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The implementation of chlorine disinfection in low-income countries reduces the risk of waterborne illness but initiates exposure to disinfection byproducts (DBPs). Like high-income countries, low-income countries typically are adopting regulations focusing on trihalomethanes (THM4) as an indicator of overall DBP exposure. However, the use of impaired water sources can decouple the formation of THM4 from other DBP classes that are more potent toxins. The documentation of DBP species other than THM4 is rare in low-income countries, where water sources may be degraded by inadequate sanitation infrastructure and other uncontrolled wastewater discharges. We measured THM4 and 21 unregulated DBPs in tap waters and laboratory-treated source waters from two cities in northwestern India. The contribution of each DBP class to the cumulative toxicity was estimated by weighting each species by metrics of toxic potency; haloacetonitriles typically were the dominant contributor, while the contribution of THM4 was negligible. THM4 concentrations did not correlate with the total toxic potency-weighted DBP concentrations. Although THM4 rarely exceeded international guidelines, DBPs of greater toxicological concern were observed in high concentrations. The total toxic potency-weighted DBP concentrations in some waters were elevated compared to conventional drinking waters in high-income countries and more closely resembled chlorine-disinfected wastewater effluents. Artificial sweeteners confirmed widespread contamination of both surface and groundwaters by domestic sewage. The results suggest that THM4 may not be an adequate indicator of overall DBP exposure in impaired water supplies prevalent in some low-income nations.

N-Nitrosodimethylamine (NDMA), an important contaminant for potable reuse of municipal wastewater, forms from reactions of dichloramine and amine precursors. Injection of concentrated free chlorine stock solutions into wastewaters containing low levels of ammonia can promote NDMA formation because the high chlorine:ammonia ratio at the point of chlorine injection fosters dichloramine formation during mixing. This study combined chemical kinetic modeling, laboratory mixing studies using deionized water and authentic wastewater effluents, and a pilot-scale disinfectant contactor at a wastewater reuse facility to demonstrate that the distribution of the injection of concentrated hypochlorite stock solutions can reduce the level of NDMA formation by ≤50% compared to injection at a single location. Modeling and deionized water experiments indicated that this reduction was associated with a reduction in the level of dichloramine formation.

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