Worker Health Study Summaries – O-toluidine Exposure

Research on long-term exposure

Tire and Rubber Company (2) (O-toluidine Exposure)


Study Background

NIOSH conducted two studies of workers at a tire and rubber manufacturing plant. The first study was conducted to evaluate whether workers at the plant had an excess risk of bladder cancer due to their exposure to o-toluidine, a chemical used in one of the plant’s departments.

How the Study was Done

The NIOSH study compared the number of bladder cancers among workers at a tire and rubber manufacturing plant from 1973 to 1988 with the number that would be expected in a similar population of New York State residents. This fact sheet will explain how the study was done.

How Work Records Were Used

Work records contained the department and the general job title for each worker. NIOSH used the work records to identify who had worked in departments where exposure to o-toluidine and aniline may have occurred. We also recorded the dates each worker held jobs in these areas.

How a Worker’s Exposure Was Determined

NIOSH classified all workers who worked in exposed departments between 1957 and 1988 as “definitely exposed” to aniline and o-toluidine. NIOSH does not have enough information to know how much exposure to o-toluidine and aniline individual workers had in the past. Therefore, NIOSH used the number of years of employment to estimate how much exposure individual workers had.

NIOSH believes that some workers in maintenance, janitorial/yard, and shipping jobs also may have been exposed. If an individual worked in any of these departments, NIOSH identified that individual as being “possibly exposed” to these chemicals.

If an individual did not work in either certain exposed departments or maintenance, janitorial/yard, or in the shipping departments the worker was identified as “probably unexposed” to either chemical.

Determining the Number of Workers Who Developed Bladder Cancer

NIOSH determined the number of bladder cancer cases from company and union records and from death certificates. NIOSH also matched the records of the workers with cases of bladder cancer listed in the New York State Cancer Registry.

How the Expected Number of Bladder Cancer Cases Was Determined

The number of bladder cancer cases expected in each group was calculated using the rate of bladder cancer in New York State for individuals of similar age and sex.


In this study, 8 cases of bladder cancer were found among workers “definitely exposed” to o-toluidine and aniline, while only 1.2 were expected.

Among workers who were “possibly exposed” to these chemicals there were 4 bladder cancer cases observed and 1.05 expected.

Among workers who were “probably exposed” to these chemicals there were 2 cases of bladder cancer, and 1.29 expected.

What Was the Likely Cause?

To try to determine the cause of an apparent increase in bladder cancer, NIOSH first identified all the chemicals used in exposed departments since 1957.

One of those chemicals, o-toluidine, is known to cause bladder cancer in animals. Therefore, this chemical is thought to be the most likely cause of bladder cancer in workers. Another chemical, aniline, which causes cancer in rats cannot be ruled out as a cause of bladder cancer in these workers.

Both o-toluidine and aniline are used to make Wingstay 100. Wingstay 100 has been manufactured since 1957. Aniline is used to make Morfax which has been manufactured since 1970. The two chemicals were used only in certain departments at the plant.

bar chart showing bladder cancer risk is 6.6 times higher than normal for the definitely exposed group, and 3.8 times higher than normal for the possibly exposed group
Determining Risk

The chart at the right shows the estimated bladder cancer risk for each exposure group. The number above each bar is the estimate of risk. The normal value for New York State residents is 1.0 and is indicated by the heavy, solid line across the chart.

Here is how to interpret the chart. Above the bar called All Workers you will see the number 3.95. That Number means that all the workers at the plant have a 3.95 times greater risk of developing bladder cancer than other residents of the state.

Workers with “definite” and “possible” exposure to aniline and o-toluidine appear to have a serious risk of developing bladder cancer.

Though workers in the “probably unexposed” group had an elevated risk of bladder cancer, the increase was small. Some workers in this group may have been exposed to aniline and o-toluidine which would increase their risk of bladder cancer. The increase in that group may also have occurred solely by chance.

For more information please call the NIOSH toll-free number at 800-356-4674.

Symptoms of Bladder Cancer and Other Urinary Tract Diseases

Bladder cancer can be treated more easily if it is caught early.

Blood in Urine

Blood in urine is a sign of possible bladder cancer. Your urine may look pink or red. There may also be spots of red in the urine. You may have blood in your urine without having any pain or other symptoms.

Changes in the Way Your Urine Looks

Your urine may appear hazy, cloudy or murky.

Changes in the Way You Urinate

You may have to urinate more often than you used to or more often than other people.

You may have to get up during the night more than two times to urinate almost every night.

You may have trouble holding your urine until you get to the toilet.

Your flow of urine may not be as strong as it used to be.

You may have pain, burning or stinging when you urinate.

After urinating you may often have to go again.


A lump may appear in your groin or in the lower part of your abdomen


You may have pain in your lower abdomen or your lower back.

These symptoms do not necessarily mean that you have bladder cancer, but do mean that you need to be checked. If any of these symptoms appear, it is important that you see your doctor at once.

Screening for Bladder Cancer

You may have developed bladder cancer without having any symptoms. Two tests are currently used to help detect bladder cancer before symptoms develop.

One is a test for blood in the urine. The other is a test for abnormal cells in the urine.

Neither of these tests will tell us whether or not you have bladder cancer. However, they can identify workers who should have further tests for bladder cancer. These tests are called screening tests.

Testing for Blood in Your Urine

There may also be so little blood in your urine that it cannot be seen. Yet this small amount of blood may be a sign of bladder cancer. Therefore, your urine should be tested for blood.

Testing Your Urine for Abnormal Cells

Another way that bladder cancer can be detected early is by looking at the cells that normally appear in your urine under a microscope. Cancer cells look different under a microscope than normal bladder cells.

Both of these tests can be done using a sample of your urine which you collect in the privacy of your home or restroom. The urine will be sent to the laboratory. If any evidence of blood or abnormal cells are found, you will need to see a doctor about further tests. These additional tests will determine whether or not you have bladder cancer.

Reducing Your Risk of Bladder Cancer

Reducing Your Exposure to Aniline and O-toluidine

NIOSH made recommendations to reduce exposure to o-toluidine and aniline, as well as to generally improve housekeeping. A letter describing our recommendations was sent to both union and company representatives.

If an individual still works in an exposed department, it is important to make every effort to avoid contact with these chemicals, particularly contact with your skin or work clothing.

Work with your supervisor and your union representative to make certain that efforts are made to reduce unsafe conditions and to ensure workers are aware of how to protect themselves from any further contact with o-toluidine and aniline.

Reducing Your Risk by Giving Up Smoking

Cigarette smoking is known to increase the risk of bladder Cancer. Cigarette smoke contains aniline and o-toluidine and many other chemicals. Therefore, to reduce your risk of bladder cancer, you should stop smoking.

Programs to help you stop smoking are available from the American Cancer Society and the American Lung Association.

For more information please call the NIOSH toll-free number at 800-356-4674.

Additional Resources

Ward E, Carpenter A, Markowitz S, Roberts D, Halperin W (1991): Excess number of bladder cancers in workers exposed to ortho-toluidine and aniline. JNCI 83(7):501-506 (Study Report)

Ward E, Sabbioni G, DeBord G, et al. (1996). Monitoring of aromatic amine exposure in workers at a chemical plant with a known bladder cancer excess. Journal of the National Cancer Institute 88:10461052.

Ruder A, Ward E, Roberts D et al. (1992). Response of the National Institute for Occupational Safety and Health to an occupational health risk from exposure to ortho-toluidine and aniline. Scandinavian Journal of Work, Environment and Health, 18:82-24.

Flesch J, Ward E, Roberts D (1990) . Preventing Bladder Cancer from Exposure to o-Toluidine and Aniline NIOSH ALERT: December 1990. DHHS (NIOSH) Publication Number 90-116

Page last reviewed: April 8, 2020