Absence of respiratory effects in subjects exposed to low concentrations of TDI and MDI.

One hundred seven subjects from a polyurethane plastic manufacturing plant have been followed over a five-year period with measurements of forced expiratory volume in 1 s (FEV1), and questionnaires on respiratory symptoms and smoking habits. Environmental concentrations of toluene diisocyanate and diphenyl methyl diisocyanate were extensively monitored to provide accurate estimates of the upper-limits of exposure of the subjects. Current mean levels of FEV1 in this population were higher than those predicted for healthy subjects. The five-year change in FEV1 did not exceed that expected from aging. No acute change in FEV1 could be demonstrated over the course of a Monday either before or after a two-week vacation. No improvement in ventilatory function was observed over the vacation period. The presence of cough or sputum was related to smoking but was not related to isocyanate exposure. The results indicate that exposure of workers to extremely low levels of isocyanates (time-weighted average concentrations of the order of 0.001 parts per million [ppm]) is not associated with chronic respiratory symptoms or effects on ventilatory capacity. The results suggest that isocyanates can be controlled to the point of eliminating effects as measured by these techniques.