Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2026 Jan 13;60(1):1241-1252.
doi: 10.1021/acs.est.5c12121. Epub 2025 Dec 31.

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

Samantha DiLoreto  1 , Huanqi He  1   2 , Jinhao Yang  1 , Patrick Milne  3 , Jiaqi Li  1 , Christopher A Impellitteri  4 , Aron Stubbins  3   5   6 , Ameet Pinto  1   7 , Ching-Hua Huang  1
Affiliations

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

Samantha DiLoreto et al. Environ Sci Technol. .

Abstract

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.

Keywords: Spearman correlation; United States; cytotoxicity; drinking water distribution systems; genotoxicity; nonregulated DBPs; random forest regression; redundancy discriminant analysis; regulated disinfection byproducts.

PubMed Disclaimer

Figures

1
1
Individual DBP concentrations (ppb in log scale) across all eight utilities: (a) chlorinated systems and (b) chloraminated systems. Values were averaged across seasons. Cells with no color indicate
2
2
Nitrosamine concentrations for each sampling site averaged over two sampling rounds (July–December 2024). Averages and standard deviation are included in SI Sheet “Data_DBPs”.
3
3
Average calculated (a) cytotoxicity and (b) genotoxicity index values in treated water samples. Values were averaged over sampling rounds and sample locations.
4
4
RDA biplot of water quality parameters and DBP concentrations grouped based on classes in (a) chlorinated and (b) chloraminated drinking water samples.
5
5
Comparison between DOC-normalized concentrations for DBP classes by different disinfectant schemes: (a) THMs, (b) HAAs, (c) HANs, (d) HAMs, (e) HNMs, (f) HKs, (g) I-THMs, and (h) I-HAAs. Some outliers removed for visualization.
See this image and copyright information in PMC

References

    1. Goslan E. H., Krasner S. W., Bower M., Rocks S. A., Holmes P., Levy L. S., Parsons S. A.. A Comparison of Disinfection By-Products Found in Chlorinated and Chloraminated Drinking Waters in Scotland. Water Res. 2009;43(18):4698–4706. doi: 10.1016/j.watres.2009.07.029. - DOI - PubMed
    1. Richardson S. D., Plewa M. J., Wagner E. D., Schoeny R., DeMarini D. M. O.. Genotoxicity, and Carcinogenicity of Regulated and Emerging Disinfection by-Products in Drinking Water: A Review and Roadmap for Research. Mutat. Res. Mutat. Res. 2007;636(1):178–242. doi: 10.1016/j.mrrev.2007.09.001. - DOI - PubMed
    1. Reid E., Igou T., Zhao Y., Crittenden J., Huang C.-H., Westerhoff P., Rittmann B., Drewes J. E., Chen Y.. The Minus Approach Can Redefine the Standard of Practice of Drinking Water Treatment. Environ. Sci. Technol. 2023;57(18):7150–7161. doi: 10.1021/acs.est.2c09389. - DOI - PMC - PubMed
    1. Chen Y., Liang Q., Liang W., Li W., Liu Y., Guo K., Yang B., Zhao X., Yang M.. Identification of Toxicity Forcing Agents from Individual Aliphatic and Aromatic Disinfection Byproducts Formed in Drinking Water: Implications and Limitations. Environ. Sci. Technol. 2023;57(3):1366–1377. doi: 10.1021/acs.est.2c07629. - DOI - PubMed
    1. Yang X., Shang C., Shen Q., Chen B., Westerhoff P., Peng J., Guo W.. Nitrogen Origins and the Role of Ozonation in the Formation of Haloacetonitriles and Halonitromethanes in Chlorine Water Treatment. Environ. Sci. Technol. 2012;46(23):12832–12838. doi: 10.1021/es302993u. - DOI - PubMed