Role of cation exchange processes on the sorption influenced transport of cationic β-blockers in aquifer sediments

The influence of cation exchange processes on the transport behavior of the cationic β-blockers atenolol and metoprolol was investigated by applying saturated laboratory column experiments. Breakthrough curves using natural sediments under different competitive conditions were generated and resulting sorption coefficients were compared. For the cationic species of atenolol (at pH = 8), the existence and dominating role of cation exchange processes were demonstrated by varying calcium concentrations. No effect of atenolol concentration on its retardation was observed within a wide concentration range. The breakthrough curve comparison of atenolol and the more hydrophobic metoprolol under constant conditions showed a significantly stronger retardation for metoprolol than for atenolol. However, additional non-polar interactions cannot explain the observed differences as they are determined to be negligible for both compounds. Due to the dominating role of cation exchange processes for the cationic species on overall sorption, a simple prediction of β-blocker transport in the subsurface by using KOC values derived from log KOW–log KOC correlations is not feasible.

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► Column experiments with two cationic β-blockers on natural sediments.
► Strong effects of concentration of inorganic cations on retardation of β-blockers.
► No effect of atenolol concentration on retardation over several orders of magnitude.
► Cation exchange processes control the sorption of cationic β-blockers.
► Prediction of β-blocker transport by means of log KOW–log KOC correlations not suitable.