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OCCURRENCE, GENOTOXICITY, AND CARCINOGENICITY OF EMERGING DISINFECTION BY-PRODUCTS IN DRINKING WATER: A REVIEW AND ROADMAP FOR RESEARCH
Citation:
RICHARDSON, S. D., P. J. MICHAEL, E. D. WAGNER, R. S. SCHOENY, AND D. M. DEMARINI. OCCURRENCE, GENOTOXICITY, AND CARCINOGENICITY OF EMERGING DISINFECTION BY-PRODUCTS IN DRINKING WATER: A REVIEW AND ROADMAP FOR RESEARCH. MUTATION RESEARCH. Elsevier Science Ltd, New York, NY, 636(1-3):178-242, (2007).
Impact/Purpose:
This review was undertaken to provide the necessary information and guidance for prioritizing DBP and drinking water research.
Description:
Occurrence, Genotoxicity, and Carcinogenicity of Emerging Disinfection By-products in Drinking Water: A Review and Roadmap for Research
Summary of Paper
What is study?
This is the first review of the 30 year's research effort on the occurrence, genotoxicity, and carcinogenicity of disinfection by-products (DBPs) in drinking water. This comprehensive review of the literature (more than 300 references) provides the first assessment of what is known about these endpoints for the DBPs both in terms of health effects (genotoxicity and carcinogenicity) and occurrence levels. The study integrates these topics and develops a strategy for prioritizing DBP and drinking water research.
Why was it done?
A comprehensive review of the DBP and drinking water literature has never been done, and after 30 years, it was time to see what has been learned and what still needs to be done in this important area of environmental science. 'The lack of such a review has prevented a thoughtful assessment of the current state of knowledge in DBP research and has hindered the development of a comprehensive plan for future research based on what has been learned already. Thus, this review was undertaken to provide the necessary information and guidance for prioritizing DBP and drinking water research.
What is the impact to the field and the agency?
We think that this paper will have a large impact in the field of DBP and drinking water research by providing a comprehensive assessment of the current state of knowledge in this area and guidance regarding research needs. We think it will serve an important role within and outside of the Agency in providing the foundation for DBP and drinking water research in the areas of genotoxicity and carcinogenicity for many years ahead.
Abstract
Disinfection by-products (DBPs) are formed when disinfectants (chlorine, ozone, chlorine dioxide, or chloramines) react with naturally occurring organic matter, anthropogenic contaminants, bromide, and iodide during the production of drinking water. Here we review 30 years of research on the occurrence, genotoxicity, and carcinogenicity of 85 DBPs, 11 of which are currently regulated by the U.S., and 74 of which are considered emerging DBPs due to their moderate occurrence levels and/or toxicological properties. These 74 include halonitromethanes, iodo-acids and other unregulated halo-acids, iodo-trihalomethanes (THMs), and other unregulated halomethanes, halofuranones (MX [3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] and brominated MX DBPs), haloamides, haloacetonitriles, tribromopyrrole, aldehydes, and N-nitrosodimethylamine (NDMA) and other nitrosamines. Alternative disinfection practices result in drinking water from which extracted organic material is less mutagenic than extracts of chlorinated water. However, the levels of many emerging DBPs are increased by alternative disinfectants (primarily ozone or chloramines) compared to chlorination, and many emerging DBPs are more genotoxic than some of the regulated DBPs. Our analysis identified 3 categories of DBPs of particular interest. Category 1 contains 8 DBPs with some or all of the toxicologic characteristics of human carcinogens: 4 regulated (bromodichloromethane, dichloroacetic acid, dibromoacetic acid, and bromate) and 4 unregulated DBPs (formaldehyde, acetaldehyde, MX, and NDMA). Categories 2 and 3 contain 43 emerging DBPs that are present at moderate levels (sub-low µg/L): category 2 contains the 26 of these that are genotoxic (including chloral hydrate, which is also a rodent carcinogen); and category 3 contains the remaining 17 for which little or no toxicological data are available. In general, the brominated DBPs are both more genotoxic and carcinogenic than are chlorinated compounds, and iodinated DBPs were the most genotoxic of all but have not been tested for carcinogenicity. There were toxicological data gaps for even some of the 11 regulated DBPs as well as for most of the 74 emerging DBPs. A systematic assessment of DBPs for genotoxicity has been performed for ~60 DBPs for DNA damage in mammalian cells and 16 for mutagenicity in Salmonella. A recent epidemiologic study found that much of the risk for bladder cancer associated with drinking water was associated with three factors: THM levels, showering/bathing/swimming (i.e., dermal inhalation exposure), and genotype (having the GSTT1-1 gene). This finding, along with mechanistic studies, highlights the emerging importance of dermal/inhalation exposure to the THMs, and possibly other DBPs, and the role of genotype for risk for drinking water-associated bladder cancer. More than 50% of the total organic halogen (TOX) formed by chlorination and more than 50% of the total organic carbon (TOC) formed by ozonation have not been identified chemically. The potential interactions among the 600 identified DBPs in the complex mixture of drinking water to which we are exposed by various routes is not reflected in any of the toxicology studies of individual DBPs. The categories of DBPs described here, the identified data gaps, and the emerging role of dermal/inhalation exposure provide guidance for drinking water and public health research.
