Mutagenicity in Salmonella of halonitromethanes: a recently recognized class of disinfection by-products in drinking water.

Halonitromethanes (HNMs) are a recently identified class of disinfection by-products (DBPs) in drinking water. They include chloronitromethane (CHN), dichloronitromethane (DCNM), trichloronitromethane (TCNM), bromonitromethane (BNM), dibromonitromethane (DBNM), tribromonitromethane (TBNM), bromochloronitromethane (BCNM),dibromochloronitromethane (DBCNM), and bromodichloronitromethane (BDCNM). Previous studies of TCNM, DCNM, CNM, and TBNM found that all four were mutagenic in bacteria, and a recent study showed that all nine induced DNA damage in CHO cells. Here, all nine HNMs were evaluated in the Salmonella plate-incorporation assay +/- S9 using strains TA98, TA100, TA104, TPT100, and the glutathione transferase theta (GSTT1-1)-expressing strain RSJ100. All were mutagenic, most with and without S9. In the absence of S9, six were mutagenic in TA98, six in TA100, and three in TA104; in the presence of S9, these numbers were five, seven, and three, respectively. Thus, the HNMs-induced base substitutions primarily at GC sites as well as frameshifts. Although five HNMs were activated to mutagens in RSJ100 -S9, they produced < or =2-fold increases in revertants and potencies <506 rev/micromol. The rank order of the HNMs by mutagenic potency in TA100 +S9 was (BCNM DBNM) > (TBNM CNM > BNM DCNM BDCNM) > (TCNM = DBCNM). The mean rev/micromol for the three groupings, respectively, were 1423, 498, and 0, which classifies the HNMs as weak mutagens in Salmonella. Reaction of the dihalo and monohalo HNMs with GSH, possibly GSTT1-1, is a possible mechanism for formation of ultimate mutagenic products. Because the HNMs are mutagenic in Salmonella (present study) and potent clastogens in mammalian cells [Environ. Sci. Technol. 38 (2004) 62], their presence in drinking water warrants further research on their potential health effects.