Leaching Behavior and Redox Sensitivity of Drug Residues During Bank Filtration

The occurrence and fate of various pharmaceutical residues during bank filtration was investigated between 2002 and 2005 within an interdisciplinary research project entitled NASRI (Natural and Artificial Systems for Recharge and Infiltration). Transport and the redox sensitivity of the compounds were studied both in column experiments and “on-site” at different field sites in Berlin, Germany, where bank-filtered water is used for drinking water production. The principal lessons from the NASRI project were that removal of drug residues at bank filtration sites mainly occurs in the upper (colmation) layer but for a few compounds it also happens in the ground water aquifer. The good removal of hydrophobic pharmaceuticals such as bezafibrate, indomethacin and estrogenic steroids can directly be linked to their high log K_OW values and are explainable by hydrophobic sorption. For polar drug residues, other non-hydrophobic mechanisms (e.g. hydrogen bonds, ion exchange effects) are additionally important because simple relationships between removal rates and log K_OW’s do not account for such mechanisms. In many cases, microbial degradation plays an important role and the prevailing redox conditions can be important for the removal rates of the specific compounds. Complete or at least good removal was observed for estrogenic steroids, antimicrobial drugs, bezafibrate, indomethacin, diclofenac and several other compopunds. Phenazone-type drugs, clofibric acid and carbamazepine showed only poor or even very poor removal both under oxic but especially under anoxic conditions. Residues of AMDOPH and primidone were little or not affected either under oxic or reducing conditions. Besides its potential to remove microbes and other contaminants from surface water, bank-filtration also be a useful tool to remove drug residues or to lower their concentrations in water from contaminated raw water sources. Bank filtration will, however, not be sufficient for a complete removal of all kinds of pharmaceutical residues including their metabolites.