Amidst the wave of marijuana legalization in 2016, researchers at the University of Pittsburgh, led by Alexander Star and Ervin Sejdic, began working on a device to detect THC in breath. Star, a chemistry professor, and Sejdic, a professor of electrical and computer engineering, announced in August that their marijuana breathalyzer is almost ready for mass production.
THC, or delta-9-tetrahydrocannabinol, is the main psychoactive component in marijuana. THC binds to carbon nanotubes within the device, which are 1/100,000 the size of human hair, and effectively alters their electrical properties. By measuring the difference in electrical properties of the nanotubes, the device is able to determine how much THC is present in the breath.
“Nanotechnology sensors can detect THC at levels comparable to or better than mass spectrometry, which is considered the gold standard for THC detection,” said the university’s Swanson School of Engineering in a news release.
Now, the researchers are studying the correlation between the device’s readings and the person’s level of impairment—if such a correlation exists. Whereas alcohol breathalyzers determine impairment by measuring the amount of alcohol in the breath (using the “blood to breath” or “partition” ratio), Sejdic said such a correlation for marijuana “is basically missing, from a scientific point of view.”
“So when it comes to these marijuana breath tests, that’s the million-dollar question right now,” said Chris Halsor, a Denver lawyer who focuses on issues around legal cannabis, in an interview with NPR.
Even if the device was able to accurately portray a person’s level of impairment, there is still the legal question of what level should be considered safe for driving. It took decades for scientists, lawmakers, police and the public to set the legal limit for alcohol as 0.08 percent blood alcohol concentration and to determine whether a machine could be trusted in a court of law over a police testimony. Now, although some states have already created legal guidelines, the same arguments are playing out over marijuana.
Halsor is an adversary of blood or breath tests, and is worried that cops might defer to them rather than “actually evaluating the individuals and looking at how they’re performing physically, mentally and cognitively.”
In particular, he’s worried about the lack of human testing that occurs on these devices due to the federal classification of cannabis as a Schedule I substance. Despite this, Star and Sejdic are pushing to test their device in human trials, and are hopeful that the federal government will be more lenient towards researchers looking at the correlation between smoking and impairment.
“It’s a kind of both ethical and legal issue,” said Sejdic. “Given that the marijuana is still a Schedule I substance, it’s difficult to actually carry out any research related to this substance.”