Journal of Exposure Science and Environmental Epidemiology (2007) 17, 288–297 r 2007 Nature Publishing Group All rights reserved 1559-0631/07/$30.00 www.nature.com/jes Indoor ultrafine particle exposures and home heating systems: A cross-sectional survey of Canadian homes during the winter months SCOTT WEICHENTHAL, ANDRE DUFRESNE, CLAIRE INFANTE-RIVARD AND LAWRENCE JOSEPH Department of Epidemiology, Biostatistics and Occupational Health, Faculty of Medicine, McGill University, Que´bec, Canada Exposure to airborneparticulate matter has a negative effect onrespiratory health inboth childrenandadults. Ultrafineparticle (UFP) exposures a re of particular concern owing to their enhanced ability to cause oxidative stress and inflammation in the lungs. In this investigation, our objective was to examine the contribution of home heating systems (electric baseboard heaters, wood stoves, forced-air oil/natural gas furnace) to indoor UFP exposures. We conducted a cross-sectional survey in 36 homes in the cities of Montre´ al, Que´ bec, and Pembroke, Ontario. Real-time measures of indoor UFP concentrations were collected in each home for approximately 14 h, and an outdoor UFP measurement was collected outside each home before indoor sampling. A home-characteristic questionnaire was also administered, and air exchange rates were estimated using carbon dioxide as a tracer gas. Average UFP exposures of 21,594 cmÀ3 (95% confidence interval (CI): 14,014, 29,174) and 6660 cmÀ3 (95% CI: 4339, 8982) were observed for the evening (1600–2400) and overnight (2400–0800) hours, respectively. In an unadjusted comparison, overnight baseline UFP exposures were significantly greater in homes with electric baseboard heaters as compared to homes using forced-air oil or natural gas furnaces, and homes using wood stoves had significantly greater overnight baseline UFP exposures than homes using forced-air natural gas furnaces. However, in multivariate models, electric oven use (b ¼ 12,253 cmÀ3, 95% CI: 3524, 20,982), indoor relative humidity (b ¼ 1136 cmÀ3 %, 95% CI: 372, 1899), and indoor smoking (b ¼ 18,192 cmÀ3, 95% CI: 2073, 34,311) were the only significant determinants of mean indoor UFP exposure, whereas air exchange rate (b ¼ 4351 cmÀ3 hÀ1, 95% CI: 1507, 7195) and each 10,000 cmÀ3 increase in outdoor UFPs (b ¼ 811 cmÀ3, 95% CI: 244,1377) were the only significant determinants of overnight baseline UFP exposures. In general, our findings suggest that home heating systems are not important determinants of indoor UFP exposures. Journal of Exposure Science and Environmental Epidemiology (2007) 17, 288–297. doi:10.1038/sj.jes.7500534; published online 11 October 2006 Keywords: ultrafine particles, exposure assessment, indoor air quality, indoor particle sources. Introduction Hohr et al., 2002; Nygaard et al., 2004), with a recent study reporting a threshold dose of 20 cm2 for acute lung inflamma- Ultrafine particles (UFPs) have diameters less than 100 tioninmice (Stoeger et al., 2006). However, the chemical nanometers (nm), and although they contribute little to compositionof UFPs likely also plays role indeterminingtheir airborne particle mass, they are the predominant particle overall toxicity (Ovrevik and Schwarze, 2006). size by number (Donaldson et al., 2001; Oberdo¨ rster et al., UFPs are efficiently deposited in the human airway 2005). In recent years, increased attention has focused on the (Wilson et al., 1985; Jaques and Kim, 2000; Kim and respiratory effects of UFPs as animal studies have consis- Jaques, 2005), with the majority of 20–100 nm particles tently demonstrated their ability to generate oxidative stress depositing in the respiratory bronchioles and alveoli (Bolch and inflammation in the lungs (Oberdo¨ rster et al., 1994; Li et al., 2001; Lazardis et al., 2001). People with asthma or et al., 1996; Afaq et al., 1998; Zheng et al., 1998; Brown chronic obstructive pulmonary disease may be particularly et al., 2001; Dick et al., 2003; Zhou et al., 2003a, b; Gilmour susceptible to the respiratory effects of UFPs, as deposition et al., 2004; Gilmour et al., 2004; Shwe et al., 2005). Several is greater inthese individuals (Brownet al., 2002; Chalupa studies suggest that the large surface area of UFPs is an et al., 2004). Indeed, ambient UFP concentrations have important determinant of their ability to cause airway beenassociated with a decrease inpeak expiratory flow rate inflammation (Oberdo¨ rster et al., 1994; Brownet al., 2001; (Peters et al., 1997; Penttinen et al., 2001) as well as wheezing, shortness of breath, and cough in asthmatic adult populations (Von Klot et al., 2002). Similar investigations 1. Address all correspondence to: Scott Weichenthal, Department of have beenconductedinpopulationsof asthmatic children Epidemiology, Biostatistics and Occupational Health, Faculty of Medi- (Pekkanen et al., 1997; Tiitanen et al., 1999), but separating cine, McGill University, 3450 University Street, FDA Building room 31, the independent effects of different sized particles was difficult Montre´ al, Que´ bec, Canada H3A 2A7. Tel: þ 1 514 495 2905. in these studies owing to their high inter-correlations. Fax: þ 1 514 398 7153. E-mail: [email protected] Received 1 May 2006; accepted 31 July 2006; published online 11 October Nevertheless, variations in peak expiratory flow rates were 2006 more strongly associated with ambient UFP concentrations Indoor ultrafine particle exposures Weichenthal et al. in one of these studies relative to larger particles (Pekkanen email a researcher and were telephoned in return to schedule et al., 1997). Recently, UFP exposures were shown to an appointment for in-home sampling and questionnaire contribute to oxidative DNA damage in healthy adults, with completion. All participants also signed an informed consent indoor exposures contributing most to cumulative exposure form. The primary selectioncriteria was the type of home levels owing to the large amount of time people spend heating system, and 38 volunteers expressed interest in study indoors (Vinzents et al., 2005). Therefore, future population- participation. We were unable to visit two of these 38 homes based studies interested in the respiratory effects of UFPs for reasons of poor weather conditions and a death in the may need to include indoor measures of UFP exposure to family. Of the remaining 36 homes, 10 relied primarily on a capture anaccurate depictionof cumulative exposure profiles. forced-air natural gas furnace for heat, 10 relied on a forced- Indoor sources of UFPs have been investigated in a air oil furnace, nine relied on electric baseboard heaters, and number of studies, and include cooking systems, portable sevenrelied ona wood stove. Five of the sevenwood stoves heaters, burning candles, tobacco smoke, natural gas clothes were the stand-alone type, which produces radiant heat for dryers, and others (Li et al., 1993; Abt et al., 2000; Wallace, warmth and two were forced-air wood furnaces. 2000; Dennekamp et al., 2001; Wallace and Howard-Reed, 2002; Morawska et al., 2003; He et al., 2004; Wallace et al., In-Home Monitoring Scheme and Questionnaire 2004; Afshari et al., 2005; Husseinet al., 2005; Matson, In-home monitoring was conducted over a 16-h time period 2005; Wallace, 2005). However, studies to date have which included the evening cooking period (1600–2400 generally been conducted in 15 or fewer homes and have hours) and overnight hours (2400–800 hours), when other not compared indoor UFP exposures according to the type potential indoor sources of UFPs besides home heating of home heating system. Such a comparison is warranted as systems were not expected to be active. One researcher visited heating systems such as electric radiators have been identified each home once to set-up and another to collect instruments. as a source of indoor UFPs (Afshari et al., 2005), and are During the first home visit, a home-characteristic question- oftenactive for manymonthsof the year. To address this naire was administered to participants to obtain information issue, we conducted a cross-sectional survey of indoor UFP on the age and size of the home, vacuuming and dusting exposures in 36 residences during winter 2006. Our primary frequency, type of cooking system (electric or natural gas), objective was to compare indoor UFP exposures between types of cooking appliances used, use of a kitchen exhaust homes with electric baseboard heaters, wood stoves, forced- fan, number of smokers, burning candles, use of portable air natural gas furnaces, and forced-air oil furnaces as these heaters, and use of a natural gas clothes dryer. systems are most commoninCanadianhomes (Natural Resources Canada, 1994, 2000). Although sources such as Instrumentation cooking were expected to produce greater indoor UFP UFP concentrations (cmÀ3) were monitored using two TSI numbers, we expected home heating systems to have a larger P-Trak 8525 UFP counters. These are direct reading influence on overnight exposures because these systems are condensation particle counters capable of 8 h of continuous generally the only potential sources that are active during this data logging before alcohol refill is needed. In addition, time period. Specifically, we expected home heating systems these instruments can detect particles as small as 20 nm to play a role in determining baseline UFP exposure levels at concentrations up to 5 Â 105 cmÀ3.Ineachhome,one during the overnight hours, with electric baseboard heaters P-Trak was programmed to sample inthe kitchenduringthe and wood stoves contributing most owing to the exposed evening hours (1600–2400 hours) and a second P-Trak was nature of the heating elements on these types of systems. programmed to sample overnight (2400–0800 hours) in the main living area. A 1-min sampling interval was used for all continuous indoor UFP measurements, meaning that Methods throughout the sampling period an indoor UFP measure- ment was recorded every minute and that the value recorded Home Selection and Locations was the average UFP concentration over the previous This study was conducted in 30 single-family homes and six minute. Before indoor UFP monitoring, a short outdoor town-house apartments between the months of December UFP measurement was recorded for each home.