You've heard about the dangers of secondhand cigarette smoke, but what about secondhand bong smoke?

The haze after a bubbly bong hit may appear harmless, but a new study published Wednesday in JAMA Network Open found bystanders may be inhaling air pollutants at concentrations more than twice federal air quality limits.

Researchers at the University of California, Berkeley, measured fine particulate matter (PM2.5) in a real-world setting where a group of young adults socially smoked cannabis with a bong for two hours in an ordinary household living room. An aerosol monitor was placed where a nonsmoker might sit, recording PM2.5 levels before, during and after eight sessions.

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