NIOSH Study of Uranium Miners
Why the Study Was Done
The original study began in 1950 because of suspicions that uranium mining caused lung cancer. Studies have continued even after we were sure about this.
It has provided important information about how much radon exposure causes lung cancer.
How the Study Was Done
Subjects
The study included 3,238 white and 757 nonwhite (mainly Navajo) miners. They all took part in Public Health Service (PHS) medical exams in the 1950s.The mines were located on the Colorado Plateau in Arizona, New Mexico, Utah, and Colorado.
Records
The mortality study described here was based on records. The four types of records used were: work histories, radon measurements in the mines, smoking histories, and death certificates for deceased miners.
Death Rates
We first looked at the death rates for men in the states where the miners lived. This gave us the expected number of deaths. Then we compared this to the number of deaths seen among uranium miners.
If the number of deaths from specific diseases is more than expected, then exposures in the mines may be the reason.
What the Study Found for White Miners
Lung Cancer
We found strong evidence of an increased risk for lung cancer in white uranium miners.
The risk was 6 times greater than normal in white miners (about 64 expected, 371 seen).
This was mainly due to exposure to radon gas or its decay product, radon daughters, in the mines.
The radon daughters give off radiation in the lung when they are breathed in. This causes the lung cancer.
The longer miners worked or the greater their exposure to radon daughters (as measured by working level months), the greater the risk for lung cancer.
Smoking also causes lung cancer. White miners who smoked were more likely to get lung cancer than nonsmokers.
However, even nonsmokers had an increased risk of lung cancer compared to the general population.
Lung Diseases
We also found strong evidence for other lung diseases (not cancer), especially pneumoconiosis. This risk was 24 times higher than normal in whites (less than 2 expected, 41 seen).
This category includes many different lung diseases. The category includes silicosis, a disease caused by breathing in mining dust. Silicosis causes severe breathing problems. The longer miners worked, the more likely they were to develop one of these lung diseases.
Tuberculosis (TB)
The risk of TB was about 4 times greater than normal in white miners (about 3½ expected, 13 seen).
The risk of TB could have been related to silicosis. People with silicosis are more likely to get TB.
Only a few deaths from TB have occurred in recent years, but this is something to be on the watch for.
Emphysema
The risk of emphysema was about 2½ times greater than normal in white miners (about 22½ expected, 56 seen).
The risk of emphysema could possibly have been related to smoking. People who smoke are more likely to get emphysema.
Other significant causes
White miners had a greater risk of death from injuries. The risk of injuries was about 2 times normal (about 68 expected and 143 seen).
White miners also had a greater risk of death from "benign and unspecified cancers" and "diseases related to the blood". Both of these categories had small numbers and the results were of borderline significance.Therefore, the confidence of the results is not high.
Among white miners, the total number of deaths was greater than expected. This was an unusual finding because working people are usually healthier than the general population.
What the Study Found for Non-White Miners
Researchers are more confident of the results of studies involving thousands of people. The non-white study group was somewhat small (757).
Because of its size, we may have missed some other illnesses connected to mining in this group.
Risks for death were lower, in general, among non-white miners than white miners.
Lung Cancer
The risk for lung cancer was 3 times greater than normal in non-white miners (about 10 expected, 34 seen). This was mainly due to exposure to radon gas or its decay products radon daughters in the mines.
The radon daughters give off radiation in the lung when they are breathed in. This causes the lung cancer.
The longer miners worked or the greater their exposure to radon daughters (as measured by working level months), the greater the risk for lung cancer.
Smoking also causes lung cancer. White miners who smoked were more likely to get lung cancer than nonsmokers. Non-white miners smoked much less than white miners. This probably protected them from having even higher lung cancer rates.
Lung Diseases
The risk for other lung diseases was 2½ times higher than normal in non white miners (about 8 expected, 20 seen). This category includes many different lung diseases. They include those caused by breathing in mining dust, such as silicosis. Silicosis causes severe breathing problems.
The longer miners worked, the more likely they were to develop one of these lung diseases.
Tuberculosis (TB)
The risk of TB was about 2½ times greater than in non-white miners (about 4½ expected, 12 seen).
The risk of TB could have been related to silicosis. People with silicosis are more likely to get TB.
Only a few deaths from TB have occurred in recent years, but this is something to be on the watch for.
Total Deaths
Unlike white miners, non-white miners had slightly fewer than expected total deaths.
We don't know why the white miners had greater risks than non-white miners.
However, we think that the white miners' greater risk of lung cancer and lung disease was because many more of them smoked than non-white miners.
Thank You
The PHS/NIOSH study helped us learn more about the hazards of uranium mining. It has helped to bring about badly needed improvements in mining conditions. It also has helped to answer other questions about radon exposure.
The main question is what level of radon in the basements of some homes is hazardous.
Any Questions?
If you have any questions about this study or would like a copy of the technical reports, call the NIOSH toll-free number: 1-800-356-4674