Identification of Factors Influencing Variability in Disinfection Byproducts and Their Toxicity in Chlorinated and Chloraminated Drinking Water Distribution Systems across the United States

Drinking water distribution
systems (DWDSs) are dynamic environments
where disinfection byproducts (DBPs) form and transform, shaped by
factors such as the disinfectant type, water chemistry, biofilms,
and pipe materials. Understanding the occurrence and drivers of DBP
formation within DWDSs is essential for evaluating water quality and
potential health risks. This study examined DBP occurrence and variability
across eight utilities in the United States, three using chlorination
and five using chloramination (as secondary/residual disinfectants),
by analyzing 152 quarterly samples collected from multiple locations
within each distribution system. Regulated DBPs were found at the
highest concentrations. Haloacetonitriles (HANs) and haloacetic acids
(HAAs) contributed most to the predicted toxicity. Spearman correlations,
redundancy discriminant analysis, and random forest regression revealed
how key influencing predictors of DBPs vary between chlorinated and
chloraminated systems. Elevated dissolved organic carbon (DOC) and
primary disinfectant type were the two most important contributors
to DBP formation, with DOC most influential in chloraminated systems
and primary disinfectant type (HOCl vs O3) in chlorinated
systems. Variations in DBP concentrations within individual DWDS showed
a weak dependence on water age. This study provides a novel data set
linking DBP occurrence to water quality parameters and demonstrates
how such data can be leveraged to understand DBP dynamics and inform
future risk management in water distribution systems.