Passive exposure
Passive exposure is an issue that still causes confusion in interpretation of results. It essentially deals with the passive inhalation of marijuana or hashish smoke and the unwitting ingestion of cocaine or marijuana. Although passive exposure to crack (free-base cocaine) smoke has been claimed as an excuse for a positive urine benzoylecgonine, there is no evidence that this is valid. In two studies that investigated this (Baselt et al. 1991; Cone et al. 1995), no urine specimens gave immunoassay readings above 300 ng/mL. However, unwitting ingestion of cocaine may result in positive urine specimens with the cut offs currently used. There is no doubt that an individual who ingests a drink fortified with cocaine can test positive. In one study (Baselt and Chang 1987) in which a volunteer consumed 25 mg cocaine hydrochloride, urine benzoylecgonine concentrations were greater than 300 ng/mL for 48 hours. The question most often raised is the use of decocainised coca teas. As with decaffeinated coffee, these teas contain small amounts of cocaine; one study found an average of 4.8 mg per tea bag (Jackson et al. 1991). After the ingestion of one cup of this tea, immunoassay results were positive for 21–26 hours. Obviously, the more regular the use, the more likely these specimens are to be positive and to be so for longer periods. In regulated industries, these samples would be validated as positives as these are not legitimate uses of cocaine. Outside these industries, more flexibility may be applied in interpreting the result.
Passive inhalation of cannabis smoke continues to be an excuse offered by donors for their positive results. There is no doubt that environmental exposure to cannabis smoke can occur through passive inhalation, but the question is, does it produce measurable concentrations in urine and if so for what time? In a number of early studies (Perez-Reyse et al. 1982; Law et al. 1984; Morland et al. 1985) there was evidence for the presence of THCA in urine after passive exposure, but the concentrations measured were orders of magnitude lower than the cut-offs in use in workplace drug testing. In a more extreme study by Cone et al. (1987) volunteers were exposed to 4 and 16 cannabis cigarettes for 1 hour for six consecutive days. After exposure to four cigarettes, few urine specimens were positive, while after 16 cigarettes many more specimens were positive with a maximum THCA concentration of 87 ng/mL reported by GC-MS. The authors stressed, however, that these were extreme conditions, in that exposure was in a nonventilated, tightly sealed, small room and that it occurred for multiple days. In fact, the smoke was of such intensity that goggles were required by a number of the volunteers. It is generally accepted that social exposure to cannabis smoke (at parties, in outdoor arenas) will not result in a positive urine specimen.
