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A Toxicological Perspective on Disinfection ByProducts
Citation:
SIMMONS, J. E. A Toxicological Perspective on Disinfection ByProducts. Presented at American Water Works Association (AWWA) Meeting, Washington, DC, June 12 - 16, 2011.
Impact/Purpose:
This talk will summarize recent data on individual DBPs (individual THMs and HAAs), defined mixtures (THM, HAA and THM + HAA mixtures), and complex mixtures of DBPs formed during disinfection by chlorination and ozonation, evaluated in vivo and in vitro.
Description:
Disinfection of water is essential for reduction of microbes harmful to human health and chemical disinfection is considered one of the major public health triumphs of the 20th Century. An unintended consequence of disinfection with oxidizing chemicals is formation of disinfection byproducts (DBPs). DBP number, chemical type and concentration are dependent on source-water and treatment-scenario characteristics. Although more than 600 DBPs have been identified, ~50% of the total organic halide (TOX) mass formed during chlorination remains unidentified. Some epidemiological investigations have suggested associations between human consumption of chlorinated drinking water and adverse health outcomes such as developmental and reproductive effects, and bladder, colon and rectal cancer. The health effects observed in some epidemiological studies are unexpected based on the available data from experimentalanimal single-chemical DBP studies. Potential reasons for these discrepancies will be explored. Understanding the human health risk(s) associated with consumption and use of chemically disinfected water will require relevant toxicological information on individual DBPs, defined DBP mixtures of known composition and complex, environmentally realistic mixtures of DBPs. Individual DBP assessments are essential but do not account for potential interactions that influence toxicity. Component-based assessment of simple, defined mixtures are needed as four trihalomethanes (THMs, chloroform, bromoform, bromodichloromethane and chlorodibromomethane) and five haloacetic acids (HAAs, monochloro-, dichloro-, trichloro-, monobromo-, and dibromoacetic acid) are regulated together, respectively, under a total THM and a total HAA standard, Defined mixture data provide important information, but are not by themselves sufficient because a significant portion of the DBP mixture mass remains unidentified. Methods are needed to determine the portion of any observed toxicity attributable to the unidentified fraction of the mixture. This talk will summarize recent data on individual DBPs (individual THMs and HAAs), defined mixtures (THM, HAA and THM + HAA mixtures), and complex mixtures of DBPs formed during disinfection by chlorination and ozonation, evaluated in vivo and in vitro. Because practical limitations currently prohibit all individual chemicals and chemical mixtures from being evaluated, options for grouping chemicals and for extrapolation from known to unknown scenarios are presented. (This abstract does not represent EPA policy.)