Reducing Risk from Unidentified Trace Organic Contaminants

The organic matter in the water produced by an aerobic biological wastewater treatment plant consists of essentially two components: (1) synthetic organic chemicals (SOCs) of anthropogenic origin, as defined by the Environmental Protection Agency (EPA) Office of Drinking Water, and (2) natural organic matter (NOM), which is mostly an ill-defined set of compounds generated through microbial metabolism (see discussion in Chapter 2). Reclaimed water generally holds higher concentrations of both types of components than conventional drinking water supplies do. However, in both reclaimed water and conventional drinking water supplies, the SOCs may not be distinguishable from the NOM. And either water may hold significant quantities of chemicals having potent toxicological properties (e.g., endocrine disrupters, pharmaceutical agents or metabolites, or hormones).

The state of our knowledge concerning SOCs has improved since the 1982 National Research Council report Quality Criteria for Water Reuse (NRC, 1982). Extensive lists of organic compounds have been generated based on known ground water contaminants, the priority and toxic pollutant lists of the Clean Water Act, and the Drinking Water Priority List (53 Federal Register 1892, January 1988, updated 56 Federal Register 1470, January 1991).

Using these lists as a guide, analytical methods have been developed to detect most of the organic compounds of concern in industrial discharges, in raw sewage and treated sewage, and in drinking water supplies. The discharge of priority pollutants to the sewer and to the environment has been regulated and enforced by monitoring requirements. As a result of these efforts, more is known about the anthropogenic chemicals in sewage today, and discharge of these compounds to the nation's sewers is more tightly controlled than was the case in 1982. While concern about chemical risk from reclaimed water remains, the potential for risk management is greater today than in 1982.

The largely uncharacterized organic matter in natural water, in conventionally treated wastewater, and in reclaimed water consists of large organic macromolecules usually identifiable in only the broadest way (e.g., by functional groups, molecular weight, aromacity, or acid/base solubility). As explained in Chapter 2, we have a poor understanding of the differences, if any, between NOM generated in biological sewage treatment processes and NOM generated in a conventional watershed. A credible argument can be made that the same biochemical processes produce the organic matter in both circumstances, and their chemistry is



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