Contamination and spatial distribution of heavy metals in topsoil surrounding a mega cement factory

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Contamination and spatial distribution of heavy metals in topsoil

surrounding a mega cement factory

Clement

Oluseye

Ogunkunle,

Paul

Ojo

Fatoba

ABSTRACT

ThisstudyassessedthelevelofcontaminationofthetopsoilbyPb,Cu,Cr,CdandZnandthespatialdistribution oftheseheavymetalsaroundacementfactory.Thirty–eightcompositesoilsampleswerecollectedaroundthe cementfactoryandsubjectedtonitric–perchloricaciddigestion.Totalmetalcontentsofthesoilweredetermined byflameatomicabsorptionspectrophotometry(FAAS)andthedatageneratedwereanalyzedstatistically.Spatial mappingofthedistributionofheavymetalswasdonethroughtheuseofInverseDistanceWeightedtechnique (IDW)ofArcGIS10.TheresultsshowedthatthecontaminationdomainofCdwasintheextremedomainwhilePb andCulevelsinthesoilwereinthesevereandmoderatecontaminationdomains.ZnandCrposednopotential environmentalhazardbecauseoftheirlowlevelinthesoil.ThespatialmappingoftheheavymetalsindicatedPb andCuenrichmentofthesoilnotonlytocomefromcementproductionactivitiesbutalsofromvehicular activitieswhileCdenrichmentofthesoilwasmainlyfromthecementproduction.MappingofZnandCr distributionshowedthattheirenrichmentsinthesoilwerefromcementproductionactivities.Fromthese findings,itishighlyrecommendedthatenvironmentalauditingofthecementproductionlinebecarriedoutto reducethereleaseofpollutants.Itisalsoimportantthatremediationactivitiesbecarriedoutonthesoilto reducethelevelsofCd,PbandCutoavertpotentialecologicaldisasters.

Keywords:Cementfactory,contamination,heavymetals,spatialmapping,cementpollution

CorrespondingAuthor:

Clement Oluseye Ogunkunle

:+234Ͳ806Ͳ2176518 :ogunkunle.co@unilorin.edu.ng seyeogunkunle@yahoo.com

1.

Introduction

Soilhasbeenrecognizedasthemajorsinkforanthropogenic

heavymetaldepositionthroughvariouspathways(Harrisonetal.,

1981;Lietal.,2001;Al–KhashmanandShawabkeh,2006;Rashed,

2010;Guoetal.,2012).Thecontaminationofsoilbyheavymetals

canbeproblematiconseverallevelsbecausetheydonotdegrade

biologically(Emmanueletal.,2009)andthisalwaysresultin

severalsoildisfunctionsleadingtoconcernsabouttheenvironͲ

mentalquality.Metalcontaminatedsoilposesriskstohumansand

animalsthroughingestionofplantsthathavebioaccumulatedtoxic

metalsfromcontaminatedsoil(Turner,2009).Duetothehazards

posedbyheavymetalsinsoil,determinationoftheirlevelsinthe

soilisanecessaryindicatorshowinganthropogenicinputinthe

environment(Mantaetal.,2002;Addoetal.,2012;Guoetal.,

2012).Italsoassistsinthedevelopmentofremediationactivities

andpolicies.Thisisduetothefactthatcontributionofheavy

metalstoenvironmentalproblemsfromindustries,miningand

allied routes were investigated in many studies recently

(Ndiokwere,1984;Addoetal.,2012).

Cementproductionisanimportantemissionsourceofheavy

metalssuchasCd,Cr,Cu,PbandZn(Adejumoetal.,1994;

Schuhmacheretal.,2004;Al–KhashmanandShawabkeh,2006;

Isiklietal.,2006).Theseheavymetalsaredepositedintosoilat

variousdistances(Schuhmacheretal.,2009)dependingonwind

velocityandparticlesize(CPCB,2007)throughcementdustsand

stackfumes.Themajorityofheavymetalsincementdustoriginate

fromrawmaterials.AsAchternboschetal.(2003)reportedthat

typicalcementrawmaterialscontain25mg/kgofCr,21mg/kgof

Cu,20mg/kgofPband53mg/kgofZnandabout50%ofthetotal

Cd, Cuand Zn load in cement areintroduced throughraw

materials.Majorityofemittedheavymetalsareknowntobetoxic

tohumansandplants,evenatlowconcentrations(Kabata–Pendias

andMukherjee,2007)withverylargesetofhealthconsequences

fromexposuretoitssoilcontaminationdependingonpollutant

type/species, pathway of exposure and vulnerability of the

exposedpopulation(eitherchildren,adultsoraged)(Adekolaet

al.,2012).Therefore,themainobjectivesofthisresearchwere(i)

todeterminethelevelofheavymetalcontaminationand,(ii)

analyzethespatialvariationofheavymetalsinthesurrounding

topsoiloftheLafarge–CementWAPCOfactory,SWNigeria.The

studywascarriedoutinthewetseasonsoftheyear2011and

2012inSagamu,alocalsettlementsouthwesternNigeria.

2.

Materials

and

Methods

2.1.Studyarea

ThestudyareaistheimmediateenvironmentoftheLafarge– CementWAPCO(formerlyWestAfricanPortlandCement)whichis

situatedinSagamu,southwestNigeria(6°50'7°00'N;3°45'4°00'E)

(Figure1).ThefactoryisthesecondworksofLafarge–Cement

WAPCOinNigeriaandlocated72kmsoutheastofIbadan(largest

cityinWestAfrica)and67kmnorthwestofLagos(Africa’ssecond

mostpopulouscity).Thefactorywasestablished,commissioned

andbecamefullyoperationalin1978withthepresentproduction

capacityof900000tonnes/year(LafargeCementWAPCOPLC,

2011).Theareastandsonalow–lyinggentundulatingterrainwith

altituderangingbetween30and61mabovesealevel.Theareais

characterizedby high annual temperature,high rainfall,high

classifiedashumidtropicalregion(Akanni,1992).Thesoiltypeof

ShagamuisFerralitic(Aweto,1981)andFerruginous(Ilalokhoinet

al,2013).Theclimateisclassifiedashumidtropicalclimaticzone

(Adamson,1996)andcontrolledbytheTropicalMaritimeand

TropicalContinentalairmasses(Ilalokhoinetal,2013).Themean

annualrainfallofShagamufor2012was1100mm(NIMET,2012).

ThegeologyofShagamucomprisesofsedimentaryrockswhich

consistsofAbeokutaformation(Adegoke,1969).Itisreportedto

behighly fossiliferous andconsists of depositsoflimestone

(GbadeboandBankole,2007),sandwithsandstone,siltstone,clay,

mudstoneandshaleinterbed.AccordingtoAgbaje(2009),the

basalconglomerateofAbeokutaformationhaspoorlyrounded

quartzpebbleswithasilicifiedandferruginoussandstonematrix.

TheprevailingwinddirectionwasSouthwesterlyattheperiodof

study(wetseasonperiod–June–October)whiletheprevailingwind

speedrangedrangebetween2.52to3.55m/sandinthedry

season.Theprevailingwinddirectioninthedryseason(November

toMarch)isNortheasterly.

2.2.Samplingandchemicalanalysis

Samplingwascarriedoutinthewetseasonsof2011and2012

intheareasurroundingthefactoryexcludingthenorthernpartof

thefactorybecauseofthepresenceofswamps.Apartofthedata

collectedin2011hasbeenreportedinOgunkunleandFatoba

(2013).Atotalof38compositetopsoilsampleswerecollectedin

the west, south and the east parts of the factory. Twenty

compositesampleswerecollectedin2011whiletheremaining18

compositesampleswerecollectedin2012,bothsamplingsinthe

wetseason(AugustandSeptember).Sixteencompositesamples

werecollectedinthewest,twelvecompositesamplesinthesouth

whiletensampleswerecollectedintheeast.Ateverysampling

pointcoordinatesweretakenbyahand–heldGPS(Garmin2H).

Threesubsampleswerecollectedatthedepthof0–15cmwithin

10mradiusofapointusingasoilauger.Thesampleswerebulked

togethertoobtainacompositesampleandrecordedagainstthe

coordinateposition.Thesoilsamplescollectedwereplacedin

polyethylene bags, properly labeled and transported to the

laboratory.Beforechemicalanalysisinthelaboratory,thesoil

sampleswereair–dried,sievedthrougha2–mmsievemeshto

removecoarsematerialanddebris,andpulverizedintopowder.

ThepHwasdeterminedinasoilsolution(1:2.5)usingaglass

electrodepHmeter (PHC–3Cmodel)andtheorganicmatter

contentwasdeterminedusingignitionmethodofPeltolaand

Astrom(2003)andReddyetal.(2009)basedon1gofthesoil

sample.Onegramofthepulverizedsamplewasdigestedin10mL

ofHNO3(70%SigmaAldrich,Germany)and5mLofHCLO4(70%

SigmaAldrich,Germany)accordingtoJiangetal.(2011)onan

electrichotplate.Digestioncontinueduntilfumesturnedtowhite

which indicatedcompletedigestionoforganicmatter inthe

sample.DigestedsamplewasfilteredusingWhatmanNo.42filter

paperintoa–250mLbeakeranddilutedwithdeionizedwaterto

25mL.LevelsofPb,Cu,CrandZninthedigestedsampleswith

blanksofthereagentsweredeterminedusingFAAS(BulkScientific

210VGPandPerkinElmerAAnalyst200).DetectionlimitsforBulk

Scientific210VGPusedwere0.08mg/L,0.005mg/L,0.04mg/L,

and0.005mg/LwhiledetectionlimitsforVarianAAnalyst200

were0.18mg/L,0.025mg/L,0.018mg/Land0.006mg/LforPb,

Cu,CrandZnrespectively.Duplicatesampleanalysisandsoil

standardreferencematerial193BGCOD310Awereemployedto

checktheaccuracyofanalysis.Referencematerial193BGCOD

310Awassubjectedtothesamewetdigestionateverytenth

digestionofthesoilsamples.Theamountofmetalrecoveredin

mg/kgwasdeterminedaccordinglyusingtheFAAS.Therecovery

percentage wasdetermined bydividing the recoveredmetal

contentofthereferencematerialdigestedbythecertifiedamount

multipliedby100.Calibrationforeachelementwasdoneusing

seriesofworkingstandardsolutions(CPIInternational,USA)and

calibrationgraphwithcorrelationcoefficient(r2)>0.999.

2.3.Dataanalysis

DataweresubjectedtoAnalysisofVariance(ANOVA)and

significantmeanswereseparatedbyDuncanMultipleTestRange

(Al–KhashmanandShawabkeh,2006) at 5%probabilitylevel.

SpearmanCorrelationanalysiswasalsoemployedtodetermine

therelationshipsexistingamongtheheavymetals.Contamination

levelsofthestudiedheavymetalsweredeterminedaccordingto

thefollowingequation:

CFi=Ci/Cref (1)

where,CFiisthecontaminationfactor/index,Ciisthemetal

concentrationsateachsamplingpoint,andCrefistheevaluation

criterionofthemetal(Hakanson,1980).Theevaluationcriteriain

Equation(1)arethepermissiblelimitsofheavymetals(Pb–

70mg/kg,Cu–63mg/kg,Cr–64mg/kg,Cd–1.4mg/kgandZn–

200mg/kg) for soil by CCME (2007). CF<1 indicates no

contamination,CF=1–2suspectedcontamination,CF=2–3.5slight

contamination, CF=3.5–8 moderate contamination, CF=8–27

severecontamination,CF>27extremecontamination(Gonzalez– Miqueoetal.,2010).

Geo–statisticsinterpolationandmappingwascarriedthrough

InverseDistanceWeighted(IDW)techniquebyusingArcGIS10

[Environmental System Research Institute (ESRI), Redlands,

Canada].Thismethodassumesthattheinfluenceofthevariable

beingmappeddecreaseswithdistancefromitssampledlocation

andreliesmainlyontheinverseofthedistanceraisedtoamatheͲ

maticalpowerwhichcontrolsthesignificanceofknownpointson

theinterpolatedvaluesbasedontheirdistancefromtheoutput

point(WatsonandPhilip,1985).

3.

Results

and

Discussion

3.1.Heavymetallevelsofthetopsoilaroundthecementfactory

RecoveryrateofthereferencematerialanalyzedbyFAASBulk

scientific210VGPrangedfrom96%to112%whiletherecovery

rateofreferencematerialanalyzedbyVarianAAnalyst200ranged

from83.8%to110.8%.

Table1showedtherangeofvariationanddescriptivestatisͲ

ticsforthedistributionofheavymetalconcentrationsinthesoil.

ThepHofthesoilwasslightlyacidic,withrangesfrom5.1to8.5.

Organicmattercontentsofthesoilrangedfrom1.3%to15.0%

withthemeanvalueof5.6,whichindicatedthatthesoilwasrich

in organic matter content(Table1).The descriptivestatistics

showedthatallthemetalsexceptZnwerenormallydistributedby

thelowvaluesoftheskewness.ThisisinagreementwithReimann

andFilzmoser(2000),reportedthatgeochemicaldataarebimodal

andnon–normal.PbandCuhadhighconcentrations(469.2and

404.4mg/kgrespectively)withhighvariations.Cdratednextinsoil

content(298.9mg/kg)whileCrandZnsoilcontentswere186.2

and 168.1mg/kg respectively(Table1).This high Pb and Cu

contentofthesoilprincipallycouldhavecomefromthesynergistic

depositioneffectsfromcementproductionoperationsandtraffic

activities.PbandCuareknowntobepartofheavymetalsreleased

duringcementproduction(CarrerasandPignata,2002;Banatet

al., 2005; Kakareka and Kukharchyk, 2011). However, the

substantiallyhighconcentrationscouldbeattributedtoother

sourceslikethereleasefromvehicularactivities(Farmakiand

Thomaidis,2008;Wangetal.,2009)sincethefactoryislocated

closetoanintersectionofseveralmajorroadswhichwouldhave

contributedtothehighconcentrationsreported.Thesignificantly

highsoilcontentsofPbandCuinthisstudywasconsistentwith

thefindingsofAl–KhashmanandShawabkeh(2006),Bietal.

(2006),andWuetal.(2010)butcontrarytothefindingsofAdekola

etal.(2012)onasimilarcementfactoryinnorth–centralNigeria.

Thisinconsistencyinthefindingscanberelatedtotheshortperiod

ofproductionactivitiesofthefacilitystudiedbyAdekolaetal.

(2012).Significant(p<0.01)negativecorrelationsexistedbetween

thesoilpHandsoilcontentsofPb,CuandCd(r=–0.614,–0.529

and–0.685,respectively).ThisshowedthatpHofthesoilseemed

tobeamajorfactoraffectingtheamountsofPb,CuandCdinthe

soil;anyincreaseinthesoilpHreducesthesoilcontentofthese

metals.Thesignificantpositivecorrelation(0.482)betweenPband

Cucontentsofthesoilaroundthefactory(p<0.01)alsosignifies

thepossiblecommonpollutionsourceofthetwoheavymetals

(Table2).ThepresenceofCdinthesoilcouldpartlybelinkedto

theemissionsfromcementproductiondue to itssignificant

correlationswithPbandCu(r=0.554and0.662,respectively,

p<0.01)(Table2).Cdhasbeenreportedtobereleasedasaresult

oftherawmaterialsusedinthecementproduction(Scoullos,

2001) but usually in low concentrations (Al–Khashman and

Shawabkeh,2006).Butitssignificantlyhighconcentrationinthe

soilcouldnotevidentlybelinkedtoanthropogenicactivitiesofthe

cementfactory.Theonlyexplanationforthehighsoilcontentof

becausethesoilisferralitic.Olaide(1987)reportedthatsubstantial

amountsofPbandCdarereleasedduringferraliticweathering

throughoxidationandleaching.CrandZnarepresentinthesoilin

concentrationsthatareaboveothersimilarstudies(Al–Khashman

andShawabkeh,2006;MandalandVoutchkov,2011).Observed

highconcentrationsinthepresentstudyisattributedtothelong

yearsofoperationofthisfacilityasithasbeeninoperationfor

morethanthreedecadesandisstillinfulloperation.Therewasno

significantcorrelationbetweenCrandZnandtheirsoilcontents

arestatisticallythesame(p<0.05).ThissuggeststhatCrandZnare

notfromthesamepollutionsource,althoughtheyareboth

supposedpollutantsfromindustrialactivitieslikecementproducͲ

tion(ATSDR,2000;CarrerasandPignata,2002;Banatetal.,2005).

ItisalsoworthytonotethatCrisametalindicatinggeogenicload

asitisreleasedfromparentrocks(Facchinellietal.,2001;Takacet

al.,2009).Therefore,rapidweatheringofparentrockscouldhave

contributedtothehighCrloadtothesoilaroundthefactory.But

mechanicalabrasionofvehicleswiththeassociatedtirewearsmay

haveaddedtotherelativelyhighaccumulationofZnparticlesfrom

thecementdustemissionsinthesoil(CarrerasandPignata,2002;

Al–Khashman,2004).

ComparisonofthelevelsofPb,Cu,Cr,CdandZninsoiltothe

recommendedlimitsoftheCanadianCouncilforMinistersofthe

EnvironmentshowedthatconcentrationsofPb,Cu,CrandCdin

thesoilwerebeyondtheacceptedlimitsinagriculturallands.

Considering the target values for remediation developed by

NigerianDepartmentofPetroleumResources(DPR),Pb,Cu,Crand

Cdwerealsoabovethetargetvalues(Table1).

Distributionofheavymetalconcentrationsinsoilaccordingto

theaxesarepresentedinFigure2.Nosampleswerecollectedat

thenorthduetothepresenceofswamp.ThepHofsoilwasslightly

acidicinallthestudiedaxes(east,westandsouthaxes)ofthe

cementfactorywithoutanysignificantdifference(p<0.05)whereas

thesoilshowedhighfertilityintheeastaxiswiththepattern:

southчwestчeast(Figure2aand2b).

Nosignificantdifference(p<0.05)wasobservedinthemean

Pb,Cu,CrandCdconcentrationsofthesoilintheeast,westand

southaxes(Figures2c–2f).Thisshowsthatprobablythesoilin

eachofthecardinaldirectionsreceivedthesimilaramountof

pollutantdeposition.Thereportedmetalconcentrationsinthesoil

werehigherthanthefindingsofAddoetal.(2012)wherehighconͲ

centrationsofPb,Cu,CrandZnwereobservedatthesoutheastof

DiamondcementfactoryinGhana.MeanconcentrationsofZnin

thesoiloftheeastandthewestwerethestatisticallysamebut

significantlyhigherthanthesoilcontentofthesouth(p<0.05)

(Figure2g).Thisisbecausethewestaxisofthefactoryiswherethe

productionactivitiesarecarriedout(OgunkunleandFatoba,2013)

andcoupledwithdifferentvehicularactivitiesduetotheseveral

intersectionsofroadsnetworksatthewesternend.Gbadeboand

Bankole(2007)alsoreportedhighconcentrationsofZnintheair

samplesanddustofthewesternendofthefactory.Theeastern

endisafallowlandofpreviousquarryactivitiesbutonewould

haveexpectedhigherZnconcentrationinsoilofthesouthernaxis

thataccommodatethepresentquarrywhereactiveminingisbeing

carriedout.

Table1.Descriptivestatisticsoftotalmetalcontents(mg/kg)ofthesoilofthestudyarea

Metal n Minimum Maximum Mean SD Skewness Kurtosis Referencelimitsc

Targetvalued pH 38 5.1 8.5 6.5 1.1 0.650 –0.721 NA NA O.M(%)b 38 1.3 15.0 5.6 3.1 1.284 1.793 NA NA Pb(mg/kg) 38 99.8 992.1 469.2a 291.1 0.436 –1.240 70 35 Cu(mg/kg) 38 41.4 999.2 404.4a 313.7 0.768 –1.115 63 0.30 Cr(mg/kg) 38 18.8 362.1 186.2a 90.0 0.074 –0.889 64 20 Cd(mg/kg) 38 4.2 962.1 298.9a 326.0 0.491 –1.472 1.4 100 Zn(mg/kg) 38 56.1 509.2 168.1a 109.9 1.755 2.438 200 a valueswithdifferentletterswithinthesamecolumnaresignificantlydifferentatP<0.05 b referstoorganicmattercontent;valueswithdifferentletterswithinthesamecolumnaresignificantlydifferentatp<0.05 c CCME(2007) d DPRͲEGASPIN(2002)

Table2.Spearman'scorrelationcoefficientsamongheavymetalsinthetopsoil

Correlations pH OM Pb Cu Cr Cd Zn pH CorrelationCoefficient 1.000 Sig.(2–tailed) OM CorrelationCoefficient 0.450 a 1.000 Sig.(2–tailed) 0.005 Pb CorrelationCoefficient –0.614 a –0.212 1.000 Sig.(2–tailed) 0.000 0.201 Cu CorrelationCoefficient –0.529 a –0.264 0.482a 1.000 Sig.(2–tailed) 0.001 0.110 0.002 Cr CorrelationCoefficient 0.211 0.167 –0.232 –0.540 a 1.000 Sig.(2–tailed) 0.205 0.316 0.160 0.000 Cd CorrelationCoefficient –0.685 a –0.367b 0.554a 0.662a –0.383b 1.000 Sig.(2–tailed) 0.000 0.023 0.000 0.000 0.018 Zn CorrelationCoefficient –0.029 0.026 –0.047 –0.034 –0.152 0.099 1.000 Sig.(2–tailed) 0.865 0.877 0.779 0.840 0.363 0.555 a Correlationissignificantatthe0.01level(2–tailed). b Correlationissignificantatthe0.05level(2–tailed).

Figure2.Meanvaluesof(a)pH,(b)organicmattercontent,(c)Pb,(d)Cu,(e)Cr,(f)Cdand(g)Znatvariousaxessurroundingthecementfactory.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

3.2.Contaminationlevelsofthesoilbyheavymetalsaroundthe

cementfactory

PercentagecontaminationdomainofPb,Cu,Cr,CdandZn

whichistheratiooffrequencyofeachcontaminationdomainand

totalfrequencyofalldomainsmultipliedby100arepresentedin

Figure3.LargestcontaminationdomainsforPbaresevereand

moderatecontaminationthattook37%eachofallthesample

locationswhilesuspectedandslightlycontaminationdomainsare

13%each(Figure3a).ThesamepatternisalsoevidentforCu

contaminationofthesoilaroundthecementfactory;largest

percentageofdomainwasalsorecordedsevereandmoderate

contaminations(32%and34%respectively)(Figure3b).Thisisan

evidenceofthehighpollutionstatusofthesoilaroundthecement

factorybyPbandCuandthereisneedforremediationactions.Cr

posedlittlepollutionstatustothesoilbecauselargerpercentage

of the contamination domain was recorded for slightly and

suspectedcontamination(40%and26%respectively)(Figure3c).

ThisimpliesthatCrcontentinthesoilposelittleconcernfor

remediationofthesurroundingofthefactory.PercentagecontamͲ

inationdomainsofCdinallthesamplinglocationsshowedthat

extremecontamination(55%)doubledtheseverecontamination

levelandtripledthemoderatecontaminationlevel(Figure3d).

ThisisanindicationofseriouspotentialecologicaldisasterfromCd

levelinthesoil.Morethan50%ofthecontaminationdomains

correspondedtoextremecontaminationbyCdwhichisrecognized

asverymobileinair–soil–plantsystem(Wieczoreketal.,2005).Zn

contaminationofthesoilposenotoxicologicalconcernsincethe

largestpercentagedomainwassuspectedcontamination(78%)

whichindicatesnoimpendingdangerfromZn(Figure3e).

Though,thefactoryhasimprovedontheirairpollutioncontrol

systembyreplacingtheelectrostaticprecipitatorwithafilterbay

dustcollectionsystemin2011butitisstillhighlyimportantthat

remediationofthesoilshouldbedonetoavertanypotential

ecologicalorhealthhazardsfromCd,PbandCupollution.

3.3.Spatialmappingoftheheavymetaldistributionsinthe

topsoilaroundthecementfactory

InterpolationmappingofspatialspreadofPb,Cu,Cr,Cdand

ZnusingInverseDistanceWeightedtechniqueofArcGIS10is

showninFigure4.Asshowninthemaps,similarpatternof

hotspots (high soil metalconcentrations)aroundthe cement

factoryisobservedinthespatialdistributionofallthemetals

exceptZn.HighconcentrationsofPbandCuwereobservedinthe

soilatthesoutheastandsouthwestofthefactory,someinthe

immediatevicinitywhilesomearefarawayfromthefactory

(Figure4aand4b).Thisisapointertothefactthatthesourceof

highPbandCupollutionaroundthecementfactorycannotbe

limitedtothereleasefromthecementproductionbutcouldalso

Figure3.Percentagecontaminationlevelsof(a)Pb,(b)Cu,(c)Cr,(d)Cdand(e)Zninthesoilaroundthecementfactory. 13%

13%

37% 37%

Suspectedcontamination Slightcontamination Moderatecontamination Severecontamination

D

3E

5% 5%

24%

34% 32%

Nocontamination Suspectedcontamination Slightcontamination Moderatecontamination

E

&X

5%

26%

40% 29%

Nocontamination Suspectedcontamination Slightcontamination Moderatecontamination

F

&U

3% 16%

26% 55%

Suspectedcontamination Moderatecontamination Severecontamination Extremecontamination

G

&G

18%

74% 8%

Nocontamination Suspectedcontamination Slightcontamination

involveseveralothersourceslikevehicularactivities.Thespatial

mappingofthedistributionofPbandCucorroboratedtheearly

submissionthatofseveralsourcesofpollutionfortheseheavy

metals.ThesamepatternalsoappliedtoCrbutmajorityofthe

hotspotslocatedatthesoutheastofthefactorywhilethelowCr

concentration(<101.1mg/kg)werefoundaroundthewesternaxis

(Figure4c).ThedistributionoflowCrconcentrationsaroundthe

westernaxiscanonlyadjudgedtopollutionfromtheproduction

lineofcementplusthevehicularactivitieswhilehotspotsatthefar

endofthesoutheastofthefactorymaybeduetogeogenicrelease

ofCrfromparentrock.Asearlierstated,Crareusuallyreleasedin

largeamountfromparentrocks(Facchinellietal.,2001;Takacet

al.,2009)andrapidweatheringofthisparentrocksmaybe

implicatedinthehotpotsofCratthefarsoutheastendofthe

factory.HighconcentrationsofCd(>348.8mg/kg)wereevenly

distributionaroundtheimmediatevicinityofthecementfactory

whilelowlevelofsoilCd(<87.3mg/kg)werewithin2kmdistance

fromthecementfactorytowardsthesoutheastandthesouthwest

(Figure4d).ThisfindingofevenspatialdistributionofCdinthesoil

showedthatthemainsourceofthepollutionisthroughaerial

depositionandtheonlyrouteforthishighamountofCdcanonly

befromthecementproductionthroughthestack.Itisalso

importanttonotethathotspotswerealsoevenlydistributedfar

beyondseveralkilometersatthesouthwesternend,probably

aidedbywinddirectionandvelocity.Thispossiblyindicatedaerial

depositionofCdintothesoilasthemainpossiblerouteofsoil

contamination.Thisruledoutagriculturalactivitiesaspossible

collaboratorintheenrichmentofthesoilwithCdbecauseifthe

enrichmentcamefromfertilizerapplications,scatteredhotspots

shouldhavebeenobservedaroundthearea.Theevenspatial

distributionmayalsobeenhancedbythereleasefromtheparent

rocksincethesoilisferraliticwhichisasourceofCdenrichmentof

soil(Olaide,1987).Theimmediatesurroundingsofthecement

factorycontainlowZnconcentrations(<124.4mg/kg)withhotͲ

spotslocatedfarawayfromthecementfactorytowardsthe

southeastandsouthwest,probablyduetowinddispersionofdust.

The even distribution of soil Zn concentrations in the

immediatevicinityofthefactoryshowedthatenrichmentcould

onlybefromtheactivitiessurroundingcementproductionand

probablybecausetheZnisinlargerparticles,solateraldispersion

islow(Abbasietal.,2012).

Figure4e.SpatialdistributionofZninsoilsusingInverseDistanceWeightedtechnique(ArcGIS10).

4.

Conclusion

Thisinvestigationoflevelsofheavymetalsinsoilaroundthe

Lafarge–CementWAPCOfactoryhasrevealedextremecontamͲ

inationbyCdandseverecontaminationsbyPbandCu.Fromthe

spatialmapping,itwasclearthatenrichmentofthesoilbyCd

around the cement factory was due to cement production

activitieswhiletherewasasynergisticcontributionfromboth

cementproductionandvehicularactivitiesintheenrichment/

contaminationofthesoilbyPbandCu.Apparently,CrandZnpose

noenvironmentalconcernbecauseoftheirrelativelylowerlevels

inthesoil.

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