Association organic compounds humic matter

Most of the organic nitrogen in natural waters is bound to or built into structural components of humic substances (Bronk, 2002 Schnitzer, 1985). It has been demonstrated both in laboratory experiments and in field observations that proteinaceous matter bound to humic substances becomes bioresistant (Carlson et al., 1985 Hubberten et al., 1994). In pioneering studies on DON phototransformation Amador et al. (1989, 1991) showed that a significant part of amino acids associated with humic matter becomes bioavailable after irradiation. On the other hand, longterm irradiation of a mixture of protein and DOM compounds resulted in decreased bioavailability (Keil and Kirchman, 1994). The loss of bioavadabihty of the protein required presence of DOM, supporting that the DOM either interacted direcdy... 

Of the other forms of nonresidual associations, some metal-organic compounds, for example, fulvic and humic acids, have been shown to be particularly effective in the transfer of (toxic) metals from inorganic matter into organisms 51). According to Table II, where data of humate extractions with O.IN NaOH are compared, these effects should be more relevant for iron, copper, zinc, and lead in the sample from the Rhine River than in the sediment material from Lake Constance. The other nonresidual metal associations (easily reducible, carbonates, moderately reducible forms) partly indicate higher percentages in Lake Constance sediments (Mn and Pb), whereas others (chromium, copper, and zinc) are enriched in the Rhine sample. 

The Incorporation of non-polar compounds Into sedimentary organic matter Is of Interest In a pure geochemical sense, but also has practical environmental Implications. "Bound" pollutants would be undetected In many environmental studies because such studies typically employ simple solvent extraction the quantitative significance of bound pollutants must be ascertained to produce an accurate assessment of contamination. Also, the biological availability of sedimentary pollutants could depend on the nature of their association with organic matter. For example, "bound" PCB s entrapped within humic matrices might be less accessible to benthic fauna than "free" PCB s. 

The occurrence of HCP In HA fractions and Its absence In FL fractions suggests that the pollutant was strongly associated with organic matter and was probably deposited In the sediments In bound form. HCP may have been covalently bound to organic matter and released hydrolytically during base treatment. Laboratory studies support these observations Miller et al. (53) demonstrated that HCP covalently binds to rat tissue protein (In vitro) and Mathur and Morley (54) showed that a structurally similar compound, methoxychlor (2,2 -bls(jj-methoxyphenyl)l,l,l-trlchloroethane), strongly associated with a synthetic humic acid. 

The effect of dissolved organic matter on the solubility of DDT and two PCB congeners is illustrated in Figure 2.8. This study demonstrates that the solubility of the chlorinated hydrocarbon was increased with the amount of soil humic acid added. It must be emphasized that this increase does not result from an effect on the solvent but it is due to the association of the solute with the dissolved humic acid. With these hydrophobic compounds it would appear that the association is due to their partitioning into rather than adsorption onto the humic acid since the two PCB congeners do not compete, that is, the trichlorobiphenyl does not reduce the association of the pentachlorobiphenyl. (The partitioning process is discussed in more detail in the analysis of the sorption in soil.)... 

Proteinases in soil extracts have been assayed using casein and substituted amides and peptides as assay substrates. Mayaudon et al. found that the casein hydrolysing activities of soil extracts were directly related to soil organic matter contents and inversely related to clay contents. Specific activities doubled when associated coloured humic compounds were removed from the extracts. The partially-purified proteinases appeared to be of a serine protease type as judged from their responses to inhibitors. Optimal activity occurred at pH 8.5 and at 50 0. The estimated Km value (22mg casein ml was considerably higher than those (0.15 and 0.54mg casein ml reported by Nannipieri et for proteinases of crude extracts from two soils. 

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