Why the chemicals are considered of concern:
Diisocyanates are a group of chemicals—within the larger isocyanate family of chemicals—primarily used to make polyurethane polymers found in products ranging from bowling balls to insulation foam. During polyurethane synthesis, diisocyanates react with other chemicals—a process called curing—to form polyurethane polymer chains. When the curing reaction is complete and virtually no unreacted diisocyanates remain, the polyurethane product is said to be “cured.” Cured products, which contain fully reacted diisocyanates incorporated into polyurethane polymers, are essentially non-toxic. However, unreacted diisocyanates – whether those remaining unreacted in cured products or those present in uncured products – are highly toxic, especially to the respiratory system.
Diisocyanates are known to induce and exacerbate asthma, damage the lung, cause irritation of the skin, eyes, nose and throat, and in severe cases, result in death. They have also been linked to cases of hypersensitivity pneumonitis (inflammation of the lungs) and pulmonary edema (fluid in the lungs). A specific diisocyanate – toluene diisocyanate (TDI) – has been identified by the International Agency for Research on Cancer (IARC), as carcinogenic in animals, while the U.S. National Toxicology Program (NTP) considers it a "reasonably anticipated human carcinogen."
Exposure to diisocyanates occurs most often through inhalation, although skin contact can also cause irritation and sensitization. Exposure potential is increased when products containing diisocyanates are sprayed or heated.
Diisocyanates are chemical sensitizers, that is, repeated exposure results in increasing sensitivity to their effects such that even low levels of exposure can trigger severe asthmatic reactions. In addition, asthmatic response can be delayed by up to 12 hours following exposure.
The two most commonly used diisocyanates are Methylene Diphenyl Diisocyanate (MDI) and Toluene Diisocyanate (TDI), which make up about 90% of the entire diisocyanates market. They are frequently used in the automobile and construction industries and are a leading cause of occupational asthma (see here, here and here). The National Institute for Occupational Safety and Health (NIOSH) highlights several case reports of isocyanate-induced asthma, respiratory problems, and in a few cases, death. In fact, each year about 280,000 workers are exposed to diisocyanates, yielding a substantial prevalence of isocyanate-induced asthma.
Consumers are vulnerable bystanders to commercial application of diisocyanates when used to seal concrete, wooden decks and roofs. More recently, potential exposure of the general public to diisocyanates has risen due to the increasing availability of household products containing these chemicals. In particular, do-it-yourself homeowners may inadvertently expose themselves to higher levels of diisocyanates as commercial-grade polyurethane products become ever more available to consumers.
Children are especially susceptible to diisocyanate exposure and resulting illness. Diisocyanate vapors are heavier than air and settle close to the ground, leaving children more vulnerable to inhalation and skin absorption. In addition, children breathe in more air relative to their body size compared to adults. In one case study, school children were exposed to MDI from a polyurethane-based artificial surface applied to an athletic track. Of the children exposed to fumes from the track material, 60% with no prior history of asthma reported asthma-like symptoms of shortness of breath and coughing, and many students suffered eye and throat irritation, nausea, headaches and vomiting.
Air releases of diisocyanates are of concern because of the potential for direct inhalation exposure. Diisocyanates can also react with water in the air – a process called hydrolysis – to form other hazardous chemical compounds called diamines (TDI forms toluene diamine; MDI forms methylene diphenyl diamine). The stability of diisocyanate and diamine compounds in air depends in part on humidity levels. Under conditions of low humidity, diisocyanates may remain stable enough to be transported across long distances.
Where the chemicals are most commonly found:
Diisocyanates are found in a broad range of products, including adhesives, sealants, binders, coatings, spray paints, whiteboard paints, rubbers, plastics and crafts materials. They are used extensively in industries that produce and repair automobiles, boats, furniture, appliances and electronics.
Many other products contain diisocyanates in an uncured and much more toxic form, however, usually in the form of liquids, sprays, aerosols or foams that stiffen as polyurethane polymers are formed through the curing process. The curing time for polyurethane products has been shown to be variable. As a result, the recommended amount of time one should wait before entering an area in which diisocyanate-containing products have been applied also varies. The curing rate depends on several factors, including product type, application method and ventilation. Diisocyanate-containing products remain hazardous until curing is complete.
Of note, government programs have incentivized the use of polyurethane foams for increasing energy efficiency. These products are used for insulation and are available in uncured forms as “pour in place” foam, spray polyurethane foam (SPF), and one-component foam (OCF).
The Occupational Safety and Health Administration (OSHA) regulates worker exposure to diisocyanates through the establishment of permissible exposure limits (PEL). OSHA also requires the use of personal protective equipment when workers are using diisocyanates. Employers are charged with determining appropriate protective equipment for hazards encountered by their employees and training of employees on how and when to use such equipment.
Under the Clean Air Act, diisocyanates are regulated as hazardous air pollutants. The Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) regulate diisocyanates as hazardous when present in wastes.
Twenty diisocyanates are subject to Section 313 of the EPA’s Emergency Planning and Community Right to Know Act (EPCRA). This section requires businesses to report environmental chemical releases and waste management of identified toxic chemicals. The reported information is subsequently made publicly available on the EPA Toxics Release Inventory.
In the European Union, measures have been taken to limit MDI in consumer products under the EU’s REACH Regulation. Since December 27, 2010, MDI has been banned in quantities greater than 0.1% in products sold to the general public. Products exceeding that limit may only be sold to consumers if they contain approved protective gloves and are visibly marked with the chemical hazards, application instructions and warnings of the health risks associated with product use.
What should be done:
Users of products containing uncured diisocyanates should take all necessary precautions to protect themselves when using these products. This starts with informing yourself as to whether the products you use contain diisocyanates. Call the product manufacturer when chemical ingredients aren’t listed or if you are unsure whether listed ingredients are diisocyanates. Do-it-yourselfers should be especially wary and take extreme precaution when using uncured polyurethane products, including using personal protective equipment (PPE). Workers must also use appropriate PPE and those sensitized to diisocyanates should cease work with these chemicals to avoid severe health complications.
Industry should look towards the use of new non-isocyanate polyurethane alternatives. There is a new class of non-isocyanate polyurethanes and isocyanate-free expanding foam products that show potential. These products are purported to be equally as effective as their isocyanate counterparts, less costly to produce and safer, all claims that must be further evaluated and substantiated.
The widespread, expanding and largely unregulated use of dangerous diisocyanates in consumer products underscores the larger problem of inadequate chemicals policies and the need for reform of the Toxic Substances Control Act (TSCA). Effective TSCA reform would assure that full safety data would be generated and made available to consumers, and that consumer uses of these chemicals be shown to be safe. As it stands, there is little information on consumer uses and consumer exposure to diisocyanate-containing products. Unfortunately, current TSCA does not provide EPA with authority to require better chemical use information from industry, let alone adequate chemical testing, as a condition for entering or remaining on the market.
In April 2011, Senator Lautenberg introduced legislation that would provide critical reforms to TSCA: the Safe Chemicals Act of 2011. Among other things, this legislation would enable EPA to obtain and provide public access to better use, hazard and exposure information on chemicals. This necessary reform would improve public protection from diisocyanates and the thousands of other chemicals poorly regulated in the US. Show your support for stronger toxic chemicals regulation here.