Rare Earth Element Concentrations in Brazilian Benchmark Soils

Ygor Jacques Agra Bezerra da Silva Clístenes Williams Araújo do Nascimento Yuri Jacques Agra Bezerra da Silva Caroline Miranda Biondi Cinthia Maria Cordeiro Atanázio Cruz Silva About the authors

ABSTRACT:

Studies regarding background concentrations of rare earth elements (REEs) are scarce and have mainly focused on a limited number of soil types from the northern hemisphere. The aim of this study was to determine REE concentrations in thirty-five benchmark soils of Brazil. Composite soil samples were taken from areas under native vegetation or with minimal anthropogenic influence. Concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Lu, Dy, Er, Ho, Tb, Tm, Y, Sc, and Fe were determined by ICP-OES using a cyclonic spray chamber/nebulizer system after microwave acid digestion. Results were assessed by descriptive statistics, Pearson correlation, and principal component analysis (PCA). Regression analyses among Fe, organic carbon, and REEs were performed to provide a tool for estimating REE concentrations in soils. The REE concentrations in the Brazilian benchmark soils were in the following order: Ce > La > Nd > Pr > Y > Sm > Gd > Sc > Dy > Yb > Eu > Er > Tb > Ho > Lu > Tm. The clear decoupling between light and heavy rare earth elements in soils, indicated by multivariate analysis, is mainly related to differences in parent material. The lowest REE concentrations were found in sandy sediments, whereas the highest REE concentrations were observed in basalt, biotite gneiss, and clayey sediments. The organic carbon and Fe concentrations can properly predict REE concentrations in soils; such a finding can assist in estimating REE concentrations in soils not only in Brazil but also in similar soils developed under tropical conditions.

Keywords:
lanthanides; scandium; yttrium; metals; trace elements

INTRODUCTION

Rare earth elements (REEs) are a group of metals comprised of yttrium (Y), scandium (Sc), and 14 elements of the lanthanide series (lanthanum to lutetium). These last 14 elements are generally divided into two groups: light (lanthanum to europium) and heavy (gadolinium to lutetium) elements (Hu et al., 2006Hu Z, Haneklaus S, Sparovek G, Schnug E. Rare earth elements in soils. Commun Soil Sci Plant Anal. 2006;37:1381-420. doi: 10.1080/00103620600628680
https://doi.org/10.1080/0010362060062868...
; Du and Graedel, 2011Du X, Graedel TE. Global in-use stocks of the rare earth elements: a first estimate. Environ Sci Technol. 2011;45:4096-101. doi: 10.1021/es102836s
https://doi.org/10.1021/es102836s...
; Sadeghi et al., 2013Sadeghi M, Morris GA, Carranza EJM, Ladenberger A, Andersson M. Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry. J Geochem Explor. 2013;133:160-75. doi: 10.1016/j.gexplo.2012.10.015
https://doi.org/10.1016/j.gexplo.2012.10...
). The denomination "rare" might lead to misunderstandings since they can be as abundant in the Earth's crust as copper, nickel, or lead (Haxel et al., 2002Haxel GB, Hedrick JB, Orris GJ. Rare earth elements - critical resources for high technology. USGS Fact Sheet 087-02. Washington, DC: U.S. Geological Survey; 2002.). For instance, cerium (Ce) is the 25th most abundant element in the Earth's crust and its concentration in soil is often similar to that of Zn (Tyler, 2004Tyler G. Rare earth elements in soil and plant systems - A review. Plant Soil . 2004;276:191-206. doi: 10.1007/s11104-005-4888-2
https://doi.org/10.1007/s11104-005-4888-...
). In addition, REEs are found in more than 200 minerals, mainly phosphates, carbonates, silicates, and Fe- and Mn-oxides (Henderson, 1984Henderson P. Rare earth element geochemistry: Developments in geochemistry. Amsterdam: Elsevier ; 1984. v.2.).

Given their unique physical and chemical properties, REEs are widely used for multiple purposes, such as industrial production of technological devices (Strauch et al., 2008Strauch G, Moder M, Wennrich R, Osenbruck K, Glaser HR, Schladitz T, Muller C, Schirmer K, Reinstorf F, Schirmer M. Indicators for assessing anthropogenic impact on urban surface and groundwater. J Soils Sedim. 2008;8:23-33. doi: 10.1065/jss2007.06.234
https://doi.org/10.1065/jss2007.06.234...
; Long et al., 2010Long KR, van Gosen BS, Foley NK, Cordier D. The principal rare earth elements deposits of the United States - a summary of domestic deposits and a global perspective. Virginia U.S. Geological Survey; 2010. (Scientific Investigations Report, 2010-5220).; Robert and David, 2012Robert JW, David JR. United States Environmental Protection Agency - USEPA. Rare earth elements: a review of production, processing, recycling, and associated environmental issues. Washington, DC: 2012. (EPA600/R-12/572).) and agricultural fertilizers (Pang et al., 2002Pang X, Li D, Peng A. Application of rare-earth elements in the agriculture of China and its environmental behavior in soil. Environ Sci Pollut Res. 2002;9:143-8. doi: 10.1007/BF02987718
https://doi.org/10.1007/BF02987718...
; Kobayashi et al., 2007Kobayashi Y, Ikka T, Kimura K, Yasuda O, Koyama H. Characterization of lanthanum toxicity for root growth of Arabidopsis thaliana from the aspect of natural genetic variation. Funct Plant Biol. 2007;34:984-94. doi: 10.1071/FP07133
https://doi.org/10.1071/FP07133...
). These and other technical innovations will strongly increase REE demand in the near future; hence, accumulation of these elements in the soil may become an environmental concern (Zeng et al., 2006Zeng Q, Zhu JG, Cheng HL, Xie ZB, Chu HY. Phytotoxicity of lanthanum in rice in Haplic Acrisols and Cambisols. Ecotoxicol Environ Saf. 2006;64:226-33. doi: 10.1016/j.ecoenv.2005.03.016
https://doi.org/10.1016/j.ecoenv.2005.03...
; D'Aquino et al., 2009D'Aquino L, Pinto MC, Nardi L, Morgana M, Tommasi F. Effect of some light rare earth elements on seed germination, seedling growth and antioxidante metabolism in Triticum durum. Chemosphere. 2009;75:900-5. doi: 10.1016/j.chemosphere.2009.01.026
https://doi.org/10.1016/j.chemosphere.20...
; Du and Graedel, 2011Du X, Graedel TE. Global in-use stocks of the rare earth elements: a first estimate. Environ Sci Technol. 2011;45:4096-101. doi: 10.1021/es102836s
https://doi.org/10.1021/es102836s...
).

Data on soil background concentrations of trace (Salonen and Korkka-Niemi, 2007Salonen VP, Korkka-Niemi K. Influence of parent sediments on the concentration of heavy metals in urban and suburban soils in Turku, Finland. Appl Geochem. 2007;22:906-18. doi: 10.1016/j.apgeochem.2007.02.003.
https://doi.org/10.1016/j.apgeochem.2007...
; Biondi et al., 2011Biondi CM, Nascimento CWA, Fabricio Neta AB, Ribeiro MR. Teores de Fe, Mn, Zn, Cu, Ni e Co em solos de referência de Pernambuco. Rev Bras Cienc Solo. 2011;35:1057-66. doi: 10.1590/S0100-06832011000300039
https://doi.org/10.1590/S0100-0683201100...
; Preston et al., 2014Preston W, Nascimento CWA, Biondi CM, Souza Júnior VS, Silva WR, Ferreira HA. Valores de referência de qualidade para metais pesados em solos do Rio Grande do Norte. Rev Bras Cienc Solo . 2014;38:1028-37. doi: 10.1590/S0100-06832014000300035
https://doi.org/10.1590/S0100-0683201400...
; Alfaro et al., 2015Alfaro MR, Montero A, Ugarte OM, Nascimento CWA, Accioly AMA, Biondi CM, Silva YJAB. Background concentrations and reference values for heavy metals in soils of Cuba. Environ Monit Assess. 2015;187:4198-207. doi: 10.1007/s10661-014-4198-3
https://doi.org/10.1007/s10661-014-4198-...
) and major elements (Montserrat and Camarero, 2010Montserrat B, Camarero L. Major and trace elements in soils in the Central Pyrenees: high altitude soils as a cumulative record of background atmospheric contamination over SW Europe. Environ Sci Pollut Res. 2010;17:1606-21. doi: 10.1007/s11356-010-0349-4
https://doi.org/10.1007/s11356-010-0349-...
; Hannan and Tanguma, 2012Hannan MA, Tanguma J. Concentrations of trace and major elements in Mission-Progresso (Texas) soils. J Radioanal Nucl Chem. 2012;291:745-51. doi: 10.1007/s10967-011-1545-5
https://doi.org/10.1007/s10967-011-1545-...
; Dantu, 2014Dantu S. Spatial distribution and geochemical baselines of major/trace elements in soils of Medak district, Andhra Pradesh, India. Environ Earth Sci. 2014;72:955-81. doi: 10.1007/s12665-013-3014-7
https://doi.org/10.1007/s12665-013-3014-...
) are easily found in the literature. However, data regarding REEs are comparatively scarce and have mainly focused on determination of REEs in a limited number of soil types (Turra et al., 2011Turra C, Fernandes EAN, Bacchi MA. Evaluation on rare earth elements of Brazilian agricultural supplies. J Environ Chem Ecotoxicol. 2011;3:86-92.; Damascena et al., 2015Damascena KFR, Amaral RS, Santos Júnior JA, Genezini FA, Silva AA, Menezes RSC. Rare-earth elements in uranium deposits in the municipality of Pedra, Pernambuco, Brazil. J Radioanal Nucl Chem. 2015;304:1053-8. doi: 10.1007/s10967-015-3934-7
https://doi.org/10.1007/s10967-015-3934-...
). Given that REE concentrations are influenced by soil parent materials and pedogenesis processes, such studies are not able to estimate the variability of REE concentrations expected in soils. Thus, the study of benchmark soils can yield a set of REE data that covers a wide range of pedogeological conditions and might be used in estimation of REEs on a more national or global scale. A benchmark soil is one of large extent within one or more major land resource areas, one that holds a key position in the soil classification system, one for which there is a large amount of data, one that has special importance for one or more significant land uses, or one that is of significant ecological importance (USDA, 2004).

Geochemical associations between trace elements and Fe concentrations in soils are often reported (Hamon et al., 2004Hamon RE, Mclaughlin MJ, Gilkes RJ, Rate AW, Zarcinas B, Robertson A, Cozens G, Radford N, Bettenay L. Geochemical indices allow estimation of heavy metal background concentrations in soils. Global Biogeochem Cycles. 2004;18:1-6. doi: 10.1029/2003GB002063
https://doi.org/10.1029/2003GB002063...
; Alfaro et al., 2015Alfaro MR, Montero A, Ugarte OM, Nascimento CWA, Accioly AMA, Biondi CM, Silva YJAB. Background concentrations and reference values for heavy metals in soils of Cuba. Environ Monit Assess. 2015;187:4198-207. doi: 10.1007/s10661-014-4198-3
https://doi.org/10.1007/s10661-014-4198-...
); therefore, regression equations may predict trace element concentrations in soils based on such correlations. This can avoid costly sampling and analysis when levels of potentially toxic elements need to be known for a great number of soil samples (Alfaro et al., 2015). Likewise, high correlations between Fe and REE concentrations can be useful for estimating the concentrations of REEs in soils.

Taking into account the growing global economic importance of REEs, the use of these elements in several Earth science fields (Laveuf and Cornu, 2009Laveuf C, Cornu S. A review on the potentiality of rare earth elements to trace pedogenetic processes. Geoderma . 2009;154:1-12. doi: 10.1016/j.geoderma.2009.10.002
https://doi.org/10.1016/j.geoderma.2009....
; Li et al., 2013Li X, Chen Z, Chen Z, Zhang Y. A human health risk assessment of rare earth elements in soil and vegetables from a mining area in Fujian Province, Southeast China. Chemosphere . 2013;93:1240-6. doi: 10.1016/j.chemosphere.2013.06.085
https://doi.org/10.1016/j.chemosphere.20...
; Chen et al., 2014; Abbott et al., 2015Abbott AN, Haley BA, McManus J, Reimers CE. The sedimentary flux of dissolved rare earth elements to the ocean. Geochim Cosmochim Acta. 2015;154:186-200. doi: 10.1016/j.gca.2015.01.010
https://doi.org/10.1016/j.gca.2015.01.01...
; Pagano et al., 2015Pagano G, Guida M, Tommasi F, Oral R. Health effects and toxicity mechanisms of rare Earth elements - Knowledge gaps and research prospects. Ecotoxicol Environ Saf. 2015;115:40-8. doi: 10.1016/j.ecoenv.2015.01.030
https://doi.org/10.1016/j.ecoenv.2015.01...
), and the scarcity of data available for Brazil (Pérez et al., 1997Pérez DV, Saldanha MFC, Meneguelli NA, Moreira JC, Vaitsman DS. Geoquímica de alguns solos brasileiros. Rio de Janeiro: Embrapa Solos; 1997. (Boletim Informativo).; Paye et al., 2016Paye HS, Mello JWV, Mascarenhas GRLM, Gasparon M. Distribution and fractionation of the rare earth elements in Brazilian soils. J Geoch Exp. 2016;161:27-41. doi: 10.1016/j.gexplo.2015.09.003
https://doi.org/10.1016/j.gexplo.2015.09...
) and other tropical regions, this study was carried out to determine the REE concentrations in soils of a Brazilian benchmark collection that represents all the soil orders found in the country. Additionally, we demonstrate that a geochemical association exists between Fe and REEs in these soils. Such a finding can aid in estimating and tracing REE concentrations in soils.

MATERIALS AND METHODS

Sampling and sample preparation

The study area extends from the coastal region to the semiarid zone of the state of Pernambuco, Brazil (Figure 1), and covers sites with different soil and geological settings.

Annual average rainfall ranges from 500 mm to 2,200 mm and air temperature ranges from 24 °C to 28 °C for semiarid and coastal regions, respectively. In the coastal zone, soils are often developed upon tertiary sediments or crystalline rocks - usually deep and highly weathered - with relief ranging from slightly to strongly rolling; vegetation is mainly composed of evergreen broad-leaf tropical forest. In the semiarid region, soils are generally shallow owing to the long dry season, which in turn decreases the chemical weathering and leaching process; vegetation is mainly deciduous forest, known locally as hypoxerophilous caatinga, and dense tree-shrub deciduous vegetation, classified locally as hyperxerophilous caatinga, somewhat similar to a dry season deciduous thornbush savannah (Nascimento et al., 2006Nascimento CWA, Oliveira AB, Ribeiro MR, Melo ÉEC. Distribution and availability of zinc and copper in benchmark soils of Brazil. Commun Soil Sci Plant Anal . 2006;37:109-25. doi: 10.1080/00103620500403895
https://doi.org/10.1080/0010362050040389...
).

A total of 35 composite topsoil samples were taken from areas covered by native vegetation or with minimal anthropogenic influence, representing a wide diversity of soil classes and parent materials (Table 1). Consequently, the soils also exhibit wide variability regarding physical and chemical properties (Table 2). Soil samples were air dried and passed through a 2-mm mesh nylon sieve, ground in an agate mortar, and passed through a stainless steel 0.3-mm mesh sieve (ABNT No. 50).

Quality control and quality assurance (QC/QA)

For REE and Fe determination, 1.000 g of soil was digested in Teflon vessels with 9 mL of HNO3 and 3 mL of HCl in a microwave oven (USEPA, 1998). This method is recommended by the Brazilian Council for the Environment to assess potentially toxic concentrations of elements in soil (Conama, 2009). All the extracts were transferred to 25 mL certified flasks (NBR ISO/IEC) filled with ultrapure water (Millipore Direct-Q System) and filtered through slow filter paper (Macherey Nagel(r)). High purity acids were used in the analysis (Merck PA).

Calibration curves for REE and Fe determination were prepared from standard 1,000 mg L-1 (Titrisol(r), Merck). Analysis was performed only when the coefficient of determination (R2) of the calibration curve was higher than 0.999. Analytical data quality and standard operational procedures such as curve recalibration and analyses of blanks and the standard reference materials SRM 2710a Montana I Soil and SRM 2709 San Joaquin soil (NIST, 2002) were performed. All analyses were carried out in duplicate. Concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Lu, Dy, Er, Ho, Tb, Tm, Y, Sc, and Fe were determined by inductively coupled plasma (ICP-OES/Optima 7000, Perkin Elmer); in order to improve both sensitivity and stability for REE measurements, a cyclonic spray chamber/nebulizer system was coupled to the ICP.

Figure 1
Distribution of soil sampling sites in the state of Pernambuco, Brazil.

Statistical analysis

Results were assessed by descriptive statistics, Pearson correlation, and principal component analysis (PCA). Principal component analysis has been widely used for studying geochemical data (Carranza, 2008Carranza EJM. Geochemical anomaly and mineral prospectivity mapping in GIS. Handbook of Exploration and Environmental Geochemistry. Amsterdam: Elsevier; 2008. v.11.; Sadeghi et al., 2013Sadeghi M, Morris GA, Carranza EJM, Ladenberger A, Andersson M. Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry. J Geochem Explor. 2013;133:160-75. doi: 10.1016/j.gexplo.2012.10.015
https://doi.org/10.1016/j.gexplo.2012.10...
; Agnan et al., 2014Agnan Y, Delmas NS, Probst A. Origin and distribution of rare earth elements in various lichen and moss species over the last century in France. Sci Total Environ. 2014;487:1-12. doi: 10.1016/j.scitotenv.2014.03.132
https://doi.org/10.1016/j.scitotenv.2014...
; Silva et al., 2015Silva YJAB, Cantalice JRB, Singh VP, Nascimento CWA, Piscoya VC, Guerra SMS. Trace element fluxes in sediments an environmentally impacted river from a coastal zone of Brazil. Environ Sci Pollut Res. 2015;22:14755-66. doi: 10.1007/s11356-015-4670-9
https://doi.org/10.1007/s11356-015-4670-...
) and consists of converting the original group of variables into a new uncorrelated group of equal dimension. Such groups are known as principal components - linear combination of the original variables - which aim to explain the maximum level of total variability associated with these independent variables (Manly, 2008Manly BJF. Métodos estatísticos multivariados: uma introdução. 3a ed. Porto Alegre: Bookman; 2008.). To extract the significant principal components while diminishing the contribution of variables with little importance, we employed Varimax rotation (Kaiser, 1958Kaiser HF. The varimax criterion for analytic rotation in factor analysis. Psychometrika. 1958;23:187-200. doi: 10.1007/BF02289233
https://doi.org/10.1007/BF02289233...
). Regression analyses among Fe, organic carbon (OC), and REEs were tested to provide a tool for estimating REE concentrations in soils.

Table 1
Soil class according to Soil Taxonomy and Brazilian System of Soil Classification, parent material, and locations of soils

RESULTS AND DISCUSSION

Quality control and quality assurance (QC/QA)

Percentage recoveries of REEs from the certified materials ranged from 79 to 98 % for SRM 2710a and 52 to 93 % for SRM 2709 (Table 3). The highest recoveries were observed for Yb, Lu, Sm, and Gd: SRM 2710a (98, 97, 95, and 90 %, respectively) and SRM 2709 (93, 83, 85, and 80 %, respectively), while Nd, Ce, La, and Sc showed the lowest recoveries. Since the digestion method used (USEPA 3051A) is not able to extract REEs from silicates (NIST, 2002), in general, the lower the recovery, the higher the association of the element with these soil silicate minerals.

Table 2
Mean, maximum, minimum, and median concentrations and standard deviation for physical and chemical properties of Brazilian benchmark soils
Table 3
Mean contents of rare earth elements (REEs) recovered for certified reference material (SRM 2710a Montana soil and SRM 2709 San Joaquin soil) by USEPA method 3051A

REEs concentration in soils

Average REE concentrations in soils were in the following order: Ce > La > Nd > Pr > Y > Sm > Gd > Sc > Dy > Yb > Eu > Er > Tb > Ho > Lu > Tm (Figure 2). The REE concentrations in the soil is mainly governed by parent materials (Liu, 1988Liu Z. Rare earth elements in soil. In: Guo BS, Zhu WM, Xiong BK, Ji YJ, Liu Z, Wu ZM, editors. Rare earth elements in agriculture (in Chinese). Beijing: China Agricultural Science and Technology Press; 1988. p.22-44.; Hu et al., 2006Hu Z, Haneklaus S, Sparovek G, Schnug E. Rare earth elements in soils. Commun Soil Sci Plant Anal. 2006;37:1381-420. doi: 10.1080/00103620600628680
https://doi.org/10.1080/0010362060062868...
), but weathering conditions, organic matter, and clay concentrations are also important to determine these levels (Tyler, 2004Tyler G. Rare earth elements in soil and plant systems - A review. Plant Soil . 2004;276:191-206. doi: 10.1007/s11104-005-4888-2
https://doi.org/10.1007/s11104-005-4888-...
). The abundance of REEs found here is very similar to that reported for soils of Brazil (Paye et al., 2016Paye HS, Mello JWV, Mascarenhas GRLM, Gasparon M. Distribution and fractionation of the rare earth elements in Brazilian soils. J Geoch Exp. 2016;161:27-41. doi: 10.1016/j.gexplo.2015.09.003
https://doi.org/10.1016/j.gexplo.2015.09...
) and other countries (Wei et al., 1991Wei FS, Zheng CJ, Chen JS, Wu YY. Study on the background contents on 61 elements of soils in China. J Environ Sci. 1991;12:12-20.; Yoshida et al., 1998Yoshida S, Maramutsu Y, Tagami K, Uchida S. Concentrations of lanthanide elements, Th, and U in 77 Japanese surface soils. Environ Int. 1998;24:275-86. doi: 10.1016/S0160-4120(98)00006-3
https://doi.org/10.1016/S0160-4120(98)00...
; Tyler and Olsson, 2002; Sadeghi et al., 2013Sadeghi M, Morris GA, Carranza EJM, Ladenberger A, Andersson M. Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry. J Geochem Explor. 2013;133:160-75. doi: 10.1016/j.gexplo.2012.10.015
https://doi.org/10.1016/j.gexplo.2012.10...
) and follows the Oddo-Harkins rule, which holds that elements with an even atomic number (such as Ce) are more common than elements with an odd atomic number (such as La).

The average Ce and La concentrations (43.48 and 20.79 mg kg-1, respectively) were higher than those for Zn and Cu (19.61 and 9.25 mg kg-1); Pr and Nd (9.61 and 17.70 mg kg-1) were also found in higher concentrations than trace elements (Ni and Co) measured in the same soils (Biondi et al., 2011Biondi CM, Nascimento CWA, Fabricio Neta AB, Ribeiro MR. Teores de Fe, Mn, Zn, Cu, Ni e Co em solos de referência de Pernambuco. Rev Bras Cienc Solo. 2011;35:1057-66. doi: 10.1590/S0100-06832011000300039
https://doi.org/10.1590/S0100-0683201100...
). In addition, the average Gd concentration was greater than the average Cd concentration generally found in Brazilian soils (Paye et al., 2010Paye HS, Mello JWV, Abrahão WAP, Fernandes Filho EI, Dias LCP, Castro MLO, Melo SB, França MM. Valores de referência de qualidade para metais pesados em solos no estado do Espírito Santo. Rev Bras Cienc Solo . 2010;34:2041-51. doi: 10.1590/S0100-06832010000600028
https://doi.org/10.1590/S0100-0683201000...
; Santos and Alleoni, 2013Santos SN, Alleoni LRF. Reference values for heavy metals in soils of the Brazilian agricultural frontier in Southwestern Amazônia. Environ Monit Assess . 2013;185:5737-48. doi: 10.1007/s10661-012-2980-7
https://doi.org/10.1007/s10661-012-2980-...
; Preston et al., 2014Preston W, Nascimento CWA, Biondi CM, Souza Júnior VS, Silva WR, Ferreira HA. Valores de referência de qualidade para metais pesados em solos do Rio Grande do Norte. Rev Bras Cienc Solo . 2014;38:1028-37. doi: 10.1590/S0100-06832014000300035
https://doi.org/10.1590/S0100-0683201400...
). Tm, Lu, Ho, and Tb were the least abundant heavy rare earth elements (HREEs) in soils; their values are comparable to those often reported for Mo and are related to the very low concentration in primary minerals.

The lowest sum of REEs occurred in soils derived from sandy sediments: profiles 28 (9.26 mg kg-1), 25 (9.54 mg kg-1), 3 (13.31 mg kg-1), and 10 (14.84 mg kg-1) (Table 1). Studying REE distribution in Sweden, Sadeghi et al. (2013Sadeghi M, Morris GA, Carranza EJM, Ladenberger A, Andersson M. Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry. J Geochem Explor. 2013;133:160-75. doi: 10.1016/j.gexplo.2012.10.015
https://doi.org/10.1016/j.gexplo.2012.10...
) also observed the lowest contents in sandstones. The highest REE concentrations in Brazilian benchmark soils were derived from basalt, biotite gneiss, and clayey sediments, profiles 7 (549 mg kg-1), 16 (525 mg kg-1), and 12 (410 mg kg-1), respectively. The sum of light rare earth elements (LREEs) in soils was equal to 95.56 mg kg-1. The maximum LREE concentrations were observed for the soil with the highest clay content (Figure 2). These values are much higher than the average in the Earth's crust and indicate that LREE enrichment took place in these soils. Several authors report LREE accumulation in clayey soils (Minarik et al., 1998Minarik L, Zigova A, Bendl J, Skrivan P, St'astny M. The behaviour of rare earth elements and Y during the rock weathering and soil formation in the Ricany granite massif, Central Bohemia. Sci Total Environ. 1998;215:101-11. doi: 10.1016/j.still.2010.09.007
https://doi.org/10.1016/j.still.2010.09....
; Dong et al., 2001Dong WM, Wang XK, Bian XY, Wang AX, Du JZ, Tao ZY. Comparative study on sorption/desorption of radioeuropium on alumina, bentonite and red earth: effects of pH, ionic strength, fulvic acid, and iron oxides in red earth. Appl Radiat Isotopes. 2001;54:603-10. doi: 10.1016/S0969-8043(00)00311-0
https://doi.org/10.1016/S0969-8043(00)00...
; Kanazawa and Kamitani, 2006Kanazawa Y, Kamitani M. Rare earth minerals and resources in the world. J Alloys Comp. 2006;408/412:1339-43. doi: 10.1016/j.jallcom.2005.04.033
https://doi.org/10.1016/j.jallcom.2005.0...
; Prudêncio et al., 2011Prudêncio MI, Dias MI, Waerenborgh JC, Ruiz F, Trindade MJ, Abad M. Rare earth and other trace and major elemental distribution in a pedogenic calcrete profile (Slimene, NE Tunisia). Catena. 2011;87:147-56. doi: 10.1016/j.catena.2011.05.018
https://doi.org/10.1016/j.catena.2011.05...
; Ahn et al., 2014Ahn JS, Youm J, Cho YC, Shin SC, Cho WH. Geochemical survey of rare earth elements (REEs) in the concealed ore body of Hongcheon, Korea. Environ Earth Sci. 2014;72:2153-61.).

The sum of REEs in soils of Brazil was 107.54 mg kg-1; this value is slightly higher than the average concentrations in Japan and Sweden, but lower than those in China and Europe (Table 4). The higher REE concentration in China is due to rich soil parent materials that comprise 23 % of the world's proven reserves (18.59 Mt, in 2009) (TSCIOPRC, 2012).

Figure 2
Data on the concentrations of light rare earth elements (LREE) (a) and heavy rare earth elements (HREE) (b) in Brazilian benchmark soils

Correlation matrix

Significant positive correlations among REEs were observed (Table 5). The correlation coefficients ranged from 0.54 (Ce-Er) to 0.99 (Ce-Pr), at p<0.05 and p<0.01, respectively. The highest correlations were observed among the following LREEs: La-Ce (0.96), La-Pr (0.97), Ce-Pr (0.99), and Pr-Nd (0.96), and the HREEs: Gd-Y (0.94), Dy-Ho (0.94), Dy-Tb (0.95), and Er-Ho (0.96). High correlations among REEs serve as useful tracers in the environment. Organic C and Fe contents play an important role in LREE and HREE distribution, respectively; however, a clear relationship between clay content and LREEs and HREEs was not observed in the matrix correlation; therefore, multivariate statistical analysis was used to further address this relationship.

Principal component analysis

Principal component analysis (PCA) was carried out based on the strong positive correlation among REEs and their multivariate normal distribution. The entire data set showed principal components (PC) with eigenvalues higher than unity and explained roughly 89 % of the total variance of REE distribution. PC1 and PC2 accounted for 80 and 8.9 % of total variance, respectively (Figure 3). PC1 had the highest loadings for Eu (0.66), Gd (0.80), Yb (0.83), Lu (0.84), Dy (0.77), Er (0.92), Ho (0.83), Tb (0.74), Y (0.83), Sc (0.80), Fe (0.76), and Clay (0.61), whereas PC2 was mainly correlated with La (0.90), Ce (0.94), Pr (0.94), Nd (0.86), Sm (0.77), and organic carbon (OC) (0.90). The clear decoupling between LREEs (PC2) and HREEs (PC1 - except for Eu) in soils is mainly related to differences in parent material, atomic weight, ionic radii, coordination numbers (c.n.), and electronegativity (Henderson, 1984Henderson P. Rare earth element geochemistry: Developments in geochemistry. Amsterdam: Elsevier ; 1984. v.2.; Laveuf and Cornu, 2009Laveuf C, Cornu S. A review on the potentiality of rare earth elements to trace pedogenetic processes. Geoderma . 2009;154:1-12. doi: 10.1016/j.geoderma.2009.10.002
https://doi.org/10.1016/j.geoderma.2009....
). For instance, LREEs often occupy the larger sites of 8-10 c.n. and concentrate in carbonates and phosphates, whereas HREEs usually occupy 6-8 c.n. sites and are predominant in oxides and some phosphates (Kanazawa and Kamitani, 2006Kanazawa Y, Kamitani M. Rare earth minerals and resources in the world. J Alloys Comp. 2006;408/412:1339-43. doi: 10.1016/j.jallcom.2005.04.033
https://doi.org/10.1016/j.jallcom.2005.0...
). REE distribution and mineralization data in Sweden also exhibited two distinct groupings - HREEs and LREEs in soils (Sadeghi et al. (2013Sadeghi M, Morris GA, Carranza EJM, Ladenberger A, Andersson M. Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry. J Geochem Explor. 2013;133:160-75. doi: 10.1016/j.gexplo.2012.10.015
https://doi.org/10.1016/j.gexplo.2012.10...
). Based on their results, the major difference was related to the distribution patterns in the parent material underlying northern Sweden.

Table 4
Mean concentrations of rare earth elements (REEs) in soils of Brazil compared to international soil data and Earth's crust
Table 5
Pearson correlation matrix between rare earth elements (REEs), Fe, clay and organic carbon (OC)

The highest loadings for OC with LREES and Fe with HREEs (Figure 3) clearly suggest their geochemical association. Organic C seems to have little influence on HREE distribution; furthermore, as incorporation of REEs in the Fe-Mn-oxide structure is limited, REEs rarely substitute Fe in the of Fe-oxide lattice (Braun et al., 1993Braun JJ, Pagel M, Herbillon A, Rosin C. Mobilization and redistribution of REEs and Thorium in a syenitic lateritic profile: A mass-balance study. Geochim Cosmochim Acta . 1993;57:4419-34. doi: 10.1016/0016-7037(93)90492-F
https://doi.org/10.1016/0016-7037(93)904...
). Such assumptions give rise to the question: Could Fe and/or OC be good predictors of REE concentrations in soils? As a matter of fact, we found a well-defined natural association between Fe and the sum of HREEs (Figure 4b), as well as between OC and the sum of LREEs (Figure 4a).

Linear regression analyses were carried out to address the geochemical association between individual REEs and Fe and OC concentrations. Coefficients of determination ranged from 0.40 to 0.97 (Table 6). As suggested by PCA, HREEs were strongly associated with Fe concentration in soils, whereas LREEs were poorly associated with Fe contents, except for Nd, Sm, and Eu, which were regarded as medium REEs (Laveuf and Cornu, 2009Laveuf C, Cornu S. A review on the potentiality of rare earth elements to trace pedogenetic processes. Geoderma . 2009;154:1-12. doi: 10.1016/j.geoderma.2009.10.002
https://doi.org/10.1016/j.geoderma.2009....
). Moreover, the highest standard error of estimate values observed, the measure of the accuracy of predictions for a regression line, was for La (20), Ce (47), Pr (10), and Nd (16).

Iron accounted for 82 and 74 % of the variation of Yb and Tb distribution (Table 6). Significant correlations demonstrated that Fe is useful in predicting HREE (including medium REEs, such as Sm and Eu) background concentrations in benchmark soils not only in Brazil but concentrations under tropical soil conditions when equations are properly calibrated on a more global scale. Nevertheless, attempts must be made in order to not extrapolate Fe concentrations ranging from 840 to 94,500 mg kg-1, respectively. The high geochemical association between Fe and HREEs might be related to preferential scavenging of the HREEs by pedogenic minerals, most probably Fe-oxyhydroxides (Brioschi et al., 2013Brioschi L, Steinmann M, Lucot E, Pierret MC, Stille P, Prunier J, Badot PM. Transfer of rare earth elements (REE) from natural soil to plant systems: implications for the environmental availability of anthropogenic REE. Plant Soil. 2013;366:143-63. doi: 10.1007/s11104-012-1407-0
https://doi.org/10.1007/s11104-012-1407-...
). The influence of Fe oxide contents on the bioavailability of REEs was also reported by Fang et al. (2007Fang J, Wen B, Xiao-Quan S, Huan-Hua W, Jin-Ming L, Shuzhen Z. Evaluation of bioavailability of light rare earth elements to wheat (Triticum aestivum L.) under field conditions. Geoderma. 2007;141:53-9. doi: 10.1016/j.geoderma.2007.05.014
https://doi.org/10.1016/j.geoderma.2007....
). The ongoing release of HREEs during the dissolution of Fe oxyhydroxides suggested that these elements are preferentially associated with Fe oxyhydroxides (Pédrot et al., 2015Pédrot M, Dia A, Davranche M, Gruau G. Upper soil horizons control the rare earth element patterns in shallow groundwater. Geoderma. 2015;239/240:84-96. doi: 10.1016/j.geoderma.2014.09.023
https://doi.org/doi: 10.1016/j.geoderma....
). Significant positive correlations (p<0.01) between Fe oxides and REEs (except for Ce) were obtained in agricultural soils from German (Loell et al., 2011Loell M, Reiher W, Henningsen PF. Contents and bioavailability of rare earth elements in agricultural soils in Hesse (Germany). J Plant Nutr Soil Sci. 2011;174:644-54. doi: 10.1002/jpln.201000265
https://doi.org/10.1002/jpln.201000265...
); however, no significant correlation was observed between OC and REEs (except for Ce). They suggested that Fe oxides seem to trap Ce based on positive Ce anomaly in crystalline oxides or concretions; in addition, the complexation capacity of organic C is higher with Ce than with other REEs.

Figure 3
Principal component analysis of rare earth elements (REEs) in Brazilian soils.

Figure 4
Relationship between light rare earth elements (LREE) and organic carbon (OC) (a) and heavy rare earth elements (HREE) and Fe (b) concentrations

Table 6
Regression parameters for the association between rare earth elements (REEs) and concentrations of organic carbon (OC) and Fe in soils

CONCLUSIONS

Average REE concentrations in benchmark soils of Brazil were in the following order: Ce > La > Nd > Pr > Y > Sm > Gd > Sc > Dy > Yb > Eu > Er > Tb > Ho > Lu > Tm and were related to underlying parent material. The lowest REE concentrations were found in sandy sediments, whereas the highest REE concentrations were observed in basalt, biotite gneiss, and clayey sediments.

Organic carbon and Fe concentrations can properly predict REE concentrations in the soils studied; this finding can assist in estimating REE concentrations in soils not only in Brazil but in similar soils developed under tropical conditions.

REFERENCES

  • Abbott AN, Haley BA, McManus J, Reimers CE. The sedimentary flux of dissolved rare earth elements to the ocean. Geochim Cosmochim Acta. 2015;154:186-200. doi: 10.1016/j.gca.2015.01.010
    » https://doi.org/10.1016/j.gca.2015.01.010
  • Agnan Y, Delmas NS, Probst A. Origin and distribution of rare earth elements in various lichen and moss species over the last century in France. Sci Total Environ. 2014;487:1-12. doi: 10.1016/j.scitotenv.2014.03.132
    » https://doi.org/10.1016/j.scitotenv.2014.03.132
  • Ahn JS, Youm J, Cho YC, Shin SC, Cho WH. Geochemical survey of rare earth elements (REEs) in the concealed ore body of Hongcheon, Korea. Environ Earth Sci. 2014;72:2153-61.
  • Alfaro MR, Montero A, Ugarte OM, Nascimento CWA, Accioly AMA, Biondi CM, Silva YJAB. Background concentrations and reference values for heavy metals in soils of Cuba. Environ Monit Assess. 2015;187:4198-207. doi: 10.1007/s10661-014-4198-3
    » https://doi.org/10.1007/s10661-014-4198-3
  • Biondi CM, Nascimento CWA, Fabricio Neta AB, Ribeiro MR. Teores de Fe, Mn, Zn, Cu, Ni e Co em solos de referência de Pernambuco. Rev Bras Cienc Solo. 2011;35:1057-66. doi: 10.1590/S0100-06832011000300039
    » https://doi.org/10.1590/S0100-06832011000300039
  • Braun JJ, Pagel M, Herbillon A, Rosin C. Mobilization and redistribution of REEs and Thorium in a syenitic lateritic profile: A mass-balance study. Geochim Cosmochim Acta . 1993;57:4419-34. doi: 10.1016/0016-7037(93)90492-F
    » https://doi.org/10.1016/0016-7037(93)90492-F
  • Brioschi L, Steinmann M, Lucot E, Pierret MC, Stille P, Prunier J, Badot PM. Transfer of rare earth elements (REE) from natural soil to plant systems: implications for the environmental availability of anthropogenic REE. Plant Soil. 2013;366:143-63. doi: 10.1007/s11104-012-1407-0
    » https://doi.org/10.1007/s11104-012-1407-0
  • Carranza EJM. Geochemical anomaly and mineral prospectivity mapping in GIS. Handbook of Exploration and Environmental Geochemistry. Amsterdam: Elsevier; 2008. v.11.
  • Chen LM, Zhang GL, Jin ZD. Rare earth elements of a 1000-year paddy soil chronosequence: Implications for sediment provenances, parent material uniformity and pedological changes. Geoderma. 2014;230/231:274-9. doi: 10.1016/j.geoderma.2014.03.023
    » https://doi.org/10.1016/j.geoderma.2014.03.023
  • Claessen MEC, organizador. Manual de métodos de análise de solo. 2a ed. Rio de Janeiro: Centro Nacional de Pesquisa de Solos; 1997.
  • Conselho Nacional do Meio Ambiente - Conama. Resolução nº 420, de 28 de dez. de 2009. Dispõe sobre critérios e valores orientadores de qualidade do solo quanto à presença de substâncias químicas e estabelece diretrizes para o gerenciamento ambiental de áreas contaminadas por essas substâncias em decorrência de atividades antrópicas. Brasília, DF. [acesso: 12 ago 2015]. Disponível em:Disponível em: http://www.mma.gov.br/port/conama/legiabre. cfm?codlegi0620
    » http://www.mma.gov.br/port/conama/legiabre. cfm?codlegi0620
  • Damascena KFR, Amaral RS, Santos Júnior JA, Genezini FA, Silva AA, Menezes RSC. Rare-earth elements in uranium deposits in the municipality of Pedra, Pernambuco, Brazil. J Radioanal Nucl Chem. 2015;304:1053-8. doi: 10.1007/s10967-015-3934-7
    » https://doi.org/10.1007/s10967-015-3934-7
  • Dantu S. Spatial distribution and geochemical baselines of major/trace elements in soils of Medak district, Andhra Pradesh, India. Environ Earth Sci. 2014;72:955-81. doi: 10.1007/s12665-013-3014-7
    » https://doi.org/10.1007/s12665-013-3014-7
  • D'Aquino L, Pinto MC, Nardi L, Morgana M, Tommasi F. Effect of some light rare earth elements on seed germination, seedling growth and antioxidante metabolism in Triticum durum Chemosphere. 2009;75:900-5. doi: 10.1016/j.chemosphere.2009.01.026
    » https://doi.org/10.1016/j.chemosphere.2009.01.026
  • Defelipo BV, Ribeiro AC. Análise química do solo, metodologia. 2a ed. Viçosa, MG: Universidade Federal de Viçosa; 1997.
  • Dong WM, Wang XK, Bian XY, Wang AX, Du JZ, Tao ZY. Comparative study on sorption/desorption of radioeuropium on alumina, bentonite and red earth: effects of pH, ionic strength, fulvic acid, and iron oxides in red earth. Appl Radiat Isotopes. 2001;54:603-10. doi: 10.1016/S0969-8043(00)00311-0
    » https://doi.org/10.1016/S0969-8043(00)00311-0
  • Du X, Graedel TE. Global in-use stocks of the rare earth elements: a first estimate. Environ Sci Technol. 2011;45:4096-101. doi: 10.1021/es102836s
    » https://doi.org/10.1021/es102836s
  • Fang J, Wen B, Xiao-Quan S, Huan-Hua W, Jin-Ming L, Shuzhen Z. Evaluation of bioavailability of light rare earth elements to wheat (Triticum aestivum L.) under field conditions. Geoderma. 2007;141:53-9. doi: 10.1016/j.geoderma.2007.05.014
    » https://doi.org/10.1016/j.geoderma.2007.05.014
  • Hamon RE, Mclaughlin MJ, Gilkes RJ, Rate AW, Zarcinas B, Robertson A, Cozens G, Radford N, Bettenay L. Geochemical indices allow estimation of heavy metal background concentrations in soils. Global Biogeochem Cycles. 2004;18:1-6. doi: 10.1029/2003GB002063
    » https://doi.org/10.1029/2003GB002063
  • Hannan MA, Tanguma J. Concentrations of trace and major elements in Mission-Progresso (Texas) soils. J Radioanal Nucl Chem. 2012;291:745-51. doi: 10.1007/s10967-011-1545-5
    » https://doi.org/10.1007/s10967-011-1545-5
  • Haxel GB, Hedrick JB, Orris GJ. Rare earth elements - critical resources for high technology. USGS Fact Sheet 087-02. Washington, DC: U.S. Geological Survey; 2002.
  • Henderson P. Rare earth element geochemistry: Developments in geochemistry. Amsterdam: Elsevier ; 1984. v.2.
  • Hu Z, Haneklaus S, Sparovek G, Schnug E. Rare earth elements in soils. Commun Soil Sci Plant Anal. 2006;37:1381-420. doi: 10.1080/00103620600628680
    » https://doi.org/10.1080/00103620600628680
  • Kaiser HF. The varimax criterion for analytic rotation in factor analysis. Psychometrika. 1958;23:187-200. doi: 10.1007/BF02289233
    » https://doi.org/10.1007/BF02289233
  • Kanazawa Y, Kamitani M. Rare earth minerals and resources in the world. J Alloys Comp. 2006;408/412:1339-43. doi: 10.1016/j.jallcom.2005.04.033
    » https://doi.org/10.1016/j.jallcom.2005.04.033
  • Kobayashi Y, Ikka T, Kimura K, Yasuda O, Koyama H. Characterization of lanthanum toxicity for root growth of Arabidopsis thaliana from the aspect of natural genetic variation. Funct Plant Biol. 2007;34:984-94. doi: 10.1071/FP07133
    » https://doi.org/10.1071/FP07133
  • Laveuf C, Cornu S. A review on the potentiality of rare earth elements to trace pedogenetic processes. Geoderma . 2009;154:1-12. doi: 10.1016/j.geoderma.2009.10.002
    » https://doi.org/10.1016/j.geoderma.2009.10.002
  • Li X, Chen Z, Chen Z, Zhang Y. A human health risk assessment of rare earth elements in soil and vegetables from a mining area in Fujian Province, Southeast China. Chemosphere . 2013;93:1240-6. doi: 10.1016/j.chemosphere.2013.06.085
    » https://doi.org/10.1016/j.chemosphere.2013.06.085
  • Liu Z. Rare earth elements in soil. In: Guo BS, Zhu WM, Xiong BK, Ji YJ, Liu Z, Wu ZM, editors. Rare earth elements in agriculture (in Chinese). Beijing: China Agricultural Science and Technology Press; 1988. p.22-44.
  • Loell M, Reiher W, Henningsen PF. Contents and bioavailability of rare earth elements in agricultural soils in Hesse (Germany). J Plant Nutr Soil Sci. 2011;174:644-54. doi: 10.1002/jpln.201000265
    » https://doi.org/10.1002/jpln.201000265
  • Long KR, van Gosen BS, Foley NK, Cordier D. The principal rare earth elements deposits of the United States - a summary of domestic deposits and a global perspective. Virginia U.S. Geological Survey; 2010. (Scientific Investigations Report, 2010-5220).
  • Manly BJF. Métodos estatísticos multivariados: uma introdução. 3a ed. Porto Alegre: Bookman; 2008.
  • Minarik L, Zigova A, Bendl J, Skrivan P, St'astny M. The behaviour of rare earth elements and Y during the rock weathering and soil formation in the Ricany granite massif, Central Bohemia. Sci Total Environ. 1998;215:101-11. doi: 10.1016/j.still.2010.09.007
    » https://doi.org/10.1016/j.still.2010.09.007
  • Montserrat B, Camarero L. Major and trace elements in soils in the Central Pyrenees: high altitude soils as a cumulative record of background atmospheric contamination over SW Europe. Environ Sci Pollut Res. 2010;17:1606-21. doi: 10.1007/s11356-010-0349-4
    » https://doi.org/10.1007/s11356-010-0349-4
  • Nascimento CWA, Oliveira AB, Ribeiro MR, Melo ÉEC. Distribution and availability of zinc and copper in benchmark soils of Brazil. Commun Soil Sci Plant Anal . 2006;37:109-25. doi: 10.1080/00103620500403895
    » https://doi.org/10.1080/00103620500403895
  • National Institute Of Standards and Technology - NIST. Standard Reference Materials - SRM 2709, 2710 and 2711Addendum Issue Date: 18 January 2002. [accessed on May 21, 2015]. Available at: Available at: http://ts.nist.gov/MeasurementServices/ReferenceMaterials/archived_certificates
    » http://ts.nist.gov/MeasurementServices/ReferenceMaterials/archived_certificates
  • Pagano G, Guida M, Tommasi F, Oral R. Health effects and toxicity mechanisms of rare Earth elements - Knowledge gaps and research prospects. Ecotoxicol Environ Saf. 2015;115:40-8. doi: 10.1016/j.ecoenv.2015.01.030
    » https://doi.org/10.1016/j.ecoenv.2015.01.030
  • Pang X, Li D, Peng A. Application of rare-earth elements in the agriculture of China and its environmental behavior in soil. Environ Sci Pollut Res. 2002;9:143-8. doi: 10.1007/BF02987718
    » https://doi.org/10.1007/BF02987718
  • Paye HS, Mello JWV, Abrahão WAP, Fernandes Filho EI, Dias LCP, Castro MLO, Melo SB, França MM. Valores de referência de qualidade para metais pesados em solos no estado do Espírito Santo. Rev Bras Cienc Solo . 2010;34:2041-51. doi: 10.1590/S0100-06832010000600028
    » https://doi.org/10.1590/S0100-06832010000600028
  • Paye HS, Mello JWV, Mascarenhas GRLM, Gasparon M. Distribution and fractionation of the rare earth elements in Brazilian soils. J Geoch Exp. 2016;161:27-41. doi: 10.1016/j.gexplo.2015.09.003
    » https://doi.org/10.1016/j.gexplo.2015.09.003
  • Pédrot M, Dia A, Davranche M, Gruau G. Upper soil horizons control the rare earth element patterns in shallow groundwater. Geoderma. 2015;239/240:84-96. doi: 10.1016/j.geoderma.2014.09.023
    » https://doi.org/doi: 10.1016/j.geoderma.2014.09.023
  • Pérez DV, Saldanha MFC, Meneguelli NA, Moreira JC, Vaitsman DS. Geoquímica de alguns solos brasileiros. Rio de Janeiro: Embrapa Solos; 1997. (Boletim Informativo).
  • Preston W, Nascimento CWA, Biondi CM, Souza Júnior VS, Silva WR, Ferreira HA. Valores de referência de qualidade para metais pesados em solos do Rio Grande do Norte. Rev Bras Cienc Solo . 2014;38:1028-37. doi: 10.1590/S0100-06832014000300035
    » https://doi.org/10.1590/S0100-06832014000300035
  • Prudêncio MI, Dias MI, Waerenborgh JC, Ruiz F, Trindade MJ, Abad M. Rare earth and other trace and major elemental distribution in a pedogenic calcrete profile (Slimene, NE Tunisia). Catena. 2011;87:147-56. doi: 10.1016/j.catena.2011.05.018
    » https://doi.org/10.1016/j.catena.2011.05.018
  • Robert JW, David JR. United States Environmental Protection Agency - USEPA. Rare earth elements: a review of production, processing, recycling, and associated environmental issues. Washington, DC: 2012. (EPA600/R-12/572).
  • Sadeghi M, Morris GA, Carranza EJM, Ladenberger A, Andersson M. Rare earth element distribution and mineralization in Sweden: An application of principal component analysis to FOREGS soil geochemistry. J Geochem Explor. 2013;133:160-75. doi: 10.1016/j.gexplo.2012.10.015
    » https://doi.org/10.1016/j.gexplo.2012.10.015
  • Salonen VP, Korkka-Niemi K. Influence of parent sediments on the concentration of heavy metals in urban and suburban soils in Turku, Finland. Appl Geochem. 2007;22:906-18. doi: 10.1016/j.apgeochem.2007.02.003.
    » https://doi.org/10.1016/j.apgeochem.2007.02.003.
  • Santos SN, Alleoni LRF. Reference values for heavy metals in soils of the Brazilian agricultural frontier in Southwestern Amazônia. Environ Monit Assess . 2013;185:5737-48. doi: 10.1007/s10661-012-2980-7
    » https://doi.org/10.1007/s10661-012-2980-7
  • Silva YJAB, Cantalice JRB, Singh VP, Nascimento CWA, Piscoya VC, Guerra SMS. Trace element fluxes in sediments an environmentally impacted river from a coastal zone of Brazil. Environ Sci Pollut Res. 2015;22:14755-66. doi: 10.1007/s11356-015-4670-9
    » https://doi.org/10.1007/s11356-015-4670-9
  • Situation and policy of China's rare earth industry, white paper (English Version). The State Council Information Office of the People's Republic of China; 2012. [accessed on: June 10, 2015]. Available at: Available at: http://www.scio.gov.cn/zfbps/ndhf/2012/Document/1175419/1175419.htm ; 2012.
    » http://www.scio.gov.cn/zfbps/ndhf/2012/Document/1175419/1175419.htm
  • Strauch G, Moder M, Wennrich R, Osenbruck K, Glaser HR, Schladitz T, Muller C, Schirmer K, Reinstorf F, Schirmer M. Indicators for assessing anthropogenic impact on urban surface and groundwater. J Soils Sedim. 2008;8:23-33. doi: 10.1065/jss2007.06.234
    » https://doi.org/10.1065/jss2007.06.234
  • The State Council Information Office of the People's Republic of China - TSCIOPRC. Situation and policy of China's rare earth industry, white paper (English Version). 2012. [accessed on: June 10, 2015]. Available at: Available at: http://www.scio.gov.cn/zfbps/ndhf/2012/Document/1175419/1175419.htm ;2012.
    » http://www.scio.gov.cn/zfbps/ndhf/2012/Document/1175419/1175419.htm
  • Turra C, Fernandes EAN, Bacchi MA. Evaluation on rare earth elements of Brazilian agricultural supplies. J Environ Chem Ecotoxicol. 2011;3:86-92.
  • Tyler G, Olsson T. Conditions related to solubility of rare and minor elements in forest soils. J Plant Nutr Soil Sci . 2002;165:594-601. doi: 10.1002/1522-2624(200210)165:5<594::AID-JPLN594>3.0.CO;2-K
    » https://doi.org/10.1002/1522-2624(200210)165:5<594::AID-JPLN594>3.0.CO;2-K
  • Tyler G. Rare earth elements in soil and plant systems - A review. Plant Soil . 2004;276:191-206. doi: 10.1007/s11104-005-4888-2
    » https://doi.org/10.1007/s11104-005-4888-2
  • United States Department of Agriculture - USDA. National Engineering Handbook: Part 630-Hydrology. Washington, DC: USDA Soil Conservation Service. [accessed: Jul 2004]. Available at: Available at: http://www.soils.usda.gov/technical/handbook/contents/part630.html
    » http://www.soils.usda.gov/technical/handbook/contents/part630.html
  • United States Environmental Protection Agency - USEPA. Method 3051a - Microwave assisted acid digestion of sediments, sludges, soils, and oils. 1998. Revision Feb 1st 2007. [Accessed on: Jun 16, 2015]. Available at: Available at: http://www.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/3051a.pdf
    » http://www.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/3051a.pdf
  • Wei FS, Zheng CJ, Chen JS, Wu YY. Study on the background contents on 61 elements of soils in China. J Environ Sci. 1991;12:12-20.
  • Yeomans JC, Bremner JM. A rapid and precise method for routine determination of organic carbon in soil. Commun Soil Sci Plant Anal . 1988;19:1467-76. doi: 10.1080/00103628809368027
    » https://doi.org/10.1080/00103628809368027
  • Yoshida S, Maramutsu Y, Tagami K, Uchida S. Concentrations of lanthanide elements, Th, and U in 77 Japanese surface soils. Environ Int. 1998;24:275-86. doi: 10.1016/S0160-4120(98)00006-3
    » https://doi.org/10.1016/S0160-4120(98)00006-3
  • Zeng Q, Zhu JG, Cheng HL, Xie ZB, Chu HY. Phytotoxicity of lanthanum in rice in Haplic Acrisols and Cambisols. Ecotoxicol Environ Saf. 2006;64:226-33. doi: 10.1016/j.ecoenv.2005.03.016
    » https://doi.org/10.1016/j.ecoenv.2005.03.016

  • How to cite:

    Silva YJAB, Nascimento CWA, Silva YJAB, Biondi CM, Silva CMCAC. Rare Earth Element Concentrations in Brazilian Benchmark Soils. Rev Bras Cienc Solo. 2016;40:e0150413.

Publication Dates

  • Publication in this collection
    2016

History

  • Received
    24 Oct 2015
  • Accepted
    16 May 2016
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