The particles are smaller but the risks appear to be bigger. We’re talking air pollution, here, folks. Not so long ago EPA regulations were on the basis of pretty large partiles, ten microns in size. Then a considerable body of work indicated that much smaller particulate matter, size around 2.5 microns were a much better measure of risk. Like a lot of things, though, as our measurements get better we are finding effects, sometimes big ones, with ever smaller particles. A recent study published in Circulation Research and reported by Bloomberg says that unregulated extremely fine particles, less then 0.2 microns particles not measured at all by most methods, produce serious cardiovascular effects. The work is with animal models but the model used has been quite informative about human health:
Nano-size pollutants from vehicles can lead to plaque buildup in the arteries, putting people at risk of cardiovascular problems, researchers said in a study published today in Circulation Research, a journal of the American Heart Association. The pollutants may cause arteries to harden by impairing the protective qualities of so-called good cholesterol.
The U.S. Environmental Protection Agency doesn’t regulate the nano-size particles, which can’t be captured using current filtering technology. The pollutants, abundant in urban areas, are less than 0.18 micrometers in size and cause four times more artery buildup than particles four times larger, said Jesus Araujo, director of environmental cardiology at University of California, Los Angeles. (Bloomberg)
The apparent mechanism involves the promotion of inflammation in artery walls. The inflammatory cytokines caused by the nanoparticles promoted the development of arterial plaques that obstructed blood flow. The role of inflammation in plaque formation has been known for some time but this connects it with the ultrafine particles characteristic of urban air. While the study was done with mice (what did you expect, they’d use people?), the air was good old Los Angeles freeway, vintage 2007. Mice breathed either downtown LA freeway air or the same air filtered to remove the ultrafines. The mice breathing freeway air had 55% more plaquing and the plaques were 25% bigger than the filtered air mice. And it all happened pretty quickly.
So far large scale epidemiologic studies haven’t been able to find a “no effect” level for air pollution. If there is one, we are a long way away from it in most urban areas.
Does this kind of news make you anxious? Just take a couple of deep breaths.