Many pharmaceuticals, biocides, pesticides, surfactants and illicit drugs are positively charged at environmentally relevant conditions. Strong sorption to dissolved colloids and soil and sediment particles affect bioavailability and transport processes in contaminated environments and laboratory toxicity tests.
Ion-exchange controls sorption of cationic compounds in soils, at acidic sites in natural organic matter (NOM) and at negatively charged clay mineral surfaces [1-3]. Na+ and Ca2+ affect ionic interactions between organic cation and ion-exchange site, while additional nonionic interactions can strengthen sorption. To better understand which soil components dominate overall sorption, in this study we compared sorption affinities towards NOM and two clay minerals for a diverse set of >50 organic cations, including both simple and complex molecular structures.