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Formation of mutagenic activity as a result of aqueous chlorination of a model humic acid substrate has been previously demonstrated. In the present study, solvent extracts of solutions of the chlorinated model substrate, which responded positively in the Ames test, were analyzed by gas chromatography/mass spectroscopy (GC/MS) in an attempt to identify the mutagenic components. Results of GC/MS analyses of methylene chloride, ether, and closed-loop-stripping extracts indicated that trihalomethanes and haloacetic acids, -acetonitriles, -propanones, -propenah, -propenenitriles, -propenes, -phenols, and -thiophenes were formed by the aqueous chlorination of humic acid at neutral pH. The concentrations of nine of the halogenated byproducts accounted for about onefourth of the total organic halogen (TOX) content of the aqueous chlorinated humic acid solution. The similarity of mutagenic compounds identified in this study with compounds previously identified in drinking water suggests that the reaction of chlorine with natural aquatic humic material is a likely source of mutagen formation in drinking water. Some data on the production of halogenated compounds from the chlorination of the model humic acid in the presence of bromide (Br-) are also included.

Chlorination of humic and fulvic acid results in the formation of direct-acting mutagenicity, detectable in the Salmonella/microsome assay (Ames test). This mutagenicity is being characterized as part of an overall effort aimed at evaluating potential health risks associated with the presence of mutagenic chemicals in drinking water. A number of chlorinated organic compounds, including several known mutagens, have been identified and quantified in diethyl ether extracts of chlorinated humic acid solutions. However, the total mutagenicity of these compounds accounts for only about 7% of the original mutagenicity. Synergistic or antagonistic interactions among the identified components have been ruled out as possible explanations for the failure to account for a higher percentage of the activity. Recent progress has been made to separate the activity into neutral and strong acid fractions. Further isolation of the strong acids by high-pressure liquid chromatography (HPLC) has resulted in the purification of the mutagenicity into a major peak of activity with a specific mutagenicity of about 20,000 TA100 revertants per milligram. Several trichlorohydroxyfuranone isomers have been tentatively identified in this fraction. The contribution of these types of compounds to the mutagenicity of chlorinated humic acid is under investigation.

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