Is Genotoxicity Associated with Disinfection Byproducts in Potable Reuse and Conventional Drinking Water Additive?

Abstract

We have previously shown that the Chinese hamster ovary (CHO) cell chronic cytotoxicity of disinfection byproducts (DBPs) in a mixture of DBPs is additive, supporting the use of the sums of measured concentrations of DBPs weighted by metrics of cytotoxic potency to compare the DBP-associated cytotoxicity of disinfected waters. Researchers applied this approach to estimate the genotoxicity of disinfected waters using the metrics of genotoxic potency derived from the CHO cell acute genotoxicity assay, but the additivity of DBP genotoxicity in a mixture has not been determined experimentally. In this study, we analyzed the CHO cell acute genotoxicity of five defined mixtures containing regulated and unregulated DBPs at the relative concentrations measured in two drinking waters and three potable reuse waters. The genotoxicity of DBPs in mixtures is less than additive, indicating antagonism. We observed antagonism in the subset mixtures containing only regulated DBPs or unregulated DBPs. Regulated DBPs were predicted to contribute substantially to the overall genotoxicity under the additivity assumption. However, quantitative bioassay results indicated that regulated DBPs are minor contributors to the genotoxicity of the mixtures compared with unregulated DBPs. Conducting quantitative genotoxicity analyses of water samples should be encouraged rather than only employing estimates of the calculated genotoxicity.

Mammalian Cell Genotoxicity of Potable Reuse and Conventional Drinking Waters

“…The CAT values attributable to regulated and unregulated (semi)volatile DBPs used in the comparisons above were discounted by 8 and 31%, respectively, to reflect the antagonism we previously observed for defined mixtures of these DBPs using this bioassay. 58 Even if no such discounting were applied (i.e., if the genotoxicity of these DBPs were additive), BCAT would typically have an equal or greater contribution toward the total genotoxicity as CAT (Figures S41−S43). The importance of the BCAT fraction is in agreement with recent works by other scientists showing that nonvolatile DBPs are more important drivers of developmental toxicity, cytotoxicity, genotoxicity, and oxidative stress than (semi)volatile DBPs.…”

“…The CAT values attributable to regulated and unregulated (semi)­volatile DBPs used in the comparisons above were discounted by 8 and 31%, respectively, to reflect the antagonism we previously observed for defined mixtures of these DBPs using this bioassay . Even if no such discounting were applied (i.e., if the genotoxicity of these DBPs were additive), BCAT would typically have an equal or greater contribution toward the total genotoxicity as CAT (Figures S41–S43).…”

“…We previously created defined mixtures of (semi)­volatile DBPs measured in a different set of authentic potable reuse and conventional drinking water samples at CFs relative to these water samples comparable to those achieved by the extraction and concentration protocol used in the current study. Analysis of these concentrated defined mixtures showed that, while the CHO cell cytotoxicity of DBP mixtures was additive, the genotoxicity measured for mixtures of regulated and (semi)­volatile unregulated DBPs was only 2–13% and 25–38%, respectively, of the genotoxicity CAT predicted for the same mixtures, indicating that these mixtures of (semi)­volatile DBPs exhibited antagonism with respect to genotoxicity in all five waters . For this study, where the (semi)­volatile DBPs in the water samples were concentrated to a similar degree as the previous mixture evaluation, we assumed that the genotoxicity contributed by regulated and unregulated (semi)­volatile DBPs is 8 and 31%, respectively, of CAT theoretical , the averages of the ranges observed in our previous study .…”

“…58 For this study, where the (semi)volatile DBPs in the water samples were concentrated to a similar degree as the previous mixture evaluation, 58 we assumed that the genotoxicity contributed by regulated and unregulated (semi)volatile DBPs is 8 and 31%, respectively, of CAT theoretical , the averages of the ranges observed in our previous study. 58 While this treatment reflects the antagonism observed for these contaminants at the CFs employed in this study, antagonism has the effect of reducing the importance of these (semi)volatile DBPs relative to the nonvolatile DBPs captured by BCAT. Hence, the CAT accounting for this antagonism is referred to as discounted CAT; Table S11 provides CAT theoretical and discounted CAT values for all samples.…”

“…Analysis of these concentrated defined mixtures showed that, while the CHO cell cytotoxicity of DBP mixtures was additive, the genotoxicity measured for mixtures of regulated and (semi)volatile unregulated DBPs was only 2–13% and 25–38%, respectively, of the genotoxicity CAT predicted for the same mixtures, indicating that these mixtures of (semi)volatile DBPs exhibited antagonism with respect to genotoxicity in all five waters . For this study, where the (semi)volatile DBPs in the water samples were concentrated to a similar degree as the previous mixture evaluation, we assumed that the genotoxicity contributed by regulated and unregulated (semi)volatile DBPs is 8 and 31%, respectively, of CAT theoretical , the averages of the ranges observed in our previous study . While this treatment reflects the antagonism observed for these contaminants at the CFs employed in this study, antagonism has the effect of reducing the importance of these (semi)volatile DBPs relative to the nonvolatile DBPs captured by BCAT.…”