Sorption influenced transport of ionizable pharmaceuticals onto a natural sandy aquifer sediment at different pH

The pH-dependent transport of eight selected ionizable pharmaceuticals was investigated by using saturated column experiments. Seventy-eight different breakthrough curves on a natural sandy aquifer material were produced and compared for three different pH levels at otherwise constant conditions. The experimentally obtained KOC data were compared with calculated KOC values derived from two different log KOW–log KOC correlation approaches. A significant pH-dependence on sorption was observed for all compounds with pKa in the considered pH range. Strong retardation was measured for several compounds despite their hydrophilic character. Besides an overall underestimation of KOC, the comparison between calculated and measured values only yields meaningful results for the acidic and neutral compounds. Basic compounds retarded much stronger than expected, particularly at low pH when their cationic species dominated. This is caused by additional ionic interactions, such as cation exchange processes, which are insufficiently considered in the applied KOC correlations.

► Column experiments with eight ionizable pharmaceuticals on natural sediment. ► Screening of sorption behavior under influence of pH (78 breakthrough curves). ► Comparison with two log KOW–log KOC correlations. ► Strong influence of pH for anionic, cationic and zwitter-ionic compounds. ► Retardation increases for cations and decreases for anions with ionic character.