THC from vaping deposits on room surfaces, creating potential third-hand exposure | Research

The takeaway

THC was detected on surfaces in a room where cannabis was vaporized, at levels ranging from 348 to 4,882 ng/m2, demonstrating that cannabis vapor leaves measurable residue on surfaces.

People who vape cannabis indoors, landlords, parents, and occupational health researchers.

THC found on surfaces up to 4,882 ng/m2 after vaping

What the researchers found

THC was detected on 6 of 15 surface samples collected from a room where cannabis was vaporized, at quantifiable levels of 348-4,882 ng/m2. All control samples from outside the study room were negative.

Why it matters

Third-hand tobacco smoke exposure (from surface residue) is a recognized health concern. This is the first study to show that cannabis vapor similarly deposits on surfaces, creating a potential exposure pathway for non-users in shared spaces.

The numbers in context

6 of 15 surface samples positive for THC. Levels: 348-4,882 ng/m2. All negative controls were clean.

How the study worked

Surface samples were collected using isopropanol-imbued non-woven wipes from hard surfaces and objects in a room where cannabis was vaporized. Samples were analyzed using LC-ESI-MS/MS with online extraction. Standardized three-pattern swabbing protocol was used.

What this study cannot tell us

Single room study. Unknown how long THC persists on surfaces. Unknown whether surface-deposited THC is bioavailable through skin contact. Only THC was measured; other cannabinoids were not assessed.

How to read the evidence

Preliminary: proof-of-concept study in a single room with small sample number.

When this study was published

Published in 2019.

The bigger picture

As cannabis vaping increases in homes, workplaces, and rental properties, surface deposition could lead to unintended cannabinoid exposure for children, pets, and non-users who touch contaminated surfaces.

Questions still open

Can surface-deposited THC be absorbed through skin contact? Does it accumulate over time with repeated use? Would standard cleaning remove it? Could surface THC cause a positive drug test?

Common questions

What is third-hand exposure?

Third-hand exposure occurs when residue from smoke or vapor deposits on surfaces and is later encountered by touching those surfaces. This is different from secondhand exposure (inhaling nearby smoke/vapor).

Is this a health risk?

Unknown at this point. The study demonstrated that THC deposits on surfaces, but whether the amounts are sufficient to cause health effects through skin contact or ingestion has not been studied.

Read the original research

Surface Detection of THC Attributable to Vaporizer Use in the Indoor Environment.

Scientific reports, 9(1), 18587

View on PubMed ↗Publisher’s paper ↗

Citation

Sempio, Cristina; Lindley, Emily; Klawitter, Jost; Christians, Uwe; Bowler, Russell P; Adgate, John L; Allshouse, William; Awdziejczyk, Lauren; Fischer, Sarah; Bainbridge, Jacquelyn; Vandyke, Mike; Netsanet, Rahwa; Crume, Tessa; Kinney, Gregory L. (2019). Surface Detection of THC Attributable to Vaporizer Use in the Indoor Environment.. Scientific reports, 9(1), 18587. https://doi.org/10.1038/s41598-019-55151-5