Biological and air monitoring of exposure to isocyanates

Abstract: Exposure to isocyanates may induce disorders in the airways of workers. Therefore, application, development and validation of methods for exposure assessment is of great importance. In the present study, we have determined the personal air and biomarker levels of isocyanates for a group of occupationally exposed workers (n=170) in different types of industrial processes. Also, the biomarker levels were determined for a control group consisting of occupationally unexposed workers (n=121). A method with filters impregnated with 1-(2-methoxyphenyl)piperazine (2MP) was used for personal air monitoring of exposure in different types of manufacturing processes. The field performance of the 2MP method was evaluated. Short-term stationary measurements was collected in parallel with an impinger method using dibutylamine (DBA) in toluene. Also, the long-term performance was evaluated by parallel sampling with consecutive sampling by the 2MP method itself. The 2MP method was found to underestimate the air levels of some isocyanates. Correction factors were calculated that may adjust for these observed losses. A new bioanalytical method for determination of biomarkers of aromatic diisocyanates was validated. This method is more convenient, better characterized and more robust than previous methods. The biomarker levels of aromatic diisocyanates were determined in the two groups of workers and upper reference limits (URLs) were calculated. The URLs may be useful in a screening test to assess whether a worker is occupationally exposed to diisocyanates or not. The biomarkers of 4,4'-methylene diisocyanate (MDI) were present in 97% of the occupationally unexposed workers. This indicates an unknown source of background exposure. For the exposed workers, there were strong correlations between urinary and plasma biomarker levels of isocyanates and between air and biomarker levels of isocyanates. The biomarkers of toluene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI) and MDI were shown to be applicable as an index of exposure. For TDI, strategies for biological monitoring of exposure were established, and biological limit values were proposed.