Allergic contact dermatitis from a diisocyanate in wool processing

Review of the occupational exposure to isocyanates: Mechanisms of action

Polyurethanes are useful polymers in a large variety of technical and consumer products that are generally made from diisocyanates and polyols or similar compounds. Toluene diisocyanate (TDI), 4,4'-methylenediphenyl diisocyanate (MDI) and 1,6'-hexamethylene diisocyanate (HDI) are useful for polyurethane products. Isocyanates are reactive chemicals that can be handled without problems in manufacturing or technical environments. In general, consumers may only have contact with these chemicals on rare occasions. The objective of this study was to review the mechanisms of action of inhalation of isocyanates. This paper describes, in summary, the potential occupational exposure to isocyanates, the chemistry and reactivity of isocyanates, the results from genotoxicity studies, investigative toxicity studies, metabolism and results from epidemiology studies on isocyanate-exposed workers. The overall conclusion is that because humans are not exposed to high levels of respiratory isocyanate particles, concerns over the possible development of lung tumors should not be relevant. There are many mechanisms of action induced by isocyanates, but those entities are unclear. This is because these mechanisms act simultaneously and are complex.

Evaluation of self-reported skin problems among workers exposed to toluene diisocyanate (TDI) at a foam manufacturing facility

Toluene diisocyanate, or TDI (CAS 584-84-9) is a well-known asthmagen and respiratory irritant. TDI is also known for its ability to irritate the skin and mucous membranes. To further investigate the dermal effects of TDI, NIOSH investigators conducted a cross-sectional study at a flexible foam manufacturing plant. A total of 114 workers participated in the study. Participants completed a medical questionnaire, provided blood for antibody testing to TDI and other allergens, and a subset of participants reporting skin symptoms underwent skin patch testing to a standard diisocyanate panel. Production line workers were more than twice as likely to report skin problems as those working in nonproduction areas (PRR = 2.66; 95% CI = 1.14-16.32; P = 0.02). Age, gender and duration of employment at the plant were comparable among participants working in production and nonproduction areas. Of the 100 participants who provided blood samples for antibody testing, specific IgG antibody to TDI was detected in two individuals, and none of the samples demonstrated specific IgE antibody to TDI. Of the 26 workers who underwent skin patch testing, none developed reactions to the diisocyanate allergens. These results suggest that the skin symptoms among study participants represent an irritant rather than an immunologic reaction to TDI, or to an unidentified allergen present in the foam.

Occupational allergic contact dermatitis caused by isocyanates

Between 1978 and 2001, 22 patients were diagnosed with occupation-related allergic contact dermatitis from isocyanates and/or polyurethanes in our clinic. 13 had a positive reaction to the isocyanates, of whom 10 also reacted to diaminodiphenylmethane (MDA), which is used in the production or processing of isocyanates and polyurethanes; 9 reacted only to MDA. The object of the present study was to identify the trades and industries responsible for the development of contact allergy to these resins. Such patients must be patch tested with the isocyanates contacted at work, and account must be taken of positive reactions to MDA as a marker for isocyanate sensitivity.

Evaluation of the SureSpot direct-reading instrument for the determination of polymeric MDI aerosols

Recent studies in our laboratories have focused on the reliability of direct-reading instruments for the determination of airborne isocyanate concentrations. The evaluation of airborne isocyanates is complicated because these substances exist as diisocyanate monomers and polyisocyanate oligomers, both in the vapor and aerosol phases. The studies showed that a number of direct-reading instruments, including the SureSpot test kit, do not allow an accurate determination of isocyanates in the aerosol phase. Using a test chamber, concentrations of various commercial polymeric methylenediphenyl diisocyanates (PMDI) were generated in the aerosol phase to examine the correlation between the SureSpot monitor and two laboratory methods. The results obtained with the SureSpot and laboratory methods correlated poorly. More precisely, the results indicated that the SureSpot direct-reading instrument had a distinctive response to each commercial PMDI and, in addition, it was not accurate for the determination of total PMDI in the aerosol phase. It seemed that the analytical response of the SureSpot is based on a calibration curve only reliable for MDI and not for the determination of PMDIs in the aerosol phase. Further investigation also indicated that the calibration provided by the manufacturer could not be converted into a linear curve over the suggested MDI concentrations range. An appropriate calibration procedure was developed in our laboratories for the SureSpot to accurately determine all commercial PMDIs without great variability.