Researchers at McMaster University in Hamilton, Ontario, Canada, have established a first-ever link between urban air pollution and genetic damage that can be passed on from generation to generation. In a study published in the most recent issue of the U.S. journal Proceedings of the National Academy of Sciences, biologists at the university found that male laboratory mice that were placed downwind of two different steel mills in and around Hamilton for 10 weeks underwent one and a half to two times as many genetic mutations as a control group placed in a rural, mill-less area; the damaged genes were then passed on to the mice’s offspring. The scientists warned that genetic mutations can increase the risk of cancer and birth defects and said human genes were likely to be affected in the same way, but stopped short of making a direct comparison between the fate of the lab mice and human health.