Human health risk assessment and geochemical mobility of rare earth elements in Amazon soils

https://doi.org/10.1016/j.scitotenv.2021.151191Get rights and content

Highlights

  • Rare earth elements bound to residual fraction represents 80% of the total content.

  • Rare earth oral bioaccessibility represents less than 20% of the total contents.

  • The 0.01 M CaCl2 extraction was able to estimate the oral bioaccessibility.

  • Human health risks associated to rare earth oral exposure were considerably low.

Abstract

Rare earth elements (REEs) are a grouping of elements that encompasses lanthanides, yttrium and scandium due to their similar chemical properties and occurrence in ore deposits. Over the past few decades, economic interest in REEs has increased due to their use in several types of industries such as high-tech, medicine and agriculture. Extraction of REEs has been followed, in general, by incorrect disposal of tailing and waste, creating hazardous conditions in several countries. However, the magnitude of the possible impacts on ecosystem and human health are relatively unknown, especially in tropical systems. Thus, the objectives of this study were to assess the geochemical mobility and the bioaccessibility of REEs based on a series of chemical extractions and in vitro essay. We also tested two promising simple protocols (0.01 mol L−1 CaCl2 and 0.43 mol L−1 HNO3) for measuring REE bioaccessible fractions through a single extraction. Our findings show that the bioavailable fractions represent less than 20% of the ΣREEs fraction in all soil samples examine. Similarly, the oral bioaccessibility obtained by two in vitro methods (Gastric protocol and Gastric-Intestinal protocol) and by the single extraction tests represented less than 20% of the ΣREE contents. The non-carcinogenic risks and the carcinogenic risks associated to REEs oral exposure were low for children and adults. The extractions with 0.01 mol L−1 CaCl2 showed great potential as a method for measuring the REEs bioaccessible fraction.

Introduction

Rare earth elements (REEs), which encompass the lanthanides, yttrium and scandium, have similar atomic radii and are predominantly trivalent (REE3+), although Ce4+ and Eu2+ may occur in some environments (Aide and Aide, 2012). Having similar chemical characteristics, REEs may substitute for each other in crystal lattices, which leads to multiple occurrences of REEs in the same ore deposits and other rock types within the Earth's crust. REEs abundance within rocks is often close to 0.01% to 0.02%, and these elements can be found in a diversity of minerals such as carbonates, oxides, phosphates and silicates (Loell et al., 2011; Ramos et al., 2016). The only exception is Promethium (Pm), which is radioactive and rapidly decays (half-life is 2.62 years) (Khan et al., 2017).

Use of REEs in technology, medicine, and agriculture has increased in the last decades (Pagano et al., 2015). The rapidly expanding use of REEs has resulted in poor containment and disposal of mine waste, extraction by-products, and pose-use waste (Xinde et al., 2000). The REEs exhibit a patterns consistent with other emergent contaminants that can threaten human and ecosystem health (Mihajlovic et al., 2014). Several health complications can result upon human exposure to REEs that include respiratory problems and neurological damage (Meryem et al., 2016; Pagano et al., 2019), restriction in protein synthesis (Gonzalez et al., 2014), and oxidative stress and tissue damage to liver, lungs and kidneys (Pagano et al., 2015).

The possible impacts of REEs on ecosystems are relatively unknown, especially in tropical systems. In Brazil, for example, studies involving REEs have been mainly concentrated outside of the topical zones and only total concentration in soils have been examined (Pereira et al., 2019; Sá Paye et al., 2016; Silva et al., 2016). Recently, however, high levels of REEs were reported for soils of the Amazon in Brazil (Ferreira et al., 2021a). Total concentration, however, are not representative of risk to either humans or ecosystems (Li et al., 2014). Rather, the propensity for exposure and transfer into the living organisms needs to be assessed to understand human and ecosystems health threats (Khadhar et al., 2020).

Gaining and understanding of how REEs bind to different soil solid phases may provide information about their transport, availability and ecosystem threats associated (Mihajlovic et al., 2014). Classically, sequential extraction has been used to examine the phases hosting the elements within soils, which can then be used to project possible bioavailable fractions. (Mihajlovic et al., 2014; Wang and Liang, 2015). On the other hand, the sequential extraction methods are not sufficient for defining phase association or the propensity for uptake within humans.

In recent decades, the concept of bioaccessibility has been used to define elemental concentrations available for human uptake (Wang et al., 2017). Ingestion of soil is as a major route of exposure to many soil contaminants (Oomen et al., 2002). For this reason, the bioaccessible fraction is normally measured through in vitro essays that mimic the effects of gastrointestinal human tract parameters (Drexler and Brattin, 2007; Juhasz et al., 2007). Different in vitro protocols have been used in assess the bioaccessibility of elements and their health risks (Li et al., 2014).

The use of in vitro tests to simulate the gastrointestinal tract is lengthy and laborious (Mingot et al., 2011). In order to streamline and minimize difficulties related to gastro-intestinal protocols, simplified (single step) extractions have been reported as a possible alternative (Rao et al., 2010) that can provide a fast and relative low-cost assessment (Oomen et al., 2002; Pelfrêne et al., 2020). Previous reports involving trace elements in Brazilian and European soils (Rodrigues et al., 2010a, Rodrigues et al., 2018) and REEs in soils of European and Asian countries (Rao et al., 2010) have presented promising results about the use of unbuffered, mild extractions and diluted acids as simplified protocols to determine bioaccessibility. However, the characteristics of soils used in these studies are considerably different in comparison to the characteristics of tropical soils, such as those in the Amazon region, especially in terms of pH values and rock-derived nutrient concentrations, which may change the efficiency of these potential extractors to assess the REEs bioaccessibility in Amazon soils.

Here, we present the first assessment of the reactivity, bioaccessibility, and health human risk of REEs (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in tropical soils of Brazilian Amazon. We also evaluated the efficiency of two low-cost simple (single-step) protocols, using 0.01 mol L−1 CaCl2 (unbuffered solution) and 0.43 mol L−1 HNO3 (diluted acid solution), to determine the REEs bioaccessibility. Our study presents a clear understanding of the reactivity of REEs in Amazon soils, including data about REEs concentrations in different geochemical pools and the concentrations available for human absorption.

Section snippets

Study area and geological settings

The Amazonas state is the largest state of Brazil, having an area of 1,550,000 km2 and bordering Colombia, Peru and Venezuela. The population of Amazonas state is around 4.2 million, with more than 52% of the state population living in the capital (IBGE, 2019). The average temperature in Amazonas state is 26 °C, the average humidity is 80%, and the precipitation levels range from 2200 mm to 3200 mm (Alvares et al., 2013). Two climate types are presented in Amazon State: Tropical rainforest

Soil parameters

The pHKCl values ranged from 3.1 to 5.7, and pHw ranged from 3.7 to 6.8 (Table S5). The sum of bases (SB) was considered low (< 20 cmolc/dm−3) in most samples, and it ranged from 23.6 cmolc/dm−3 to 0.1 cmolc/dm−3. The cation exchange capacities (CECe) were less than 5.97 cmolc/dm−3. The cation exchange capacities at pH 7 (CECpH7) ranged from 2.8 cmolc/dm−3 to 8 cmolc/dm−3. TOC was less than 1.2% in all soil samples. The PRem values ranged from 4.4 to 50 mg L−1. Particle-size analysis

Soil properties

The acidity and the low base cation content observed are common features of Amazon soils due to the strong weathering processes (Horbe et al., 2007; Lima et al., 2006; Mafra et al., 2002). The Amazon soils have been under strong weathering conditions (wet tropical climate) over at least 45 million of years, resulting in the destruction of primary minerals and removal of silica necessary for generation or preservation of 2:1 secondary minerals, which explains the nutrient poverty of these soils (

Conclusions

The sequential extraction procedure showed that the REEs content in Amazon soils are distributed in ascending order: organic matter fraction (~1%) < exchangeable fraction (~4.3%), Fe/Mn oxides (~4.3%) < residual phase (~90.1%). Thus, the bioavailable fractions (exchangeable phase, organic matter phase and oxalate extractable phase) represent less than 20% of the total amount of REEs in these soils.

Similarly, the concentrations obtained by single-step extraction using 0.43 mol L−1 HNO3 showed

Credit authorship contribution statement

Matheus da Silva Ferreira: Conception or design of the work, Data collection, Laboratory procedures, Data analysis and interpretation, Drafting the article, Critical revision of the article, Final approval of the version to be published. Maurício Paulo Ferreira Fontes: Conception or design of the work, Data analysis and interpretation, Drafting the article, Critical revision of the article, Final approval of the version to be published. Maria Tereza Weitzel Dias Carneiro Lima: Conception or

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES (Brasil) – through the project Programa Nacional de Cooperação Acadêmica - PROCAD 2013 - Finance Code 001.

References (80)

  • B.L. Larner et al.

    Comparative study of optimised BCR sequential extraction scheme and acid leaching of elements in the certified reference material NIST 2711

    Anal. Chim. Acta

    (2006)
  • C. Laveuf et al.

    Rare earth elements as tracers of pedogenetic processes

    (2008)
  • J. Li et al.

    Bioaccessibility of antimony and arsenic in highly polluted soils of the mine area and health risk assessment associated with oral ingestion exposure

    Ecotoxicol. Environ. Saf.

    (2014)
  • X. Liu et al.

    Rare earth and yttrium phosphate solubilities in aqueous solution

    Geochim. Cosmochim. Acta

    (1997)
  • A. Lu et al.

    Application of microwave extraction for the evaluation of bioavailability of rare earth elements in soils

    Chemosphere

    (2003)
  • B. Meryem et al.

    Distribution of rare earth elements in agricultural soil and human body (scalp hair and urine) near smelting and mining areas of Hezhang, China

    J. Rare Earths

    (2016)
  • J. Mihajlovic et al.

    Geochemical fractions of rare earth elements in two floodplain soil profiles at the Wupper River, Germany

    Geoderma

    (2014)
  • J. Mingot et al.

    Assessment of oral bioaccessibility of arsenic in playground soil in Madrid (Spain): a three-method comparison and implications for risk assessment

    Chemosphere

    (2011)
  • M. Mittermüller et al.

    A sequential extraction procedure to evaluate the mobilization behavior of rare earth elements in soils and tailings materials

    Chemosphere

    (2016)
  • G. Pagano et al.

    Rare earth elements in human and animal health: state of art and research priorities

    Environ. Res.

    (2015)
  • G. Pagano et al.

    Human exposures to rare earth elements: present knowledge and research prospects

    Environ. Res.

    (2019)
  • A. Pelfrêne et al.

    Evaluation of single-extraction methods to estimate the oral bioaccessibility of metal(loid)s in soils

    Sci. Total Environ.

    (2020)
  • C.R.M. Rao et al.

    Comparison of single and sequential extraction procedures for the study of rare earth elements remobilisation in different types of soils

    Anal. Chim. Acta

    (2010)
  • S.M. Rodrigues et al.

    Evaluation of an approach for the characterization of reactive and available pools of 20 potentially toxic elements in soils: part II - solid-solution partition relationships and ion activity in soil solutions

    Chemosphere

    (2010)
  • S.M. Rodrigues et al.

    Evaluation of an approach for the characterization of reactive and available pools of twenty potentially toxic elements in soils: part I - the role of key soil properties in the variation of contaminants' reactivity

    Chemosphere

    (2010)
  • S.M. Rodrigues et al.

    Evaluation of a single extraction test to estimate the human oral bioaccessibility of potentially toxic elements in soils: towards more robust risk assessment

    Sci. Total Environ.

    (2018)
  • M. Rodríguez-Barranco et al.

    Cadmium exposure and neuropsychological development in school children in southwestern Spain

    Environ. Res.

    (2014)
  • N.R. Šmuc et al.

    Geochemical characteristics of rare earth elements (REEs) in the paddy soil and rice (Oryza sativa L.) system of Kočani field,Republic of Macedonia

    (2012)
  • R.A. Sutherland

    Comparison between non-residual Al, Co, Cu, Fe, Mn, Ni, Pb and Zn released by a three-step sequential extraction procedure and a dilute hydrochloric acid leach for soil and road deposited sediment

    Appl. Geochem.

    (2002)
  • C. Xinde et al.

    Assessment of the bioavailability of rare earth elements in soils by chemical fractionation and multiple regression analysis

    Chemosphere

    (2000)
  • Y. Yan et al.

    Provenance and bioaccessibility of rare earth elements in atmospheric particles in areas impacted by the optoelectronic industry

    Environ. Pollut.

    (2020)
  • J.L. Yost et al.

    Soil organic carbon in sandy soils: a review

  • M.T. Aide et al.

    Rare earth elements: their importance in understanding soil genesis

    ISRN Soil Sci.

    (2012)
  • C.A. Alvares et al.

    Köppen's climate classification map for Brazil

    (2013)
  • V.H. Alvarez et al.

    Determinação e uso do fósforo remanescente

    Bol. Inf. da socBras. Ciência do Solo

    (2000)
  • K. Boros et al.

    Comparison of gastric versus gastrointestinal PBET extractions for estimating oral bioaccessibility of metals in house dust

    Int. J. Environ. Res. Public Health

    (2017)
  • L. Brioschi et al.

    Transfer of rare earth elements (REE) from natural soil to plant systems: implications for the environmental availability of anthropogenic REE

    Plant Soil

    (2013)
  • S. Cornu et al.

    Transfer of dissolved Al, fe and si in two amazonian forest environments in Brazil

    Eur. J. Soil Sci.

    (1998)
  • Geodiversidade do estado do Amazonas

    Programa Geol. do Bras. Levant. da Geodiversidade.

    (2010)
  • M. Cunha et al.

    REE distribution pattern in plants and soils from Pitinga mine—Amazon, Brazil

    Open J. Geol.

    (2012)
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