Illicit drug consumption estimated by wastewater analysis in different districts of Milan: A case study

Wastewater analysis is a new approach developed to estimate illicit drug (ID) consumption in large communities, such as a city. We tested the ability of this approach to detect differences in consumption in different districts of a city.

Consumption of cocaine, heroin, tetrahydrocannabinol (THC) (cannabis active principle), amphetamine, methamphetamine and ecstasy was estimated by analysis of selected drug excretion residues in composite 24 h samples of untreated urban wastewater by liquid chromatography-tandem mass spectrometry. Samples were collected from the inlet of the three main Milan wastewater treatment plants (WWTP), each serving a district of the city (west, center and east). In each WWTP, samples were taken daily for seven consecutive days in November 2010 and March 2011.

We observed significant differences of ID consumption (expressed as mg/day/1000 inhabitants) among districts: consumption of some ID was significantly higher in the eastern district (P < 0.01 for THC, P < 0.001 for cocaine and P < 0.0001 for heroin by one-way analysis of variance), while consumption of methamphetamine and amphetamine was higher in the central area (P < 0.0001). Overall, from 2010 to 2011, ID consumption decreased in all the districts, in line with a recent population survey showing decreases from 25 to 55% in the annual prevalence of ID users in Italy.

This approach may help to detect ID consumption in different districts of a city and may be useful for planning interventions aimed at specific city areas and substances.