Analytical capabilities of BCR protocol to estimate the mobility of

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Agricultural and Environmental Chemistry

Analytical capabilities of BCR protocol to estimate the mobility of nutrients and toxic elements from mineral fertilizer Luiza GR Albuquerque, Gislayne A R Kelmer, Delmarcio Gomes Silva, Ricardo A A Couto, Pedro Vitoriano Oliveira, and Alexandre Minami Fioroto J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b00822 • Publication Date (Web): 04 Jun 2018 Downloaded from http://pubs.acs.org on June 4, 2018

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Journal of Agricultural and Food Chemistry

Analytical capabilities of BCR protocol to estimate the mobility of nutrients and toxic elements from mineral fertilizer

Alexandre M. Fioroto, Luiza G. R. Albuquerque, Gislayne A. R. Kelmer, Delmarcio G. Silva, Ricardo A. A. Couto and Pedro V. Oliveira*

Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, CEP 05508-000, São Paulo, SP, Brazil

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ACS Paragon Plus Environment


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ABSTRACT

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The Community Bureau of Reference (BCR) sequential extraction was applied to

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investigate the mobility of potentially toxic elements (As, Cd, Cr, and Pb) and nutrients

5

(P, Ca, Mg, Cu, Fe, Mn, and Zn) in a multi-nutrient mineral fertilizer based on

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phosphate rocks supplemented with 10% (w w-1) of a micronutrient mixture (raw

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material used as a micronutrient source). For both samples As and Cd are more mobile,

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while Cr remained in the solid residue. A higher mobility of Pb was observed in

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micronutrient mixture; however, the high concentration of P (8.3% w w-1) in fertilizer

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could have decreased Pb mobility due to Pb3(PO4)2 formation. The nutrients had a great

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mobility, except Fe, which remained almost totally in the residual fraction in both

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samples. X-ray diffraction, scanning electron microscopy and energy dispersive

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spectroscopy analyses of solid residues showed that the way in which elements are

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distributed in sample particles can affect their mobility.

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KEYWORDS: BCR, Sequential extraction, Mobility, Fertilizer, Inductively Coupled

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Plasma Optical Emission Spectrometer

18 19 20 21 22 23 24 25

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INTRODUCTION

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Fertilizers are used to supply nutrients to soil in order to increase its fertility and,

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consequently, agricultural productivity. Phosphate rocks are a raw material that is

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commonly used for mineral fertilizer manufacturing because they are a rich source of

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phosphorus, an essential macronutrient for plants. Chemical analysis of phosphate rocks

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from several countries has shown that it consists of macronutrients (calcium,

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magnesium and phosphorus) and micronutrients (e.g., boron, copper, iron, manganese,

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molybdenum and zinc).1, 2 However, many studies have reported that phosphate rocks

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are also a source of potentially toxic elements to human and animal, such as arsenic,

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chromium, cadmium, lead, mercury, and nickel.3-11 Furthermore, when the composition

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of some micronutrients, such as copper, iron, zinc and manganese is below the required

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concentration, fertilizer producers add raw materials from ore mixtures and industrial

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by-products to supply the desired content of these elements. Depending on the raw

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material used, this process can also be an additional source of potentially toxic elements

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(e.g., arsenic, cadmium, lead, mercury, and nickel).12, 13 For this reason, quality control

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of fertilizers and raw materials, regarding macro and micronutrients and contaminants

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evaluation is necessary to guarantee effective fertilization and prevent crop

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contamination and environmental damage.

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The presence of potentially toxic elements in mineral fertilizer can contaminate

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agricultural soils, increasing the concern regarding health risks to humans and animals,

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as well as adverse effects on the soil ecosystems. However, the contribution of toxic

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elements from mineral fertilizer to the soil depends on their mobility in this media and

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environmental behavior. Consequently, the determinations of total concentrations are

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not sufficient, but chemical fractionation and speciation are important to predict the

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feasibility of nutrients and potentially toxic elements to be absorbed by plants and

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evaluate the impact of eventual environmental contamination.14, 15

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The fractionation of potentially toxic elements employing sequential extraction

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methods that represent environmental conditions has been used to assess mobility

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information. Mobility is evaluated in leaching studies to assess the environmental

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impact caused by these elements. Series of reagents are added to the same solid sample

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and the fractions of species extracted in the first steps are generally more weakly bound

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to solid matrix, which can be related to the potential of mobility of these species.16

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The classic work of Tessier et al. published in 1979 proposed a sequential

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extraction method for element fractionation into five target fractions: exchangeable,

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bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual.17 In

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the early 1990s, the Community Bureau of Reference (BCR) established a sediment

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sequential extraction protocol, which differs from the method of Tessier by the

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replacement of the first two steps by a single step. Afterward, BCR recommended a

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revised protocol in 1999, in order to improve its reproducibility. These procedures have

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been widely applied to assorted samples of environmental interest, mainly soil and

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sediment.18, 19

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In this context, researches related to element mobility in fertilizer samples, using

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BCR sequential extraction protocol, are predominantly focused on waste products used

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as soil amendments. However, most of these products are organic residues, for instance,

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sugarcane waste products,20,

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different types of sludge.20, 23-28 These works purpose not only to evaluate the extraction

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of elements contained in soil amendments, but also to verify the effect on the mobility

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of elements present in soils.20-22 Soil evaluation demonstrates that potentially toxic

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element concentrations are generally higher and also more mobile in agricultural soils

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by-products from paper-making industries,22 and

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than non-agricultural soils, and that fertilization is one of the agricultural activities

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responsible for it.14 BCR sequential extraction was also employed to estimate Zn

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mobility in polluted soil with or without compost amendment and compared to its

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distribution and speciation within different organs of the edible plant.29 There are also

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studies focused on inorganic materials, such as the assessment of elements mobility in

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industrial wastes used as soil amendments (lime, desulphurization slag, and fly ash),14,

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28, 30

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industry by-products31,

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samples.33

evaluation of the transfer rate of elements from phosphate rock ore to fertilizer 32

and element fractionation directly in phosphate fertilizer

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Considering this overview, the present work aims to apply the BCR protocol to

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evaluate the mobility of potentially toxic elements (As, Cd, Cr, and Pb) and some

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nutrients (P, Ca, Mg, Cu, Fe, Mn, and Zn) in a multi-nutrient mineral fertilizer and a

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raw material (micronutrient mixture) that is added to it, both produced in Brazil.

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This is the first time that the BCR protocol is applied to investigate the mobility

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of a multi-nutrient fertilizer used in crops, and in a raw material used to balance the

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micronutrients composition. The analyses of the raw material allowed the origin of

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potentially toxic elements in the fertilizer to be investigated. Furthermore, X-Ray

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Diffraction (XDR) and Scanning Electron Microscopy in combination with Energy

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Dispersive Spectroscopy (SEM-EDS) analyses were also employed to characterize the

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solid residues from extractions and provide additional information to correlate with

96

fractionation results.

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MATERIAL AND METHODS

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Apparatus. An inductively coupled plasma optical emission spectrometer (ICP OES)

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(iCAP serie-6000, Thermo Fisher Scientific, Cambridge, England), equipped with duo-

102

viewed plasma, charge injection device (CID) detector, Echelle polychromator and a

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radiofrequency source of 27.12 MHz was used for the determination of the total and

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extractable contents of As, Ca, Cd, Cr, Cu, Fe, Mg, Mn, P, Pb, and Zn. The operating

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parameters for the ICP OES are shown in Table 1.

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In order to identify crystalline phases in fertilizer samples and solid residues

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after extractions, an X-ray diffractometer (DRX-Miniflex, Rigaku, Tokyo, Japan) was

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used, which operates at 30 kV and CuKα radiation (1.5418 A). The data were collected

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from 1.5° to 70°, at 2θ rate of 0.02° s-1. A field emission Scanning Electron Microscope

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(SEM), model JSM 7401F (JEOL Ltda., Peabody, Massachusetts, EUA), operating at an

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accelerating voltage of 30.0 kV to 0.1 kV, resolution of 1.0 nm (15 kV) and 1.5 nm (1

112

kV) and maximum magnification of 1,000,000 times was used for the sequential

113

extraction residue analysis.

114

For the total determination of elements, the samples were digested in a

115

microwave oven, operating on a single reaction chamber (SRC) design (model Ultra

116

WAVETM, Milestone, Sorisole, BG, Italy), using nitrogen for cavity pre-pressurization.

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A shaker table, model Q225 M (Quimis, São Paulo, SP, Brazil) was used for solution

118

homogenization and stirring during the extraction procedures. The sequential extraction

119

steps that required heating were carried out in a water bath, model Q226M2 (Quimis). A

120

pHmeter, model DM-20 (Digimed, São Paulo, SP, Brazil), was used to adjust the pH of

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extract solutions. A centrifuge, model Q222TM (Quimis), was used for solid separation

122

in each sequential extraction step.

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Reagents and samples. The stock solutions from Titrisol® standard analytical solutions

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containing 1000 mg L-1 of arsenic (As2O4), calcium (CaCl2), cadmium (CdCl2),

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chromium (CrCl3), copper (CuCl2), iron (FeCl3), magnesium (MgCl2), manganese

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(MnCl2), phosphorus (H3PO4), lead (Pb(NO3)) and zinc (ZnCl2) in acid media, all from

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Merck (Merck, Darmstadt, Germany), were used to prepare reference solutions by

129

appropriate dilution with high-purity deionized water (18.2 MΩ cm), obtained from a

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Milli-Q® water purification system (Millipore, Belford, MA, USA). Nitric acid 65% (w

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v-1), hydrofluoric acid 48% (w v-1), acetic acid glacial 99.85% (w v-1), hydrogen

132

peroxide 30% (w v-1), hydroxylamine hydrochloride, ammonium acetate (Merck) and

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boric acid (Sigma-Aldrich, Saint Louis, MO, USA) were used for sample digestion or to

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prepare the extract solutions.

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A multi-nutrient mineral fertilizer based on phosphate rocks supplemented with

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10% (w w-1) of a micronutrient mixture provided by LANAGRO (Laboratório Nacional

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Agropecuário, Brazil) was used to apply the BCR extractions. This fertilizer is a

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standard used worldwide to supply nutrients for soil dedicated to diverse crops. The

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micronutrient mixture used to prepare this fertilizer was also analyzed. It is a raw

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material concentrated of micronutrients (e.g., B, Co, Cu, Fe, Mn, Mo, Ni and Zn) added

141

to the final composition of fertilizer.

142 143

Microwave-assisted digestion. The total element concentrations were determined using

144

a procedure which was previously published in the literature.2 Masses around 150 mg of

145

fertilizer and micronutrient mixture samples were digested in an Ultra WAVETM

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microwave oven, using a diluted acid mixture of 3 mL of HNO3 + 0.5 mL of HF + 0.2g

147

of H3BO3 + 2.5 mL of H2O, and the following heating program: temperature = 250°C;

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ramp = 20 min and hold = 30 min. This method was also used to digest solid residues

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from the sequential extraction.

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Sequential extraction. For the fractionation of potentially toxic elements (As, Cd, Cr

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and Pb) and nutrients (P, Ca, Mg, Cu, Fe, Mn and Zn), 1 g of mineral fertilizer and

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micronutrient mixture (n=3) were sequentially extracted, following each steps of the

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BCR procedure:18

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(I)

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added to 1 g of samples in a polypropylene tube. Then, the sample remained under

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agitation on a shaker table (250 rpm) for 16 hours at room temperature.

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(II)

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adjusted with HNO3) was added to solid residue from the previous extraction step.

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Again, the sample remained under agitation on a shaker table for 16 hours at room

161

temperature.

162

(III)

163

loosely covered and the sample was digested at room temperature for 1 hour with

164

occasional shaking. Then, it was heated at 85°C in a water bath for 1 hour.

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Subsequently, the tube was uncovered to reduce the volume to less than 3 mL. Again,

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10 mL of hydrogen peroxide were added and sample was heated at 85°C in a water

167

bath; after 1 hour, the tube was uncovered to reduce the volume to 1 mL. Finally, 50 mL

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of 1 mol L-1 ammonium acetate was added and the sample remained under agitation on

169

a shaker table for 16 hours at room temperature.

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(IV)

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regia by ISO 11466 method. However, in this work, the solid residues were transferred

Exchangeable, soluble in weak acid – 40 ml of 0.11 mol L-1 acetic acid was

Reducible – 40 mL of 0.5 mol L-1 hydroxylamine hydrochloride (pH 1.5 -

Oxidizable – 10 mL of hydrogen peroxide was added to the residue, the tube was

Residual – Finally, the BCR protocol proposes the sample digestion with aqua

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to microwave oven vessels and digested by the procedure used for total elemental

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determination.2

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In each step, after extraction, the mixtures were centrifuged (3400 rpm) for 20

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min and supernatants were transferred carefully to other tubes with a pipette. Between

176

the extraction steps, the residual solid was washed with 5 mL of water (shaking 250 rpm

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for 15 min), the mixture was centrifuged and the supernatant discarded. Then, the solid

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washed was reserved for the next extraction step. The extract solutions were diluted and

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analyzed by ICP OES. The reference solutions used for calibrations were prepared in

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each extractor medium in order to minimize the possibility of transport and spectral

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interferences. Furthermore, matrix interference effect was evaluated by addition and

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recovery test of elements in each extract from the sequential extraction procedures.

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In Fig. 1, a workflow diagram shows a graphic overview of experimental procedures.

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X-Ray Diffraction analysis. The XRD analysis was carried out in order to identify

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crystalline structures present in the samples and residues of sequential extractions. Thus,

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it would be possible to evaluate compounds that were not solubilized during each

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fractionation step.

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The residual solid from each BCR fraction were collected (I – Exchangeable; II

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– Reducible; III – Oxidizable), dried in oven at 60°C for 48 hours and homogenized in a

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mortar. Samples were prepared on a glass base and analyzed by XRD. The American

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mineralogist crystal structure database (AMCSD) was used to assign diffractograms

194

signals and identify crystalline compounds present in the samples and those that

195

remained after each extraction step.34

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SEM-EDS analysis. The residual solid of the last stage of the sequential extraction of

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fertilizer (solid of the residual fraction that would be digested in the microwave oven)

199

was analyzed by Scanning Electron Microscopy (SEM) and by Energy Dispersive X-

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Ray Spectrometry (EDS), aiming at the topochemical study of elemental composition of

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particles present in the solid.

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RESULTS AND DISCUSSION

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Total elements concentration. The results of total elements concentration determined

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in fertilizer and micronutrient mixture samples are presented in Table 2. As the multi-

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nutrient fertilizer used in this research is composed of a known proportion of

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micronutrient mixture (10% w w-1), it was possible to estimate the percentage of

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elements that are provided from this raw material and those deriving from other

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unknown sources. For example, As concentrations in fertilizer and in micronutrient

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mixture are 61 mg kg-1 and 75.9 mg kg-1, respectively (Table 2). Whereas this fertilizer

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is composed of 10% (w w-1) of micronutrient mixture, it is possible to estimate that

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around 7.59 mg kg-1 of As is from this raw material, which corresponds to 12% of the

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total As concentration present in multi-nutrient fertilizer sample. Therefore, it is

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possible to infer that the difference of around 53.4 mg kg-1 (88%) of As is from other

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sources of contamination, such as raw materials added to provide macronutrients (e.g.

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phosphate rocks). On the other hand, using the same approach, it is possible to infer that

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the contribution of Cd (88%), Cr (92%) and Pb (121%) to the multi-nutrient fertilizer

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composition are from micronutrient mixture used as raw material. In relation to the

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micronutrients Cu (68%), Fe (68%), Mn (83%) and Zn (88%) it can be confirmed that

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the main source is the micronutrient mixture.

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Elements fractionation by BCR sequential extraction. In Fig. 2 are shown the results

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of elements fractionation by sequential extractions from the fertilizer and micronutrient

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mixture samples. Extracted percentages were calculated based on the total element

225

concentrations (Table 2). Extractions were performed in triplicates and all relative

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standard deviations (standard deviation/average concentration x 100%) were less than

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15%. The addition of known concentrations of elements (As, Ca, Cd, Cr, Cu, Fe, Mg,

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Mn, P, Pb, and Zn) and recovery was carried out for the extract solutions of each step of

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sequential extraction procedure to evaluate interference effects during ICP OES

230

analysis. Good recoveries were obtained for the majority of elements added to the

231

extract of step I (exchangeable and soluble in acetic acid), step II (reducible), step III

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(oxidizable) and step IV (residual), ranging from 80% to 120%.

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Mass balances were calculated considering the concentration (mg kg-1) of the

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elements obtained in each extraction step (I to IV) and compared with the total

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concentration of elements (Table 2). In general, mass balances ranged from 70% to

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119% for both samples, except for Fe (65%), for the multi-nutrient fertilizer. These

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recoveries were fit for the intended purpose, because the sequential fractionation

238

procedure has many stages and can be subject to errors, mainly from analyte losses.

239

Thus, it is possible to carry out a quantitative evaluation of element fractionation and a

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possible correlation with their mobility.

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The sequential extraction results for fertilizer sample (Fig. 2A) show that the

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highest As concentration was extracted in the first step (53%); thus, it is weakly bound

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to the matrix and, consequently, it is more mobile. On the other hand, during

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micronutrient mixture extraction, As was present in reducible and residual fractions

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(Fig. 2B). As already mentioned, 88% of As is possibly derived from sources such as

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phosphate rocks (Table 2); therefore, besides this raw material presents a high As

247

concentration, the As species from this source presents a higher mobility.

248

Apatite, mainly fluorapatite (Ca5(PO4)3F), is the predominant mineral in

249

phosphate rocks, which are used in the production of phosphate fertilizers. These

250

minerals are treated with H2SO4 to increase the solubility of phosphate, a primary

251

nutrient.31, 32 In these minerals, the substitution of PO4-3 for AsO4-3 can naturally occur

252

due to its structural and electronic similarities.35 This information justifies the similarity

253

between the As and P fractionation profiles (Fig. 2A) and their high mobility. In

254

addition, it can be confirmed that As comes from phosphate rocks.

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In Table 2, it is estimated that micronutrient mixture is the main source of Cd, Cr

256

and Pb contamination. The fractionation profiles of Cd and Cr observed for

257

micronutrient mixture were similar to profiles obtained for multi-nutrient fertilizer.

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Whereas Cd was extracted in the first step and presents a higher mobility, no significant

259

fractions of Cr were extracted in any step and almost all Cr remained in solid residue.

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Lead in the micronutrient mixture was predominantly extracted during step II (43%).

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Although a mobile fraction of 18% appears to be low, considering the total

262

concentration (Table 2), it is equivalent to 1290 mg kg-1, thus it is a significant risk of

263

environmental contamination. As Pb contamination can be totally from micronutrient

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mixture, similar fractionation profiles for fertilizer and micronutrient mixture were

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expected (Fig. 2A and 2B); however, the first step, which represents the higher mobile

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fraction, decreases from 18% to 1%. Some studies have demonstrated Pb stabilization in

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soils by phosphorus-rich amendments attributable to the high affinity of Pb for

268

phosphate-based ligands to form Pb phosphate precipitates.36 Thus the high

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concentration of P (8.3% w w-1) in fertilizer could have decreased Pb mobility due to

270

Pb3(PO4)2 precipitation in a weak acid medium (step I).

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Besides contaminant fractionation, some nutrients and micronutrients were also

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investigated in order to evaluate fertilizer quality. In this way, primary (P) and

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secondary (Ca and Mg) nutrients present a great fraction extracted from fertilizer in the

274

first step, with values of 59%, 42%, and 21%, respectively. However, significant

275

concentrations were obtained for reducible and residual fractions. As previously

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mentioned, the micronutrients Cu, Fe, Mn and Zn are mostly provided from

277

micronutrient mixture (Table 2). Iron remained almost completely in the residual

278

fraction in both samples (Fig. 2A and 2B); therefore, the micronutrient mixture

279

demonstrated to be a poor source of this element. Manganese also had no great

280

mobility, as only 11% of this element was extracted from micronutrient mixture in the

281

first step; however, the same fraction obtained for fertilizer increased to 25%.

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Nevertheless, it is not possible to confirm whether this element interacts with fertilizer

283

matrix, improving its solubility, or if this fraction increase is from Mn provided by other

284

sources. On the other hand, Cu and Zn were mostly extracted in first step, thus they

285

present better mobility.

286 287

X-Ray Diffraction analysis. The results of fertilizer and micronutrient mixture samples

288

XRD analysis are shown in Fig. 3A and 3B, respectively. For better visualization of the

289

results, the diffractograms were divided into fragments, presenting only the signals of

290

highest intensity of each crystalline structure identified in the samples. Potassium

291

ammonium hydrogen phosphate (KNH4HPO3), anhydrite (CaSO4), quartz (SiO2),

292

dolomite (CaMg(CO3)2) and magnetite (Fe3O4) structures were identified in fertilizer

293

samples (Fig. 3A), while only quartz and magnetite were found in the micronutrient

294

mixture (Fig. 3B).

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The collected solid residues from sequential extraction were weighed in order to

296

estimate the mass of sample solubilized after each extraction step. During this

297

fractionation procedure, 80% of the original mass of fertilizer had been solubilized in

298

the first extraction step, 92% in the second and 94% in the third. For the micronutrient

299

mixture, the percentage solubilized after each step was 42%, 56% and 58%,

300

respectively. Due to the partial sample solubilization, the remaining insoluble

301

crystalline compounds are more concentrated in the solid residues. Thus, a gradual

302

DRX signal increase for each extraction stages (Steps I, II and III) can be observed (Fig.

303

3A and 3B).

304

Quartz and magnetite structures were identified in both samples and remained

305

present in solid residues of all steps (Fig. 3A). This information is in agreement with

306

sequential extraction results (Fig. 2A and 2B): according to the BCR procedure, it was

307

expected that the iron oxide had been solubilized in step II (reducible fraction);

308

however, it remained insoluble throughout the process.

309

The first step of fractionation aims to extract exchangeable cations and

310

compounds, which are soluble in weak acid. Therefore, carbonates should be also

311

solubilized in this step (step I). However, dolomite was completely solubilized only in

312

step II (reducible fraction). Thus, the acetic acid concentration could not be sufficient,

313

and part of the carbonate would only be solubilized in reducible fraction, which has an

314

extractor solution in a more concentrated strong acid medium.

315

The anhydrite was also identified in the fertilizer sample and, as well as

316

dolomite, was only fully solubilized in the second extraction step, which explains the

317

fraction of 29% of Ca extracted in this step (Fig. 2A). Potassium ammonium hydrogen

318

phosphate, source of primary nutrients (NPK), was solubilized in the first step.

319

Therefore, they have good mobility.

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SEM-EDS analysis. To confirm the composition and non-mobility of some elements

321

present in the fertilizer, a SEM-EDS was attained of the final residue of BCR extraction

322

(Fig. 4A and 4B). The SEM image (Fig. 4A) shows crystalline structures not solubilized

323

after tree steps of sequential extraction. These structures presented different shapes (e.g.

324

spherical and octahedral) and sizes particles, easily identified in the image. The

325

highlighted region indicates where EDS measurements were carried out. The spectrum

326

of this region is shown in Fig. 4B. The EDS of a specific region of SEM revealed the

327

presence of Al, Mg and Si, which can attributed to the occurrence of quartz structure in

328

the final residue. Additionally, the presence of Fe, Mn and Zn associated to this

329

structure confirm the low mobility of these elements, as demonstrated by the BCR

330

extractions (Fig. 2A). These elements could be incorporated into hardly soluble

331

crystalline structures (quartz or aluminosilicate), so they would hardly be leached and

332

solubilized during extractions. This could also be occurring with other elements, such as

333

Cr. Although Cr was not identified in the particle analyzed by EDS, it could also be

334

incorporated into hardly soluble crystalline structures in other particles; therefore, this

335

could be one of the reasons why Cr showed low mobility.

336

The correlating elemental determination of extracts with solid residue analysis

337

by DRX and SEM-EDS shows that not only does the chemical form affect element

338

mobility, but the way in which they are distributed in sample particles also does. An

339

example of this is the new fertilizers produced from nanomaterials, which are

340

synthesized and designed with particle size, structure and shape able to efficiently

341

supply nutrients for plants.37, 38

342

It is important to point out that the mobility of nutrients and contaminants from

343

the fertilizer may change in contact with agricultural soil, because other parameters

344

should be considered, such as soil composition, pH, humidity, presence of organic

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345

matter, microorganism, substances (exudates) secreted by the plants, and climatic

346

conditions. Although the mobility of elements can be affected by the soil, the

347

information obtained by the elements fractionation by BCR procedure was important to

348

understand the real contribution of raw materials to the final composition of the multi-

349

nutrient mineral fertilizer.

350 351

AUTHOR INFORMATION

352 353

Corresponding Author

354

*Phone: +55 11 3091 9104, e-mail: [email protected] (P. V. Oliveira)

355

ORCID ID

356

Pedro V Oliveira

357

https://orcid.org/0000-0003-1483-8288

358 359

ACKNOWLEDGMENTS

360 361

The authors are grateful to the Conselho Nacional de Desenvolvimento

362

Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de

363

São Paulo (FAPESP) for financial support. AMF and PVO also thanks the CNPq for the

364

research opportunities and fellowship provided. The authors express their gratitude to

365

Lanagro for providing samples and to Anacom Científica/Milestone and Nova

366

Analítica/Thermo Scientific for making equipment available to use.

367 368 369

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486

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489 490

21



491

FIGURE CAPTIONS

492 493

Figure 1. Workflow diagram of experimental procedures.

494 495

Figure 2. Percentage of each element using the BCR sequential extraction protocol: (A)

496

for multi-nutrient mineral fertilizer; and (B) for micronutrient mixture raw material used

497

as micronutrients source.

498 499

Figure 3. Diffractograms fragments in signal regions attributed to potassium

500

ammonium hydrogen phosphate (KNH4HPO3), anhydrite (CaSO4), quartz (SiO2),

501

dolomite (CaMg(CO3)2) and magnetite (Fe3O4) structures of fertilizer (A) and

502

micronutrient mixture (B) residues of sequential extractions.

503 504

Figure 4. Scanning Electron Microscopy and Energy Dispersive X-Ray Spectrometry:

505

(A) Residue of the step 3 of BCR protocol, and (B) EDS of the selected area (Operation

506

condition: Accelerating Voltage: 5.0 kV; Magnification of SEM: 30000X).

22


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Table 1. Operational set up for analysis using axial-view inductively coupled plasma optical emission spectrometry

Parameter

Selected condition

Power

1250 W

Nebulizer

Burgener Mira Mist®

Spray chamber

Cyclonic

Plasma gas-flow

12 L min-1

Auxiliary gas-flow

0.6 L min-1

Nebulizer gas-flow

0.5 L min-1

Wavelength (nm)a

As (I) 189.042, Ca (II) 318.128, Cd (II) 226.502, Cr (II) 283.563, Cu (I) 324.754, Fe (II) 259.940, Mg (I) 285.213, Mn (II) 259.373, Ni (I) 341.476, P (I) 177.495, Pb (II) 220.353, Zn (II) 213.856

a

(I) Atomic emission line and (II) ionic emission line

23



Page 24 of 29

Table 2. Total concentrations of elements in multi-nutrient mineral fertilizer and micronutrient mixture raw material, as well as, an estimative of the contribution of the micronutrient mixture to elements concentrations in the fertilizer, based on known proportion of micronutrient mixture (10% w w-1) in the fertilizer Contribution of Element

Fertilizer

Micronutrient mixture

micronutrient mixturea

a

As (mg kg-1)

61 ± 3

75.9 ± 0.8

12%

Cd (mg kg-1)

9.9 ± 0.3

87 ± 2

88%

Cr (mg kg-1)

339 ± 26

3,133 ± 101

92%

Pb (mg kg-1)

583 ± 2

7,050 ± 4

121%

P (% w w-1)

8.3 ± 0.3

0.17 ± 0.01

0%

Ca (% w w-1)

8.7 ± 0.3

4.71 ± 0.04

5%

Mg (% w w-1)

1.17 ± 0.03

1.39 ± 0.01

12%

Cu (% w w-1)

0.24 ± 0.04

1.61 ± 0.05

68%

Fe (% w w-1)

2.11 ± 0.08

14.35 ± 0.01

68%

Mn (% w w-1)

0.66 ± 0.04

5.4 ± 0.2

83%

Zn (% w w-1)

1.35 ± 0.02

11.93 ± 0.01

88%

The estimative of micronutrient mixture contribution on the fertilizer composition.

Based on known proportion of micronutrient mixture (10% w w-1) in the fertilizer

24


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Figure 1

25



Figure 2

26


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Page 27 of 29


Figure 3

27



Figure 4

28


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TOC Graphic

29


Analytical capabilities of BCR protocol to estimate the mobility of

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