Investigating the Performance of Exposure Assessment Techniques Used to Monitor Air and Dermal Exposures to Monomeric and Polymeric 1,6-Hexamethylene Diisocyanate
Monomeric and polymeric 1,6-hexamethylene diisocyanate (HDI) is widely used in clearcoat products used in the automotive repair industry. Inhalation exposure has been considered the primary exposure route and the primary cause of isocyanate-induced sensitization in automotive refinishing industry workers. Although many studies have been performed to investigate inhalation exposure to HDI, the literature is conflicting as to what type of air sampling device most reliably measures exposure levels. More recently, concerns about the role of dermal exposure in isocyanate induced sensitization and asthma have been raised. Dermal exposure has been documented among these workers, yet methods to measure skin exposure are not validated or standardized, and the penetration patterns and absorption rates of monomeric and polymeric HDI are not known. The objective of this study was to evaluate inhalation and dermal sampling methods for monomeric and polymeric HDI. We conducted a study comparing 13 different air samplers, which are commonly used in research studies as well as by practicing industrial hygienists for regulatory purposes, for their ability to monitor air exposures to HDI. We also developed and evaluated a patch sampler to measure dermal exposures to HDI and compared it with the tape-strip method. Our results indicate that methods commonly used to measure air and dermal exposure to HDI likely underestimate exposure. We also investigated the time-dependent penetration patterns of HDI in human skin. We observed that these compounds were readily absorbed and penetrated into the skin and that the composition of the clearcoat mixture may affect the penetration rate of the individual isocyanate compounds (both monomeric and polymeric). Our results indicate that the dose received through dermal exposure to HDI-containing clearcoats in the occupational setting has a significant potential to exceed the absorbed dose received at the equivalent air concentration corresponding to the established regulatory limits for inhalation exposure. A critical need exists to monitor dermal exposure quantitatively in exposed worker populations and to re-evaluate regulatory exposure limits for isocyanate exposures
