Occupational Asthma, Lung Function Decrement, and Toluene Diisocyanate (TDI) Exposure: A Critical Review of Exposure-Response Relationships

In recent years, occupational asthma has become the most frequent occupational lung disease in many countries. Reports and statements on the frequency of occupational asthma due to isocyanates are quite contradictory. In order to clarify the issue, a critical review of the medical literature of the past half century worldwide has been performed, with special emphasis on toluene diisocyanate (TDI) as the main representative of the isocyanate family. Nine longitudinal workplace studies of 2,751 persons under risk allow calculation of incidences of occupational asthma due to toluene diisocyanate. Annual incidences had repeatedly been above five percent before 1980, and have decreased to zero to 0.7 percent since 1980. There is a downward trend during the last half century that clearly parallels the downward trend of toluene diisocyanate exposure in some studies. Prevalences of occupational asthma due to toluene diisocyanate can be estimated from 10 cross-sectional studies, based on 788 persons. Prevalences had repeatedly been above 10 percent before 1985, and have been mostly between zero and 10 percent in recent years.