HDI is the common name for hexamethylene diisocyanate. It is also known as 1,6-hexamethylene diisocyanate, 1,6-diisocyanatohexane, Mondur HX, and Desmodur H. It is a pale yellow liquid with a strong odor. HDI is found in hardening agents for automobile paints.
Pathways for HDI in the environment
HDI is most often found in air near locations where spray paints that contain it as a hardening agent are used. HDI in the air can enter the soil and water. HDI can also enter the soil if products containing it are dumped directly onto the soil. HDI can enter the water supply by washing out of soil that contains it or if products with HDI are dumped directly into water. Once it is in soil or water, HDI does not easily evaporate, so general air pollution is not expected. HDI breaks down very quickly in water or sunlight, so it probably will not build up in the environment.
Exposure to HDI
The most common products that contain HDI are called hardening agents and are used to spray-paint cars. The most common way a person can be exposed to HDI is by breathing air that contains it as a vapor or mist, like that made when spray-painting a car. Most of the people who are exposed to HDI work in the automotive painting industry or in areas where this is done. If you do this kind of work, you can be exposed to more HDI if you do not wear the right protective safety equipment such as a respirator or mask. If your safety equipment does not fit right or does not work properly when you are using products that contain HDI, you may be exposed to larger amounts. You can probably absorb some HDI through your skin. You could also accidentally swallow HDI if it is on your hands and you do not wash them before eating, drinking, or smoking.
Unless you have been employed in the automobile refinishing or other business where painters manually mix two-component polyurethane paint systems, it is unlikely that you will be exposed to large amounts of HDI.
Pathways for HDI in the body
The most common way HDI enters your body is by breathing air that has it in it. You can probably absorb some HDI through your skin, and you can also accidentally swallow HDI if it is on your hands and you do not wash them before eating, drinking, or smoking. Once inside your body, HDI breaks down very quickly and is quickly excreted in the urine. Some HDI can attach itself to protein in your blood, but we do not know how long it takes for this form of HDI to break down and be excreted.
Health effects of HDI
To protect the public from the harmful effects of toxic chemicals and to find ways to treat people who have been harmed, scientists use many tests.
You should know that one way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify such health effects as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.
Additionally, there are vigorous national and international efforts to develop alternatives to animal testing. The efforts focus on both in vitro and in silico approaches and methods. For example, the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences (NIEHS) created the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) in 1998. The role of NICEATM is to serve the needs of high quality, credible science by facilitating development and validation—and regulatory and public acceptance—of innovative, revised test methods that reduce, refine, and replace the use of animals in testing while strengthening protection of human health, animal health and welfare, and the environment. In Europe, similar efforts at developing alternatives to animal based testing are taking place under the aegis of the European Centre for the Validation of Alternative Methods (ECVAM).
How HDI affects your health depends on how much is in the air you breathe. Tests using laboratory animals showed that breathing in high concentrations of HDI can irritate the nose, eyes, and throat. High concentrations have also caused pneumonia, difficulty in breathing, and death in some animals. Swallowing high concentrations of HDI also killed laboratory animals. When placed on the skin of these animals, HDI caused redness, irritation, and irreversible skin damage. People would probably be affected in many of the same ways if they were exposed to large amounts of HDI in air.
Many people who breathe in vapors from products with small amounts of HDI for many months or many years may develop an allergic, asthma-like reaction. Symptoms usually develop very slowly over a long time (months or years), but they can also develop within a couple of weeks after first breathing in HDI. At low concentrations, sensitized workers develop a burning sensation and a feeling of tightness in the chest, a cough (with and without phlegm), fever, and chills. They have a hard time breathing during their work day when using a product containing HDI. These signs usually are not seen on weekends, during vacations, or any time the person is not using a product that contains HDI. These reactions usually begin again soon after the person returns to work and begins to use the product with HDI.
Some studies in laboratory animals showed that, when breathed in over a long time, HDI did not produce cancer. No studies that show that HDI can cause cancer in people have been found.
Medical tests for exposure to HDI
Before you ask for special medical tests for HDI, you should talk with your doctor and tell him you work in a place that uses products that contain HDI. There are no good medical tests for finding out if you have been exposed to HDI. Some tests are available that measure the antibodies against HDI your body makes after you have been exposed to it. However, these blood tests are not very good because they can react with other substances that look like HDI in your blood. The test can show that you have been exposed to HDI when really you have not been exposed to it (false positives). Also, some people do not develop antibodies to HDI after they have been exposed. Another test looks for the breakdown products of HDI in the urine. This test is only good if you were exposed to HDI within the last 12–15 hours. It is not a good test to find out if you have been exposed to low amounts of HDI over many months or years.
Unless you have been employed in the automobile refinishing or other business where painters manually mix two-component polyurethane paint systems, it is unlikely that you have been exposed to significant amounts of HDI. Your doctor can give you more information on medical tests that are available for determining if you have been exposed to HDI.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.