A source-to-dose assessment of population exposures to fine PM and ozone in Philadelphia, PA, during a summer 1999 episode

Abstract

A novel source-to-dose modeling study of population exposures to fine particulate matter (PM 2.5 ) and ozone (O 3 ) was conducted for urban Philadelphia. The study focused on a 2-week episode, 11-24 July 1999, and employed the new integrated and mechanistically consistent source-to-dose modeling framework of MENTOR/SHEDS (Modeling Environment for Total Risk studies/Stochastic Human Exposure and Dose Simulation). The MENTOR/ SHEDS application presented here consists of four components involved in estimating population exposure/dose: (1) calculation of ambient outdoor concentrations using emission-based photochemical modeling, (2) spatiotemporal interpolation for developing census-tract level outdoor concentration fields, (3) calculation of microenvironmental concentrations that match activity patterns of the individuals in the population of each census tract in the study area, and (4) population-based dosimetry modeling. It was found that the 50th percentiles of calculated microenvironmental concentrations of PM 2.5 and O 3 were significantly correlated with census-tract level outdoor concentrations, respectively. However, while the 95th percentiles of O 3 microenvironmental concentrations were strongly correlated with outdoor concentrations, this was not the case for PM 2.5 . By further examining the modeled estimates of the 24-h aggregated PM 2.5 and O 3 doses, it was found that indoor PM 2.5 sources dominated the contributions to the total PM 2.5 doses for the upper 5 percentiles, Environmental Tobacco Smoking (ETS) being the most significant source while O 3 doses due to time spent outdoors dominated the contributions to the total O 3 doses for the upper 5 percentiles. The MENTOR/SHEDS system presented in this study is capable of estimating intake dose based on activity level and inhalation rate, thus completing the source-to-dose modeling sequence. The MENTOR/SHEDS system also utilizes a consistent basis of source characterization, exposure factors, and human activity patterns in conducting population exposure assessment of multiple co-occurring air pollutants, and this constitutes a primary distinction from previous studies of population exposure assessment, where different exposure factors and activity patterns would be used for different pollutants. Future work will focus on incorporating the effects of commuting patterns on population exposure/dose assessments as well as on extending the MENTOR/SHEDS applications to seasonal/annual studies and to other areas in the U.S.

Biologically based modeling of multimedia, multipathway, multiroute population exposures to arsenic

“…To improve the exposure assessment approach further, the methodology first developed for the SHEDS model was modified and incorporated through new, generalized code into the Modeling ENvironment for TOtal Risk studies (MENTOR) (Georgopoulos et al, 2005(Georgopoulos et al, , 2006bGeorgopoulos and Lioy, 2006;Georgopoulos, 2007), which is designed to analyze not only exposures to individual contaminants but to assess physiologically based target tissue dose to Multiple co-occurring contaminants and Multimedia, Multipathway, Multiroute exposures (4M) for specific individuals or for studyspecific populations. MENTOR-4M, in addition to addressing the issue of simultaneous exposures to multiple contaminants for any specific individual within the population of concern, provides a new, enhanced framework of source-to-dose analyses, as it allows calculations of tissue-specific dose (and corresponding biomarker levels), employing Physiologically Based Pharmacokinetic (PBPK) modeling.…”

An approach for estimating exposure to ambient concentrations

“…Such fields can contribute to epidemiological studies by allowing more spatial and temporal information to be incorporated in the exposure fields, and by enabling cohort studies to take advantage of the information in daily activity diaries. It should be noted although that spatially interpolated fields of ambient concentrations are just one component of personal exposure models, such as MENTOR/SHEDS (Georgopoulos et al, 2005) and the Urban Exposure Management tool (Floisand et al, 2006). These models also take account of residential and occupational environments, journey-time exposure (Gulliver and Briggs, 2005) and air flow that actually enters the human respiratory tract.…”

A Focus on Particulate Matter and Health

“…They find, in part, that there is a difference between the deposition rates of hydrophobic and curbside particles, largely determined by their hygroscopicity. Such results can be used to evaluate recent model developments, such as recent sourceto-dose modeling that estimates the spatial-and sourcespecific intake of pollutants (48).…”