Options for incorporating children’s inhaled dose into human health risk assessment

Abstract

Increasing attention has been placed on inhalation dosimetry in children because of children’s greater air intake rate and unique windows of vulnerability for various toxicants and health outcomes. However, risk assessments have not incorporated this information because dosimetric adjustments have focused upon extrapolation across species rather than across age groups within the human population. The objectives of this study were to synthesize information regarding child/adult intake and dosimetry differences for particles and gases for potential application to risk assessment. Data and models gathered at a 2006 workshop and more recent studies were reviewed to better understand lung development and inhaled dose in children. The results show that child/adult differences exist both on a chemical intake basis and on a deposited or systemic dose basis. These differences can persist for several years and are not captured by standard intraspecies uncertainty factors or by USEPA’s reference concentration (RfC) methodology. Options for incorporating children’s inhalation exposures into human risk assessments include (1) 3-fold default air intake adjustment for the first 3 years of life with a reduced factor for older children; (2) superseding this default via simplified dosimetry models akin to USEPA’s RfC methodology modified for children; (3) utilizing more sophisticated models with better anatomical and air flow descriptions; (4) running these models with input distributions to reflect interchild variability; (5) developing more advanced approaches involving imaging techniques and computational fluid dynamic (CFD) models. These options will enable children’s inhaled dose to have a quantitative role in risk assessment that has been lacking and will establish a basis for ongoing research.

Acknowledgements

The authors appreciate the review and contributions made by Ami Parekh, ICF Services Company, L.L.C.

Declaration of interest

This project was funded by contract no. EP-W-04-049 between USEPA and ICF Services Company, L.L.C., with a subcontract (no. 28OR00785) arranged by ICF Services Company, L.L.C., with G.G.

Disclaimer: The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the University of Connecticut or United States Environmental Protection Agency.