Johanna Katz is a Cornell Iscoll intern at EDF. Jennifer McPartland, Ph.D., is a Health Scientist.
Toxic chemicals called diisocyanates are long-established as occupational hazards known to cause severe respiratory problems to workers who use or are otherwise exposed to them (see here). In fact, diisocyanates are the number one cause of workplace-induced asthma (see here and here). Recently, potential exposure of the general public to diisocyanates has grown, as these chemicals are increasingly used in consumer products. This is certainly a troubling trend considering that the primary health effect of these chemicals, asthma, is a massive and growing public health problem, especially among children. And some of the newest uses of diisocyanates are in products to which children are quite likely to be exposed.
Asthma is at an all-time high, affecting more than 24 million Americans, and creating astronomical health and productivity costs upwards of $20 BILLION each year. And while diisocyanates are but one of many contributors to the increasing rate of asthma in the general population, we surely don’t need to be bringing more products containing such chemicals into our homes, schools, and workplaces. That will only make matters worse.
So what exactly are diisocyanate chemicals, where are they found, and what’s the federal government trying to do about them? Read on to find out.
A diisocyanate is any of several chemical compounds that has two reactive isocyanate groups (N=C=O) in its structure. Isocyanates react with another group of chemicals called polyols to form a family of polymers commonly known as polyurethanes. Products containing polyurethanes are numerous, varied and found everywhere: from couch cushioning to roller blade wheels to deck sealant.
Waiting for the cure
Not all of these products are necessarily hazardous. Their potential toxicity is dependent on whether and to what extent the product is cured or uncured. In fully cured polyurethane products, the reactive diisocyanates have been incorporated into polyurethane polymers and virtually no unreacted diisocyanates remain. These products – a good example is a bowling ball – contain cured polyurethanes and can be considered essentially non-toxic.
In contrast, products containing diisocyanates that are not yet incorporated into polyurethane polymers are uncured (i.e. still reactive) and remain toxic until and unless the curing process is complete. And herein lies the problem. Without complete curing, exposure to toxic diisocyanates continues to be possible through inhalation and skin absorption. Uncured polyurethane products include adhesives, sealants, coatings, paints, craft materials and insulating foams. Among other uses, uncured diisocyanate products are used in the manufacture and repair of cars, boats, furniture, appliances and electronics.
So how long can it take for curing to complete? Well, the answer is not simple. Polyurethane cure time is influenced by a number of factors, including what other ingredients are contained in a polyurethane product (e.g., oil-based vs. water-based polyurethane floor finish), the product’s mode of application (e.g., painted by brush or roller versus sprayed), the amount of surrounding air flow during and after application, and other environmental conditions during and after application (like temperature and humidity).
While it is difficult to make generalizations about cure time, some studies suggest that curing can take a long time. For example, a recent paper showed that the cure time for aliphatic isocyanates-containing autobody spray paint varies between 48 minutes and 32 days, depending on drying conditions and the paint formulation. This study also found unbound isocyanate-containing particles on the painted surfaces days or weeks after drying. Hence, there can be substantial variability in polyurethane paint curing times.
Occupational exposure to diisocyanates
Diisocyanates are a known cause of occupational asthma. Annually, over 280,000 workers in the US are exposed to diisocyanates and it is estimated that between 1-20% of these workers develop asthma or other respiratory conditions from diisocyanate exposure. Occupational data has also shown a link between diisocyanate exposures and hypersensitivity pneumonitis (inflammation of the lungs) and pulmonary edema (fluid in the lungs).
Asthma can develop from a single high-dose exposure or from continued exposure to lower levels of the chemicals. Diisocyanates are chemical sensitizers, whereby over time exposure to lower and lower concentrations of the chemicals can elicit an asthmatic response. In addition, asthmatic reactions can be delayed by up to 12 hours following exposure.
Several cases of occupational and bystander diisocyanate exposure and consequent detrimental effects are detailed in the Center for Disease Control and Prevention’s (CDC) publication on “Preventing Asthma and Death from Diisocyanate Exposure.” Included in the report are descriptions of illness caused from single exposure to toluene diisocyanate (TDI) at high concentrations, like this incident:
Two police officers developed asthma-like illness after a single exposure to TDI in the immediate vicinity of a tank car that had overturned on the highway. After briefly directing traffic at the accident scene, both officers received medical care for severe symptoms, including burning eyes, throat irritation, cough, chest tightness, and difficult breathing. Treatment included steroids and a bronchodilator.
Both police officers developed a chronic bronchospastic disorder after their relatively brief exposure to high concentrations of TDI. Though considerable improvement has occurred in both cases, symptoms have persisted for more than 7 years.
Also included in the report are descriptions of occupational exposure that have even resulted in death, like this case of exposure to methylene diphenyl diisocyanate (MDI):
A maintenance worker became ill after repairing an MDI foaming system at a plant that manufactured artificial plants with polyurethane foam bases. The worker later suffered recurrent bouts of respiratory illness (diagnosed as isocyanate- induced Hypersensitivity Pneumonitis).
After showing further respiratory symptoms associated with isocyanate exposure, the worker quit his job but continued to experience coughing and progressive loss of lung function. His illness was eventually complicated by productive cough, weakness, sweats, muscle aches, and shortness of breath. Ultimately, he died.
Worksite evaluations found detectable air concentrations of MDI and inadequate ventilation systems in the foaming areas. Vapors and aerosols were observed rising into the faces of employees working with the foam. Skin contact with the curing foam was also noted during the survey.
Cases in which bystanders are exposed to commercial or institutional uses of polyurethane products are also a concern. The CDC describes a case in which teachers were unknowingly exposed to diisocyanates from roofing materials used at their school:
The management of a large metropolitan school district contacted NIOSH for assistance after a university study documented asthma in 13 of approximately 85 staff members from a middle school. The report further suggested that as many as 34 staff members might be asthmatic.
NIOSH investigators determined that large quantities of polyurethane foams and isocyanate coating materials had recently been applied to the school roof on several occasions. School staff members reported odors during roofing application, suggesting possible exposures to roofing materials that included isocyanates. Later air sampling during a test pour of the roofing materials at another location indicated the release of isocyanates during roofing and a potential for exposure.
This report amply illustrates the strong link between diisocyanate exposure and respiratory illness. For even more information on the occupational hazards of diisocyanates check out these links, which discuss exposures in different industries: spray on truck bed lining, automobile foam production, automobile paint, upholstery, bathtub refinishing, electroplating, and paraoccupational exposure from a machine shop and from wood varnish.
Public exposure to diisocyanates
Despite overwhelming epidemiological evidence of the harms of diisocyanates to workers and bystanders, they continue to be used widely with little regulation. In one exposure incident, children at an elementary and junior-high school were exposed to MDI through inhalation. The source? Workers were paving an athletic track with a polyurethane artificial surface containing diisocyanates (MDI) dissolved in a solvent (xylene).
Within 20 minutes of a change of wind direction, students in nearby buildings reported sickness. Of the 2700 students in buildings near the track, 203 students complained of ailments that were likely a result of contaminant exposure. Students suffered eye and throat irritation, nausea, headache, vomiting, cough and dyspnea (shortness of breath), with nearly half of the exposed students complaining of at least four of those symptoms. Hospitalized students required inhaled bronchodilators to relieve symptoms of irritant-induced asthma, also known as reactive airways dysfunction syndrome.
The incidence of affected students was plotted on a graph against distance from exposure and showed a clear linear relationship between the two variables. While incidence decreased further away from the exposure site, symptoms were still reported by students up to 150 meters away (that’s nearly 500 ft or roughly 1.5 football fields)! Those exposed might also have become sensitized to diisocyanates and could be at a higher risk of developing asthma in the future. Read the entire study of this incident here.
Physiological data indicate that children are generally more vulnerable to environmental health hazards for a number of reasons. Their surface-area-to-body-weight ratio is larger than adults, and they breathe in more air per pound of body weight than do adults. Children are especially susceptible to inhalation of diisocyanates because these chemicals are heavier than air and thus lie closer to the ground where children spend more time relative to adults. In a nation in which one in 10 children is diagnosed with asthma, we think uncured diisocyanates have no business being used around children.
Consumers’ and children’s exposure to diisocyanates
Despite clear hazards, diisocyanate-containing consumer products are widely available for purchase.
For example, “IdeaPaint” is a new polyurethane-based dry-erase board paint. This product has recently been picked up by Lowes, making it widely available to consumers. One of the paint’s main ingredients is hexamethylene diisocyanate (HDI), which has been linked to asthma in occupational studies.
The company defends the safety of its product by stating “Once it is dry it emits no harmful chemicals.” Yet the company acknowledges that its product takes an estimated seven days to cure, or at temperatures below 60°F, up to 28 days. For the integrity of the paint finish, the product instruction manual advises against writing on the freshly coated area for one week after application; however, no warnings are presented on potential inhalation hazards during cure time.
The product’s safety information is mainly found on the material safety data sheets (MSDS) posted on the company’s website. This kind of data sheet is typically used for reference in science labs and industry. And while decipherable by chemists, MSDSs are largely inaccessible to the average product user.
The MSDS for the company’s CRE-8 brand product lists the chemical components of the paint and associated hazards, including a number of known or suspected toxic chemicals in addition to HDI: styrene, dibutyltin dilaurate, and 2-butoxyethanol. (Note: The identities of 10 of the product’s 25 ingredients are not listed because they are claimed to be “trade secret”).
The MSDS lists the PEL, TWA and STEL values for the chemical components, all various measures of acceptable air concentrations of compounds as determined by OSHA for worker exposure. We’d wager a guess that the typical consumer is clueless as to what these values means and is incapable of testing for compliance with these air levels. Moreover, general worker exposures limits to chemicals set by OSHA are typically much higher than levels that are acceptable for the general public, especially children, who are virtually certain to experience exposure as bystanders as products are used.
Perhaps realizing that its MSDS is not very user-friendly, the company has posted to its website a letter issued by a scientist it hired to review the MSDS. Because they were not disclosed on the MSDS, the trade secret chemicals contained in the product were not specifically evaluated, just the general class to which they belong. Indeed, the identities of these ingredients are blacked out and replaced with the term “proprietary component” in the letter.
The letter asserts, without providing any documentation, the safety of the proprietary components mainly based merely on the fact that it is used in a lot of other products. It briefly acknowledges a concern for product inhalation while drying, and separately mentions that curing needs to proceed to completion in order to remove the hazard – but then fails to acknowledge or distinguish between the drying time (about 2-hours) versus the subsequent and often much longer curing time.
That’s hardly a basis for being able to conclude with any confidence that this or similar products are safe.
Despite the abundance of safety concerns raised by a product containing diisocyanates, “IdeaPaint” markets its product as “green.” The company explains that its product eliminates the need for a wooden board (therefore saving energy in shipping), as you can simply paint right on your kitchen wall, your child’s bed frame or kids’ school desks – all uses suggested on the company’s website.
Think back to the case study involving school children exposed to diisocyanates from track sealant fumes. Students suffered from asthma-like symptoms at distances of up to 500 feet away from the track, where sealant was applied in open air. Now consider your own home or your child’s schoolroom. Where would 500 feet away from the application site place you or your kids?
Concerns about the increased availability of diisocyanate-containing products have been raised by the Environmental Protection Agency (EPA). The agency recently issued chemical action plans for two of the most commonly used diisocyanates, methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI). We applaud the agency for scrutinizing the widespread use of these toxic chemicals.
These examples illustrate a much broader problem and need: Diisocyanates are among hundreds of chemicals we know are toxic that are in widespread use without adequate demonstration of their safety (see reviews of other toxic chemicals here). And there are thousands more chemicals about which we know too little to determine their hazards, uses or exposures.
That’s why EDF and hundreds of other health and environmental groups representing more than 11 million Americans are demanding that our main chemical safety law be brought into the 21st century.
Companies that make and use chemicals we know can cause or exacerbate asthma should be required to show that they’re safe before selling us products containing them that we bring them into our homes and schools.
Otherwise, they may literally leave us gasping for breath.