What's All The Fuss About?

Most of us are aware of the obvious problems associated with woodsmoke - irritation of the nose, sinuses, and throat, coughs, hair and clothes smelling of smoke, being unable to open windows because of a neighbour's smoking chimney, finding it difficult to exercise outdoors in the evenings. But is it just an irritating annoyance, or can woodsmoke actually be harmful?

The fact that woodsmoke poses a real risk to health arises from two sources

• the concentration of fine particles, especially PM2.5, that is particulate matter less than 2.5 microns in diameter;
• carcinogenic compounds, in particular, benzo(alpha)pyrenes.

1. Health Risk from Fine Particles

In Sydney, Dr Geoff Morgan of NSW Health analysed the relationship between particulate air pollution and death rates. After adjusting for temperature, weather and seasonal variation, a robust relationship was found between particle pollution and death rates. It is estimated that 400 people die prematurely each year in Sydney from particulate air pollution. Particle levels (and deaths) were generally found to be higher in the colder months, when two thirds of these particles originate from the 13% of households which burn wood. In Armidale, about 55% of households use solid fuel and 40-50% of these (ie 25% of households), use the heater 24 hours a day. This explains why Armidale has very much higher levels of particle pollution than Sydney. (See comparison with Sydney, above).

This graph shows annual mortality vs annual PM2.5 air pollution (from Dockery et al., New Engl J Med, Dec 1993). Note the 6 US cities were chosen to be representative of the range of air pollution in the US. The value for Armidale isn't strictly comparable. It applies to winter only. Outside the wood heating season, Armidale air pollution is virtually zero.

Numerous other health studies around the world have confirmed the association between fine particulate air pollution and adverse respiratory and cardiac health effects. A recent World Health Organisation report concluded that there was no safe level of particulate air pollution.
 
Researchers at Harvard University have recently conducted an experiment, involving two groups of rats with bronchitis, one group were exposed to air with particulate concentrations similar to those measured in parts of Armidale ( graph ), and the other group exposed to filtered air only. 37% of the rats exposed to the particles died within 3 days, while none of those in the second group died. This result demonstrates a direct cause and effect relationship between fine particles and premature death.
   

More information can be obtained from:

US EPA fact sheet: Health And Environmental Effects of Particulate Matter  A very good summary of the health effects.
Readable article in the Philadelphia Enquirer
Harvard Uni Summary
Research idea for Armidale
Premature mortality due to particulate pollution in 239 American Cities
Summary of studies of respiratory effects of exposure to wood smoke.
Research report showing woodsmoke inhalation compromises important pulmonary immune defence mechanisms leading to increased incidence of respiratory infection.
Recent report on relationship between PM10 air pollution and causes of  infant deaths in the U.S.:-
     Overview of report and access to copy to download
     Authors' abstract of report
 

2. Health Risk from Carcinogens

We may think of air pollution in the US as predominantly from cars, but 42% of cases of failure to meet air quality standards were due at least in part to residential wood burning (RWB). In addition, more than 30% of all mutagenic (cancer-causing) material emitted to the atmosphere in the US each year comes from wood combustion. The proportion in areas with cold winters and significant numbers of wood heaters would obviously be much higher.

A US EPA study (Lewtas et al., 1991) has concluded that the lifetime cancer risk from woodstove emissions may be 12 times greater than exposure to an equal amount of cigarette smoke.

A recent research study has found a direct link between a specific carcinogen found in woodsmoke and cigarette smoke, and mutations in the gene associated with human lung cancer. Benzo(alpha)pyrene is one of several carcinogenic chemicals which have been measured in woodsmoke. In fact, over 100 chemicals found in cigarette smoke have also been identified in woodsmoke. In Launceston, Tasmania, which experiences similar levels of woodsmoke to Armidale, but with a larger population exposure, "disturbingly high levels of carcinogens such as benzo(a)pyrene" were measured in 1991 and 1992, which were 2 - 3 times higher than levels measured in London over a similar period. (Report on an investigation by an expert Working Party into Air Pollution, Environmental Health & Respiratory Diseases, Launceston and Upper Tamar Valley, Tasmania, 1991-94.)

The web-page prepared by Doug Johnson, at the Ministry of Environment, British Columbia, contains a good overview of the byproducts of woodsmoke combustion, and their associated health effects. This is well worth reading before you light the fire tonight. British Columbia has serious problems with several areas impacted by woodsmoke pollution from residential woodburning, burn-off of land clearing residue, and burning of saw-mill residue. This document describes how harmful byproducts are formed from the hydrocarbons and organic compounds in wood, if the combustion process is starved of oxygen or if the wood has a high moisture content. "Many of the pollutants contained in wood smoke are strongly associated with chronic respiratory impacts such as increased airway resistance and decreased vital capacity. Most researchers believe that these impacts far outweigh all other possible human health impacts".
"Common pollutants produced by incomplete combustion of wood (PIC), and their potential human health impacts, are :-

• Acrolein - irritation of the eyes and respiratory tract.
• Carbon Monoxide (CO) - angina in people with heart disease, lethal at very high concentrations.
• Formaldehyde (HCHO) - headaches, respiratory tract irritation, probably carcinogenic.
• Nitrogen Oxides (NO_x) - bronchial congestion, lung edema (fluid congestion), fibrotic changes in the lungs.
• Particulate - fine particulate, i.e., particulate matter with an aerodynamic diameter less than or equal to a nominal 10 micrometres (PM₁₀), penetrates to the lung’s alveolar region and may affect lung function. As humans are acutely most sensitive to fine particulate compared to other contaminants, the inhalable particulate portion of the PIC is an appropriate one on which to focus combustion-related air quality management strategies. As such, a more detailed discussion regarding the characteristics and impacts of fine particulate is presented.
• Polynuclear Aromatic Hydrocarbons (PAHs) - PAHs are among the most harmful of the products of incomplete combustion. Certain PAHs (e.g., Benzo(a)Pyrene*) are probable human carcinogens and are classified as air toxics. Exposure to such PAHs is associated with a small, but not insignificant, cancer risk.
• Volatile Organic Compounds (VOCs) - respiratory irritation and illness, some (e.g., benzene) are carcinogenic."

For detailed chemical analysis of woodsmoke see also the paper by J A Cooper and analysis by US EPA.

How does wood heating compare with other heating methods.