Modeling Human Exposure to Indoor Contaminants: External Source to Body Tissues

A quest to identify suitable organic tracers for estimating children's dust ingestion rates

Chemical exposure via dust ingestion is of great interest to researchers and regulators because children are exposed to dust through their daily activities, and as a result, to the many chemicals contained within dust. Our goal was to develop a workflow to identify and rank organic chemicals that could be used as tracers to calculate children's dust ingestion rates. We proposed a set of criteria for a chemical to be considered a promising tracer. The best tracers must be (1) ubiquitous in dust, (2) unique to dust, (3) detectable as biomarkers in accessible biological samples, and (4) have available or obtainable ADME information for biomarker-based exposure reconstruction. To identify compounds meeting these four criteria, we developed a workflow that encompasses non-targeted analysis approaches, literature and database searching, and multimedia modeling. We then implemented an ad hoc grading system and ranked candidate chemicals based on fulfillment of our criteria (using one small, publicly available dataset to show proof of concept). Initially, five chemicals (1,3-diphenylguanidine, leucine, piperine, 6:2/8:2 fluorotelomer phosphate diester, 6:2 fluorotelomer phosphate diester) appeared to satisfy many of our criteria. However, a rigorous manual investigation raised many questions about the applicability of these chemicals as tracers. Based on the results of this initial pilot study, no individual compounds can be unequivocally considered suitable tracers for calculating dust ingestion rates. Future work must therefore consider larger datasets, generated from broader measurement studies and literature searches, as well as refinements to selection criteria, to identify robust and defensible tracer compounds.

Modeling the bioaccessibility of inhaled semivolatile organic compounds in the human respiratory tract

The bioaccessibility of semivolatile organic compounds (SVOCs) via inhalation has rarely been studied, as indicated by the literature. There is no model to calculate the SVOC bioaccessibility following inhalation, and measurement data have focused on only a few polycyclic aromatic hydrocarbons (PAHs) in the particle phase. The present work developed a mechanistic model to address the mass transfer of inhaled SVOCs among the gas, particle and mucus phases in the human respiratory tract. The model considers (1) the SVOC partitioning between the gas and particle phases as well as between the gas and mucus phases and (2) the deposition of gas- and particle-phase SVOCs in the mucus of the respiratory tract. Based on the model, the inhalation bioaccessibility for 72 SVOCs was calculated. The SVOCs were measured in French dwellings at the nationwide scale, and their median concentrations in both the gas and particle phases were used for the bioaccessibility calculations. The results show that the inhalation bioaccessibility varies considerably from one compound to another, e.g., between 0.62 and 1.00 for phthalates, between 0.71 and 0.79 for polybrominated diphenyl ethers (PBDEs), between 0.48 and 0.56 for polychlorinated biphenyls (PCBs), between 0.48 and 1.00 for different chemical families of pesticides and between 0.48 and 0.90 for PAHs.