The effect of EDTA on the groundwater transport of thorium through sand

► EDTA has been shown to enhance thorium migration through sand significantly. ► Transport involves ternary interactions between Th-EDTA complexes and the sand. ► The concentration of thorium and EDTA affects the transport mechanism. ► A simple chemical model has been developed to explain thorium behaviour at low concentrations. ► Evidence is provided for mobile EDTA-stabilised thorium colloidal transport at high thorium and EDTA concentrations.