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7 Hazard Considerations and Study Selection for Deriving Toxicity Values
Pages 76-81

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From page 76...
... The chapter also includes directions for characterizing sources of uncertainty and confidence in the derived toxicity values. RESPONSIVENESS TO PREVIOUS NATIONAL ACADEMIES REPORTS Previous reviews by the National Academies commented heavily on the processes used for selecting studies, and the current handbook attempted to address these concerns.
From page 77...
... The 2014 National Academies report recommended that EPA develop IRIS-specific guidelines for communicating uncertainty, and, in response, Chapter 13 of the handbook includes a section on characterizing uncertainty and communicating confidence in the derived toxicity values. CRITIQUE OF METHODS FOR STUDY SELECTION AND DERIVING TOXICITY VALUES Chapters 12 and 13 of the handbook focus on steps to be taken after systematic review, specifically the processes by which studies are selected and toxicity values are derived, and many aspects of sections in those chapters positively add to the overall assessment process.
From page 78...
... Similar to the previous chapters, Chapter 12 is unclear as to how mechanistic data and other supporting studies should be used, or how this information should be incorporated into the assessment process. The chapter suggests that summary tables be used to document study selection and graphical comparisons be used for toxicity value selection, but no examples are provided, leaving the design up to those conducting an IRIS assessment.
From page 79...
... for the IRIS program to transition away from using traditional deterministic approaches for deriving reference values and instead use probabilistic methods to derive risk-specific values. Since the 2014 National Academies report, several publications have further refined probabilistic approaches (e.g., Chiu and Slob, 2015; WHO & IPCS, 2018)
From page 80...
... Because the handbook does not clearly distinguish between evaluations made as part of hazard identification and considerations specific to toxicity value derivation, an analyst may be led to repeat evaluations made earlier in the assessment process. Recommendation 7.1: The handbook should provide a clearer, step-by-step de scription of study selection, using a framework incorporating the different steps of hazard identification (including study evaluation, synthesis, and integration)
From page 81...
... Finding and Tier 3 Recommendation Finding: Chapter 13 of the handbook is primarily a reference chapter that directs users to various historical EPA guidance documents for deriving toxicity values, most of which have not been updated to reflect the most recently used procedures. The IRIS program and its handbook would benefit from being able to refer to updated EPA guidance.

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