Mutagenicity studies in Salmonella: residues of ozonated and/or chlorinated water fulvic acids.

Aqueous residues of ozonated, chlorinated, and ozonated/chlorinated water fulvic acids (WFA) were tested for induction of His+ reversion in Salmonella typhimurium strain TA100 in fluctuation tests for mutagenicity. The data suggest that ozonation of natural organics present in sources of drinking water can prevent subsequent formation of by-products of chlorination that are mutagenic in bacteria. Ozonation of the WFA at different pH and at varying dose levels produced residues that were not or were only weakly mutagenic. Chlorination of WFA or of previously ozonated WFA led to residues that were highly mutagenic. However, mutagen formation in the ozonated/chlorinated residues could be prevented, depending upon the pH of the WFA solutions during ozonation—mutagenicity decreased as pH increased. This decrease in mutagenicity is associated with previous observations of enhanced ozone decomposition into its highly reactive oxidant species at higher pH. Since ozonation seems to be more effective at alkaline pH, alkaline raw water sources seem to be the best candidates for water treatment that involves ozonation.