WASHINGTON -- Sooty air pollution can cause genetic damage that can be passed along to offspring, Canadian researchers reported Thursday in a study on mice.
Follow-up work is needed to learn if people can inherit pollution-damaged DNA that harms their health. In the meantime, the discovery is sure to increase scientists' worry about particulates, the microscopic soot particles emitted by factories, power plants and diesel-burning vehicles.
The good news: Air filters protected the mice.
These airborne particles are linked to a growing list of health problems, including asthma and heart disease, in the people who breathe high levels of the particles.
But there had been little evidence that any air pollutant might cause the kind of genetic damage that can be inherited -- until Canadian scientists in 2002 housed mice downwind from steel mills and tested their offspring. The males passed on double the DNA mutations as mice living in the cleaner countryside.
The question was why.
Now those same researchers, from Ontario's McMaster University, report in the journal Science that they've found the culprit: airborne particulate matter, better known as soot.
In the new experiments, biologist James Quinn and colleagues housed two groups of mice near the steel mills for 10 weeks. One group breathed outside air, while the other was housed in a chamber equipped with HEPA filters -- high-efficiency air filters designed to catch microscopic particles.
Then, the mice were bred and their offspring checked for specific DNA mutations that are passed through the father's sperm.
Mice that breathed filtered air had mutation rates 52 percent lower than the mice exposed to full-strength steel mill pollution.
The specific sperm changes measured aren't linked to disease, but they're similar to a type of DNA damage that is. Quinn said more study is needed to see if they're a marker for potential health problems, and whether pollution-spurred mutations in disease-causing genes could be inherited, too.
Regardless, Quinn said the study's practical value may be in showing the effectiveness of air filtration. The HEPA filters blocked particulates, and nature does the same thing -- particulates adhere to tree leaves -- which has implications for policy-makers who must decide on road-building and tree-cutting projects, he said.
Quinn couldn't say if the particulates themselves or toxic chemicals that attach to them damaged the sperm. But one suspect is a group of particulate-clinging chemicals called polycyclic aromatic hydrocarbons, or PAHs, some of which are known to be cancer-causing.
Air samples showed daily PAH exposure near the steel mills was 33 times as high as in the nearby cleaner countryside -- but HEPA filtering of the urban air blocked most of those chemicals as well, the study concluded.
The Environmental Protection Agency already has ordered tougher curbs on ultra-fine particulate pollution because of concern about effects on the elderly, children and people with respiratory illnesses. In December, it plans to reveal which parts of the country aren't in compliance.
Tiny enough to be inhaled deeply into the lungs, these particulates enter the bloodstream and move through the body.
"At the moment, we are grappling with the fact that even though the air is visibly cleaner, we're still finding adverse health effects" from particulates, said Hopkins' Samet.
If those same particles make it all the way to sperm-forming cells, "that would be quite a remarkable sequence" -- one that needs confirmation, Samet cautioned. Still, the potential for affecting next generations makes it "both a public health issue and an issue for the ecosystem," he said.