Combined isotope and enantiomer analysis to assess the fate of phenoxy acids in a heterogeneous geologic setting at an old landfill

► We assessed the fate of phenoxy acids at a landfill site in a clay till geology. ► For the first time enantiomer and isotope analysis were combined for phenoxy acids. ► For the first time CSIA was applied for phenoxy acids using field samples. ► Degradation was indicated in the hotspot and along the flow paths of clay till. ► Alterations of the degradation mechanism were revealed by the combined approach.