Carbamazepine, carbamazepine epoxide and dihydroxycarbamazepine sorption to soil and occurrence in a wastewater reuse site in Tunisia.

Treated wastewater is being increasingly used for irrigation and aquifer replenishment through artificial recharge. However, wastewater reuse can result in contamination of exposed soil and groundwater by chemicals such as some pharmaceuticals and their metabolites. The fate of these molecules depends largely on their capacity to sorb onto soil and aquifer materials during infiltration. In this study, the sorption isotherm of carbamazepine (CBZ), an anti-seizure medication, and two of its metabolites, i.e. carbamazepine-10,11-epoxide (CBZ-EP) and 10,11-dihydro-10,11-dihydroxycarbamazepine (DiOH-CBZ), were determined in two soils in laboratory assays. In the field, the presence of CBZ and its metabolites were investigated in soil and in groundwater underlying an irrigated area with treated wastewater. The results showed that CBZ had the highest carbon normalised sorption coefficients in the two tested soils (irrigated soil and a Lufa SP2.4 reference soil) followed by CBZ-EP and DiOH-CBZ, indicating the relatively higher mobility of CBZ metabolites compared to CBZ. The chromatographic analysis revealed that CBZ and its two metabolites were present in treated wastewater used for irrigation and in groundwater. In soil samples, CBZ concentrations showed a build-up taking place with irrigation. The mobility of metabolites in soil and their potential biodegradation require further investigation.