What is the respiratory retention of inhaled hexamethylene di-isocyanate?

Development of a new SPE UPLC-MS/MS method for extraction and quantitation of toluene diamine on gloves following toluene diisocyanate exposure

RATIONALE

Toluene diisocyanate (TDI) is a highly reactive isocyanate commonly used as a mixture of 2,4- and 2,6- isomers in the production of flexible foams. Exposure to TDI occurs primarily through vapour inhalation in workplaces where TDI is produced or used, but dermal exposure is also possible during some tasks. To ensure workplace safety, accurate monitoring of TDI and toluene diamine (TDA) levels is required. Methods of quantifying field effectiveness of gloves in preventing dermal exposure have not been established. Therefore, there is a need to develop a new practical method for assessing glove effectiveness for TDI/TDA.

METHOD

A new offline SPE UPLC-MS/MS method for the quantitation of TDA isomers from TDI-exposed gloves was developed. Gloves were dipped in a solution of 1% acetic acid leading to a full conversion to TDA. TDA-free amine compounds were derivatized with acetic anhydride to increase chromatographic retention and signal intensity.

RESULTS

2,4-Diaminotoluene-α, α, α-d3 (2,4-d₃ -TDA) was selected as a surrogate standard to minimise the variability in sample preparation and instrumental sensitivity. The choice of UPLC-MS/MS operated in multiple reaction monitoring (MRM) mode allowed to reach much lower limits of detection (LOD). The LOD of the method was 6.86 and 2.83 ng/mL (0.03 and 0.01 μg) for 2,6-TDA and 2,4-TDA, respectively. The limit of quantitation (LOQ) was 22.85 and 9.42 ng/mL (0.11 and 0.05 μg) for 2,6-TDA and 2,4-TDA, respectively.

CONCLUSION

A new UPLC-MS/MS analytical method has been developed to determine field effectiveness of gloves for preventing dermal exposure to TDI/TDA. The new technique overcomes some limitations for measuring putative dermal exposure to isocyanates and may be useful in exposure monitoring and future research on isocyanate health risks.

Is the analysis of histamine and/or interleukin-4 release after isocyanate challenge useful in the identification of patients with IgE-mediated isocyanate asthma?

Isocyanates are a well-known and frequent cause of occupational asthma. The implementation of specific inhalation challenges (SICs) is the gold standard in asthma diagnosis supporting occupational case history, lung function testing, specific skin prick tests and the detection of specific IgE. However, the diagnosis is not always definitive. An interesting new approach, analyses of individual genetic susceptibilities, requires discrimination between a positive SIC reaction arising from IgE-mediated immune responses and one from other pathophysiological mechanisms. Hence, additional refinement tools would be helpful in defining sub-classes of occupational asthma and diagnosis. We used total IgE levels, specific IgE and SIC results for sub-classification of 27 symptomatic isocyanate workers studied. Some mutations in glutathione S-transferases (GSTs) are suspected either to enhance or to decrease the individual risk in the development of isocyanate asthma. Our patient groups were assessed for the point mutations GSTP1*I105V and GSTP1*A114V as well as deletions (null mutations) of GSTM1 and GSTT1. There seems to be a higher risk in developing IgE-mediated reactions when GSTM1 is deleted, while GSTT1 deletions were found more frequently in the SIC positive group. Blood samples taken before SIC, 30-60 min and 24h after SIC, were analyzed for histamine and IL-4, classical markers for the IgE-mediated antigen-specific activation of basophils or mast cells. We suggest that the utility of histamine measurements might provide an additional useful marker reflecting isocyanate-induced cellular reactions (although the sampling times require optimization). The promising measurement of IL-4 is not feasible at present due to the lack of a reliable, validated assay.

Inhalation dosimetry of hexamethylene diisocyanate vapor in the rat and human respiratory tracts

Hexamethylene diisocyanate (HDI) is a reactive chemical used in the commercial production of polyurethanes. Toxic effects in rodents exposed to HDI vapor primarily occur in the nasal passages, yet some individuals exposed occupationally to concentrations exceeding current regulatory limits may experience temporary reduction in lung function and asthma-like symptoms. Knowledge of interspecies differences in respiratory tract dosimetry of inhaled HDI would improve our understanding of human health risks to this compound. HDI uptake was measured in the upper respiratory tract of anesthetized Fischer-344 rats. Nasal uptake of HDI was >90% in rats at unidirectional flow rates of 150 and 300 ml/min and a target air concentration of 200 ppb. Uptake data was used to calibrate nasal and lung dosimetry models of HDI absorption in rats and humans. Computational fluid dynamics (CFD) models of the nasal passages were used to simulate inspiratory airflow and HDI absorption. Transport of HDI through lung airways was simulated using convection-diffusion based mass transport models. HDI nasal uptake of 90% and 78% was predicted using the rat and human nasal CFD models, respectively. Total respiratory tract uptake was estimated to be 99% in rats and 97% in humans under nasal breathing. Predicted human respiratory uptake decreased to 87% under oral breathing conditions. Absorption rates of inhaled HDI in human lung airways were estimated to be higher than the rat due to lower uptake in head airways. Model predictions demonstrated significant penetration of HDI to human bronchial airways, although absorption rates were sensitive to breathing style.

Elimination kinetics of diisocyanates after specific inhalative challenges in humans: mass spectrometry analysis, as a basis for biomonitoring strategies

Background

Isocyanates are some of the leading occupational causes of respiratory disorders, predominantly asthma. Adequate exposure monitoring may recognize risk factors and help to prevent the onset or aggravation of these aliments. Though, the biomonitoring appears to be most suitable for exposure assessment, the sampling time is critical, however. In order to settle the optimal time point for the sample collection in a practical biomonitoring approach, we aimed to measure the elimination of isocyanate urine metabolites.

Methods

A simple biomonitoring method enabling detection of all major diamine metabolites, from mono-, poly- and diisocyanates in one analytical step, has been established. Urine samples from 121 patients undergoing inhalative challenge tests with diisocyanates for diagnostic reasons were separated by gas chromatography and analyzed with mass spectrometry (GC-MS) at various time points (0-24 h) after the onset of exposure.

Results

After controlled exposures to different concentrations of diisocyanates (496 ± 102 ppb-min or 1560 ± 420 ppb-min) the elimination kinetics (of respective isocyanate diamine metabolites) revealed differences between aliphatic and aromatic isocyanates (the latter exhibiting a slower elimination) and a dose-response relationship. No significant differences were observed, however, when the elimination time patterns for individual isocyanates were compared, in respect of either low or high exposure or in relation to the presence or absence of prior immunological sensitization.

Conclusions

The detection of isocyanate metabolites in hydrolyzed urine with the help of gas chromatography combined with mass spectrometric detection system appears to be the most suitable, reliable and sensitive method to monitor possible isocyanate uptake by an individual. Additionally, the information on elimination kinetic patterns must be factored into estimates of isocyanate uptake before it is possible for biomonitoring to provide realistic assessments of isocyanate exposure. The pathophysiological elimination of 1,6-hexamethylene diamine, 2,4-diamine toluene, 2,6-diamine toluene, 1,5-naphthalene diamine, 4,4'-diphenylmethane diamine and isophorone diamines (as respective metabolites of: 1,6-hexamethylene diisocyanate, 2,4-toluene diisocyanate and 2,6 toluene diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate and isophorone diisocyanates) differs between individual isocyanates' diamines.

Respiratory protection from isocyanate exposure in the autobody repair and refinishing industry

This study, part of the Survey of Painters and Repairers of Auto bodies by Yale (SPRAY), evaluated the effectiveness of respiratory protection against exposure to aliphatic polyisocyanates. A total of 36 shops were assessed for respiratory protection program completeness; 142 workers were measured for respirator fit factor (FF) using PortaCount Plus respirator fit tester. Twenty-two painters from 21 shops were sampled using NIOSH method 5525 to determine the workplace protection factor (WPF) of negative pressure, air-purifying half-facepiece respirators equipped with organic vapor cartridges and paint prefilters during spray-painting and priming activities. Only 11 shops (30%) had written respiratory protection programs. Eighty percent of all fit tested workers passed the test on the first try with FF >or= 100, and 92% passed the second test after respirator use training. Overall geometric mean (GM) FF was 1012 for all fit tested workers. Significant differences on pass rate (92% vs. 72%) and on FF (1990 vs. 736) were found between previously fit tested workers vs. nontested workers. Twenty-nine WPF samples were collected. The outside facepiece GM concentration of total isocyanate group (NCO) was 378.4 micro g NCO/m(3) with 96% concentrations exceeding the U.K. short-term exposure limit, 70 micro g NCO/m(3), but no in-facepiece concentrations exceeded the limit. The GM WPF of total NCO was 319 (GSD 4) and the 5th percentile was 54. WPF of total NCO was positively correlated with the duration of painting task. FF positively correlated with WPF when FF was <or=450 but negatively correlated with WPF when FF was >450. We conclude that negative pressure, air-purifying half-facepiece respirators equipped with organic vapor cartridges and paint prefilters provide effective protection against isocyanate exposure in spray and priming operations if workers are properly trained and fitted.

Workplace monitoring of isocyanates using ion trap liquid chromatography/tandem mass spectrometry

A sensitive liquid chromatography/ion trap tandem mass spectrometry method was developed for the qualitative and quantitative detection of isocyanates in air. The method is based on derivatization of isocyanates with 1-(2-methoxyphenyl)piperazine during air sampling. The extracts are analyzed using an ion trap LC/MS system equipped with an electrospray (ESI) ion source. The method shows high linearity, specificity, accuracy and precision. The limits of detection are 40x to 55x lower than with UV-based methods.

Diisocyanate asthma: clinical aspects and immunopathogenesis

Diisocyanates, highly reactive chemicals used in the production of polyurethanes, are currently the most frequently reported cause of chemically induced occupational asthma and their use continues to rise. The prevalence of diisocyanate asthma among exposed workers is estimated to range from 5% to 15%. Routes of exposure include the respiratory tract and skin. Workplace exposures are difficult to quantify and control, and there is no simple diagnostic test for the disease. This review considers recent concepts in exposure. clinical aspects and pathogenesis of the disease. The pathogenesis of diisocyanate asthma remains unclear, with evidence supporting both immunological and nonimmunological mechanisms. Knowledge of the chemical reactivity of diisocyanates, the target biomolecules, and the cellular sites of reaction are fundamental to understanding diisocyanate toxicity and disease. Recent findings of chemical interactions with biological nucleophiles will be described. The importance of diisocyanate-adducted biomolecules will be emphasized and their potential contributions to pathogenesis discussed. It is anticipated that greater understanding of the immunopathogenesis of diisocyanate asthma, including the initial cell/diisocyanate reactions, should lead to clinically useful markers of exposure and early disease.