NMR study of the role of water in contaminant uptake into clean and contaminated soils
A major problem for the environment today is soil contamination. Recently, it was proposed that water penetration controlled "non-labile" uptake of contaminants into soils. An in depth look at this proposal, however, suggested that soil wetting processes themselves were not well understood. Therefore, a detailed study of water interaction with air-dried clean soils, soil components, artificial soils, contaminated wettable soils and contaminated water repellent soils was undertaken. Mechanisms for soil wetting, which suggest conformational rearrangement and processes with energies on the order of chemical processes, are proposed. Also, necessary conditions for the development of water repellency in soils, which involves a critical level of contamination and a critical climatic event, are proposed. A further study of trace xenobiotic uptake was also pursued. For this, a new method of monitoring kinetic sorption processes was developed using fluorescence. Because of the limitations associated with fluorescence (specifically, the requirement that molecules must contain a significant quantity of chromophores in order to display fluorescence which consequently, often results in an increased molecular size), a larger molecule than had been previously studied in these laboratories was monitored. A multicomponent study of sorption into clean, wettable but contaminated and water repellent soils led to the conclusion that water does exercise control over "non-labile" uptake. However, for the large molecule used, "non-labile" sorption was significantly faster than in other studies, and did not correlate at all with wetting processes. This led to a survey of the literature that yielded the surprising result that contaminant uptake has a strong dependence on contaminant size. This appears to be more significant than many other factors, including water uptake. Finally, to support the mechanisms that had been proposed for water uptake and the development of water repellency, molecular modeling work on building block structures was done. Monomer units of the Steelink structures were used to simulate soils, rather than the conventional large polymer. Using a Monte Carlo approach resulted in a reasonable set of conformers. Calculations illustrate molecular mechanisms for proposed wetting and development of water repellency mechanisms.
Bibliography: p. 209
Todoruk, T. R. (2003). NMR study of the role of water in contaminant uptake into clean and contaminated soils (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/13202