Fecal contamination, antibiotic resistance and organic micropollutants in full-scale constructed wetlands in northern Portugal rural areas

Background and Aims Constructed wetlands (CWs) are recognized as a promising alternative or complement to traditional wastewater treatments. Their cost-effectiveness and seamless integration into natural landscapes, fostering wildlife habitats, are notable advantages. This study aimed to assess the efficacy of three horizontal subsurface flow CWs with Phragmites australis for reducing fecal contamination, antibiotic resistance, and organic micropollutants (OMPs). Methods Influent, effluent, and sediments samples (n=36) collected throughout 2023 were examined for cultivable Escherichia coli and total coliforms, 10 biomarkers for anthropogenic contamination and 16S rRNA gene by qPCR, 119 OMPs by LC-HRMS, and 16S rRNA-based bacterial community analysis. Results The reduction in fecal contamination (log-units) was of <4.8 for E. coli, <4.0 for total coliforms, and <3.6 for genetic biomarkers. Target OMPs showed variable removal rates, with different substances persisting after treatment (e.g. acetaminophen, fenofibric acid, irbesartan, oxazepam). The bacterial community was dominated by Pseudomonadota (>40%), and treatment led to the reduction of Bacillota and Actinomycetota and increase of the “Halobacterota” and Verrumicrobiota relative abundance. Conclusions The results reveal that the growth of macrophytes and climatic conditions, particularly temperature, influenced the treatment effectiveness, improved during summer. However, the capacity of the plants to uptake bacteria/genes from wastewater has been suggested and its meaning in pathogens ecology is being investigated.