Removal of contaminants from freshwaters and estuarine waters by constructed and natural wetlands towards river catchment protection through nature-based solutions

Background Constructed wetlands (CWs) and saltmarshes are promising nature-based solutions for mitigating the release of metals and pharmaceuticals into aquatic ecosystems. Nevertheless, their performance under multi-contaminant conditions requires further in-depth investigation to better understand the underlying processes and interactions. This study evaluated the removal, retention and accumulation of Cu, Cd, ketoprofen and venlafaxine in freshwater CW mesocosms using Canna indica and in estuarine wetland microcosms with Sporobolus maritimus and Juncus maritimus. Methods CWs were operated under batch conditions for 4-weeks. Estuarine microcosms included combinations of plants, sediment and elutriate exposed to contaminants over 7-days. Metals and pharmaceuticals were determined in CW effluents using AAS and SPE-HPLC, respectively. Metals in plant tissues and substrate/sediment were determined by AAS after high pressure acid microwave digestion. Results CWs achieved very high removal efficiencies, >99% for metals and > 99.9% for pharmaceuticals. In estuarine microcosms, sediments acted as the primary sink for Cu, Cd and venlafaxine, with metals removal from elutriate solution frequently >90%. Both halophytes predominantly accumulated metals in their belowground tissues, indicating limited translocation to their aerial organs and a phytostabilisation strategy. In contrast, the contribution of plants to the removal of pharmaceuticals was limited. Venlafaxine showed high attenuation in sediment-containing systems (elutriate removal >90%), whereas ketoprofen exhibited low and variable removal from elutriate, particularly in the absence of sediment (<10%). Conclusions Overall, contaminants attenuation was primarily determined by system characteristics rather than interactions between co-occurring contaminants. In CWs, C. indica presence provides an efficient barrier limiting the transfer of metals and pharmaceuticals from freshwater to downstream ecosystems. In estuarine environments, remediation was largely driven by sediment retention, complemented by metal accumulation in saltmarsh plants. These findings highlight the importance of selecting nature-based remediation strategies according to the specific environmental context and to the behaviour of contaminants under realistic multi-contaminant conditions.