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Disinfection Byproduct Health Effects 

Since the discovery of chlorination byproducts in drinking water in 1974, numerous 

toxicological studies (studies on the health effects from exposure to high dosages 

contaminants usually involving animals in a lab) have been conducted. These 

studies have shown several disinfection byproducts to be carcinogenic in laboratory animals 

(e.g., including bromate, certain trihalomethanes and haloacetic acids). Some disinfection 

byproducts have also been shown to cause adverse reproductive or developmental effects in 

laboratory animals (e.g., chlorite and certain trihalomethanes and haloacetic acids). 

However, there is considerable uncertainty involved in using the results of high-dose, 

toxicological studies of some byproducts occurring in disinfected drinking water to estimate 

the risk to humans from chronic exposure to low doses of these and other byproducts. 

In the area of epidemiology (studies of the factors that influence disease in human 

populations), a number of studies have been completed investigating the relationship 

between exposure to chlorinated surface water and cancer. Some have suggested an 

increased cancer risk to those exposed to chlorinated waters while others have demonstrated 

none. In issuing the Stage 1 Disinfectants/Disinfection Byproducts Rule based on evidence 

then available, EPA stated that while the agency cannot conclude there is a causal link 

between exposure to chlorinated surface water and cancer, these studies have suggested an 

association, albeit small, between bladder, rectal, and colon cancer and exposure to 

chlorinated surface water. There are fewer epidemiology studies evaluating the association 

between exposure to disinfection byproducts and reproductive and developmental effects. 

Again, some have suggested an increased risk from exposure to disinfection byproducts while 

others have shown none. There remains considerable debate in the scientific community on 

the significance of these contradictory findings concerning chlorinated water and disinfection 

byproducts. As with cancer, EPA stated in its Stage 1 Disinfectants/Disinfection Byproducts 

Rule that, based on data then available, the agency can not conclude there is a causal link 

between exposure to disinfection byproducts and reproductive and developmental effects. In 

sum, EPA believes the weight-of-evidence presented by the available epidemiological studies 

on chlorinated drinking water and toxicological studies on individual disinfection byproducts 

support a potential hazard concern and warrant regulatory action at this time such as that 

taken in the Stage 1 Disinfectants/Disinfection Byproducts Rule. 

An extensive research effort (1997 Update to ORD's Strategic Plan, National Toxicology 

Program) is currently underway to better understand the potential risks attending exposure 

to disinfection byproducts. While this research is being completed, an agreement among 

water suppliers, environmental groups, consumer groups, and regulatory agencies has been 

reached, resulting in the publication of a Stage 1 Disinfectants/Disinfection Byproducts Rule

by EPA in the Federal Register in December 1998. The participants recommended that while 

additional information, especially on health effects, is needed, the Stage 1

Disinfectants/Disinfection Byproducts Rule was considered the best course of action to reduce 

potential risks from disinfection byproducts in the near term. 

Information Collection Rule (ICR)

http://www.epa.gov/enviro/html/icr/dbp_health.html

Last updated on Thursday, October 27, 2011

EPA | Envirofacts | ICR Page 1 of 1

http://www.epa.gov/enviro/html/icr/dbp_health.html 11/10/2011