Where there's smoke, there's asthma
A Darwin study has shown that asthma cases increase markedly during bushfires.
A team of scientists led by the Menzies School of Health Research in the Northern Territory conducted a seven-month study looking at the relationship between the concentration of particles in the air from bushfire smoke, and people reporting to the Emergency Department of the Royal Darwin Hospital with asthma.
Their findings were published earlier this year in the June issue of the Medical Journal of Australia.
The researchers found there is a linear relationship between asthma cases and smoke concentration, namely the thicker the smoke, the greater the number of asthma sufferers. And asthma cases more than doubled above a certain smoke concentration.
"In Darwin, there is no other source of atmospheric pollution, so when you get a bad pollution event, you can be 100 per cent certain it is due to bushfires", said team member Dr David Bowman, from the Key Centre for Tropical Wildlife Management, at the Northern Territory University.
Airborne particles range in diameter from 0.005 µm to about 100 µm (a µm, or micrometre, is one-thousandth of a millimetre). Smoke is a cocktail of fine particles within this size range. The finer the particles suspended in the air, the deeper their lung penetration.
PM10 or PM2.5 describe particles in terms of their maximum diameter in micrometres, so PM10 refers to particles up to 10µm in diameter. The national pollution standard (which measures the weight of particles in a cubic metre of air) is a maximum average of 50µg/m3 PM10 in one day not to be exceeded on any more than five days a year.
Not surprisingly, breathing in such particles is damaging to respiratory and cardiovascular health. In Sydney, fine particle air pollution accounts for 397 premature deaths out of a total of 21,500 every year.
Previous Australian studies have found little or no evidence that bushfire smoke resulted in more asthma cases, even during Sydney's extreme fire event in 1994. These studies were over a short timespan, and it was difficult to isolate the effect of the smoke from other urban pollution.
The Darwin study found a significant increase in asthma cases with each 10µg/m3 increase in PM10 concentration. When the PM10 level was above 40µg/m3, asthma presentations each day increased by nearly 2.4 times than on days when PM10 levels were less than 10µg/m3.
Over a seven-month period, 265 people presented with asthma, an average of 8.5 per week. PM10 levels ranged from 2 to 70µg/m3, averaging 20.84µg/m3 per day. The national standard of 50µg/m3 was exceeded on a total of six days.
In Sydney, there have been two major peaks in PM10 levels in the last week with the dust storm and bushfire smoke sending measurements off the scale and beyond 200µg/m3.
According to the NSW Environment Protection Authority, there have already been 10 other 'exceedence days' in Sydney so far this year.
"There is debate about whether PM10 is appropriate, and we would like to look at the finer PM2.5 particles. There is mounting evidence that PM2.5 is an important factor in adverse health effects", Dr Bowman said.
Earlier this month, Australia's Environment Ministers released a draft standard for non-compulsory reporting by States about PM2.5 levels.
Dr Bowman said their Darwin work is a preliminary study that gives 'proof of concept' for continuing research there.
"Darwin is an ideal natural laboratory for a whole complex of reasons our fire-prone environment, the large areas of bushland surrounding the city, the absence of any source of industrial air pollution, and one central repository of data in the Darwin Hospital."
Dr Bowman also said the research highlights the information needs of land managers, fire controllers, public health authorities, and environmental monitoring agencies, and the need to set up a prospective rather than a retrospective study.
"The biggest deficiency of our preliminary study is that we have no knowledge of the fire events that cause variation in smoke pollution," he said.
"Under what circumstances can you burn landscapes to reduce fuel loads and not expose populations to any injurious levels of smoke pollution?"