Grantee Research Project Results
1999 Progress Report: Metabolic Fate of Halogenated Disinfection By-Products In Vivo, and Relation to Biological Activity
EPA Grant Number: R825957Title: Metabolic Fate of Halogenated Disinfection By-Products In Vivo, and Relation to Biological Activity
Investigators: Ball, Louise M.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Hahn, Intaek
Project Period: January 23, 1998 through January 22, 2001
Project Period Covered by this Report: January 23, 1998 through January 22, 1999
Project Amount: $460,848
RFA: Drinking Water (1997) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
Halogenated byproducts of drinking water disinfection are of concern because of their widespread human consumption and the current uncertainty regarding their health effects. Haloacids as a class are the most abundant of the halogenated disinfection byproducts (DBPs). Many of these compounds are suspect carcinogens and, in addition, may form macromolecular adducts that could be useful as biomarkers of exposure to disinfectants. This project attempts to elucidate mechanisms of biological activity and disposition of haloacids. Two specific approaches will be followed, one directed towards DBPs that appear to be highly biologically active though present at low levels, and the other directed towards DBPs that are highly abundant, even if less potent biologically. The two approaches are:- Identification and quantitation of macromolecular adducts formed in vivo by the haloacetic acids (chloroacetic acid, dichloroacetic acid), from their brominated analogs (bromoacetic acid, dibromoacetic acid), and from the mixed haloacetic acid (bromochloroacetic acid). Quantities of adducts sufficient for detailed structural elucidation often are difficult or impossible to obtain by direct modification of DNA; hence, direct chemical synthesis will be undertaken to provide standards for investigation of adduct formation in vivo.
- Investigation of the metabolism and disposition of MX, to identify the chemical nature and mechanism of formation of metabolites of the potent bacterial mutagen (Z)-2-chloro-3-(dichloromethyl)-4-oxobutenoic acid, more commonly known in its ring-closed form as 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone or MX (for Mutagen "X"). Structural identification of MX metabolites and their tissue distribution in the rat will be carried out to gain an understanding of the nature of the active species present at potential target organs, and the levels and duration of internal exposure.
Progress Summary:
In Year 1, we obtained evidence from mutagenicity assays that glutathione-mediated pathways did not lead to mutagenic products from dichloroacetic acid, but that glutathione conjugates may contribute to the toxicity of this compound. In Year 2, we investigated whether this conclusion also held true for brominated analogs. We used the Ames plate incorporation assay to measure the production of genotoxic species in the form of mutations. We added glutathione (GSH), NAD+, or both, to evaluate the effects of these co-factors on the activity of the haloacetic acids and to define the metabolic pathway(s) that produced genotoxic products. While glutathione appeared to increase the toxicity of dichloroacetic acid, for the brominated species bromoacetic acid and bromochloroacetic acid, the effects of glutathione amounted to detoxication, in the form of a decrease in toxicity for monobromoacetic acid and of mutagenicity for bromochloroacetic acid. Our ultimate goal at this stage was to prioritize the different haloacetic acids for in vivo metabolic studies; preference would be given to the most mutagenic compounds for investigation of potential in vivo DNA adduct formation. Bromochloroacetic acid proved to be the most consistently mutagenic of the haloacids assayed. Synthesis and characterization of putative DNA adducts from haloacetic acids is in progress.We originally had developed the hypothesis that a glutathione-dependent pathway could contribute to formation of genotoxic metabolites from dihaloacetic acids. However, our results indicate that the presence of glutathione does not enhance the mutagenicity of haloacetic acids in the Ames plate incorporation assay, but that interaction with glutathione is biologically important for detoxication of some members of this class of compounds; the outcome of that interaction would appear to differ depending on the nature of the halogen substituent. Overall, knowledge of the chemical structures of macromolecular adducts formed will provide information on routes of genotoxic activity. In addition, this information constitutes the foundation for development of assays to measure rates of adduct formation and loss, and the development of biomarkers of exposure and effect.
Future Activities:
Our goals for the coming months are to establish a measure for interaction of the haloacetic acids with glutathione, and to initiate in vivo studies with the most mutagenic of the haloacetic acids, bromochloroacetic acid.Supplemental Keywords:
drinking water, exposure, effects, metabolism, dose-response, carcinogen, mutagen, mammalian, animal, organism, enzymes, chemicals, environmental chemistry, environmental biology, analytical., RFA, Scientific Discipline, Water, Chemical Engineering, Environmental Chemistry, Chemistry, Analytical Chemistry, Biochemistry, Drinking Water, Biology, halogenated disinfection by-products, biomarkers, bacterial mutagen, exposure and effects, animal model, chemical byproducts, disinfection byproducts (DPBs), exposure, community water system, treatment, carcinogenicity, genotoxicity, haloacetic acids, macromolecular adducts, metabolism, drinking water contaminants, drinking water system, ratProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.