PROPERTIES OF NATURAL ORGANIC MATTER (NOM) RELEVANT TO CONSIDERATIONS OF TRANSPORT AND TRANSFORMATIONS OF ANTHROPOGENIC CHEMICALS

Natural organic matter is well known for its metal complexation abilities, interactions with oxides and other mineral phases, and oxidation/reduction properties. However, the variability of these properties is not well understood, partially because research on NOM samples has been conducted on operationally defined NOM fractions such as fulvic and humic acids, and partially because of the limited number of NOM samples, especially aquatic ("dissolved") NOM, that have been well-characterized. Here we report the quantification of a wide variety of chemical and physical properties for a group of NOM samples, representing a number of global climates and ecoregions. The samples represent rivers, groundwater, and water leachates from detritus from a number of plant species important in the catchment basins of the sampled rivers and/or selected for their unique NOM characteristics. Measurements include elemental analyses, pH and acid/base titrations, infrared, fluorescence, visible/ultraviolet and nuclear magnetic resonance spectra, metal complexation capacities, interactions with metal oxide minerals, and abilities to mediate oxidation/reduction reactions. These data show a wide variation in chemical and physical properties, depending on the origin and geochemical history of the samples. Here, the importance of NOM properties in processes involving anthropogenic chemicals is highlighted in order to illustrate the potential importance of NOM in pollutant transport and transformations. It is clear the NOM in most rivers represents a significant source of metal complexation capacity. For example, at 1mM organic carbon, a level not uncommon in rivers and streams, copper concentrations of about 1.0mM can routinely be transported by aquatic NOM. For redox reactions, a similar importance of NOM in, for example, mineral sulfide oxidation or reductions of nitroaromatic compounds is also documented for natural levels of NOM in rivers and groundwaters. Use of NOM as part of "natural" remediation schemes for organic contaminants is discussed.