Mutual Effects of pH and Competing Cations on the Mobility of Metoprolol in Saturated Quartz Sand: Parameter Estimation and Mobility Prediction Using Retardation Modeling

Abstract

Predicting the fate of organic compounds in the aquatic environment remains a challenge due to the complexity of natural systems and diverse interactions with surfaces. In this study, the transport behavior of the β-blocker metoprolol (MTP) was studied in water-saturated columns filled with quartz sand (pH 3–11; [NaCl] of 1, 10, and 100 mmol L–1). A significant dependence of MTP retardation on pH and [NaCl] was observed ranging from a 10-fold retardation at pH 6 and 1 mmol L–1 NaCl to virtually none at pH 11. A retardation model was implicated considering (1) the speciation of MTP, (2) the surface reactions of MTPH+, and Na+ with charged surface silanol groups SiO– of quartz, and (3) the protolysis reaction between SiO– and SiOH. Modeling was performed using the complete dataset of 43 retardation values at once (R2 = 0.998). Exemplary predictions were performed for three aquifer settings to illustrate general trends in mobility. This comprehensive approach is an important basis for environmental fate prediction of organic contaminants in the future.