Natural organic matter (NOM) is derived from plant or microbial residues, or it is produced in situ in water by life cycles and by a variety of decomposition pathways. Humic material (HM) is found in surface water. Its concentration is typically about 50% of the DOM. HM itself consists of the fulvic acid (FA) fraction that is soluble in water of all pH values and has an average molar mass M of 500-2000 g moh. In contrast, the humic acid (HA) fraction is only soluble under acidic conditions. HA has an average molar mass M of 2000-5000 g mol and higher (Sigg and Stumm, 1996). The composition and structure of HM or of hu-... 

Based on detailed analyses of the chemical nature of SOM, Hatcher and Spiker (1988) have extended this humification model to include other resistant biopolymers, including plant cutin and suberin, and microbial melanins and paraffinic macromolecules. During decomposition, these biopolymers are selectively preserved and modified to become part of what can be operationally defined as humin (acid and alkali insoluble component of humus) (Hatcher and Spiker, 1988 Rice, 2001). The humin becomes progressively enriched in acidic groups leading to the formation of first humic acids and then fulvic acids, which under this degradative scheme of SOM formation would be regarded as the most humified of humic substances (Stevenson, 1994). 

Finally, humic and fulvic acids can act as chemical weathering agents by complexing reactions. Early work was carried out on metal oxides and the differential leaching of cations leading to the decomposition of rocks and minerals is frequently cited. Many early experiments on the role of humic and fulvic acids in the breakdown of rocks and minerals are summarized by Ong et... 

Tan, K.H., 1975. The catalytic decomposition of clay minerals by complex reaction with humic and fulvic acid. Soil Sci., 120 188—194. 

The presence of humic and fulvic acids in surface waters and groundwaters will have a significant influence on the transport and fate of metals, radionuclides, and organic contaminants in the environment. These natural organic acids can either transport or immobilize contaminants, depending on the environmental conditions. Humic and fulvic substances can also retard or enhance the photochemical decomposition of pesticides or toxic organics. Therefore, to be sucessfiil any remediation strategies must consider the effects of humic materials. If properly understood, this behavior can be used to manipulate pollutant solubilization and facilitate containment or cleanup of contaminated sites. 

Type of Peat Botanical Type Degree of Decomposition (%) Ash %) Bitumen Readily Hydrolyzable Substances Hemi- cellulose Humic Acids Fulvic Acids Nonreadily Hydrolyzable Substances Nonhydrolyzed Residue... 

Table 4 shows mean values for the relative distribution of amino acids in acid hydrolyzates of humic acids and fulvic acids extracted from the same soils. These data are expressed as a-amino nitrogen of each amino acid x 100/total amino acid nitrogen. An inspection of the data in Table 4 indicates, with few minor exceptions, similarities in the amino acid composition of humic acids and fulvic acids. Acid hydrolysis appears to destroy about one-half of the amino sugars and there are losses of threonine and serine (Sowden, 1959, 1969). No corrections are made for their decomposition because the ammonia-nitrogen would then require correction, and a valid correction for it is not possible. The ammonia nitrogen increases with length of time of hydrolysis (Khan and Sowden, 1971). 

De Haan, H. (1977). Effect of benzoate on microbial decomposition of fulvic acids in Tjeukemeer (The Netherlands). Limnot. Oceanogr. 22, 38-44,... 

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