Exposure study on chemosensory effects of ε-caprolactam in the low concentration range

Objective Aim of the study was to examine possible chemosensory effects of ε-caprolactam in the low concentration range relevant to indoor environmental conditions. Methods Twenty healthy subjects (10 male, 10 female) aged from 21 to 38 years were exposed for 6 h, respectively, to 0, 0.15, 0.5 and 5 mg/m 3 ε-caprolactam vapours in a randomized and double-blind method. As a measure of trigeminal stimulation of the eye, blink frequency was video-recorded four times per day and evaluated by using a new semi-automatic, computer-assisted method compared to baseline recording and manual counting. Digital slit lamp photographs were taken at the same time to examine conjunctival hyperaemia. A standardized ophthalmologic grading scale was used to measure redness of the eyes objectively. Active anterior rhinomanometry compared nasal resistance before and after exposure. Subjective ratings of discomfort and mental orientation were assessed using the German version of the Swedish Performance Evaluation system (SPES). As a measure of personality traits, positive and negative affectivity was determined (PANAS). Results Six hour exposures to ε-caprolactam revealed no significant dose–response relationship concerning blink frequency, nasal resistance and redness of the bulbar conjunctiva. Subjective ratings of discomfort (sum scores) significantly increased only at the highest concentration of 5 mg/m 3 . However, the increase in discomfort was only moderate, ranging between “not at all” and “somewhat”. Significant increases of the subjective detection of malodour (subscore) already occurred at 0.15 mg/m 3 , showing no adaptation over time. Irritation of the eyes or upper airways was not reported. Conclusions Exposure to ε-caprolactam vapour did not elicit any acute health effects in a concentration range up to 0.5 mg/m 3 . Even at the highest concentration of 5 mg/m 3 , we could only find a slight increase in subjective symptoms, mainly due to an unincisive increase of perception of malodour.