|Title||Use of Chemical Models and Structure—Activity Relationships to Identify Novel Disinfection By-Products of Potential Toxicological Concern|
|Publication Type||Book Chapter|
|Year of Publication||2008|
|Authors||Bull RJ, Reckhow DA|
|Book Title||Occurrence, Formation, Health Effects and Control of Disinfection Byproducts in Drinking Water|
|Series Volume||ACS Symposium Series|
|Publisher||American Chemical Society|
Chlorinated drinking water has been epidemiologically associated with increased risk of cancer, especially in the bladder, and adverse reproductive outcomes. A large number of chemicals have been identified as disinfection by-products (DBPs). Several by-product classes, such as the trihalomethanes and haloacetic acids, have received substantial toxicological study. Although many of these have been found carcinogenic in animals, the combination of low potency as carcinogens and/or low concentrations in drinking water make them unlikely causes of the cancer risk of the magnitude suggested by epidemiology studies. To provide some direction for the resolution of this discrepancy, a strategy was developed to predict formation of novel by-products through reactions of chlorine with substructures found in natural organic matter (NOM). These potential disinfection by-products (DBPs) were examined using a quantitative structure toxicity relationship (QSTR) program, TOPKAT®, to identify those chemicals of suff cient toxicologic potency to account for epidemiologic findings, if present. A "weight of evidence" strategy was utilized to rectify the predictions of the multiple cancer models within TOPKAT® to identify those compounds that were most probably potent carcinogens. Potential developmental toxicants were identified with the single model provided in TOPKAT®. A substantial effort was made to verify/deny predictions by literature search; examining both descriptive and mechanistic data to evaluate the prediction. Several haloquinones and related chemicals appear to be the most interesting. It is of note that formation of haloquinones would be favored with chloramine relative to chlorine disinfection.