Isocyanates - Aldehydes

Isocyanates

An isocyanate is a low molecular weight highly reactive chemical which contains at least one isocyanate group in its structure.  Chemicals containing two isocyanate groups are called diisocyanates.  The most common isocyanates are toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and methylene diphenylmethane diisocyanate (MDI).  Isocyanates don’t have a distinctive odor.  Some isocyanates are odorless while if you are able to detect the odor of others, you are already over the exposure standard threshold.  Some isocyanates such as methyl isocyanate (MIC) are highly toxic and hazardous to human health.

Isocyanates are used to make polyurethane which is used both commercially and industrially.  Products such as coatings, adhesives, paints, coated fabrics, pesticides, rigid foam, insulation, furniture foam, mattresses foam, spandex fibers, automobile bumpers, car seat foam, and truck bed liners are all made with polyurethane and contain isocyanates.

Both acute (high-concentration – short time period) and chronic (low-concentration - long time period) exposures to isocyanates may cause health effects.  This includes sensitization to isocyanates resulting in hypersensitivity pneumonitis or occupational asthma.  Sensitization of a susceptible individual can cause the development of asthma-like symptoms following later exposure to even very low levels of isocyanates.  The exposure to isocyanates can be either by respiratory inhalation or by dermal contact.  Evidence has suggested that dermal (skin) contact can result in respiratory sensitization. 

Workers in industries where spray-applied polyurethane compounds such as painting automobiles or truck bed liner installation are particularly at high risk of development of these negative health effects.  They may also experience persistent or recurring eye irritation, nasal congestion, dry or sore throat, cold-like symptoms, cough, shortness of breath, wheezing, or chest tightness.  Severe asthma associated with isocyanate exposure has also been reported as resulted in death.

The risks of health effects can be mitigated by preventing exposure to isocyanates by introducing engineering controls such as closed systems and proper ventilation. Workers should use proper personal protective equipment such as respirators and personal protective clothing to prevent dermal exposures.  Finally, early recognition of sensitization and prompt and strict elimination of exposures is essential to reduce the risk of long-term or permanent respiratory problems for workers who may have become sensitized.

Aldehydes

Aldehydes are chemicals which are both highly reactive and abundant within our environment.  They can occur in the air we breathe, the food we consume, and the products we use.  Some exposures are lifestyle choices such as tobacco cigarettes, e-cigarettes, and alcohol, while others are ubiquitous in our environment such as certain foods, beverages, cosmetics, and hand sanitizers.  To prevent harm, the human body has an enzyme called aldehyde dehydrogenase 2 (ALDH2) which metabolizes the highly reactive aldehyde into a less reactive form.  Unfortunately, some individuals have a genetic variant of ALDH2 which has decreased effectiveness and results in the increased risk of individuals developing diseases such as cancer and cardiovascular disease.

Environmental aldehydes primarily include acrolein, acetaldehyde, and formaldehyde.  Acrolein is considered a human carcinogen whose inhalation irritates the upper respiratory tract.  International Agency for Research on Cancer (IARC) has classified acetaldehyde and formaldehyde as Group 1 carcinogens.  The primary toxic properties of aldehydes are due to their electrophilic nature, which can modify DNA and proteins or block biological pathways which can result in cytotoxic, mutagenic, and carcinogenic effects. 

The most commonly tested for aldehyde is by far formaldehyde, other aldehydes and ketones can be detected with a modification of the basic analytical procedure.  These include Acetaldehyde, Acetone, Acrolein, Benzaldehyde, Butyraldehyde, Crotonaldehyde, 2,5-Dimethylbenzaldehyde, Hexanaldehyde, Isovaleraldehyde, Methyl ethyl ketone, Propionaldehyde, [o,m,p]-Tolualdehyde, and Valeraldehyde.