Biological monitoring as a valid tool to assess occupational exposure to mixtures of 2,4-:2,6-toluene diisocyanate

Background and Objectives: Despite its advantages over environmental monitoring, biological monitoring of
exposure to 2,4-:2,6-toluene diisocyanate (TDI) mixtures is still underused. The present study was designed in order
to evaluate the feasibility and reliability of biological monitoring in a factory producing polyurethane foam
blocks. Methods: Airborne TDI isomers were sampled by both static and personal pumps and determined by
HPLC with fluorimetric detection. Specific metabolites 2,4- and 2,6-toluenediamine (TDA) were determined by
gas chromatography-mass spectrometry on hydrolysed urine samples collected from 16 workers at the beginning of
the workweek and both before (BS) and at the end (ES) of the 4th workday. Additional samples were collected at the
end of the 1st half-shift and at the beginning of the 2nd half-shift in 5 workers. Results: In the foam production
shop, TDI values were on average about 20 μg/m3, with higher levels in the 2nd half-shift and peak levels in workers
operating along the polymerization tunnel. Average TDI levels were significantly correlated with ES TDA
concentrations (p<0.0001). TDA showed a fast urinary elimination phase leading to progressively higher TDA
levels either during the shift (5 workers) and at the end-of-shift. A slower elimination phase with a weekly accumulation
was demonstrated by values at the beginning of the workweek (higher than in unexposed subjects) and by
their elevation in subsequent BS samples. Conclusions: The study demonstrates the feasibility and reliability of
biological monitoring in workers exposed to 2,4-:2,6-TDI mixtures. This approach can provide information about
both the daily and weekly exposure levels.