Contents and bioavailability of rare earth elements in agricultural soils in Hesse (Germany)

Abstract

With increasing agricultural and industrial use of rare earth elements (REEs), input of REEs into the pedosphere has risen in parallel. Since total REE budgets for soils in Germany are mainly unknown, this pilot study investigates the concentrations of REEs in three loess soil profiles under agricultural land use in the Wetterau region, Germany. There were no significant REE applications in the past, so the presented data can be considered as background concentrations of REEs in soils. In addition to the total REE contents (aqua regia digestion), potentially plant‐available (EDTA) and at actual conditions available, mobile (NH4NO3) REEs have been determined for each horizon. Interactions between REE availability and properties of soils are explained after assessing several chemical and physical properties. The results reveal a wide range of total REE contents, ranging from 222 to 423 mg kg–1. With 10.1% of total REE amounts, the potentially plant‐available proportions of REEs are generally low. In contrast, yttrium, which showed high available proportion of 24.8%, was found to be comparable with Cd. Cerium is the most abundant REE in aqua regia digests, whereas only small amounts in the potentially plant‐available fraction were found. Thus negative cerium anomalies could be concluded concerning its potential availability. Generally, bioavailability of REE had significant correlations between clay contents and Fe and Mn oxides for the majority of REEs. Due to moderately high pH (CaCl2) in soils (average 6.6) the mobile fraction for most of the elements was not detectible.

Distribution and mobility of scandium and yttrium in selected types of soils in Poland

“…In the study of other horizons, especially in surface horizons, the contents of bioavailable fractions were found in low proportions. Also Loell et al (2011) found a similar tendency of the fractions of rare earth elements. The percentage sequences of the elements in t h e five fractions in diagnostic genetic horizons are presented in Table 4.…”

“…The mean concentration of potentially bioavailable (∑F1-F2) REEs, extracted by 1M MgCl2, was for scandium and yttrium respectively: 0.05 and 1.10 mg kg -1 . Soil properties, such as low pH values, and low Corg contents, increase solubility of REEs (Loell et al, 2011, Tyler and Olsson 2005, Kabata-Pendias and Pendias, 1993, 1984. Accordingly, soil properties must be taken into account while studying the REEs' availability.…”

87Sr/86Sr and trace element mapping of geosphere-hydrosphere-biosphere interactions: A case study in Ireland

“…The water soluble and/or exchangeable fractions are commonly targeted for studying biogeochemical cycling (e.g. Drouet et al, 2007;Fang et al, 2007;Frei et al, 2009;Leybourne and Johannesson, 2008;Loell et al, 2011;Miller et al, 1993;Poszwa et al, 2000;Tyler, 2004) …”

“…Thus, despite the well-established complexities of REE chemistry in soils (e.g., reflecting a combination of host mineral effects, pH controls, complexation) (Byrne and Sholkovitz, 1996;Deberdt et al, 2002;Elderfield et al, 1990;Lawrence and Kamber, 2006;Matsunaga et al, 2015;Noack et al, 2014;Pédrot et al, 2015a;Tricca et al, 1999) originating from igneous rock, sandstone, and shale tending to have higher REE contents than soils developed from loess and calcareous rock (Hu et al, 2006;Loell et al, 2011). In general, the high REE in the basalt-dominated soil indicates the most easily leachable REE fraction, which likely reflects the lack of poorly leachable REErich phases and the high abundance of Fe/Mn-oxy(hydroxides) with potentially adsorbed REE.…”

“…Yu et al, (2007) speculated that the relative enrichment of Y to Ho and the other REE is due to the difference in its transportation in the metabolic pathway or its bioavailability in ambient seawater. In another case study, Loell et al, (2011), measured the total REE contents (aqua regia digestion), potentially plant-available (EDTA) and mobile (NH4NO3) in loess soils. The authors found that the EDTA fraction represented on average 10.1% of the total REE soil contents with a notably high available proportion of Y (mean 24.8%, max 39%).…”