Emerging contaminants: assessing the release of pharmaceuticals via managed aquifer recharge

Managed aquifer recharge (MAR) is a vital water management strategy that infiltrates surface water or wastewater effluent into aquifers through soil and sediment. However, this process can introduce pharmaceutically active compounds (PhACs) and their metabolites, posing environmental risks. This study investigates the transport behavior of four selected PhACs-caffeine, carbamazepine, diclofenac, and ibuprofen-under neutral pH conditions using column experiments in both unsaturated and saturated porous media. PhACs and a tracer solution were introduced into the system, and experimental results were simulated using the CXTFIT model to determine retardation and degradation factors. Experimental findings indicate high mobility for carbamazepine and ibuprofen across both unsaturated and saturated conditions with high recovery (> 88%) and negligible degradation (< 0.05). Ibuprofen behaved similarly identical to the tracer in unsaturated medium and with small adsorption/desorption in saturation with a retardation factor of ~ 1, while carbamazepine showed slight retardation and tailing effects showing higher persistence in the water, with high dispersion in unsaturated medium. Diclofenac significantly degrades in saturated media (45% recovery) but increases release under unsaturated conditions (91% recovery). This indicates the release of diclofenac through the vadose zone but can undergo degradation and retardation in aquifers. Caffeine exhibited high retardation and degradation, with a low recovery rate (27-30%) under both conditions, suggesting that degradation or irreversible adsorption may have occurred independently of moisture content during transport. This finding highlights the differences in mobility and degradation across unsaturated and saturated zones, posing long-term contamination risks of PhACs. This underscores the need for robust monitoring and management to prevent groundwater contamination from pharmaceuticals, pathogens, and antibiotic-resistant bacteria, especially when using wastewater effluent or stormwater for recharge.