The effects of illegal drug use are difficult to grasp in their full scope, but it leaves traces behind in the environment. Drug residuals enter the wastewater system through human urine.

The Ministry of Food and Drug Safety’s annual analysis of sewage has found residuals of methamphetamine in all samples collected nationwide last year, although its concentration level was down from previous years.

Cocaine, which had so far been detected in limited metropolitan locations only, showed a clear upward trend in both detection points and concentration levels.

The findings are another indication of South Korea being “not safe from illegal drug use,” according to Chae Gyu-han, director of the ministry’s Narcotics Control Division.

The latest study, commissioned to a Pusan University lab, was conducted on a total of 57 samples taken from sewage treatment centers nationwide.

Meth was detected in all of the samples analyzed, as it has been since the research began in 2020.

The estimated daily consumption of the drug per 1,000 people has steadily decreased, from 24.16 milligrams in 2020 to 23.18 milligrams in 2021, 18.07 milligrams in 2022 and 14.40 milligrams in 2023.

As for cocaine, it was detected in samples from five sewage treatment plants, including Seoul, Gyeonggi Province and Busan. However, its estimated usage increased from 0.37 milligrams in 2020 to 1.43 milligrams in 2023.

The drug was first detected in Sejong City last year.