The first research lines of the Unit is towards an enhanced understanding of the molecular structure of NOM or Humic Substances and of its reactivity with contaminants in the environment. Due to the heterogeneity of the NOM, no molecular formulation of its structure has been yet accepted by the scientific community. Humic substances or NOM are believed to be macropolymers synthesized by oxidative coupling of smaller molecules of plant and microbial origin. What is conspicuously lacking in the concerned literature is a serious conformational analysis of NOM in solution with advanced methods.

This Unit has first focused research on the conformational changes of dissolved humic substances by High Performance Size Exclusion Chromatography (HPSEC) in interactions with alcohols, and mineral and organic acids. Concomitantly, it was chosen to study the reactivity of model humic compounds with a number of simple organic compounds present in the environment and with a number of xenobiotic compounds. A complete characterization of the humic matter is commonly obtained by: 1. solid- or liquid-state ¹³C-NMR spectroscopy;  2. FTIR spectroscopy mainly with DRIFT accessory; 3. High pressure size-exclusion chromatography (HPSEC) and relative software to evaluate the distribution in molecular sizes; 4. Elemental analyses; 5. Wet chemical methods. The reactivity of these humic substances as solid phases are tested towards some widely used pesticides and toxic contaminants (triazines, glyphosate, 2,4-D, paraquat, chlorophenols, cholorobenzenes, polyaromatic hydrocarbons) by analytical devices such as HPLC, GC-MS, NMR and by using both ¹⁴C- and ¹³C-labelled compounds. Recently, Diffusion Order NMR spectroscopy (DOSY) has been applied to determine the dimensional sizes of different NOM samples. DOSY-NMR can be coupled with measurements of NMR relaxation times to calculate the binding constants between environmental pollutants and humic matter.

The body of results produced by this Unit and in collaborations with other international research groups demonstrated that NOM structure should not be viewed as macropolymers, as commonly believed and reported in the literature, but as a supramolecular association of small heterogeneous molecules that weakly self-assemble mainly by dispersive and hydrogen bondings.  Moreover, the parallel work on the adsorption on humic matter of xenobiotics of different polarity has shown that adsorption is a function of the molecular structure and conformational complexity of humic substances and varies with contaminants polarity.

Another exciting result of the recent research period that confirms the self-associating nature of supramolecular humic association is the concomitant evidence that the use of enzymatic and biomimetic catalyzers (metal-porphyrins) in oxidation reactions are able to effectively increase the molecular size of humic material by forming true covalent bonds between small sub-units. The size obtained after oxidative catalysis cannot be altered again by the use of acids as described earlier. Such humic polymerization due, most probably, to oxidative couplings of phenolic compounds is more advanced with large aromatic carbon content in the humic structures. These results were successfully obtained when the polymerization of NOM was attempted in situ in soils. This approach, together with the incorporation of compost in soils, represents the focus of a FISR project coordinated by the head of this group. The objective of this large national project is to prove that the reduction of the rate of soil organic matter mineralization occurs also in field conditions under agricultural production and a reduction of natural CO2 emissions from soil is possible at a large scale. The evidence of such processes of OC stabilization in soils may help to meet the Kyoto Protocol objectives.

More recently, the group has attempted a complete molecular characterization of humic matter. We have developed a methodology of sequential chemical fractionation and subsequent characterization of separated molecules by GC-MS and ESI-MS that so far accounts for more than 80 % of weight of humic matter. A last fraction obtained after disruption of  ether and glycosidic bonds, mainly an aromatic fraction as by NMR measurements, is presently under study to increase its solubility and detectability by mass-spectrometry.

A further line of research of the Unit is the use of NOM as natural surfactant to be employed in washings contaminated soils. This technique has been developed during the INCA-Sisifo project to which this group collaborated. Washings with humic matter solutions has been proved to efficiently remove a large percentage of polyaromatic hydrocarbons (PAH) from sediments of Naples harbor and soils from the contaminated area of Bagnoli in Naples. Furthermore, this procedure has been recently adopted to remediate sediments from the Venice lagoon from heavy metals and organic compounds.