International Programme on Chemical Safety

Chemical-Specific Adjustment Factors (CSAF)

In 2005 WHO published guidance for risk assessors on the use of chemical-specific toxicokinetic and toxicodynamic data to address interspecies differences and interindividual differences (human variability) in dose/concentration-response assessment, for example, in the process of estimating tolerable intakes or margins of exposure. The use of factors derived in this way has the potential to reduce uncertainty and better characterize variability compared to the use of traditional default uncertainty factors.

In 2015-16, a project was undertaken under the WHO Chemical Risk Assessment Network to review and summarize the state-of-the-science in this topic area in the period since the 2005 guidance was published. A Working Group of experts from Network institutions carried out an analysis of more than 100 examples of chemical risk assessments obtained from global regulators or from the published literature. A summary of the lessons learned and the challenges associated with CSAF development identified from the analysis of these examples was published in a journal article.

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