ORGANIC GEOCHEMISTRY AND WATER QUALITY

Organic geochemistry had its beginnings in understanding the origin of coal, oil, and gas deposits. Investigations of fossil fuels led to the study of recent diagenesis in the water column and sediments, in areas of high productivity, still with the emphasis on understanding how organic material (OM) accumulates and is preserved through time. The study of OM in fresh water started with the analyses of humic substances that cause water to be colored (Gelbstoff). The low concentrations of OM in surface and ground waters (generally less than 2.0 mg/L) can impart taste and odor to drinking water and have proven to be significant in processes such as the complexation of metals. The effects of man-made chemicals in the environment were recognized when chlorinated solvents were reported in the drinking water at New Orleans in 1975 and DDT was found to be persistent and accumulate in tissues. These three fields of study, the organic geochemistry of fossil fuels, the examination of naturally-occurring humic substances in water, and the release of organic contaminants in the environment have been merging in the last decade. For example, as a result of the chlorination of water supplies, the importance of humic substances in water was recognized in the formation of disinfection by-products. A solution to minimize the formation of these chlorinated products is to determine the chemical composition of the dissolved OM and limit contact of the reactive components with chlorine. Spills from the petroleum industry in the environment have led to a greater understanding of how components of oil degrade in near-surface environments and what molecular markers are the most useful to understand fate and transport of hydrocarbons. Another example of merging fields is the recent finding of pharmaceuticals, hormones, and wastewater contaminants in streams that receive effluent from water treated facilities. Some of these compounds are only produced synthetically and some have both synthetic and natural sources, which may prove difficult to differentiate. These examples illustrate the unique challenges that complex problems present and demonstrate the need for understanding natural processes and environmental chemistry to address water quality issues.