The current study leveraged the protocol of an ongoing IRB approved clinical trial investigating the efficacy of cannabis for chronic and experimental pain alleviation (Colorado Multiple Institutional Review Board [COMIRB] 14–1909). All participants to the clinical trial provided written informed consent and the study was conducted in accordance with Good Clinical Practice guidelines and the Declaration of Helsinki. Environmental sampling was performed in between drug administration visits and no human subjects were involved. The double-blind study protocol exposed participants to vaporized whole plant cannabis (approximately 4.5–5.4% THC and a placebo with 0.002% THC) provided by the National Institute on Drug Abuse (NIDA) Drug Supply Program. The clinical trial was conducted in a single drug administration room (27.26 m3) on the University of Colorado Anschutz Medical Campus, Clinical Translation Research Center that was equipped with a high efficiency ventilation system that replaces room air in less than two minutes when activated. Each participant in the clinical trial underwent 3 drug administration visits in the room: one session with active vaporized THC cannabis and 2 with placebo cannabis plant material. The blinded study pharmacist prepared the plant material for vaporization in the secured schedule 1 medication room across the hall from the administration site. The plant material was rehydrated within 12 to 24 hours of administration. The pharmacist delivered the prepared product to the administration room and assembled the Volcano Vaporizer. The clinical trial used a Volcano Vaporizer (Storz-Bickel, Tuttlingen, Germany) in which 400 mg of cannabis or placebo was vaporized at 200 °C into an 8 liter balloon3. The filtration fan was turned on prior to inflating the balloon and study personnel left the room. A valve on the balloon allowed the participant to interrupt, at will, the inhalation from the balloon and limited the release of vapor into the indoor environment. The subjects inhaled using the Fulton puff method: 5 seconds inhale, 10 seconds hold, 40 seconds to exhale before their next inhalation. Participants were required to inhale 4 puffs from a balloon and then had the option to inhale up to 4 more puffs from a second balloon. Upon completion of administration the study pharmacist expelled the remaining vapor (if any) towards the ceiling ventilation system and returned the used product to the secured schedule 1 medication room for disposal/storage.

Surface sampling

The objects in the drug administration room included one fixed and one movable table, a reclining chair, a Grooved Pegboard Task assessment and the vaporizer. The room itself had two sealed windows that extend to the ceiling. During our surface sampling period, study personnel cleaned the study area by wiping only the tables at the beginning of each month with Sani-Cloth germicidal disposable wipes, which were imbued with a mixture of ammonium chlorides derivatives (0.5%), water (45%) and isopropyl alcohol (IPA, 55%) (PDI, Orangeburg, NY, USA). For this reason, the protocol to quantify third-hand exposures was implemented over 2 sampling periods: one at the beginning of the month, after the tables had been cleaned, and one at the end of the month after 6 study visits took place. Since the study staff cleaned only the tables, the other sampled surfaces would represent THC accumulation over time.

Furthermore, due to the double-blind nature of the study, we could not know whether a specific study visit used active or placebo cannabis, so we focused on the possible accumulation of THC on surfaces after repeated administrations of both active and placebo cannabis. However, we were able to estimate the number of active visits that took place in the administration room based on the number of subjects that completed all the three visit of the study. At the time of the first sampling, 44 study visits had occurred in the drug administration room and 12 subjects completed the study allowing for a minimum of 12 active cannabis administrations to a maximum of 18. At the time of the second sampling, 6 additional visits had occurred resulting in 50 total study visits in the room and 13 subjects completed the study allowing for a minimum of 13 active cannabis administration sessions to a maximum of 21.

Due to the lipophilicity of THC and other cannabinoids, samples were collected using non-woven wipes imbued with a mixture of water and isopropyl alcohol (IPA) (30:70, v/v) (Novaplus, Irving, TX, USA). Samples were obtained at the two sampling periods from surfaces that would not be damaged by IPA. In the first sampling period, samples were collected from the tables, the floor, the chair seat, the Grooved Pegboard Task assessment, the door knob, the vaporizer and the window bar. During the second sampling period, samples were collected from the tables, the windowsill and the Grooved Pegboard Task assessment. Rectangular areas of 0.06 m2 (printer paper sheet) were identified by placing adjacent printer paper sheets next to a corner on a large surface such as the tables. One 0.06 m2 area was sampled from each flat surfaces such as the tables, the window bar, and the floor; non-flat surfaces were sampled by swabbing the surface as completely as possible. Since only the tables were cleaned at the beginning of the month, the same areas on the fixed and movable tables were sampled during both the first and second sampling period to test for THC accumulation occurred between the two sampling period. Three wipes were used for the same area on each surface tested. The following swabbing patterns were used: back and forth starting from the top left corner to the bottom right corner of the area, up and down from the bottom left corner to the top right corner of the area and small circular motions starting at the center moving out. All 3 wipes were placed in the same glass vial using a bent paperclip to reduce handling, gloves and paperclips were changed after each sampling to avoid possible cross-contamination.

To test how easily THC could be removed from surfaces, a set of three surfaces of identical contingent area (0.036 m2) were identified on the windowsill; one was sampled using 1 swab, one using 2 swabs and one using 3 swabs. In order to blind the analytical laboratory, additional swabs were inserted in the glass vials without being used so that each sample tube contained three swabs. To test if three swabs were sufficient to completely remove THC from a surface, during the second sample collection, we swabbed twice the area located on the movable table, 10 minutes apart to allow the complete evaporation of the IPA solution.

Furthermore, negative controls were collected from three different locations: the laboratory bench after thorough cleaning with Sani-Cloth germicidal disposable wipes; the face of the clock situated outside the administration room and three different location in a non-user house.

Quantification of THC on the Wipes using LC-MS/MS

The THC reference material and its isotope labeled internal standard Δ9-tetrahydrocannabinol-d3 (THC-d3) were purchased from Cerilliant (Round Rock, TX). Wipe specimens were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Briefly, the three wipes collected from each surfaces were soaked in the glass vials with 2 mL of methanol containing the internal standards (0.25 ng/mL). One thousand two hundred µL was collected and transferred into a 1.5 mL low binding polypropylene vial (Sarstedt, Nümbrecht, Germany). Specimens were dried overnight using a speed-vac (Centrivap, Labconco, Kansas City, MO, USA). Dried samples were reconstituted with 550 µL of methanol and briefly vortexed. After adding 450 µL of water, specimens were vortexed and centrifuged (at 26,000 g, 4 °C, 20 min, MR 23i, Thermo Scientific, Waltham, MA, USA). The supernatant was transferred into an HPLC vial for analysis. THC was analyzed by LC-MS/MS on a Sciex API5000 tandem mass spectrometer (Sciex, Concord, ON, Canada) via a turbo V ion source operated in the positive electrospray ionization (ESI) mode. The mass spectrometer operated in positive multiple reaction monitoring (MRM) mode. Monitored transitions for THC are reported in Table 1, transitions in bold were used for THC quantification. Two hundred fifty µL of the samples were injected onto a 4.6 · 12.5 mm online extraction column (Zorbax XDB C8, Agilent Technologies) with a particle size of 5 µm. Samples were loaded and washed with a mobile phase of 45% methanol supplemented with 0.1% formic acid and 55% 0.1% formic acid in water. The flow was increased from 0.5 mL/min to 1.5 mL/min within one minute. The extraction column was kept at room temperature. After 1 minute, the switching valve was activated and the analytes were eluted in the backflush mode from the extraction column onto a 4.6 · 50 mm Poroshell Eclipse C18, 2.7 µm analytical column (Agilent Technologies). The analytical column was kept at 60 °C. The organic solvent (B) consisted of 20% isopropanol, 20% methanol and 60% acetonitrile and the aqueous solvent (A) consisted of water supplemented with 0.1% formic acid. The analytical gradient started with a flow rate of 0.75 mL/min and 60% of solvent B for the first minute. Within the following 3 minutes, the flow rate and the organic solvent content were increased to 1 mL/min and 95% solvent B, respectively. From 4 to 6 minutes, the solvent B was increased to 100%. At minute 6.2 the system returned to starting conditions for 1.8 minutes to equilibrate for the following injection. The nebulizer current was set to 5 µA, the source gas 2 was set to 40 (arbitrary units), the source temperature was set to 450 °C, the entrance potential and the collision cell exit potential were set to 10 V and 11 V, respectively. Calibration curves were prepared by spiking 0.017 m2 of clean smooth surface with known amounts of THC (5–50 ng) resulting in an area concentration range of 295 ng/m2 to 2959 ng/m2. Lower limit of quantification (LLOQ) were establish as signal-to-noise ratio ≥8, no significant interferences and accuracy and imprecision within ±20% (n = 6). Surface recovery efficiency was calculated by comparing samples spiked on the surface and spiked directly on the swabs and swab matrix effect by comparing samples spiked on the swabs and extracted neat solutions in absence of swabs. To test how easily THC could be removed from surfaces, a set of three surfaces of identical contingent area (0.017 m2) were identified on the laboratory bench and spiked with 10 ng of THC; one was sampled using 1 swab, one using 2 swabs and one using 3 swabs. In order to simulate the experimental conditions, additional swabs were inserted in the glass vials without being used so that each sample tube contained three swabs.

Table 1 LC-MS/MS parameters for THC and internal standard on surfaces. Transition in bold was used for THC quantification. Full size table

Analyst software version 1.6.2 was employed for data acquisition and MultiQuant version 2.1.1 for data analysis (Sciex, Foster City, CA, USA). THC concentrations were quantified based on the THC/internal standard ratios. The calibrator were fitted using a linear equation in combination with 1/x weighting.