Levels of Drugs in the Wastewater of Canadian Cities

Additional information

Purpose

The purpose of the Canadian Wastewater Survey (CWS) drug component is to measure the levels of drug residues from controlled and illegal drugs in the wastewater of several municipalities across Canada. The CWS collects wastewater in 7 municipalities: Halifax, Montréal, Toronto, Prince Albert, Saskatoon, Edmonton, and Metro Vancouver. Combined, these cities cover a population approaching 9 million people. The number of wastewater treatment plants from which samples were collected in each municipality is as follows: Halifax (3), Montreal (2), Toronto (4), Prince Albert (1), Saskatoon (1), Edmonton (1), Vancouver (5). Data from the CWS provide information that complements and enhances other Statistics Canada programs related to economic and social statistics that include health and lifestyle conditions. Although the CWS started collection in 2019, this dashboard displays data from 2022 to 2023.

Wastewater-based epidemiology

Measuring drug levels in wastewater can complement other sources of data on drug use (e.g. deaths, drug seizure data) by providing information on geographical and temporal trends. After a drug is used, the body breaks it down, producing drug metabolites that are excreted in feces and urine and enter the wastewater system. Some amount of the consumed drug (parent drug) can be excreted intact alongside its metabolites. The measurement of specific metabolites in the wastewater can reflect the use of their parent drugs by the population serviced by the wastewater plant. By considering the number of people served by the wastewater treatment plant, a value of daily excreted amount of drug per capita can be calculated (daily load per capita).

Importantly, the values presented are estimates of the excreted amount of drug metabolites in the wastewater and do not correspond directly to consumption levels of the parent drugs. Another source of the parent drug in wastewater could be unconsumed drug dumped into the sewer system.

Wastewater samples are collected for seven consecutive days starting the second Monday of every month (2022) or the second Wednesday (2023). Each sample is a composite of 24 hours of influent arriving at the wastewater treatment plant. The samples are shipped to a laboratory of the Health Canada’s Regulatory Operations and Enforcement Branch in Toronto (Ontario) and analyzed by mass spectrometry to measure drug metabolites concentrations. The daily loads per capita are calculated by considering the total volume of influent arriving to the treatment plant in the day of sampling and the estimated population in the sewershed. The population estimates based on 2021 StatCan Census of Population and projected forward using growth estimates for the census subdivisions including each treatment plant catchment. Missing samples were multiply imputed to create valid monthly estimates and variances. The imputation model accounts for the location, month, day of week of the missing samples and substances’ levels in the wastewater for other days of the week. From the daily results, the CWS produces monthly estimates of levels (mass loads per capita) of drug metabolites in the wastewater of each municipality.

Measured substances

The CWS currently includes estimates for ten substances. Among them are excreted products of controlled and illegal drugs.

Some drug metabolites are exclusive to their parent drug, such as benzoylecgonine to cocaine, i.e. they are not excretory products of any other drug's metabolism. Because they clearly point to a particular drug, these metabolites are ideal targets for wastewater-based drug epidemiology. Unfortunately, not every drug of interest has such suitable specific metabolites.

• Amphetamine: a widely used stimulant.
• Cannabis (THC-COOH): a derivative of tetrahydrocannabinol which is the primary psychoactive compound in cannabis.
• Cocaine (Benzoylecgonine): the primary and an exclusive metabolite of cocaine, a stimulant drug.
• Codeine: a prescription painkiller medication and also available in some places as an over-the-counter medication. Codeine is metabolized to morphine and excreted as unchanged codeine.
• Fentanyl (Norfentanyl): the primary metabolite of fentanyl, a potent prescription painkiller medication that is often obtained from illicit sources and misused.
• Ecstasy (MDMA): 3,4-methylenedioxymethamphetamine (MDMA) is ecstasy also known as "molly", a psychoactive drug used for recreational purposes.
• Methadone: a synthetic drug used to treat opioid dependence and chronic pain.
• Methamphetamine: a potent stimulant drug.
• Morphine: a potent painkiller medication. Many opiates produce morphine when metabolized. For example, morphine is the most abundant metabolite of heroin and of its main metabolite, 6-monoacetylmophine. Morphine is also an excretory product of morphine itself and its derivatives, and of codeine. Thus, consumption of codeine and of other drugs that contain codeine derivatives will also contribute to morphine levels in the wastewater.
• Oxycodone: a prescription painkiller medication that is often obtained illegally and misused.

Limitations and other considerations

Wastewater-based epidemiology is an inexpensive and powerful tool for estimating city-level drug consumption. However, there are some limitations in the analysis and interpretation of estimates from wastewater samples:

• The CWS is not designed to produce data that is representative of the entire Canadian population.
• The population coverage by the area served by the wastewater treatment plant varies for each municipality.
• The results from the analysis do not provide insights about those who use drugs, such as their demographics, drug co-consumption, or specific location. They can only provide information about the overall drug consumption trends in the region.
• Moderate and small differences between cities must be interpreted carefully since each city's wastewater sewershed is different and that can be in part the source of the differences in results between cities. Some cities can have larger floating populations.
• Drug residues degrade in the wastewater and may be converted into other compounds. It is important to note that the absence of detection of a drug residue in the wastewater does not necessarily mean the parent drug was not consumed. For example, this could be due to high chemical instability of the drug metabolite in wastewater. This loss of residue can occur at different stages: in wastewater, in transport after collection, and in storage (at decreased intensity due to the frozen storage of the samples, which may affect comparability of the results between two different time frames).

References

• Subedi, B. & Burgard, D. (2019). Wastewater-Based Epidemiology as a Complementary Approach to the Conventional Survey-Based Approach for the Estimation of Community Consumption of Drugs. Wastewater-Based Epidemiology: Estimation of Community Consumption of Drugs and Diets. Ed(s) Subedi, B., Burgard, D., & Loganathan, B. ACS Symposium Series; American Chemical Society. Washington, DC. https://pubs.acs.org/doi/pdf/10.1021/bk-2019-1319.ch001

• Other international programs
  • Wastewater analysis and drugs, a program of the European Union Drugs Agency
  • National Wastewater Drug Monitoring Program reports of the Australian Criminal Intelligence Commission