Distributions for time, interspecies and intraspecies extrapolation for deriving occupational exposure limits.

Area of Science:

• Toxicology
• Occupational Health
• Risk Assessment

Background:

• Deriving occupational exposure limits (OELs) involves complex extrapolation steps with inherent uncertainties.
• Existing methods for time, interspecies, and intraspecies extrapolation require empirical database improvements.

Purpose of the Study:

• To improve the empirical database for time, interspecies, and intraspecies extrapolation in OEL derivation.
• To develop distributions modeling uncertainties associated with each extrapolation step.
• To inform the selection of assessment factors (AFs) for OEL setting.

Main Methods:

• Utilized National Toxicology Program (NTP) and REACH data for time and interspecies extrapolation.
• Compiled human toxicokinetic and toxicodynamic variability studies for intraspecies extrapolation.
• Developed distributions of dose descriptor ratios and interindividual susceptibility.

Main Results:

• NTP data yielded more reliable results than REACH data.
• Geometric means for time extrapolation were consistent with or slightly higher than previous evaluations.
• Intraspecies variability distributions showed medians of 7.25 (1% incidence) and 3.56 (5% incidence).
• Derived distributions for interspecies extrapolation confirmed allometric scaling suitability.
• Assessment factors (AFs) currently used in the EU show variable protection probabilities (10%-95%).

Conclusions:

• The study provides a robust database and methods for transparent and informed selection of AFs.
• The findings support harmonization of OEL derivation methods by comparing achieved protection levels.
• Improved extrapolation models enhance the reliability of occupational exposure limits.