Secondhand marijuana smoke (SHMS): Exposure occurrence, biological analysis and potential health effects

Marijuana remains one of the most commonly used psychoactive substances across the globe, yet conclusive evidence about the toxic effects resulting from its exposure is still insufficient. The dearth of high-quality information specific to the toxic effects and thus, potential health implications of marijuana use and related exposures, constitute a critical research need given the emerging liberalization and increasing rates of marijuana use (Glantz et al., 2018 [1]; Hall and Degenhardt, 2009). Marijuana is most commonly smoked, is widely viewed as being less harmful compared to tobacco (Padilla et al., 2014 [3]), and now ranks as the world's second most-popular combustible product following tobacco cigarettes (UNODC, 2018; Murray et al., 2007 [5]; Wei et al., 2016, 2018). Within this context, it is anticipated that the general population's exposure to secondhand marijuana smoke (SHMS) is likely to increase (Wang et al., 2016 [8]). In this chapter, we present an overview of the existing evidence regarding occurrences, biological analyses, and potential adverse health effects of SHMS exposure. We focus our discussion on the recent progress in biomonitoring approaches utilized for assessing SHMS exposure, including selection of biological matrices and exposure biomarkers, and development of the bio-analytical assays. We highlight the challenges that require consideration when interpreting SHMS biomonitoring data in exposure assessments, and provide some suggested directions for future research.