Isocyanates. Anthropogenic Compounds. Berlin: Springer Berlin Heidelberg; 1991. pp. 1-95. [DOI: 10.1007/978-3-540-46757-1_1]

Determination of isocyanate specific albumin-adducts in workers exposed to toluene diisocyanates

Toluene diisocyanates (2,4-TDI and 2,6-TDI) are important intermediates in the chemical industry. Among the main damages after low levels of TDI exposure are lung sensitization and asthma. It is therefore necessary to have sensitive and specific methods to monitor isocyanate exposure of workers. Urinary metabolites or protein adducts have been used as biomarkers in workers exposed to TDI. However, with these methods it was not possible to determine if the biomarkers result from exposure to TDI or to the corresponding toluene diamines (TDA). This work presents a new procedure for the determination of isocyanate-specific albumin adducts. Isotope dilution mass spectrometry was used to measure the adducts in albumin present in workers exposed to TDI. 2,4-TDI and 2,6-TDI formed adducts with lysine: N(ϵ)-[({3-amino-4-methylphenyl}amino)carbonyl]-lysine, N(ϵ)-[({5-amino-2-methylphenyl}amino)carbonyl]-lysine, and N(ϵ)- [({3-amino-2-methylphenyl}amino)carbonyl]-lysine. In future studies, this new method can be applied to measure TDI-exposures in workers.

Carcinogenic risk of toluene diisocyanate and 4,4'-methylenediphenyl diisocyanate: epidemiological and experimental evidence

Diisocyanates are highly reactive compounds widely used, for example, in the production of polyurethane foams, elastomers, paints, and adhesives. The high chemical reactivity of these compounds is also reflected in their toxicity: diisocyanates are one of the most important causes of occupational asthma but also other adverse effects, such as irritation and toxic reactions, have been described in exposed subjects. One of the open questions is whether occupational isocyanate exposure is a carcinogenic hazard. The few epidemiological studies available have been based on young cohorts and short follow-up and are not conclusive. Toluene diisocyanate (TDI) has been classified as carcinogenic in animals on the basis of gavage administration studies, but no conclusions are available on inhalation exposure. For 4,4'-methylene diphenyldiisocyanate (MDI) there is suggestive evidence for carcinogenicity in rats. The possible carcinogenic mechanism of TDI and MDI is not clear. Both chemicals have been positive in a number of short-term tests inducing gene mutations and chromosomal damage. The reactive form could be either the diisocyanate itself or may derive from the metabolic activation of the aromatic diamine derivatives formed by hydrolysis. TDI and MDI react with DNA in vivo and in vitro. However, the structure of the adducts has not been identified. Especially from the in vivo experiment it is not known if the adducts are a product from the reaction with the isocyanate or the corresponding amine. In conclusion, both TDI and MDI are highly reactive chemicals that bind to DNA and are probably genotoxic. The alleged animal carcinogenicity of TDI and MDI would suggest that occupational exposure to these compounds is a carcinogenic risk. The few epidemiological studies available have not, however, been able to clarify if TDI and MDI are occupational carcinogens.

Chemical behaviour of seven aromatic diisocyanates (toluenediisocyanates and diphenylmethanediisocyanates) under in vitro conditions in relationship to their results in the Salmonella/microsome test

There are conflicting results on the mutagenicity of toluenediisocyanate (TDI) and diphenylmethanediisocyanate (MDI). It was found that the organic solvent chosen to dissolve the compounds dictates the outcome of the bacterial tests. The Salmonella/microsome tests showed uniformly mutagenic effects for all the compounds that were predissolved in DMSO. Due to the instability of aromatic diisocyanates in DMSO this solvent was replaced by ethyleneglycoldimethylether (EGDE). TDI and MDI endured the dissolving and were therefore still available for the subsequent bacterial tests. Furthermore, no aromatic diamines (TDA or MDA) could be detected in EGDE prior to the start of the assays. The Salmonella/microsome tests, however, revealed unexpected differences between TDI and MDI. As previously published the four types of MDI showed negative results, whereas the data presented in this paper demonstrated mutagenic effects of all three types of TDI if EGDE is the solvent. To gain deeper insight into the chemical changes that occurred during the Salmonella/microsome test, the possible reactions were modelled in the laboratory by mixing predissolved diisocyanates with a defined surplus of water and monitoring the progress of the chemical reactions by analytical methods. Additionally, the quality of the model was checked by exposing solutions of 2,6-TDI and 4,4'-MDI to the real biological test environment. In both cases, the reaction patterns of TDI were different to those of MDI. Within 1 min, which is the maximum time needed to mix the predissolved compounds with water before they are poured onto the agar plate, the TDI content was reduced in favour of different ureas and TDA. In addition water was replaced by the complete set of test ingredients. While the TDA content remained more or less constant, the amount of residual TDI was reduced considerably. Reactions of MDI were markedly slower than those of TDI. More than 90% of the predissolved MDI remained intact when it was mixed with water. The biological test ingredients accelerated the reduction of the MDI content. Within 45 s, more than two thirds of the MDI disappeared. Evidently, the chemical reactions continue during incubation. It is assumed that the contrasting results of TDI and MDI in the Salmonella/microsome test are due to the different reaction patterns-and reaction products-of the predissolved diisocyanates created under the specific conditions of the test. These findings indicate that the chemical interactions between reactive test compounds and solvents or test media need to be considered in the interpretation of the relevance of test results.

Studies on the effect of the solvents dimethylsulfoxide and ethyleneglycoldimethylether on the mutagenicity of four types of diisocyanates in the Salmonella/microsome test

The mutagenicity of isomers and homologs of diphenylmethanediisocyanate (4,4'-diisocyanatodiphenylmethane, 2,4'-diisocyanatodiphenylmethane, a mixture of monomeric MDI isomers, and polymeric MDI), containing 55-100% of monomeric MDI, was determined in the Salmonella/microsome test using dimethylsulfoxide (DMSO) and ethyleneglycoldimethylether (EGDE) as solvents. Positive results were obtained for DMSO solutions of all four diisocyanates in the presence of S9 mix containing 30% S9 fraction. Uniformly negative results were found when the diisocyanates were dissolved in EDGE. These results correspond to those of analytical investigations. A small amount of diaminodiphenylmethane (MDA) is one of the reaction products formed when MDI is dissolved in commercial DMSO. No MDA could be detected in solutions of MDI in EGDE. It is therefore concluded that the positive results obtained with diisocyanates in DMSO solutions are due to the formation of MDA. This is artificially formed through the hydrolysis of MDI, caused by traces of water that are always present in DMSO. These findings indicate that DMSO is an inappropriate solvent and should therefore not be used in any in vitro study with diisocyanates. EGDE may be a suitable replacement. The positive test results reported so far for DMSO solutions of MDI are thus only of limited relevance for risk evaluation.