Ecosystems Research Division 

What is in Our Drinking Water? 

Identification of New Chemical Disinfection By-products (DBPs) 

What is a DBP? A drinking water disinfection by-product (DBP) is formed when the chemical used for disinfecting the drinking water 

reacts with natural organic matter and/or bromide/iodide in the source water. Popular disinfectants include chlorine, ozone, chlorine 

dioxide, and chloramine. Source waters include rivers, lakes, streams, groundwater, and sometimes seawater. We have only 

known about DBPs since 1974, when chloroform was identified by Rook as a DBP resulting from the chlorination of tap water. Since 

then, hundreds of DBPs have been identified in drinking water. 

So what? Millions of people in the U.S. are exposed to these drinking water DBPs every day. While it is vitally important to disinfect

drinking water, as thousands of people died from waterborne illnesses before we started disinfection practices in the early 1900s, it 

is also important to minimize the chemical DBPs formed. Several DBPs have been linked to cancer in laboratory animals, and as a 

result, the U.S. EPA has some of these DBPs regulated. However, there are many more DBPs that have still not been identified and 

tested for toxicity or cancer effects. Currently, we have only identified about 50% of the total organic halide (TOX) that is measured 

in chlorinated drinking water. There is much less known about DBPs from the newer alternative disinfectants, such as ozone, 

chlorine dioxide, and chloramine, which are gaining in popularity in the U.S. Are these alternative disinfectants safer than chlorine? 

What kinds of by-products are formed? And, what about the unidentified chlorine DBPs that people are exposed to through their drinking water--both from drinking and 

showering/bathing? The objective of our research is to find out what these DBPs are--to thoroughly characterize the chemicals formed in drinking water treatment--and to 

ultimately minimize any harmful ones that are formed. 

Our research approach 

z Gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), and gas chromatography/infrared spectroscopy (GC/IR) 

techniques are used to identify the unknown by-products 

z NIST and Wiley mass spectral databases are used first to identify any DBPs that happen to be present in these databases 

z Because many DBPs are not in these databases, most of our work involves unconventional MS and IR techniques, as well as a great deal of scientific interpretation of the 

spectra 

z High resolution MS provides empirical formula information for the unknown chemical (e.g., how many carbons, hydrogens, oxygens, nitrogens, etc. are in the chemical’s 

structure) 

z Chemical ionization MS provides molecular weight information when this is not provided in conventional electron ionization mass spectra 

z IR spectroscopy provides functional group information (e.g., whether the oxygens are due to a carboxylic acid group, a ketone, an alcohol, or an aldehyde) 

z LC/MS is used to identify compounds that cannot be extracted from water (the highly polar, hydrophilic ones), as well as the high molecular weight, nonvolatile DBPs. This 

is a major missing gap in our knowledge about DBPs--so far, most DBPs identified have been those that are easily extracted from water and are volatile enough to analyze 

by GC/MS 

z Novel derivatization techniques are also applied to aid in the identification of highly polar DBPs 

z Formation and fate & transport studies are conducted to better understand how certain priority DBPs are formed and transformed in treatment and distribution systems 

Currently 

We recently completed an iodo-DBP occurrence study (published in the Nov. 15, 2008 issue of Environmental Science & Technology; ES&T 2008, 42 (22), 8330-8338) that 

involved the measurement of iodo-acid DBPs and iodo-THMs in drinking waters from 23 cities across the U.S. and Canada, and the study of their genotoxicity and cytotoxicity. 

We identified the iodo-acids for the first time as part of a large nationwide occurrence study of priority DBPs (mentioned below), and they are important because iodoacetic acid 

was found to be highly genotoxic (to mammalian cells), and it is more genotoxic than the regulated chloro/bromo-haloacetic acids (ES&T 2004, 38 (18): 4713-4722). This study 

helped to underscore the increased formation of iodo-DBPs with chloramination, which is an increasingly popular disinfectant used in the U.S. 

The first phase of the Four Lab Study was also published recently (see special issue of Journal of Toxicology and Environmental Health, Part A, October 22, 2008 issue), where 

we combined chemical and toxicological characterization (with an emphasis on newer reproductive and developmental effects) of complex DBP mixtures. This study is called the 

Four Lab Study because it involves the collaboration of scientists from the four national laboratories/centers of the U.S. EPA: The National Health and Environmental Effects 

Research Laboratory, the National Exposure Research Laboratory, the National Risk Management Research Laboratory, and the National Center for Environmental 

Assessment. The Four Lab Study serves to address potential health concerns that cannot be addressed directly by the toxicological study of individual DBPs or defined DBP 

mixtures, and in essence, provides toxicological information for the complete drinking water mixture: both the known DBPs, as well as the unidentified fraction of DBPs. Drinking 

water treated with chlorine or ozone-chlorine was concentrated by reverse osmosis to maintain a water matrix suitable for the animal studies. The next phase of this work is also 

nearing completion and included a larger battery of toxicological endpoints and focused on chlorinated drinking water. 

Our earlier nationwide DBP occurrence study was published in ES&T in the Dec. 1, 2006 issue (ES&T, 2006, 40, 7175-7185), and can also be found in its full 400+ page report at 

EPA/600/R-02/068. This large study involved the sampling of drinking waters across the U.S. (disinfected with the different disinfectants and with different water quality, including 

elevated levels of bromide in the source water). A group of >50 DBPs that resulted from a prioritization of >500 DBPs in the literature for predicted adverse health effects was 

quantified in these drinking waters. Fate and transport studies were also conducted in the drinking water distribution systems to determine whether these DBPs changed in 

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concentration or were transformed in the distribution systems. In addition to obtaining important quantitative information on these new DBPs (to help in prioritizing health effects 

testing), important new discoveries were made regarding the use of alternative disinfectants. While the use of alternative disinfectants lowered the levels of the four regulated 

trihalomethanes and five haloacetic acids (as compared to chlorine), many of the other prioritized DBPs were formed at higher levels with these alternative disinfectants. For 

example, the highest levels of iodinated DBPs were found in chloraminated drinking water, the highest levels of halonitromethanes were found in pre-ozonated drinking water, 

and dihaloaldehydes were highest at a plant using chloramines and ozone. 

Our new work includes investigating other potential sources of iodine in the formation of iodo-DBPs and investigating the influence of the length of free chlorine contact time 

(before ammonia addition to form chloramines) on their formation. In other research, a toxicity-based identification approach (using mammalian cell and medaka fish assays) is 

being used to focus identification efforts on the most toxic drinking water fractions, with an emphasis on obtaining new information on high molecular weight DBPs (which are 

believed to make up approximately 50% of the halogenated DBPs produced). 

Recent results 

z A recent iodo-DBP occurrence study (ES&T 2008, 42 (22), 8330-8338) has provided the first quantitative occurrence data for highly genotoxic iodo-acid DBPs and 

information on their formation (along with iodo-THMs) in chloraminated drinking water, along with the first toxicity data for iodo-THMs and iodo-acids (beyond the first work 

on iodoacetic acid) 

z The first phase of the Four Lab Study (Environ. Toxicol. Health, Pt. A, 2008, 71, 1125-1132 and following papers in this issue) reports results from an integrated 

chemical/toxicological research study to investigate the toxicological effects of complex DBP mixtures 

z A Nationwide DBP Occurrence Study (ES&T, 2006, 40, 7175-7185) provided important new quantitative information on unregulated DBPs that have the potential to cause 

adverse health effects based on a structure-activity analysis (Woo et al., 2002); several of these DBPs have concentrations similar to some that are already regulated 

z The use of alternative disinfectants can produce higher levels of these DBPs, as compared to chlorine 

z Collaborations are ongoing with health effects researchers to study selected DBPs for potential adverse health effects 

Gordon Research Conference on DBPs 

The second Gordon Research Conference on drinking water DBPs will be held August 9-14, 2009, at Mount Holyoke College in South Hadley, Massachusetts. Like the first one 

initiated in 2006 (where scientists from 22 countries came), this conference will bring together scientists from different disciplines: chemists, toxicologists, epidemiologists, 

engineers, clinicians, human exposure scientists, risk assessors, and regulators to address the issues with drinking water DBPs. Ben Blount from the Centers for Disease Control 

and Prevention (CDC) will be the Chair of the 2009 conference. Contact Ben Blount (bkb3@cdc.gov) or Susan Richardson (richardson.susan@epa.gov) for more information. 

Useful publications 

Weinberg, H. S., S. W. Krasner, S. D. Richardson, and A. D. Thruston, Jr. The Occurrence of Disinfection By-Products (DBPs) of Health Concern in Drinking Water: Results of a 

Nationwide DBP Occurrence Study. EPA/600/R02/068. U.S. Environmental Protection Agency, National Exposure Research Laboratory, Athens, GA. 2002. 

Richardson, S. D., F. Fasano, J. J. Ellington, F. G. Crumley, K. M. Buettner, J. J. Evans, B. C. Blount, L. K. Silva, T. J. Waite, G. W. Luther, A. B. McKague, R. J. Miltner, E. D. 

Wagner, and M. J. Plewa. 2008. Occurrence and Mammalian Cell Toxicity of Iodinated Disinfection Byproducts in Drinking Water. Environ. Sci. Technol., 42 (22): 8330-8338. 

Plewa, M. J., M. G. Muellner, S. D. Richardson, F. Fasano, K. M. Buettner, Y.-T. Woo, A. B. McKague, and E. D. Wagner. 2008. Occurrence, Synthesis, and Genotoxicity of 

Haloacetamides: An Emerging Class of Nitrogenous Drinking Water Disinfection Byproducts. Environ. Sci. Technol., 42 (3), 955-961. 

Richardson, S. D., A. D. Thruston, Jr., S. W. Krasner, H. S. Weinberg, R. J. Miltner, M. G. Narotsky, and J. E. Simmons. 2008. Integrated Disinfection Byproducts Mixtures 

Research: Comprehensive Characterization of Water Concentrates Prepared from Chlorinated and Ozonated/Postchlorinated Drinking Water. J. Toxicol. Environ. Health, Pt. A, 

71: 1165-1186. 

Simmons, J. E., S. D. Richardson, T. F. Speth, R. J. Miltner, G. Rice, K. M. Schenck, E. S. Hunter, III, and L. K. Teuschler. 2008. Research Issues Underlying the Four-Lab 

Study: Integrated Disinfection Byproducts Mixtures Research. J. Toxicol. Environ. Health, Pt. A, 71: 1125-1132. 

Miltner, R. J., T. F. Speth, S. D. Richardson, S. W. Krasner, H. S. Weinberg, and J. E. Simmons. 2008. Integrated Disinfection Byproducts Mixtures Research: Disinfection of 

Drinking Waters by Chlorination and Ozonation/Postchlorination Treatment Scenarios. J. Toxicol. Environ. Health, Pt. A, 71: 1133-1148. 

Speth, T. F., R. J. Miltner, S. D. Richardson, and J. E. Simmons. 2008. Integrated Disinfection Byproducts Mixtures Research: Concentration by Reverse Osmosis Membrane 

Techniques of Disinfection Byproducts from Water Disinfected by Chlorination and Ozonation/Postchlorination. J. Toxicol. Environ. Health, Pt. A, 71: 1149-1164. 

Rice, G., L. K. Teuschler, S. D. Richardson, T. F. Speth, and J. E. Simmons. 2008. Integrated Disinfection Byproducts Mixtures Research: Assessing Reproductive and 

Developmental Risks Posed by Complex Disinfection Byproduct Mixtures. J. Toxicol. Environ. Health, Pt. A, 71: 1222-1234. 

Weisel, C. P., S. D. Richardson, B. Nemery, G. Aggazzotti, E. Baraldi, E. R. Blatchley, III, B. C. Blount, K-H. Carlsen, P. A. Eggleston, F. H. Frimmel, M. Goodman, G. Gordon, S. 

A. Grinshpun, D. Heederik, M. Kogenvinas, J. S. LaKind, M. J. Nieuwenhuijsen, F. C. Piper, S. A. Sattar. 2008. Childhood Asthma and Environmental Exposures at Swimming 

Pools: State of the Science and Research Recommendations. Environ. Health Perspect., in press. 

Muellner, M. G., E. D. Wagner, K. McCalla, S. D. Richardson, Y.-T. Wood, and M. J. Plewa. 2007. Haloacetonitriles vs. Regulated Haloacetic Acids: Are Nitrogen Containing 

DBPs More Toxic? Environ. Sci. Technol., 41 (2): 645-651. 

Zwiener, C., S. D. Richardson, D. M. DeMarini, T. Grummt, T. Glauner, and F. H. Frimmel. 2007. Drowining in Disinfection By-Products? Swimming Pool Water Quality 

Reconsidered. Environ. Sci. Technol., 41 (2): 363-372. 

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Plewa, M. J., M. G. Muellner, S. D. Richardson, F. Fasano, K. M. Buettner, Y.-T. Woo, A. B. McKague, and E. D. Wagner. 2007. Occurrence, Synthesis, and Mammalian Cell 

Cytotoxicity and Genotoxicity of Haloacetamides: An Emerging Class of Nitrogenous Drinking Water Disinfection By-Product. Environ. Sci. Technol., 42 (3): 955-961. 

Richardson. S. D. 2008. Environmental Mass Spectrometry: Emerging Contaminants and Current Issues. Anal. Chem., 80(12): 4373-4402. 

Richardson, S. D., C. Rav-Acha, and G. D. Simpson. 2009. Chlorine Dioxide Chemistry, Reactions, and Disinfection By-Products. In Chlorine Dioxide in Drinking Water 

Treatment, American Water Works Association Research Foundation, in press. 

Richardson, S. D., M. J. Plewa, E. D. Wagner, R. Schoeny, and D. M. DeMarini. Occurrence, Genotoxicity, and Carcinogenicity of Emerging Disinfection By-Products in Drinking 

Water: A Review and Roadmap for Research. 2007. Mutat. Res., 636: 178-242. 

Richardson, S. D. Water Analysis: Emerging Contaminants and Current Issues. 2007. Anal. Chem., 79(12): 4295-4324. 

Krasner, S. W., H. S. Weinberg, S. D. Richardson, S. Pastor, R. Chinn, M. J. Sclimenti, G. Onstad, and A. D. Thruston, Jr. 2006. The Occurrence of a New Generation of 

Disinfection Byproducts. Environmental Science & Technology, 40 (23): 7175-7185. 

Richardson. S. D. Environmental Mass Spectrometry: Emerging Contaminants and Current Issues. 2006. Analytical Chemistry, 78 (12): 4021-4046. 

Richardson, S. D., and T. Ternes. 2005. Water Analysis: Emerging Contaminants and Current Issues. Analytical Chemistry, 77(12): 3807-3838. 

Cemeli, E., E. D. Wagner, D. Anderson, S. D. Richardson, and M. J. Plewa. 2006. Modulation of the Cytotoxicity and Genotoxicity of the Drinking Water DBP Iodoacetic Acid by 

Suppressors of Oxidative Stress. Environmental Science & Technology, 40 (6): 1878-1883. 

Vincenti, M., S. Biazzi, N. Ghiglione, M. C. Valsania, and S. D. Richardson. 2005. Comparison of Highly- Fluorinated Chloroformates as Direct Aqueous Sample Derivatizing 

Agents for Hydrophilic Analytes and Drinking Water Disinfection By-Products. Journal of the American Society for Mass Spectrometry, 16 (6): 803-813. 

Plewa, M. J., E. D. Wagner, S. D. Richardson, A. D. Thruston, Jr., Y.-T. Woo, and A. B. McKague. 2004. Chemical and Biological Characterization of Newly Discovered Iodoacid 

Drinking Water Disinfection Byproducts. Environmental Science & Technology, 38(18): 4713-4722. 

Zwiener, C., and S. D. Richardson. 2005. Drinking Water Disinfection By-Product Analysis by LC/MS and LC/MS/MS. Trends in Analytical Chemistry, 24(7): 613-621. (Invited 

review article for special thematic issue on Liquid Chromatography-Tandem Mass Spectrometry). 

Plewa, M. J., E. D. Wagner, P. Jazwierska, S. D. Richardson, P. H. Chen, and A. B. McKague. 2004. Halonitromethane Drinking Water Disinfection Byproducts: Chemical 

Characterization and Mammalian Cell Cytotoxicity and Genotoxicity. Environmental Science & Technology, 38(1): 62-68. 

Kundu, B., S. D. Richardson, P. D. Swartz, P. P. Matthews, A. M. Richard, and D. M. DeMarini. 2004. Mutagenicity in Salmonella of Halonitrometanes: A Recently Recognized 

Class of Disinfection By-Product in Drinking Water. Mutation Research, 562: 39-65. 

Kundu, B., S. D. Richardson, C. A. Granville, D. T. Shaughnessy, N. M. Hanley, P. D. Swartz, A. M. Richard, and D. M. DeMarini. 2004. Comparative Mutagenicity of 

Halomethanes and Halonitromethanes in Salmonella TA100: Structure-Activity Analysis and Mutation Spectra. Mutation Research, 554: 335-350. 

Richardson, S. D. 2004. Environmental Mass Spectrometry: Emerging Contaminants and Current Issues. Analytical Chemistry, 76(12): 3337-3364. 

Simmons, J. E., L. K. Teuschler, C. Gennings, T. F. Speth, S. D. Richardson, R. J. Miltner, M. G. Narotsky, K. D. Schenck, E. S. Hunter, III, R. C. Hertzberg, III, and G. Rice. 

 2004. Component-Based and Whole-Mixture Techniques for Addressing the Toxicity of Drinking Water Disinfection Byproducts Mixtures. Journal of Toxicology & Environmental 

Health, 67: 741-754. 

Richardson, S.D., J. E. Simmons, and G. Rice. 2002. DBPs: The Next Generation. Environmental Science & Technology, 36(9): 198A-205A. 

Woo, Y.-T., D. Lai, J. L. McLain, M. K. Manibusan, and V. Dellarco. 2002. Environmental Health Perspectives, 110 (Suppl. 1): 75-87. 

Richardson, S. D., A. D. Thruston, Jr., C. Rav-Acha, L. Groisman, I. Popilevsky, V. Glezer, A. B. McKague, M. J. Plewa, and E. D. Wagner. 2003. Tribromopyrrole and Other 

DBPs Produced by the Disinfection of Drinking Water Rich in Bromide. Environmental Science & Technology, 37(17): 3782-3793. 

Richardson, S. D. 2003. Water Analysis: Emerging Contaminants and Current Issues. Analytical Chemistry, 75(12): 2831-2857. 

Richardson, S. D. 2003. Disinfection By-Products and Other Emerging Contaminants in Drinking Water. Trends in Analytical Chemistry, 22(10):666-684. 

Chen, P. H., S. D. Richardson, S. W. Krasner, G. Majetich, and G. L. Glish. 2002. Hydrogen Abstraction and Decomposition of Tribromonitromethane and Other Trihalo 

Compounds by GC/MS. Environmental Science & Technology, 36(15): 3362-3371. 

Simmons, J. E., S. D. Richardson, T. F. Speth, R. J. Miltner, G. Rice, K. M. Schenck, E. S. Hunter, III, and L. K. Teuschler. 2002. Development of a Research Strategy for 

Integrated Technology-Based Toxicological and Chemical Evaluation of Complex Mixtures of Drinking Water Disinfection Byproducts. Environmental Health Perspectives, 110

(Supp. 6): 1013-1024. 

Arbuckle, T. E., S. E. Hrudey, S. W. Krasner, J. R. Nuckols, S. D. Richardson, P. Singer, P. Mendola, L. Dodds, C. Weisel, D. L. Ashley, K. L. Froese, R. A. Pegram, I. R. Schultz, 

J. Reif, A. M. Bachand, F. M. Benoit, M. Lynberg, C. Poole, and K. Waller. 2002. Assessing Exposure in Epidemiologic Studies to Disinfection By-products in Drinking Water: 

Report from an International Workshop. Environmental Health Perspectives, 110 (Supp. 1): 53-60. 

Richardson, S. D., T. V. Caughran, T. Poiger, Y. Guo, and F. G. Crumley. 2000. Application of DNPH Derivatization with LC/MS to the Identification of Polar Carbonyl 

Disinfection By-products in Drinking Water. Ozone: Science & Engineering, 22: 653-675. 

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Last updated on Thursday, December 17th, 2009. 

WCMS 

Richardson, S. D., A. D. Thruston, Jr., T. V. Caughran, P. H. Chen, T. W. Collette, T. L. Floyd, K. M. Schenck, B. W. Lykins, Jr., G.-R. Sun, and G. Majetich. 1999. Identification 

of New Ozone Disinfection By-products in Drinking Water. Environmental Science & Technology, 33: 3368-3377. 

Richardson, S. D., A. D. Thruston, Jr., T. V. Caughran, P. H. Chen, T. W. Collette, T. L. Floyd, K. M. Schenck, B. W. Lykins, Jr., G.-R. Sun, and G. Majetich. 1999. Identification 

of New Drinking Water Disinfection By-products Formed in the Presence of Bromide. Environmental Science & Technology, 33: 3378-3383. 

Richardson, S. D., A. D. Thruston, Jr., T. V. Caughran, P. H. Chen, T. W. Collette, K. M. Schenck, B. W. Lykins, Jr., C. Rav-Acha, and V. Glezer. 2000. Identification of New 

Drinking Water Disinfection By-products from Ozone, Chlorine Dioxide, Chloramine, and Chlorine. Water, Air, and Soil Pollution, 123: 95-102. 

 

*For more information, contact Susan Richardson at richardson.susan@epa.gov

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