- Email: [email protected]
Human olfactory detection of packaged cannabis
Journal Pre-proofs Human Olfactory Detection of Packaged Cannabis Avery N. Gilbert, Joseph A. DiVerdi PII: DOI: Reference:
S1355-0306(19)30204-7 https://doi.org/10.1016/j.scijus.2019.10.007 SCIJUS 852
To appear in:
Science & Justice
Received Date: Revised Date: Accepted Date:
13 July 2019 20 October 2019 27 October 2019
Please cite this article as: A.N. Gilbert, J.A. DiVerdi, Human Olfactory Detection of Packaged Cannabis, Science & Justice (2019), doi: https://doi.org/10.1016/j.scijus.2019.10.007
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 The Chartered Society of Forensic Sciences. Published by Elsevier B.V. All rights reserved.
Human Olfactory Detection of Packaged Cannabis
Avery N. Gilberta,*, Joseph A. DiVerdib aHeadspace
Sensory LLC, Fort Collins, Colorado 80528 USA
bDepartment
of Chemistry, Colorado State University, Fort Collins, Colorado 80523 USA
*Corresponding author. Address for corresponding author: Avery N. Gilbert, 2002 Battlecreek Drive #8303, Fort Collins, CO 80528 USA. E-mail addresses: [email protected] (A.N. Gilbert), [email protected] (J.A. DiVerdi).
Declaration of Interest Funding for research materials and participant incentives was provided by Headspace Sensory, LLC, and by XTR Systems, LLC. Avery N. Gilbert is Founder and Managing Member of Headspace Sensory, LLC. Joseph A. DiVerdi is Founder and CEO of XTR Systems, LLC. Gilbert and DiVerdi have provided expert witness testimony involving cannabis odor.
Human Olfactory Detection of Packaged Cannabis
Abstract
Olfactory detection of cannabis aroma by police officers can be the basis for warrantless searches of motor vehicles in many jurisdictions in the United States. The odor source is these cases is often dried cannabis flower contained in various casual wrappings as well as in more elaborate packaging. Here we investigate whether packaging format alters the detectability of the cannabis. Two cannabis strains and five packaging formats were evaluated. Untrained observers were presented with two containers and asked to identify, based only on smell, the container that held a sample of packaged cannabis (the other container held identical, but empty, packaging material). The results showed that open and casually packaged cannabis was identified with high accuracy, while material packaged in doubly vacuum-sealed plastic was correctly identified at rates no different from chance. The results may help address issues involving the detectability of cannabis aroma in law enforcement and other scenarios.
Keywords Cannabis; Odor detection; Olfactory ability; Scent; Drug detection
1. Introduction That the dried flower of Cannabis sativa L. has a characteristic and easily detected odor is an assertion found in innumerable police reports and court decisions, and forms the basis for the “in plain smell” doctrine regarding warrantless searches [1, 2, 3]. Yet the empirical basis for such claims is remarkably thin. For example, while the volatile compounds in cannabis flower have been extensively studied by means of analytic chemistry, there was, until recently, no systematic, empirical description of its aroma. New studies using quantitative sensory evaluation find that cannabis aroma is not uniform: individual strains (cultivars) have distinctive aroma profiles [4, 5]. Under the plain smell doctrine, a warrantless search of a vehicle is permitted when an officer smells cannabis, even when it is concealed from view and enclosed in a bag or other container. Empirical evidence regarding the olfactory detectability of concealed cannabis is sparse. The one available study, which replicated the circumstances of three New Jersey criminal apprehensions for cannabis, found that claims made by police officers were implausible when tested experimentally [6]. Court decisions [e.g., 7] have also raised questions about the olfactory perception of cannabis with respect to claims made by police. In this study we examine the olfactory detectability of dried cannabis flower contained in casual packaging formats often encountered in motor vehicle stops, as well as in a more elaborate type of packaging, namely vacuum-sealed plastic. We do so with a simple headspace containment technique and a two-alternative forced choice sensory methodology.
2. Materials and methods 2.1. Ethics statement
This research protocol was approved by the Colorado State University Institutional Review Board: Social, Behavioral & Education Research, Protocol #18-8050H. Each participant provided informed written consent. At no time did participants come into direct contact with the cannabis samples. Retail sale of marijuana for recreational use to adults 21 years of age and older has been legal in the state of Colorado since January 1, 2014.
2.2. Participants Study participants were recruited via a notice posted to an online bulletin board for the local community. The text stated that cannabis “users, non-users, former users all welcome”, and that participation was limited to persons between the ages of 21 and 50. In addition to recruiting new participants via the online posting, we contacted people who had taken part in our earlier studies and indicated a willingness to take part in future research. Participants were paid $20.
2.3. Cannabis samples Cannabis samples were purchased from two dispensaries in Fort Collins licensed for retail recreational sale by the state of Colorado: LivWell and Verts Neighborhood Dispensary. One ounce (28g) each of Golden Goat and Mob Boss dried cannabis flower were purchased. These strains were selected in order to represent the aromatic variability that exists in cannabis. Previous quantitative sensory evaluations [4, 5] found that these strains have distinct aroma profiles: Golden Goat was characterized as citrus, lemon, sweet, pungent, while Mob Boss was described as earthy, woody, and herbal.
Strain designations provided by the retail dispensaries were used as a matter of convenience. Their use does not imply a position regarding the taxonomic validity or botanical derivation of either sample.
2.3. Packaging of Cannabis samples Cannabis from each strain was divided into five 5g samples for use in the odor detection trials, and one 3g sample used to familiarize participants with the target odors beforehand (see section 2.4 below). Cannabis samples were presented in five different conditions: (1) in an open glass bowl of 6 oz (177 ml) capacity; (2) inside a resealable, zipper-type, polyethylene food storage bag (Ziploc® Quart Storage Bags, S. C. Johnson & Son, Inc., 17.7 x 18.8 cm); (3) inside a high-density polyethylene produce bag (Crown Poly Pull-N-Pak®, 38 x 50 cm); (4) inside a certified child resistant, polypropylene, pop-top container (XIT® Brand Products, 30 dram (110.9 ml); and (5) inside doubly vacuum sealed food storage plastic (Mainstays™ Vacuum Sealer Rolls, 11 inches x 16 feet (28 x 487.7 cm), made of polyethylene and nylon) sealed with a Ziploc® V203 Vacuum Sealer Machine. Each cannabis sample was paired with a control sample consisting of identical, but empty, packaging. Cannabis and control samples were stored in glass jars in a freezer at −2ºC, and thawed at room temperature for 2 hr before testing.
2.3. Odor sampling chambers Cannabis and blank samples were placed in odor sampling chambers that allowed volatiles to accumulate and be sampled by sniff test participants. The chambers were 2 US gallon (7.6 L) white HDPE buckets (Leaktite, Leominster, MA) with bails removed, and covered with two white lids from the same manufacturer. A 7 x 7 cm rectangular opening (touching the inner circumference of the lid’s raised edge) was cut into one lid to provide a sniffing port. A second, unperforated lid was placed on top of the lid with the sniffing port. This allowed the sample odor to accumulate in the interior headspace of the bucket. The unperforated top lid was removed just prior to the participant’s sniffing and replaced immediately afterward. An alphanumeric code (placed on the bucket and lids opposite the side facing the test participant) uniquely identified each sample to the test administrator and provided an alignment cue for the sniffing port. Cannabis and control samples were placed in the odor sampling chambers for one hour before testing. A tent of folded aluminum foil was placed loosely over each stimulus/blank to provide additional visual screening while allowing air to circulate freely around the stimulus/blank.
2.4. Test procedure The participant was seated at a table and wore a blindfold (Mack’s® Dreamweaver™ Contoured Sleep Mask). Two odor sampling chambers were placed side by side on the table in front of the participant. The participant’s task was to sniff each chamber and indicate the one containing cannabis. Ten stimulus pairs (cannabis sample plus corresponding blank packaging sample) were presented in randomized order to each participant. In addition, the left-right placement of the blank and cannabis samples was randomized across trials for each participant. Participants were allowed to sniff the odor sampling chambers as many times as needed in order
to make a decision. Prior to the test, the participant was shown a dummy odor sampling chamber and allowed to practice sniffing from it. The participant also sniffed 3 g samples of Golden Goat and Mob Boss from 1 US pint (473 ml) Mason jars in order to become familiar with the target odors.
3. Results 3.1. Participant demographics Twenty-one people (11 men, 10 women) aged 21 and older (mean 29.7 ± 7.6 years) were tested. All subjects reported having purchased and used cannabis since January 1, 2014. High rates of purchase (≥94.2%) and use (≥92.3%) were seen also in previous studies [4, 5] despite efforts to recruit nonusers.
3.2. Data analysis The binomial test (IBM SPSS version 24) was used to determine whether the proportion of correct answers differed significantly from that expected by chance, i.e., 50%. The results (Table 1) indicate that seven of the ten samples were detected at a proportion significantly above that expected by chance. Cannabis samples in the open bowl, Ziploc bag, and HDPE bag were all detected with 100% accuracy; the results were identical for both cannabis strains. In addition, one of the samples (Mob Boss) presented in a pop-top cannister was correctly identified at a statistically significant level. One cannabis sample presented in a pop-top cannister, and both samples presented in doubly vacuum sealed-plastic, were identified at levels that were not statistically different from chance.
____________________________________________________________________________ Packaging format Cannabis strain Proportion correct P value ____________________________________________________________________________ Open bowl Open bowl
Golden Goat Mob Boss
21/21 (100%) 21/21 (100%)
<.000001 <.000001
* *
Ziploc® bag Ziploc® bag
Golden Goat Mob Boss
21/21 (100%) 21/21 (100%)
<.000001 <.000001
* *
HDPE bag HDPE bag
Golden Goat Mob Boss
21/21 (100%) 21/21 (100%)
<.000001 <.000001
* *
Pop-top cannister Pop-top cannister
Golden Goat Mob Boss
15/21 (71%) 20/21 (95%)
.078 .000021
n.s. *
Doubly vacuum sealed Golden Goat 15/21 (71%) .078 n.s. Doubly vacuum sealed Mob Boss 9/21 (43%) .66 n.s. ____________________________________________________________________________ Table 1 The proportion of correct responses for each packaging format and cannabis strain. Asterisk indicates a statistically significant result. 4. Discussion Using smell alone, untrained consumers were able to identify, with perfect accuracy, the sampling chamber holding 5 g of cannabis when the sample was presented in an open bowl, inside an HDPE produce bag, or inside a resealable polyethylene food storage bag. Volatile compounds released by the cannabis were able to migrate through these forms of packaging and create headspace concentrations sufficient to enable easy olfactory identification. In contrast, the cannabis sample could not be identified reliably when packaged in doubly vacuum-sealed plastic. This method of packaging restricted the release of cannabis volatiles to such an extent as to reduce the accuracy of olfactory identification to chance levels. The results for pop-top cannisters, commonly used as packaging for retail cannabis sales in licensed dispensaries, were
mixed. One sample was identified with high accuracy (95% correct) while the other was identified at a rate indistinguishable from chance. We cannot account for this difference, but can speculate that variability in the manufacturing process leaves some cannisters with less tightly fitting tops than others. This experiment used odor sampling chambers with a volume of 2 US gallons (7.6 L). It is possible that the open cannabis sample, as well as the samples placed inside HDPE and polyethylene bags, might emit enough volatiles to allow accurate detection in an enclosed space of greater volume absent other physical barriers (but see 5 Conclusions below). Conversely, the inability of test panelists to accurately identify the cannabis aroma in our sampling chambers implies that the task would be correspondingly more difficult in a larger contained space, such as a motor vehicle.
5. Conclusions In 2004, Doty, et al. [6] attempted to, among other objectives, “determine whether a group of men and women could distinguish the odor of packaged marijuana from that of a matched blank odor source”. In one portion of their study, blindfolded test subjects were presented two plastic garbage bags: one containing five 1 lb packets of “pressed and processed Mexican marijuana” and the other similarly bundled crushed newspapers. Their task was to indicate the bag that smelled like marijuana. The nine participants unanimously selected the marijuanacontaining bag (a statistically significant outcome). The present study extends this exploration by asking how accurately people can smell cannabis when it is inside various forms of packaging. Our results show that typical casual packaging, namely HDPE produce bags and polyethylene food storage bags, was ineffective at limiting aroma diffusion from dried cannabis flower.
However, doubly vacuum-sealed plastic reduced diffusion of cannabis odor to levels where olfactory detection was no better than chance. There is an important caveat to these results: the near flawless detection of cannabis odor through produce and food storage bags is specific to our experimental conditions and may not generalize to real world contexts involving larger air volumes and physically partitioned storage spaces. For example, Doty, et al. [6] also examined the ability of observers to identify cannabis odor in the passenger compartment of an automobile when the sample was located the vehicle’s trunk. Under these circumstances, the cannabis sample—the same one detected without error when sniffed from a garbage bag—was detected at a rate no better than chance. Thus, an aroma easily detected at point-blank range may be rendered statistically undetectable through a combination of dilution and additional physical containment. Further, dilution through diffusion into a larger physical space can alter the character of an odor mixture: the relative perceived intensity of each molecular component changes with concentration according to unique psychophysical functions. Thus, it is possible that cannabis aroma, if sufficiently diluted, could remain detectable as a smell but not be accurately identifiable as cannabis. Another limitation of the present study is that we examined cannabis aroma in the absence of competing ambient odors. In the real world conditions of a traffic stop, unrelated odors such as air fresheners, fast food containers, tobacco, tobacco smoke, perfume, and scented body sprays may also be present in a vehicle’s interior. Indeed, some of these scents are deliberately used by drivers and passengers to mask the odor of cannabis. Studies in olfactory psychophysics have shown that it is difficult for observers to identify individual components from mixtures of three or more odors [18]. The ability of human observers to selectively detect cannabis aroma against a background of unrelated odors deserves further study.
The detection of cannabis odor through packaging involves two factors: the release of volatiles from the plant material, and the diffusion of these compounds through the packaging barrier. Terpenes are generally regarded as the key physical basis of cannabis odor. They are the most abundant volatiles in mature plants and dried flowers [8, 9]. They are produced in such quantities that cannabis cultivation facilities may contribute to an increase in regional ozone concentrations [10, 11]. There is substantial variation in terpene abundance across strains, but a relatively small number of these compounds show up repeatedly [8]. While smell has been used informally to track microbiological contamination of cannabis resin [12], the combined analytical and sensory research required to identify key aroma compounds in cannabis (e.g., gas chromatography-olfactometry) has yet to be published. It is important to note that the relative abundance of a terpene is not correlated with its olfactory impact [9, 13]. The diffusion of volatile plant compounds through packaging materials is of interest to food chemists and such studies have examined some of the terpenes found in cannabis. Limonene, for example, diffuses through thermosealable films such as ultra-low-density polyethylene and modified poly(ethylene terephthalate) [14], as well as through gable-top paper cartons containing chilled orange juice [15]. Linalool and eucalyptol have been shown to diffuse through a variety of polymeric films including low-density polyethylene, polypropylene, nylon, and metalisedpolyethylene terephthalate (MPET) [16]. The diffusion rates of these terpenes vary across different types of plastic. The ability of key cannabis aroma volatiles to deliver recognizable cannabis aroma outside of plastic packaging deserves further exploration. We used small enclosures to capture headspace volatiles from gram-quantity samples of dried cannabis flower. Enclosures of similar scale have been used to calculate emission rates of terpenes from living cannabis plants [17]. Our method offers a useful approach to modeling the
dispersion of cannabis aroma within (and from) a confined space, such as the interior of a motor vehicle. Many criminal cases invoking the plain smell doctrine involve automobiles or trucks [2]. Odor dispersion from industrial marijuana grows, i.e., a large interior space containing massively distributed odor sources, would require a different approach. Interpretation of the plain smell doctrine is complicated in states where possession of a small amount of cannabis, or possession by persons with medical marijuana cards, has been legalized. In these instances, the mere presence of cannabis odor by itself may no longer imply criminal activity. This raises the question of whether the quantity of cannabis can be estimated by an olfactory assessment alone [3]. That there are statistically defined limits to the concentration at which a given odor can be detected is a basic principle of sensory psychophysics, and one that undercuts the presumption that, when cannabis is present, its odor can always be detected [6]. One legal commentator [1] notes that the plain smell doctrine does not imply an unchallenged reliance upon odor perception, and that it ought to be accompanied by a recognition that there are limits to the detection of any odor. In this view, each sense modality should “be allowed to operate within its own sphere of reliability,” and that to be relied upon in legal proceedings the odor of contraband needs to be distinctive, strong and persistent [1]. Given the results of the present study, smell-based searches where the material was vacuum sealed within one or more layers of plastic may lie beyond the “sphere of reliability.”
References [1] M.A. Sprow, Wake up and smell the contraband: Why courts that do not find probable cause based on odor alone are wrong, Wm. & Mary L. Rev. 42 (2000-2001) 289-318.
[2] S.F. Mandiberg, Marijuana prohibition and the shrinking of the Fourth Amendment, McGeorge L. Rev. 43 (2012) 23-51. [3] M.P. Hoxsie, Probable cause: Is the “plain-smell” doctrine still valid in Arizona after the AMMA? Ariz. L. Rev. 57 (2015) 1139-1161. [4] A.N. Gilbert, J.A. DiVerdi, Consumer perceptions of strain differences in Cannabis aroma, PLoS ONE 13 (2018) e0192247, doi: 10.1371/journal.pone.0192247. [5] A.N. Gilbert, J.A. DiVerdi, Use of rating scales versus check-all-that-apply ballots in quantifying strain-specific Cannabis aroma, J. Sensory Studies (2019) e12499, DOI: 10.1111/joss.12499. [6] R.L. Doty, T. Wudarski, D.A. Marshall, L. Hastings, Marijuana odor perception: Studies modeled from probable cause cases, Law Hum. Behav. 28 (2004) 223–233. [7] State of Kansas v. Lawrence C. Hubbard, Case No. 113,888 Kansas Supreme Court, December 7, 2018. [8] J.K. Booth, J. Bohlmann, Terpenes in Cannabis sativa – From plant genome to humans, Plant Sci. 284 (2019) 67-72, https://doi.org/10.1016/j.plantsci.2019.03.022. [9] S. Rice, J.A. Koziel, Characterizing the smell of marijuana by odor impact of volatile compounds: an application of simultaneous chemical and sensory analysis, PLoS ONE 10 (2015a) e0144160, doi:10.1371/journal.pone.0144160. [10] J. Plautz, Growth of legal pot farms drives smog worries, Science 363 (2019) 329, DOI: 10.1126/science.363.6425.329. [11] C-T. Wang, C. Wiedinmyer, K. Ashworth, P.C. Harley, J. Ortega, Q. Z. Rasool, W. Vizuete, Potential regional air quality impacts of cannabis cultivation facilities in Denver, Colorado, Atmos. Chem. Phys. 2019b in press, https://doi.org/10.5194/acp-2019-479.
[12] M. Pérez-Moreno, P. Pérez-Lloret, J. González-Soriano, I. Santos-Álvarez, Cannabis resin in the region of Madrid: Adulteration and contamination, Forensic Sci. Int. 298 (2019) 3438, https://doi.org/10.1016/j.forsciint.2019.02.049. [13] S. Rice, J.A. Koziel, The relationship between chemical concentration and odor activity value explains the inconsistency in making a comprehensive surrogate scent training tool representative of illicit drugs, Forensic Sci. Int. 257 (2015b) 257-270, http://dx.doi.org/10.1016/j.forsciint.2015.08.027. [14] P. Hernandez-Muñoz, R. Catalá, R. Gavara, Effect of sorbed oil on food aroma loss through packaging materials, J. Agric. Food Chem. 47 (1999) 4370-4374, https://pubs.acs.org/doi/10.1021/jf9901791. [15] R. Aoki, A. Tokuda, Y. Shigemura, M. Mineki, Y. Sato, Aroma leakage from orange juice packed in gable-top paper containers for chilled distribution, Shokuhin Eiseigaku Zasshi 58 (2017) 229-233. doi: 10.3358/shokueishi.58.229. PMID: 29081459. [16] P. Leelaphiwat, R.A. Auras, G.J. Burgess, J.B. Harte, V. Chonhenchob, Preliminary quantification of the permeability, solubility and diffusion coefficients of major aroma compounds present in herbs through various plastic packaging materials. J. Sci. Food Agric. 98 (2018) 1545-1553, doi: 10.1002/jsfa.8626. [17] C.-T. Wang, C. Wiedinmyer, K. Ashworth, P.C. Harley, J. Ortega, W. Vizuete, Leaf enclosure measurements for determining volatile organic compound emission capacity from Cannabis spp., Atmos. Environ. 199 (2019a) 80-87, https://doi.org/10.1016/j.atmosenv.2018.10.049.
[18] D.G. Laing, G.W. Francis, The capacity of humans to identify odors in mixtures, Physiol. Behav. 46 (1989) 809-814, https://www.sciencedirect.com/science/article/abs/pii/0031938489900413.
Highlights: >Cannabis odor can justify warrantless searches by police in some jurisdictions >The detectability of cannabis odor was tested in a 2-alternative forced choice test >Cannabis in HDPE and re-sealable sandwich bags was detected with high accuracy >Cannabis in double vacuum-sealed plastic was detected only at chance levels
Acknowledgments We thank Ali Schultz for her advice on experimental design, and Verts Neighborhood Dispensary in Fort Collins for supplying empty pop-top cannisters. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
S1355-0306(19)30204-7 https://doi.org/10.1016/j.scijus.2019.10.007 SCIJUS 852
To appear in:
Science & Justice
Received Date: Revised Date: Accepted Date:
13 July 2019 20 October 2019 27 October 2019
Please cite this article as: A.N. Gilbert, J.A. DiVerdi, Human Olfactory Detection of Packaged Cannabis, Science & Justice (2019), doi: https://doi.org/10.1016/j.scijus.2019.10.007
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 The Chartered Society of Forensic Sciences. Published by Elsevier B.V. All rights reserved.
Human Olfactory Detection of Packaged Cannabis
Avery N. Gilberta,*, Joseph A. DiVerdib aHeadspace
Sensory LLC, Fort Collins, Colorado 80528 USA
bDepartment
of Chemistry, Colorado State University, Fort Collins, Colorado 80523 USA
*Corresponding author. Address for corresponding author: Avery N. Gilbert, 2002 Battlecreek Drive #8303, Fort Collins, CO 80528 USA. E-mail addresses: [email protected] (A.N. Gilbert), [email protected] (J.A. DiVerdi).
Declaration of Interest Funding for research materials and participant incentives was provided by Headspace Sensory, LLC, and by XTR Systems, LLC. Avery N. Gilbert is Founder and Managing Member of Headspace Sensory, LLC. Joseph A. DiVerdi is Founder and CEO of XTR Systems, LLC. Gilbert and DiVerdi have provided expert witness testimony involving cannabis odor.
Human Olfactory Detection of Packaged Cannabis
Abstract
Olfactory detection of cannabis aroma by police officers can be the basis for warrantless searches of motor vehicles in many jurisdictions in the United States. The odor source is these cases is often dried cannabis flower contained in various casual wrappings as well as in more elaborate packaging. Here we investigate whether packaging format alters the detectability of the cannabis. Two cannabis strains and five packaging formats were evaluated. Untrained observers were presented with two containers and asked to identify, based only on smell, the container that held a sample of packaged cannabis (the other container held identical, but empty, packaging material). The results showed that open and casually packaged cannabis was identified with high accuracy, while material packaged in doubly vacuum-sealed plastic was correctly identified at rates no different from chance. The results may help address issues involving the detectability of cannabis aroma in law enforcement and other scenarios.
Keywords Cannabis; Odor detection; Olfactory ability; Scent; Drug detection
1. Introduction That the dried flower of Cannabis sativa L. has a characteristic and easily detected odor is an assertion found in innumerable police reports and court decisions, and forms the basis for the “in plain smell” doctrine regarding warrantless searches [1, 2, 3]. Yet the empirical basis for such claims is remarkably thin. For example, while the volatile compounds in cannabis flower have been extensively studied by means of analytic chemistry, there was, until recently, no systematic, empirical description of its aroma. New studies using quantitative sensory evaluation find that cannabis aroma is not uniform: individual strains (cultivars) have distinctive aroma profiles [4, 5]. Under the plain smell doctrine, a warrantless search of a vehicle is permitted when an officer smells cannabis, even when it is concealed from view and enclosed in a bag or other container. Empirical evidence regarding the olfactory detectability of concealed cannabis is sparse. The one available study, which replicated the circumstances of three New Jersey criminal apprehensions for cannabis, found that claims made by police officers were implausible when tested experimentally [6]. Court decisions [e.g., 7] have also raised questions about the olfactory perception of cannabis with respect to claims made by police. In this study we examine the olfactory detectability of dried cannabis flower contained in casual packaging formats often encountered in motor vehicle stops, as well as in a more elaborate type of packaging, namely vacuum-sealed plastic. We do so with a simple headspace containment technique and a two-alternative forced choice sensory methodology.
2. Materials and methods 2.1. Ethics statement
This research protocol was approved by the Colorado State University Institutional Review Board: Social, Behavioral & Education Research, Protocol #18-8050H. Each participant provided informed written consent. At no time did participants come into direct contact with the cannabis samples. Retail sale of marijuana for recreational use to adults 21 years of age and older has been legal in the state of Colorado since January 1, 2014.
2.2. Participants Study participants were recruited via a notice posted to an online bulletin board for the local community. The text stated that cannabis “users, non-users, former users all welcome”, and that participation was limited to persons between the ages of 21 and 50. In addition to recruiting new participants via the online posting, we contacted people who had taken part in our earlier studies and indicated a willingness to take part in future research. Participants were paid $20.
2.3. Cannabis samples Cannabis samples were purchased from two dispensaries in Fort Collins licensed for retail recreational sale by the state of Colorado: LivWell and Verts Neighborhood Dispensary. One ounce (28g) each of Golden Goat and Mob Boss dried cannabis flower were purchased. These strains were selected in order to represent the aromatic variability that exists in cannabis. Previous quantitative sensory evaluations [4, 5] found that these strains have distinct aroma profiles: Golden Goat was characterized as citrus, lemon, sweet, pungent, while Mob Boss was described as earthy, woody, and herbal.
Strain designations provided by the retail dispensaries were used as a matter of convenience. Their use does not imply a position regarding the taxonomic validity or botanical derivation of either sample.
2.3. Packaging of Cannabis samples Cannabis from each strain was divided into five 5g samples for use in the odor detection trials, and one 3g sample used to familiarize participants with the target odors beforehand (see section 2.4 below). Cannabis samples were presented in five different conditions: (1) in an open glass bowl of 6 oz (177 ml) capacity; (2) inside a resealable, zipper-type, polyethylene food storage bag (Ziploc® Quart Storage Bags, S. C. Johnson & Son, Inc., 17.7 x 18.8 cm); (3) inside a high-density polyethylene produce bag (Crown Poly Pull-N-Pak®, 38 x 50 cm); (4) inside a certified child resistant, polypropylene, pop-top container (XIT® Brand Products, 30 dram (110.9 ml); and (5) inside doubly vacuum sealed food storage plastic (Mainstays™ Vacuum Sealer Rolls, 11 inches x 16 feet (28 x 487.7 cm), made of polyethylene and nylon) sealed with a Ziploc® V203 Vacuum Sealer Machine. Each cannabis sample was paired with a control sample consisting of identical, but empty, packaging. Cannabis and control samples were stored in glass jars in a freezer at −2ºC, and thawed at room temperature for 2 hr before testing.
2.3. Odor sampling chambers Cannabis and blank samples were placed in odor sampling chambers that allowed volatiles to accumulate and be sampled by sniff test participants. The chambers were 2 US gallon (7.6 L) white HDPE buckets (Leaktite, Leominster, MA) with bails removed, and covered with two white lids from the same manufacturer. A 7 x 7 cm rectangular opening (touching the inner circumference of the lid’s raised edge) was cut into one lid to provide a sniffing port. A second, unperforated lid was placed on top of the lid with the sniffing port. This allowed the sample odor to accumulate in the interior headspace of the bucket. The unperforated top lid was removed just prior to the participant’s sniffing and replaced immediately afterward. An alphanumeric code (placed on the bucket and lids opposite the side facing the test participant) uniquely identified each sample to the test administrator and provided an alignment cue for the sniffing port. Cannabis and control samples were placed in the odor sampling chambers for one hour before testing. A tent of folded aluminum foil was placed loosely over each stimulus/blank to provide additional visual screening while allowing air to circulate freely around the stimulus/blank.
2.4. Test procedure The participant was seated at a table and wore a blindfold (Mack’s® Dreamweaver™ Contoured Sleep Mask). Two odor sampling chambers were placed side by side on the table in front of the participant. The participant’s task was to sniff each chamber and indicate the one containing cannabis. Ten stimulus pairs (cannabis sample plus corresponding blank packaging sample) were presented in randomized order to each participant. In addition, the left-right placement of the blank and cannabis samples was randomized across trials for each participant. Participants were allowed to sniff the odor sampling chambers as many times as needed in order
to make a decision. Prior to the test, the participant was shown a dummy odor sampling chamber and allowed to practice sniffing from it. The participant also sniffed 3 g samples of Golden Goat and Mob Boss from 1 US pint (473 ml) Mason jars in order to become familiar with the target odors.
3. Results 3.1. Participant demographics Twenty-one people (11 men, 10 women) aged 21 and older (mean 29.7 ± 7.6 years) were tested. All subjects reported having purchased and used cannabis since January 1, 2014. High rates of purchase (≥94.2%) and use (≥92.3%) were seen also in previous studies [4, 5] despite efforts to recruit nonusers.
3.2. Data analysis The binomial test (IBM SPSS version 24) was used to determine whether the proportion of correct answers differed significantly from that expected by chance, i.e., 50%. The results (Table 1) indicate that seven of the ten samples were detected at a proportion significantly above that expected by chance. Cannabis samples in the open bowl, Ziploc bag, and HDPE bag were all detected with 100% accuracy; the results were identical for both cannabis strains. In addition, one of the samples (Mob Boss) presented in a pop-top cannister was correctly identified at a statistically significant level. One cannabis sample presented in a pop-top cannister, and both samples presented in doubly vacuum sealed-plastic, were identified at levels that were not statistically different from chance.
____________________________________________________________________________ Packaging format Cannabis strain Proportion correct P value ____________________________________________________________________________ Open bowl Open bowl
Golden Goat Mob Boss
21/21 (100%) 21/21 (100%)
<.000001 <.000001
* *
Ziploc® bag Ziploc® bag
Golden Goat Mob Boss
21/21 (100%) 21/21 (100%)
<.000001 <.000001
* *
HDPE bag HDPE bag
Golden Goat Mob Boss
21/21 (100%) 21/21 (100%)
<.000001 <.000001
* *
Pop-top cannister Pop-top cannister
Golden Goat Mob Boss
15/21 (71%) 20/21 (95%)
.078 .000021
n.s. *
Doubly vacuum sealed Golden Goat 15/21 (71%) .078 n.s. Doubly vacuum sealed Mob Boss 9/21 (43%) .66 n.s. ____________________________________________________________________________ Table 1 The proportion of correct responses for each packaging format and cannabis strain. Asterisk indicates a statistically significant result. 4. Discussion Using smell alone, untrained consumers were able to identify, with perfect accuracy, the sampling chamber holding 5 g of cannabis when the sample was presented in an open bowl, inside an HDPE produce bag, or inside a resealable polyethylene food storage bag. Volatile compounds released by the cannabis were able to migrate through these forms of packaging and create headspace concentrations sufficient to enable easy olfactory identification. In contrast, the cannabis sample could not be identified reliably when packaged in doubly vacuum-sealed plastic. This method of packaging restricted the release of cannabis volatiles to such an extent as to reduce the accuracy of olfactory identification to chance levels. The results for pop-top cannisters, commonly used as packaging for retail cannabis sales in licensed dispensaries, were
mixed. One sample was identified with high accuracy (95% correct) while the other was identified at a rate indistinguishable from chance. We cannot account for this difference, but can speculate that variability in the manufacturing process leaves some cannisters with less tightly fitting tops than others. This experiment used odor sampling chambers with a volume of 2 US gallons (7.6 L). It is possible that the open cannabis sample, as well as the samples placed inside HDPE and polyethylene bags, might emit enough volatiles to allow accurate detection in an enclosed space of greater volume absent other physical barriers (but see 5 Conclusions below). Conversely, the inability of test panelists to accurately identify the cannabis aroma in our sampling chambers implies that the task would be correspondingly more difficult in a larger contained space, such as a motor vehicle.
5. Conclusions In 2004, Doty, et al. [6] attempted to, among other objectives, “determine whether a group of men and women could distinguish the odor of packaged marijuana from that of a matched blank odor source”. In one portion of their study, blindfolded test subjects were presented two plastic garbage bags: one containing five 1 lb packets of “pressed and processed Mexican marijuana” and the other similarly bundled crushed newspapers. Their task was to indicate the bag that smelled like marijuana. The nine participants unanimously selected the marijuanacontaining bag (a statistically significant outcome). The present study extends this exploration by asking how accurately people can smell cannabis when it is inside various forms of packaging. Our results show that typical casual packaging, namely HDPE produce bags and polyethylene food storage bags, was ineffective at limiting aroma diffusion from dried cannabis flower.
However, doubly vacuum-sealed plastic reduced diffusion of cannabis odor to levels where olfactory detection was no better than chance. There is an important caveat to these results: the near flawless detection of cannabis odor through produce and food storage bags is specific to our experimental conditions and may not generalize to real world contexts involving larger air volumes and physically partitioned storage spaces. For example, Doty, et al. [6] also examined the ability of observers to identify cannabis odor in the passenger compartment of an automobile when the sample was located the vehicle’s trunk. Under these circumstances, the cannabis sample—the same one detected without error when sniffed from a garbage bag—was detected at a rate no better than chance. Thus, an aroma easily detected at point-blank range may be rendered statistically undetectable through a combination of dilution and additional physical containment. Further, dilution through diffusion into a larger physical space can alter the character of an odor mixture: the relative perceived intensity of each molecular component changes with concentration according to unique psychophysical functions. Thus, it is possible that cannabis aroma, if sufficiently diluted, could remain detectable as a smell but not be accurately identifiable as cannabis. Another limitation of the present study is that we examined cannabis aroma in the absence of competing ambient odors. In the real world conditions of a traffic stop, unrelated odors such as air fresheners, fast food containers, tobacco, tobacco smoke, perfume, and scented body sprays may also be present in a vehicle’s interior. Indeed, some of these scents are deliberately used by drivers and passengers to mask the odor of cannabis. Studies in olfactory psychophysics have shown that it is difficult for observers to identify individual components from mixtures of three or more odors [18]. The ability of human observers to selectively detect cannabis aroma against a background of unrelated odors deserves further study.
The detection of cannabis odor through packaging involves two factors: the release of volatiles from the plant material, and the diffusion of these compounds through the packaging barrier. Terpenes are generally regarded as the key physical basis of cannabis odor. They are the most abundant volatiles in mature plants and dried flowers [8, 9]. They are produced in such quantities that cannabis cultivation facilities may contribute to an increase in regional ozone concentrations [10, 11]. There is substantial variation in terpene abundance across strains, but a relatively small number of these compounds show up repeatedly [8]. While smell has been used informally to track microbiological contamination of cannabis resin [12], the combined analytical and sensory research required to identify key aroma compounds in cannabis (e.g., gas chromatography-olfactometry) has yet to be published. It is important to note that the relative abundance of a terpene is not correlated with its olfactory impact [9, 13]. The diffusion of volatile plant compounds through packaging materials is of interest to food chemists and such studies have examined some of the terpenes found in cannabis. Limonene, for example, diffuses through thermosealable films such as ultra-low-density polyethylene and modified poly(ethylene terephthalate) [14], as well as through gable-top paper cartons containing chilled orange juice [15]. Linalool and eucalyptol have been shown to diffuse through a variety of polymeric films including low-density polyethylene, polypropylene, nylon, and metalisedpolyethylene terephthalate (MPET) [16]. The diffusion rates of these terpenes vary across different types of plastic. The ability of key cannabis aroma volatiles to deliver recognizable cannabis aroma outside of plastic packaging deserves further exploration. We used small enclosures to capture headspace volatiles from gram-quantity samples of dried cannabis flower. Enclosures of similar scale have been used to calculate emission rates of terpenes from living cannabis plants [17]. Our method offers a useful approach to modeling the
dispersion of cannabis aroma within (and from) a confined space, such as the interior of a motor vehicle. Many criminal cases invoking the plain smell doctrine involve automobiles or trucks [2]. Odor dispersion from industrial marijuana grows, i.e., a large interior space containing massively distributed odor sources, would require a different approach. Interpretation of the plain smell doctrine is complicated in states where possession of a small amount of cannabis, or possession by persons with medical marijuana cards, has been legalized. In these instances, the mere presence of cannabis odor by itself may no longer imply criminal activity. This raises the question of whether the quantity of cannabis can be estimated by an olfactory assessment alone [3]. That there are statistically defined limits to the concentration at which a given odor can be detected is a basic principle of sensory psychophysics, and one that undercuts the presumption that, when cannabis is present, its odor can always be detected [6]. One legal commentator [1] notes that the plain smell doctrine does not imply an unchallenged reliance upon odor perception, and that it ought to be accompanied by a recognition that there are limits to the detection of any odor. In this view, each sense modality should “be allowed to operate within its own sphere of reliability,” and that to be relied upon in legal proceedings the odor of contraband needs to be distinctive, strong and persistent [1]. Given the results of the present study, smell-based searches where the material was vacuum sealed within one or more layers of plastic may lie beyond the “sphere of reliability.”
References [1] M.A. Sprow, Wake up and smell the contraband: Why courts that do not find probable cause based on odor alone are wrong, Wm. & Mary L. Rev. 42 (2000-2001) 289-318.
[2] S.F. Mandiberg, Marijuana prohibition and the shrinking of the Fourth Amendment, McGeorge L. Rev. 43 (2012) 23-51. [3] M.P. Hoxsie, Probable cause: Is the “plain-smell” doctrine still valid in Arizona after the AMMA? Ariz. L. Rev. 57 (2015) 1139-1161. [4] A.N. Gilbert, J.A. DiVerdi, Consumer perceptions of strain differences in Cannabis aroma, PLoS ONE 13 (2018) e0192247, doi: 10.1371/journal.pone.0192247. [5] A.N. Gilbert, J.A. DiVerdi, Use of rating scales versus check-all-that-apply ballots in quantifying strain-specific Cannabis aroma, J. Sensory Studies (2019) e12499, DOI: 10.1111/joss.12499. [6] R.L. Doty, T. Wudarski, D.A. Marshall, L. Hastings, Marijuana odor perception: Studies modeled from probable cause cases, Law Hum. Behav. 28 (2004) 223–233. [7] State of Kansas v. Lawrence C. Hubbard, Case No. 113,888 Kansas Supreme Court, December 7, 2018. [8] J.K. Booth, J. Bohlmann, Terpenes in Cannabis sativa – From plant genome to humans, Plant Sci. 284 (2019) 67-72, https://doi.org/10.1016/j.plantsci.2019.03.022. [9] S. Rice, J.A. Koziel, Characterizing the smell of marijuana by odor impact of volatile compounds: an application of simultaneous chemical and sensory analysis, PLoS ONE 10 (2015a) e0144160, doi:10.1371/journal.pone.0144160. [10] J. Plautz, Growth of legal pot farms drives smog worries, Science 363 (2019) 329, DOI: 10.1126/science.363.6425.329. [11] C-T. Wang, C. Wiedinmyer, K. Ashworth, P.C. Harley, J. Ortega, Q. Z. Rasool, W. Vizuete, Potential regional air quality impacts of cannabis cultivation facilities in Denver, Colorado, Atmos. Chem. Phys. 2019b in press, https://doi.org/10.5194/acp-2019-479.
[12] M. Pérez-Moreno, P. Pérez-Lloret, J. González-Soriano, I. Santos-Álvarez, Cannabis resin in the region of Madrid: Adulteration and contamination, Forensic Sci. Int. 298 (2019) 3438, https://doi.org/10.1016/j.forsciint.2019.02.049. [13] S. Rice, J.A. Koziel, The relationship between chemical concentration and odor activity value explains the inconsistency in making a comprehensive surrogate scent training tool representative of illicit drugs, Forensic Sci. Int. 257 (2015b) 257-270, http://dx.doi.org/10.1016/j.forsciint.2015.08.027. [14] P. Hernandez-Muñoz, R. Catalá, R. Gavara, Effect of sorbed oil on food aroma loss through packaging materials, J. Agric. Food Chem. 47 (1999) 4370-4374, https://pubs.acs.org/doi/10.1021/jf9901791. [15] R. Aoki, A. Tokuda, Y. Shigemura, M. Mineki, Y. Sato, Aroma leakage from orange juice packed in gable-top paper containers for chilled distribution, Shokuhin Eiseigaku Zasshi 58 (2017) 229-233. doi: 10.3358/shokueishi.58.229. PMID: 29081459. [16] P. Leelaphiwat, R.A. Auras, G.J. Burgess, J.B. Harte, V. Chonhenchob, Preliminary quantification of the permeability, solubility and diffusion coefficients of major aroma compounds present in herbs through various plastic packaging materials. J. Sci. Food Agric. 98 (2018) 1545-1553, doi: 10.1002/jsfa.8626. [17] C.-T. Wang, C. Wiedinmyer, K. Ashworth, P.C. Harley, J. Ortega, W. Vizuete, Leaf enclosure measurements for determining volatile organic compound emission capacity from Cannabis spp., Atmos. Environ. 199 (2019a) 80-87, https://doi.org/10.1016/j.atmosenv.2018.10.049.
[18] D.G. Laing, G.W. Francis, The capacity of humans to identify odors in mixtures, Physiol. Behav. 46 (1989) 809-814, https://www.sciencedirect.com/science/article/abs/pii/0031938489900413.
Highlights: >Cannabis odor can justify warrantless searches by police in some jurisdictions >The detectability of cannabis odor was tested in a 2-alternative forced choice test >Cannabis in HDPE and re-sealable sandwich bags was detected with high accuracy >Cannabis in double vacuum-sealed plastic was detected only at chance levels
Acknowledgments We thank Ali Schultz for her advice on experimental design, and Verts Neighborhood Dispensary in Fort Collins for supplying empty pop-top cannisters. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.