Comparative Cytotoxicity of Six Iodinated Disinfection Byproducts on Nontransformed Epithelial Human Colon Cells

Exposure to disinfection byproducts (DBPs) in chlorinated drinking water has been positively associated with increased risk of colon, bladder, and rectum cancers. Iodinated DBPs (I-DBPs) are of concern as this class exhibits enhanced cytotoxicity and genotoxicity compared to those of chlorinated and brominated equivalents in Chinese hamster ovary (CHO) cells. We tested the impact of six I-DBPs on immortalized normal human colon epithelial cells (CCD 841 CoN). Our assay showed the following rank order of cytotoxicity of the I-DBPs: iodoacetic acid (IAA) > iodoacetamide (IAcAm) > bromoiodoacetamide (BIAcAm) > chloroiodoacetamide (CIAcAm) > bromoiodoacetic acid (BIAA) ≈ diiodoacetic acid (DIAA). The enhanced cytotoxicity of IAA compared with those of other haloacetic acids agrees with studies conducted on CHO cells. IAcAm was found to be 3.5 times more cytotoxic than BIAcAm and 9.4 times more cytotoxic than CIAcAm. The cytotoxicity of both dihaloacids (i.e., BIAA and DIAA) was <1% of that of the monohaloacid...