Using Wastewater to Track Illegal Drug Usage

Statistics Canada has published an experimental dataset representing the controlled substances component of the Canadian Wastewater Survey. In other words, wastewater was periodically tested over 2022 and 2023 and sampled for the presence of drugs like amphetamine, cocaine, ecstasy (MDMA), fentanyl, methadone, methamphetamine, and oxycodone. Wastewater from Halifax, Montreal, Toronto, Prince Albert, Saskatoon, Edmonton, and Vancouver was included in the survey.

If such drugs are being used, then the evidence should enter the system by way of our toilets. And disparities in trace concentrations over time and between locations might help us understand usage patterns and the health and legal implications. We’ll start with some general observations based on the data:

• Cocaine consistently shows the highest per capita load among all substances and across most cities, particularly Halifax, Montreal, and Edmonton. Montreal peaked at an astounding 2,212.6 mg/1,000 people/day in December 2022. That’s an average of 2.2 mg per person each day - and that’s just the stuff getting flushed down the toilet.

• Methamphetamine loads are notably high in Edmonton and Saskatoon, with Edmonton consistently reporting the highest values, including a score of 1,741.8 mg/1,000 people/day in May 2022.

• Strangely, oxycodone loads are very low across all cities, typically below 20 mg/1,000 people/day, suggesting limited non-medical use or strict prescription controls. And fentanyl loads are even lower (0.06–1.28 mg/1,000 people/day). This does not seem to accurately reflect consumption patterns as they’re widely understood.

• Ecstasy looks very much like a big-city drug, with usage the highest in Vancouver, Montreal and Toronto.

Here’s how each city’s averages looked in 2022:

And here are the average scores from 2023:

It would be interesting to better understand the structural underpinnings of some of those regional disparities. Although that’ll have to wait for better data.

My next step for this review was to correlate that data with Statistics Canada incident-based crime statistics (measured in rates per 100,000 population) that are available for most of those cities. Specifically, I gathered data from 2022 and 2023 on possession violations for cocaine, methamphetamines, ecstasy (MDMA), and opioids (other than heroin) in Halifax, Montreal, Toronto, Saskatoon, Edmonton, and Vancouver.

Ideally, I suppose, law enforcement agencies should be identifying and processing offenders at roughly the same rates as we’re seeing the drugs themselves in our wastewater.

Here’s what those incident rates (per 100,000 population) looked like in 2022:

And this is how it looked 2023:

There was a strong positive correlation (0.85, p < 0.01) between methamphetamine loads and possession incidents. This suggests that cities like Edmonton and Saskatoon are doing a good job focusing their attention on the communities that need it the most. And it also implies that the wastewater data reliably reflects real-world methamphetamine-related criminal activity.

By contrast, there were - at best - weak correlations between wastewater sampling for other drugs and law enforcement activities. It’s possible that we’re looking at the results of resource constraints or operational blind spots within some police forces. Or perhaps municipal officials still need to fine-tune their methodologies for measuring wastewater.

Either way, this is a positive and promising use of “surveillance” in support of public health and safety that doesn’t (yet) present a threat to civilian privacy.