Wastewater monitoring can reveal community drug patterns without identifying how many individuals used methamphetamine. A large international study measured amphetamine and methamphetamine residues across 120 cities during 2011–2017. Its basic result was a mass load normalized to population, not a count of drug-positive residents.
How extensive was the sampling?
González-Mariño and colleagues included catchments served by 143 wastewater treatment plants in 120 cities across 37 countries. More than 60 million people were represented at least once. Those cumulative coverage figures do not mean that every city was sampled in every year.
Sampling typically covered seven consecutive days in March or April each year, targeting a normal week without major festivals or holidays. Twenty-six European cities supplied at least five years of data. Short annual snapshots can support comparisons, but they are not continuous year-round surveillance.
What did the laboratory actually measure?
Laboratories used liquid chromatography–tandem mass spectrometry to quantify parent amphetamine and methamphetamine in raw wastewater, alongside markers of other drugs. Concentrations in ng/L were combined with wastewater flow and estimated catchment population to calculate loads in mg per 1,000 people per day.
The denominator was the estimated population contributing to that sewer system. It was not the number of people consuming the drug. The numerator was measured mass passing through the sampled wastewater, subject to collection, analytical and sewer-process uncertainties.
Why can a larger load have several explanations?
A higher drug mass can be compatible with more people using the drug, greater consumption by the same number of people, different purity, or differences in excretion and sewer conditions. The chemical measurement alone does not distinguish those possibilities.
Direct disposal can also contribute. The study excluded some unusually affected locations from certain summary calculations because drug-manufacturing discharges could overwhelm the consumption signal. A quantity entering a sewer is not automatically a quantity that passed through a human body.
Why is amphetamine especially difficult to attribute?
Amphetamine can enter wastewater after amphetamine consumption, prescribed use, methamphetamine metabolism or disposal. The study estimated amphetamine consumption from the full amphetamine load without subtracting every potential non-illicit or metabolite contribution.
Consequently, a map labeled amphetamine cannot automatically be interpreted as a map of illicit amphetamine use. The authors specifically discussed this limitation in areas with high methamphetamine consumption or substantial prescription amphetamine use. Analytical separation of amphetamine from methamphetamine is necessary but does not by itself resolve each compound’s source.
What about the estimated number of doses?
The researchers applied average excretion factors and assumed drug doses to estimate consumption. They also summed estimated doses across several stimulants. These calculations add assumptions about dose, purity and administration patterns to the underlying mass measurements.
An estimated dose count is not a count of unique consumers: one person may account for multiple doses, and different substances in the combined total need not have been taken by the same individuals. Combined-dose estimates also excluded cannabis because of additional measurement uncertainty.
What conclusions remain useful?
The study found geographically distinct stimulant patterns and described wastewater data as complementary to surveys and seizure information. Comparisons were qualitative where indicators measured different things. Few sampled cities within a country could not establish a representative national rate.
For careful reporting, retain the collection week, catchment, analyte, mass unit and population estimate. Distinguish a measured load from a modeled consumption estimate. This historical dataset cannot establish present-day local prevalence, identify an individual consumer, or provide evidence of anyone’s impairment.
Source
González-Mariño I, Baz-Lomba JA, Alygizakis NA, et al. Spatio-temporal assessment of illicit drug use at large scale: evidence from 7 years of international wastewater monitoring. Addiction. 2020;115(1):109–120; online 2019. doi:10.1111/add.14767.
Leave a Reply