Abstract
Hundreds of different disinfection byproducts form in drinking water following necessary treatment with chlorine and other disinfectants, and many of those byproducts can damage DNA and increase the risk of cancer. This study offers the first side-by-side comparison of cancer risk assessments based on toxicological and epidemiological studies of disinfection byproducts using a comprehensive contaminant occurrence dataset for haloacetic acids and trihalomethanes, two groups of disinfection byproducts that are regulated in drinking water. We also provide the first analysis of a new occurrence dataset for unregulated haloacetic acids that became available from the latest, fourth round of the U.S. EPA-mandated unregulated contaminant monitoring program (UCMR4). A toxicological assessment indicated that haloacetic acids, and in particular brominated haloacetic acids, are more carcinogenic and are associated with a greater number of attributable cancer cases than trihalomethanes. Based on the toxicological analysis, cumulative lifetime cancer risk due to exposure to trihalomethanes and haloacetic acids for community water systems monitored under UCMR4, estimated with standard default parameters for body weight and water intake, corresponds to 7.0 × 10−5 (3.5 × 10−5–1.3 × 10−4). The same analysis conducted with age sensitivity factors to account for elevated risk in infants and children yielded a cumulative risk estimate of 2.9 × 10−4 (1.7 × 10−4–6.2 × 10−4). Epidemiological data suggest that lifetime cancer risk from disinfection byproducts for the U.S. population served by community water systems is approximately 3.0 × 10−3 (2.1 × 10−4–5.7 × 10−3), or a lifetime cancer risk of three cases per thousand people. Overall, this analysis highlights the value of using human data in health risk assessments to the greatest extent possible.
Highlights
Drinking water treatment with disinfectants, such as chlorine, chloramine, and ozone creates a variety of reactive chemical intermediates and disinfection byproducts that may be harmful to human health and the environment [1,2]
Individual disinfection byproducts show differences in both cancer potency and overall toxicity [42,57,59,60]. This differential toxicity is reflected in the diversity of carcinogen classifications for individual disinfection byproduct substances published by the U.S Environmental Protection Agency (EPA), National Toxicology Program Report on Carcinogens, and International Agency for Research on Cancer (Table 8)
Carcinogenic to humans (Group 2B) [59]; Probable human carcinogen (Group B2) [65]; Likely to be carcinogenic to humans by all routes of exposure under exposure conditions that lead to cytotoxicity and regenerative hyperplasia in susceptible tissues; not likely to be carcinogenic to humans by any route of exposure under exposure conditions that do not cause cytotoxicity and cell regeneration [65]; Dibromochloromethane
Summary
Drinking water treatment with disinfectants, such as chlorine, chloramine, and ozone creates a variety of reactive chemical intermediates and disinfection byproducts that may be harmful to human health and the environment [1,2]. Chlorine-based water disinfection, introduced at the beginning of the 20th century, has saved countless lives and drastically decreased the incidence of water-borne microbial diseases transmitted through drinking water. Epidemiological research has reported associations between adverse health effects and the presence of disinfection byproducts in tap water at concentrations that generally meet applicable national drinking water standards [3]. Multiple studies have reported an increased risk of bladder cancer in association with exposure to drinking water disinfection byproducts [4,5,6], and the risk of other cancers has been suggested [7,8].
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