Global occurrence and distribution of drugs of abuse in rivers: A comprehensive systematic review.

The presence of drugs of abuse in freshwater systems is an emerging environmental concern with potential ecological implications. This systematic literature review examines the global occurrence and distribution of ten highly consumed drugs in rivers, including stimulants (cocaine, amphetamine, methamphetamine, 3,4-methylenedioxy-methamphetamine or MDMA, ketamine) and opioids (codeine, fentanyl, methadone, morphine, tramadol). Using a multi-stage screening process, we identified peer-reviewed articles published between 2012 and 2022, yielding a final dataset covering 225 unique rivers and 865 distinct sampling points across diverse geographic regions. Mean river concentrations ranged from 9 ng/L for MDMA to 8091 ng/L for cocaine. Findings indicate significant regional differences, with stimulant concentrations generally higher in North and South American rivers, and opioid levels higher in African rivers. The review also highlights a disconnect between drug doses used in most ecotoxicity studies and typical levels found in surface waters, and a lack of data on drug attenuation kinetics in rivers. Future research should prioritize assessing drug persistence and aquatic toxicity under environmentally realistic conditions to guide risk assessment efforts and support more effective strategies for mitigating drug pollution in freshwater ecosystems.