Removal and persistence of pharmaceuticals in Induced River Bank Filtration system in low-flow regime

Induced RiverBank Filtration (IRBF) systems may provide reliable and safe drinking water, but at the same time the presence of pharmaceutical active compounds (PhACs) residues in surface- and ground-water raises concerns over their potential health and environmental impacts. We present here the first field-based dataset on PhACs in an IRBF system during low-flow conditions, highlighting the fate of these compounds in a highly conductive, organic-matter poor aquifer. Data were gathered in four samplings run over a one month time. Surface water PhACs concentrations remained low and stable (generally lower than 10 ng/L), yet groundwater showed significant variability (from few to one hundred ng/L), with Ibuprofen, Clarithromycin and Diclofenac reaching levels up to 100 times higher, likely due to retardation processes. While Atenolol, Naproxen, and Metformin were rapidly removed, Ibuprofen, Carbamazepine, and Sulfamethoxazole remained detectable at the drinking water well (at about 1 ng/L concentration), likely due to low microbial uptake at low concentrations. All PhACs showed removal rates above 75 %, but Sulfamethoxazole, supporting the effectiveness of IRBF systems, even in advective-dominant aquifers. Increasing travel distances to target wells for improving attenuation may not be a reliable solution, as other sources of contamination may be introduced in the system. Calculated degradation rates were generally higher than in laboratory studies, reinforcing the need for in-situ data, capturing the complexity of aquifer conditions, including subsurface heterogeneities, groundwater flow patterns, and geochemical variability. High-resolution monitoring is essential: monthly sampling risks missing critical processes such as sorption/desorption. The Serchio River IRBF system proved effective at reducing PhACs presence in drinking water well below 0.1 μg/L, highlighting its value as an energy-efficient treatment method. To ensure safe use of IRBF, future research must integrate geochemical, and metabolite tracking information, along with a proactive approach to designing degradable PhACs, hence, reducing the need on downstream treatment systems.