Methamphetamine and ketamine use in major Chinese cities, a nationwide reconnaissance through sewage-based epidemiology

• Nationwide reconnaissance on methamphetamine and ketamine uses in China.
• Methamphetamine loads showed no clear geographic pattern.
• Ketamine loads showed an overall increasing trend from north to south.
• Ketamine removal much lower than methamphetamine removal.
• There were net outflows of methamphetamine and ketamine in several provinces.

Sewage-based epidemiology was applied to examine geographic variations in methamphetamine (METH) and ketamine (KET) use in China. Influent and effluent wastewater samples were collected from 36 sewage treatment plants (STPs) in 18 major cities that cover all the geographic regions of the country. Mean METH loads of the cities ranged from 12.5 ± 14.9 to 181.2 ± 6.5 mg/1000 inh/d, whereas mean KET loads ranged from <0.2 to 89.6 ± 27.4 mg/1000 inh/d. No clear geographical pattern was observed in METH use, although slightly lower use in north and east China relative to other regions can be suggested. In contrast, an overall increasing trend from the north to the south was evident for KET loads. Apparent METH removal was greater than 80% at most STPs, whereas KET removal was less than 50% at most STPs and was even negative (i.e., measured effluent concentrations were greater than influent concentrations) at a significant number of STPs. Results in Beijing, Shanghai, and Shenzhen indicate that METH use in China may have increased substantially since 2012, whereas KET use did not significantly change, if not decreased. Comparison between seizures and estimated consumptions reveals that seizures in most Chinese provinces are far less than consumptions. In several provinces (e.g., Guangdong and Yunan), however, seizures were found to exceed consumptions, indicating that a significant fraction of METH and KET seized in these provinces is destined for consumption in other places.