Six years ago, scientists found that herring gulls living near steel mills around the harbour in Hamilton, Ontario tended to have high DNA mutation rates. These mutations were then transferred to the next generation of gulls, increasing the offspring’s chances of developing genetic diseases like cancer and birth defects. Researchers suspected at the time that air pollution was causing the mutations, but they couldn’t eliminate other factors, such as polluted water or contaminated fish, that also could have been responsible.
Last week, scientists published a paper indicating that air pollution is indeed the likely culprit behind the mutations. What’s more, there’s no reason why human DNA should be immune from the same pollution. So our genes may also be damaged and inherited by our children. It’s sobering to think that chemicals in our air affect us at a genetic level. Few studies have been done on this topic outside examinations of animals exposed to radioactive dust from nuclear accidents.
To examine the effect of air pollution, the researchers exposed two groups of mice for 10 weeks – one just one kilometre from two of Hamilton’s steel mills, the other 30 kilometres away in a rural area. They fed both groups the same diet, gave them bottled water and tended to them in the same way. Essentially, the only difference between the two groups was the air they breathed.
The offspring of the group housed near the steel mills suffered from up to twice as many mutations as offspring from the rural group. Those “steel mill” mice also produced 20 per cent smaller litters. The researchers conclude: “We therefore attribute the effect on inherited mutations in the offspring of sentinel mice directly to variation in air quality between the steel and the rural field sites.”
First gulls, now mice. There’s a good chance that air pollution is causing mutations in humans as well. Mice and humans are both mammals and share 99 per cent of the same genes. What’s bad for them is generally bad for us too. In this case, the damage seems to affect mostly male mice and their offspring, but the researchers caution that female mice are likely not immune.
That male mice were especially affected is cause for concern given that they were only exposed to the polluted air for 10 weeks. Steelworkers tend to be male and may be exposed to high levels of pollutants for years. Similarly, those living in the immediate vicinity of mills will be exposed for long periods of time, thereby increasing the chances of genetic damage.
Yet the steel industry response to the study was shocking. One industry spokesperson actually told the Canadian Press: “We dismiss this study as speculative and irresponsible.” I guess I shouldn’t be surprised. The response is reminiscent of the tobacco industry line when confronted with evidence of the harm caused by smoking. Rather than saying, “Wow, that’s a disturbing finding. We’ll fund further studies and look at ways to reduce our emissions in the meantime,” the industry simply dismisses sound science out of hand.
Tobacco and steel share another commonality – the chemicals thought to be responsible for the mutations in the Hamilton mouse study are also found in cigarette smoke. They’re called polycyclic aromatic hydrocarbons, or PAHs, a group of about 100 different chemicals that are created largely when fossil fuels are burned, but are also found in charred food and cigarettes. PAH levels around steel mills in Hamilton are 50 times higher than in rural areas.
“There is an urgent need to investigate the genetic consequences associated with exposure to chemical pollution through the inhalation of urban and industrial air,” say the Hamilton researchers. Indeed, with the vast majority of us now living in urban areas and millions of people exposed to air pollution from steel mills, coal-fired power plants and automobiles, we cannot afford to simply accept the industry line of doing nothing – especially when it could be the next generation that suffers the most.