US study of miners links heavy exposure to diesel exhaust to increased risk of lung cancer death; researchers suggest implications for urban areas with high exhaust concentrations
05 March 2012
In a study of non-metal miners in the US, federal government scientists report that heavy exposure to diesel exhaust increased risk of death from lung cancer. The study was carried out by researchers from the National Cancer Institute (NCI), part of the National Institutes of Health, and the National Institute for Occupational Safety and Health (NIOSH), part of the Centers for Disease Control and Prevention, both parts of HHS.
According to the investigators, this is the first study based on estimates of quantitative historical exposure to diesel exhaust to yield a statistically significant, positive increase in lung cancer risk with increasing diesel exposure with adjustment for potential confounding from cigarette smoking and other risk factors for lung cancer.
Health outcomes associated with exposure to diesel exhaust were reported in two complementary papers, distributed on 2 March 2012, from the Journal of the National Cancer Institute and posted to the JNCI website today. Both papers reported an exposure-response relationship with higher risks at increased exposure levels.
The first (Attfield et al.) documented the risk of dying from any cause, with an emphasis on lung cancer, using data from the full study population (the cohort study). The team found that the risk of lung cancer among heavily exposed underground workers was five times the risk observed among workers in the lowest exposure category.
The second (Silverman et al., the case-control study) reported on the lung cancer deaths in the cohort study. In the case-control study, investigators obtained detailed information on lung cancer risk factors, including smoking, employment in other high-risk jobs, and history of other respiratory diseases.
When the investigators took into account smoking and other lung cancer risk factors, the data showed a three-fold risk of lung cancer death overall and about a five-fold risk for heavily exposed underground workers, which is consistent with the cohort analysis.
For never-smokers, risk of lung cancer death increased with increasing diesel exhaust exposure. Although based on small numbers, non-smokers with the highest level of diesel exposure were seven times more likely to die from lung cancer than non-smokers in the lowest exposure category.
In sum, our results provide further evidence supporting a causal effect of diesel exhaust exposure on lung cancer mortality in humans. We observed a statistically significant exposure–response relationship after we adjusted for possible confounding from smoking and other established and hypothesized lung cancer risk factors. The exposure–response curve showed a steep increase in risk with increasing exposure at low-to-moderate levels followed by a plateauing or perhaps a decline in risk among heavily exposed subjects.
Our findings are important not only for miners but also for the 1.4 million American workers and the 3 million European workers exposed to diesel exhaust, and for urban populations worldwide. Some of the higher average elemental carbon levels reported in cities include Los Angeles (4.0 µg/m3), the Bronx (6.6 µg/m3), nine urban sites in China (8.3 µg/m3), Mexico City (5.8 µg/m3), and Estarreja, Portugal (11.8 µg/m3). Environmental exposure to average elemental carbon levels in the 2-6 µg/m3 range over a lifetime as would be experienced in highly polluted cities approximates cumulative exposures experienced by underground miners with low exposures in our study.
Because such workers had at least a 50% increased lung cancer risk, our results suggest that the high air concentrations of elemental carbon reported in some urban areas may confer increased risk of lung cancer. Thus, if the diesel exhaust/lung cancer relation is causal, the public health burden of the carcinogenicity of inhaled diesel exhaust in workers and in populations of urban areas with high levels of diesel exposure may be substantial.—Silverman et al.
The research, all part of the “Diesel Exhaust in Miners Study”, was designed to evaluate cancer risk from diesel exhaust, particularly as it may relate to lung cancer, among 12,315 workers at eight non-metal mining facilities. The facilities were located in Missouri (1 limestone mine), New Mexico (3 potash mines), Ohio (1 salt mine), and Wyoming (3 trona mines, which process an ore used in soda ash).
The investigators selected underground mines for their study setting because the heavy equipment used in these mines frequently runs on diesel fuel. In the fairly enclosed environments of these mines, exhaust builds up in the air to levels considerably higher than those found in other occupational settings—such as trucking depots or shipyards—and many times higher than the air inhaled by the general population. The investigators selected only non-metal mines because of their characteristically low levels of other exposures that may be related to lung cancer risk, such as radon, silica, and asbestos.
It was vitally important to undertake a large study of diesel exhaust and lung cancer based on a quantitative assessment of historical exposure, taking into account smoking and other potentially relevant factors in order to estimate lung cancer risk.—Debra T. Silverman, lead author of the case-control study
Silverman is chief of the Occupational and Environmental Epidemiology Branch in the Division of Cancer Epidemiology and Genetics (DCEG) at NCI.
To quantify exposure for each worker, the investigators collected thousands of measurements of constituents of diesel exhaust in the air at each mine and combined those data with historical exposure information. Diesel exhaust levels were quantified by measurements and estimates of one of its key components, respirable elemental carbon, which is considered the best index of diesel exhaust in underground mining. The same exposure measurements were used in both the cohort and case-control analyses. The methods for this effort were published previously in four papers in the Annals of Occupational Hygiene in 2010. A fifth paper—an evaluation of the exposure assessment—was published March 2012 in the same journal.
In an Editorial in JNCI accompanying the two papers there, Dr. Lesley Rushton, Department of Epidemiology and Biostatistics, Imperial College London, noted that:
These studies in miners make an important contribution to the body of evidence about DEE [diesel engine exhaust] and are timely given the forthcoming International Agency for Research on Cancer (IARC) monograph meeting this year at which the current IARC categorization of DEE as a group 2A (probable human) carcinogen will be reconsidered.
...These results indicate that stringent occupational and particularly environmental standards for DEE should be set and compliance ensured to have an impact on health outcomes. In the occupational situation, in addition to lower emission and more efficient engines, reduction in DEE can be achieved through: 1) engineering controls such as improved ventilation and regular maintenance of vehicles; 2) improving worker practices such as limiting the number of vehicles, particularly in closed spaces, and turning off engines when not in use; and 3) as a last resort, the use of appropriate respiratory protective equipment.
Reduction in the general environment presents more of a challenge, although some of the occupational control measures are also relevant. However, the necessity for such reduction is becoming increasingly apparent and is essential if the health of large numbers of people is not to be compromised.
Attfield MD, Schlieff PL, Lubin JH, et al. (2012) The diesel exhaust in miners study: a cohort mortality study with emphasis on lung cancer. J Natl Cancer Inst. doi: 10.1093/jnci/djs035
Silverman DT, Samanic CM, Lubin JH, et al. (2012) The diesel exhaust in miners study: a nested case-control study of lung cancer and diesel exhaust. J Natl Cancer Inst. doi: 10.1093/jnci/djs034
Lesley Rushton (2012) The Problem With Diesel. (editorial) J Natl Cancer Inst. doi: 10.1093/jnci/djs13
Patricia A. Stewart, Roel Vermeulen, Joseph B. Coble, Aaron Blair, Patricia Schleiff, Jay H. Lubin, Mike Attfield, and Debra T. Silverman (2012) The Diesel Exhaust in Miners Study: V. Evaluation of the Exposure Assessment Methods. Ann Occup Hyg doi: 10.1093/annhyg/mes020
“Journals Warned to Keep a Tight Lid on Diesel Exposure Data” Sam Kean, Science Insider, 17 February 2012
"The investigators selected underground mines for their study setting because the heavy equipment used in these mines frequently runs on diesel fuel. In the fairly enclosed environments of these mines, exhaust builds up in the air to levels considerably higher than those found in other occupational settings—such as trucking depots or shipyards—and many times higher than the air inhaled by the general population. The investigators selected only non-metal mines because of their characteristically low levels of other exposures that may be related to lung cancer risk, such as radon, silica, and asbestos."
A clever way to use a test sample that's already contained and sorted.
Posted by: ai_vin | 05 March 2012 at 10:53 AM
Since it was recently reported here on GCC that gasoline BC emissions are vastly underestimated for gasoline engines (http://www.greencarcongress.com/2012/02/liggio-20120229.html), how much of the ambient EC levels in the referenced study can be apportioned to diesel, and how much can be apportioned to other sources like gasoline engines?
All on-road diesel vehicles manufactured in the U.S. since January 2007 are effectively required to use particle filters (DPF) to meet existing emission regulations, so mitigation measures are already being applied to diesel technology. Off-road diesel equipment will also effectively be required to use DPF shortly. Implications for a study such as this seem to be outdated in light of the mitigation already being implemented.
Posted by: Carl | 05 March 2012 at 11:27 AM
With UN saying 4.5 million people a year are dying worldwide due to particulate matter such as diesel exhaust, it's about time some stats were released.
I wonder why they restricted their study to lung cancer, when other cancers would be more appropriate. The true damage from particulate matter is the smaller particles below 2.5 micron that pass through the lungs directly into the bloodstream...and hence into all organs.
The particles themselves contain "the most toxic substances ever tested" according to Japanese researchers.
Posted by: Rick Crammond | 05 March 2012 at 11:58 AM
Well Carl, this is where the 2 studies can compliment each other. Mines are a closed environment where diesels are used to the exclusion of gasoline engines.
Posted by: ai_vin | 05 March 2012 at 12:59 PM
This is very interesting. I would have never guessed that diesel particulate could be a health issue. Next thing ya know someone is going to say that cigarettes are bad for your health.
Posted by: Brotherkenny4 | 05 March 2012 at 02:01 PM
@Ai vin - I'm not questioning the legitimacy of this study in its DPM correlation to lung cancer, just the contribution of diesel to the total EC inventory. If we remove all "unfiltered" diesel equipment from urban locations, will the resulting ambient EC really become negligible, especially in light of the underestimation of gasoline EC emissions from the other referenced study? In other words, diesel isn't the only source, and may not even be the major source, of EC.
Or maybe I'm misunderstanding your point?
Posted by: Carl | 05 March 2012 at 02:20 PM
Many fine particles emissions, pollution and harmful products have willfully been under-reported to protect interested parties financial profit margins.
Small ans fine particles emission, from ICEVs, are only one of many sources polluting the air we breath and water we drink. Domestic wood fire places, BBQ, coal fired power plants, cement factories, agriculture fires, quarries, stone polishing and many industries are also contributing but probably not as much as our 240,000,000 gas guzzlers, or is it more?
Posted by: HarveyD | 05 March 2012 at 06:11 PM
@Carl - I know you're not questioning the legitimacy of this study.
And yes, in most places diesel isn't the only source, and may not even be the major source, of pollutants. I was just trying to point out that in this study they found an environment (the selected mines) where it IS the major source, maybe even the only source, of pollutants. So now they can quantify the effects of this ONE source when they move out of the controlled environment of the mines and subtract it from any numbers they crunch on the effects of pollution where they have two or more sources (with one of those sources being diesel) to find out what the effects are from the non-diesel sources. Clearer?
On to another/different point. You're asking about "gasoline EC emissions from the other referenced study" right? My question: What do you mean by "EC" ??? Your referenced study was talking about "black carbon" - 'BC' not "EC" - so I'm assuming it's just a typo on your part, correct or no?
Posted by: ai_vin | 05 March 2012 at 08:56 PM
@ai vin - yes, that's clearer, and I agree.
As to your second point, I was assuming the terms "elemental carbon" (EC) and "black carbon" (BC) were being used interchangeably. Is this incorrect?
Posted by: Carl | 06 March 2012 at 05:35 AM
No, it's not incorrect. The inconsistency just confused me is all.
Posted by: ai_vin | 06 March 2012 at 01:08 PM
them to “explain” variables that have no material relationship to US ethanol production: the US price of natural gas and unemployment rates in the US and the European Union. Morel1 Tips
Posted by: Edward Son | 07 December 2012 at 03:47 AM