MDA IN PLASMA AS A BIOMARKER OF EXPOSURE TO PYROLYZED MDI-BASED POLYURETHANE - CORRELATIONS WITH ESTIMATED CUMULATIVE DOSE AND GENOTYPE FORN-ACETYLATION

The object of this study was to investigate whether exposure of pipe-l ayers to thermal degradation products of diphenylmethane diisocyanate (MDI) could be assesssed by analysing 4,4-methylenedianiline (MDA) in hydrolysed plasma and urine, and whether the genotype for N-acetylatio n affected these biomarker levels. Blood and urine samples were drawn from 30-pipe-layers who had been welding poly-urethane (PUR) insulated pipes during the preceding 3 months. MDA in hydrolysed plasma and uri ne was determined with a gas chromatography-mass spectrometry techniqu e, and genotype for N-acetylation was analysed with a polymerase chain reaction technique. MDA in plasma was detected in 18 of the 30 pipe-l ayers. Their plasma concentrations of MDA varied from 0.05 to 8.48 mu g/1. There was a significant negative correlation between time since l ast welding of PUR-insulated pipes and P-MDA (r(s) = 0.50, P = 0.005). There was also a significant positive correlation between the estimat ed number of welded PUR-insulated pipes during the preceding 3 months and P-MDA (r(s) = 0.68, P = < 0.001). No significant association betwe en genotype of N-acetylation and P-MDA was observed in a multiple regr ession analysis when adjustment was made for the estimated cumulative exposure to thermal degradation products of MDI. MDA in urine was dete cted in only four of the 30 pipe-layers. These four subjects had been welding PUR pipes on the same day as the sampling, or on the day befor e. The present results indicate the spot plasma samples analysed for M DA may give a rather good estimate of exposure to MDI during the prece ding months. P-MDA, but not U-MDA, therefore seems to be a useful biom arker of long-term exposure to MDI. The individual N-acetylation capac ity did not affect the plasma levels of MDA.