(Portland, OR)  --  Recreational marijuana users who engage in dabbing might want to rethink their intake method.  Researchers at Portland State University say they've discovered a known carcinogen in dabbing vapor.  The scientists say they've discovered that the cancer-causing compound benzene is formed when butane hash oil is heated to very high temperatures to form the vapor that dabbers inhale.  The researchers found that heating the oil above 900 degrees Fahrenheit produced six times as much of the carcinogen as is normally present in the air we breathe.