Wood-burning appliances and indoor air quality

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Abstract

Wood heating represents an interesting economic alternative to electrical or heating oil and gas systems. However, many people are concerned about poor indoor air quality in homes equipped with wood-burning appliances. We conducted a study in the Quebec City region (Canada) to verify the extent of indoor air contamination, and to examine the frequency of respiratory symptoms and illnesses among occupants of wood-heated homes. One child attending primary school (median=8 years old; range=5–14 years old) and an adult (median=37 years old; range=23–52 years old) were recruited in each eligible house. Eligible houses were without known sources of combustion products (smokers, attached garage, oil or gas furnace, gas stove, etc.) except for wood-burning appliance. Out of the 89 houses included in the study, 59 had wood-burning appliances. Formaldehyde, nitrogen dioxide, respirable particles (PM10) and carbon monoxide were measured in a sub-set of 49 houses (41 with a wood-burning appliance and 8 without). The frequency of respiratory symptoms and diseases among participants were documented using a daily symptom diary. Concentrations of contaminants were low in most houses, both with or without a wood-burning appliance. Globally, there was no consistent relationship between the presence of a wood-burning appliance and respiratory morbidity in residents. Nevertheless, residents who mentioned being exposed to fumes emitted by such an appliance reported more respiratory illnesses and symptoms. The presence of animals or molds, and keeping windows closed most of the time in winter were other factors associated with respiratory problems. We conclude that wood burning appears to be a respiratory health risk for occupants if the appliance is not maintained and used properly.

Introduction

According to a recent study, more than 400 000 (6%) and 900 000 (14%) Canadian one-family dwellings are heated totally or partially with wood (RNC and SCHL, 1993). There are several types of wood heating. Of these, wood stoves, including slow combustion stoves, are clearly the most common (RNC and SCHL, 1993).

Wood smoke is a source of a large spectrum of particulate and gaseous air pollutants such as respirable particles (PM10) including fine particulate matter (PM2.5), and non-respirable particles, carbon monoxide (CO), nitrogen dioxide (NO2), several aldehydes (the main one being formaldehyde, HCHO), as well as polycyclic aromatic hydrocarbons (PAH) (Boleij and Brunekreef, 1989). Although there is concern about the potentially carcinogenic long-term effects (Pierson et al., 1989) of this last family of compounds, the others may cause respiratory or general illness with short-term exposures.

A number of studies have been carried out in non-industrialized (Albalak et al., 1999, Brauer et al., 1996, Naeher et al., 2000, Naeher et al., 1996, Matsuki et al., 1996, Yadav et al., 1996) and industrialized countries (Moschandreas et al., 1980, Lao et al., 1982, Sexton et al., 1984, Leaderer et al., 1990, Perritt et al., 1990) to investigate the relationship between the presence of wood-burning systems and the indoor air quality of homes where they are found. However, very few have used a design by which these systems could be isolated as the only source of combustion products. We conducted a study in the Quebec City region (Canada), whose main objective was to compare the indoor air quality in homes in which a wood heating appliance was the only source of combustion products to other homes in which there was no source of combustion products. More specifically, we measured the concentration of different contaminants (CO, NO2, HCHO and PM10) in houses where a wood-burning appliance was used as a source of heat, and compared the results to those collected in households where none was used. Finally, we examined the prevalence of respiratory symptoms of the residents in the two categories of homes, as well as the relationship between the measured contaminants and the occurrence of symptoms.

Section snippets

Materials and methods

Once the protocol was approved by the Ethics Committee of Laval University's Faculty of Medicine, recruitment was conducted from the school environment. Letters were distributed to students in five primary schools in three municipalities located within 50 km of Quebec City. The first two communities had populations of 13 249 and 15 929 residents, respectively, while the third was smaller with a total of 4321 inhabitants. We enrolled adults and children in homes without sources of combustion

Results

The 89 homes participating in the study consisted of 82 single-family homes, 4 duplexes, 1 mobile home, 1 townhouse, and 1 modular home. Of the 89 adults who completed the symptom diary, 12 (13.5%) were men and 77 (86.5%) were women. Their ages varied between 23 and 52 years, with a median of 37 years. The children consisted of 43 (48.3%) boys and 46 (51.7%) girls between 5 and 14 years of age, with a median of 8 years.

Table 1, Table 2 summarize the results of the sampling conducted in the 49

Measurement of contaminants

Contaminants were measured for 12- or 24-h periods. Consequently, the measurements provide only a relatively limited picture of the exposure. However, they were taken when the wood-burning appliance was operating. Also, the small sample size for houses without a wood-burning appliance limits the validity of the statistical comparisons. Nevertheless, the results of the monitoring for these dwellings is in agreement with the fact that they were selected on the basis of the absence of any sources

Conclusion

In the current study, the sources of combustion products were controlled. Even though data collection involved a limited sample, the use of a symptom diary gave a precise portrait of morbidity, and the relationship between fumes and respiratory symptoms and illnesses is, at least for lower respiratory pathologies and symptoms, not only stable and statistically significant, but also logical from a physiological and toxicological viewpoint. It is important that owners of homes with a wood-burning

Acknowledgements

This study was supported by the Canada Mortgage and Housing Corporation. We want to thank the people in charge of the school boards and schools, as well as the parents and children who participated in the project. We also wish to thank D. Fugler, D.B. Blanchette, M. Laberge, N. Tremblay, D. Bellemare, K. Dupuis and H. Shaver.

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