Biological monitoring of workers exposed to 4,4′-methylenediphenyl diisocyanate (MDI) in 19 French polyurethane industries

Objectives To study the range of urinary levels of 4,4'-methylenedianiline (MDA), a metabolite of methylenediphenyl diisocyanate (MDI), across factories in the polyurethane industries and to evaluate the validity of this biomarker to assess MDI occupational exposure. Methods Workers exposed to MDI, as well as non-occupationally exposed subjects, were studied and pre- and post-shift urine samples were collected from 169 workers of 19 French factories and 120 controls. Details on work activities and practices were collected by a questionnaire and workers were classified into three job categories. The identification and quantification of the total urinary MDA were performed by high-performance liquid chromatography with electrochemical detection (HPLC/EC). Results For all the factories, MDA was detectable in 73% of the post-shift urine samples. These post-shift values, in the range of < 0.10 (detection limit)-23.60 mu g/l, were significantly higher than those of the pre-shift samples. Urinary MDA levels in the control group were in the range of < 0.10-0.80 mu g/l. The degree of automation of the mixing operation (polyols and MDI) appears as a determinant in the extent of exposure levels. The highest amounts of MDA in urine were found in the spraying or hot processes. The excretion levels of the workers directly exposed to the hardener containing the MDI monomer were significantly higher than those of the other workers. In addition, skin exposure to MDI monomer or to polyurethane resin during the curing step were always associated with significant MDA levels in urine. Conclusions Total MDA in post-shift urine samples is a reliable biomarker to assess occupational exposure to MDI in various industrial applications and to help factories to improve their manufacturing processes and working practices. A biological guiding value not exceeding 7 mu g/l (5 mu g/g creatinine) could be proposed in France.