Transferability of Aliphatic Isocyanates from Recently Applied Paints to the Skin of Auto Body Shop Workers

Abstract

Isocyanates, the essential cross-linking chemicals used to make polyurethane, are potent sensitizers and a common cause of occupational asthma. In addition, isocyanate (NCO) skin contact may contribute to the development of isocyanate asthma. Prior work has shown that unbound NCO can persist on recently spray coated auto body parts after appearing dry. The purpose of this study was to assess whether isocyanate skin exposure can result from handling such surfaces. Quantitative surface and skin wipe sampling for total NCO was performed on test panels sprayed with aliphatic isocyanate coatings, and on paired skin samples obtained from participants who had rubbed the recently dried surfaces. Surface and skin samples, obtained from 18 workers in five auto body shops, were prepared following NIOSH method 5525 (modified for skin samples), and isocyanate species derived from hexamethylene diisocyanate and isophorone diisocyanate were analyzed using high-performance liquid chromatography with ultraviolet and fluorescence detectors. Quantifiable unbound NCO species were detected on 84.2% of all sprayed surfaces sampled after initially considered dry. Only 7 out of a total of 104 (6.7%) non-compounded skin samples obtained after contact with the recently dried coatings had detectable quantities of free NCO. The 7 positive samples, all obtained at the initial sampling time (t₀), had a geometric mean of 0.016 μg NCO cm⁻² (range: 0.002–0.88 μg NCO cm⁻²). Only 1 of 12 (8.3%) of skin samples obtained after compounding contained detectable free NCO. The risk of substantial human isocyanate skin exposure from contact with the dry appearing (yet not fully cured) isocyanate coatings evaluated in this study appears to be low, although other isocyanate coatings and tasks may pose a greater risk of NCO skin exposure.

Keywords:

• asthma
• auto body
• clearcoat
• compounding
• hexamethylene diisocyanate
• isocyanates
• occupational skin exposure
• primer

ACKNOWLEDGMENTS

This research was supported in part by the American Chemistry Council Aliphatic Diisocyanates Panel and the European Aliphatic Isocyanates Producers Association and the National Institutes of Health (NIH-NIEHS) K24-ES000355 (CAR). We also wish to offer a special thanks to all of the auto body shops and their workers who participated in the study.