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