An assessment of detection canine alerts using flowers that release methyl benzoate, the cocaine odorant, and an evaluation of their behavior in terms of the VOCs produced

Highlights

• Results of this paper validate the reliability of canine evidence in court.

• The odor profiles of snapdragon flowers were found to be statistically different than cocaine.

• Methyl benzoate is not necessarily the dominant odor produced by snapdragon flowers.

• Narcotic detection canines never falsely alerted to snapdragon flowers.

Abstract

In recent years, the high frequency of illicit substance abuse reported in the United States has made the development of efficient and rapid detection methods important. Biological detectors, such as canines (Canis familiaris), are valuable tools for rapid, on-site identification of illicit substances. However, research indicates that in many cases canines do not alert to the contraband, but rather to the volatile organic compounds (VOCs) that are released from the contraband, referred to as the “active odor.” In 2013, canine accuracy and reliability were challenged in the Supreme Court case, State of Florida v. Jardines. In this case, it was stated that if a canine alerts to the active odor, and not the contraband, the canine's accuracy and selectivity could be questioned, since many of these compounds have been found in common household products. Specifically, methyl benzoate, the active odor of cocaine, has been found to be the most abundant compound produced by snapdragon flowers. Therefore, the purpose of this study is to evaluate the odor profiles of various species of snapdragon flowers to assess how significantly methyl benzoate contributes to the total VOC profile or fragrance that is produced. Particularly, this study examines the VOCs released from newly grown snapdragon flowers and determines its potential at eliciting a false alert from specially trained detection canines. The ability of detection canines to differentiate between cocaine and snapdragon flowers was determined in order to validate the field accuracy and discrimination power of these detectors. An optimized method using headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS–SPME/GC–MS) was used to test the different types and abundances of compounds generated from snapdragon flowers at various stages throughout the plants’ life cycle. The results indicate that although methyl benzoate is present in the odor profile of snapdragon flowers, other compounds are present that contribute significantly, if not more, than that of methyl benzoate. Canine teams, from various police departments throughout South Florida, certified for narcotics detection, took part in this study. Two canine trials involving 21 canines teams were performed by exposing the teams to 4 different species of snapdragon flowers. Of the 21 canine teams tested, none alerted to the snapdragon flowers presented, while all (100%) alerted to real cocaine samples, the positive control. Notably, the results revealed that although methyl benzoate is produced by snapdragon flowers, certified narcotics detection canines can distinguish cocaine's odor profile from that of snapdragon flowers.

Introduction

According to the 2012 National Survey on Drug Use and Health (NSDUH), over 23 million Americans, were said to be current users of illicit substances, representing 9.2% of the population. It was also reported that 1.6 million people were current users of cocaine, one of the most commonly abused illicit drugs in the United States [1]. The high frequency of illicit substance abuse in the United States has made the development of efficient and rapid detection methods exceedingly important. While many forms of instrumentation and technology have been utilized for on-site detection and screening, biological detectors, more specifically, canines (Canis familiaris), represent one of the most reliable, versatile, rapid, and cost effective real-time detection tools for contraband [2], [3].

Ongoing research attempts to understand detector dogs by studying which odors dissipate from specific targets, which odors induce a response from a trained canine, and the threshold levels associated with said target odor [4], [5]. Additionally, a canine's ability to discriminate between a single odor verses a pool of combined odors containing traces of the single target odor, is a complex issue that is continuously brought up when a canine's field validity is debated [6]. Moreover, previous studies have shown that it is not the actual illicit material that induces an alert by detection canines, but specific components that comprise the substance's signature odor profile [4]. These odor signatures are volatile organic compounds (VOCs) that have been identified in the headspace of the target substance in question, for example, methyl benzoate has been identified as an active signature odor of cocaine [2], [4]. In other words, the studies indicate that it is the odor of methyl benzoate, not cocaine, that elicits an alert from the canine [4]. Studies have also shown that a detection canine's absolute threshold, or limit of detection, for methyl benzoate was calculated to be 10 parts per billion (ppb), revealing the canine's high level of sensitivity [7], [8], [9]. While these findings have assisted in improving canine training and efficiency, as well as assisted in validating a canine's discrimination power in court, the results have also raised some questions with regards to canine detection accuracy. Recently, the reliability of narcotic detection canines was challenged within the forensic community and the legal system [10].

In 2013, the Supreme Court case, State of Florida v. Joelis Jardines scrutinized the use of detection canines [10]. This case debated whether a warrantless “sniff” from a detection canine, performed at the doorstep of a private residence, violated the Fourth Amendment of the United States Constitution, which prohibits unlawful search and seizure. In this argument, the Respondent held the belief that the use of the canine “sniff” without a warrant, is, in fact, unconstitutional. The counsel for the respondent used scientific evidence to back up their claim, and in doing so, discredited the use of detection canines under these circumstances. It was stated that since canines are alerting to the active odor of the substance, and not the contraband itself, the selectivity and accuracy of the canine could be called into question, since many of these odors are present in common household items [10]. The case specifically highlighted methyl benzoate, which was recently found to be the most abundant compound produced by popular landscaping flowers, such as snapdragons (Antirrhinums) [10], [11]. Thus, the question arose as to whether snapdragon flowers, contained in flower beds or bouquets, would cause canines to alert and falsely indicate that cocaine is present when it is, in fact, just the flowers producing the methyl benzoate.

Snapdragon flowers (Fig. 1), belonging to the genus Antirrhinum and family Scrophulariaceae, are cool weather plants, ranging from 20 to 100 cm in height. These flowers, owing their name to their petals resembling that of a dragon's mouth, are native to southern Europe, but the popularity of the flower, has caused it to spread throughout the United States [12].

Most flowers, including the snapdragon flower, owe their reproductive success to their emitted floral scent, capable of attracting specific pollinators [11], [13], [14], [15]. The VOCs that constitute the flower's fragrance vary from species to species with respect to the number, type, and relative abundances of compounds. The composition of the flowers’ odor profile and total odor production changes throughout the plants’ life cycle and emit their maximum levels when the flower is ready for pollination. Newly opened flowers have under developed anthers (pollen producing structures) and therefore produce less odor/scent, as they are not ready for pollination. After pollination, the amount of scent released by the plant decreases, and continues to decrease until the end of the flower's life cycle [11], [14], [16]. Dudareva et al. and Negre et al. conducted research monitoring the production of methyl benzoate, specifically, from snapdragon flowers. Studies showed that the Maryland True Pink cultivar emitted the most methyl benzoate, making up 60% of the total volatiles. It was also found that unopened buds released no methyl benzoate, but began to emit, upon opening, at very low levels. The production of methyl benzoate reached its peak 5–7 days after anthesis, or after the flower had opened, and then declined thereafter [11], [14]. Additionally, methyl benzoate production was found to be highest during the daylight hours of 9 am and 4 pm, due to the high activity of pollinators during those hours [11], [14].

While the odors emitted by snapdragon flowers, particularly, the release of methyl benzoate, have been extensively studied, little is known about whether the flower's fragrance will elicit a false alert from specially trained narcotics detection canines, as surmised during the Supreme Court case, State of Florida v. Joelis Jardines (2013). Therefore, the purpose of this study is to evaluate the odor profiles of various species of snapdragon flowers to assess the significance of methyl benzoate to the overall fragrance produced. In addition, specially trained narcotics detection canines were used to determine if the flower's fragrance would result in a false alert. The ability of canines to differentiate between cocaine and snapdragon flowers, that have similar odor pools, was determined in order to validate the field accuracy and discrimination power of detector canines.