Toluene diisocyanates (TDI) are commonly used in polyurethane (PU)-related products. TDIs have been documented as the leading cause of occupational asthma. Skin exposure to TDI in the workplace is common. However, no studies in the literature have investigated the exact biomarker concentration profile for skin TDI absorption through any in vivo animal studies. In this study a rat model was used to evaluate the TDI skin absorption to explore the dose-response pattern and to determine the kinetic characteristics of urinary toluene diamine (U-TDA) during skin exposure. TDIs were topically exposed on the dorsum of rat skin at 0.2%, 1% and 5%. Consecutive urine samples were collected for 6 days and U-TDA were analysed using GC/ECD. It was demonstrated in this rat study that absorption of 2,4- and 2,6-TDI through skin contact is possible. A clear dose-dependent skin absorption relationship for 2,4- and 2,6-TDI was demonstrated by the AUC, Cmax findings and accumulative amounts (r > or = 0.968). U-TDA concentration profiles in 6-day consecutive urine samples fit well in the first-order kinetics, although higher order kinetics could not be excluded for the high dose. The apparent half-lives for excretory urinary TDA were about 20 h consistent at various skin exposures. It is concluded that skin absorption of TDI was confirmed in a rat model and a clear dose-dependent skin absorption relationship for 2,4- and 2,6-TDI was demonstrated. Excretory U-TDA concentrations in 6-day consecutive urine samples via skin exposure reveal the first-order kinetics and the half-lives were about 20 h.

Objectives: To determine nationwide 2,4 -and 2,6 -toluene diisocyanates ( TDI ) concentrations among polyurethane ( PU ) resin, PU foam, and other TDIrelated industries in Taiwan. The ratios of 2,4 -/ 2,6 -TDI and the noncarcinogenic risk among these three industries were also investigated. Method: Personal and fixed -area monitoring of TDI concentrations as well as questionnaires were performed for 26 factories in Taiwan. The modified OHSA 42 method was applied in sampling and analysis. Noncarcinogenic hazard index was estimated for these three industries based on the average concentration measurements. Results: Significant differences of TDI concentrations were found among the three industry categories. For personal monitoring, PU foam was found to have the highest TDI levels [ 18.6 ( ± 33.6 ) and 22.1 ( ± 42.3 ) ppb for 2,4 -and 2,6 -TDI ], Others average [ 8.3 ( ± 18.9 ) and 10.2 ( ± 17.2 ) ppb ], and PU resin lowest [ 2.0 ( ± 3.5 ) and 0.7 ( ± 1.2 ) ppb ]. The estimated average hazard indices were found to be 310 -3310. Conclusion: A substantial percentage of airborne TDI concentrations among in Taiwan industries exceeded current TDI occupational exposure limit, and significant difference of TDI levels were found among the three industry categories. The control remedy for the tasks of charging and foaming should be enforced with the highest priority. A separate 2,6 -TDI exposure standard is warranted.