Do particulates cause blood clots?

Do fossil-fueled power plants cause blood clots in peoples’ legs? That’s the suggestion of new research reported in the May 12 issue of the Archives of Internal Medicine, one of the publications of the Journal of the American Medical Association.

Exposure to PM-10 particulates, says the study by researchers at the Harvard School of Public Health, may be linked to “deep vein thrombosis,” clots in the lower extremities that are associated with heart disease and stroke. A team led by Andrea Baccarelli looked at 870 patients diagnosed with the deep blood clots in Lombardy, Italy, between 1995 and 2005. The study included a control group of 1,210 individuals who did not have deep vein thrombosis, but lived in the same regions as the patients under study.

According to a JAMA news release, “Individuals with deep vein thrombosis tended to have higher exposure to particulate air pollution than controls.” The risk, concluded the study, increased by 70% “for every increase” in PM-10 the prior year.

“Given the magnitude of the observed effects,” said the authors, “and the widespread diffusion of particulate pollutants, our findings introduce a novel and common risk factor into the pathogenesis of deep vein thrombosis and, at the same time, give further substance to the call for tighter standards and continued efforts aimed at reducing the impact of urban air pollutants on human health.”

If true, this study offers further support for attempts to increase pollution controls on coal and gas-fired power plants. Particulate controls were one of the first environmental regulations governing fossil plants and have continued to be a major, expensive, and often contentious, issue.

But the Harvard researchers may be overstating their case. Here are three caveats to keep in mind.

First, reproducibility is the key to solid science. This is a first-of-a-kind study. There must be others to replicate it before anyone can say this work is even close to definitive. It must get, and survive, serious scrutiny as to methodology and whether anyone else, anywhere else, can find the effect.

Second, this is epidemiology. While a powerful tool, epidemiology also has aspects of black magic about it. For example, 70% sounds like a lot, but isn’t when it comes to epidemiological studies, where many confounding factors are beyond the ability of the researchers to control. I learned this from the late Marvin Schneiderman, one of the founders of epidemiology at the National Cancer Institute, when I worked at the National Institutes of Health in the 1970s, and from the late David Rall, long-time director of the National Institute of Environmental Health Sciences.

In this JAMA study, I found no evidence (I may have missed it) that the researchers factored in cigarette smoking among the patients or the control group. That could skew the results, as it has skewed the Environmental Protection Agencies studies of uranium miners and radon in the 1950s and 1960s.

It may also be the case that the time series for the study – 10 years – is not sufficient. For example, in the late 1970s, noted epidemiologist Renate Kimbrough reported preliminary results of a study of the effect of PCBs on workers at a General Electric transformer plant. She found statistically significant cancers, and the Environmental Protection Agency, without any kind of regulatory proceeding, promptly banned PCBs.

Some 30 years later, Kimbrough completed her epidemiological study and found that the GE plant workers had fewer cancer incidences, and were generally healthier, than the general public, although they had higher levels of PCBs in their blood. Nonetheless, PCBs are still routinely characterized in media coverage as “cancer-causing.”

Third, what is the mechanism? Epidemiology is a fine detective tool to provide clues. But it isn’t hard evidence. Until there is an understanding of the biological mechanism – based on in vitro and in vivo research – it’s hard to pin down the effect.

Does the newly-reported research justify additional regulation of PM10, or support current regulation? Beats me. There’s more to this story.

Responses

Created: 5/14/2008 12:42:57 AM by Miro Susta

This is a very interesting but not convincing story. Everybody knows that we need power generation facilities; and almost everybody knows that not all of these facilities are environmentally friendly. But comparing with period, say we 30 years ago, our modern power plants are much cleaner as they ever been in the past. Talking about particulates, gas fired power plants are particulate free. And most of the new (and majority of the older) coal fired power plants using ESP for particulate separation. Such ESP have efficiency of 99% and higher. Can you compare with particulates caused by automotive traffic? I believe that this causes more damage to human health than any kind of power generation facility.

Created: 5/13/2008 1:31:15 PM by P. Mumbas

You're right, there's MUCH more to this story. First, I do not understand what particulates you refer to from gas-fired power plants. Do you suggest that particulates are produced by using natural gas to produce energy? If so please identify how and under what conditions. Second, any criticism of a medical study undertaken by an acknowledged and respected research group based on hearsay is hardly scientific particularly when hedging your bets so early in the discussion with the caveat "may be overstating". Perhaps data and not vague references would be better received. Third, if coal plants produce particulates, why not direct the discussion of particulates to how to better control them rather that focusing on the "messenger", the scientific study (ies)? Research in this instance suggests continued search by energy producers to seek cleaner solutions to our increasingly messy energy world and not necessarily a call for further regulation. If there is verifiable and contradictory epidemiological evidence proving that particulates are harmless, you have not cited them. Further you have overlooked a salient albeit implied point of the research, i.e., energy production does not have to be something old reworked. Energy producers may need entirely new paradigms to solve the problems facing them. If medical evidence is presented and the debate continues, as you finally note at the very end of your piece, perhaps we'll all find solutions that we can not only live with but can benefit from. Thank you.