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Approaches to determining regulatory values for carcinogens with particular reference to bromate
1Independent Consultant, 89 Heath End Road, Flackwell Heath, High Wycombe, Bucks HP10 9EW, UK. john.fawell@johnfawell.co.uk
Toxicology
|February 10, 2006
Summary
Establishing safe drinking water standards for bromate, a potential disinfectant byproduct, is challenging due to uncertain cancer mechanisms. Research is needed to refine risk assessments for bromate exposure.
Area of Science:
- Environmental Science
- Toxicology
- Risk Assessment
Background:
- Developing standards for animal carcinogens presents challenges, particularly for genotoxic substances where low-dose extrapolation is difficult.
- Bromate is a contaminant from water disinfection (hypochlorite, ozone) and a former flour improver, known to cause rodent cancers.
- Species-specific sensitivities and tumor types, along with an uncertain carcinogenic mechanism for bromate, complicate risk assessment.
Purpose of the Study:
- To evaluate the challenges in setting acceptable levels for bromate in drinking water.
- To investigate the mechanism of bromate-induced carcinogenicity and its implications for risk assessment.
- To refine risk assessment strategies for bromate, considering its behavior at low doses and relevant tumor sites.
Main Methods:
- Review of existing methodologies for setting standards for genotoxic and non-genotoxic carcinogens.
- Analysis of bromate's toxicological data, including genotoxicity, dose-response relationships, and potential inactivation pathways.
- Comparison of risk assessment outcomes from different regulatory bodies (WHO, USEPA, Canada).
Main Results:
- Standard setting for genotoxic substances often relies on linear extrapolation, which is experimentally unverifiable at low doses.
- Bromate exhibits complex behavior, with evidence for genotoxicity but also potential non-linear dose-response and inactivation by antioxidants.
- Discrepancies in regulatory assessments highlight the sensitivity of outcomes to assumptions about linearity and relevant tumor sites.
Conclusions:
- The mechanism of bromate carcinogenicity remains uncertain, impacting the appropriateness of linear extrapolation for risk assessment.
- Accurate determination of acceptable bromate levels requires understanding its low-dose behavior and identifying the most relevant tumor sites for human risk.
- Refining risk assessment is crucial for setting practical and protective drinking water standards for bromate, especially concerning disinfection byproducts.
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