Chinese police set fire to seized drugs. [Photo/Xinhua]

China is using an unusual technique to monitor illegal drug issues in dozens of cities to trace the source by analyzing the chemicals of sewage or the metabolites in human urine.

Li Xiqing, an environmental chemist at Peking University who has helped police across the country to fight against drugs, said Zhongshan, a drug hot spot in South China's Guangdong province, is monitoring wastewater to assess the effectiveness of its anti-drug operations.

The police in Zhongshan have successfully tracked down and arrested a drug dealer through sewage monitoring technology, he noted.

He also said a number of cities in China will start collecting sewage data as early as next year to help police identify potential drug users.

Though many countries -- including Belgium, the Netherlands, Spain and Germany -- have now adopted wastewater-based epidemiology (WBE) to monitor drug problems, the data collected are mainly used in epidemiological studies rather than setting policies.

"It's worth mentioning that China seems to be actually acting on the technique," said Daniel Burgard, a chemist at the University of Puget Sound.

According to Li, by the end of this year, the central and local governments will invest at least 10 million yuan ($1.5 million) to develop the WBE monitoring technique, and he expects the figure to at least double annually for the next few years.

Li is pushing for the method to be used internationally, including as part of the UN's drug control policies. "The experiences and lessons learned in the application of WBE will be highly relevant to other countries," he said.

Li's team tested the contents of two of the most common synthetic drugs, meth and ketamine, in the nation's sewage two years after the central and local governments launched their anti-drug campaign in 2013.

The team found that the use of meth and ketamine dropped 42 percent and 67 percent respectively after the campaign launched. Li believes the reduction in drug abuse is the result of anti-drug efforts.