When Wastewater Carries Pharmaceuticals and Resistance: Can Constructed Wetlands Retain Them?

18 06 2026

Antibiotic residues and genes that enable bacteria to survive exposure to these drugs are increasingly entering rivers, lakes and groundwater together with wastewater. Even low concentrations of pharmaceutical compounds may exert selective pressure, promoting the survival of resistant microorganisms and the further spread of antibiotic resistance. Conventional wastewater treatment plants are expensive and are not always designed to remove such contaminants. As a result, there is growing interest in constructed wetlands, which use plants, filtration media and microorganisms to treat wastewater.

Although such nature-based solutions are increasingly promoted, particularly in low- and middle-income countries, data from large, full-scale operational systems have so far remained limited. It has therefore been unclear how effectively these systems perform when treating wastewater on the scale of an entire city.

An international research team led by scientists from the Faculty of Biology at the University of Warsaw investigated the fate of pharmaceutical compounds, bacterial communities and antibiotic resistance genes during the passage of wastewater through Europe’s largest passive treatment system: the vertical-flow constructed wetland in Orhei, Moldova. The facility serves nearly 26,000 inhabitants and covers an area of 35,000 square metres.

Samples were collected at different points along the treatment pathway, from raw wastewater to the final treated effluent discharged into the Răut River. The researchers used metagenomic profiling, which involves analysing all genetic material present in a sample, to characterise bacterial communities and identify antibiotic resistance genes. This approach was complemented by targeted chemical analyses of 59 pharmaceutical compounds and an assessment of their potential effects on freshwater biota.

In total, 783 bacterial families were identified across the system. Their number decreased substantially in the final effluent compared with raw sewage, while the relative abundance of bacteria typical of wetland environments increased. The researchers also detected 150 types of antibiotic resistance genes conferring resistance to 16 antibiotic classes. Their cumulative abundance decreased by almost 80% after the wastewater had passed through the treatment system. Genes associated with resistance to fosfomycin, nitroimidazoles and rifamycins, among others, were not detected in the final effluent. However, genes associated with sulfonamide resistance persisted throughout all treatment stages.

Of the 29 antibiotics analysed, 13 were detected, and the removal efficiency of individual antibiotics ranged from 85% to 100%. Some other pharmaceuticals, including carbamazepine and alprazolam, proved more difficult to remove. Nevertheless, the estimated environmental risk to freshwater biota was low for all compounds detected in the treated effluent.

The study shows that a constructed wetland can function not only as a filtration system, but also as a biological reactor in which microbial community composition changes and some pharmaceutical residues and antibiotic resistance genes are progressively reduced. These findings support the use of nature-based solutions in One Health-oriented wastewater management, an approach that recognises the close links between human, animal and environmental health.

However, the system did not remove all contaminants. The persistence of sulfonamide resistance genes and certain recalcitrant pharmaceuticals highlights the need for continued monitoring and the development of additional treatment steps.

The article, entitled “The occurrence and removal of antibiotic residues and antibiotic resistance genes in the largest European constructed wetland at Orhei (Moldova)”, was published in the journal Environmental Pollution. The authors from the Faculty of Biology at the University of Warsaw are Mikołaj Wołącewicz, MSc, Przemysław Decewicz, PhD, and Prof. Łukasz Dziewit from the Institute of Bioengineering. The research was conducted in collaboration with the Catalan Institute for Water Research and the University of Girona in Spain, as well as Nicolae Testemițanu State University of Medicine and Pharmacy in Moldova.

The study was carried out as part of the PhageLand project within the JPIAMR programme and was funded in Poland by the National Science Centre under grant no. 2021/03/Y/NZ9/00141.

Congratulations to the authors on the publication!

Link to the publication: https://doi.org/10.1016/j.envpol.2026.128381