Air pollution can cause heritable mutations in mice, according to a field study of exposure to ambient air near a steel mill. The finding is likely to hold true in humans and other vertebrates, the researchers say, deepening concern over pollution's long-term effects.
Research into the effects of air pollution on human and animal health has focused on the impact of individual pollutants on respiratory function in the laboratory. Many scientists have found signs of harm, but it was unknown whether they would occur in the real world. Moreover, no experiments have addressed whether ambient air pollution can increase the rate of heritable mutations, which could lead to an increase in birth defects and cancer.
Now, researchers have combined aspects of lab and field experiments by exposing caged mice to ambient air near a steel mill and at an unpolluted control site for 10 weeks. Afterwards, they returned the mice to the lab, let ones within each group interbreed, and took some cells from the tails of both the mice and their offspring. They then measured the length of a stretch of noncoding DNA that is prone to environmentally induced insertions and deletions, which allows for an easy determination of the mutation rate.
Mice that had lived around the steel mill had up to twice as many mutations as control mice, and their offspring had the same mutation rate; apparently some of the mutations had occurred in their gametes and had been passed down to the next generation. Previous studies have suggested that the method gives a reliable indicator for the number of mutations in coding DNA, the researchers say--even in humans. The team, led by geneticist Christopher Somers of McMaster University in Hamilton, Canada, report their findings online 9 December in the Proceedings of the National Academy of Sciences.
The results are "extraordinarily important" but need to be reproduced at more sites to be sure that steel mills are to blame, says geneticist John Heddle of York University in Toronto. And a stronger link to mutations that directly cause disease would strengthen the case. Nevertheless, he says, "There hasn't been a paper as important as this in the field of environmental mutagenesis in a very long time, perhaps 30 years."