Dose-Response Assessment

The process for deriving the UL is described in this section and is summarized in Box 3-1. It includes selection of the critical data set, identification of a critical endpoint with its NOAEL (or LOAEL), and assessment of uncertainty.

Box 3-1

Development of Tolerable Upper Intake Levels (ULs)



  • Evidence of adverse effects in humans

  • Causality

  • Relevance of experimental data

  • Mechanisms of toxic action

  • Quality and completeness of the database

  • Identification of distinct and highly sensitive subpopulations



  • Data selection

  • Identification of no-observed-adverse-effect level (NOAEL) (or lowest-observed-adverse-effect level [LOAEL]) and critical endpoint

  • Uncertainty assessment

  • Derivation of a UL

  • Characterization of the estimate and special considerations

Data Selection

The data evaluation process results in the selection of the most appropriate or critical data set(s) for deriving the UL. Selecting the critical data set includes the following considerations:

  • Human data are preferable to animal data.

  • In the absence of appropriate human data, information from an animal species whose biological responses are most like those of humans is most valuable.

  • If it is not possible to identify such a species or to select such

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