Release, Cross-Media Transport, and Retained Inventory of Rare Earth Elements from Informal Electronic Waste Recycling

Abstract

Rare earth elements (REEs) are essential for modern electronics and are increasingly entering electronic waste (e-waste) streams. Informal recycling can release REEs into the environment, but their sources, transfer pathways, and retained inventories remain poorly quantified. Here, we combine microscopic particle characterization, neodymium (Nd) isotopes, Bayesian source apportionment, and a Level III steady-state multimedia aquivalence (SMA) model to characterize REE sources, cross-media transport, and retained inventories in Guiyu, China. Spatial clustering of REE concentrations near historical recycling sites, together with spherical and angular particles, supported anthropogenic inputs from thermal treatment and mechanical fragmentation. Isotopic mixing models estimated that geogenic contributions remained dominant, whereas e-waste contributions accounted for 21.4%, 16.4%, and 33.6% of REEs loading in soil, road dust, and sediment, respectively. Fly ash and wastewater sludge were the main anthropogenic end-members, pointing to combustion and acid-leaching pathways. Multimedia modeling identified land-to-river export as the dominant cross-media pathway, with soil runoff and surface wash-off serving as major vectors to aquatic systems. The retained inventory within the modeled solid compartments, including soil, road dust, and sediment, was estimated at 1.68 × 103 t ΣREE, with an uncertainty range of 0.555 × 103 to 4.74 × 103 t. Scenario extrapolations to 2030 projected annual REE releases of 3.98 × 103 t under historical recycling intensities and 1.32 × 103 t under regulated management. These findings suggest that informal e-waste recycling can shift recoverable REEs into persistent environmental reservoirs, making secondary remobilization an additional concern beyond direct emissions.