Elevated concentrations of methyl isocyanate and isocyanic acid in cigarette smoke

Monoisocyanates are usually intermediates of industrial processes but alkyl-isocyanates and isocyanic acid can also be created when nitrogen-containing compounds thermally degrade. One of the most notable monoisocyanates, methyl isocyanate (MIC), was accidentally released to the surrounding from a pesticide plant in the Bhopal disaster of 1984, where it killed several thousand and injured many more (Mishra et al. Int J Occup Med Environ Health 22(3):193-202 2009). MIC is known to have adverse effects on the respiratory system and other mucous membranes. Links between cigarette smoking and exposure to monoisocyanates have been suggested but not properly evaluated. The aim of the present study was to measure isocyanates in direct smoke and exhaled smoke to determine the potential exposure for the smoker and for people inhaling secondhand smoke. Concentrations of isocyanates were determined in direct cigarette smoke from three different generic cigarette brands using Supelco easysampler ASSET EZ4-NCO and impingers with dibutylamine solution in toluene. Exhaled smoke was measured using easysamplers only and one cigarette brand. Both isocyanic acid (ICA) and MIC were found in direct cigarette smoke at high concentrations (MIC 965-12144 µg/m³, ICA 943-5729 µg/m³) using either sampling system. Ethyl isocyanate (EIC) and n-propyl isocyanate (PIC) could also be quantified in direct smoke in all three cigarette brands but at much lower concentrations. Measurements of exhaled smoke found MIC in one sample (5.3 µg/m³) but no quantifiable levels of ICA or other monoisocyanates. Direct inhalation of cigarette smoke leads to high exposure for ICA and MIC, which exceeds levels set for occupational exposure after only a few cigarettes.