Speciation of Selected Heavy Metals in Some Soils of Egypt

Speciation of Selected Heavy Metals in Some

Soils of EgyptR.R. Shahin and M.A. Abdel·Hamid

24 Egypt. J. Soil Sci. 33, No.3. pp. 305·327 (1993)

(7:, \ . Li I '). S'

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Soil Science Department, Faculty ofAgriculture, Cairo

University, Cairo, Egypt.

T he distribution of trace elements among various chemical

forms was studied in sixteen surface soils, representing the

Torrifluvents. Fluvaquents, Calciorthids and Torripsamments in

Egypt. A sequential extraction scheme was used to fractionate Mn,

Zn. Ni, Cr, V, Ti, Al and Pb into mobile, amorphous Fe oxide bound

(AFeOXI. Mn oxide bound (MnOX) and residual (RESI forms.

Among all the studied soils, Torrifluvents were higher in average

total concentrations of most metals. followed by Fluvaquents. while

Calciorthids and Torripsamments were the least.

DTPA extracted fraction of all the investigated metals was the

highest in Torrifluvents, except for Pb, then it decreases in the follo­

wing order:

Torrifluvents > Fluvaquents > Calciorthids :;. Torripsamments

DTP A extractable Mn forms the largest percentage of its total as it

reaches 11% Torrifluvents, then it decreases in the folliwng order:

Mn :;. Zn :;. Pb > Ni :;. V "" Cr :;. Al "" Ti,

AFeOX fraction constituted 25·39% of total Mn and Zn, while it

forms < 5% of total Cr. < 2% of total Ai or Ti,:&25% of total Pb, 18­

40% of total V and 10-24% of total Ni, Alluvial soils contained the

highest AFeOX fraction of these metals, except for V and Ni, compa­

red with calcareous and sandy soils.

MnOX fraction constituted 60·85% of Zn, Ni. Pb, Ti, V and AI.

This indicates that MnOX fraction may be of greater consequence in

the chemistry of these metals in the soils of.Egypt. Both MnOX and

AFeOX fractions are of the same importance in the chemsitry of Mn

in these soils.

RES fractions of Mn, Zn, Ni and V form 2-7% of total metals. Cr,

AI, Ti and Ph associated with RES fraction constituted 23-28%,

18-45%, 22-38%, and 13-20% of total metal, respectively.

Total metals and various forms showed significant correlations

with silt %. clay%, organic matter content and CEC of soils. No signi­

ficant correlations were found with pH and ECe of the soils.

Key Words : Trace elements - Heavy metals - Sequential extrac­

tion - Soil types.

During the last decade. numerous investigations dealing with trace ele­

ments in soils have been conducted in order to assess micronutrient avai­

lability to plants Or pointing out the continuing pollution of soils by

heavy metals,

306 R.R. SHAHIN AND M.A. ABDEL-HAMID

As soils consist of complex mixtures of different organic and inorga­nic materials, the binding mechanisms of heavy metals in soils are mani­fold and vary with composition, reaction and redox potential of the soil.Thus, a metal may found in different species according to whether itbound to various reacting surfaces of soil components with different bon­ding energies.

The use of sequential extraction or fraction of trace elements furni·shes detail information about their origin, mode of occurrence, biologicaland physicochemical availability, mobilization and downward movementin agricultural and polluted soils. Several systems of fractionation havebeen proposed and the fractions usually separated are water soluble,exchangeable, bound 'to carbonate, organic matter, Fe and Mn oxidesand residual mineral fractions (Tessier et aL, 1979; Shuman, 1979 &1985; Levesque & Mathur, 1986; Mathur & Levesque, 1988 and Sigel etal; 1988). The selection of a reagent for extracting a given form of themetal from the soil and the sequence of extraction affect not only the par­titioning of metals in different fractions, but also the total amounts ofmetals in that fraction.

The distribution of selected metals in different fractions varies consi­derably in soils. The objective of this study is elucidate the distributionof some metals among various fractions and the relationships of thesemetals fractions with certain soil porperties. Total metals in soils werealso compared with metal fractions values obtained by sequential extrac­tions.

Material and Methods

The Ap horizons (0-30 cm) were sampled from sixteen Egyptian soils(Fig. 1). The soils were selected to represent most of soil types found inEgypt. Some physical and chemical characteristics along with the soilclassification, using Soil Taxonomy (USDA, 1975), are presented inTable 1. The collected soil samples were air dried, ground and screenedthrough a 2 mm sieve. Particle size distribution was determined follo­wing the International Pipette method (Piper, 1950), electrical conducti­vity (ECe) in soil paste solution extractions (Jackson, 1967), organic ma­tter using the modified Walkely and Black method (Jackson, 1967),cation exchange capacity and exchangeable cations (Gohar, 1954) andCaC03 content using Collin's Calcimeter method (Wright, 1939).

EgyptJ. Soil Sci. 33, No.3 (1993)

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308 R.R. SHAHIN AND M.A. ABDEL-HAMID

A sequential fractionation was used to obtain the following forms ofeach of the studied elements :

A . Mobile fraction (soluble + exchangeable), was extracted by DTPA(Lindsay a~d Norvell, 1978).

TABLE I. Selected soil properties of the studied soils.

Location CEC Particle size distributionpH ECe O.M. CaC03 meql C.S. F.S. Silt Clay

(Soil Taxonomy) dS/m % % l00g % % % %

HAMOUL 7.5 1.9 1.9 1.8 41.6 0.5 16.5 42.5 40.5Vertic Torrifluvents

-,.

ROSSETA 7.6 1.7 2.0 3.9 42.7 8.0 20.0 27.0 45.0Typic Torrifluvents

ZEFTA 7.8 1.1 1.6 2.6 36.5 2.0 21.5 43.0 33.5Typic Torrifluvents

TEL KEBIER 8.1 2.9 1.4 1.7 19.6 45.5 17.5 13.0 22.0Typic Torrifluvents

,BENI·SUEF 7.6 1.2 1.7 2.4 38.9 1.5 22.5 42.0 34.0Typic Torrifluvents

ASWAN 7.6 0.9 0.5 8.7 21.4 12.0 52.0 11.5 25.5Typic Torrifluvents

MANZALA(R) 8.1 6.8 1.4 2.4 40.7 0.5 24.0 31.5 44.0Vertic Fluvaquents

MANZALA (Vl 7.5 29.5 1.9 3.9 44.0 1.0 19.0 30.5 50.0Typic Fluvaquents

BITTER LAKES 7.9 20.9 0.9 2.2 41.9 0.5 24.5 32.0 40.5Typic Fluvaquents

IDKU (Rl 7.9 4.9 1.4 3.2 44.2 0.5 10.0 43.0 46.5Vertic Fluvaquents

IDKU 7.5 5.8 1.8 3.2 41.5 1.0 22.0 33.5 43.5Typic Fluvaquents

MARYUIT 8.0 2.5 1.0 26.3 17.0 6.5 51.0 17.0 25.5Typic Calciorthids

ARISH (CL) 7.9 1.1 0.3 16.0 18.0 1.0 35.0 31.0 33.0Typic Calciorthids

ARISH (C) 7.8 6.3 0.4 50.5 28.4 1.0 18.0 32.0 48.0Typic Calciorthids

SALHIA 7.5 2.6 0.3 2.4 8.0 67.5 14.5 8.5 10.0Typic Torrisamments

ARISH (Sl 7.5 3.4 0.3 16.0 '7.0 50.5 29.5 8.5 11.5Typic Calciorthids

Egypt J. Soil Sci. 33, No.3 (1993)

SPECIA:I'ION OF SELECTED HEAVY METALS 309

B - Immobile fractions :1. amorphous iron oxide (AFeOX) fraction, was extracted using the

Dithionite-Citrate-Bicarbonate (DCB) extractant (Mehra andJackson, 1960),

2. occluded in iron and manganese oxides (MnOX) fraction, wasextracted using HCl extractant (Bakhtar et al; 1987),

3. bond in structure of silicate minerals, residual fraction (RES),was extracted using HF-HCI04 (Tessier et al, 1979).

All procedures were carried out in duplicate. The various extractswere analysed for Mn, Zn, Ni, Cr, V, Ti, AI, and Pb by Inductively Cou­pled Argon Plasma Emission Spectroscopy (lCAP-OES) using pneuma­tic nebulization which offers the distinct advantage of accurate, fastsimultaneous and multi-element analysis. The analysis was conducted. inthe Department of Soil and Environmental Sciences, University of Cali­fornia, Riverside.

Results and DiscussionTotal content of metals

Data presented in Table 2 show that among all the studied soils, Tor­rifluvents have the highest average total concentrations of most metals,followed by Fluvaquents, while Calciorthids and Torripsamments arethe least. This could be attributed to pedogenic differences, in one hand,and to the init¥ differences in soil properties on the otherhand.

It is indicated from Table 2 that the computed average of totalmetals, exception being Zn, in Torrifluvents are higher than the' 'world"average, while Zn content is similar to "world" average. Fluvaquentsshow similar Pb content to "world" average, while total Zn and Mn arewell below the "world'taverage and total Cr, Ni, Ti, V, and AI are higherthan the "world" averages. Calciorthids and Torripsamments- showlower total contents of metals than "world II averages. This could beattributed to the discrepancies in pedogenic environment of each soilgroup of soil Taxonomy. Noteworthy to mention that all metals rangesand computed averages lie within the normal range reported by Bowen(1966) and Barrow and We~ber (1972).

Parameters values reveal that silt and clay contents, organic matterand CEC are the most important soil parameters affecting total metalscontents in the studied soils. Statistical analysis Table 3, show that mostof these metals are significantly correlated to organic matter, CEC, siltand clay contents, exception being for Ti. All metals are negatively signi­ficantly correlated with coarse sand fraction. V, Ti, AL and Pb are negati­vely significantly correlated with CaCOa % in soils. This suggests thatmost of metal contents are associated with clay and silt fraction (Shahin,1989).

Egypt J. Soil Sci. 33. No.3 (1993)

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312 R.R. SHAHIN AND M.A. ABDEIrHAMID

DTPA-extractable metalsThe concentration of metals extracted with DTPA are presented in

Table 4 and Fig. 2 & 3. It is clearly noticed that DTPA extracted frac­tions have the largest percentage of total Mn as it reaches 11% of totalMn in case of Torrifluvents, then it decreases in the folowing order:

order : Mn > Zn > Pb > Ni > V = Cr > AI = Ti% of total: 1-p, 1-4, 1-3, 1, < 1 , <0.05It is worthy to mention that the DTPA extracted fraction of all

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Egypt J. Soil Sci. 33. No.3 (1993)

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SPECIATION OF SELECTED HEAVY METALS 313

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Egypt J. Soil Sci. 33, No.3 (1993)

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SPECIATION OF SELECTED HEAVY METALS 315

Torrifluvents > Fluvaquents > Calciorthids > TorripsammentsFor Pb the extractable amount decreases in the following order:Torripsamments > Torrifluvents = Fluvaquents > Calciorthids

Certain soil properties affected the distribution of metals in DTPAextractable form. It is clearly noticed that DTPA extracted fraction ofMn, Zn, Ni and Al are significantly correlated to silt and clay content inthe soils (Table 5). This is simply because of the adsorption of these ele­ments on the active surfaces of clay and silt sized soil particles. Cr and Tiextracted by DTpA show significant correlation with silt content only,which may be attributed to the enrichment of this fraction with both ele­ments (Shahin, 1989). On the other hand, extracted Pb and V with DTPAdidn't show any correspondence to the variations in clay and silt COn­tents in the studied soils (Table 5).

In addition, DTPA-extractable metals exception being V; Ti and Alare highly and significantly correlated to soil organic matter content, asthe mobile fraction of Mn, Zn and Ni increased by increasing organicmatter percentage. This suggests the presence of a significant part ofthese metals in the studied soils, especially alluvial ones, whereasorgano-metal complexes are adsorbed on active surfaces. Exceptionbeing V, Al and Ti as these elements are more likely to be present in thesoil environment as inorganic forms (Sigel, 1985).

The effect of soil salinity on DTPA-extracted fraction has been alsoinvestigated by comparing virgin and cultivated soils at Manzala andIdku, within the group of Fluvaquents, Results show that the highlysaline virgin soils contain higher DTPA-extracted Mn, Zn and Ni frac­tions than the cultivated ones in both locations. This could be a result ofhigh ionic strength, high redox potential and water logged conditionsprevailing in these virgin soils.

Considering Mn and Zn as micronutrient for plants, Soltanpour andSchwab (1977) considered 0.9 mg/kg DTPA extractable Zn and 1.8mg/kg DTPA extractable Mn to be "low". By these criteria only Salhia(Torripsamments) have low value of DTPA extractable Mn. Seven soils(Manzala (R), Bitter lakes, Idku (V), Maryuit, Arish (CL), Arish (S) andSalhia) were low in DTPA-extractable Zn. However, using the criticallevel (1.15 mglkg) derived by Edlin et al: (1983) nine of the sixteen soilswould likely to be deficient in Zn. These soils represent the Fluvaquents,Calciorthids and Torripsamments. Experimental data using a variety ofcrops would be required before the results can be accepted with highlevel of confidence due to the fact that soil analysis will not be adequateto identify crop and nutrient interaction factors affecting bioavilability.

Egypt J. Soil Sci. 33, No.3 (1993)

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318 R.R. SHAHIN AND M.A. ABDEL·HAMID

Dithionite-citrate-bicarbonate (DCB) extractable metalsIn the present work, sodium dithionite-citrate-bicarbonate (DCB)

extractant was used to give the metals occluded in amorphous iron oxi­des (AFeOX). Data presented in Table 6 and Fig. 2&3 show that Mnassociated with AFeOX fraction constituted 37-39% of total Mn of eachsoil group. The average Zn content associated with AFeOX fractionconstituted 25 to 32% of total Zn in the studied soils. Pb extracted withDCB constituted 25% for alluvial soils and only 3-5% for Claciorthidsand Torripsamments. Data also reveal that 4-5% of the total Crt < 2% oftotal Al orland Ti are extracted by DCB. This indicates that a significantamount of Mn, Zn and Pb is occluded in amorphous iron oxides (AFeOX)fraction. A relative small fraction of other metals (i.e. Cr, Aland Ti) couldbe occluded and/or adsorbed on the surfaces of free oxides and clay parti­cles. It is also found that alluvial soils (Torrifluvents and Fluvaquents)contain the highest DCB-extractable fraction of these elements compa­red to both Claciorthidsand Torripsamments. This could be attributedto the presence of higher contents of amorphous inorganic materials inalluvial soils compared with other soil types (El Abaseri, 1974; Abdel­Hamid, 1979; Shahin et al; 1982). Exceptions being recorded for Ni andV. Data reveal that V associated with AFeOX fraction constituted18-24% of total V, exception Torripsamments. Torripsamments showhigher V associated with AFeOX fraction, as it reached 40% of total V.Ni associated with AFeOX fraction constituted 10% and 24% of total Nifor alluvial Calciorthids and Torripsamments, respectively. This indica­tes that Ni in calcareous, and sandy soils is more associated with freeiron oxides than in alluvial soils.

The statistical analyses (Table 7) show that metals associated withAFeOX fraction, exception being Zn, are significantly related primarilyto silt, CEC and organic matter content of the studied soils. Mn, Ni andAl extracted with DCB are significantly correlated with clay content.

Hydrochloric Acid (Hel) extractable metals

After extraction with DCB, the samples under investigation havebeen sequentially extracted with HCl to obtain the metals incorporatedin crystalline iron and manganese oxides (MnOX) fraction. Data presen­ted in Table 8 and Fig. 2 and 3 show that MnOX fractions of all investi­gated elements were higher than AFeOX fraction. The MnOX fractionrepresent 45·55% of total Mn, 60-85 of total Zn, 65-85% of total Ni, 65­75% of total Cr, 47-77% of totalPb, 60-79% of total V. 45-82% of total Aland 61-78% of total Ti, This indicates that the majority of these metalsare present mostly in crystalline mineral forms in the different soilgroups. Among the studied soils, Torrifluvents and Fluvaquents showthe highest HCl extracted metal fractions; except for Mn and Pb. This ismay bedue to their differences in pedogensis and mineralogical composi-

EgyptJ. Soil Sci. 33, No.3 (19931

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SPECIATION OF SELECTED HEAVY METALS 321

tion. Mn and Ph seemed to be present in both AFeOX and MnOx frac­tions with relatively similar percentages. especially in alluvial soils, aspreviously mentioned.

Statistically, significant correlations are verified between MnOXfraction of all the studied elements and clay, silt and organic matter con­tents as well as CEC (Table 9). This finding again confirmed the con­gruent dissolution of these elements from soil components by HCI. as astrong extractant. However, MnOX fraction expresses the metal contentthat slowly transform to labile pool along with the other metal transfor­mation processes performed in the soiL I t is worthy to notice that DCBand HCI extracted Ti and Al are negatively significant correlated toCaC03 content which confirmed the presence of these elements mainly inthe framework structure of silicates (Tables 7 and 9).Hydrofluoric acid (HF) extractable metals

Data presented in Table 10 and Fig. 2 and 3 show that AI, Ti, Cr, andPb are predominated in the residual soil material as a result of sequentialextractions. This indicates the presence of these elements in the moststable soil minerals. The Residual (RES) fraction of Cr constituted 23­28% of all studied soils. The RES fraction of AI, Ti and Pb from the allu­vial soils are significantly lower (18,22 and 13%, respectively) than thoseof sandy and calcareous soils (45, 38 and 20%, respectively). This couldbe attributed to the dominance of secondary minerals (i.e. clay minerals)with low and medium stability to HCI in alluvial soils. while highly sta­ble minerals (i.e. most of primary minerals) predominates sandy soils.Therefore. considerable amounts of structure Al and Ti extracted withHCI resulting in higher amounts of these metals in MnOX fraction. Thehigh percentages of Cr and Pb found in the RES fractions could beexplained by Sposito (1983) mentioned that Cr found as isomorphoussubstitution for Fe and Al in spinel group and illitic group minerals, whe­reas Pb is found as isomorphous substitution for K in feldspars and micaand for Ca in feldspars, pyroxenes, amphiboles and carbonates. On theother hand, very low amounts of Mn, Zn, Ni and V are remained (2-7%) inRES fractions of all the studied soil samples.

Statistical analyses (Table 11), show significant correlations bet­ween AI, Ti, Pb and Cr associated with RES fraction and both clay andsilt contents.

In conclusion, it could be said that MnOX fraction may be of higherconsequence than AFeOX fraction in Zn, Ni, Cr, Ti, Pb, V and Al che­mistry in the studied soils. AFeOX fractions play the second importantrole in the chemistry of Zn and V, with greater importance in Torripsam­merits and Calciorthids, AFeOX fractions play an important role in thechemistry of Ni in calcareous and sandy soils, while the role of Pbappears in the alluvial soils. Both MnOX and AFeOX fraction are of thesame importance in the chemistry of Mn in the studied soils.

Egypt J. Soil Sci. 33, NO.3 (1993)

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SPECIATION OF SELECTED HEAVY METALS 325

References

Abdel-llamid, M. A, (19791 Study on distribution of day minerals as a result of migrationof clays with water percolation in some salt-affected soils, Egypt, MSc. Thesis,Faculty of Agriculture. Cairo University (19791.

Bakhtar, D., Bradford G.R. and Land, L.J. (19871 Dissolution of soils and geologic mate­rial for total elemental analysis by ICAP/or AAS. Workshop on Agricultural Methodsfor Selenium, other elements and on Quality control/Quality Assurance". Sponsoredby U.S. salinity? Drainage Task Force. March 24-25, 1987, Sacramento, CA, USA.

Berrow, M.L. and Webber. J. U9721 Trace elements in sewage sludges. Journal of theScience of Food and Agriculture, 23, 90.

Bowen, H.J.M. (19791 "Environmental Chemistry ofElements" Academic Press, London,U.K.

Bowen. H.J.M. (19661 "Trace Elements in Biochemistry': Academic Press. London. NewYork.

Davies, RE. and Jones. L.H.P. (19881 Micronutrient and toxic elements. Pages 780-814in A. Wild, ed. Russell's "Soil Conditions and Plant Growth." 11th ed. Longman. Har­low. U.K.

Edlin, V.M.; KaramaDos. R.E. and and Halstead, E.H. U9831 Evaluation of soil extractantsfor determining Zn and Cu deficiengy in Saskatchewan soils". Commun: Soil; Sci. PlantAnaL 14, 1167.

EI-Abaseri, M.A. (19741 A comparative mineralogical study of Burullus Lake and sou'them adjacent soils. Ph.D. Thesis Faculty of Agriculture. Cairo University.

Gohar, A.A.I. (19541 The influence of exchangeable cations on soil properties of Egyptiansoils M.Sc. Thesis. Fac. Agric. Cairo University.

Jackson, M.L. (19671. "Soil Chemical Analysis" Prentice Hall of India. Private. Ltd. NewDelhi.

Levesque, M. and Mathur, S.P ..(19861 Soil tests for copper, iron, manganese and zinc inHistosols; 1. The influence of soil properties, iron. manganese and zinc on the leveland distribution of copper. Soil Sci. 142. 153.

Lindsay, W.L. and Norvell, W.A. (19781 Development of a DTAP soil test for zinc. iron.manganese and copper. Soil Sci. Soc. Am. J. 42.421.

Mathur. S.P. and M. Levesque (19881 Soil tests for copper. iron. manganese and zinc inHistosols: 2. The distribution of iron and manganese in sequential extracts. Soil Sci.145.

Mehra. O'-P. and Jackson. M.L. (19601 Iron oxide removal from soils and clays by adithionite-oitrate system buffered with sodium bicarbonate ". Clays & Clay Miner. 7,317.

Norrish, K. (19751 "The geochemistry and mineralogy of trace elements. " Pages 55·81 inD.J.D. Nicholas and A.R. Egan, eds, Trace Elements in Soil-Plant-Animal System.Academic Press, New York. N.Y.

Piper. C.S. (19501 Soil and Plant Analysis. Inter. Sci. Publishers. Inc.• New York.

EgyptJ. Soil Sci. 33, No.3 (19931

326 R.R. SHAHIN AND M.A. ABDEL-HAMID

Shahin, R.R. U9891 Distribution of selected trace and major elements in some soils ofEgypt as related. to their characteristics. Bgypt. J. AppL Sci; 4 (41, 301.

Shahin, R.R.; Zaghloul, K.F.; Wahdan, A.A. and Shakwky, M.E. (19821 Effect of amor­phous materials-clay minerals association on surface reactivity of some soil clays.Res. Bull: No. 1906, Fac. of Agric. Ain Shams Unit!.

Shuman, L.M. U9851 "Fractionation method for soil micro-elements" Soil Sci. 140,11-12.

Shuman, L.M. (19791 "Zinc, manganese and copper in fractions." Soil Sci. 127,10.

Sigel, H. 119851, "Metal Ions in Biological Systems" Copyright by Marcel Dekker, Inc.N.Y.-

Soil Survey Staff (19751 "Soil Taxonomy, a basic system of soil classification of makingand interpreting soil survey" Soil Conservation Service, USSA, Handbook No.436.

Soltanpour, P.N. and Schwab, A.P. (1917) "A new soil test for simultaneous extraction ofmacro and micro-nutrients in alkaline soils." Commun. Soil Sci. Plant AnaL 8, 195.

Sposito, G. (1983) In Applied Environmental Geochemistry (I. Thornton, ed.l, AcademicPress, London, Chap. 5.

Tessier, A.,CampbeU, P.G.C. and Bi8sion, M. U979) "Sequential extraction procedure forspeciation ofparticulate trace metals. " Anal Chern. 51,844.

Wright, C.H. (19391 "Soil Analysis" Thomas Murby and Co., London.

Egypt. J. Soil Sci. 33, No.3 pp.

..

I

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SPECIATION OF SELECTED HEAVY METALS 327

~ • ~ • jAWJ 4J11i'~~J \.o;aJ

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Egypt. J. son Sci. 33, No.3 (1993)