Cancer risk assessment for dioxane based upon a physiologically-based pharmacokinetic approach

Area of Science:

• Toxicology
• Pharmacokinetics
• Risk Assessment

Background:

• A 1974 bioassay showed dioxane increased liver tumors in rats at high doses.
• Conventional risk extrapolation assumes human sensitivity is 5.5 times higher than rats.
• This method may overestimate human cancer risk due to dioxane's saturable metabolism.

Purpose of the Study:

• To develop a physiologically-based pharmacokinetic (PB-PK) model for dioxane.
• To establish a quantitative link between administered and internal dioxane doses.
• To accurately estimate human cancer risk from lifetime dioxane exposure.

Main Methods:

• Developed a physiologically-based pharmacokinetic (PB-PK) model for dioxane.
• Used time-weighted average liver dioxane concentration as a dose surrogate.
• Extrapolated rodent bioassay data to estimate human risk at low exposure levels.

Main Results:

• The PB-PK model identified a human cancer risk dose surrogate of 280 µmol/L (59 mg/kg/day) for a 10(-5) risk level.
• The 95% lower confidence limit for the dose surrogate was 1.28 µmol/L (0.8 mg/kg/day).
• Conventional risk assessment may overestimate human dioxane cancer risk by up to 80-fold.

Conclusions:

• Physiologically-based pharmacokinetic modeling provides a more accurate human risk assessment for dioxane.
• Uncorrected extrapolation from rodent bioassays overestimates dioxane's carcinogenic risk to humans.
• This PB-PK approach refines safe exposure limits for dioxane by accounting for metabolic differences.