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Formaldehyde (FA) is irritating to the eyes and respiratory tract at low concentrations, The derived NOEL and LOEL resp. are inconsistent. Therefore it was the aim of our studies to examine the possible occurrence of sensory irritation and subjective symptoms in human volunteers exposed to formaldehyde concentrations relevant to the workplace. Another objective was to clarify whether hyper- and hyposensitive humans show different reactions.
Methods
Sixty-two healthy volunteers (52 men, 10 women) were exposed for 5 consecutive days, 4 hours a day, to FA-concentrations of 0.0, 0.3, 0.4 and 0.5 ppm. Additional peak-exposures (15 minutes) of 0.6, 0.8 and 1.0 ppm were performed.
Subjective pain reception by nasal applied carbon dioxide (CO2) served as indicator for unspecific sensitivity. The following parameters were examined before and after exposure: subjective rating of symptoms (SPES questionnaire), conjunctival redness, eye blinking frequency, tearfilm break-up time, nasal flow, and olfactory function.
Results
Blinking frequency and conjunctival redness, ranging from slight to moderate, increased significantly after short-term peak exposures of 1.0 ppm that occured at a baseline exposure of 0.5 ppm FA. Results of the subjective ratings indicated eye and olfactory symptoms at concentrations as low as 0.3 ppm. Nasal irritation was reported at concentration levels of 0.5 ppm plus peaks of 1.0 ppm. Significant differences in the results of target parameters between hyper- and hyposensitive subjects were not detectable. However, hypersensitive participants exhibit more „olfactory symptoms“ than hyposensitive volunteers.
Discussion
The results of the study indicated eye irritation as the most sensitive parameter. Minimal objective eye irritation was observed at a level of 0.5 ppm with peaks of 1,0 ppm which was defined as LOEL. Hyper- and hyposensitivity as determined by CO2-induced nasal irritation did not significantly influence the results.