Odor, Irritation and Perception of Health Risk

This article by Dr. P. Dalton, of the Monel Institute, discusses the issues involved in assessing the potential for volatile chemicals to elicit chemosensory irritation in the upper respiratory tract.  She discusses the data in setting Occupational Exposure Limits (OELs) that are protective of both comfort and well being for the majority of workers.  The author poses four questions that she feels are significant to understanding and evaluating these issues.  The questions are:

What is the relationship between odor and chemosensory irritations, and how can these sensations be distinguished at a sensory level?

Odor and sensory irritation may be perceived as a single event by the exposed individual.  However, two sensory pathways are present; the olfactory nerve which gives rise to the sensation of odor, and the trigeminal, glossopharyngeal or vagal nerves which give rise to temporary burning, stinging, tingling or painful  sensation in the eyes and upper respiratory tract.  In a given study, the investigator must assess the psychological relationship that characterizes the person’s perception of the intensity of the odor.

How can the human response to odors and irritants be measured?

According to Dr. Dalton, there are two psychophysical methods that are valuable in estimating the odor as well as the sensory irritation of a given chemical.  The first is sensory scaling which correlates a change in concentration and the subject’s report of perceived irritation intensity.  The second method is the measurement of absolute thresholds for irritation by a process called nasal lateralization.  This method uses normosmic individuals, subjects with a normal sense of smell.  In this method, a chemical vapor is presented to one nostril while clean air is presented to the other nostril.  If the concentration is above the odor threshold, the subject can detect a smell which can not be localized to a nostril.  If, however, the concentrations exceed the concentration for trigeminal activation, then the subject can discriminate or lateralize which nostril has been stimulated.

What are the dominant factors that can affect the perception of odor and irritation?

Several sources of variation exist and can influence odor, irritation and health perception.  These include inter-individual variations in sensitivity which may stem from physiological differences including age, sex or exposure history.  Furthermore, the subject’s expectations and beliefs about a chemical can also affect the study results.  Social factors may also influence the subject’s response.  Additionally, personality variability can also affect a subject response to a given chemical.

How can this information be used in the process of recommending occupational exposure limits for volatile chemicals?

Exposures to chemicals can elicit biochemical and physiological changes in the ocular and upper respiratory tract that may be insufficient to produce discomfort.  Conversely, workers may report irritation and health symptoms in the absence of objective markers of sensory irritation and at concentrations below the threshold for adverse effects.

In this effort, both objective and subjective methods can be used to establish irritant potency as long as the studies are well controlled and properly designed.  Differences in test populations must also be noted by the investigators.  The investigation should also look for response bias within the tested subjects and hence manipulate or quantify the degree of bias.

Both objective measures of irritation obtained in conjunction with subjective response can lead to valuable input to the decision making process for determining occupational exposure limits.  Dr. Dalton also notes that distinguishing between exposure concentrations that elicit local effects of sensory irritation in the upper respiratory tract and the concentrations that elicit self-reports of irritation is a key component in establishing OELs that are protective of workers.

 

Source: Dalton, P. 2002.  Odor, Irritation and Perception of Health Risk. Int. Arch Occup. Environ. Health 75:283-290.

By Arlene Weiss, MS, DABT
Contributing Editor