A Cambridge study into the chemical composition of marijuana smoke – at a time when the drug’s use and legalisation is on the rise in certain countries – has revealed that a single puff contains more than 100 toxic chemicals.
Our study demonstrates how smoke from a marijuana joint produces larger, potentially hazardous particles than a tobacco cigarette on average, and it is this difference in the size of the particles and other physical characteristics, that can determine where in the lungs they, and the chemicals they’re composed of, get deposited.Dr Adam Boies
The research is the first to demonstrate the similarities between marijuana and tobacco smoke in terms of their physical and chemical properties. It reveals that potentially hazardous particles in marijuana smoke are on average 29% larger than the particles found in tobacco smoke, and the total particulate matter (also known as particle pollution) contained in a typical marijuana joint, is of a mass 3.4 times greater than that of a tobacco cigarette. This mass – or ‘tar’ – as it can also be referred to in this instance, is commonly associated with tobacco smoke. It is a mixture of non-gaseous materials, consisting mostly of a viscous liquid, produced by burning the cigarette/joint and inhaled by the smoker. The results are published in the journal Scientific Reports.
In order to compare and contrast the two types of smoke, Dr Adam Boies, Reader in Nanomaterials and Aerosol Engineering, and his team used a dedicated smoking machine, that acts like a lung, to help draw the desired volume of smoke from both samples. This machine collected a smoke sample for both filtered tobacco cigarettes and non-filtered marijuana joints, which involved programming a series of smoking routines, such as varying the volume and timing of the puff of smoke.
The aerosol measurements were collected in two ways. For real-time measurements, smoke was collected in sample bags that were pre-filled with dilution air and discarded after a single use. This method allowed the properties of the particles to be measured and their physical characteristics catalogued more or less immediately, without interference from any outside impurities. For post-analysis measurements, smoke was collected using filters positioned immediately downstream of the tobacco cigarette or marijuana joint. These filters enabled the researchers to trap the smoke and measure characteristics of the total particulate matter externally, allowing additional chemical and physical analysis of the smoke.
The experiments were completed by Cambridge researchers Brian Graves, Robert Nishida and Tyler Johnson, at the University of Alberta’s Department of Mechanical Engineering, in Canada, where marijuana has been legalised.
Dr Boies, whose wider research expertise extends to air quality, transportation emissions and engineered nanoparticles for energy applications, said the results of this study should be used as a guide to inform future studies into the health impacts of smoking marijuana.
“While the health effects of tobacco smoke have been extensively studied, the same cannot be said of marijuana smoke,” said Dr Boies. “With use of the drug on the rise around the world, and legalisation following suit in certain countries, do we have adequate knowledge of the risks to health? Our study demonstrates how smoke from a marijuana joint produces larger, potentially hazardous particles than a tobacco cigarette on average, and it is this difference in the size of the particles and other physical characteristics, that can determine where in the lungs they, and the chemicals they’re composed of, get deposited. For example, larger particles may end up in the throat and the upper airways, whereas smaller particles generally deposit deeper into the lungs, finding their way into the microscopic tiny air sacs, known as alveoli, where oxygen is exchanged for carbon dioxide. This is why an investigation into the differences in particle size between marijuana and tobacco smoke is significant.”
Adam M. Boies et al. ‘Comprehensive characterization of mainstream marijuana and tobacco smoke’. Scientific Reports (2020). DOI: 10.1038/s41598-020-63120-6