Trace Metal Contamination Characteristics and Health Risks Assessment of Commelina africana L ...

15 Pages·2016·1.67 MB·English

Hindawi Publishing Corporation
Applied and Environmental Soil Science
Volume 2016, Article ID 8178901, 14 pages
http://dx.doi.org/10.1155/2016/8178901
Research Article
Trace Metal Contamination Characteristics and Health
Commelina africana
Risks Assessment of L. and Psammitic
Sandflats in the Niger Delta, Nigeria
NsikakU.Benson,1 PaulA.Enyong,2andOmowunmiH.Fred-Ahmadu1
1AnalyticalandEnvironmentalChemistryUnit,DepartmentofChemistry,CovenantUniversity,Km10IdirokoRoad,Ota,Nigeria
2DepartmentofChemistry,UniversityofUyo,Uyo,Nigeria
CorrespondenceshouldbeaddressedtoNsikakU.Benson;[email protected]
Received27May2016;Revised29June2016;Accepted6September2016
AcademicEditor:YongchaoLiang
Copyright©2016NsikakU.Bensonetal. This is an open access article distributed under the Creative Commons Attribution
License,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperly
cited.
ThepurposeofthisstudywastoinvestigateandquantifytracemetalconcentrationsinCommelina africanaL.andpsammitic
sandflats from an intertidal coastal ecosystem in Niger Delta, Nigeria, and to evaluate their spatial distribution, degree of
contamination,andsourceapportionment.Theenvironmentalrisksassociatedwithsoilcontaminationwereelaboratelyassessed
using potential ecological risk index, sediment quality guidelines, and enrichment relative to background levels. The mean
concentrations of Cd, Cr, Ni, Pb, and Zn in sandflat soil samples are 0.76 ± 9.0 × 10−2, 7.39 ± 8.7 × 10−1, 2.28 ± 0.35,
0.024±4.0×10−3,and74.51±2.55mg/kg,respectively.Metallevelsindicatestrong variabilitywith sampling sites.Theorder
oftracemetalconcentrationsintheCommelinaafricanaL.samplesisZn > Ni> Cr> Pb > Cd.Theconcentrationsvariedwith
thesamplelocations;andthelevelsofPb(0.05to0.08mg/kg)atalllocationsarefoundtobesignificantlybelowpermissiblelevel
of0.3mg/kg.Potentialsourcesofmetalloadingsmaybeassociatedwithlocalisedordiffusedanthropogenicactivities.Theaverage
carcinogenicrisksarebelow1.0×10−6thresholdvalues,andthesandflatsoilsarenotconsideredtoposesignificanthealtheffects
tochildrenandadultmalesandfemales.However,thecarcinogenicityandnoncarcinogenicityrisksrankingdecreasefollowingthe
orderchildren > adult males > adult females.Comparatively,thehazardquotientandhazardindexindicatethatthepsammitic
sandflatsmightposeahealthrisktochildreninfuture.
1.Introduction tracemetalsarenaturallyubiquitous[12,13].Althoughsome
trace metals are present as natural nutrient components
Pollutioninvestigations incoastalecosystemsofNigerDelta of the soil environment, introduced through weathering
have revealed that human mediated activities can adversely processes,most,however,originatefromavarietyofhuman
altertheecologicalintegrityoffragileaquaticsystemsinthe mediated activities [14–18]. In the Niger Delta, crude oil
region, resulting in bioaccumulation of chemical contami- pollution and petrochemical activities have been identified
nants by zoobenthos [1–4], sediment enrichment [5], and asmajor anthropogenic activities that significantly promote
impactonspeciesabundanceandbiomass[6,7].Mostequa- theintroductionoftracemetalsintoboththeterrestrialand
torial wetlands and ultisol systems in the Niger Delta serve aquaticenvironments[5,19,20].
asprimary recipients of petroleum exploration-exploitation Wetland soils act as both sinks and carriers for trace
wastes and domestic and industrial wastes generated by metals and could provide valuable information on the pol-
multinational oil companies that are found in the region. lutionpatternandhistoryofsuchecosystems[21,22].Trace
Studieshaveindicatedenhancedlevelsoftracemetalsinsoil, metals present in the soil are capable of undergoing chem-
surfacewater,sediments,andbiotafromaquaticecosystems ical transformation from solids to ionic species or through
in the area [8–11]. In the wetlands and soil environment, biomethylationintoorganometallicmoieties[23].Also,they
2 AppliedandEnvironmentalSoilScience
N
Nigeria
W E
S
5∘10󳰀0󳰀󳰀N
5∘0󳰀0󳰀󳰀N
4∘50󳰀0󳰀󳰀N
4∘40󳰀0󳰀󳰀N
4∘30󳰀0󳰀󳰀N
7∘50󳰀0󳰀󳰀E 8∘0󳰀0󳰀󳰀E 8∘10󳰀0󳰀󳰀E 8∘20󳰀0󳰀󳰀E 8∘30󳰀0󳰀󳰀E
Settlements Mangrove swamp
Sampling points Water
0 5 10 20 30
(Kilometers)
Figure1:QuaIboeEstuarymangroveecosystemshowingthesamplinglocationalongDouglasCreek.Insert:mapofNigeriashowingthe
locationofthestudyarea.
couldbereleasedinbothparticulateanddissolvedformsand factor (Cf), modified contamination degree (mCD), and
are known to have high affinities for fine-grained sediment geoaccumulation index (𝐼 ); (d) to evaluate the coastal
geo
and soil particulates [24–27]. However, the fate, transport, soil quality and environmental risks of investigated trace
and pollution characteristics of trace metals in the wetland metals by comparison with soil quality guidelines (SQGs);
soils have become an important problem due to their toxic (e) to identify the possible sources of trace metal pollution
effects,accumulation,andbioconcentrationthroughthefood and to assess their ecotoxicological significance; and (f) to
chain[28,29]. assesspotential noncarcinogenicandcarcinogenicrisksdue
Tracemetalsintroducedintotheenvironmentarecapable to inhalation, dermal contact, and oral ingestion exposure
of having toxicological implications on terrestrial inver- pathways.
tebrates, humans, and the natural environment [30–32].
Adversehealtheffects,suchaslungandskincancer,prostatic 2.Materialsand Methods
proliferativelesions,peripheralneuropathy,kidneydysfunc-
tion, dermal lesions, and peripheral vascular disease, have 2.1. Study Area. The Douglas Creek is a major tributary of
been attributed to trace metals pollution. However, metal QuaIboeEstuary(Figure1).Theestuaryischaracterizedby
toxicitymainlydependsonthemetalspeciationandbioavail- shallowintertidalmudflatsthataresurroundedbymangroves
ability,aswellasonthemeansofuptake,accumulation, and and is perennially subjected to sediment deposition from
excretion rates of the organisms [24, 28, 33–35]. Therefore, Qua Iboe River and marine sand from the Atlantic Ocean.
elucidatingthepotentialsources,ionicforms,ecosystemvari- It is located close to several coastline settlements within an
ability,pollutionstatus,andenvironmentalrisks,assessment oil producing area in Southeastern Nigeria. The Qua Iboe
of trace metals in wetland soil environment is a critical EstuaryandDouglasCreekliewithinlatitude4∘30󸀠to4∘45󸀠N
tool in understanding the contamination characteristics of and longitude 7∘30󸀠 to 8∘00󸀠E. It serves as the receiving
suchecosystems.Italsoprovidesexpositoryinformationfor water body for residential, agricultural, and petrochemical
environmentalpollutionpreventionandcontrol. wastesgeneratedfrommultinationaloilcompanieslocatedin
Thepresentstudywasinitiatedwiththefollowingobjec- theoilproducingcommunities.Theestuaryischaracterized
tives:(a)todeterminethelevelsoftracemetalsaccumulation by fine sandy beaches fringed with mangrove swamps and
anddistributionincoastalsandflats,flora,andfaunafroman tidal mudflats on which Nypa palm vegetation dominates.
estuarineecosystem,(b)toevaluatepotentialecologicalrisks Thestudy area is characterized bya humid tropical climate
from metal pollution using different indices such as metal withanannual rainfallofabout4021mm,averagehumidity
pollutionindex(MPI)andtransferfactors(TFs);(c)toassess of 80%, and mean minimum and maximum temperatures
∘ ∘
the degree of trace metal pollution using contamination of 22 C and 30 C, respectively. There are two predominant
indices such as pollution load index (PLI), contamination seasons,dryandwetseasons.ThewetseasonbeginsinMarch
AppliedandEnvironmentalSoilScience 3
Table1:Reference(SRM8704)concentrationvalues,analyticalresults,andpercentagerecovery.
SRM8704referencevalues AASresults
Metals Accuracy(%recovery)
(mg/kg) (mg/kg)(𝑛=3)
Cadmium 2.94±0.29 3.03±0.04 102.96
Chromium 121.90±3.80 119.47±1.64 98.01
Nickel 42.90±3.70 40.86±0.18 95.23
Lead 150.00±17.00 156.04±6.95 104.23
Zinc 408.00±15.00 398.60±10.54 97.67
orAprilandisusuallycharacterizedbyheavystormsofshort pulverizedintofinepowder,andstoredinwell-labeledZiploc
duration.Thedryseason,whichnormallylasts3–5months,is bags. Precisely 1.0g of each plant sample was accurately
comparatively short,beginninginNovemberandextending weighedinto10mLconicalflaskand1mLHClO4 and7mL
to February. Tidal currents are strong especially during the of40%HFwereaddedanddigestedslowlyfor2hoursusing
wetseasons along estuary upperreaches and creekand this amodifiedmethodofVaneˇketal.[36].Afterdigestion,they
playsanimportantroleinsedimentation, biotadistribution, were allowed to cool and later were heated and the content
trace metal laden, waste transportation, and industrial and wasevaporateduntilfumesofHClO4 appeared.Theresidue
domesticwastetransportation. was allowed to cool and 1mL H2SO4 added and heated
again to drive off HClO4. After cooling, all samples were
2.2. Sampling. A total of 30 plant and soil samples were dilutedwithalittlewaterandfilteredinto25mLvolumetric
eachcollected fromthestudyareaalong amarked transect. flasks fitted with a glass funnel and Whatman number 1
Plant and soil samples were collected during two separate filter paper. Thefiltrates were later madeup to 25mL mark
trips from five designated grids: DC-V, DC-W, DC-X, DC- withdistilledwater.Alsoblankswerepreparedfollowingthe
Y,andDC-ZmappedoutalongthestretchofDouglasCreek aboveprocedure,withallreagentsexcludingthesample.The
extending into Qua Iboe Estuary. Ateach sampling station, solutions were used for the determination of trace metals.
triplicates of the plants and soil samples were obtained and Acid eluates desorbed from the filter, and 30 digested soil
carefullytransferredintocleanpolyethyleneglasscontainers. and plant sample solutions and the reagent blanks were
A short core sampler was used to collect the soil from the analysed for the concentrations of Zn, Pb, Cd, Ni, and Cr
top 0 to 15cm of the soil surface and homogenized and using an atomic absorption spectrometer (S Series S4 AA
thesubsampleswerestoredinlabeledblackpolythenebags. System,ThermoElectronCorporation).Inordertoevaluate
Plantsampleswerealsohandpickedalongthetidalshoresof theprecisionofeachmethodofdigestion forsoiland plant
DouglasCreekandthoroughlycleanedwithfreshwatertoget samples,thetracemetalanalyseswereruninduplicates.
rid of soil before transferring them into labeled aluminium
foil. The samples were all stored in ice-packed coolers and
2.4. Quality Assurance. Buffalo River Sediment Reference
transportedtothelaboratory.Theywerefurtherrefrigerated
∘ Material (SRM 8704), sourced from National Institute of
in the laboratory at 4 C to inhibit microbial activities and
Standards and Technology (US),intended primarily foruse
preservetheintegrityofthesamplespriortoanalysis.
in the analysis of sediments, soils, or materials of a similar
matrix wasanalysed with thesoilsamples forquality assur-
2.3.AnalyticalProceduresforSamplePretreatmentandChem-
ancepurposes.Referencevaluesandtheanalyticalresultsfor
ical Analysis. The soil samples were air-dried by exposure
the concentrations of five trace metals are given in Table1.
toambient air for 48 hours and manually sorted to remove
The recoveries of the AAS analytical results for Cd, Cr,
stones, sticks, organic matter, and shells from the air-dried
Ni, Pb, and Zn ranged between 97.67 and 104.23%. The
samples, pulverized using porcelain pestle and mortar, and
concentrations of certified materials SRM 8704 indicated
sieved through a 2mm mesh and sieved to collect less
than 63𝜇m grain sizes. 2.0g of each sample was digested resultswithintherangeofthereferencevalues.Therefore,the
methodemployedforthisworkisreliableandreproducible.
with a solution of concentrated HCl (6.0mL) and HNO3 Blanks were also monitored throughout the analysis of the
(0.3mL) to near dryness and allowed to cool before 20mL
soilsamplesandblanksubtractionswereemployedtocorrect
of5.0MHNO3solutionwasadded.Thedigestedsoilsample
metalconcentrationsobtainedforsoilsamples.
solution was allowed to stay for about 12 hours before they
werefiltered.Thefiltratesweresubsequentlytransferredinto
100mL volumetric flask and made up to the mark with 2.5. Statistical Analysis. The data were analysed using the
0.5MHNO3priortoelementalanalysis.Areagentblankwas XLSTAT-Prosoftware(AddinSoft,Inc.,NY,USA).Pearson’s
also prepared using a mixture of HCl and HNO3 following correlation analysis and factor analysis were employed to
the stepwise analytical procedure described for the sample explore the interrelationship among trace metals in soil
preparation. samples and also attempt to identify their probable origin.
On the other hand, the plant samples were oven dried The various statistical analyses were performed with a 95%
at 80∘C for 24 hours to prevent microbial decomposition, confidenceinterval(significance𝑝<0.05).
4 AppliedandEnvironmentalSoilScience
2.6.PollutionIndicators. Onthe basis of observed data, the meansveryhighdegreeofcontamination; 16 ≤ mCD < 32
relativegradation ofcontamination levelsbytracemetalsin impliesextremelyhighdegreeofcontamination;andmCD≥
ultisols can be achieved using pollution indices (PIs) and 32referstoultrahighdegreeofcontamination.
efficient risks assessment approaches. However, the evalua- PLIwasevaluatedusingTomlinson’spollutionloadindex
tionofpollutionloadingstatusandtheestimationofimpacts (PLI)[40]andisexpressedasthe𝑛throotoftheproductof
associated with human induced events on coastal wetland 𝑛 Cf as
soilscouldbeattainedthroughgeochemicalapproachessuch
asgeoaccumulationindexandenrichmentfactor[16,37]. PLI=[Cf1×Cf2×⋅⋅⋅×Cf𝑛]1/𝑛, (4)
where 𝑛 is the number of metals and Cf𝑛 is the Cf value
2.7.SoilContaminationIndicesandPotentialEcologicalRisks. of metal 𝑛. PLI is classified as follows according to the
Theunderlistedcontaminationindiceswereadoptedtoeval- contamination degree:backgroundconcentration(PLI= 0),
uate trace metals contamination assessment in soil samples unpolluted(0<PLI≤1),unpollutedtomoderatelypolluted
collected from the study area: (i) degree of contamination (1 < PLI ≤ 2), moderately polluted (2 < PLI ≤ 3),
(CD);(ii)modifiedcontamination degree(mCD);(iii)con- moderatelytohighlypolluted(3< PLI≤ 4),highlypolluted
tamination factor (Cf); (iv) pollution load index (PLI); (v) (4<PLI≤5),orveryhighlypolluted(PLI>5)[16,41].
pollutionindex(PI)andNemerowintegratedpollutionindex
Additionally, the pollution index (PI) was used to eval-
(NIPI);and(vi)geoaccumulationindex(𝐼 )[37].Thesingle
geo uate soil pollution by comparing the metal concentrations
metal and multimetal potential ecological risk indices were
obtained in this study with Dutch soil guidelines [42].
alsocalculatedforCd,Cr,Ni,Pb,andZn.
AccordingtoLeeetal.[37],PIisexpressedas
The CD was calculated to assess the holistic impact
of multimetals on the environment [22, 38]. The formula 𝐶
PI= 𝑛, (5)
developedbyHa˚kanson[39]wasusedforthecalculation of 𝑇
𝑛
CD:
𝑛 where𝐶𝑛istheconcentrationofanindividualtracemetaland
CD=∑Cf𝑖, (1) 𝑇𝑛 is the corresponding target concentration of Dutch soil
guidelines, which consider different land-use types and are
𝑖=1
basedonextensivestudiesofboththehumanandecotoxico-
𝐶𝑖 logicaleffectsofsoilcontaminants[43].Nemerowintegrated
Cf𝑖 =[ 𝐶m𝑖conc], (2) pollutionindex(NIPI)wasalsoemployedfortheassessment
bkg oftheoverallpollutionintegrityoftheinvestigatedecosystem
whereCf𝑖iscontamination factorofmetal𝑖,𝐶𝑖mconc ismean [44].TheNIPIwascalculatedusingthefollowingequation:
concentration, and 𝐶𝑖bkg is background value of individual NIPI=[0.5×(𝐼2 +𝐼2 )]1/2, (6)
metal. The degree of contamination is classified into low mean max
degree of contamination (CD ≤ 6), moderate degree of where𝐼 isthemeanvalueofallpollution indicesofthe
contamination (6 < CD ≤ 12), considerable degree of metalscmoenasnideredand𝐼 isthemaximumvalue.According
contamination (12 < CD ≤ 24), and very high degree of toChengetal.[45],thecmlaaxssificationofNIPIisasfollows:safe
contamination (CD > 24). The Cf is derived by dividing (NIPI ≤ 0.7),precaution(0.7 < NIPI ≤ 1),slightlypolluted
theconcentration ofselectedtracemetalbythebackground (1 < NIPI ≤ 2), moderately polluted (2 < NIPI ≤ 3), or
value. The gradation of Cf is as follows: Cf < 1 indicates heavilypolluted(NIPI>3).
low degree of contamination; 1 ≤ Cf < 3 indicates The index of geoaccumulation (𝐼 ) is a common
moderatecontamination; 3 ≤ Cf < 6indicatesconsiderable approach employed to estimate metalsgeeonrichment above
contamination; and Cf ≥ 6 shows very high degree of background or baseline concentrations in soil or sediment.
contamination. The 𝐼 values for the studied trace metals were calculated
geo
ThemCDisanempiricalassessmentoftheoveralldegree usingthefollowingequationdevelopedbyMu¨ller[46]:
ofcontaminationbypollutantsinadesignatedecosystemand
𝐶
ismathematicallyexpressedasfollows: 𝐼 =log ( 𝑛 ), (7)
geo 2 1.5𝐵
mCD= ∑𝑛𝑖=𝑛1Cf𝑖, (3) where 𝐶𝑛 is the measured concentra𝑛tion of selected metal
(𝑛)inthesoilsampleand𝐵𝑛isthegeochemicalbackground
whereCfiscontaminationfactor,𝑛isthenumberofanalysed inaverage shaleofmetal(𝑛).Inthisstudy, thegeochemical
tracemetals,and𝑖is𝑖thmetal. backgroundsoilconcentrationsofCd,Cr,Ni,Pb,andZnwere
The following classifications and descriptions are avail- 0.3,90,68,20,and95mg/kg,respectively, andwereusedin
able for modified degree of contamination in soil: mCD < calculating the𝐼 values[47].Thecoefficient 1.5isusedto
geo
1.5refers tonil tovery low degree of contamination; 1.5 ≤ detect variations in the background data due to lithogenic
mCD<2indicateslowdegreeofcontamination;2≤mCD< [48, 49] and anthropogenic influences [50]. 𝐼 consists of
geo
4impliesmoderatedegreeofcontamination; 4 ≤ mCD < 8 seven grades. According to Mu¨ller [46], 𝐼 consists of 7
geo
indicates high degree of contamination; 8 ≤ mCD < 16 classes. The corresponding relationships between 𝐼 and
geo
AppliedandEnvironmentalSoilScience 5
Table2:Summarystatisticsoftracemetalconcentrations(mg/kg)insandflatsandCommelinaafricanaL.fromthesandybeachesofDouglas
Creek.
Tracemetals Min. Max. Mean Std.deviation CV%
Zn 71.43 77.850 74.51 2.553 3.42
Pb 0.019 0.030 0.024 0.004 16.67
Soil Cd 0.695 0.900 0.759 0.090 11.84
Ni 1.750 2.600 2.278 0.346 14.91
Cr 6.100 8.120 7.392 0.875 11.77
Zn 225.90 252.2 239.26 11.801 4.93
Pb 0.050 0.080 0.058 0.013 22.41
C.africanaL. Cd 0.150 0.750 0.304 0.250 82.24
Ni 10.65 26.750 19.152 7.289 38.07
Cr 7.879 13.824 9.642 2.383 24.69
thedegreeofmetalpollutionlevelareasfollows:unpolluted metals from soil to plants. In this study, the transfer factor
(𝐼 ≤ 0),unpollutedtomoderatelypolluted(0 < 𝐼 ≤ 1), wasdeterminedusing
geo geo
moderately polluted (1 < 𝐼 ≤ 2), moderately to heavily
phpeooallllvuuittlyeeddto((𝐼2ex<tr>e𝐼m5ge)eo.ly≤po3l)lu,theegdeaov(i4ly<po𝐼lgleuote≤d (53),<or𝐼egxeotre≤me4l)y, TF𝑝 = 𝐶𝐶𝑖𝑝𝑖𝑠, (9)
geo
The overall toxicity and potential ecological hazards where 𝐶𝑖 is the 𝑖 metal concentration in the plant material
𝑝
posed by metals in soil were assessed using a method
(dryweight basis) and 𝐶𝑖 isthe total concentration of the 𝑖
proposed by Ha˚kanson [39]. The potential ecological risk 𝑠
metalinthesoil(dryweightbasis)[53,54].Inaddition,metal
index(PERI)primarilyevaluatestheprobabledegreeoftrace
pollutionindex(MPI)wasemployedasameansofcomparing
metal contamination taking into consideration the relative
thetotalmetalconcentration ofCommelinaafricanaL.with
toxicity of the overall metals and the short-to-long-term
responseoftheenvironment.Theriskindex(𝑅𝐼)iscalculated therespectivesampling sites.MPIisexpressedaccordingto
thefollowingequation[55,56]:
basedonthefollowingequation:
𝐶𝑖 MPI=[𝐶1×𝐶2×𝐶3×⋅⋅⋅×𝐶𝑛]1/𝑛, (10)
𝐸𝑖 =∑𝑇𝑖( 𝑠),
𝑓 𝑟 𝐶𝑖
𝑛 (8) where𝑛isthenumberofmetalsand𝐶𝑛istheconcentration
ofmetal𝑛inCommelinaafricanaL.ondryweightbasis.
𝑅 =∑𝐸𝑖,
𝐼 𝑓
3.ResultsandDiscussion
where 𝑅𝐼 is the sum of individual risk factors for all trace
metals; 𝐸𝑖 is the monomial PERI for individual metal; 3.1. Trace Metal Content. Metal levels in the Commelina
𝑓
𝐶𝑖 and 𝐶𝑖 are the observed and background values of africanaL.andsoilsampleshavebeenassessedforzinc(Zn),
𝑠 𝑛
concentrations of metals, respectively; and 𝑇𝑖 is the toxic lead (Pb), cadmium (Cd), nickel (Ni), and chromium (Cr),
𝑟 and the results are presented in Table2. The results show
responsefactorforasingletracemetal.𝑇𝑖forCd,Cr,Ni,Pb,
𝑟 thatmean concentration ofmosttracemetals inthecoastal
andZnare30,2,5,5,and1,respectively[39,51].Thepotential
sandflats exceeded the recommended guideline values. The
ecological risk 𝑅𝐼 is classified as follows: 𝑅𝐼 < 95 low risk; mean concentrations of Cd, Cr, Ni, Pb, and Zn in sandflat
95 ≤ 𝑅𝐼 < 190 moderate risk; 190 ≤ 𝑅𝐼 < 380 high risk; soilsampleswere0.76±9.0×10−2,7.39±8.7×10−1,2.28±
and 𝑅𝐼 ≥ 380 very high risk, while the potential ecological 0.35,0.024±4.0×10−3,and74.51±2.55mg/kg,respectively.
riskindexassociated with an individual metal 𝐸𝑖𝑓 isranked Notably, the metal levels indicate strong variability with
asfollows: 𝐸𝑖 < 40low risk;40 ≤ 𝐸𝑖 < 80moderaterisk; samplingsites.Theobservedvariability andenhancedmetal
𝑓 𝑓
80 ≤ 𝐸𝑖 < 160considerablerisk;160 ≤ 𝐸𝑖 < 320highrisk; levelscouldhavebeeninfluencedbychangesintransportand
𝑓 𝑓
and𝐸𝑖 ≥320veryhighrisk[18,52]. sedimentation modes from surrounding intertidal ecosys-
𝑓 tem. Additionally, these variations may be attributed to
differences in the rates of metal solubility in soils which is
2.8. Assessment of Pollution and Bioaccumulation Index in predominantly controlled by pH, amount of metals cations
CommelinaafricanaL. Bioaccumulation indexcan beused exchange capacity, organic carbon content, and oxidation
toprovidearelativeevaluationofthedegreeofcontamination state of the system [57]. The order of mean concentrations
through uptake or exposure. This is sometimes referred to in the C. africana L. samples was Zn > Ni > Cr >
as a plant uptake factor or transfer factors (TFs) of heavy Pb > Cd. However, Cd level (0.75mg/kg) in C. africana L.
6 AppliedandEnvironmentalSoilScience
Table 3: Pollution indicators for trace metals in sandflats from 3 80
DPooullugltaiosnCirnedekic.es Zn D0C.7-7V D0C.7-8WSamDp0Cl.8e-2sXitesD0C.8-0Y D0C.7-5Z IMean Cf/geo12..1525 0000....00011.204826 Cr Ni Pb 234567000000 vidual ecologicalrisk index
Pb 0.001 0.001 0.001 0.001 0.001 0.5 di
10 n
I
Cf Cd 2.34 2.33 2.31 2.67 3.00 0 0
Ni 0.03 0.03 0.04 0.03 0.04 Cd Cr Ni Pb Zn
Cr 0.09 0.08 0.07 0.09 0.07
Cf
Zn 0.512 0.520 0.546 0.535 0.508 I
geo
Pb 0.001 0.001 0.001 0.001 0.001 Ef
𝐼geo Cd 1.558 1.556 1.544 1.778 2.000 Figure2:IndividualecologicalriskindexandmeanCf/𝐼geovalues
Ni 0.017 0.021 0.025 0.023 0.025 oftracemetalsforsandflatssoilsamplesofDouglasCreek.
Cr 0.059 0.059 0.051 0.060 0.045
Cd 3.219 3.234 3.251 3.595 3.859
mCD 0.644 0.647 0.650 0.719 0.772 fossil fuel combustion (excessive gas flaring) and untreated
waste disposal, and carcinogenic risk associated with Cd is
potentiallyofhealthandenvironmentalconcerns.
Thedegreeofcontamination (CD)andmodifieddegree
from location DC-W was far above FAO/WHO maximum
of contamination (mCD) were calculated using (1) and
levelof0.2mg/kg[58].
(3), respectively, and the derived contamination values are
Althoughthereisnoauthoritativereferencedetailingthe
presentedinTable3.ResultsindicatethattheCDandmCD
regulated background values of trace metals in Nigeria, it
at all sites generally showed low degree of contamination.
is obvious that observed metal levels except Cd in sandflat
Interestingly,bothvaluesdidnotexhibitcorrelativevariabil-
soilsamplesdidnotexceedbackgroundvaluesorregulatory itywiththeselectedsitesandmaybeconsideredtobeinthe
standards of heavy metals from other parts of the world
range of unperturbed variability. This might be a function
[59, 60]. Trace metals in soils have been shown to be
of the hydrodynamic conditions of the aquatic ecosystem
very useful indicators of environmental pollution [61–63].
at the period of obtaining the soil samples. However, the
Thus, the environmental quality of this sandflat soil raises contaminationrankingoftracemetalsonthebasisofpercent
serioushealth concerns especially considering itsusageasa contributiontoCDandmCDisCd>Zn>Cr>Ni>Pb.
recreationalarea,wherepeoplecomeintodirectcontactwith Table3showstheresultsofthecalculated𝐼 valuesand
geo
contaminant soil and dust particles. Some of the dominant Figure2 presents the mean 𝐼 values for each trace metal
geo
sourcesoftracemetalloadingstothesandflatsoilmaybedue inthesandflatssoilsamplesoftheinvestigatedsites.The𝐼
geo
towastesdepositedfromlocalisedordiffusedsourcessuchas
valuesforCr,Ni,Pb,andZnindicatedlessvariabilityamong
crudeoilspill,fuelcombustion(gasflaring),wastesdisposal, the sampling sites and were within 0 < 𝐼 ≤ 1 implying
geo
trafficemission,petrochemicals,fertilizers,andpesticides. thatthesoilsampleswereunpollutedtomoderatelypolluted.
Thecalculated𝐼 valuesforCdshowedthatthesoilsamples
geo
3.2. Evaluation of Soil Pollution Indices. The contamination were moderately polluted (1 < 𝐼 ≤ 2) at all sites. It is
geo
factor values were calculated using (2) and are listed in imperative toemphasize that the average 𝐼 values for Cd
geo
Table3. The mean Cf values calculated for studied trace wererelativelyhigherthanothertracemetals,suggestingthat
metals in psammitic sandflat soil samples were in the fol- the soil samples from the Douglas sandy beach must have
lowingorder:Cd(2.53)>Zn(0.78)>Cr(0.08)>Ni(0.03) beencontaminatedbyCdduetoanthropogenicactivities.
> Pb (0.001) (Figure2). Cf values less than 1 (one) and The pollution load index provides an integrated con-
those between 1 and three are considered to pose low and tamination assessment based ontheCf ofeachtrace metal.
moderate degree of contamination, respectively. Therefore, The PLI values for Cd, Cr, Ni, Pb, and Zn are presented in
the results of the present study at the various sites showed Figure3andranged between0.086and0.097atDC-Wand
thatthesoilsamplestakenfromthebeachofDouglasCreek DC-Z sites, respectively. As indicated by these PLI values,
were moderately contaminated by Cd whereas Cr, Ni, Pb, the sandflat samples of the present study are unpolluted,
and Zn indicated low degree of contamination. Cadmium withPLIvaluesbetweenzeroandoneforallsites.However,
could be introduced to soil, air, and aquatic environment it must be noted that the present day PLI values obtained
throughanthropogenicinputssuchasfossilfuelcombustion, forsoilsamplesweredominatedbyindividualcontributions
application of phosphate fertilizers, and waste dumping of Cd and Zn. The calculated pollution index (PI) and the
and incineration [43, 64]. Cd is a known carcinogen that Nemerow integrated pollution index (NIPI) values of trace
can potentially cause adverse effects to human kidneys, metalsinforeshorepsammiticsoilsamplesofDouglasCreek
lungs, and bones. Thus, the relatively high Cf value of Cd arepresentedinTable4.Resultsindicatethatthesandybeach
indicating moderate contamination is significant. However, ofthisaquaticecosystemwasnotpollutedbutcontamination
considerable contamination is likely through uncontrolled rankingisprecautionary(0.7<NIPI≤1).
AppliedandEnvironmentalSoilScience 7
Table4:Comparisonofpollutionindices(PIs)oftracemetalsinsandflatsoilsofDouglasCreekandotherstudies.
Cd Cr Ni Pb Zn 𝐼 𝐼 NIPI
mean max
Mean 0.76 7.39 2.28 0.02 74.51
Targetvaluea 0.8 100 35 85 140
Thisstudy 0.95 0.074 0.065 0.0003 0.53 0.32 0.95 0.71
OdewandeandAbimbola[76] 0.2 0.6 0.5 0.6 0.7 0.5 0.9 0.7
Dutchsoilguidelines[42]a.
Table5:Soil-to-planttransferfactorsofstudiedtracemetals. 0.1
SampleID Cd Cr Ni Pb Zn
DC-V 0.29 1.10 13.26 2.00 3.13 dex 0.095
n
DC-W 1.07 1.09 10.85 2.63 3.05 d i
a
DC-X 0.30 1.33 10.57 2.61 3.09 n lo 0.09
o
DC-Y 0.26 0.97 4.47 2.00 3.31 uti
DC-Z 0.17 2.27 4.63 2.67 3.48 oll 0.085
P
0.08
3.3.EvaluationofPollutionandBioaccumulationIndex. MPI DC-V DC-W DC-X DC-Y DC-Z
resultsindicated thatthecalculated valuesvaried withsam- Sampling sites
plingsitesand wereafunctionofthetotal concentration of
Figure3:PollutionloadindexofmetalsatsamplingsitesofDouglas
individual trace metals. The highest MPI value (4.42) was
Creek.
obtained at DC-W site followed by 3.75 at DC-X and then
3.46atDC-Zsite.ThelowestMPIvalueof2.95forCommelina
africanaL.wasrecordedatdownstream ofthecreekatDC-
ranking of trace metals in line with the mean PERIs for
Y site. Moreover, transfer factor is one way through which
individual metal stressors is Cd > Zn > Ni > Cr > Pb.
the mobility of metal by plants can be assessed. The soil-
to-plant transfer factor (TF) values recorded for different However,onthebasisofthecalculated𝑅𝐼value(𝑅𝐼 = 77),a
samples sites are presented in Table5. The results revealed lowecological risk(𝑅𝐼 < 95lowrisk)wasindicated forthe
multielementsconsideredinthisstudy.
thatNi(13.26)inDC-VandZn(3.48)inDC-Zsoilhadthe
highesttransferfactorvaluewhileCd(0.17)andCr(0.97)in
soils from DC-Z and DC-Y stations, respectively, reported 3.5. Principal Component Analysis (PCA). The principal
thelowesttransfer factorvalue inthestudyarea. Themetal component analysis (PCA) of variables was performed to
bioavailability from soil to the plant as indicated by the extractsignificantprincipalcomponents(PCs).Theresultsof
transfer factor values for the five sample stations decreased 𝑛-PearsonPCAperformedfurtherexploredtherelationships
intheorder:TF > TF > TF > TF > TF .Ahigher between the trace metals and also clarify their possible
Ni Zn Pb Cr Cd
valueoftransferfactorimpliesthetendencyofmoremobile sources. Table6 summarises the factor loadings of trace
and available metals [53]. Generally, Ni element exhibited metalsforsandflatandCommelinaafricanaL.,groupedinto
highervalvesofTFatallthesampling sitesasshownonthe threeprincipalcomponentmodels.Theloading plotsofthe
table when compared with the results of other trace metals PCs are presented in Figure4. The Eigen values of PC1
underinvestigation. and PC2 associated with sandflat soil were greater than 1
and in general accounted for 86.63% of the variability in
concentrations oftracemetals.PC1indicatedthat59.88%of
3.4. Evaluation of Potential Ecological Risks. The potential
the total variance was positively related to Cd, Pb, and Ni,
ecological risks assessment of trace metals in sandflat soil
withCdandPbshowingrelativelyhighfactorloadings,while
samplesoftheinvestigated ecosystemwerecalculated based
Cr indicated a strong negative relationship. On the other
on (8). Results of average potential ecological risk index of
each trace metal are presented in Figure2. Calculated 𝐸𝑖 hand, PC2, which explained 26.76% of the total variance,
𝑓 indicatedstrongpositiveinterrelationshipsforNiandZn.
values for Cr (0.16), Ni (0.17), Pb (0.006), and Zn (0.78)
indicated low degree of risk, while Cd 𝐸𝑖 value indicated It is worthy of note that the positive loading of Cd, Ni,
𝑓 and Pbwith PC1could possibly suggestthat contamination
moderaterisk(40 ≤ 𝐸𝑖𝑓 < 80).Thisresultagain highlights of the sandflat soil samples might have been influenced by
possiblecontamination concerns associated withCd,which anthropogenicpollutionsources.TheEigenvaluesofPC1and
is likely due to fossil fuel burning in the region over the PC2derivedforCommelinaafricanaL.samplesindicatethey
years. Interestingly, other researchers have reported that weregreaterthan1andaccountedfor83.32%ofthevariability
Cd contribution to potential ecological risk index of the intrace metallevels. PC1wasthemostsignificant principal
environment is very significant [61, 65]. Thecontamination component and was dominated by Cd, Cr, Ni, Pb, and Zn,
8 AppliedandEnvironmentalSoilScience
𝐶 ×AF×EF×ED×SA×ABS
Table6:PCAfactorloadingsoftheconcentrationsoftracemetals EDD = metal
forsandflatsoilandC.africanaL.samples. dermal Bw×AT
×10−6,
Factorcomponents
𝐹1 𝐹2 𝐹3
EDI
Zn −0.477 0.830 0.207 THQ𝑖 =[RfD𝑖],
Pb 0.880 −0.223 0.212
𝑛
Cd 0.923 −0.107 0.308 HI=∑THQ𝑖,
Ni 0.663 0.724 0.038 𝑖=1
Sandflat
Cr −0.837 −0.251 0.475 (11)
Eigenvalue 2.994 1.338 0.410 where𝐶 is the concentration (mg/kg) of trace metal in
metal
Variability(%) 59.879 26.755 8.207 sandflat sample; EF is the exposure frequency (365d/year);
Cumulative% 59.879 86.634 94.841 EDistheexposuredurationequalto6yand18yforchildren
agedbetween 1and6years and6and 18years, respectively,
Zn 0.833 −0.470 0.037
and 52.4 years for adults (World Bank 2013 estimate for
Pb 0.849 0.516 −0.021 averagelifeexpectancyinNigeria)[69];IR istheingestion
ing
Cd −0.690 0.304 0.637 rate(100and50mg/dayforchildrenandadults,resp.);IR
inh
Ni −0.724 0.430 −0.500 isinhalationrate[70];Bwistheaveragebodyweight(70,48,
C.africanaL. and19kgforadultsandchildren,resp.)andATistheaverage
Cr 0.791 0.600 0.083
exposuretimefornoncarcinogens (2190d,age1–6y;6570d,
Eigenvalue 3.042 1.124 0.664 age6–18y;19162.5d,adults);PEFistheparticulateemission
Variability(%) 60.838 22.483 13.285 factor(m3/kg)=1.36×109;SAistheexposedskinsurfacearea
2 2
Cumulative% 60.838 83.321 96.606 (cm ); AF is the adherence factor (kg/cm -day);ABS isthe
dermalabsorptionfactor;andRfDistheoralreferencedose
Htyipgeh.factorloadingsforeachprinciplecomponentarehighlightedwithbold (mgkg−1day−1). The variable 𝑖 denotes the 𝑖th trace metal.
The RfDs for Cd, Cr, Ni, Pb, and Zn are 0.001, 0.003, 0.02,
−1 −1
0.0035,and0.3mgkg d ,respectively[71].However,target
which accounted for 60.84% of the total variance. A very hazard quotient or hazardindex≤1indicates that potential
highloadingofCr(0.791),Pb(0.849),andZn(0.833)inthe adverse health impacts from ingestion are unlikely, while
PC1componentandtheinvestigatedtracemetalsindicateda THQ or HI > 1 suggests that adverse chronic effects are
significantlypositiveinterrelationship.Additionally,thehigh likelyfromdirectoralingestionofcontaminatedsandflatssoil
loading of Cd (0.690) and Ni (0.724) on the first principal [66].Moreover,toassessthecarcinogeniceffects,theaverage
componentindicatedstrongnegativecorrelation. daily dose is multiplied by the corresponding slope factor
(SF)toproducealevelofcancer risk[16, 72].However,the
aggregatecarcinogenicriskwasevaluatedasasummationof
3.6. Potential Health Risk Assessment. The health effects
theindividualcancerriskacrossinhalationexposurepathway
that mightbeattributed tononcarcinogenic trace metals in
as
soil/sand/dustcouldbeevaluatedbycomparinganexposure
viaoralingestionoveraspecifiedtimeperiodwithareference Risk=∑EDD𝑖×SF𝑖. (12)
dose (RfD) for each metal over a similar exposure period.
Thisnoncancerriskassessmentratioistermedtargethazard
quotient(THQ)[66].TheRfDisthetoxicitythresholdvalue, Tables 7 and 8 present the calculated results for noncar-
whichisspecificforeachchemicalcontaminant.However,in cinogenic hazard index for children and adults (males and
ordertoevaluatetheoverallexposurepotentialforcombined females) in Nigeria, assessed by considering the exposure
chroniceffectscausedbyallthemetalcontaminants,ahazard to trace metal contaminated sandflat soils via ingestion,
index (HI) approach was adopted. The HI is equal to the inhalation,anddermalcontactpathways.Thepotentialrisks
arithmeticsumofindividualmetalTHQs[66].Theestimated in terms of the minimum, maximum, and average hazard
dailydoseexposurethroughoralingestion(EDD ),dermal indices of trace metals in sandflat soil samples for children
ing
(EDD )andinhalation absorption(EDD ),THQ,and and adult males and females were less than 1. Thus, these
dermal inh
HI is determined by the following equations, respectively populationsareunlikelytofaceanypotentialhealthrisks[73].
[66–68]: AspresentedinTable8,Cd,Cr,andNimayposerelatively
significantnoncarcinogenichealthriskstotheselectedpop-
𝐶 ×EF×ED×IR ulationcomparedtoPbandZn.Forinstance,consideringthe
EDD = metal inh,
inh Bw×AT×PEF totalhazardquotients(THQs)forinhalationofsandflatsoils
in children, Cd, Cr, and Ni accounted for 33.55%, 32.67%,
𝐶 ×EF×ED×IR and33.56%ofthecalculatedhazardindex,respectively,while
EDD = metal ing ×10−6,
ing Bw×AT Pb and Zn contributed the relatively insignificant 0.22%.
AppliedandEnvironmentalSoilScience 9
Table7:Noncarcinogeniceffectsduetooralingestionexposuretosandflatsoiltracemetals.
Cd Cr Ni Pb Zn
Estimateddailydose(EDD )
ing
Min. 0.0035 0.0307 0.0088 0.0001 0.3756
Children(1–6years) Max. 0.0045 0.041 0.0131 0.0002 0.3929
Mean 0.0038 0.0373 0.0115 0.0003 0.3761
Min. 0.0014 0.0122 0.0035 0.00004 0.1487
Children(6–18years) Max. 0.0018 0.0162 0.0052 0.00006 0.1555
Mean 0.0015 0.0148 0.0046 0.00005 0.1489
Min. 0.0004 0.0043 0.0012 0.00001 0.0524
Adults Max. 0.0006 0.0057 0.0018 0.00002 0.0548
Mean 0.0005 0.0052 0.0016 0.00002 0.0525
Targethazardquotient(THQ)
Min. 0.0035 0.0103 0.0004 0.00002 0.0012
Children(1–6years) Max. 0.0045 0.0137 0.0007 0.00004 0.0013
Mean 0.0038 0.0124 0.0006 0.00003 0.0012
Min. 0.0014 0.0041 0.0002 0.00001 0.0004
Children(6–18years) Max. 0.0018 0.0054 0.0003 0.00002 0.0005
Mean 0.0015 0.0049 0.0002 0.00001 0.0004
Min. 0.0005 0.0014 0.00006 0.000003 0.0002
Adults Max. 0.0006 0.0019 0.00009 6.00E−06 0.0002
Mean 0.0005 0.0017 0.00008 4.00E−06 0.0002
Hazardindex(HI) Min. Max. Mean
1–6years 0.015 0.02 0.018
6–18years 0.006 0.008 0.007
Adults 0.002 0.003 0.003
Sandflat soil (F1 and F2: 86.63%) C. africana L. (F1 and F2: 83.32%)
0.6 1
0.4 0.8
Cr Cr
Pb 0.6
0.2
Pb
Cd Ni
0.4
0
%) %)
6.75 −0.2 2.48 0.2 Cd
2 2 0
F2 ( −0.4 F2 ( −0.2
−0.6 −0.4
−0.8 Ni −0.6 Zn
Zn
−1 −0.8
−1.2 −0.8 −0.4 0 0.4 0.8 1.2 −1.2 −0.8 −0.4 0 0.4 0.8 1.2
F1 (59.88%) F1 (60.84%)
Figure4:Factorloadingsofprincipalcomponents1and2fortracemetalsconcentrationinsandflatandC.africanaL.samplesshowingthe
totalvarianceexplainedbyeachcomponent.
Results for potential exposure through dermal contact in higher noncarcinogenic effects on children and adults due
children showed that Cd and Cr concentrations accounted totheir lowRfDvalues orenhanced concentrations insoils
for73.31%and25.49%,respectively,towardsthetotalhazard [16]. Similarly, in adult females, the THQs of Cd and Cr
indexvalue,whileNi,Pb,andZnrepresentabout1.19%.Pre- represented 73.31% and 25.49% of the total hazard index
viousstudies onhealth risksassessment ofsoiltracemetals (HI )valueforexposureduetoinhalation,whilebothtrace
tot
indicatedthatCd,Cr,andNiexposurecouldposerelatively metalsaccountedforabout98.81%oftheHI valueforrisks
tot
10 AppliedandEnvironmentalSoilScience
010101010101030303060505030303 010101
Q −−−−−−−−−−−−−−− −−−
malesDermalcontact 3DD(mg/m-day)THdermal −4.19E064.19E−5.43E065.43E−4.58E064.58E−7.88E061.31E−1.05E051.75E−9.55E061.59E−2.64E054.88E−3.92E057.26E−3.43E056.35E−4.90E099.35E−7.75E091.48E−6.31E091.20E−6.41E051.06E−6.71E051.12E−6.42E051.07E−1.03E04−1.22E04−1.13E045.56E7.25E6.24E
Adult EQ −07−07−07−07−07−07−08−08−08−10−09−09−08−08−08 −07−07−07
TH 1.09E1.42E1.20E3.21E4.28E3.89E1.38E2.06E1.80E8.58E1.36E1.10E3.92E4.10E3.93E 4.85E6.33E5.68E
urepathways. Inhalation D(mg/kg-day)inh −1.09E10−1.42E10−1.20E10−9.94E10−1.28E09−1.17E09−2.77E10−4.11E10−2.59E10−3.60E12−3.00E12−4.74E12−1.18E08−1.23E08−1.18E08−1.31E08−1.42E08−1.34E08
s D
o E
p
ex 010101010101030303050505030303 010101
inhalationanddermal alesDermalcontact 3D(mg/m-day)THQdermal −−5.01E065.01E−−6.49E066.49E−−5.47E065.47E−−9.41E061.57E−−1.25E052.08E−−1.14E051.90E−−3.15E055.83E−−4.68E058.67E−−4.10E057.60E−−5.87E091.12E−−9.26E091.76E−−7.54E091.44E−−7.66E051.27E−−8.01E051.33E−−7.67E051.28E−1.23E04−1.46E04−1.34E04−6.65E−8.67E−7.46E
for fem ED
dult Adult Q −08−07−08−07−07−07−09−08−08−10−10−10−08−08−08 −07−07−07
anda TH 7.91E1.02E8.64E2.31E3.08E2.80E9.96E1.48E1.29E6.18E9.76E7.93E2.82E2.95E2.82E 3.49E4.56E4.09E
ren ation day)
xforchild Inhal D(mg/kg-inh −7.91E11−1.02E10−8.64E11−6.94E10−9.24E10−8.41E10−1.99E10−2.96E10−2.59E10−2.16E12−3.41E12−2.78E12−8.47E09−8.86E09−8.48E09−9.45E09−1.02E08−9.67E09
e D
nd E
i
nichazard ontact THQ −1.57E01−2.03E01−1.72E01−4.93E02−6.56E02−5.97E02−1.83E03−2.72E03−2.38E03−3.51E06−5.54E06−4.50E06−4.00E04−4.19E04−4.01E04 −2.07E01−2.72E01−2.34E01
ncarcinoge DermalcEDDdermal3mg/m-day)−1.12E08−1.45E08−1.23E08−9.85E08−1.31E07−1.19E07−9.89E06−1.47E05−1.29E06−1.84E09−2.91E09−2.36E09−2.40E05−2.51E05−2.41E05−3.84E05−4.58E05−4.22E05
o (
N
Table8: 6years)ation THQ −1.97E09−8.49E06−7.17E06−5.76E07−5.75E05−6.98E06−1.84E05−2.48E08−7.17E06−1.54E09−2.43E09−1.97E09−7.02E08−1.10E04−4.40E08 −8.69E07−1.94E04−2.14E05
Children(1–InhalEDDinhmg/kg-day)−1.97E10−2.55E10−2.15E10−1.73E09−2.30E09−2.09E09−4.96E10−7.36E10−6.45E10−5.38E12−8.49E12−6.91E12−2.10E08−2.20E08−2.11E08−2.34E08−2.53E08−2.40E08
(
Conc.mg/kg) 0.690.900.766.108.127.391.752.602.280.020.030.0274.4377.8574.51min.valuesmax.valuesmeanvalues
( ororor
fff
kkk
Conc.Metallevels Min.CdMax.MeanMin.CrMax.MeanMin.NiMax.MeanMin.PbMax.MeanMin.ZnMax.MeanCumulativerisCumulativerisCumulativerisHImin.valueHImax.valueHImeanvalue