The first fruit of data has been released from a unique pilot project aimed at measuring Canadian marijuana use through sewage, and the results are depressing.
Canada Canada sampled wastewater from treatment plants in Halifax, Montreal, Toronto, Edmonton and Vancouver between March and August and analyzed the resulting metabolism of THC, the main psychoactive cannabis compound.
The aim of the study, which has been used in Europe for many years, is to track the use of pots before and after a recreational marijuana after legalization last October.
"This has been done elsewhere in the world, but here is the first jurisdiction to do continuously for so many cities," said Tony Peluso, assistant director with Statistics Canada.
Halifax is higher than average
Preliminary results show that the cannabis use rate per head is about 540 microgram per person per week.
Of the five sampled cities, Halifax – the smallest site in the study – was higher than the average use per head at 1,310 microgram per person per week. However, the study also indicates that the error margins for the city are quite large at 707 microgram per head.
The east coast city was followed by Montreal in 976 microgram per person per week. Vancouver was the lowest average of the five sampled cities, which is 288 microgram per person per week.
Difficult to measure
Although this type of study, called an epidemiology based on wastewater, is cost-effective and can produce rapid solutions, Statistics Canada stated that a number of variables affect results, including temperature, acidity, and the presence of chemicals industrial or bacteria are wastewater.
In its online summary of the results, the agency said "the differences may not necessarily reflect a real difference in use, but this may be the result of a sampling or a statistical methodology."
"For example, the wastewater treatment works in Halifax had to locate in the city's core area and as a result, the use of cannabis could not be measured represents the entire city's metropolitan population," he said the summary.
More sampling to come
In other cities, suburban treatment plants where lower cannabis could also be sampled. As a result, Statistics Canada said that interactive comparisons are not as important as tracking future changes.
"What we are most interested in is if Halifax is increasing usage over time," said Peluso.
The sampling will continue until April 2019. The wastewater survey will be used in conjunction with individual surveys, but Peluso noted that people tend to undermine their use of cannabis.
Canada Statistics also use wastewater sampling to try to monitor the use of other drugs, including opiates, but Peluso said it was too early to decide whether it could be measured correctly.