THURSDAY, March 31, 2022 (HealthDay News) -- Smoking pot through a bong doesn't protect the nonsmokers in the room from the dangers of secondhand smoke, a new study warns.
Bongs have been touted as a safe way to protect nonsmokers from secondhand marijuana smoke. But it can expose them to extremely high concentrations of fine particulate matter — five to 10 times greater than levels from wildfires in the San Francisco Bay Area in September 2020, according to senior researcher Katharine Hammond. She is a professor of environmental health sciences at the University of California, Berkeley.
"Cannabis bong smoking in the home generated several times greater particulate matter than tobacco cigarettes and hookah," Hammond said.
Even 12 hours after pot smoking stopped, concentrations of fine particulate matter remained high and unhealthy for sensitive people, the study found. "Secondhand cannabis smoke greatly exceeds air pollution standards," Hammond warned.
A bong is a water pipe that filters and cools pot smoke to give a smoother, more intoxicating effect.
"There is no risk-free level of exposure to secondhand tobacco smoke, and secondhand cannabis smoke contains similar toxins and is presumably not safe," Hammond said.
Secondhand marijuana smoke has the potential to cause significant disease, and smoking pot should be included with tobacco cigarettes in clean indoor air policies, she suggested.
"The adverse health effects of fine particulate matter are well established," Hammond said, adding that exposure has been shown to cause early death, reduced lung function, and increased risk of death from lung cancer and heart disease.
Matthew Springer, a professor of medicine in the division of cardiology at the University of California, San Francisco, said it's clear that secondhand smoke from both tobacco and cannabis can reach unhealthy levels for bystanders. And, he added, using a bong generates a lot of smoke.
"The smoke that passes through the water is still smoke that gets inhaled and then exhaled, and any smoke generated by the material itself as it's smoldering is going to add to the overall secondhand smoke in the room," Springer said. "That would seem to go without saying, but as with any device perceived by the public as safer, it's useful to see real numbers indicating that, indeed, use of bongs does not prevent bystanders from being exposed to significant amounts of secondhand smoke."
Whether or not larger particles in the water are removed, it's the fine particles that make it far into the lungs and damage them, as well as the heart and blood vessels, Springer noted.
"Whether or not bong use results in more secondhand smoke than other products, clearly it can still result in high levels, and it was notable that the stuff persisted in the room for hours," he added.
For the study, Hammond and her UC Berkeley colleague Patton Khuu Nguyen measured levels of fine particulate matter — called PM2.5 — before, during and after eight pot smoking sessions in one living room. An aerosol monitor measured PM2.5 concentrations where a nonsmoker might sit.
During six sessions, bong smoking increased PM2.5 levels between 100-fold and 1000-fold. They rose more than 20-fold in two other sessions, the investigators found.
The study authors also found that cannabis bong smoking generated PM2.5 levels four times higher than that produced by cigarettes or smoking tobacco in a waterpipe.
As such, Hammond said efforts to reduce exposure to secondhand marijuana smoke are needed. Such measures could include having marijuana smoke-free environments like those for tobacco and not smoking indoors.
"Bong smoking leads to extremely high and very unhealthy secondhand smoke particle concentrations above [U.S. Environmental Protection Agency] standards that persist even hours after smoking ceases," she said. "Our report and previous studies should guide efforts to educate the public on the potential adverse health effects of secondhand cannabis smoke on nonsmokers."
Cynthia Hallett, president and CEO of Americans for Nonsmokers' Rights, reviewed the study findings.
"There are a lot of similarities between secondhand tobacco smoke and secondhand cannabis smoke," she said. "Both have carcinogens and toxins and have the potential to cause respiratory problems, whether that's asthma or lung cancer."
Hallett isn't against legalization of marijuana or smoking it, but she thinks that bystanders should be protected from its secondhand smoke. She sees a parallel between the way tobacco companies fought smoke-free laws and how cannabis is being commercialized using many of the same tactics to thwart indoor smoking restrictions.
"The challenge is that we're getting pushback from marijuana proponents and cannabis industry proponents in trying to advocate for indoor smoking spaces," Hallett said.
Having no-pot-smoking laws, like no-tobacco-smoking laws, is essential to protect people from the harms of secondhand marijuana smoke, she said.
"We want to make sure that nonsmokers are not unfairly exposed to harmful products," Hallett said. "We also don't want to build another generation addicted to tobacco or cannabis products."
The study was published online March 30 in JAMA Network Open.
For more on secondhand marijuana smoke, head to the American Nonsmokers' Rights Foundation.
SOURCES: S. Katharine Hammond, PhD, professor, environmental health sciences, University of California, Berkeley; Matthew Springer, PhD, professor, medicine, University of California, San Francisco; Cynthia Hallett, MPH, president and CEO, Americans for Nonsmokers' Rights, Berkeley, Calif.; JAMA Network Open, March 30, 2022, online