Neurobehavioral effects of exposure to propionic acid revisited—Does psychosocial stress interfere with distractive effects in volunteers?

•4 h exposure to 0.3 and 0–20 ppm propionic acid with or without psychosocial stress.•Level of exposure impacted performance in two out of six neurobehavioral tests.•Effects of propionic acid exposure and psychosocial stress were non-additive.•Stress interfered with neurobehavioral and eye-blink effects of 0–20 ppm.•Stress increased subjective adverse effects during 0.3 ppm exposure.

Local irritants stimulate the nervous system via chemosensory pathways that trigger cognitive distraction, subjective complaints about impaired health, and physiological defense reflexes (e.g. eye-blinks). At workplaces and in the environment chemical exposures often co-occur with psychosocial stress. This study investigated if stress modulates adverse effects of exposure to the local irritant and malodorant propionic acid (PA). Forty-eight participants were randomly assigned to an experimental (false negative feedback + salient surveillance) or control group. In a cross-over design, both groups were exposed for 4 h to PA in concentrations of 0.3 and 0–20 ppm (time-weighted average = 10 ppm). In the experimental group, the stress protocol induced moderate psychosocial stress as indicated by salivary cortisol and subjective responses. Despite concentration-dependent increases in chemosensory perceptions and symptoms, the level of exposure to PA had no impact upon the results of four out of six neurobehavioral tests. In the sustained attention test, there was a significant increase in error rates that corresponded to the exposure levels. However, a concentration-dependent impairment of spatial working memory and an adverse increase in eye-blink frequency were restricted to the control group. Stressed participants had shorter simple reaction times and high eye-blink frequency irrespective of exposure suggesting enhanced alertness. Psychosocial stress increased complaints, ocular irritation and unspecific symptoms at the end of the 0.3 ppm exposure to a level that was comparable with that in the control group during exposure to 0–20 ppm. Results indicate that the adverse effects of a local irritant and psychosocial stress are non-additive.