Worker Health Study Summaries

Research on long-term exposure

Uranium Miners (1)

2000

Study Background

The National Institute for Occupational Safety and Health (NIOSH) is a part of the US Public Health Service (PHS). The PHS and NIOSH have conducted a series of studies since 1950 on the health of uranium miners.

The PHS began the study in 1950 because of concerns that uranium mining causes lung cancer. (We know that miners were not informed of these concerns at the time). We call it a mortality study because it looks at whether miners have been dying of certain diseases at a higher than normal rate.

NIOSH researchers took over the study in the 1970s, and it has been “updated” several times. The following describes the results of the most recent update.

How the Study Was Done

The mortality study did not include all uranium miners. The study group was only made up of uranium miners who worked underground for at least one month. Also, each miner must have taken part in at least one of the medical exams conducted by the PHS between 1950 and 1960.

First we obtained miners’ work histories. We obtained smoking histories from the medical exams. Next we used death certificates to find out what miners died from. Then we compared the death rates in miners to death rates in the general population of the mining states. The rates in the general population gave us the number of expected deaths in miners. When the number of deaths in miners is greater than the expected number, then an association with mining is suspected.

Because death rates are different for people of different races, we did one study on 3,238 white miners. We did a second study on 757 Native American, African American, and Asian miners. (All but 4 of the 757 miners were Native Americans, mainly Navajo). The following will review the results from each study.

Radon Gas and “Radon Daughters”

From the start, radioactive radon gas and radon “daughters” in the air were suspected as the cause of the lung cancer. Radiation can be thought of like invisible radio waves (only radio waves are harmless) or like specks of dust so tiny they are invisible. We estimated how much of the radon daughters each miner was exposed to by a unit called the working level month. We then looked to see if death rates increased with higher working level months.

This exposure-response relationship is strong evidence of an association between disease and exposure. It is used to show that the longer a miner is exposed to radon gas, the greater may be the risk of lung cancer.

Results for White Uranium Miners

The study looked at all causes of death. Only the causes of death listed below were significantly above normal. The results for all other causes of death were within the normal range.

Lung cancer

We found strong evidence for an increased risk for lung cancer in white uranium miners. We expected about 64 deaths, but found 371. This means we found about 6 times more lung cancer deaths than expected.

There was an exposure-response relationship with exposure to radon daughters in the mines. When radon daughters are breathed in, they decay radioactively in the lung. This can cause lung cancer.

Pneumoconiosis

We also found strong evidence for pneumoconiosis, a type of lung disease (other than cancer) which is caused by dust. We expected less than 2 deaths, but found 41. There were about 24 times more of these deaths than expected.

This category includes silicosis, a disease caused by breathing in a particular mining dust, silica. Silicosis causes scarring of the lung and severe breathing problems. The risk of these lung diseases was greater the longer miners had worked in the mine.

Tuberculosis

We expected to see about 3 ½ deaths from the infectious lung disease tuberculosis (TB), but we saw 13. This is about 4 times more deaths than expected. This could have been related to the silicosis. People with silicosis are more likely to get TB.

Emphysema

We expected to see about 22 ½ deaths from emphysema but found 56. This is 2 ½ times more deaths than expected. Some of this result could have been related to cigarette smoking. People who smoke are more likely to get emphysema.

Injuries

We expected to see about 68 deaths from injuries and found 143. This is over 2 times more deaths than expected.

Benign cancers and diseases of the blood

We also saw a greater risk of deaths from the categories “benign and unspecified cancers” and “diseases of the blood”. Both of these categories had small numbers of deaths. Therefore, it is possible that the increased risk may not be due to mining.

All deaths

Finally, we saw a greater risk for “all deaths combined”. We expected 986 deaths and found 1,595. This is 1 ½ times more deaths than expected.

Results for Non-White Uranium Miners

The study looked at all causes of death. Only the causes of death listed below were significantly above normal. The results for all other causes of death were within the normal range.

Lung cancer

We found strong evidence for an increased risk for lung cancer in non-white uranium miners. We expected about 10 deaths, but found 34. This means we found over 3 times more lung cancer deaths than expected.

There was an exposure-response relationship with exposure to radon daughters in the mines. When radon daughters are breathed in, they decay radioactively in the lung. This can cause lung cancer.

Pneumoconioses and other lung diseases

We also found strong evidence for pneumoconioses and other lung diseases (other than cancer). We expected about 8 deaths, but found 20. This means there were about 2 ½ times more of these deaths than expected.

This category includes many different diseases. They include silicosis. a disease caused by breathing in a particular mining dust, silica. Silicosis causes scarring of the lung and severe breathing problems. The risk of these lung diseases was greater the longer miners had worked in the mine.

Tuberculosis

We expected to see about 4 ½ deaths from the infectious lung disease tuberculosis (TB), but we saw 12. There were about 2½ times more of these deaths than expected. This could have been related to the silicosis. People with silicosis are more likely to get TB.

Limitations of the NIOSH Uranium Miners Health Study

Small Study Size

The study of the non-white miners was somewhat small with a total of only 757 miners.

Researchers are more confident of the results of studies with thousands of people in them.

Because of the small study size of the non-white miners, we may have missed some other illnesses connected to this mining group.

We are somewhat more confident of the results of the study of 3,238 white miners.

Mortality

Since this was a mortality study, it only looked at causes of death among miners.

This study was not able to look at non-fatal injuries or at health problems that do not cause death.

Many miners today are still experiencing the effects of mining.

For example, they may still suffer from injuries that took place while mining. Or they may suffer from breathing problems. However, we were not able to take these conditions into account.

Uranium Millers

This study did not include uranium millers. However, NIOSH is in the process of planning a new study of uranium millers. This study will be completed in the years to come.

Environmental Pollution

The uranium mining and milling industries caused environmental pollution.

They may have affected the health of community members other than workers. However, our study could not address these important issues.

Questions and Answers

Why did NIOSH study Uranium Miners?

Uranium Miners were exposed to radon gas, a radioactive material thought to cause lung cancer.

Uranium Miners were exposed to mining dust, thought to cause lung disease.

NIOSH made the study to find if uranium miners have an increased risk for lung cancer and other lung disease when compared to the U.S. general public.

Who was included in the NIOSH study?

• Uranium miners who worked underground more than one month before 1964
• Uranium miners who completed a medical exam between 1950 and 1960
• A total of 3,238 white miners and 757 mainly Navajo miners

How did NIOSH do the study?

• We looked at how many months uranium miners were exposed to radon gas.
• We reviewed each miner’s past smoking history.
• We obtained death certificates for miners who had died.
• We compared the number of deaths from lung cancer and other lung disease in uranium miners to that of the general public who lived in the same states.
• We determined if the number of deaths from lung cancer and lung disease increased in uranium miners with longer exposure to radon gas.

What were the study results for White Miners?

We found the following deaths were greater among white uranium miners compared to the general public:

• Lung Cancer – If the risk to uranium miners was the same as the risk to the general public, we would have expected 64 deaths from lung cancer. Instead we found 371. This was nearly 6 times more deaths than expected.

  The longer a white miner was exposed to radon gas, the greater the risk of lung cancer.

• Pneumoconiosis – we expected less than 2 deaths and found 41. This was nearly 24 times more deaths than expected.

  This category included silicosis, a lung disease caused by breathing in a particular mining dust, silica. Silicosis causes scarring of the lung and severe breathing problems.

• Tuberculosis – we expected 3 ½ deaths and found 13. This was nearly 4 times more deaths than expected.
• Emphysema – we expected 22 ½ deaths and found 56. This was 2 ½ times more deaths than expected.

  The longer a miner worked in a mine, the greater the risk of lung disease.

• 

  Injuries – we expected about 68 deaths from injuries and found 143. This was over 2 times more deaths than expected.

• Benign and Unspecified Cancers – we expected less than 3 ½ deaths and found 8. This was about 2 ½ times more deaths than expected. This category includes cancers that are usually not fatal (benign) or when the exact type of cancer is not listed on the death certificate (unspecified).
• Diseases of the Blood – we expected less than 3 deaths and found 7. This is also about 2 ½ times more deaths than expected.
• All Deaths Combined – we expected 986 and found 1,595. This is over 1 ½times more deaths than expected. This was an unusual finding because working people are usually healthier than the general population.

What were the study results for Navajo and other Non-White Miners?

We found the following deaths were greater among non-white uranium miners compared to the general public:

• Lung Cancer – we expected only 10 deaths and found 34. This was over 3 times more deaths than expected.

  The longer a miner was exposed to radon gas, the greater the risk of lung cancer.

• Other Lung Diseases – we expected less than 8 deaths and found 20. This was over 2½ times more deaths than expected.

  This category included many diseases. They include silicosis, a lung disease caused by breathing in silica. Silicosis causes scarring of the lung and breathing problems.

• 

  Tuberculosis – we expected 4½ deaths and found 12. This was over 2½ times more than expected.

  The longer a miner worked in a mine, the greater the risk of lung disease.

How can you help protect your own health?

If you smoke, you should stop.

Smoking greatly increases the risk of lung cancer and other lung disease in miners who breathed radon and dust. Smokers who quit now will reduce their risk even though they may have smoked for many years.

See your doctor if:

– you have trouble breathing
– you cough a lot
– you often feel tired

See your doctor for a skin test for tuberculosis (TB).

Eat lots of fresh fruits and vegetables. At least 5 servings each day may help to prevent lung cancer.

Where can you get additional information?

For more information about the study, call NIOSH toll-free at:

800-356-4674

For more information about lung cancer, call:

National Cancer Institute
800-4-CANCER

American Cancer Society
800-227-2345

For more information about lung disease, call:

American Lung Association
800-586-4872

Any Questions?

You or members of your family may have additional questions about the NIOSH study or would like a copy of the technical report. If so, call our toll-free number: 800-356-4674.

Radiation Exposure Compensation Program

In 1990, Congress passed a bill known as the Radiation Exposure Compensation Act (RECA). One of the purposes was to compensate (pay) eligible uranium miners who developed certain diseases (or their families) up to $100,000. These diseases are: lung cancer, fibrosis of the lung, pulmonary fibrosis, cor pulmonale related to fibrosis of the lung, and moderate or severe silicas is or pneumoconiosis.

This bill includes an apology to you and others:

“The Congress apologizes on behalf of the Nation to the (affected individuals) and their families for the hardship they have endured.”

To find out if you are eligible for compensation, or you have other questions on this program, call the toll-free number at the Justice Department: 800-729-RECP

or write to:

Radiation Exposure Compensation Program
U.S. Department of Justice
P.O. Box 146 Ben Franklin Station
Washington, D.C.
20044-1046

To receive other information about occupational safety and health
problems, call 800-35-NIOSH (800-356-4674), or visit the NIOSH Homepage on the World Wide Web at: www.cdc.gov/niosh.

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 to Study Participants

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: 800-356-4674

Steps to Protect Your Health

This section has information for former miners today.

Even though former uranium miners have an elevated risk for certain diseases, that does not mean that you will get one. Also, there are steps you can take right now that will help prevent these diseases.

Smoking is terrible for the lungs and causes lung cancer, especially in people exposed to radon gas. If you smoke, NIOSH recommends that you quit. Even if you have smoked for a long time, stopping now will improve your health.

See your doctor if you have trouble breathing, cough continuously, or feel very tired. Take a copy of these materials to your doctor.

Ask your doctor about having a simple skin test for tuberculosis (TB).

Eating a variety of fresh fruits and vegetables every day may help prevent lung cancer.

For more information on cancer, you should contact any of the following agencies:

The National Cancer Institute is a federal agency that studies cancer. They can answer questions about cancer. They also can provide the names of doctors in your area who treat cancer. Their toll-free number is: 800-4-CANCER

The American Cancer Society can answer questions about cancer. They also provide classes to stop smoking. Call their toll-free number to find the office closest to you: 800-227-2345

The American Lung Association can answer questions about lung diseases, including cancer. They also provide classes to stop smoking. Call their toll-free number to find the office closest to you: 800-586-4872

For Navajos desiring medical assistance, contact the Native American Health Service in your area.

Additional Resources

Roscoe RJ, Deddens JA, Salvan A, Schnorr TM. Mortality among Navajo uranium miners. Am J Public Health 1995;85(4):535-540. (Study Report)

Roscoe RJ. An update of mortality from all causes among White uranium miners from the Colorado Plateau study group. Am J Ind Med 1997;31:211-222. (Study Report)