Predicting personal exposure of Windsor, Ontario residents to volatile organic compounds using indoor measurements and survey data
Introduction
To date, many studies have relied upon ambient fixed-site monitoring stations such as Environment Canada's National Air Pollution Surveillance (NAPS) network to characterize population air pollution exposures. However, research has consistently shown that ambient concentrations of volatile organic compounds (VOCs) are often much lower than corresponding personal exposure levels (Wallace et al., 1985; Anderson et al., 2001; Edwards et al., 2001; Kim et al., 2002; Adgate et al., 2004; Sexton et al., 2004a, Sexton et al., 2004b). Therefore, those epidemiological studies employing outdoor measurements may result in exposure measurement error and biased risk estimates (Payne-Sturges et al., 2004). This in turn may constitute a substantial source of uncertainty for risk-based regulatory decision making.
Few studies such as this one obtain simultaneous repeated measurements for personal, indoor, and outdoor concentrations of air pollutants using Summa™ canisters, as well as collect information relevant to characterizing exposure based on participant's daily activities, housing characteristics, and proximity to point sources (Edwards et al., 2001; Adgate et al., 2004; Sexton et al., 2007). Additionally, this study is particularly unique as it collected a total of 10 repeated measurements within two seasons per participant.
Windsor, Ontario was selected, as several local industries, including automotive manufacturing plants, long lines of idling trucks at the border between Canada and the US, and long-range transportation of air pollution from the north eastern US (Diamond and Parker, 2004; Ontario Ministry of Environment, 2007) have made poor air quality a concern for both residents and authorities. Comparison of Canadian and US time activity databases by Leech et al. (2002) also revealed that Canadian adults spend on average 2% less time outdoors in the winter and over 4% less time indoors at home in the summer than their US adult counterparts, which could result in small differences in exposure to air pollutants. However, in general, like in most industrialized countries, Canadians, spend between 80% and 90% of their time indoors, which includes at home, at work, in restaurants and in shopping centers (Klepeis et al., 2001; Leech et al., 2002; Schweizer et al., 2007).
The objectives of the study were to:
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understand exposure patterns of individuals residing in a community impacted by a range of different pollutant sources;
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describe indoor, outdoor and personal VOC levels within a Canadian city and study seasonal differences;
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investigate the relationships between indoor, outdoor and personal concentrations of different VOCs to identify environmental sources;
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identify reasons for differences in exposure through the development of personal prediction models, thereby identifying contributing factors captured by the participant time activity diary, the daily monitoring questionnaire (use of household and personal care products) and the baseline survey (housing characteristics).
This paper presents descriptive results for 18 VOCs with detailed personal modeling for 14 of them. Results of this study provide relevant Canadian information on exposure to several VOCs that are on the Canadian Environmental Protection Act (CEPA, 1999) Toxic Substances List.
Section snippets
Collection of data
Over 8 successive weeks per session, six of the 48 homes were sampled concurrently for 5 consecutive days, beginning on a Monday (day 0) and ending on a Saturday (day 5). At 24±3 h intervals, teams of two technicians visited each home to change samplers, check equipment and administer questionnaires. Air samples were collected using cleaned and evacuated Summa™ canisters. At each home, three VOC canisters were deployed every 24 h. One 6.0 L canister was placed inside the participant's home,
Description of VOC concentrations, and air exchange rates
Table 1 summarizes MDLs, detection frequencies and geometric means for the 18 VOCs in both seasons, within all three exposure categories. As previously stated, acrylonitrile, ethylene oxide, hexachlorobutadiene and vinylchloride were removed from further analysis due to a significant number of non-detectables.
Seasonal variations in VOC concentrations are associated with differences in emission sources and rates, temperature, and to the rate of reactions with other chemicals. Not surprisingly,
Conclusions
Summa™ canisters were used to obtain personal, indoor and outdoor concentrations of VOCs allowing us to observe the relationships between seasons, microenvironments and a select number of VOCs. Not surprisingly, the concentrations of the majority of VOCs were higher in the summer than in the winter with indoor concentrations contributing more to personal exposures than outdoor concentrations. Results of mixed effects models indicate that personal exposure to these VOCs can be largely predicted
Acknowledgments
We would like to thank the study participants and Health Canada staff Ryan Kulka, Hongyu You, Keith Van Ryswyk, Dave Van Rijswijk and Alison Jones for their enormous efforts. We would also like to thank the students of the University of Windsor, Air Zone and Environment Canada staff Anita Philipose and Luyi Ding. We also wish to thank Dr. Jeremy Sarnat, Dr. Allen Vette, Dr. Miranda Loh and Dr. Sonja Sax for their guidance and Dr. Paul Villeneuve and Nicolas Gilbert for their valued comments on
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