Assessing Additivity of Cytotoxicity Associated with Disinfection Byproducts in Potable Reuse and Conventional Drinking Waters

Abstract

Recent studies used the sum of the measured concentrations of individual disinfection byproducts (DBPs) weighted by their Chinese hamster ovary (CHO) cell cytotoxicity LC50 values to estimate the DBP-associated cytotoxicity of disinfected waters. This approach assumed that cytotoxicity was additive rather than synergistic or antagonistic. In this study, we evaluated whether this assumption was valid for mixtures containing DBPs at the concentration ratios measured in authentic disinfected waters. We examined the CHO cell cytotoxicity of defined DBP mixtures based on the concentrations of 43 regulated and unregulated DBPs measured in eight drinking and potable reuse waters. The hypothesis for additivity was supported using three experimental approaches. First, we demonstrated that the calculated additive toxicity (CAT) and bioassay-based calculated additive toxicity (BCAT) of the DBP mixtures agree within 12% on a median basis. We also found an additive toxicity response (CAT ≈ BCAT) between the regulated and unregulated DBP classes. Finally, the empirical biological cytotoxicity of the DBP subset mixtures, independent of the calculated toxicity, was additive. These results support the validity of using the sum of cytotoxic potency-weighted DBP concentrations as an estimate of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters.

Disinfection byproducts formed during drinking water treatment reveal an export control point for dissolved organic matter in a subalpine headwater stream

“…Although unregulated DBP classes (e.g. haloacetaldehydes and haloacetonitriles) occur at lower concentrations than regulated THMs and HAAs, they can contribute more to the cytotoxicity associated with disinfection byproducts than regulated THMs and HAAs in conventional drinking waters ( Lau et al., 2020 ). This lends further credence to the application of UV 254 screening during synoptic watershed sampling to understand potential DBP formation during drinking water treatment.…”

Controlling disinfection byproducts from treated wastewater using adsorption with granular activated carbon: Impact of pre-ozonation and pre-chlorination

“…It is noted this toxicity calculation approach might be limited by not considering synergistic effects, differences between human and animal cells, and association with human health risk ( McKenna et al., 2019 ). Though Lau et al. (2020) validated using the sum of cytotoxic potency weighted DBP concentrations as an estimate of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters, including potable reuse waters.…”

“…Ambient bromate, NDMA, THM4, and HAA5 were also measured and monitored throughout the treatment train to assess pre-oxidation implications on DBP formation. The study utilizes calculated cytotoxicity and genotoxicity quantities from methods reported elsewhere to identify and provide comparisons of the pre-oxidiation GAC treatment options ( Allard et al., 2015 ; Chuang and Mitch, 2017 ; Krasner et al., 2016 ; Lau et al., 2020 ; Plewa et al., 2017 ; Smith et al., 2010 ). Specifically, the toxic potencies of DBPs formed during formation potential experiments were calculated by normalizing measured concentrations to published cytotoxicity and genotoxicity lethal concentrations of individual DBPs ( Wagner and Plewa, 2017 ).…”

Influence of bromide and iodide on the formation of disinfection by-products in drinking water treatment

“…This gives the contribution of each DBP to the overall calculated toxicity and allows the prioritization of DBPs not only based on their concentrations but also their toxicity. It has recently been showed that the additivity of individual toxicities was representative of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters [55]. Several studies reported the importance of Br-and/or I-DBPs over Cl-DBPs using this approach [55][56][57][58][59][60].…”

“…It has recently been showed that the additivity of individual toxicities was representative of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters [55]. Several studies reported the importance of Br-and/or I-DBPs over Cl-DBPs using this approach [55][56][57][58][59][60]. I-DBPs exhibiting particularly high toxicity, despite their usually much lower concentration in treated waters may be important toxicity drivers.…”