You are here:
TOXICOLOGIC AND CHEMICAL EVALUATION OF ALTERNATIVE DISINFECTION TREATMENT SCENARIOS
Impact/Purpose:
The objective is to address concerns related to the potential health effects from exposure to DBPs that cannot be addressed directly from toxicological studies of individual DBPs or simple DBP mixtures. The purpose is to evaluate the relative toxicity of drinking water samples that vary by disinfection technique and selected water quality parameters. An important component of understanding the human health implications of any toxicity observed with the complex mixtures will be research directed toward identification of those individual components or classes of DBPs that contribute most to the overall toxicity of the mixture.
Description:
More than 500 disinfecting byproducts have been identified. They result from the reaction of the disinfectants with the natural organic matter present in source waters. The concentrations and bromo/chloro speciation of these disinfection byproducts (DBPs) are influenced by source water characteristics such as pH, total organic carbon concentration, bromide concentration and temperature as well as the choice of disinfecting agent(s) and its(their) concentration(s). Many DBPs are still unidentified; for chlorination, the known DBPs might account for less than 50% of the mass of total organic halide. Epidemiologic investigations suggest associations (albeit weak) between human consumption of chlorinated drinking water and adverse health outcomes including reproductive and developmental effects such as increased spontaneous abortions and low birth weight and bladder and rectal cancer.
In the absence of more definitive epidemiological data sets, characterizations of the human health risks posed by exposures to DBPs can be developed through toxicologic evaluations of the complex mixture itself or of the components of the mixture. Toxicologic evaluation of the complex mixture, rather than assessment of each individual chemical separately, is preferred because this option better characterizes the real human exposure, as well as accounting for any compounded effects from exposure to the low levels of multiple DBPs that are found in drinking water. Thus, a critical data gap in DBP mixtures research is toxicological evaluation in experimental animals of those endpoints identified as of concern from epidemiology studies. These endpoints are reproductive/developmental effects and cancer. In response to this identified data gap, the various organizations with the U.S. EPAs Office of Research and Development have engaged in joint research planning. The result is a research plan for joint chemical and toxicological characterization of mixtures of DBPs that are produced by two different drinking water treatment processes, leading to a more informed quantitative risk assessment of DBPs. Our joint purpose is to address concerns related to potential health effects from exposure to DBPs that cannot be addressed directly from toxicologic studies of individual DBPs or defined DBP mixtures.
This research plan is designed to evaluate real-world complex mixtures obtained by concentration of disinfected water. Using three phases of research, pre-trial runs, a trial run, and a full study, the plan proposes to a) generate health-effects and chemical-identity information for a surface water disinfected by chlorination; b) generate health-effects and chemical-identity information for the same surface water disinfected by pre-ozonation and post-chlorination; and, c) compare the potential health risks associated with consumption of water disinfected by these two treatment scenarios. The plan proposes a succession of studies that are logical steps to follow, but may be difficult to implement, due to a number of challenging technical issues. The pre-trial and trial runs, along with the external peer-review of the research plan, was used to revise and refine the research proposed in the plan. The present effort is focused on disinfection by chlorination.
A multi-disciplinary team of investigators from a wide array of disciplines is involved. Necessary areas of expertise include: water treatment engineering; DBP source and occurrence information; analytical chemistry; target-organ toxicology; mixtures toxicology; statistical analysis and experimental design; and, risk assessment. The Project Coordinator is Jane Ellen Simmons, NHEERL. The steering committee members are: Sid Hunter, NHEERL; Dick Miltner, NRMRL; Glenn Rice, NCEA; Susan Richardson, NERL; Kathy Schenck, NRMRL; Jane Ellen Simmons, NHEERL; Thomas Speth, NRMRL; and, Linda Teuschler, NCEA. Participating investigators are: John Lipscomb, NCEA; and Larry Claxton, Tony DeAngelo, MarinaEvans, Jerome Goldman, Gary Klinefelter , BobLuebke, Ginger Moser and Rex Pegram, NHEERL.