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Inhalation Toxicology
International Forum for Respiratory Research
Volume 19, 2007 - Issue 1
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Original

Woodsmoke Health Effects: A Review

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Pages 67-106 | Received 22 Mar 2006, Accepted 04 Aug 2006, Published online: 03 Jul 2010
 

Abstract

The sentiment that woodsmoke, being a natural substance, must be benign to humans is still sometimes heard. It is now well established, however, that wood-burning stoves and fireplaces as well as wildland and agricultural fires emit significant quantities of known health-damaging pollutants, including several carcinogenic compounds. Two of the principal gaseous pollutants in woodsmoke, CO and NOx, add to the atmospheric levels of these regulated gases emitted by other combustion sources. Health impacts of exposures to these gases and some of the other woodsmoke constituents (e.g., benzene) are well characterized in thousands of publications. As these gases are indistinguishable no matter where they come from, there is no urgent need to examine their particular health implications in woodsmoke. With this as the backdrop, this review approaches the issue of why woodsmoke may be a special case requiring separate health evaluation through two questions. The first question we address is whether woodsmoke should be regulated and/or managed separately, even though some of its separate constituents are already regulated in many jurisdictions. The second question we address is whether woodsmoke particles pose different levels of risk than other ambient particles of similar size. To address these two key questions, we examine several topics: the chemical and physical nature of woodsmoke; the exposures and epidemiology of smoke from wildland fires and agricultural burning, and related controlled human laboratory exposures to biomass smoke; the epidemiology of outdoor and indoor woodsmoke exposures from residential woodburning in developed countries; and the toxicology of woodsmoke, based on animal exposures and laboratory tests. In addition, a short summary of the exposures and health effects of biomass smoke in developing countries is provided as an additional line of evidence. In the concluding section, we return to the two key issues above to summarize (1) what is currently known about the health effects of inhaled woodsmoke at exposure levels experienced in developed countries, and (2) whether there exists sufficient reason to believe that woodsmoke particles are sufficiently different to warrant separate treatment from other regulated particles. In addition, we provide recommendations for additional woodsmoke research.

Notes

*Here, we use the term “smoke” to refer to the entire mixture of gases, solid particles, and droplets emitted by combustion.

*Although “woodsmoke” is the substance of primary interest in this report, evidence related to smoke from other biomass (agricultural residues, grass, etc.) is also examined where relevant.

*It should be noted that most studies have used gas chromatography/mass spectrometry (GC/MS) to characterize the chemical content of woodsmoke. GC is a very efficient tool for separating complex mixtures of organic chemicals. Combined with MS, the technique allows for highly sensitive, specific and accurate detection and quantification of a range of organic chemicals in environmental samples. GC/MS fails to detect compounds that are nonvolatile or thermally labile, however. The application of novel methods, such as liquid chromatography–mass spectrometry (LC/MS), that are appropriate for analysis of nonvolatile or thermally labile compounds will further expand the list of chemicals known to be present in biomass smoke.

*All confidence intervals reported here are at the 95% level.

*Total lung capacity (TLC) is the volume of air contained in the lungs after maximal inhalation.

Functional residual capacity (FRC) measures the amount of air remaining in the lungs after a normal tidal expiration.

Carbon monoxide diffusing capacity (DLCO) provides an assessment of the ability of gases to diffuse across the blood–gas barrier, that is, from the alveoli into the blood.

**Residual volume (RV) is the amount of air remaining in the lungs after a maximal exhalation.

*In a subsequent toxicological examination involving rabbits, these same investigators found that repeated PM10 instillations into the respiratory tract resulted in increased production of PMNs in the bone marrow and an acceleration of their release into the blood, both of which were associated with the numbers of particles ingested by the animals' alveolar macrophages (Mukae et al., Citation2001).

*A thorough summary of emissions from woodsmoke was published several years ago (Larson & Koenig, Citation1994).

*See the Chinese IAQ database (Sinton et al., Citation1996) and the non-Chinese IAQ database (Saksena et al., Citation2003) both available at http://ehs.sph.berkeley.edu/krsmith.

See also , which shows the estimate for total global health effects for indoor and outdoor air pollution.

*A similar conclusion was reached in 2006 in IARC Monograph #95, in which household combustion of biomass was rated as Category 2A, limited human evidence with supporting animal evidence (Straif et al., Citation2006).

A recent conference abstract, however, has shown a clear effect of lowered blood pressure from women whose woodsmoke exposures were lowered in a randomized clinical trial of improved stoves with chimneys in Guatemala (McCracken et al., Citation2005).

The summary results of the CRA were released in the World Health Report (WHO, 2002; Ezzati et al., Citation2002) and were published in detail in Smith et al. (Citation2004).

*In terms of health impact. The largest constituents of woodsmoke in terms of mass are, in order, CO2 and CO.

*Because the primary emphasis of this article is not developing countries, only two recommendations are listed here.

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