Findings of the NIOSH Mortality Study
The NIOSH study helped us learn more about the hazards of cadmium exposure. This information will help workers exposed to cadmium around the world.
Why the Study Was Done
The purpose of the study was to see whether exposure to cadmium was associated with increased death rates in workers when compared to the general population.
How the Mortality Study Was Done
NIOSH conducted an initial mortality study and 2 updates. Mortality means that the study looked at causes of death.
The study took place between 1976 and 1986. It included a total of 625 production workers (current and former). They all had worked between 1940 and 1969. They may have worked before 1940 or after 1969, too.
This kind of study is done without contacting the individual worker because it is based on records. The study did not involve medical exams. It included living and deceased workers.
We used government records to find out which workers had died. Death certificates reported the cause of death. NIOSH usedpublic records to find out the death rate for certain diseases in the general population. NIOSH used work histories and cadmium air measurements to estimate how much cadmium each worker had been exposed to through 1976.
NIOSH compared the death rates in workers exposed to cadmium to the death rates in the public. We did this for many diseases. When the death rate is higher in workers, the reason sometimes (but not always) is due to workplace exposures.
What the Mortality Study Found
Overall Death Rate
Overall, cadmium workers had lower death rates than the general public. For example, heart disease death rates were lower.
Lung Cancer
NIOSH found that cadmium workers who had worked for at least 2 years definitely had a higher death rate for lung cancer. This was probably due to breathing in cadmium.
As the first chart below shows, the more cadmium a worker was exposed to, the more likely he developed lung cancer.
Smoking causes lung cancer. But, overall, the cadmium workers don't smoke more than the general public.NIOSH has smoking information on only 14 of the 24 men who died of lung cancer. 13 of the 14 were cigarette smokers.
Workers employed at the plant before 1926 (when the plant was an arsenic smelter) had a very high risk of lung cancer-more than 7 times greater than normal. This was probably due to high arsenic levels.
For workers hired since 1926, NIOSH thinks that both smoking and cadmium probably contributed to the lung cancer. Arsenic may have contributed to a lesser extent
Other Diseases
NIOSH had much weaker evidence that cadmium exposure was associated with cancer of the prostate gland and digestive disease (mainly stomach ulcers).
We are not sure that these 2 problems are related to cadmium, though.
Exposure Levels
The areas with the highest cadmium levels in the past were: calcine, roaster, sampling, mixing, solution, retort, foundry, pigment, and tankhouse. These departments are listed roughly in descending order of exposure.
The level in retort may still be high, but in general levels are much lower today than in the past.
An Estimate of Risk-Lung Cancer and Cadmium Exposure
NIOSH estimated how much cadmium each worker had been exposed to at the plant by the end of 1976. We assigned each worker to the low, medium, or high cadmium exposure group.
Charts
The charts show the risk of dying from lung cancer for cadmium workers at the plant. They give the risks for the 3 exposure groups.
The first chart shows the risk for all workers hired from 1926 through 1969. The second chart shows the risk for workers hired between 1940 and 1969.
Each bar shows the estimate of risk of dying from lung cancer. They are estimates of how the group of workers compares to normal. Normal is the general population of Colorado.
The "normal" value is 1.0. The lines across the charts show the normal value. When the bar is below 1.0, cadmium workers have less risk. When the bar is above 1.0, they have more risk.
First Chart - Workers Hired 1926-1969
Here is how to interpret the risk estimates in the first chart:
- Workers in the low group had about half the risk of other Coloradoans.
- Workers in the medium group were about 2 and a half times more likely to die of lung cancer.
- Workers in the high exposure group were almost 4 times more likely to die of lung cancer.
The chart shows that the risk went up as exposure to cadmium increased. This is important evidence that cadmium exposure is associated with lung cancer.
Second Chart - Workers Hired 1940-1969
The risks in the second chart are interpreted the same way. For example, workers in the high exposure group had about 1¾ times the risk of other Coloradoans.
Workers in the medium exposure group also had an elevated risk of lung cancer. Workers in the low group didn't have a higher risk.
Other Facts
All deaths from lung cancer took place in employees who had worked for at least 2 years.
We can compare the risks shown in charts 1 and 2 to the risk of cigarette smoking. Smokers are about 9 times more likely to die of lung cancer than non-smokers.10% of the 234 workers who died by 1984 had died of lung cancer. In the general U.S. population, about 8% of white men die of lung cancer.