Toxic Chemicals

Air Toxics

Benzene and polycyclic aromatic hydrocarbons (PAH).  The NSW DECC Emissions Inventory reports that motor vehicles emit 1833 tonnes of benzene and 173 tonnes of PAH in Sydney; woodheaters emit 463 tonnes of benzene and 69 tonnes of PAH.  With more than 2.86 million registered vehicles in Sydney, but only 0.106 million woodheaters, the average wood-heater emits 7 times as much benzene and 11 times as much PAH in Sydney as the average vehicle.  Toluene is a recognised cause of neurodevelopmental disorders and subclinical brain dysfunction. Exposure during early fetal development can cause brain injury at doses much lower than those affecting adult brain function.

PAH in wood vs cigarette smoke.  PAH are the most well-known toxins in both cigarette and wood smoke.  The the U.S. EPA has designated 16 PAH compounds as priority pollutants.  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, a typical correctly operated wood heater used for 1 day produces as many PAH as in the smoke of 0.5 - 7 million cigarettes. 

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. (2005).

Tumour initiation tests on mice.   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)

        DNA damage in human cell lines.
"In conclusion, woodsmoke particulate matter (WSPM) generated more DNA damage than traffic-generated PM per unit mass in human cell lines, possibly due to the high level of polycyclic aromatic hydrocarbons in WSPM. This suggests that exposure to WSPM might be more hazardous than PM collected from vehicle exhaust with respect to development of lung cancer."

More information
Comparison of Toxic Chemicals in Wood and Cigarette Smoke
Genetic damage in babies and reduced IQ at age 5 from PAH exposure  Comparison of pollution from the average passenger car and the average wood heater.
Polycyclic Aromatic Hydrocarbons (PAH)  "The primary source of PAHs in air is the incomplete combustion of wood and fuel for residential heating." US National Toxicology Program, Report on Carcinogens, Eleventh Edition (2005)

Comparison of PAHs and other chemicals covered by the Australian Air Toxics or Air Quality National Environment Protection Measure (NEPM) in wood and cigarette smoke (from: comparison of Toxic Chemicals in Wood and Cigarette Smoke )

Acrolein, in wood and cigarette smoke, inhibits the immune system.  Another important chemical is acrolein, shown in 2005 to be the chemical in cigarette smoke responsible for inhibiting the immune system.  Using a woodheater for 1 day produces as much acrolein as in the smoke of 26,000 cigarettesBreathing 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. 
        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.