Rare Earths as Emerging Trace Element Contaminants in the Soil

This review examines recent publications on rare earth elements (REE) in soils, critically evaluating their role as emerging soil contaminants. We emphasized new findings and main gaps using a previous review paper published in 2016 by our research group as a reference point. Three major subjects were prioritized: (1) sources, background levels, and behavior of REE in soils; (2) plant development and metabolism as affected by REE exposure; and (3) environmental and human health risk assessments of REE in the soil environment.

Publications addressing the occurrence and fate of REE in the soil environment have more than tripled in the last decade. Coincidentally, global REE exploration has more than doubled in the past 7 years. Because of their unique features, the global demand for REE is expected to increase by at least 50% in the next 10 years. As soils are the main sink of contaminants, we must continue to investigate the consequences of the unceasing addition of these elements in soil ecosystems.

We highlighted the main sources of REE, their background levels in selected global soils, and their physicochemical behavior. The relationship between REE and plants revealed potential benefits such as environmental stress tolerance. Finally, ecological and human health risk assessment data for REE in soils were carefully discussed in terms of their potential adverse effects on biota. We conclude with a survey in which prominent authors working with REE answered questions about challenges and opportunities for innovative research on REE in soil-plant-animal/human systems.