What Are The Health Effects Of Isocyanates?

Because isocyanates are highly reactive, exposure can result in primary irritation, sensitization and hypersensitivity reactions (allergic reactions). The breathing system, the eyes and the skin are the main areas affected by exposure.

   It is also important to consider the additives or solvents used in the production of polyurethane. Catalysts such as metal salts (for example, organotin compounds) or tertiary amines may be used. Combustion-retarding agents and blowing agents may also be added to the preparation and are usually organic phosphates or phosphonates and may contain chlorine or bromine. Methylene chloride or chlorofluorocarbons have been used as blowing agents in the manufacture of polyurethane foam.

Breathing System Effects:

   Adverse effects to the breathing system associated with isocyanate exposure include acute (short-term) or chronic (long-lasting) effects due to a single overexposure, chronic breathing problems caused by long-term low level exposure, occupational asthma and hypersensitivity pneumonitis (allergic reaction of the lungs).

Respiratory Diseases Associated with Isocyanates (See Reference #7) Direct irritation of the respiratory tract Asthma Chronic obstructive pulmonary disease Hypersensitivity pneumonitis (allergic inflammation of the lungs) Pulmonary disease-anemia syndrome (hemorrhagic pneumonitis (bleeding in the lungs))

   The major concern with isocyanate exposure and the breathing system is asthma (refer to OHCOW Information Bulletin on Occupational Asthma). Typically, asthma begins near the end of the work day, continues through the night improving somewhat in the morning hours, and happening in the same pattern the next day.

   Sensitized workers have reported symptoms at extremely low levels of exposure (1 part per billion (ppb)). Although asthma medication may control or prevent symptoms in these workers, a fatal attack of asthma may unexpectedly occur. Also, medication may not alter the natural history of asthma, and continued exposure to isocyanates may lead to more severe and prolonged disease that may generalize to other agents. Even after exposure stops, respiratory symptoms may continue for years.

   Scientific studies of TDI-exposed workers show that 5% to 20% of workers exposed to TDI may become sensitized to the chemical, although values of up to 30% have been reported depending on exposure levels and criteria used to define sensitivity. There seems to be no relationship between a history of allergy or atopy (genetic link) and the development of isocyanate-induced asthma.

   Varying periods of isocyanate exposure (months to years) may exist before asthma develops. Although it has been suggested that the development of isocyanate-induced asthma requires about 2 years of exposure to develop, the latency period is so unpredictable that such generalizations are difficult to make.

Clinical Features of Isocyanate-Induced Asthma (See Reference #1) Typically, there is no history of pre-existing asthma. Worker is exposed to isocyanates. Recurrent asthma occurs in relation to the workplace. Most often, there is improvement away from the workplace. Once the worker is sensitized, episodes of asthma recur following exposure to subirritant levels of isocyanates. In chronic cases, recurrent asthma can develop with exposure to non-specific irritants unrelated to isocyanates and away from the workplace.

   Smoking and TDI effects on lung function were found not to be additive.