In an unprecedented investigation into water pollution in Hong Kong’s river and estuary systems, researchers have uncovered a dominant and overlooked contributor to pharmaceutical contamination: over-the-counter (OTC) drugs. Contrary to prior assumptions that prescription medications pose the greatest environmental hazard due to their complex chemical structures and targeted usage, everyday medicines like painkillers, antihistamines, and even caffeine—common and easily accessible—make up a staggering 85% of pharmaceutical pollutants entering these aquatic ecosystems during the wet season. This revelation, spearheaded by Professor Kenneth Mei-Yee Leung of the City University of Hong Kong (CityUHK), underscores a critical shift in understanding environmental toxicology and highlights the urgent need for holistic, strategic interventions.
The study, a collaboration between CityUHK’s State Key Laboratory of Marine Environmental Health and the Guangdong Research Institute of Water Resources and Hydropower in China, deployed an integrative analytical framework balancing ecological risk assessment with a river-estuary-sea continuum perspective. This novel modeling approach aligns persistence, mobility, and toxicity (PMT) parameters with the transport trajectories of pharmaceuticals, reflecting their dynamic movement across complex aquatic networks. The result is a finely tuned identification and prioritization of pollutants, transcending traditional localized risk assessments that have long failed to capture the systemic nature of pharmaceutical contamination.
Pharmaceuticals, due to their intricate molecular characteristics, exhibit a high degree of solubility and persistence in aqueous environments, facilitating wide dispersal across riverine systems and estuarine waters before ultimately entering marine ecosystems. This mobility poses far-reaching ecological risks, especially for sensitive species inhabiting transitional aquatic habitats. The study notably flagged substances such as caffeine, paracetamol, cetirizine, cimetidine, sitagliptin, and fexofenadine as priority pollutants with elevated toxicity potentials, threatening vulnerable marine fauna like the Indo-Pacific humpback dolphin, an endangered species with critical habitat dependencies within the region.
Professor Leung emphasizes that OTC pharmaceuticals act as “pseudo-persistent” pollutants—a concept describing substances that, despite rapid degradation, maintain constant environmental presence due to continuous usage and pollution input. This insight contradicts the prevalent notion that only long-lived, stubborn contaminants demand attention and calls for revised regulatory frameworks and environmental monitoring programs to encompass frequently consumed, easily accessible drugs incapable of traditional classification as persistent pollutants.
The team’s approach synergizes environmental chemistry, toxicological data, and hydrological modeling to simulate propagation paths of these contaminants from terrestrial sources through river-estuary corridors and into coastal systems. This comprehensive model integrates molecular persistence, hydrodynamic flows, and toxicological thresholds to create a robust algorithm prioritizing pharmaceuticals based on ecological threat magnitude and potential for bioaccumulation. Such a holistic assessment is a significant advance beyond site-specific hazard evaluations, which inadequately inform management decisions and often underestimate cumulative ecological impacts.
A striking finding of this study was that approximately 80% of the investigated pharmaceuticals satisfy the PMT criteria, implying that most drugs in circulation have considerable environmental mobility and ecological persistence risks. This prevalence demands urgent attention to sewage treatment technologies. Retrofitting conventional wastewater infrastructure with advanced treatment modalities capable of targeting pharmaceutical residues, alongside stormwater retention systems in key discharge rivers, promises substantial mitigation potential with relatively focused investment and policy support.
The repercussions of pharmaceutical pollution extend beyond chemical contamination. The alteration of aquatic microbial communities, promotion of antimicrobial resistance, and impairment of key ecological functions underscore the multifaceted negative impacts. This research advocates reframing pharmaceutical pollution not as a fragmented local problem but as a continuum challenge, requiring transboundary collaboration, multi-scalar monitoring, and cross-sectoral governance inclusive of public health and environmental protection agencies.
Public awareness emerged as a fundamental pillar of comprehensive solutions. Professor Leung stresses the vital role of community engagement and education campaigns encouraging proper medication disposal practices. Discarding unused or expired drugs through institutional collection systems rather than improper discarding or flushing can drastically reduce pollutant loads entering waterways. However, the study identifies a critical gap in governmental guidance and infrastructure supporting safe disposal, signaling a pressing policy frontier for environmental health advocacy groups worldwide.
This paradigm-shifting work also highlights a significant disconnect between pharmaceutical consumption patterns and environmental regulation, urging policymakers to recalibrate frameworks to integrate aquatic transport models and PMT assessments into standard environmental risk analyses. Coordinated action across pharmaceutical industry stakeholders, health care providers, environmental agencies, and local communities is paramount to develop sustainable, scalable solutions that address the upstream sources and downstream consequences of pharmaceutical pollution holistically.
The CityUHK-led research marks a substantial leap forward in understanding the complexity of pharmaceutical contaminants flowing through river-estuary continuums and marine transitions. By moving beyond fragmented assessments to an integrative, systemic viewpoint, the study paves the way for more effective pollution control strategies with considerable ecological, public health, and socioeconomic implications. It serves as a clarion call for a new era of environmental science that marries chemical, biological, and hydrological expertise to safeguard planet health against the silent but pervasive threat of pharmaceutical pollution.
As the global community grapples with an expanding pharmaceutical footprint in natural waters, the findings from Hong Kong’s rivers resonate beyond regional boundaries. They exemplify how common, ubiquitously consumed OTC medicines can disproportionately influence aquatic contaminants and ecological integrity, challenging regulators, scientists, and citizens alike to rethink assumptions and act decisively. Integrating cutting-edge modeling with stakeholder collaboration and education could form a blueprint for urban water quality management worldwide, fostering healthier ecosystems and resilient human-environment interactions for future generations.
Contact: Kenneth Mei-Yee Leung, City University of Hong Kong, kmyleung@cityu.edu.hk
Subject of Research: Not applicable
Article Title: Uncovering prevalence of environmentally mobile pharmaceuticals and their priority control strategies in river-estuary continuum of Hong Kong
Web References: http://dx.doi.org/10.1016/j.enceco.2026.02.021
Image Credits: City University of Hong Kong
Keywords: Environmental health, Pharmaceutical pollution, River-estuary continuum, Over-the-counter drugs, Persistence Mobility Toxicity (PMT), Aquatic ecosystems, Indo-Pacific humpback dolphin, Water contamination risk assessment
