A Nasal Chemosensory Performance Test for Odor Inspectors

Odors are the cause for most air pollution complaints by citizens. Common sources of community odors include the following types of facilities: wastewater treatment, composting, landfills and industry. In communities across the country, odor issues are addressed in a variety of ways. Often odor regulations and ordinances place a limit on the strength of ambient odors. The strength of an odor in the ambient air is measurable using either a butanol intensity scale or a “scentometer” device. However, the odor inspector’s olfactory sensitivity is a factor in measuring the odor strength in the ambient air. “Sniffin’ Sticks” is a commercially available test of nasal chemosensory performance based on pen-like odor dispensing devices. A modified version of the standard “Sniffin’ Sticks” odor threshold test was developed and administered to 39 Odor Inspectors of a Regulation Enforcement Agency. The Odor Inspectors were assessed approximately once a month during the months of January to October, where the majority of individuals were tested eight times. A measure of central tendency and variation was calculated for each of the Regional Agency Offices (n=6). Also, the test was administered to 39 Trained Odor Assessors of an Odor Evaluation Laboratory. The Assessors were tested twice during a single month. It was found that the mean individual score from the Odor Inspector group was 7.33 (s=1.47). The mean individual score from the Odor Assessor group was 9.45 (s=1.17). A z-test of the comparison of population means (α=0.05) showed that the mean group scores were statistically significant, thus the two sample populations could not have been drawn from the same statistical population. The purpose of a standardized nasal chemosensory test method is to determine the olfactory threshold of an individual or a group and compare this olfactory sensitivity data with other published normative values. This paper presents the findings from an initial test cycle in an ongoing study that will establish a reliable method for olfactory screening, provide olfactory threshold data for odor inspectors and assessors, and generated recommended performance criteria for odor inspectors, assessors and monitors. INTRODUCTION This paper presents a justification for a standardized method to test the nasal chemosensory performance of odor inspectors, odor investigators and odor monitors. A measurable element of an individual’s chemosensory function is their odor detection threshold. An odor detection threshold is the point in which an observer becomes aware of an odorous substance (ASTM, 1997). Odor detection thresholds characterize an individual’s and a group’s sensitivity to odor. This characterization becomes essential in settings where individuals will be evaluating the strength of the odor in the ambient air and how it corresponds to the mandated acceptable levels of the odor. Thus, determining the sensitivity of the individual observing the odor is critical to support the accuracy of their assessment. A practice that describes a method of accurately obtaining the sensitivity of individuals and/or groups can be integrated into agencies with officers who serve as odor inspectors or into facilities with employees serving as odor monitors or complaint responders. Control of the test conditions and establishment of test criteria can generate data that is reliable and accurate. This data then serves as a reference for the reliability of the individual’s ability to detect the odors they are observing. The test scores derived from olfactory screening are the most reliable when they are obtained following a standard test procedure. “Sniffin’ Sticks” (Burghart) as an instrument for determining nasal chemosensory performance has been previously investigated. Many authors have described the routine use of these devices in medical clinics to determine olfactory capacities of patients (Hummel et al, 1997). In these studies, they have been effective in the measurement of individual olfactory threshold levels (sensitivity), using n-butanol as the reference odor. A multicenter investigation provided normative olfactory threshold values a large population of healthy subjects (n=551) in relation to different age group using the “Sniffin’ Sticks” as the test instrument (Kobal, et al 2000). This previously published research supports using the “Sniffin’ Sticks” as the test instrument for routine screening of nasal chemosensory performance in individuals who will be monitoring facility odors or enforcing odor limits. It is assumed that olfactory sensitivity varies as a result of random fluctuations in factors such as alertness, attention, fatigue, health status and variability of presentation techniques (ASTM, 1997). Thus, the precision of the results of an individual’s olfactory threshold may be based on 1) the number of times that the individual takes the test and, 2) the clarity of directions under which the test is operated. It is recognized that the amount of training an individual receives influences their detection threshold. Establishing the necessary test criteria for the method of sample presentation for threshold determination was conducted in the present study. The current study attempts to obtain n-butanol thresholds for individuals in two test groups and the group scores based on an operating practice called the “Standard Procedure for Testing Individual Odor Sensitivity”, utilizing “Sniffin’ Sticks” as the test instrument. METHODOLOGY Odor screening was conducted using the Odor Pen Kit (St. Croix Sensory, Inc), which is a commercially available method for measuring the olfactory sensitivity. The Odor Pen Kit contains one set of “Sniffin’ Sticks”, a blindfold for the test individual, and odorless non-latex gloves for the test administrator (Figure 1). The “Sniffin’ Sticks” pens are felt tip markers in which the pen is impregnated with an odor agent. The odor agent used for olfactory threshold screening is n-butanol. Fourteen pens contain the n-butanol solution at different concentrations and two pens are odorless. The “Sniffin’ Sticks” manufacturer performed the preparation of the test solutions of n-butanol. Figure 1. The St. Croix Sensory Odor Pen Kit. Included in the picture are the blindfold, non-latex gloves and the set of 14 n-butanol pens (red) and odorless blank pens. All test individuals were tested following the same procedure. The procedure is called the “Standard Procedure for Testing Individual Odor Sensitivity”. The objective is to identify the detection threshold of the test individual by correct detection of the odor pen in a triad. The presentation method of the odor pens is a triangular force choice method, also known as 3-Alternative Forced Choice (ASTM, 1997). A pen triad is made up of three pens, two are blank pens and a third is an odor pen. The test individual is required to distinguish between the three pens by declaring which pen contains an odor. If no odor is perceived, the test individual is to assign a response of guess to one of the three odor pens. After a response is made, the test proceeds to the next pen triad. The next triad contains an odor pen with a greater n-butanol concentration than the previous series. The logic of the test is that the potential for the test individual to identify the odor pen increases as the test moves to the next concentration level. The increasing concentration levels will continue until the test individual correctly identifies the odor pen in a triad for two test levels. The level where a pen is first correctly identified as the odor pen is the score for the test individual and thus the odor threshold score of the individual. The odor sensitivity score for each of the participants was calculated by averaging the odor pen number (concentration level) associated with their first correct detection of the n-butanol pen in the triad. The odor pens were sorted and presented in ascending concentrations of n-butanol. The concentration values of the odor pens is undetermined, therefore, quantitative n-butanol values are not available. Olfactory sensitivity was determined in two study groups, the Odor Inspectors and the Trained Odor Assessors. The Standard Procedure and the Odor Pen Kit was the method of assessment used for both groups (Figure 2). Figure 2. A Test Individual being administered a n-butanol pen from the Odor Pen Kit. The Odor Inspector study group was made up of six Regional Agency Offices. Each of the Regional Offices received an Odor Pen Testing Kit and a copy of the “Standard Procedure”. The testing period began in January and is on-going. However, this paper represents data collected between January and October, 2003. The same Odor Pen Testing Kits were used throughout the entire testing period. Minor revisions were made to the Standard Procedure twice between January and October. Each Regional Office designated one Odor Inspector to serve as test administrator throughout the study. The test administrator learned the test method as described by the Standard Procedure. There was no consideration given to the age or sex of the Odor Inspector tested in the study. The number of Odor Inspectors in each of the offices ranged from 4 to 12 (Table 1). A total of 39 Odor Inspectors were tested. The number of times each Inspector was tested ranged from 1 to 10. The most common number of times an Inspector was tested was 8 (n=12). A threshold average emerged for each of the individuals. The Inspector’s odor detection threshold was the mean of their test scores. The Trained Odor Assessor group was made up of 39 trained odor assessors. Participation in the study group was based on volunteerism. Age and gender were not considered as Assessor attributes for inclusion in the group. The testing occurred during September 2003. The number of times each assessor was tested was twice. The test administrator for all of the evaluations used the same Odor Pen Testing Kit. The Assessor’s odor detection threshold was the average of the thresholds from the two times they were screened. Table 1. Number of Odor Inspectors in each of the Regional Agency Offices. RESULTS The olfactory detection threshold of the Odor Inspectors varied. The mean scores of the individuals ranged from 5.33 to 11.5, with a mean of 7.33 (n=39, s=1.47). Three Odor Inspectors had an olfactory sensitivity greater than 9.5. No mean scores were distributed between 13 thru 15. Three of the thirty-nine inspectors screened showed mean scores between 4.5 and 5.33. There were no detection thresholds below level 4. The frequency of mean individual scores was dispersed towards the left of the threshold range (Figure 3). The majority of Inspectors reported scores in the lower pen number range and the reported pen scores spread across 8 pens (pen level=5-12). The mode of the Odor Inspector group was odor pen 7. The frequency of each pen was calculated by rounding individual mean scores up to the corresponding odor pen if the mean score was greater than 0.5 and down to the corresponding odor pen if less than 0.5. The Odor Assessor group reported individual olfactory sensitivity mean scores between 7.0 and 12.25. Two assessors were shown to have mean threshold scores of 7.0, as well as two assessors having scores of 12.25. The mean threshold score of the group was 9.45 (n=39, s=1.17). The frequency of detection scores followed a normal distribution and was dispersed roughly in the middle of the odor pen range and spread across six pens (pen level=7-12). The mode of the Odor Assessor group was odor pen 9 (Figure 4). Pen scores were generated following the same conversion as stated in the above paragraph. A z-test of the comparison of means showed a significant difference in the mean odor detection thresholds of the Odor Assessor group and the Odor Inspector group (α=0.05). Regional Agency Office Number of Odor Inspectors RO 1 4 RO 2 7 RO 3 12 RO 4 6 RO 5 6 RO 6 4 Figure 3. The frequency of each odor pen was determined from the mean detection threshold score of an individual in the Odor Inspector Group (n=39, x=7.33, s=1.47). The mode of the group was odor pen number 7. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Odor Pen Number (Threshold) Fr eq ue nc y Figure 4. The frequency of each odor pen was determined from the mean detection threshold score of an individual in the trained Odor Assessor Group (n=39, x=9.45, s=1.17). The mode of the group was odor pen number 9. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Odor Pen Number (Threshold) Fr eq ue nc y Figure 5 displays the mean scores for each of the Regional Offices. The odor sensitivity varied between each of the offices. The mean threshold scores for the six Regional Offices ranged from 6.66 to 8.45. Odor sensitivity varied within each of the Regional Offices as well. The standard deviation was the lowest at the Regional Office 3, which reported a standard deviation of 1.64. The highest standard deviation occurred at Regional Office 5, reporting a standard deviation of 3.26. Figure 5. Olfactory sensitivity mean detection thresholds for the six Regional Offices of the Odor Enforcement Group. (RO 1=2.05, RO 2=1.66, RO 3=1.64, RO 4=1.68, RO 5=3.26, RO 6=2.61) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 RO 1 RO 2 RO 3 RO 4 RO 5 RO 6 Regional Office O do r P en N um be r ( Th re sh ol d) DISCUSSION This study provides olfactory sensitivity data in the form of odor detection thresholds from a commercially available test kit for two groups, the Odor Inspector group and the Odor Assessor group. The odor pen thresholds for these two groups both occurred within the middle range of possible odor pens. This suggests that there is a general sensitivity range within the population of individuals who will be assessing, enforcing or monitoring odors for industry, commercial and agency groups. In an attempt to obtain normative odor threshold values in healthy subjects, a previous study with “Sniffin’ Sticks” measured and compared the olfactory sensitivity (standard odorant n-butanol) in three age groups (Kobal et al, 2000). The age groups were 16-35 yrs (n=461), 36-55 yrs (n=60) and age greater than 55 yrs (n=30). The results showed that the odor detection thresholds for theses groups were 8.5 (s=3.12), 8.5 (s=2.08) and 7.6 (s=3.43), respectively. Post-hoc testing with ANOVA found differences for thresholds between subjects aged 36-55 yrs and greater than 55 yrs. Thus, these researchers concluded that odor sensitivity varies as a function of age. The findings from this study are similar to the odor detection thresholds measured in this current study within the Inspector Group and Assessor Group, where mean group thresholds were 7.33 (s=1.47) and 9.45 (s=1.17), respectively. Furthermore, the published data from the Kobal et al study may provide an explanation for the difference group means between the Inspector Group and the Assessor Group. That study showed that an individual’s olfactory function varies in relation to age, and it may be that the age categories of the individuals were aggregated within the two test groups in this current study. However, age was neither an examined attribute nor criterion for inclusion in either of the study groups. Therefore, further study of olfactory sensitivity as a function of age may be conducted in the forthcoming test cycle of this ongoing study. The mean threshold scores of the two groups tested in this study are significantly different. It is important to consider the reasons for these differences. It is likely these two groups represented to distinctly different samples of the general population, and subset groups would not necessarily be expected to have an average equivalent to the population mean. For example, the Regional Office Odor Inspectors potentially represent a narrow age range and come from similar socio-economic backgrounds. Likewise, the trained odor assessors also come from similar backgrounds and live in relatively close proximity in a few neighboring communities. Additionally, age of the assessors was not categorized and may contribute to the sensitivity profile of the assessor. Furthermore, the trained odor assessor group is familiar with the odor testing process, specifically the triangular forced choice approach, and they are familiar with the nbutanol odorant as used for assessor training and qualification and in intensity measurement procedures. This could explain why this specific sample of the population scored higher than the average reported by other studies. This study is an ongoing investigation into the odor detection threshold of odor assessors and investigators. A greater understanding of necessary performance criteria is forthcoming from continuation of this study. Nonetheless, general recommendations that can be offered to groups or agencies who will be screening odor monitors are: • Screen individuals an initial 5-6 times. This generates a profile of the individual’s sensitivity. • Screen individual’s once a month after a profile of the individual’s sensitivity has been established (mean threshold score). This will confirm their olfactory function by using pervious scores as the reference of function. Continuation of the monitoring of these study groups and additional groups will provide additional information about the population average and variability of data sets within specific samples of individuals. CONCLUSIONS Measuring the odor sensitivity of individuals who will be inspecting odors in the ambient air generates credibility for the agency or facility coordinating the monitoring. Odor detection thresholds provide credentials for the individual inspector, enforcer or assessor directing observing the odorous air. Furthermore, obtaining the threshold score of individuals who will be routinely observing odorous air is an important characterization of the individual’s sensitivity to odor and therefore allows a reference for accurate assessment of the strength of the odor in waste water, landfill, composting and other industry environments. The results of this study provide a basis for conducting assessments of olfactory sensitivity of odor inspectors, monitors and assessors with the St. Croix Sensory Odor Pen Kit (“Sniffin’ Sticks”) and the “Standard Procedure for Testing Individual Odor Sensitivity”. ACKNOWLEDMENTSWe would like to thank Donna McGinley, Nick Kreyer, Melissa McGinely and DebMethias for their help with the evaluation procedures. We are also grateful to MichaelMcGinley, P.E. for his advice during all stages of the project and for his critical reviewand useful comments on the manuscript. REFERENCESASTM International (1997), Standard Practice for Determination of Odor and TasteThresholds by a Forced-Choice Ascending Concentration Series Method of Limits, E679-91 (97), Philadelphia, PA, USA.Heinrich Burghart GmbH, Manual for Odor Sticks “Sniffin’ Sticks”, Tinsdaler Weg 175,D-22880 Wedel, Germany, Tel.: +49 (0) 4103-800 76-0, Fax: +49 (0) 4103-80076-29,Web: www.burghart.netHumel, T., Sekinger, B., Wolf, SR., Pauli, E. and Kobal, G. (1997), ‘Sniffin’ sticks:olfactory performance by the combined testing of odor identification, odor discriminationand olfactory threshold. Chemical Senses. (22): 39-52.Kobal, G., Klimek, L. 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