Asthma due to non-occupational exposure to toluene (tolylene) di-isocyanate

Skin exposure to isocyanates: reasons for concern

OBJECTIVE

Isocyanates (di- and poly-), important chemicals used worldwide to produce polyurethane products, are a leading cause of occupational asthma. Respiratory exposures have been reduced through improved hygiene controls and the use of less-volatile isocyanates. Yet isocyanate asthma continues to occur, not uncommonly in settings with minimal inhalation exposure but opportunity for skin exposure. In this review we evaluate the potential role of skin exposure in the development of isocyanate asthma.

DATA SOURCES

We reviewed the published animal and human literature on isocyanate skin-exposure methods, workplace skin exposure, skin absorption, and the role of skin exposure in isocyanate sensitization and asthma.

DATA EXTRACTION

We selected relevant articles from computerized searches on Medline, U.S. Environmental Protection Agency, Occupational Safety and Health Administration, National Institute for Occupational Safety and Health, and Google databases using the keywords "isocyanate," "asthma," "skin," "sensitization," and other synonymous terms, and our own extensive collection of isocyanate publications.

DATA SYNTHESIS

Isocyanate production and use continues to increase as the polyurethane industry expands. There is substantial opportunity for isocyanate skin exposure in many work settings, but such exposure is challenging to quantify and continues to be underappreciated. Isocyanate skin exposure can occur at work, even with the use of personal protective equipment, and may also occur with consumer use of certain isocyanate products. In animals, isocyanate skin exposure is an efficient route to induce sensitization, with subsequent inhalation challenge resulting in asthma-like responses. Several lines of evidence support a similar role for human isocyanate skin exposure, namely, that such exposure occurs and can contribute to the development of isocyanate asthma in certain settings, presumably by inducing systemic sensitization.

CONCLUSIONS

Integrated animal and human research is needed to better understand the role of skin exposure in human isocyanate asthma and to improve diagnosis and prevention. In spite of substantial research needs, sufficient evidence already exists to justify greater emphasis on the potential risks of isocyanate skin exposure and the importance of preventing such exposures at work and during consumer use of certain isocyanate products.

Use of specific inhalation challenge in the evaluation of workers at risk for occupational asthma: a survey of pulmonary, allergy, and occupational medicine residency training programs in the United States and Canada

STUDY OBJECTIVES

To document the current practice of occupational asthma (OA) diagnosis and use of specific inhalation challenge (SIC).

DESIGN, SETTING, AND PARTICIPANTS

A survey evaluating the current practice of SIC was mailed to 259 residency training programs in adult pulmonary diseases, allergy and immunology, and occupational medicine accredited in the United States and Canada during the year 2000.

RESULTS

Forty-six percent (123 of 259 programs) participated. Ninety-two programs reported that patients with OA were seen during the previous year, 15 programs reported that SIC had been performed, and 10 programs reported that patients had been referred to other sites for SIC. A total of 259 patients underwent SIC. No unexpected adverse reactions were reported. Forty-one programs reported that they had been willing to undertake SIC but were unable to do so. The most common barriers cited were lack of availability of SIC within the evaluating institution, inability to locate a site for referral, concerns about reimbursement, and lack of an appropriate diagnostic reagent for use in SIC. Seventy-four programs indicated that SIC was useful, and 34 programs included training in the use of SIC was part of the residency curriculum.

CONCLUSION

Although SIC is considered the "gold standard" for objective documentation of OA, the test is performed in only a few institutions in the United States and Canada. Many institutions indicate that SIC is not available, even when desired for patient management. Only a minority of participating residency training programs include SIC as a formal part of the training curriculum.

Determination of IgE-specificities in nasal secretions and sera of allergic subjects by crossed radio-immunoelectrophoresis

Allergen-specific IgE antibodies have not only been demonstrated in the serum, but also in the nasal secretions of allergic patients by means of the radio-allergosorbent test (RAST). In this preliminary study we adapted the technique of crossed radio-immunoelectrophoresis (CRIE) to nasal secretions in order to obtain further insight into the specificity of locally collected antibodies. Based on RAST results we compared CRIE patterns in serum, nasal secretions in 13 out of 23 grass pollen allergic subjects and two out of three house dust mite allergic subjects. In the nasal secretions the same IgE specificities were found as in the corresponding serum of the individual subject and as in a reference serum pool. These data indicate that the same specificity of IgE antibody can be found in the serum and the target organ. From these data there is no evidence for a local mucosal immune response that differs in specificity from the serum response.

Isocyanates and respiratory disease: current status

This paper reviews the known respiratory effects of isocyanates. There is good evidence to indicate that isocyanates: cause chemical bronchitis/pneumonitis; are potent pulmonary sensitizers capable of causing "isocyanate asthma"; cause nonspecific airways disease, including chronic bronchitis; can induce a general asthmatic state; and can cause hypersensitivity pneumonitis. Similar dose-response relationships are seen for both acute and chronic effects. There are plants operating in which exposures are well controlled and in which no respiratory effects can be detected. Suggestions are provided for preplacement assessment and periodic surveillance for workers exposed to these compounds.

Determination of airborne 2,4-toluenediisocyanate vapors

An accurate and convenient sampling and analytical method was developed for airborne 2,4-toluenediisocyanate (TDI). A chromophoric derivatizing reagent was used to convert the TDI to a stable urea derivative during collection for subsequent quantification by liquid chromatography. The overall accuracy (at the 95% confidence level) and precision of the method are +/- 7.9% and +/- 10.0% respectively under laboratory conditions. Long term stability was observed for both the reagent coated sorbent tube and the TDI urea derivative. A TDI concentration of 1 ppb can be detected by taking a 15-1 sample volume.

Occupational asthma in Finland

In Finland occupational asthma caused by protein allergens and reactive chemicals present in the air of work environments is increasing. This communication describes provocative challenge tests and methods for measuring exposure under simulated work conditions. The importance of lung function measurements during non-exposure and placebo periods is stressed. Especially late reactions are difficult to assess because of the great circadian variation in the lung function parameters of asthmatics. For a positive challenge test, a decrease in peak flow values of at least 15% and a clear deviation from normal circadian variation and placebo periods is required. The allergens of vegetable or animal origin primarily affect patients with an atopic constitution. Chemical allergens seem to attack all exposed workers in the same way. The report lists the occupations with risk for asthma and refers to the population at risk; bakers seem to be the group with the most risk. The importance of early diagnosis, removal of the worker from exposure and improvement of the hygienic aspects of the work environment are stressed.