http://www.cdc.gov/niosh/pgms/worknotify/uranium.html

2000

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 following has information about the results of the latest study.

Background

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.

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

• 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.
• 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.
• 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.