Rare Earth Elements (REE): Origins, Dispersion, and Environmental Implications-A Comprehensive Review

The rare earth elements (REE) comprise a group of 16 chemically very similar elements that occur widespread in rocks, soils, and water bodies, share similar ionic radii to the essential element Ca2+, and consequently also occur in biota. Given that REE form mainly trivalent cations, they also share similarities to Al3+. Compared to their chemical cognate Ca, they have a higher reactivity. Thus, their accumulation in soils may constitute a severe environmental threat. Over the last decades, the increasing use of REE in modern technology and fertilizers raised concerns about the pollution of soils and water bodies, which led to a rapidly increasing number of publications dealing with REE toxicity to plants, animals and humans, the fate of REE in soil-plant systems, REE cycling in ecosystems and impacts of REE pollution on food security. This review aims to give an overview of the current knowledge on the occurrence of REE in the total environment, including relevant environmental processes governing their mobility, chemical speciation and transfer from abiotic compartments into biota. Beginning with an overview of analytical approaches, we summarize the current knowledge on the ecology of REE in the lithosphere, pedosphere, hydrosphere and biosphere, including impacts of soil pollution on food security and public health.