Journal of Occupational and Environmental Hygiene, 4: 406–411 ISSN: 1545-9624 print / 1545-9632 online Copyright c  2007 JOEH, LLC DOI: 10.1080/15459620701341199 Slow Curing of Aliphatic Polyisocyanate Paints in Automotive Refinishing: A Potential Source for Skin Exposure Dhimiter Bello, 1 Judy Sparer, 2 Carrie A. Redlich, 2 Karim Ibrahim, 2 Meredith H. Stowe, 2 and Youcheng Liu 2 1 Department of Work Environment, University of Massachusetts Lowell, Lowell, Massachusetts 2 Occupational and Environmental Medicine Program, Yale University School of Medicine, New Haven, Connecticut Two-component, polyurethane paints containing aliphatic isocyanates are widely used in autobody spray painting. Such isocyanates can cause asthma, and skin exposure may be an important route of sensitization and may contribute to the development of isocyanate asthma. Autobody workers are frequently in contact with recently painted, dried auto parts. It is not known how fast the newly painted car surfaces are fully cured, that is, for how long unbound, isocyanate species remain on painted surfaces after initial drying. To address this question, scrap sections of auto bodies were painted and dried by autobody shop painters following regular practice. Routinely used paints were sprayed 23 different times on the parts. Drying was accomplished by baking the part in a paint spray booth by heating it with a heat lamp or air drying in the shop. The 23 sprayed surfaces were sampled at regular time intervals after drying to determine the presence of free NCO groups using the semiquantitative SWYPE technique. Quantitative isocyanate analysis was also performed on two sprayed parts using NIOSH method 5525. Geometric mean curing time of 23 painted surfaces was 56.4 hr (range: 0.8 hrs to 32 days). Unbound isocyanate species of similar composition to the original bulk material remained present on the majority of sampled painted surfaces for up to 120 hours for typical paint formulations and for 1 month for others. The actual curing of polyurethane paints in autobody refinishing can be a slow process. Unbound isocyanates may remain on the surface of painted car parts for prolonged periods (days to weeks) after dried. Such surfaces are an under-recognized potential source of skin exposure to autobody workers. Keywords autobody shop, dermal exposure, hexamethylene diiso- cyanate, isocyanate, skin, spray paint Address correspondence to: Dhimiter Bello, University of Mas- sachusetts Lowell, Department of Work Environment, Kitson Hall, Room 200 (UML North), 1 University Ave., Lowell, MA 01854; e-mail: dhimiter bello@uml.edu. INTRODUCTION I socyanates are a family of widely used reactive chemicals with the functional group N C O. Aliphatic isocyanates are used extensively in autobody refinishing, largely as blends of nonvolatile polymeric species of hexamethylene diiso- cyanate (pHDI) and isophorone diisocyanate (pIPDI), with <1% of the more volatile HDI and IPDI monomers. (1–3) There are about 35,500 autobody shops in the United States, with an estimated 205,000 workers. (4) Autobody shop workers can have substantial inhalation exposures to aliphatic polyisocyanates, (3,5,6) which can cause isocyanate asthma. (7–10) Spray painters remain one of the high- est risk occupations for developing isocyanate asthma. (11,12) There is growing concern that skin exposure to isocyanates may contribute to the development of sensitization and asthma. Several animal models using HDI, (13) MDI, (14) and TDI (15–17) have employed skin exposure with subsequent inhalation challenge to produce an asthmatic response in the lungs. Lim- ited clinical and field studies suggest that human isocyanate skin exposure may also contribute to the development of isocyanate sensitization and subsequently asthma. (18–20) It is therefore prudent to prevent skin exposure to isocyanates in the workplace, which in turn requires recognition of potential exposure sources. The focus has long been on isocyanate asthma, and ex- posure assessment and control efforts have focused largely on reducing respiratory exposures to reactive isocyanates. Skin exposure to isocyanates can also occur in such set- tings but has not been well documented. Limited studies to date (21,22) have focused primarily on isocyanate contam- ination of surfaces and skin exposure during activities such as painting and mixing. Autobody shop workers are also in contact with recently painted car parts that appear dry and polymerized, typically without use of personal protective equipment because risk of isocyanate exposure is presumed unlikely. Unmasking, wet or dry sanding, reassembly, buffing or compounding, and detailing are tasks that are done after some coating as soon as the paint is dry. These activities could result in isocyanate skin exposure if the paint is not fully cured. 406 Journal of Occupational and Environmental Hygiene June 2007