A historical review of select diisocyanates: MDI and TDI production, usage, and occupational health hazards

Diisocyanates are intermediates required for the production of polyurethane, a foam and coating material with widespread use across many industries. Knowledge regarding the potential health hazards associated with exposure to the two most widely used diisocyanates, 4,4'-Methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI), has evolved since their popularization in the early 20th century. Both compounds have been used in industry for polyurethane manufacturing for many decades. As new studies have been published, it has been shown that MDI has a similar toxicological profile to TDI. This review provides an overview of the general body of literature on the potential health hazards resulting from exposure to diisocyanates, including MDI and TDI, in the occupational environment. This review provides an understanding of what was known, by decade, about the animal and human health effects identified through laboratory and epidemiological studies, and action taken by regulatory agencies to protect workers' health as knowledge on their sensitizing effects evolved over time. The findings of this historical review indicate that the incidence of adverse health effects resulting from diisocyanate exposure has been declining since the 1950s; improved industrial controls and increased efforts by regulatory agencies and stakeholders to protect worker health are responsible for the decline.