Statistics Canada recently released the conclusions of a yearlong study examining levels of various illicit drugs, and cannabis, in the wastewater of Vancouver, Edmonton, Toronto, Montreal, and Halifax.

The pilot test study drew samples of the water in the period between March 2018 and February 2019. The research, one StatsCan claims is “the largest ever conducted in North America in terms of population covered,” was carried out in collaboration with Yargeau Laboratory of McGill University’s Department of Chemical Engineering.

The results showed that the easternmost cities, Montreal and Halifax, demonstrated the highest levels of cannabis consumption; versus Edmonton, which demonstrated the lowest.

Cannabis consumption in Montreal and Halifax appeared to be 2.5 to 3.8 times higher than the rates of the other three cities tested.

“These results demonstrate that consumption can be markedly different across the country,” the study observes.

To support the survey-based data, StatsCan is experimenting with a technique known as wastewater-based epidemiology (WBE), which the federal agency notes “has been used in Europe since 2007 to report on the consumption of different types of drugs in large cities (European Monitoring Centre for Drugs and Drug Addiction, 2016).”

“In terms of drug use, the pilot test revealed the potential for seasonal variability in the use of some drugs, including cannabis, cocaine, and codeine,” the study notes. “Clear differences also emerged in the drug profiles of the different pilot test cities. Cannabis use was higher in Montreal and Halifax, but Vancouver and Edmonton tended to have higher per-person use of methamphetamine, morphine, and codeine.”

The results are a starting point, as the agency stresses “more data is needed to determine if the observed variation is repeated.” But the study is using the results towards the establishment of a baseline measure of THC-COOH (which is excreted when a person has consumed cannabis) in wastewater pre-legalization.

Although it is “too early to determine if there has been a change in total cannabis consumption” since legalization, the study has provided a starting point to further evaluate drug consumption in major urban centres across the country.