A new study published in Forensic Science International found that even brief, passive exposure to cannabis smoke can lead to detectable levels of THC and CBD in human hair—potentially complicating forensic drug testing.
For the study, researchers from the University of Bologna exposed four volunteers to controlled cannabis smoke inside a car for 15 minutes once per week over a month. Two exposure phases were tested: one using low-THC “light cannabis” (0.5% THC) and another using higher-potency cannabis (5% THC), separated by a one-month washout period. Hair and urine samples were collected after each exposure.
Despite urine samples consistently testing negative for THC metabolites, washed hair samples showed the presence of cannabinoids. After exposure to low-THC cannabis, CBD was detected at an average of 0.05 ng/mg. In contrast, exposure to high-THC cannabis resulted in THC detection at an average of 0.02 ng/mg. These levels, the researchers note, are comparable to those seen in active drug users.
“Our study showed that hair contamination could arise in vivo even after short single exposures to cannabis and “light cannabis”, underlining the need for a careful interpretation of results of hair analysis in forensic toxicology”, concludes the study.
The full abstract of the study can be found below:
Prolonged cannabis smoke exposure could give rise to detectable levels of cannabinoids in hair, complicating forensic hair analysis interpretation. Exposure to “light cannabis”, i.e., products that are low in Δ9-tetrahydrocannabinol (Δ9-THC) and enriched in cannabidiol (CBD), can additionally lead to contamination, as shown in vitro. The aim of the present study was to assess whether detectable hair levels of Δ9-THC and CBD could arise in vivo from short, single and repeated passive exposure to cannabis and “light cannabis” and whether the two products could be distinguished.
Four volunteers underwent weekly 15-minute exposures to low-Δ9-THC (0.5 %) cannabis smoke, delivered by a pump inside a car, over a month. After 1 month of washout, exposures were repeated with the same scheme with high-Δ9-THC (5 %).
Hair and urines samples were collected after each exposure. Hair samples were tested, with and without a washing step (total n = 72), by liquid chromatography tandem mass spectrometry for Δ9-THC and CBD. Urines were tested for drug metabolites (LOD: 1.66 ng/ml).
No accumulation of drugs over exposures was shown. Urines always tested negative. Washed hair samples were positive for CBD (mean 0.05 ng/mg) after exposure to low-Δ9-THC cannabis, and for Δ9-THC (mean 0.02 ng/mg) after exposure to high-Δ9-THC cannabis, with levels also typical of drug use. The two products could be easily distinguished.
Our study showed that hair contamination could arise in vivo even after short single exposures to cannabis and “light cannabis”, underlining the need for a careful interpretation of results of hair analysis in forensic toxicology.
More articles from The Marijuana Herald:
