Workers exposed to thermal degradation products of TDI- and MDI-based polyurethane: biomonitoring of 2,4-TDA, 2,6-TDA, and 4,4'-MDA in hydrolyzed urine and plasma.

The aim of the study was to investigate biomarkers of exposure to thermal degradation products of 2,4- and 2,6-toluene diisocyanate (TDI)- and 4,4'-methylenediphenyl diisocyanate (MDI)-based polyurethane and the toxicokinetics of these products. Blood and urine were collected from 15 factory workers exposed to thermal degradation products of MDI-based polyurethane glue and TDI-based flexible foam. Four of these workers were also studied during an exposure-free period. Urine and plasma were analyzed after acidic hydrolysis and the concentrations of the isocyanates' corresponding amines, 2,4-, 2,6-toluenediamine (TDA), and 4,4'-methylenedianiline (MDA), were determined as derivatives of pentafluoropropionic anhydride by gas chromatography using chemical ionization mass spectrometry monitoring negative ions. Urinary elimination rates were in the range of < 0.01-5.7 micrograms of 2,4-TDA per hour, < 0.01-3.5 micrograms of 2,6-TDA per hour, and < 0.01-1.6 micrograms of 4,4'-MDA per hour. Plasma levels were in the range of < 0.1-5.5 ng of 2,4-TDA per mL, < 0.1-2.3 ng of 2,6-TDA per mL, and < 0.1-45 ng of 4,4'-MDA per mL. The urinary half-lives of 4,4'-MDA for four of the workers were found to be 59, 61, 73, and 82 hours. The half-lives of 4,4'-MDA in plasma were 10, 14, 16, and 22 days. Elimination rate peaks of 2,4-TDA, 2,6-TDA, and 4,4'-MDA in urine varied during and between workdays. The individual variation in plasma concentrations of 2,4-TDA, 2,6-TDA, and 4,4'-MDA with time was small, but between individuals the variation was great.