Tiny particles in the air can cause genetic mutations in the sperm of mice that are passed on to their offspring, according to a report in the 14 May issue of Science. Although the offspring seem healthy, the experiment raises the possibility that particle pollution could cause other, less innocuous DNA changes that can be passed on to the next generation. That adds a new and ominous reason to worry about the health effects of dirty air.
Over the past decade, scientists have linked soot and other tiny particles produced by combustion to heart attacks, asthma, and lung cancer, spurring a clampdown on fine particle pollution by the U.S. Environmental Protection Agency. More recently, a Canadian team reported that the offspring of gulls and mice exposed to heavy air pollution have an elevated mutation rate (ScienceNOW, 28 October 1996). But they had not pinned down whether particles or gases were the culprit.
To find out, the same researchers--James Quinn of McMaster University in Hamilton, Ontario, and colleagues--placed cages of mice at a site near a highway and two steel mills in Ontario for 10 weeks. The levels of pollution "were not that different from some big cities in Europe," says Quinn. Some mice breathed the polluted air; others breathed air passed through a fine filter. The team then bred the mice and checked their offspring for DNA mutations.The mice born to males that breathed unfiltered air had up to 2.8 times more mutations in particular stretches of noncoding DNA than did mice with fathers that breathed filtered air, or clean air at a rural site. The researchers also found much higher levels of polycyclic aromatic hydrocarbons, which are known mutagens, in particles at the polluted site, making these chemicals a leading suspect.Similar mutations have been reported in people exposed to radiation. But it is not easy to show that such mutations lead to disease in the offspring of either experimental animals or people because any cases of cancer or other illnesses would be rare. "We don't necessarily have direct evidence of what [the inherited mutations] mean for human health," says cell biologist Janet Baulch of the University of California, Davis, who studies heritable mutations caused by radiation.However, the Canadian study is "a warning," says toxicologist Heinrich Malling of the National Institute of Environmental Health Sciences. He says that if air pollution is adding harmful mutations to the human gene pool, "in the long run for society, the expenses are huge."