Dozens of cities across China are applying an unusual forensic technique to monitor illegal drug use: chemically analysing sewage for traces of drugs, or their telltale metabolites, excreted in urine. One southern city, Zhongshan, a drug hotspot, is also monitoring waste water to evaluate the effectiveness of its drug-reduction programmes, says Li Xiqing, an environmental chemist at Peking University in Beijing who is working with police in these cities.
https://www.scientificamerican.com/a...egal-drug-use/

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