The legalization of cannabis may result in increased indoor exposure to Δ9-tetrahydrocannabinol.

Cannabis is a genus of plants in the Cannabaceae family that contains tetrahydrocannabinolic acid. When heated or burned, the acid decarboxylates to form tetrahydrocannabinol (THC). Its (-)-trans-Δ9-THC isomer is a psychoactive substance that has been used as a drug for centuries. In most countries, both the private sale of cannabis products and their use for non-medical purposes are still prohibited by law. However, for some time now there has been societal and political pressure to at least partially legalize cannabis products. It can be expected that such a measure will lead to a significant increase in the consumption of cannabis. However, this also increases the possibility of involuntary passive exposure to THC and contamination of the indoor environment. In indoor sciences, THC is still a largely unknown or underrepresented substance. In this perspective paper, THC will therefore first be presented on the basis of its physical properties. Then, the distribution of THC in different indoor compartments and potential routes of passive exposure are discussed. Finally, an assessment of the future importance of THC for indoor use is made. Previous experience has shown that early monitoring is always advantageous so that preventive and protective measures can be taken quickly if necessary. [Display omitted] • The psychoactive tetrahydrocannabinol is released from cannabis smoke and vapor. • THC is a typical SVOC and accumulates in the indoor environment. • THC has been found in indoor air, house dust and on surfaces. • The planned legalization of cannabis is likely to increase passive exposure to THC. • There is a need to monitor THC indoors for preventative and protective reasons. [ABSTRACT FROM AUTHOR]