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Drinking Water and Health, Volume 9 Selected Issues in Risk Assessment (1989) / Chapter Skim
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Executive Summary
Pages 95-100

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From page 95...
... Most experimental data relate to the toxic effects of exposures to single materials, yet exposure to two or more toxic materials might produce greater deleterious effects than would be anticipated from knowledge of the effects of each of the materials considered separately. Even as few as two materials can be present in infinite dose combinations, and relative doses might affect toxicity of the mixture.
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From page 96...
... The subcommittee recommends using a modified hazard index that sums similar toxicities, incorporates multiple toxic manifestations, and suggests, under some circumstances, the use of an uncertainty factor to allow for possible synergisms. The subcommittee reviewed earlier schemes for the arbitrary grouping of substances in its efforts to devise some classification schemes that could
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From page 97...
... . USING PHYSIOLOGICALLY BASED PHARMACOKINETIC MODELl NG The new field of physiologically based pharmacokinetics warrants attention as a first step in applying existing knowledge of mechanisms of toxicity.
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From page 98...
... The subcommittee considers it likely that, if a simple analytic process were developed to provide a summary measure of an entire class of toxicologically similar constituents in drinking water, it would also detect other, potentially confounding constituents in the water. APPLICATIONS-PROBLEMS OF EXPOSURE On a practical level, ambient exposures to mixtures usually involve low concentrations of the constituents.
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From page 99...
... However, like the National Research Council Committee on Methods for the In Vivo Toxicity Testing of Complex Mixtures, this subcommittee is aware that large exposures to several carcinogens have been shown to produce synergistic interactions-e.g., in a number of studies cigarette-smoking and exposure to asbestos appear to have combined to produce a greater than additive risk of cancer although the mechanisms of carcinogenesis (in this case of asbestos and cigarette smokeitself a highly complex mixture) might be different.
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From page 100...
... OTHER ISSUES The subcommittee is aware of the possibility of substantially increased risk to some persons associated with even small exposures to chemicals, but it did not address this extensively. Because of the genetic variability of humans or because of earlier sensitizing exposures, what is apparently lowdose exposure for the majority of the population might have serious effects in a small segment of the same population.
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Key Terms

  • single materials
  • risk associated
  • volatile organic
  • toxicologically similar
  • organic chemicals

  • physiologically based
  • individual components
  • toxic materials
  • low concentrations
  • specific organ

  • biologic isolation
  • factor required
  • anticholinesterase compounds
  • empirical evidence
  • multiple chemicals

  • toxic interactions
  • reviewed earlier
  • warrants attention
  • measured concentrations
  • mixture recommend

  • current approaches
  • based pharmacokinetics
  • toxic manifestations
  • pharmacokinetic modell
  • additional exposure

  • existing knowledge
  • chemical mixture
  • deleterious effects
  • cigarette smokeitself
  • developing appropriate


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