Acidity, humic substances

Fulvic acids Humic substances that are soluble at all pHs. 

Humic acids humic substances that are precipitated in water upon acification. 

According to their acidity, humic substances are hydrophobic and are split into two groups humic and fulvic acids. Humic acids are stable molecules originating from the ageing of organic matter. They are responsible for water coloration and represent 40-60% of natural organic matter in rivers and lakes. Fulvic acids are smaller than the humic acids and are generally less aromatic than humic acids extracted from the same pool of DOM. 

The main constituents of NOM in natural water are humic substances consisting of humic and fulvic acids. Humic substances are the precursors of THMs. These must be degraded before chlorine disinfection because once THMs are formed they cannot be removed by chemical oxidation. Ozonation can degrade humic substances into low molecular weight compounds that are less reactive toward chlorine, and hence can minimize the formation of... 

Both Pu(VI) and Pu(V) are relatively strong oxidants and are reduced by organic compounds (17). Reduction of Pu(VI) was observed when Pu(VI) was equilibrated with citric acid, humic substances extracted from soil, and acidic polysaccharides (23). This reduction of Pu (VI) by humic substances is illustrated in Table IV. After 13 days, 43% of the Pu(IV) and 84% of the Pu(VI) remained in solution. Of the Pu remaining in solution in the Pu(IV) experiment, only 32% would extract into TTA-xylene [i.e., ionic Pu(IV)] upon acidification of an aliquot of the Pu(IV)-bicarbonate solution. The remainder of the unextractable, soluble Pu was found to be mostly Pu polymer as well as a small amount of Pu(VI) formed through dis-porportionation of Pu(IV). When Pu(VI) was the initial... 

Usually only a small portion of the sample is water-soluble (chlorides, nitrates, nitrites, sulphates, alkali metals — when unbound in silicates, glycides, fatty acids, humic substances). The extract for the determination of nutrients (nitrogen, phosphorus, potassium, trace elements) is prepared with the use of leaching solutions 1% citric acid, 1% potassium sulphate, 1% hydrochloric acid, calcium lactate, etc. 

Rice J.A., Weil D.A. (1994), Absolute molecular-weight distribution of fuhdc acid. Humic Substances in the Global Environment and Implications on Human Health, (Ed. N. Senesi, T.M. Miano), Elsevier Science, 355-359. 

Recently HM-type acids have been separated from the same freshwater source in parallel by DAX-8 (nonionic polymethyl methacrylate resin, analogous with XAD-8), DEAE and PVP sorbents, and tangential-flow ultrafiltration [4,14]. The total amount (% of DOM) of HM-type acids (humic substances) obtained by different sorbents were approximately 64/DAX-8, 77/DEAE, and 80/PVP, and approximately 97% of the original DOM consisted... 

In the area of municipal and iadustrial wastewater treatment, the principal environmental issue is the toxicity of residual flocculating agents ia the effluent. Laboratory studies have shown that cationic polymers are toxic to fish because of the iateraction of these polymers with giU. membranes. Nonionic and anionic polymers show no toxicity (82,83). Other studies have shown that ia natural systems the suspended inorganic matter and humic substances substantially reduce the toxicity of added cationic polymer, and the polymers have been used successfully ia fish hatcheries (84—86). Based on these results, the EPA has added a protocol for testing these polymers for toxicity toward fish ia the presence of humic acids (87). The addition of anionic polymers to effluent streams containing cationic polymers to reduce their toxicity has been mentioned ia the patent Hterature (83). 

Humic substances in sediments and soils have commonly been, defined as heteropolycondensates of decomposing plant and animal detritus 46. For lack of a better structural definition, these macromolecular substances have been divided into three categories fulvic acids and humic acid and humin. Fulvic acids and humic acids are soluble in dilute alkaline solutions, whereas humin is insoluble. 

A. Albuzio, and G. Ferrari. Modulation of the molecular size of humic substances by organic acids of the root exudates. Plant Soil 773 237 (1989). 

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