Threshold odor test

Hydrogen cyanide has frequently been associated with the odor of bitter almonds (Ballantyne 1983 Gee 1987). The threshold odor for olfactory detection of atmospheric HCN is 1 mg/L, but the odor may not be detected for various reasons, including the presence of other odors and the fact that only 20 to 40% of those tested could detect a cyanide odor. 

One method of controlling response perseveration and other anticipation factors is to use a forced choice response indication based on two or more response categories. In the measurement of odors the panelist has to report the temporal position of positive stimuli in a series of random blanks. If the concentration is below the threshold, the test subjects will guess. As the odorant concentration will increase, the relative cumulative frequency for identification of the correct sample will be greater. In order to determine the relative odor recognition a correction must be made. 

This test is based on a comparison with an odor-free water obtained by passing tap water through a column of activated carbon. The water under test is diluted with odor-free water until the odor is no longer detectable. The last dilution at which an odor is observed is the threshold odor point. 

Odor testing may be performed by a selected group of panelist to either determine the effect of various additives on the odor or taste of a medium or to determine the odor or taste sensitivity of a particular group of people. For this purpose, a series of samples is prepared in concentration scale which increases in geometric increments. At each concentration step two samples containing the medium alone are given to a panelist. The panehst should determine which sample is different firom the other two samples. The panelist should begin wifli the lowest concentration selected to be two or three concentration steps below estimated threshold. The method description contains information on sample selection and preparation, result, and precision determination. 

W. H. Stahl, ed.. Compilation of Odor andTaste Threshold Values Data, American Society for Testing and Materials Data Series 48, Philadelphia, Pa., 1973. 

The odor detection-threshold values of organic compounds, water, and mineral oil have been determined by different investigators (Table 2 and 3) and may vary by as much as 1000, depending on the test methods, because human senses are not invariable in their sensitivity. Human senses are subject to adaption, ie, reduced sensitivity after prolonged response to a stimulus, and habituation, ie, reduced attention to monotonous stimulation. The values give approximate magnitudes and are significant when the same techiriques for evaluation are used. Since 1952, the chemistry of odorous materials has been the subject of intense research (43). Many new compounds have been identified in natural products (37—40,42,44—50) and find use in flavors. 

The first element, dynamic dilution, provides a reproducible sample for each panelist. The system must minimize the loss of the odorant to the walls of the delivery apparatus, provide clean dilution air of odor-free quality, maintain a constant dilution ratio for the duration of a given test, and have no memory effect when going from high to low concentrations or switching between odorants of different character. The type of mask or port and the delivery flow rate have been found to influence the response of panelists in determining odor threshold and intensity. 

Health Hazards Information - Recommended Personal Protective Equipment Goggles or face shield dust mask Symptoms Following Exposure Inhalation of dust may causes irritation of nose and throat. Contact with eyes or skin causes irritation. Ingestion has been observed to cause tremors and muscle spasms in test animals General Treatment for Exposure INHALATION move to fresh air. EYES flush with water for at least 15 min. SKIN flush with water wash with soap and water. INGESTION get medical attention Toxicity by Inhalation (Thresholdlimit Value) Data not available Short-Term Inhalation limits Data not available Toxicity by Ingestion Grade 2 oral LDjq = 3,800 mg/kg (rat) Late Toxicity Causes cancer in rats Vapor (Gas) Irritant Characteristics Data not available liquid or Solid Irritant Characteristics Data not available Odor Threshold Not pertinent. 

Odor Threshold The minimum concentration of a substance at which a majority of test subjects can detect and identify the substance s characteristic odor. 

GENERAL CONDITIONS OF ODOR THRESHOLD DETERMINATION 2. 1 Requirements for the test area... 

Olfactory sensitivity for one individual varies about factor three due to climatological, physiological, environmental reaons etc. The sensory sensitivity also varies from odorant to odorant. So it is difficult to select a panel with a sensitivity distribution similar to that of the population. The preferred method in the United Kingdom for screening panelists uses the actual odor to be tested as a key component. In France selection is carried out on the basis of the threshold for five standard odorants. In Germany a normal sense of smell is requested of persons between the age of 18 and 50 years, in the Netherlands no exact specifications are given. Anyway, an extreme clustering around the mean or towards the extremes has to be avoided. 

Compilation of Odor and Taste Threshold Values Data, Ed. F.A.Fazzalari, ASTM Data Series DS 48A, American Society for Testing and Materials, Philadelphia, 1978. 

Specific odorants such as VFA, TIP or individual compounds can be used to indicate odour offensiveness but their absence does not give any information about the possiblity of other odorants being present. The offensive odours of treated slurry, which did not contain the 6 VFA, 3 phenols, 2 indoles or ammonia, were due to compounds not determined in these experiments. There are a large number of other odorants cited with very low threshold levels (28 29) which could be responsible for this odour offensiveness. Since the odour offensiveness test is so subjective any indicator must have... 

Since the publication of the third edition, additional data have been critically reviewed. New or additional data included in this edition are bioconcentration factors, aquatic mammalian toxicity values, degradation rates, corresponding half-lives in various environmental compartments, ionization potentials, aqueous solubility of miscellaneous compounds, Henry s law constants, biological, chemical, and theoretical oxygen demand values for various organic compounds. Five additional tables have been added Test Method Number Index, Dielectric Values of Earth Materials and Fluids, Lowest Odor Threshold Concentrations of Organic Compoimds in Water, and Lowest Threshold Concentrations of Organic Compounds in Water. 

The odor sensitivity of an experimental animal needs to be known to appreciate communication distances and performance, but it is not easily measured. The detection thresholdhzs to be distinguished from the recognition threshold. The former is the concentration at which an odor is noticed, and the latter -typically much higher - the concentration at which behavior tests in animals or verbal responses in humans show that the odor has been recognized as a specific signal, compound, or mixture. 

Thresholds are affected by the complexity of an odor. In tests with mixtures of 3,6, and 12 compounds, human subjects varied less from one another in their thresholds the more complex the odor was. The same trend was observed within individuals (Laska and Hudson, 1991). 

Fig. 15.9 shows the concentrations in a test chamber of 4-phenylcyclohexene, styrene, and 4-ethenylcyclo-hexene, another compound associated with SBR adhesives (Weschler et al., 1992b), from one carpet as a function of time (Hodgson et al., 1993). While styrene and 4-ethenylcyclohexene decrease rapidly with time, the decay of 4-phenylcyclohexene is much slower. In a house used for field studies, the concentration of 4-phenylcyclohexene remained above 2 ppb almost two months after installation, well above the odor threshold of 0.5 ppb. 

Statistical evaluations of the threshold of significant effect of methional, 1-nonanal, and phenylacetaldehyde in enzyme-inactivated beef slurries were determined. A score sheet like the one shown in Figure 4 but providing for evaluation of three rather than two samples was used. Panel members evaluated the odor quality of a standard sample (S) and three coded samples, one of which was identical with the standard. The other two samples contained the test compound at increasing concentration levels. 

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