Exposures and urinary biomonitoring of aliphatic isocyanates in construction metal structure coating

Exposure to toluene diisocyanate induces dysbiosis of gut-lung homeostasis: Involvement of gut microbiota

Toluene diisocyanate (TDI) is a major industrial compound that induces occupational asthma with steroid-resistant properties. Recent studies suggest that the gastrointestinal tract may be an effective target for the treatment of respiratory diseases. However, the alterations of the gut-lung axis in TDI-induced asthma remain unexplored. Therefore, in this study, a model of stable occupational asthma caused by TDI exposure was established to detect the alteration of the gut-lung axis. Exposure to TDI resulted in dysbiosis of the gut microbiome, with significant decreases in Barnesiella_intestinihominis, Faecalicoccus_pleomorphus, Lactobacillus_apodemi, and Lactobacillus_intestinalis, but increases in Alistipes_shahii and Odoribacter_laneus. The largest change in abundance was in Barnesiella_intestinihominis, which decreased from 12.14 per cent to 6.18 per cent. The histopathological abnormalities, including shorter length of intestinal villi, thinner thickness of muscularis, reduced number of goblet cells and inflammatory cell infiltration, were found in TDI-treated mice compared to control mice. In addition, increased permeability (evidenced by significantly reduced levels of ZO-1, Occludin and Claudin-1) and activation of TLR4/NF-κB signaling were observed in the intestine of these TDI-exposed mice. Concurrently, exposure to TDI resulted in airway hyperresponsiveness, overt cytokine production (e.g., IL-4, IL-5, IL-13, IL-25, and IL-33), and elevated IgE level within the respiratory tract. The expression of tight junction proteins is reduced and TLR4/NF-κB signaling is activated in the lung following TDI treatment. In addition, correlation analyses showed that changes in the gut microbiota were correlated with TDI exposure-induced airway inflammation. In conclusion, the present study suggests that the immune gut-lung axis may be involved in the development of TDI-induced asthma, which may have implications for potential interventions against steroid-resistant asthma.

Validation of a laboratory spray generation system and its use in a comparative study of hexamethylene diisocyanate (HDI) evaluation methods

Isocyanates are well-known irritants and sensitizers, and measuring their occupational airborne exposure is challenging due to their high chemical reactivity and semi-volatile nature. This study builds on a previous publication by our team that focused on comparing evaluation methods for isocyanates. The current research aims at developing, validating, and applying a laboratory generation system designed to replicate real-world conditions for spraying clear coats in autobody shops using hexamethylene diisocyanate (HDI)-based products. The system involved a spray gun connected to two chambers in series, enabling sample collection and analysis. The system successfully generated HDI and isocyanurate concentrations ranging from 0.008 to 0.040 mg m-3 and 0.351 to 3.45 mg m-3, respectively, with spatial homogeneity (RSD) of 5.8% and 16.5%. The particle-size distribution (MMAD) of 4 μm was measured using a cascade impactor and an electrical low-pressure impactor. The samples generated were used to correlate the amount of isocyanates collected with scanning electron microscope images of droplets on a filter. Three methods were compared to the reference method-an impinger with a backup glass fibre filter (GFF) and 1,2-methoxyphenylpiperazine (MP) based on ISO 16702/MDHS 25-in six generation experiments: (1) Swinnex cassette 13 mm GFF MP (MP-Swin); (2) closed-face cassette 37 mm GFF (end filter and inner walls) MP (MP-37); and (3) denuder and GFF dibutylamine (DBA) (ISO 17334-1 Asset). The analysis revealed clear trends regarding which sampler sections collected HDI (mainly in the vapor phase) or isocyanurate (exclusively in the particulate phase). The study found no significant bias between the tested methods (MP-Swin, MP-37, and Asset) and the reference method (impinger) for both HDI monomer and isocyanurate. The three tested methods showed limits of agreement beyond the acceptable range of ±30% (95% confidence interval), largely due to data variability, though MP-Swin and MP-37 exhibited lower variability than Asset. The results will be further evaluated in a real-world environment where similar clear coats are used.

Occupational Exposure and Health Impact Assessment of Diisocyanates in Finland

Diisocyanates are a group of chemicals widely used in different industrial applications. The critical health effects related to diisocyanate exposure are isocyanate sensitisation, occupational asthma and bronchial hyperresponsiveness (BHR). Industrial air measurements and human biomonitoring (HBM) samples were gathered in specific occupational sectors to examine MDI, TDI, HDI and IPDI and the respective metabolites from Finnish screening studies. HBM data can give a more accurate picture of diisocyanate exposure, especially if workers have been exposed dermally or used respiratory protection. The HBM data were used for conducting a health impact assessment (HIA) in specific Finnish occupational sectors. For this purpose, exposure reconstruction was performed on the basis of HBM measurements of TDI and MDI exposures using a PBPK model, and a correlation equation was made for HDI exposure. Subsequently, the exposure estimates were compared to a previously published dose-response curve for excess BHR risk. The results showed that the mean and median diisocyanate exposure levels and HBM concentrations were low for all diisocyanates. In HIA, the excess risk of BHR from MDI exposure over a working life period was highest in the construction and motor and vehicle industries and repair sectors, resulting in estimated excess risks of BHR of 2.0% and 2.6%, and 113 and 244 extra BHR cases in Finland, respectively. Occupational exposure to diisocyanates must be monitored because a clear threshold for DI sensitisation cannot be established.

Biomarkers of oxidative stress in urine and plasma of operators at six Singapore printing centers and their association with several metrics of printer-emitted nanoparticle exposures

Inhalation of nanoparticles emitted from toner-based printing equipment (TPE), such as laser printers and photocopiers, also known as PEPs, has been associated with systemic inflammation, hypertension, cardiovascular disease, respiratory disorders, and genotoxicity. Global serum metabolomics analysis in 19 healthy TPE operators found 52 dysregulated biomolecules involved in upregulation of inflammation, immune, and antioxidant responses and downregulation of cellular energetics and cell proliferation. Here, we build on the metabolomics study by investigating the association of a panel of nine urinary OS biomarkers reflecting DNA/RNA damage (8OHdG, 8OHG, and 5OHMeU), protein/amino acid oxidation (o-tyrosine, 3-chlorotyrosine, and 3-nitrotyrosine), and lipid oxidation (8-isoprostane, 4-hydroxy nonenal, and malondialdehyde [MDA]), as well as plasma total MDA and total protein carbonyl (TPC), with several nanoparticle exposure metrics in the same 19 healthy TPE operators. Plasma total MDA, urinary 5OHMeU, 3-chlorotyrosine, and 3-nitrotyrosine were positively, whereas o-tyrosine inversely and statistically significantly associated with PEPs exposure in multivariate models, after adjusting for age and urinary creatinine. Urinary 8OHdG, 8OHG, 5OHMeU, and total MDA in urine and plasma had group mean values higher than expected in healthy controls without PEPs exposure and comparable to those of workers experiencing low to moderate levels of oxidative stress (OS). The highest exposure group had OS biomarker values, most notably 8OHdG, 8OHG, and total MDA, that compared to workers exposed to welding fumes and titanium dioxide. Particle number concentration was the most sensitive and robust exposure metric. A combination of nanoparticle number concentration and OS potential of fresh aerosols is recommended for larger scale future studies.

Assessment of personal inhalation and skin exposures to polymeric methylene diphenyl diisocyanate during polyurethane fabric coating

Methylene diphenyl diisocyanate (MDI) monomers and polymeric MDI (pMDI) are aromatic isocyanates widely used in the production of polyurethanes. These isocyanates can cause occupational asthma, hypersensitivity pneumonitis, as well as contact dermatitis. Skin exposure likely contributes toward initial sensitization but is challenging to monitor and quantitate. In this work, we characterized workers' personal inhalation and skin exposures to pMDI in a polyurethane fabric coating factory for subsequent health effect studies. Full-shift personal and area air samples were collected from eleven workers in representative job areas daily for 1-2 weeks. Skin exposure to hands was evaluated concomitantly with a newly developed reagent-impregnated cotton glove dosimeter. Samples were analyzed for pMDI by liquid chromatography-tandem mass spectrometry. In personal airborne samples, the concentration of 4,4'-MDI isomer, expressed as total NCO, had a geometric mean (GM) and geometric standard deviation (GSD) of 5.1 and 3.3 ng NCO/m3, respectively (range: 0.5-1862 ng NCO/m3). Other MDI isomers were found at much lower concentrations. Analysis of 4,4'-MDI in the glove dosimeters exhibited much greater exposures (GM: 10 ng/cm2) and substantial variability (GSD: 20 ng NCO/cm2; range: 0-295 ng NCO/cm2). MDI inhalation exposure was well below occupational limits for MDI for all the job areas. However, MDI skin exposure to hands was substantial. These findings demonstrated the potential for substantial isocyanate skin exposure in work settings with very low airborne levels. This exposure characterization should inform future studies that aim to assess the health effects of work exposures to MDI and the effectiveness of protective measures.

Toluene diisocyanate occupational exposure data in the polyurethane industry (2005-2020): A descriptive summary from an industrial hygiene perspective

This article provides an overview of toluene diisocyanate (TDI) workplace air concentration data. Data were collected between 2005-2020 in workplaces across the United States, Canada, and the European Union by a number of different organizations, primarily using the sampling procedures published in OSHA Methods 42 and 5002. The data were then collated and organized by the International Isocyanate Institute. Air samples were collected from several market segments, with a large portion of the data (87%) from the flexible foam industry. The air samples (2534 in total) were categorized into "area" or "personal," and the personal samples were subcategorized into "task," "short term," and "long term." Most of the air sample concentrations (87%) were less than 5 ppb. However, the presence of airborne TDI greater than 5 ppb indicated the importance of respiratory protection in some situations; therefore, respirator use patterns were studied and summarized. Additionally, this article provides a summary of air sample concentrations at different flexible foam manufacturing job roles. The information on air sampling concentrations and respiratory protection during TDI applications collected in this paper could be useful for product stewardship and industrial hygiene purposes in the industries studied.

Biological Monitoring: Evidence for Reductions in Occupational Exposure and Risk

Aims: The aim of this publication is to explore occupational exposure trends from biological monitoring data collected over a period of more than 20 years. The data is stored within the HSE database, which holds more than 950,000 results from 120,000 workers in 8,000 companies. The data were collated for all biological monitoring results for lead, mercury, benzene, and hexamethylene diisocyanate exposures where there have been some regulatory drivers within the reported time period of the data searched.

Methods: Relevant results from sample analysed were extracted from the database and categorised by year from 1996 to the end of 2019 for individual blood lead results and individual urine results for mercury, benzene, and hexamethylene diisocyanate. Results were classed by broad occupational sector where possible. Data were reported graphically by analytical biomarker result (as 90th percentile (P90)) and number of samples per year as well as with overall summary statistics. To look at longer-term trends, results were also evaluated as P90 over 6-year periods.

Results: In the period 1996–2019, 37,474 blood lead, 11,723 urinary mercury, 9,188 urinary S-phenylmercapturic acid (SPMA, benzene metabolite) and 21,955 urinary hexamethylene diamine (HDA, metabolite of hexamethylene diisocyanate, HDI) samples were analysed and reported. Over the time period the blood lead concentrations saw the P90 reduce from 53 μg/dl 1996) to 24 μg/dl in 2019; the P90 urinary mercury levels reduced from 13.7 μmol/mol creatinine to 2.1 μmol/mol creatinine and the P90 urinary SPMA levels reduced from 133.7 μmol/mol creatinine to 1.7 μmol/mol creatinine. For HDI the P90 results reduced from 2 µmol HDA/mol creatinine in 1996–2000 to 0.7 in 2005–2010 but levels have since increased to 1.0 µmol HDA/mol creatinine (2016–2019).

Conclusion: There is strong evidence of reductions in exposure of GB workers to lead, benzene and mercury from the data presented here. These reductions may reflect the impact of national, regional and global regulatory action to reduce exposures however, the loss of high exposure industries (from either GB as a whole or just this dataset i.e., samples are being sent elsewhere) and the increase in automation or substitution also need to be considered as potential factors. The results for HDI show that whilst interventions can reduce exposures significantly, such initiatives may need to be refreshed at intervals to maintain the reductions in exposure. We have observed that exposures move between sectors over time. Waste and recycling (lead, mercury) and tunnelling through contaminated land (benzene) were sectors or tasks associated with significant exposures and may be increasingly areas of concern.

Urinary biomonitoring of occupational exposures to Bisphenol A Diglycidyl Ether (BADGE) - based epoxy resins among construction painters in metal structure coating

Epoxy resin systems based on Bisphenol A Diglycidyl Ether (BADGE) monomer and its higher oligomers are important commercial formulations used widely in construction for protective coating of steel structures, such as bridges. The literature on occupational exposures and biomonitoring of BADGE-based epoxies among construction painters is remarkably limited. In this first occupational biomonitoring study of epoxies, 44 construction painters performing mid- and top-coating were recruited from 12 metal structure coating sites in New England. Cross-shift changes in the urinary levels of total BADGE and its three major hydrolysis derivatives - BADGE·2H₂O, BADGE·H₂O, BADGE·HCl·H₂O - were assessed. Results for 81 urine samples collected from coating workers were compared with 28 urine samples of a reference group of 14 spray polyurethane foam (SPF) insulation workers. The highest concentrations of all biomarkers were found in the urine samples of mid-coat applicators. The major urinary biomarker of BADGE in this cohort of workers, BADGE·2H₂O, was detected in 100% of urine samples. The post-shift BADGE·2H₂O (specific gravity normalized data) in mid-coat applicators had a geometric mean (GM) of 1.46 ng/mL and a geometric standard deviation (GSD) of 3.6 (range, 0.2-18.7 ng/mL). The second most abundant biomarker in urine, BADGE·HCl·H₂O, was measured in 84% of samples, and had a post-shift GM(GSD) of 0.17 (2.3) ng/mL (range, <0.025-0.59 ng/mL). BADGE·2H₂O was 8.6 times more abundant than BADGE·HCl·H₂O. BADGE·H₂O was quantified only in 10% of the samples (range, 0.11-0.41 ng/mL). Free BADGE in post-shift urine, corrected for background, had GM (GSD) of 0.04 (2.5) ng/mL (range, <0.025-0.16 ng/mL). Urinary BADGE·2H₂O were significantly higher (p = 0.01) in mid-coat applicators compared to top-coat and SPF workers. Post-shift urinary BADGE·2H₂O in mid-coat applicators increased by ~2.9× (p = 0.02) and 1.36× in top-coat applicators (p = 0.18) compared to pre-shift values, but not in SPF workers (0.95×; p = 0.40). In conclusion, we demonstrate that (i) significant BADGE uptake occurs via inhalation and skin exposures during application of epoxy-containing paintings (mid-coat), suggesting the need for improvements in hygiene practices and personal protective measures; (ii) BADGE·2H₂O is a robust and sensitive biomarker for biomonitoring of exposures to BADGE-based epoxies in occupational settings; and (iii) widespread occurrence of BADGE and BADGE·2H₂O in the urine of all workers, including SPF workers, suggest common exposures from non-occupational sources, such as ingestion or do-it-yourself consumer applications of epoxy resins. In light of this observation, establishing a reliable biological monitoring guidance value (BMGV) for BADGE·2H₂O will require more background biomonitoring and health effect data. An initial reference value for BADGE·2H₂O of 0.5 ng/mL (SG-normalized) or 180 nmol/mol creatinine is being proposed as the threshold to discriminate occupational from non-occupational exposures based on the maximum values observed in the reference SPF group.

Characterization and Quantitation of Personal Exposures to Epoxy Paints in Construction Using a Combination of Novel Personal Samplers and Analytical Techniques: CIP-10MI, Liquid Chromatography-Tandem Mass Spectrometry and Ion Chromatography

Epoxy resins are extremely versatile products that are widely used in construction for coatings, adhesives, primers, and sealers. Occupational exposures to epoxies cause allergic contact dermatitis, occupational asthma, hypersensitivity pneumonitis (epoxy-resin lung) and acute decline in lung function. Despite these health concerns, there is a striking paucity of quantitative exposure data to epoxy resins in construction. The lack of practical analytical methods and suitable personal samplers for monitoring of reactive two-component epoxide systems in real-world applications has been an unmet challenge for decades. Sampling and analysis methods for epoxies should be able to collect the paint aerosols efficiently, stop polymerization reactions at the time of sample collection, and subsequently provide detailed multispecies characterization of epoxides, as well as the total epoxide group (TEG) content of a sample, to properly document the chemical composition of exposures to epoxide paints. In this work, we present the development and application of two new complementary quantitative analytical methods-liquid chromatography-tandem mass spectrometry with online ultraviolet detection and ion chromatography (IC)-for multispecies characterization of raw products, as well as inhalation and skin exposures to epoxy formulations in real-world construction applications. A novel personal sampler, CIP-10MI, was used for personal sampling of airborne epoxies. We report for the first time the results of personal inhalation and potential skin exposures to individual monomers and oligomers of bisphenol A diglycidyl ether (BADGE), as well as TEG, during metal structure coatings in construction; compare analytical results of the two analytical methods; and provide recommendations for method selection in future field studies. High inhalation and potential skin exposures to epoxies point to the need for interventions to reduce exposures among painters in construction.

Occupational Exposure to Diisocyanates in the European Union

Objectives

Diisocyanates are a chemical group that are widely used at workplaces in many sectors. They are also potent skin- and respiratory sensitizers. Exposure to diisocyanates is a main cause of occupational asthma in the European Union. To reduce occupational exposure to diisocyanates and consequently the cases of diisocyanate-induced asthma, a restriction on diisocyanates was recently adopted under the REACH Regulation in the European Union.

Methods

A comprehensive evaluation of the data on occupational exposure to the most important diisocyanates at workplaces was made and is reported here. The diisocyanates considered are methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI), accounting for more than 95% of the market volume in the EU. The exposure assessment is based on data from Chemical Safety Reports (CSRs) of REACH Registration Dossiers, workplace air monitoring data from Germany, from the UK Health and Safety Executive (HSE), and literature data relevant for the EU, and the USA.

Results

Occupational exposure to diisocyanates is particularly relevant in: (i) C.A.S.E. applications (Coatings, Adhesives, Sealants, Elastomers), (ii) production of polyurethanes (PUs) (e.g. slab-stock foam), (iii) handling of partly uncured PU products (e.g. cutting, demoulding, spray application of foam), and (iv) when diisocyanates/PUs are heated (e.g. hot lamination, foundry applications/casting forms). Ranking of the reported data on inhalation to diisocyanate exposure at workplaces (maximum values) leads to following order: (i) HDI and its oligomers in coatings, (ii) MDI in spray foam applications, (iii) TDI in manufacture of foam, (iv) TDI in manufacture of PUs and PU composite materials, (v) TDI in adhesives, (vi) MDI in adhesives, (vii) MDI in manufacture of PUs and PU composite materials, (viii) TDI in coatings, (ix) MDI in manufacture of foam, and (x) HDI in adhesives.