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Significance of pH on the Cytotoxic Potential of the Water Disinfection By-Product Iodoacetic Acid
Citation:
Richardson, V., S. Richardson, J. Simmons, M. Moyer, AND A. Deangelo. Significance of pH on the Cytotoxic Potential of the Water Disinfection By-Product Iodoacetic Acid. International Society of the Xenobiotics Conf, San Francisco, CA, October 19 - 22, 2014.
Impact/Purpose:
To be presented at the International Society of the Xenobiotics Conference, October 19-22, 2014, San Francisco, CA
Description:
Significance of pH on the Cytotoxic Potential of the Water Disinfection By-Product Iodoacetic Acid Vicki Richardson1, Susan D. Richardson2, Mary Moyer3, Jane Ellen Simmons1, and Anthony DeAngelo1, 1U.S. Environmental Protection Agency, Research Triangle Park, NC, 2University of South Carolina, Columbia, SC and 3Incell Corporation, San Antonio, TX Disinfection of water provides significant health benefits through reduction of morbidity and mortality from water-borne disease. However, disinfection by oxidizing chemicals results in the formation of disinfection byproducts (DBPs). To date, more than 600 DBPs have been identified; the US EPA regulates eleven. Iodoacids have been identified in drinking water disinfected by either chlorination or chloramination. Based on in vitro studies in Chinese hamster ovary cells, iodoacetic acid (IAA) is the most toxic DBP assessed to date. Because the iodine group in the chemical structure of IAA is possibly labile, it has been suggested that IAA is unstable under the low pH conditions in the stomach. Due to the possibility of IAA being acid labile, its bioavailability, as well as its toxic potential may be reduced. To determine whether IAA was stable at the low pH conditions of the stomach, biological and chemical endpoints were examined at pH 2 and at body temperature (37°C). To assess the biological stability of IAA, we used epithelial cells derived from normal human colon (NCM460) whose cytochrome P450 and glutathione S-transferase theta 1 (GSTT1) activities are comparable to those in the intact large intestine. Human colon cells were selected for this study as some epidemiology studies have reported associations, albeit weak, between consumption of disinfected water and colon cancer. NCM460 cells were treated (96 hours) with IAA previously incubated in acidic water (pH 2) or control water (pH 7) for 1 hour at 37°C and tested for cytotoxicity using a crystal violet growth inhibition assay (IC50). The IC50 for IAA previously incubated in acidic water or control water was 1.0x10-5 M and 1.3x10-5 M, respectively. IAA and any potential degradation products formed during the low pH, body temperature incubation were also analyzed using gas chromatography/mass spectrometry (GC/MS). The results showed no apparent degradation of IAA following exposure to pH 2 as compared to the neutral pH controls. This study, which combined analytical chemistry and toxicology, demonstrates that IAA remains intact and has similar toxic potency under conditions comparable to those of the human stomach. We have also demonstrated the utility of NCM460 cells in testing chemicals for cytotoxicity. [This abstract of a proposed presentation does not necessarily reflect the policies of the U.S. EPA.]