Statistics Canada has released its first report as part of a pilot project that explores the use of wastewater-based epidemiology (WBE) to produce statistics on cannabis consumption following national legalization.
The method has been used in Europe since 2007 to report on people’s consumption of different drugs in large cities, and StatCan issued a tender in early 2018 to launch its own pilot project based on WBE, which tracks the active cannabis ingredient THC when excreted from the body into the municipal wastewater system.
StatCan officials say they chose the WBE method due to the fact that people tend to significantly underreport use on consumption surveys. The data also helps to calculate the total amount of cannabis used, which can be used to estimate the size of the black market by subtracting retail sales from legal vendors.
The results of the new testing covered catchment areas served by 15 wastewater treatment plants in five large urban centres across the country, representing nearly 8.4 million Canadians. Testing found that between March and August of 2018, Halifax had the highest rate of cannabis consumption per capita, at 1,310 micrograms per week, with Montreal coming in second at 976. Toronto came in at 451, Edmonton at 416 and Vancouver at 288.
An epidemiologist at the BC Centre on Substance Use and a professor of cannabis science at the University of British Columbia, told The Globe and Mail in a December article that the WBE data is more than questionable. Dr. M-J Milloy noted that the amount of THC detected hinges on the potency of the strain, and that the temperature and limpidity of the water, as well as other chemicals used by the municipality, impact the consistency of the analysis.
StatCan, however, does appear to address THC potency in its latest report and acknowledges that, “annual cannabis consumption is highly sensitive to the excretion rate and THC potency, hence the need for more research into these factors before WBE can be used to make a confident estimate of total national cannabis consumption.”
For example, for cannabis with 12% potency (weight of THC in total weight of cannabis), the total estimated consumption for 2018 can range between 400 and 1,600 tonnes, depending on the excretion rate used.