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Issues in Risk Assessment (1993) / Chapter Skim
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5 Conclusions and Recommendations
Pages 61-66

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From page 61...
... The current MTD bioassay in rodents closed that gap and became the standard assay in the United States. It is neither perfect nor unalterable, and by itself it is insufficient to produce data from which accurate human health risk assessments can be made.
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From page 62...
... Because of the relationship between TD50s and MTDs of chemicals, the committee concludes that a preliminary upper bound on the potential carcinogenic potency of an untested chemical can be estimated from knowledge of its MTD. Such estimates can prove useful in setting priorities for carcinogenicity testing and in making preliminary upper-bound risk estimates of cancer risk whenever carcinogenicity bioassay results are not available.
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From page 63...
... A majority of the committee believes that the assay identifies substances that do or do not increase the incidence of cancer under the conditions of the assay and provides an operational definition of animal noncarcinogens The assay also identifies target organs, demonstrates tumor types associated with exposure, provides a consistent basis for interspecies comparisons, and can serve as a guide in designing followup studies. The majority also believes that there are as yet no validated mechanisms of carcinogenicity that support lowering the MTD and that failing to use the MTD for carcinogen screening will reduce the sensitivity of the bioassay and diminish the opportunity to compare results among chemicals and species.
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From page 64...
... If a bioassay conducted with the MTD is positive, additional studies should be performed to reduce uncertainties in predicting human responses to the test material and to assist in performing quantitative risk assessments. These additional studies should address mechanisms of cancer induction, toxicokinetics and metabolism of the material, and and physiologic responses induced by the material; they could also include validation of MTD bioassay results with epidemiologic studies.
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From page 65...
... Please use the print version of this publication as the authoritative version for attribution. after any stage in data collection.
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From page 66...
... Please use the print version of this publication as the authoritative version for attribution.CONCLUSIONS AND RECOMMENDATIONS 66
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Key Terms

  • mtd bioassay
  • carcinogenicity bioassays
  • human risk
  • additional studies
  • bioassay results

  • careful evaluation
  • responses induced
  • risk assessments
  • studies conducted
  • cell proliferation

  • carcinogenicity testing
  • target cells
  • animal noncarcinogens
  • risk whenever
  • quantitative risk

  • designing followup
  • reach consensus
  • additional tests
  • untested chemical
  • overall toxic

  • proposed mechanistic
  • doses near
  • toxic effects
  • human response
  • effects measured

  • upper bound
  • standard set
  • rodents closed
  • low doses
  • perfect nor


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