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Indoor and Outdoor Polycyclic Aromatic Hydrocarbons in Residences Surrounding a So1derberg Aluminum Smelter in Canada ERIC G. SANDERSON* AND J.-P. FARANT Department of Occupational Health, Faculty of Medicine, McGill University, 1130 Pine Avenue West, Montre´al, Que´bec, Canada H3A 1A3
Ambient air in 18 residences surrounding an aluminum smelter were sampled to study the relationship between indoor and outdoor polycyclic aromatic hydrocarbons (PAHs). Objectives of the study were to quantify the indoor distribution of PAHs, indoor/outdoor (I/O) concentration ratios, and the relationship among PAH compounds. Correlation coefficients inside residences suggested an indoor source of 2-3 ring PAHs and an external source of 4-6 ring PAHs. The I/O ratios of 4-6 ring PAHs for homes without any substantial indoor sources were below unity, indicating that the presence of these PAHs was attributable to the aluminum smelter. Least squares linear regression of the coupled measurements without indoor sources of 5-6 ring PAHs resulted in average infiltration efficiencies (PPAH) of 0.49, 0.20, and 0.47 for benzo[a]pyrene, benzo[k]fluoranthene, and benzo[g,h,i]perylene, respectively. These PPAH values suggest that simultaneous measurements of indoor and outdoor concentrations of PAHs > 4 rings predominantly associated with the fine fraction of particulate matter could provide useful estimates of particle infiltration efficiency. Overall, study results indicate that when an industrial facility is the main source of outdoor 4-6 ring PAHs, the contribution of facility emissions may greatly exceed indoor sources in nonsmoking residences.
Introduction The presence of airborne polycyclic aromatic hydrocarbon (PAHs) in residences has been linked to a combination of combustion sources. A number of studies have utilized gravimetric sampling or continuous monitoring to study the relationship between PAHs and indoor sources such as environmental tobacco smoke (ETS) (1-6), food preparation (4, 6, 7, 8), domestic heating (3, 5), and incense burning (9). Several studies have also documented the impact that the outdoor air (4, 10-12), and more specifically traffic (2, 1315), has on the quality of indoor air. Collectively, these studies indicate that nonsmoking residences tend to have 2-3 ring PAHs resulting primarily from food preparation and domestic heating (i.e. wood burning). The presence of the 4-7 ring PAHs has been largely attributed to the infiltration of outdoor air. The interface between indoor and outdoor levels is related * Corresponding author phone: +31 30 253 9496; fax: +31 30 253 9499; e-mail:
[email protected]. 5350
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to factors such as geographical location, outdoor concentrations, type of residence, building ventilation, and lifestyle (i.e. cooking methods and type of domestic heating fuel). Potential sources of indoor PAHs originating from outdoor air in Canada include anthropogenic activities such as So¨derberg aluminum smelting (16-20), iron and steel production (21, 22), road traffic (21), and domestic heating during cold weather (23). Currently no information on the relationship between indoor and outdoor PAH concentrations for a large industrial point source of PAHs is available for Canada. Nonetheless, two biological marker studies using urinary 1-hydroxypyrene (1-OHP) provide some indication on the burden of PAHs that could be linked to domestic and aluminum smelter emissions. For example, 1-OHP levels in residents living near a facility ( 4 rings could provide estimates of Finf. Given that the majority of the PAHs are found on fine particulate matter, an assumption of a particle-associated PAH infiltration efficiency of 50% recommended in the literature (39, 41) appears to be a good approximation for a typical closed residence. Although a larger portion of particulate matter could successfully penetrate the building envelope with closed doors and windows, only a fraction of the PAHs would remain suspended in the indoor air. This suggests that the important factors affecting the fate of the PAHs attached to particles are exfiltration and deposition of particles during transport through the building envelope, with little or no chemical degradation. However, to test such a hypothesis, a greater number of residences and studies are needed to investigate infiltration of particulate matter from outdoors and the related decay processes for the associated PAHs. In conclusion, concentrations of PAHs in the vicinity of the aluminum smelter had indoor and outdoor levels that were lower than reported elsewhere. The lower concentrations may, in part, be due to prevailing winds that were not predominantly from the HSS facility toward the homes during the entire 24-h sampling period and breakthrough for some of the 2-4 ring PAHs during sample collection. Nonetheless, potential exposure of individuals to 4-6 ring PAHs in closed residences during occupancy could be, at a minimum, as much as 50% of levels measured by a nearby fixed monitoring site. For this particular region, the HSS aluminum smelter is the main contributor of the indoor 4-6 ring PAHs in the absence of other combustions sources (i.e. traffic, domestic heating, and cooking). In perspective, this should not be a cause for concern when outdoor concentrations of the carcinogenic PAHs are at low levels. Total contribution to indoor concentrations from industrial facilities is also unlikely due to other important factors such as the time of year, size of the community, and lifestyle of the general population. VOL. 38, NO. 20, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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Acknowledgments The authors are grateful to the study volunteers for their cooperation and letting us into their homes. We are thankful for the technical assistance of several employees of the Beauharnois aluminum smelter, specifically Janick Potvin, Genevie`ve Latour, Pierre Henley, and Didier Chapron, without whom this project would not have been successful. We also acknowledge Stephanie Corcoran (MASc Student) and Daniel Bouchard (Department of National Defense, Canada) for their contributions to this project. The authors would especially like to thank Richard Lapointe from Alcan Incorporated for his comments and continuing support.
Supporting Information Available Detailed description of the residences (Table S1), a descriptive profile of the residences during sampling (Table S2), and a summary of the Pearson correlation coefficients for the indoor and outdoor sample concentrations (Table S3). This material is available free of charge via the Internet at http:// pubs.acs.org.
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Received for review December 8, 2003. Revised manuscript received June 1, 2004. Accepted August 3, 2004. ES030715C
