Fractionation and speciation of rare earth elements in legacy mining lakes using diffusive gradients in thin films (DGT) and single-particle ICP-MS (spICP-MS): From seasonal baselines to extreme atmospheric deposition events

ABSTRACT This study investigates the geochemical dynamics and ecological risks of rare earth elements (REE) in abandoned clay mining lakes in the second world’s largest producer of ceramic tiles in Santa Gertrudes (CDSG), Brazil. Using a multi-technique approach, combining conventional filtration, diffusive gradients in thin films (DGT), single-particle inductively coupled mass spectrometry (spICP-MS), and geochemical modelling, a seasonal baseline was established and the influence of an atmospheric particulate deposition event associated with an unprecedent 2024 wildfire episode was evaluated. Results showed that seasonal variability produced relatively minor changes in REE behaviour, whereas the 2024 atmospheric deposition event promoted substantial shifts in REE partitioning. The median total concentration (∑REE T ) surged from 3,200 ng L -1 in 2022 to 25,800 ng L -1 during the 2024 event, with Cerium (Ce) reaching a peak of 12,500 ng L -1 . A critical decoupling between fractions was observed: while the dissolved fraction (