Is radon-222 ingestion a settled environmental exposure pathway?

Area of Science:

• Environmental Science
• Radiological Health
• Toxicology

Background:

• Radon-222 ingestion from drinking water is considered a minor exposure pathway compared to inhalation.
• The U.S. National Academy of Sciences (NAS) model estimates ingestion contributes ~10% of the total radon dose.
• This partition relies on a poorly constrained biological parameter: radon absorption across the gastric wall.

Purpose of the Study:

• To re-evaluate the significance of radon-222 ingestion from drinking water.
• To challenge the established inhalation-to-ingestion dose ratio.
• To highlight the impact of unresolved biokinetic parameters on risk assessment.

Main Methods:

• Analysis of the NAS modelling framework and its underlying biokinetic parameters.
• Review of international guidance and regulatory practices for radon exposure.
• Examination of radon's role within the uranium-238 decay chain and its impact on ingestion dose.

Main Results:

• The 90/10 inhalation-ingestion partition is an estimate, not empirically constrained.
• Plausible values for the absorption parameter span two orders of magnitude.
• Radon dissolved in water acts as a transfer mechanism for other decay products.
• Standard models neglect in-vivo decay and progeny production under current assumptions.

Conclusions:

• Radon ingestion should not be considered a quantitatively resolved exposure pathway.
• The established inhalation-to-ingestion partition may be inaccurate due to modelling continuity and regulatory convention.
• Further research is needed to empirically constrain biokinetic parameters for accurate radon risk assessment.