Acute vapour inhalation toxicity of acrolein and its influence as a trace contaminant in 2-methoxy-3,4-dihydro-2H-pyran.

1. The LC50 values for acrolein (AC) vapour to Sprague-Dawley rats (combined sexes) were determined to be 26 ppm (1 h) and 8.3 ppm (4 h). Signs of severe irritancy were present, and death was due to lung injury. 2. Exposure of rats to a 2-methoxy-3,4-dihydro-2H-pyran (MDP) saturated vapour atmosphere statistically generated from liquid MDP containing 0.037% AC, caused severe irritancy and death from accumulation of AC vapour. Sparging the impure material with nitrogen gas before atmosphere generation significantly reduced or abolished lethal toxicity. 3. Dynamically generated MDP vapour atmosphere produced transient respiratory and ocular irritancy, but no mortalities. The intrinsic acute vapour inhalation toxicity of MDP is low. 4. The presence of highly volatile toxic impurities in a material may confer a significant acute inhalation toxicity and hazard under conditions of low air movement. Assessment of potential inhalation hazards from liquid mixtures may require investigation by static and dynamic methods for vapour generation.