the origins of previously unidentified carcinogens in the ground water's replenishment sources and well waters.

The Ames test and Salmonella tester strains (TA98 and TA100) were used to screen for mutagenic organics in concentrates of reclaimed water (before it was spread), storm water, imported water, and unchlorinated and chlorinated ground water. While 13 of the 56 sample concentrates tested were free of mutagens, at least one mutagenic concentrate was found from each source. Nellor et al. (1984) reported that storm water and reclaimed water yielded the highest levels of mutagenicity, followed by well water and then imported waters. More than half of the mutagens observed appeared to derive from chlorination processes. The potency of the mutagenic responses did not appear to be related to the estimated percentages of reclaimed water at the various wells.

The study also compared the mutagenicity of samples of the ground water with mutagenic responses of known compounds and found that the ground water contained low concentrations of individual mutagens. While these tests (gas chromatography-mass spectroscopy (GC-MS) methods) found four identifiable Ames mutagens (fluoranthene, benzo(a)pyrene, N-nitrosomorpholine, and N-nitropiperidine) in 6 of the 34 tested samples, Nellor et al. (1984) concluded that these compounds could not have caused the mutagenicity in all of the samples, because their frequency of occurrence, distribution in the fractions, and concentrations were not consistent with the bioassay results.

Further testing by chemical derivation techniques (including negative ion chemical ionization of GC-EIMS fractions and Ames assays of ground water and replenishment water before and after derivation) suggested that epoxides, organic halides, and two classes of electrophiles may have played a part in causing the observed mutagenicity. However, the results were not conclusive because the reactive components appeared only at part-per-trillion levels. The study identified neither the structures of these compounds nor their sources.

Since positive chemical identifications of specific mutagens could not be made and many of the estimated concentrations were very low, Nellor et al. concluded that the health significance of epoxides and organic halides at the levels found in the reclaimed waters remains in doubt. They stated that further characterization of the molecular structure and biological effects of the large numbers of apparently mutagenic halogenated organic compounds in the various waters would be necessary to confirm whether those materials pose any health risk.

Denver Potable Reuse Demonstration Project

The 3.8 x 103 m3/day (1.0 million gallons per day (mgd)) Potable

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