New study explores ways to reduce second- and third-hand THC exposure from indoor cannabis smoke

Since Canada legalized recreational cannabis in 2018, exposure to second-hand marijuana smoke in homes has been steadily increasing. In response to this growing concern, a U of T Engineering lab group, led by Professor Arthur Chan (ChemE), is investigating this source of indoor air pollution. 

We began our research on tetrahydrocannabinol (THC), which is the psychoactive part of cannabis that causes intoxication, because when we looked at second- and third-hand smoke, we started to see how much involuntary exposure happens,” says Amirashkan Askari, a ChemE PhD candidate in Chan’s lab.  

Askari is the co-author of a new study, with Chan and Professor Frank Wania (Physical and Environmental Sciences, ChemE), which models how THC behaves and transforms once it is released in an indoor environment. The model enables researchers to explore mitigation strategies that could reduce involuntary exposure levels.  

Between April 2021 and March 2022, Canadians spent $4 billion on regulated, adult-use cannabis, according to Statistics Canada. Dried cannabis accounted for 71.1% of sales, indicating that smoking is the most popular method of consumption.    

Any type of smoking, whether it is tobacco or cannabis, leaves behind a suite of pollutants that can remain in homes,” says Chan. “We now have sufficient chemical knowledge about THC to model its behavior in a typical indoor environment.”  

Moreover, involuntary THC exposure can continue long after smoking has ceased. This is due to THC’s large and complex chemical structure, which has a strong tendency to stick to surfaces and create third-hand exposure,” says Askari. 

Read the full U of T Engineering News story.