Secondhand cannabis smoke (SHCS) is a novel exposure source uncharacterized in homes but containing known health risk factors.¹ Although 27% of young adults believe SHCS exposure is safe,² cannabis smoke has several hundred toxic chemicals, carcinogens, and fine particulate matter (PM_2.5), many at higher concentrations than tobacco smoke.¹ Decades of secondhand tobacco smoke (SHTS) research demonstrate causal links to cancer, respiratory and cardiovascular diseases, preterm birth, and decreased immune function.³ These concerns have not translated to cannabis bong smoking, a popular consumption method in social settings among young adults, wherein smoke is drawn through water. However, like SHTS, 1 minute of SHCS caused significant endothelial dysfunction in rats.⁴ This cohort study measured PM_2.5 levels from social bong smoking; it is the first, to our knowledge, to quantify SHCS levels from social cannabis smoking in the home.

Levels of PM_2.5 were measured before, during, and after 8 cannabis social-smoking sessions in one 20-m² household living room (eMethods in the Supplement). An aerosol monitor (SidePak AM510; TSI Inc) measured PM_2.5 concentrations where a nonsmoker might sit. The University of California, Berkeley, Office for the Protection of Human Subjects deemed this study not human participants research and waived review. This study followed the STROBE reporting guideline. The Wilcoxon rank sum 2-sided test assessed statistical differences between PM_2.5 concentrations before and during smoking. Analysis was performed using RStudio, version 1.4 (RStudio). Two-sided P < .05 indicated statistical significance. [Read More @ JAMMA Network Open]