Organic matter functional groups

Fig. 3. Association of clay particles and the functional groups of organic matter (32).

Much of the Hgt pool was found in the upper part of the soil, which is rich in organic matter. This pattern is likely due to an elevated atmospheric deposition of Hgt over the extended period and immobilization of mercury by organic functional groups and accumulation of organic matter as part of the soil-forming process. The retention of mercury in the mor humus layer was almost complete due to the very strong association between Hgt and humic substances. 

Fig. 8. Some important functional groups of solid organic matter...

Marine chemists have had limited success in characterizing the molecular structure of organic matter, particularly for the dissolved compounds. Chemical analysis usually starts with the isolation of POM from DOM using a filter with a 0.2-p,m pore size. This is generally followed by elemental analysis. More sophisticated approaches involve structural analysis, but this is usually limited to detection of functional groups or broad classes of compounds. 

In real soils where oxides, layer silicates, organic matter and other materials are present in intimate mixtures, with the oxides and organic matter often coating the surfaces of the other materials, the different functional groups interact with... 

Lead occurs mainly in the - -2 oxidation state in soils, but it may be oxidized to Pb" +. It is the least mobile heavy metal in soils. In aerobic soils it is chemisorbed on clays and oxides forms complexes with organic matter, especially with S-containing functional groups and forms insoluble hydroxides, carbonates and phosphates. All of these increase with pH, so solubility is greatest under acid conditions. In anaerobic soils it is precipitated as the highly insoluble sulfide galena (PbS, pA = 27.5). It may also be methylated into volatile forms. 

Adsorption is the net accumulation of matter on the sohd phase at the interface with an aqueous solution or gaseous phase. In this process, the solid surface is the adsorbent and the matter that accumulates is the adsorbate. Adsorption also may be defined as the excess concentration of a chemical at the subsurface solid interface compared to that in the bulk solution, or the gaseous phase, regardless of the nature of the interface region or the interaction between the adsorbate and the sohd surface that causes the excess. Surface adsorption is due to interactions between electrical charges, or nonionized functional groups, on mineral and organic constituents. 

The environmental significance of bound residues must be considered in relation to natural organic matter (Barraclough et al. 2005). Contaminants entering the subsurface contain many functional groups similar to those of natural organic matter... 

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