Humic origin

Many fluids of natural origin contain detectable quantities of high molecular weight organic anions, such as those from humic, fulvic, and tannic acids, which can be carried to and deposited on AX membranes. Such deposits can behave as thin films partially selective to cations (6). The iaterfaces between such films and the undedyiag AX membranes then act as very thin stagnant depletion compartments and the AX membranes may exhibit polarization at current densities that are much lower than would be expected for new membranes ia the abseace of such anioas. 

According to Hatcher and co-authors47 the CP/MAS NMR technique opens up new means of distinguishing between various structural features of aquatic and ter-restric humic materials of rather old origin. They found, for instance that the aliphatic carbons of the humic substances in Holocene sediments, are dominant components suggesting an input of lipid-like materials. 

Solid state 13C NMR spectroscopy has emerged as a very useful tool for characterizing SOM (Kinchesh et al. 1995 Preston 1996). Several workers have reported that Koc of HOCs was linearly or exponentially related to the aromatic carbon contents of HAs or whole soils as determined by 13C NMR analysis (Ahmad et al. 2001 Chen et al. 1996 Chin et al. 1997 Gauthier et al. 1987 Perminova et al. 1999). The Koc value of humic materials can vary by as much as an order of magnitude, depending upon their origins (Fig. 1). 

Hot water-extractable C accounts for 1-5% of soil organic C (Leinweber et al. 1995 Sparling et al. 1998 Chan and Heenan 1999) and about 50% of this is thought to be present as carbohydrate (Haynes 2005). Because it is usually extracted from air-dried soils much of the pool originates from desiccated microbial cells but it also includes exocellular polysaccharides, root exudates, lysates and humic material (Redl et al. 1990 Leinweber et al. 1995 Sparling et al. 1998). Both hot water extractable C (Sparling et al. 1998 Chan and Heenan 1999) and hot water-extractable carbohydrate (Ball et al. 1996 Haynes and Beare 1997 Debrosz et al. 2002) have been used as indices of soil quality. 

The HS samples used in this work were obtained from the Standard and Reference Collection of HAs and FAs of the International Humic Substances Society (IHSS), with the exception of the HA from an alluvial soil. The origin and nature of HS, with the corresponding codes, abbreviations and concentrations used, are shown in Table 1. 

Table 1. Origin and nature of humic substances used with corresponding codes, abbreviations and concentrations...

Origin and nature of humic substances IHSS Code Abbreviation Concentrations used (mgL-1)... 

While in a strict sense only the last class of compounds should fall into the category of humic materials, there has been much dispute concerning the origin of the marine humic materials both Gelbstoff and the lignins have been mentioned as probable starting compounds for the marine humic and fulvic acids. 

Chen Y, Magen H, Riov Y (1994) Humic substances originating from rapidly decomposing organic matter properties and effects on plant growth. In Senesi N, Miano TM (eds) Humic substances in the global environment and implications on human health. Elsevier Science, Amsterdam, The Netherland, pp 427-443... 

Klenke et al. [5] described a technique for extraction of humic and fulvic acids from stream sediments and outlined methods for their determination. By means of flame atomic absorption spectrometry, the levels of environmentally important heavy metals (cadmium, copper, chromium, cobalt, nickel and lead) in the fulvic and humic acid extracts were compared with those in the original sediment samples. The pattern distribution of the respective metals in the two cases showed very close agreement, suggesting that the combined extract of humic and fulvic acids could be used as an indicator of the level of heavy metal pollution in flowing waters. 

Adsorption isotherm of (Aldrich) humic acid (HM) on 8-AI203 as a function of pH. Extent of adsorption was determined both by measurements of light absorption at 254 and 436 nm, respectively and by measurements of dissolved organic carbon (DOC) of the residual HM in solution (original concentration = 25 mg per liter). 

In addition to the reported differences between and within bioregions (Fig. 4), it is reported that humic material of terrestrial origin is different from... 

Dissolved humic substances (DHS) are the main constituents of the dissolved organic carbon (DOC) pool in surface waters (freshwaters and marine waters), groundwaters, and soil porewaters and commonly impart a yellowish-brown color to the water system. Despite the different origins responsible for the main structural characteristics of DHS, they all constitute refractory products of chemical and biological degradation and condensation reactions from plant or animal residues and play a crucial role in many biogeochemical processes. 

Marine organisms are rich in nitrogen and therefore the humic compounds originating from them contain high amounts of nitrogen some sedimentary humic compounds contain up to 10 times as much sulfur as the soil humic acids The nitrogen content of soil humic compounds is generally low... 

In natural water, singlet oxygen originating from humic substances has been shown, for example, to oxidize thioether pesticide contaminants such as disulfoton (Zepp et al. 1981). Irradiation of dilute hydrogen peroxide in the presence of various non-sunlight-absorbing herbicides results in enhanced oxidation of these substances (Draper and Crosby 1981). 

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