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

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Abstract

Background

Isocyanates are highly reactive chemicals used widely in metal structure coating applications in construction. Isocyanates are potent respiratory and skin sensitizers and a leading cause of occupational asthma. At present, there is no cure for isocyanate asthma and no biomarkers of early disease. Exposure reduction is considered the most effective preventive strategy. To date, limited data are available on isocyanate exposures and work practices in construction trades using isocyanates, including metal structure coatings.

Objectives

The primary objectives of this work were: i) to characterize isocyanate inhalation and dermal exposures among painters during metal structure coating tasks in construction; and ii) to assess the adequacy of existing work practices and exposure controls via urinary biomonitoring pre- and post-shift.

Methods

Exposures to aliphatic isocyanates based on 1,6-hexamethylene diisocyanate (1,6-HDI) and its higher oligomers (biuret, isocyanurate and uretdione) were measured among 30 workers performing painting of bridges and other metal structures in several construction sites in the Northeastern USA. Exposure assessment included simultaneous measurement of personal inhalation exposures (n = 20), dermal exposures (n = 22) and body burden via urinary biomonitoring pre- and post-shift (n = 53). Contextual information was collected about tasks, processes, materials, work practices, personal protective equipment (PPEs) and exposure controls, work histories, and environmental conditions.

Results

Breathing zone concentrations were the highest for biuret (median, 18.4 μg/m3), followed by 1,6-HDI monomer (median, 3.5 μg/m3), isocyanurate (median, 3.4 μg/m3) and uretdione (median, 1.7 μg/m3). The highest exposures, measured during painting inside an enclosed bridge on a hot summer day, were: 10,288 μg/m3 uretdione; 8,240 μg/m3 biuret; and 947 μg/m3 1,6-HDI. Twenty percent of samples were above the NIOSH ceiling exposure limit for 1,6- HDI (140 μg/m3) and 35% of samples were above the UK-HSE ceiling for total isocyanate group (70 μg NCO/m3). Isocyanate loading on the gloves was generally high, with a median of 129 μg biuret/pair and maximum of 60.8 mg biuret/pair. The most frequently used PPEs in the workplace were half-face organic vapor cartridge (OVC) respirators, disposable palmar dip-coated polymer gloves, and cotton coveralls. However, 32% of workers didn't wear any respirator, 47% wore standard clothing with short-sleeve shirts and 14% didn't wear any gloves while performing tasks involving isocyanates. Based on biomonitoring results, 58.4% of urine samples exceeded the biological monitoring guidance value (BMGV) of 1 μmol hexamethylene diamine (HDA)/mol creatinine. Post-shift geometric mean HDA normalized to specific gravity increased by 2.5-fold compared to pre-shift (GM, 4.7 vs. 1.9 ng/mL; p value, < 0.001), and only 1.4-fold when normalized to creatinine.

Conclusions

Exposure and biomonitoring results, coupled with field observations, support the overall conclusions that (i) substantial inhalation and dermal exposures to aliphatic isocyanates occur during industrial coating applications in construction trades; that (ii) the current work practices and exposure controls are not adequately protective. High urinary creatinine values in the majority of workers, coupled with significant cross-shift increases and filed observations, point to the need for further investigations on possible combined effects of heat stress, dehydration, and nutritional deficiencies on kidney toxicity. Implementation of comprehensive exposure control programs and increased awareness are warranted in order to reduce isocyanate exposures and associated health risks among this cohort of construction workers.

Introduction

Reactive chemical resin systems based on isocyanates are used widely in diverse construction applications for their excellent performance characteristics, such as durability, resistance to chemical and physical agents, and optical transparency. Typical applications involving isocyanates include industrial metal structures coatings (bridges, exterior and interior surfaces of industrial storage tanks, water pipes, wind turbines), interior floor coatings, grouts and terrazzo applications, gluing, sealing, concrete bonding, and masonry work. The demand for these products continues to grow, in response to a strong growth in residential construction and the need for repairs in the aging infrastructure. More than 56,000 bridges in the United States are in need of repair or replacement, increasing the expected demand for industrial coating jobs (ARTBA, 2019; Kirk and Mallett, 2018). The number of construction painters accounted for ~380,000 in 2016, and is projected to grow by 6% (or 22,000 new jobs) in the next decade (BLS, 2018). Furthermore, as energy production shifts to renewable sources, the demand for building and maintaining wind turbines will continue to increase, and with it, the demand for industrial coatings. The general industrial coatings market is expected to reach $131 billion by 2022 (Pianoforte, 2019).

Painters exposed to isocyanates are at risk of developing occupational asthma and other isocyanate-related diseases. Isocyanates are potent respiratory sensitizers and have one of the lowest occupational exposure limits ever established (5 parts per billion, ppb time 8-hr time weighted average). Isocyanates continue to be a major occupational health problem (Reilly et al., 2019; Thore and Tiotiu, 2019) and a leading cause of occupational asthma (Goossens et al., 2002; Lefkowitz et al., 2015; Lockey et al., 2015; Redlich et al., 2007), in spite of the fact that their occupational toxicology and health have been studied continuously for more than half a century. In addition to asthma, exposures to isocyanates may also induce hypersensitivity pneumonitis, chronic obstructive pulmonary disease (COPD) and accelerated loss of pulmonary function, allergic and irritant contact dermatitis, rhinitis, irritation of the upper airways, eyes, and skin and occasional skin burns (Geier et al., 2018; Goossens et al., 2002; Wisnewski et al., 2006). Deaths from acute isocyanate expsoures have been reported, although fortunately they tend to be rare (NIOSH, 2006; Reilly et al., 2019; Thore and Tiotiu, 2019).

Occupational asthma continues to be the primary health concern of isocyanate exposures, in part because there is no cure for the disease; sensitized individuals may respond to extremely low isocyanate levels (as low as 1 ppb) at work or do-it-yourslelf consumer applications or cross-react to other isocyanates and amine components in the two-pack formulations; and their asthma may progress towards a generalized, non-specific asthma that may be triggered by other respiratory irritants and pollutants (Lockey et al., 2015; Redlich et al., 2007). At present there are no reliable biochemical tests for detecting isocyanate sensitization, especially in early stages, and clinical diagnosis of isocyanate asthma is complex, invasive and expensive. The current recommendation for the management of isocyanate asthma is complete avoidance or elimination of isocyanate exposures (Baur et al., 2012). However, this solution may come at the cost of significant loss of income for affected workers, while for many of them the isocyanate asthma symptoms do not improve significantly (Ruegger et al., 2014). Therefore, exposure reduction through effective exposure controls is an important intervention strategy, and one that could yield a better long-term outcome in reducing the risk of occupational asthma and preserving the income of these workers (Baur et al., 2012; Vandenplas et al., 2011).

Little is known about exposures and disease prevalence among construction trades that use isocyanates, in particular industrial coatings. Numerous studies have investigated isocyanate exposures and respiratory disorders (Pronk et al. 2007, 2009) during coating and painting tasks in the automotive and aerospace industries, and other manufacturing sectors that produce polyurethane products (England et al., 2001; Janko et al., 1992; Pronk et al., 2006; Reeb-Whitaker et al., 2012; Reilly et al., 2019; Sparer et al., 2004). Because construction differs in significant ways from aerospace and auto manufacturing industries, the knowledge base about exposures, chemistries, workflow and work practices from those sectors cannot be transferred readily to construction applications. This significant data gap on isocyanate exposures and effectiveness of exposure controls among construction workers must be addressed with relevant field exposure assessment and biomonitoring studies.

The polyurethane coating systems used in construction are often polymeric aliphatic isocyanates based on the 1,6- hexamethylene diisocyanate (1,6-HDI) monomer and/or isophorone diisocyanate (IPDI) referred to as pHDI and pIPDI, respectively (Supplemental Material (SI), Fig. S1). These formulations are often applied as two-part systems, comprised of the isocyanate hardener (part A) and the base part (part B), which is often a mixture of solvent blends, polyols, cross-linkers, and other additives. Current part A formulations contain only traces of the volatile monomer (HDI or IPDI, each typically at <0.1–1% in commercial formulations), with >99% of the isocyanate being higher oligomeric species (Bello et al., 2002b; Fent et al., 2009; Sparer et al., 2004). After the hardener is mixed with the base, the product is typically sprayed using a spray gun, or is manually applied using a roller or a brush. Painters are exposed to isocyanates through inhalation of their vapors (for volatile monomers) and airborne aerosols, as well as through direct dermal contact with the product or contaminated tools and surfaces. Comprehensive assessments of inhalation and dermal exposures, supplemented with exposure biomarkers are essential for identifying exposure sources, as well as for evaluating the efficacy of work practices and personal protective equipment (PPE) on reducing exposures. Urinary biomonitoring of isocyanate exposures in a number of studies has relied on measuring the corresponding diamines of monomers, such as HDI and IPDI (1,6-hexamethylene diamine, HDA) and isophorone diamine, IPDA) (Gaines et al. 2010a, 2011; Pronk et al., 2006) following aggressive acid hydrolysis. Because of its short clearance half-life of a few hours (Budnik et al., 2011; Liu et al., 2004) HDA monitoring can be valuable when evaluating the efficacy of exposure controls and PPE within a short time frame such as during a working shift.

We are presenting herein the results of a field investigation that was conducted as part of a larger study on reactive isocyanate systems among construction workers. The objectives of this work were (i) to characterize chemistries of and isocyanate exposures among painters during metal structure coating tasks in construction using simultaneous measurement of air and dermal exposures, and (ii) assess adequacy of existing work practices and exposure controls through field observations and through urinary biomonitoring pre- and post-shift. Results of this work can guide development of future intervention strategies for reducing isocyanate exposure among construction painters.

Section snippets

Sampling sites and participants

Workplace sampling was performed during topcoat applications at eight unique construction sites in the Northeast United States from May 2015 to October 2018. Thirty participants were recruited over ten field trips: 23 painters involved directly with product application through spraying, rolling or brushing, 5 helpers who performed product mixing and other auxiliary tasks, and two bystanders (managers). The majority of study participants were males (7% females). Among all participants, 80% were

Work practices and personal protective equipment (PPE)

Field observation data summarized in Fig. 2 indicate that the type and frequency of PPE used in workplaces visited varied widely between and within each site. The majority of participants (~61%) used half-face organic vapor cartridge (OVC) respirators, without particulate filter. One worker (3.6%) wore a full-face OVC respirator, another one wore an N95 (3.6%), while 32% of participants did not use any respirator. About 36% of workers wore disposable polymer dip coated gloves (coating on the

Discussion

Isocyanate-based formulations such as coating products are used widely in numerous construction trades. Although common, exposures to aliphatic isocyanates during coating applications in construction have not been characterized. In this work, we report our findings of a field study to assess inhalation and dermal exposures to isocyanates, their work practices, and the current status of exposure controls, among 30 painters from ten sites in the Northeastern USA performing metal structure coating

Conclusions

Exposure and biomonitoring results, in conjunction with field observations, support the overall conclusions that (a) substantial exposures to isocyanates occur during industrial coating applications among construction painters; and that (b) the current exposure controls are not sufficiently protective. Implementation of effective exposure control programs focusing on tasks performed in enclosed spaces and increased awareness about proper PPE use are warranted in order to reduce isocyanate

Acknowledgments

This research was supported by The Center for Construction Research and Training (CPWR) through the National Institue of Occupational Safety and Health (NIOSH) Cooperative Agreement Number U60–OH009762. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of CPWR or NIOSH. The authors would like to thank all study participants and our construction industry partners who facilitated workplace access. A special thank you goes to the graduate

References (56)

  • D. Bello et al.

    Evaluation of the NIOSH draft method 5525 for determination of the total reactive isocyanate group (TRIG) for aliphatic isocyanates in autobody repair shops

    Nat. Inst. Occup. Saf. Health J. Environ. Monit.

    (2002)
  • D. Bello

    Polyisocyanates in occupational environments: a critical review of exposure limits and metrics

    Am. J. Ind. Med.

    (2004)
  • BLS US

    Occpupational Outlook Handbook, Painters, Construction and Maintenance

    (2018)
  • L.T. Budnik et al.

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

    J. Occup. Med. Toxicol.

    (2011)
  • D.M. Ceballos

    Testing of glove efficacy against sprayed isocyanate coatings utilizing a reciprocating permeation panel

    Ann. Occup. Hyg.

    (2014)
  • K.S. Creely et al.

    Assessing isocyanate exposures in polyurethane industry sectors using biological and air monitoring methods

    Ann. Occup. Hyg.

    (2006)
  • E. England et al.

    Erratum to "comparison of sampling methods for monomer and polyisocyanates of 1,6-hexamethylene diisocyanate during spray finishing operations

    Appl. Occup. Environ. Hyg

    (2001)
  • K.W. Fent

    Quantification and statistical modeling--part I: breathing-zone concentrations of monomeric and polymeric 1,6-hexamethylene diisocyanate

    Ann. Occup. Hyg.

    (2009)
  • K.W. Fent et al.

    Quantitative monitoring of dermal and inhalation exposure to 1,6-hexamethylene diisocyanate monomer and oligomers

    J. Environ. Monit.

    (2008)
  • L.G. Gaines

    Urine 1,6-hexamethylene diamine (HDA) levels among workers exposed to 1,6-hexamethylene diisocyanate (HDI)

    Ann. Occup. Hyg.

    (2010)
  • L.G. Gaines

    Effect of creatinine and specific gravity normalization on urinary biomarker 1,6-hexamethylene diamine

    J. Environ. Monit.

    (2010)
  • L.G. Gaines et al.

    Factors affecting variability in the urinary biomarker 1,6-hexamethylene diamine in workers exposed to 1,6-hexamethylene diisocyanate

    J. Environ. Monit.

    (2011)
  • J. Geier et al.

    Sensitization to diphenylmethane-diisocyanate isomers by a single accidental exposure Contact

    Dermatitis

    (2018)
  • A. Goossens et al.

    Occupational allergic contact dermatitis caused by isocyanates Contact

    Dermatitis

    (2002)
  • H. Harari et al.

    Development of an interception glove sampler for skin exposures to aromatic isocyanates

    Ann. Occup. Hyg.

    (2016)
  • R.W. Hornung et al.

    Estimation of average concentration in the presence of nondetectable values

    Appl. Occup. Environ. Hyg

    (1990)
  • H. Hou et al.

    LC-MS-MS measurements of urinary creatinine and the application of creatinine normalization technique on cotinine in smokers' 24 hour urine

    J. Anal. Methods Chem.

    (2012)
  • J. Hu et al.
    (2017)
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