Investigators at John Hopkins University in Baltimore assessed the impact of second-hand marijuana smoke exposure on six non-smoking subjects. Each of the subjects spent 60 minutes in a sealed chamber with limited or no ventilation while six other subjects smoked pot of various strengths. Following their exposure, non-smokers produced a series of urine specimens over the next 34 hours. These specimens were tested for the presence of carboxy-THC, the primary metabolite screened for in workplace drug testing programs. All six participants completed three separate sessions in the chamber.
Researchers reported that the exposure to second-hand smoke in this environment resulted in the detectable presence of carboxy THC in urine.
“Multiple presumptive positive results for non-smokers occurred by immunoassay at the 20 ng/mL cutoff concentration across the three exposure sessions,” authors wrote. “The first appearance of a presumptive positive (initial test) result at the 20 ng/mL cutoff concentration occurred in specimens collected within one to four hours following exposure. Following the appearance of the first presumptive positives, individuals continued to test positive for two to 22 hours.”
Twenty ng/mL is the standard threshold used in confirmatory workplace urine testing protocols, often referred to as GC/MS tests.
By contrast, screening assays for carboxy THC at the 50ng/mL threshold — the standard cut-off for a preliminary workplace drug test — only yielded a single positive sample, which was recorded four hours following the subject’s second-hand smoke exposure. Authors noted that this participant possessed a comparatively high body mass index compared to other participants. (Because carboxy-THC is fat soluble, subjects with a higher BMI may be more likely to test positive for its presence for prolonged periods of time.)
So, does this mean that hanging out with your pot-smoking roomies will cause you to flunk your upcoming drug test? Probably not, concluded the study’s authors, since most people won’t be in situations where they are facing GC/MS testing within the hours immediately following such extreme environmental exposure
“Cannabis potency and room ventilation were demonstrated to be two major factors in determining the extent of cannabis smoke exposure to non-smokers residing in close proximity to smokers,” they determined. “Whether test results for non-smokers would be reported as positive or negative will be highly dependent upon the sensitivity of initial and confirmatory tests and related reporting criteria. Overall, these results indicated that extreme smoke exposure can produce positive tests at lower cutoff concentrations, but not generally at the higher initial test cutoff concentration in general use by SAMHSA’s Mandatory Guidelines for Federal Workplace Drug Testing Programs.”