According to the USA Surgeon General’s report (USSGR), five of these chemicals are in cigarette smoke. However, all 16 PAH are in eucalypt smoke; you would have to smoke 16,000 - 222,000 cigarettes to produce the equivalent amount of PAH as burning 1 kg firewood in a correctly-operated heater. Most wood heaters burn about 30 kg wood per day, so to produce the PAH from the average correctly-operated wood heater would require the smoke from 0.5 - 7 million cigarettes.
Wikipedia lists three additional PAHs that are considered dangerous – coronene, benzo[j]fluoranthene, and ovalene. Although not tested for in the Australian analysis, Larson & Koenig list coronene as a constituent of woodsmoke (800-3,000 ug/kg), but the USSGR does not list it in cigarette smoke. Larson & Koenig lump the benzofluoranthenes together (600 – 5,000 ug/kg) so it is not possible to report specifically about benzo[j]fluoranthene, though the USSGR shows 6 – 21 ng of benzo[j]fluoranthene per cigarette. Ovalane is not reported as a constituent of either wood or cigarette smoke.
The other 4 pollutants covered in the Australian Air Toxics NEPM are benzene, formaldehyde, toluene and xylene. The Australian Ambient Air Quality NEPM covers particles, carbon monoxide (CO), nitrogen dioxide, ozone, sulphur dioxide and lead. With the exception of PM2.5, where a burning 1 kg of wood produces as much PM2.5 as 225 cigarettes, and lead (61 cigarettes), 1 kg wood burned in a correctly-operated heater produces as much pollution as 1,725 to 6.5 million cigarettes (see Table 1).
The Australian woodheater study lists average dioxin emissions as 4.2 ng/kg – double the value used until then in Australian emissions inventories, but there is no mention of dioxin in the USSGR.
PCDDs, PCDFs and (PCBs): polychlorinated dibenzo dioxins (PCDDs) and furans (PCDFs) and dioxin-like polychlorinated biphenyls (PCBs), are amongst the most toxic pollutants known. A 12-month study of 6 locations in Australia covering industrial and residential sites, showed that levels of these harmful pollutants were close to zero, except when wood heaters were in use, when concentrations were up to 10 times higher than the non-heating season (see graph, right from Gras et al. http://www.cmar.csiro.au/e-print/open/gras_2005a.pdf).
One other important chemical is acrolein, shown in 2005 to be the chemical in cigarette smoke responsible for inhibiting the immune system. Breathing woodsmoke is also known to suppress the immune system. For example, when mice were subjected either to woodsmoke, oil furnace fumes, or clean air for 6 hours, then challenged by a respiratory bug. 21% of those exposed to wood smoke were dead two weeks later, compared with only 5% mice exposed to fumes from the oil furnace or to clean air.. Using a woodheater for 1 day is likely to produce as much acrolein as in the smoke of 26,000 cigarettes.
This could be why infants in exposed to high levels of woodsmoke have even greater increased risk of bronchiolitis (8%) than living within 50 metres of a major highway (6%). When interviewed, the author of the research study explained that “Bronchiolitis is the number one reason why a child ends up in a hospital in the first year of life" and that this study "lets families know about concerns about infant exposure to traffic and wood-burning appliances. If they can avoid those things, they should.” http://www.medicinenet.com/script/main/art.asp?articlekey=107393.
Polycyclic aromatic hydrocarbons (PAH) are the main toxins in woodsmoke. A US study published in 2009 and study of Polish women published in April 2010 found that exposure to PAH during pregnancy is associated with reduced IQ when the children start school at age 5.
The second study of pregnant Caucasian women in Poland confirmed the results. “The effect on intelligence was comparable to that seen in NYC children exposed prenatally to the same air pollutants,” explained Frederica Perera, professor of Environmental Health Sciences. The Polish study measured exposure to benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, ibenz[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-cd]pyrene (see Table 1). Four of these PAH have the highest-listed carcinogenic potential. Two are in cigarette smoke, but all four are in woodsmoke. For the two in both wood and cigarette smoke, burning 1 kg firewood produces as much toxic PAH as in 16,000 cigarettes (Table 1).
Research published in March 2012 measured DNA adducts (genetic damage) specific to benzo[a]pyrene in umbilical cord blood, and also measured the mothers' exposure to PAH during the 3rd term of pregnancy. The study provided clear evidence that B[a]P exposure is linked to behavioural problems. The 41% of children with detectable B[a]P adducts in umbilical cord blood had a 4-fold increase in attention problems, and 2.6-fold increases in attention/hyperactivity problems and anxiety problems.
The review by Naeher notes: “Organic extracts of ambient particulate matter (PM) containing substantial quantities of woodsmoke are 30- fold more potent than extracts of cigarette smoke condensate in a mouse skin tumor induction assay (Cupitt et al., 1994)” This supports the view that, gram for gram, woodsmoke is actually worse than cigarette smoke. Although woodsmoke doesn’t contain nicotine, and studies of the chemical composition of woodsmoke are generally limited to recognised carcinogens and toxins such as PAHs and dioxins (unlike cigarette smoke which has been comprehensively studied), Table 1 shows that woodsmoke contains much higher concentrations of these chemicals than cigarette smoke. Indeed 2 chemicals with carcino­gentic potential of 1 - benzo[g,h,i]perylene and indeno[1,2,3-cd]pyrene are in wood, but not cigarette smoke.
Cigarette smoke also contains other chemicals – some beneficial if eaten e.g. linolenic acid (omega-3) and oleic acid (a key ingredient of “Lorenzo’s Oil”) and others that are clearly harmful in large doses. Some chemicals have thresholds, below which harmful effects are not detected. Others, including PM2.5 and carcinogens, have no threshold – the risk of a cancer-causing mutation is directly proportional to exposure, but there is no threshold, below which there is no risk. This comparison concentrates on the latter type of chemicals that are considered sufficiently hazardous to be included in the Australian Air Toxics NEPM, or the Ambient Air Quality NEPM.
Results from Launceston in 2003 show that fine particle measurements inside people’s homes in winter were 31.4 ug/m3 greater than in summer. A US study found that living with a 1-pack per day smoker increased exposure by 30 ug/m3. Winter in a woodsmoke-affected city such as Launceston would therefore appear to be worse than living with a 1-pack per day smoker.
Most heaters in the Australian study were operated correctly – emissions averaged 4.5 g/kg for eucalypts, with a much higher value 15.8 g/kg for pine. In contrast, a study of real-life emissions in Launceston (where households who volunteered to have their emissions measured appeared to take a lot more time and trouble to operate their heaters correctly – even adding wood in the middle of the night rather than stoking them up for an overnight burn) averaged 9.4 g/kg. A typical heater burns about 30 kg per day and, with real-life emissions of normally-operated heaters, according to Prof John Todd, of 10 to 15 g/kg of wood, will emit 300 – 450 g PM2.5 per day, the same as produced by 15,000 – 22,500 cigarettes.
With annual firewood consumption of about 4 tonnes/year, the average wood heater in Armidale emits 40 to 60 kg of PM2.5 per year, as much health-hazardous PM2.5 pollution as 267-400 passenger cars (typical emissions 0.01 g/km) each driving 15,000 km/year.
1. US Surgeon General, 1989. Reducing the Health Consequences of Smoking., 1989, Tables 5-8, p.81-89, Available at: http://profiles.nlm.nih.gov/NN/B/B/X/Y/_/nnbbxy.pdf.
2. Gras, J., Emissions from Domestic Solid Fuel Burning Appliances., 2002, Environment Australia Technical Report No. 5, March 2002. Available at: http://www.environment.gov.au/atmosphere/airquality/publications/report5/index.html.
3. Larson, T. and J. Koenig, Wood smoke: emissions and noncancer respiratory effects. Annu. Rev. Public Health, 1994. 15: p. 133-56.
4. Hildemann, L., G. Markowski, and G. Cass, Chemical composition of emissions from urban sources of fine organic aerosol. Environmental Science and Technology, 1991. 25(4): p. 744-959.
5. Lambert, C., et al., Acrolein in cigarette smoke inhibits T-cell responses. The Journal of allergy and clinical immunology, 2005. 116(4): p. 916-922.
6. Stone, R., Environmental toxicants under scrutiny at Baltimore meeting. (March 1995 Society of Toxicology conference). Science, 1995. March 24, v267 n5205 p1770(2).
7. Karr, C.J., et al., Influence of Ambient Air Pollutant Sources on Clinical Encounters for Infant Bronchiolitis. Am. J. Respir. Crit. Care Med., 2009. 180(10): p. 995-1001.
8. Perera, F.P., et al., Prenatal Polycyclic Aromatic Hydrocarbon (PAH) Exposure and Child Behavior at age 6-7. Environ Health Perspect, 2012.
9. Naeher, L., et al., Woodsmoke Health Effects: A Review. Inhalation Toxicology, 2007. 19(1): p. 67-106.
10. NHT, Technical Report No 8. Personal Monitoring of Selected VOCs: The Contribution of Woodsmoke to Exposure, 2004, CSIRO Atmospheric Research, for the Natural Heritage Trust. (available at http://www.deh.gov.au/atmosphere/airquality/publications/pem/).
11. Neas, L., et al., Concentration of indoor particulate matter as a determinant of respiratory health in children. Am. J. Epidemiol., 1994. 139(11): p. 1088-1099.
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13. Khan, L., K. Parton, and H. Doran, Cost of Particulate Air Pollution in Armidale: A Clinical Event Survey. Environmental Health, 2007. 7(2): p. 11-21. Download from: woodsmoke.3sc.net/files/Khan_07_EHJ_airpol_arm_costs.pdf.
14. Fisher, G., et al., Health and Air Pollution in New Zealand, Final Report, 2007, Health Research Council of New Zealand & Ministry for the Environment & Ministry of Transport.
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19. Clancy, L., et al., Effect of air-pollution control on death rates in Dublin, Ireland: an intervention study. Lancet, 2002. 360(9341): p. 1210-4.
We can’t keep smoke pollution out of our homes; the particles (PM2.5) are so tiny they enter our homes along with the air we need to breathe. The only way to keep them out would be to make the house airtight, but then we’d die from lack of air!
The ABS reports that in 2007-08 only 3.9% of ACT households used wood as the main form of space heating – 57.3% use gas, 35.3% electricity, 0.7% oil and 1.6% no heating. Yet the shows domestic solid fuel burning (wood – the ABS reports no other solid fuel use for space heating) is responsible for 67% of Canberra’s PAH emissions – 16,000 kg/year out of a total of 24,000 kg/year.
A UNE study published in 2007 reported that winter woodsmoke causes 8.8 additional visits per day to GPs in Armidale for respiratory complaints, or about 750 additional visits per year. The estimated economic cost was $189.35 per visit, i.e. about $142,000 per year. The community will also have to bear the cost of more serious ailments, including hospital admissions, which were not included in this total.
Assuming woodsmoke has a similar effect on health in NZ and Australia, the best estimate is that woodsmoke increases Armidale’s death rate by about 9.2%, or that the 177 residents of Armidale expected to die next year would have lived a total of 150 more years of healthy life if we had clean air. In NZ, a year of healthy life was valued at NZ$75,000. Assuming a year of life in Armidale is worth $50,000, the estimated cost of woodheaters in Armidale is 150 x $50,000 = $7.5 million.
Polycyclic aromatic hydrocarbons (PAH) are the main toxins in woodsmoke. A US study measured exposure to PAHs in women’s home environment during the third trimester of pregnancy. Measured exposure was used to split the mothers into two groups – those with PAH over 2.26 ng/m3 (high exposure) and those with PAH less than this (low exposure group).
After adjusting for the mother's intelligence, quality of the home environment, other exposures to PAHs and other relevant factors, children whose mothers were in the high exposure group scored about 5 points lower on average on several measures of IQ than those whose mothers were in the low PAH group - http://autismjabberwocky.blogspot.com/2009/07/study-watch-prenatal-airborne.html.
Wintertime PAH measurements in Armidale averaged 8.62 ng/m3 (max 24.0 ng/m3) - http://www.environment.nsw.gov.au/air/dopahhm/pahresults.htm - about 4 times higher than what was considered high PAH exposure in the IQ study.
There are about 270 births per year in the Armidale Dumaresq LGA. Given that Armidale’s winter average PAH was four times greater than what was considered high in the US study, as well city residents, people in country areas with wood heaters and some of their neighbours are likely to be affected. The wood heating season lasts for over 4 months, so a third of the 270 births (i.e. 90) are likely to be exposed to more than 2.26 ng/m3 of PAH pollution during the third trimester. If a 5 point loss of IQ leads to a $1,250 per year reduction in income, or $50,000 over a child’s lifetime, the estimated cost is $4.5 million per year.
Woodsmoke associated with many other health problems, e.g. mouth and throat cancers, middle ear infections and bronchiolitis in children. Exposure to woodsmoke was noted to produce a higher increase in the risk of bronchiolitis (8%) than living within 50 metres of a major highway. PM2.5 pollution in general is associated with cot deaths; exposure to PM2.5 in childhood is associated with increased risk of chronic obstructive pulmonary disease in adulthood – see http://www.upi.com/Health_News/2009/07/23/Particulates-in-babys-lungs-may-COPD/UPI-87811248375081/. These costs have not been quantified.
The above estimates – GP visits $142,000; lost of healthy life years $7.5 million; reduced IQ of babies: $4.5 million – amount to over $12 million per year, i.e. about $3,500 per year for every woodheater in the area.
This estimate is similar to estimated costs elsewhere, e.g. a team of 25 experts in NZ estimated that the cost of woodsmoke pollution in Christchurch was more than NZ$2,700 per heater per year. This was based on an internationally-accepted estimate (used for traffic pollution) of 4.5% increased mortality per 10 ug/m3 of PM10 exposure. Estimated costs based on the 8% increase observed in Christchurch for woodsmoke would be more than NZ$4,000 per heater per year.
Does information on health costs change people’s perception of woodheating?
2) Imagine you (or a close friend or relative) were about to start a family and you learned that exposure to a certain chemical was likely to reduce the baby’s IQ by 5 points, with some suggestions that exposure might increase the risk of autism. How much do you think should be spent on avoiding this chemical?
California’s Healthy Hearths Program (http://www.aqmd.gov/healthyhearths/Why_HH.htm) bans all wood burning devices in new buildings and also bans use of all wood burning devices whenever PM2.5 pollution is forecast to exceed the air quality standard.
The installation of new wood heaters has been banned by several local authorities, including Waverley and Pittwater, as well as for new buildings in Holroyd, Manooka Valley and the Oran Park and Turner Road Growth Precincts.
The health effects of air pollution are real. When one study of air pollution, involving six cities, was followed up, PM2.5 had dropped substantially in one city, moderately in another, remaining stable elsewhere. Death rates fell in the first two cities relative to the other four. Dublin reduced PM2.5 pollution by banning non-smokeless coal in September 1990. There were 15.5% fewer respiratory and 10.3% fewer cardiovascular deaths in the 6 years after the ban, compared with the previous 6 years – a total of 696 fewer respiratory and 1458 cardiovascular deaths during the first 6 years of the ban. Having experienced the health benefits, it is hard to imagine Dubliners would want to back to the smoky old days.
NZ also suffers from woodsmoke pollution. Measured pollution was used as input to a cost-benefit analysis (http://www.hapinz.org.nz/ ) which concluded that woodheaters in Christchurch (pop 333,000) cause 124 premature deaths, with estimated total cost of NZ$127 million per year, about $2,700 per heater per year.
This implies that living in the most polluted areas (>20µg/m3 PM10) increases mortality by about 16% (respiratory deaths by about 68%) compared to living in unpolluted areas with <1 µg/m3. An earlier 25-expert study, assuming a 4.3% increase in death rates per 10µg/m3 of PM10 exposure (the standard dose-response relationships for traffic pollution) estimated the annual health costs of woodsmoke in Christchurch exceed NZ$127 million, i.e. more than NZ$2,700 per heater per year. Using the observed 8% increase in deaths per 10µg/m3 PM10 exposure, the health cost increases to about NZ$5,000 per heater per year.