Grantee Research Project Results
2000 Progress Report: Characterization of Factors Determining Personal Exposure to Volatile Air Toxics in Urban Environments
EPA Grant Number: R826786Title: Characterization of Factors Determining Personal Exposure to Volatile Air Toxics in Urban Environments
Investigators: Esmen, Nurtan A. , Gibson, Aaron , Marcham, C. , Wang, D. , Agron, Gina , Lynch, Robert A. , Hall, Thomas A. , Moss, S. K. , Johnson, D. L. , Phillips, M. L.
Current Investigators: Esmen, Nurtan A. , Wang, D. , Lynch, Robert A. , Hall, Thomas A. , Johnson, D. L. , Phillips, M. L.
Institution: University of Oklahoma Health Sciences Center
EPA Project Officer: Chung, Serena
Project Period: October 1, 1998 through September 30, 2001 (Extended to September 30, 2002)
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $559,352
RFA: Urban Air Toxics (1998) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics
Objective:
The primary objective of the research project is to investigate how external factors influence the relationship between personal exposures and area measurements of air toxics and air particulate matter. Using a multi-city, multi-season factorial design, we are studying the distribution of personal exposures in relation to eight dichotomous macro-environmental and household factors, which are hypothesized to influence personal activity and exposure patterns. These are: (1) the size, (2) industrialization level of urban area, (3) high/low and extreme/mild seasonal temperature, (5) precipitation/no precipitation, (6) workday/off-day, (7) presence/absence of children in household, and (8) blue collar/white collar socioeconomic status.Progress Summary:
The second year of the project was devoted to the collection and analysis of field samples. To date, we recruited 31 male and 54 female subjects for the study. There were several problems encountered with the power supply of the satellite-based global positioning system (GPS). While the problems encountered do not limit the scope of the study, we are experimenting with several power supply systems to correct the difficulties encountered. The utility and the problems of the GPS system is reported in a soon to be published article.
The preliminary quantitative and qualitative analysis of the data collected from Oklahoma City study subjects with respect to the spectrum of toxic agents that constitute daily exposure experienced by these study subjects showed several interesting observations. The study subjects hitherto analyzed were primarily white collar workers, homemakers, and workers in blue collar service occupations. Personal breathing zone and area air samples were collected over a 24 hr. period using multi-bed carbon matrix thermal desorption tubes at a flow rate of approximately 35 mL/min. The monitoring period was divided between two 12-hour samples representing "nighttime" and "daytime" exposures. Area samples were collected in the subject's home and immediately outside the home. Samples were analyzed by GC/MS. Quantification of exposure concentrations was performed for toluene, benzene, hexane, acetone, trimethylbenzene, o- and p-xylene, ethylbenzene, tetrachloroethylene, octane, and dichlorobenzene. Toluene, benzene, o- and p-xylene, and ethylbenzene were commonly detected in personal samples for both day and night. Volatile organics commonly detected but not quantified included natural oils such as pinene, limonene, and eucalyptol, and aliphatic hydrocarbons probably associated with gasoline. Measured benzene personal exposures were typically less than 1 part per billion (ppb) while other quantified exposures ranged as high as 5 ppb. Ambient concentrations inside the home were typically higher than concentrations immediately outside the home. The preliminary results of this investigation indicated significantly different exposure patterns with some diurnal variation of ambient air toxics concentrations. Personal exposures were typically in the low ppb range and related to personal or work activities.
As part of the study, fan pressurization (blower door) measurements were performed to determine the permeability of the residences of some of the research subjects. The study is limited to detached single-family dwellings. The date of construction of homes in this study is more or less evenly distributed by decade from the 1930s through the 1990s. The ASHRAE Standard 119 "normalized leakage" (NL) was estimated by dividing the air exchange rate at 50 Pa by 20 or 16 for 1-story and 2-story dwellings, respectively. NL was correlated with the number of doors and windows, the age of the home, and the presence of a basement or crawl space under the home. However, these three factors tended to cluster together: newer homes were typically built on slabs and had fewer windows than older homes. Applying the criteria of Sherman (Lawrence Berkeley Laboratory, 1998) for appropriate infiltration levels based on the ASHRAE 119 leakage class of the home, approximately one-third of the homes in this study were so airtight that additional ventilation would be recommended. Nearly all homes that were found to be "too tight" were built after 1980.
These results suggest that many newer residences may be too airtight to allow adequate natural ventilation to dilute air contaminants generated from the use of consumer products inside the home. Interestingly, many of the research subjects expressed a perception that their homes were very leaky even though the homes would not be considered too loose by Sherman's criteria. Under these circumstances, concern over energy efficiency and reducing drafts may lead homeowners to tighten their dwellings without recognizing the loss of necessary infiltration of fresh air.
On the theoretical portion of the study, the difference in delivered dose for different "respirable-equivalent" aerosols with different size distributions is investigated. With the "respirable equivalence" is defined as two sampled aerosols resulting in the same mass concentration measure using a respirable dust measuring device. We used the ACGIH/ISO/CEN Respirable Fraction criterion and widely reported alveolar deposition efficiencies to calculate the dose variability introduced solely by changing the size distribution. The calculations showed that on a mass basis, the dose differences can range from negligible to approximately 9 fold. These results are surprising. Because, on the basis of number of particles, the dose difference can be more than two orders of magnitude. The calculations also showed that both the median size and geometric standard deviation of the aerosols are important. Applied to fumes and/or atmospheric condensation aerosols, results indicate that the exposure to the same respirable concentration or PM2.5 concentration of a freshly generated aerosol can be significantly different from the dose to the aged aerosol, even though the two are equivalent on a penetration-based definition. We conclude that when considering inhalation of respirable aerosols and atmospheric particles mainly observed in this study, it may be important to consider the effect of aerosol size distribution on delivered dose to respirable tissues instead of a single number measure of a particulate air toxic.
In this study, we are often faced with problems encountered in the comparison of measurements made by different sampling and/or analysis methods or the comparison of two or more samplers located in a close proximity. Clearly, the intercomparison between compatible methods (e.g., personal vs. personal) is preferred to the intercomparison between incompatible methods (e.g., personal vs. area). We have investigated the five readily available procedures for the comparative analysis of the exposure data (linear regression with displacement and rotation tests, reduced major axis regression, principle component regression, structural regression or Bland-Altman residuals). However, each of these procedures has certain restrictions and data requirements that make it preferable for specific exposure data sets. The theoretical analyses showed that by lowering the one's expectations on the accuracy and reproducibility, these readily available procedures provide either reasonable answers to the information sought or point out the magnitude of the problem. In addition, the theoretical analysis suggested that the structural regression is readily applicable for the data analysis to be used in this study.
Future Activities:
With the available study subject recruits, the investigators will continue with the major sampling phase of the study. The final year of the research will be devoted to the completion of sampling and the full analysis of the collected data.Journal Articles:
No journal articles submitted with this report: View all 27 publications for this projectSupplemental Keywords:
monitoring, South Central, particulates, air toxics., RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, Toxics, ENVIRONMENTAL MANAGEMENT, Geographic Area, particulate matter, Air Quality, air toxics, Environmental Chemistry, Health Risk Assessment, HAPS, State, VOCs, Risk Assessments, Biochemistry, Physical Processes, Children's Health, indoor air, Atmospheric Sciences, Ecology and Ecosystems, 33/50, Risk Assessment, ambient air quality, health effects, personal exposure, urban air toxics, Hexane, exposure and effects, Toluene, air pollutants, air quality models, ambient air, Xylenes, Ethyl benzene, fine particulates, exposure, air pollution, modeling, benzene, children, human exposure, hazardous air pollutants (HAPs), urban air pollution, PM, indoor air quality, fine particle levels, Volatile Organic Compounds (VOCs), Oklahoma (OK), 2, 2, 4-Trimethylpentane, Benzene (including benzene from gasoline), Styrene, Xylenes (isomers and mixture), activity patterns, exposure assessmentRelevant Websites:
http://w3.ouhsc.edu/oeh/oeh-home.htm
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.