A study from the University of California, Berkeley, has found that second hand cannabis smoke from bongs can be even more harmful than tobacco due to an increased concentration of fine particulate matter, reports The Guardian.
The researchers, who published their report on the Jama Open Network last week, conducted the experiment with students from the university. They measured levels of fine particulate matter before, during and after eight cannabis social-smoking sessions in the living room of an apartment near campus.
They found that second hand bong smoke contains fine particulate matter in much higher concentrations and is more dangerous compared with second hand tobacco smoke.
The students, who provided their own cannabis and bongs, remained anonymous and were not observed during the two-hour smoke sessions, writes Maya Yang in The Guardian story published on 2 April 2022.
“We exerted no control and gave no direction to the students on how to smoke the cannabis in the bong,” S Katharine Hammond, a professor who oversaw the study alongside graduate student Patton Khuu Nguyen, told the San Francisco Chronicle.
Hammond and Nguyen used an aerosol monitor to measure the air quality before, during and after each session, which they then compared with the data collected from tobacco smokers in a hookah setting.
They found that fine particulate matter from cannabis bong smoking was at least four times greater than the smoke produced by tobacco.
“Patton and I compared the particulate exposure from the bong hits to the air quality of the orange sky days after the wildfires of September 2020…The concentrations were five to 10 times greater in the living room during the smoking,” Hammond told the Chronicle.
According to The Guardian, the study – conducted over two months in 2018 – also found that fine particulate matter concentrations took a significantly long time to return to pre-smoking levels. In one of the sessions, the concentration stayed at more than 10 times the original concentration level, 12 hours after the group had stopped smoking.
See the link below for the full story in The Guardian.
Study details
Fine Particulate Matter Exposure From Secondhand Cannabis Bong Smoking
Patton Khuu Nguyen and S Katharine Hammond
Author Affiliations: Environmental Health Sciences Division, School of Public Health, University of California, Berkeley.
This Research Letter was published in JAMA Network Open on 30 March 2022.
Introduction
Second hand cannabis smoke (SHCS) is a novel exposure source uncharacterised in homes but containing known health risk factors. Although 27% of young adults believe SHCS exposure is safe, cannabis smoke has several hundred toxic chemicals, carcinogens and fine particulate matter (PM2.5), many at higher concentrations than tobacco smoke.
Decades of second hand tobacco smoke (SHTS) research demonstrate causal links to cancer, respiratory and cardiovascular diseases, preterm birth, and decreased immune function.
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, one minute of SHCS caused significant endothelial dysfunction in rats.
This cohort study measured PM2.5levels from social bong smoking; it is the first, to our knowledge, to quantify SHCS levels from social cannabis smoking in the home.
Methods
Levels of PM2.5 were measured before, during, and after eight cannabis social smoking sessions in one 20-m2 household living room (eMethods in the Supplement). An aerosol monitor (SidePak AM510; TSI Inc) measured PM2.5 concentrations where a non-smoker 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 two-sided test assessed statistical differences between PM2.5 concentrations before and during smoking. Analysis was performed using RStudio, version 1.4 (RStudio). Two-sided P < .05 indicated statistical significance.
Results
Home cannabis bong smoking significantly increased PM2.5 from background levels (conditions existing before the smoking began) in all sessions by 100-fold to 1000-fold for six of eight sessions; the other two sessions had high background and significantly increased PM2.5 more than 20-fold (P < .001 for all 8 sessions).
During the first 10 minutes of smoking, mean (SD) PM2.5 concentrations increased to 410 (220) μg/m3, after 15 minutes to 570 (290) μg/m3, after 30 minutes to 1000 (320) μg/m3, and went as high as 2500 μg/m3 in 1 session. The concentration during smoking increased to a mean (SD) of 1300 (280) μg/m3.
During two-hour smoking sessions, mean (SD) five-minute peak PM2.5 concentration was 1700 (460) μg/m3 and remained half that 90 minutes after smoking ceased. Each half hour after smoking ceased, mean concentration declined to 78% of peak value, then 60%, then 40% and, after 110 minutes, 31%.
In the one session monitored for 12 hours after smoking stopped, PM2.5 remained elevated at 50 μg/m3, more than 10 times the background concentration. Cannabis bong smoking in the home generated 4 times greater PM2.5 concentrations than cigarette or tobacco hookah (waterpipe) smoking.
Discussion
The PM2.5 concentrations generated in a home during social cannabis bong smoking to which a non-smoking resident might be exposed were greatly increased compared with background levels, and PM2.5 decayed only gradually after smoking ceased. After 15 minutes of smoking, mean PM2.5 (570 μg/m3) was more than twice the US Environmental Protection Agency (EPA) hazardous air quality threshold (>250 μg/m3).
If one assumes the exposure concentrations were at the mean levels observed, a single home smoking session with no other exposures would generate an estimated mean daily concentration (200 μg/m3) that greatly exceeds the average in cigarette-smoking homes (44 μg/m3), non-smoking homes (15 μg/m3), and the US EPA daily standard (35 μg/m3).
A strength of this study is that measurements were made during actual social bong smoking sessions without artificial constraints. Limitations include that cannabis smoking was not directly observed.
This cohort study suggests that, contrary to popular beliefs, bong smoking is not safe.
Decades ago, many people thought SHTS presented no health risk to non-smokers. Scientific research since then changed this perception and led to smoke-free environments. Incorrect beliefs about SHCS safety promote indoor cannabis smoking.
Non-smokers are exposed to even higher concentrations of SHCS materials during ‘hot-boxing’, the popular practice in which cannabis smokers produce high volumes of smoke in an enclosed environment.
This study’s findings suggest SHCS in the home is not safe and that public perceptions of SHCS safety must be addressed.
The Guardian story – Secondhand bong smoke worse than that from tobacco, study finds (Open access)
See also from the MedicalBrief archives
Link between secondhand marijuana smoke and respiratory infections in children
Raise awareness of second hand smoke and reduce its burden – European scientists
Secondhand smoke heightens risk of child hospitalisation – Cincinnati study