Free Radicals in Cannabis Smoke

Tobacco and cannabis smoke are both complex chemical mixtures generated through combustion of biomass material. The presence of free radicals in tobacco smoke has been established for nearly seven decades. Despite similarities between cannabis and tobacco smoke and the known presence of radicals in the latter, analysis of free radicals in cannabis smoke has yet to be conducted. In this work, electron paramagnetic resonance (EPR) spectroscopy was used to detect short-lived radicals and environmentally persistent free radicals (EPFRs) in cannabis smoke. Spin-trapping techniques were employed to aid in identification of the short-lived radicals. Congruent with findings from studies conducted on tobacco smoke, short-lived free radicals were detected in the gas phase, and EPFRs were detected in the particle phase of cannabis smoke. Gas phase results indicate the presence of oxygen-centered radicals in cannabis smoke, though the shape of the resulting EPR spectra differs slightly from that of tobacco smoke. Particle phase results for cannabis match well with those from previous studies conducted on tobacco smoke, regardless of the spin trap used (or lack thereof). Quantitative findings indicate that cannabis smoke contains approximately the same radical concentration as tobacco smoke, on the order of 10¹⁵ gas-phase spins and 10¹⁴ particle-phase spins per cannabis preroll or tobacco cigarette. The impacts of burning method (continuous vs puffing) and cannabinoid composition on radical concentrations were also investigated here. While puffing was observed to lower radical concentrations, the cannabinoid composition of the strain of cannabis burned had no observable impact on the amount or identity of free radicals detected.