Underestimation of toluene diisocyanate concentration using long-term sampling with 1-(2-methoxyphenyl) piperazine impregnated filters

Occupational exposure to toluene diisocyanate (TDI) is a known occupational hazard and the occupational exposure limits in air are very low. One of the most common methods to monitor exposure to isocyanates is to sample air through filters impregnated with 1-(2-methoxyphenyl) piperazine (2MP). In one earlier field study it was found that long-term sampling with 2MP-filters underestimated the exposure compared with consecutive short-term samples of TDI. The aim of this study was to confirm that finding in a controlled atmosphere in the laboratory. A test atmosphere of 2,4-TDI or 2,6-TDI was generated in a small test chamber and parallel long-term samples and consecutive short-term samples were collected. A total of 159 filters were exposed. The long-term samples collected significantly lower amounts of TDI than the sum of the short-term samples. For a 4-h sampling, the air levels were calculated to underestimate the exposure for 2,4-TDI by a factor of 1.4 and for 2,6-TDI by a of factor 1.3. The calculated underestimation was lower than earlier reported.