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To improve our understanding and guide future studies and applications, we review the biogeochemistry of the rare earth elements (REE). The REEs, which form a chemically uniform group due to their nearly identical physicochemical properties, include the lanthanide series elements plus scandium (Sc) and yttrium (Y). These elements, in conjunction with the neodymium isotopes, are powerful tools for understanding key oceanic, terrestrial, biological and even anthropogenic processes. Furthermore, their unique properties render them essential for various technological processes and products. Here, we delve into the characteristics of REE biogeochemistry and discuss normalization procedures and REE anomalies. We also examine the aqueous speciation of REEs, contributing to a better understanding of their behavior in aquatic settings, including the role of neodymium isotopes. We then focus on their environmental distribution, fractionation, and controlling processes in different environmental systems across the land‐ocean continuum. In addition, we analyze sinks, sources, and the mobility of REEs, providing insights into their behavior in these environments. We further investigate the sources of anthropogenic REEs and their bioavailability, bioaccumulation, and transfer along food webs. We also explore the potential effects of climate change on the cycling, mobility and bioavailability of REEs, underlining the importance of current research in this evolving field. In summary, we provide a comprehensive review of REE behavior in the environment, from their properties and roles to their distribution and anthropogenic impacts, offering valuable insights and pinpointing key knowledge gaps. Key Points: Rare earth elements (REE) are powerful tracers of both natural and anthropogenic processes within terrestrial and ocean environmentsREE are controlled by absorption, adsorption/desorption, co‐precipitation, remineralization, and particle dissolutionREE are technology‐critical metals with broad applications in the future low‐carbon global economy [ABSTRACT FROM AUTHOR]

Particulate trace metal (Cu, Cr, Ni, Pb and Zn) and major element (Fe, Mn and Al) concentrations have been determined following intensive sampling over two consecutive spring tidal cycles in the 'turbidity maximum zone' (TMZ) of the Port Jackson estuary, Australia. Salinity, temperature, pH, dissolved oxygen, suspended particulate matter (SPM) and chlorophyll a were also determined. A three-factor analysis of variance was used to test temporal variability in concentrations of particulate trace metals and major elements as a result of tidal oscillation. Estuarine master variables, such as temperature and pH, varied within a narrow range; nevertheless, the tidal signal was clear for surface and bottom waters. In surface water, no variance was detected in SPM concentrations between consecutive tidal cycles or between tidal stages (i.e. flood, ebb and slack water). In bottom water, however, SPM concentrations were significantly higher (P≤0.05) at flood tide than at slack high water and ebb tide. Concentrations of particulate trace metals and major elements in surface water do not display significant variability between tidal cycles or stages. Nevertheless, differences within each tidal stage were significant (P≤0.05) for all elements. In bottom water, only particulate Fe and Al exhibited significant differences (P≤0.05) between tidal cycles, whereas particulate Ni was the only trace element that presented significant differences (P≤0.05) between tidal stages, following the distribution of SPM, with highest concentrations at flood tide. Among the metals studied, significant variation was found at all three temporal scales examined (i.e. from hours to consecutive tidal cycles), although the patterns of variation were different for each metal. The semi-diurnal fluctuation of SPM and particulate trace metal concentrations during spring tides is interpreted as a resuspension–deposition cycle caused by cyclical oscillations of bottom currents. The results are discussed in the context of the implications of tidal cycle influence on the geochemistry and cycling of particulate trace metals in the Port Jackson estuary. [ABSTRACT FROM AUTHOR]

The Sinos river receives the effluents released by one of the most important industrial centres in South Brazil. To evaluate the environmental impact of heavy metal contamination in the Sinos river is a difficult task, because the river basin is dominated by basaltic rocks that are naturally rich in metals. Therefore, a part of the metal concentrations in the river water originates from a natural source, i.e. rock weathering. The anthropogenic sources of heavy metals are also widespread along the river. The analysis of the heavy metal concentrations in the Sinos river water was not enough either to identify spatial gradients along the river, or to quantify the anthropogenic metal inputs partially responsible for these concentrations. To estimate the anthropogenic inputs, this study proposes an approach based on massbalance of heavy metal fluxes, including the estimate of the naturalcomponent using a natural tracer (Fe). The approach estimated the metal loads released by the anthropogenic activities into the river (Total approx. 28.0 ton yr-1: Cu 1.8 ton yr-1; Zn 8.3 ton yr-1; Cr 11.4 ton yr-1; Cd 1.5 ton yr-1; and, Pb 5.0 ton yr-1), and identified the critical river segment contaminated by heavy metals (87% of the total estimated anthropogenic inputs occur in the lower basin). These resultsagree with contamination source data reported by the governmental environment agency for effluent emitted into the Sinos river. [ABSTRACT FROM AUTHOR]