Genotoxicity of disinfection byproducts and disinfected waters: A review of recent literature

The presence of water disinfection byproducts (DBPs) in tap water, resulting from disinfection processes involving chlorination or chloramination, increases the mutagenicity of the water and may pose adverse health effects. The topic was reviewed by DeMarini and coworkers in 2007. Here, we review research on the genotoxicity of DBPs published since that time. Studies, primarily using the Salmonella mutagenicity assay, have continued to show that chlorination or chloramination of source waters results in finished, tap, or swimming pool/spa water that is more mutagenic than the original source water. The genotoxic potencies of DBPs in both bacterial and mammalian cells generally rank as iodinated > brominated > chlorinated. Several DBPs are genotoxic in vivo in plants as well as in animals such as the worm Caenorhabditis elegans and the zebrafish Danio rerio. Studies primarily using the comet assay in mammalian cells have identified several non-regulated DBPs as genotoxic. However, the comet assay detects DNA damage that is generally repaired by the cells; thus, genotoxicity data more relevant to persistent mutations, such as chromosomal or gene mutations, are needed for these DBPs. Recent molecular epidemiology has indicated that activation of brominated trihalomethanes by the enzyme GSTT1 and the lack of metabolism of haloacetic acids by a variant of enzyme GSTZ1 are likely causative mechanisms for bladder cancer associated with exposure to chlorinated water. Further studies, especially in vivo, are needed to determine the ability of various DBPs, especially unregulated ones, to induce both gene as well as chromosomal mutations. Such investigations, along with additional molecular epidemiology studies, are required for a comprehensive understanding of the genotoxic and carcinogenic risks associated with DBP exposure.