Another approach is to establish a quantifiable limit of a surrogate or composite parameter that would provide some information on the concentration or behavior of unknown or suspected target compounds. The total organic carbon concentration, for instance, is widely used as a practical evaluator of water and wastewater treatment processes. Some would argue that a parameter as indiscriminating as TOC provides negligible value for indicating potential hazards associated with consumption of a water; this assertion is probably justified if one wishes to compare the risk associated with organics in different water sources, each of which contains several milligrams of TOC per liter. Further, from a strict public health perspective, removal of TOC is of limited objective value.
However, removing TOC from a water supply by any treatment process almost certainly reduces (though not necessary proportionally) the concentration of potentially hazardous, unidentified organic compounds. Diluting wastewater, as by discharging it into a receiving water, has a similar effect. Either method of reducing the contribution of treated wastewater to the DOC or TOC of a water source in a reuse situation might reduce user exposure to hazardous, unidentified wastewater compounds.
Other surrogate parameters may provide qualitative rather than quantitative information about unidentified organics. For instance, if two treated wastewaters contain equal concentrations of TOC, but one has a larger hydrophobic component and correspondingly greater value for specific ultraviolet light absorption, those differences undoubtedly reflect real and possibly important differences in the suites of organic compounds contributing to the TOC. Such analyses may make it possible to design an AWT process that targets classes of compounds specific to or particularly enriched in wastewater. Such a treatment process would convert the wastewater's population of organic molecules to one resembling naturally occurring populations. Unfortunately, such an approach begs the question of whether the distinctions being detected and reduced have significant health risks. For example, if the wastewater organics are relatively enriched in polysaccharides (a component of most foods), does it make sense to focus on polysaccharide removal simply to cause the mix of waste-derived organics to appear (and perhaps to be) more like natural organics?
Analytical chemistry techniques alone cannot address the question of risks from unknown organic chemicals. Toxicological methods must be used. However, the chemistry and toxicology can inform one another to identify the most promising and least promising areas of investigation. For example, the threat posed by endocrine disrupters was recently dis-