Odor frequency and odor annoyance Part II: dose–response associations and their modification by hedonic tone

Risk-assessment for environmental odors and the development of an appropriate guideline for protection against undue odor annoyance have long been hampered by the difficulties of assessing odor exposure and community annoyance responses. In recent years, however, dose–response associations between frequency of odor events and odor annoyance level in the affected population were established. However, the influence of hedonic tone (pleasantness–unpleasantness) and perceived odor strength (intensity) on the degree of odor annoyance have long been neglected in such studies and accompanying guidelines. In order to close this gap a pertinent field study was conducted in the vicinity of six odor emitting plants, two with pleasant (sweets production, rusk bakery), with neutral (textile production, seed oil production), and with presumably unpleasant odor emissions (fat refinery, cast iron production).

A standardized sensory method was developed (described in Part I in the accompanying paper) to quantify intensity and hedonic tone within the assessment of odor exposure by systematic field inspection with trained observers. Additionally, exposure-information, the degree of annoyance, and the frequency of general health complaints and irritation symptoms were collected from the exposed residents through direct interviews. Multiple logistic regression analysis was used to establish dose–response associations between odor frequency, intensity and hedonic tone as independent variables and annoyance or symptom reporting as the dependent variable.

It is shown that exposure-annoyance as well as exposure–symptom associations are strongly influenced by odor hedonic. Whereas pleasant odors induced little to no annoyance, both neutral and unpleasant ones did. Additional inclusion of odor intensity did not improve the prediction of odor annoyance. Frequency of reported symptoms was found to be exclusively mediated by annoyance. The results are discussed in terms of environmental stress emphasizing the WHO-definition of health.

Based on these findings the existing German guideline against undue odor annoyance was modified.