Isocyanates

Is Isocyanate Exposure and Occupational Asthma Still a Major Occupational Health Concern? Systematic Literature Review

Isocyanate, whose disease-inducing mechanism is poorly understood, with poor prognosis, is widely used. Asthma is the most frequent manifestation of prolonged exposure. We assessed the evolution of the incidence of isocyanate-induced occupational asthma over time. PubMed and Cochrane databases were systematically searched for studies published since 1990 that assessed the relationship between occupational exposure to isocyanates and asthma. We identified 39 studies: five retrospective cohort studies, seven prospective cohort studies, three of which were inception cohorts), seven observational cross-sectional studies, five literature reviews, two case series, and 13 registry studies. The incidence of occupational asthma secondary to isocyanate exposure has decreased from more than 5% in the early 1990s to 0.9% in 2017 in the United States. Despite the wide use of optimal collective and individual protection measures, the risk of occupational asthma has stabilized. Occupational asthma risk can be assessed with good sensitivity using self-questionnaires and pulmonary function tests. Occupational avoidance should be implemented as soon as possible after the first symptoms appear because the prognosis becomes increasingly poor with the persistence of exposure. It is now necessary to study specifically cutaneous sensitization to isocyanates and to define what protective equipment is effective against this mode of exposure.

Remendable thermosetting polymers for isocyanate-free adhesives: a preliminary study

Based on a model study, a new bis-cyclic monomer bearing a Diels–Alder adduct was synthesized. This monomer was polymerized with a diamine to yield a thermoresponsive polyhydroxyurethane (PHU). This PHU is remendable at around 100 °C by retro Diels–Alder reaction.

Biological monitoring of workers exposed to 4,4′-methylenediphenyl diisocyanate (MDI) in 19 French polyurethane industries

OBJECTIVES

To study the range of urinary levels of 4,4'-methylenedianiline (MDA), a metabolite of methylenediphenyl diisocyanate (MDI), across factories in the polyurethane industries and to evaluate the validity of this biomarker to assess MDI occupational exposure.

METHODS

Workers exposed to MDI, as well as non-occupationally exposed subjects, were studied and pre- and post-shift urine samples were collected from 169 workers of 19 French factories and 120 controls. Details on work activities and practices were collected by a questionnaire and workers were classified into three job categories. The identification and quantification of the total urinary MDA were performed by high-performance liquid chromatography with electrochemical detection (HPLC/EC).

RESULTS

For all the factories, MDA was detectable in 73% of the post-shift urine samples. These post-shift values, in the range of <0.10 (detection limit)-23.60 microg/l, were significantly higher than those of the pre-shift samples. Urinary MDA levels in the control group were in the range of < 0.10-0.80 microg/l. The degree of automation of the mixing operation (polyols and MDI) appears as a determinant in the extent of exposure levels. The highest amounts of MDA in urine were found in the spraying or hot processes. The excretion levels of the workers directly exposed to the hardener containing the MDI monomer were significantly higher than those of the other workers. In addition, skin exposure to MDI monomer or to polyurethane resin during the curing step were always associated with significant MDA levels in urine.

CONCLUSIONS

Total MDA in post-shift urine samples is a reliable biomarker to assess occupational exposure to MDI in various industrial applications and to help factories to improve their manufacturing processes and working practices. A biological guiding value not exceeding 7 microg/l (5 microg/g creatinine) could be proposed in France.