Research Article Trace Metal Contamination C ...downloads.hindawi.com/journals/aess/2016/8178901.pdf · Research Article Trace Metal Contamination C haracteristics and Health Risks

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Research ArticleTrace Metal Contamination Characteristics and HealthRisks Assessment of Commelina africana L and PsammiticSandflats in the Niger Delta Nigeria

Nsikak U Benson1 Paul A Enyong2 and Omowunmi H Fred-Ahmadu1

1Analytical and Environmental Chemistry Unit Department of Chemistry Covenant University Km 10 Idiroko Road Ota Nigeria2Department of Chemistry University of Uyo Uyo Nigeria

Correspondence should be addressed to Nsikak U Benson nbensoncovenantuniversityedung

Received 27 May 2016 Revised 29 June 2016 Accepted 6 September 2016

Academic Editor Yongchao Liang

Copyright copy 2016 Nsikak U Benson et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

The purpose of this study was to investigate and quantify trace metal concentrations in Commelina africana L and psammiticsandflats from an intertidal coastal ecosystem in Niger Delta Nigeria and to evaluate their spatial distribution degree ofcontamination and source apportionment The environmental risks associated with soil contamination were elaborately assessedusing potential ecological risk index sediment quality guidelines and enrichment relative to background levels The meanconcentrations of Cd Cr Ni Pb and Zn in sandflat soil samples are 076 plusmn 90 times 10minus2 739 plusmn 87 times 10minus1 228 plusmn 0350024 plusmn 40 times 10minus3 and 7451 plusmn 255mgkg respectively Metal levels indicate strong variability with sampling sites The orderof trace metal concentrations in the Commelina africana L samples is Zn gt Ni gt Cr gt Pb gt Cd The concentrations varied withthe sample locations and the levels of Pb (005 to 008mgkg) at all locations are found to be significantly below permissible levelof 03mgkg Potential sources of metal loadings may be associated with localised or diffused anthropogenic activitiesThe averagecarcinogenic risks are below 10 times 10minus6 threshold values and the sandflat soils are not considered to pose significant health effectsto children and adult males and females However the carcinogenicity and noncarcinogenicity risks ranking decrease following theorder children gt adult males gt adult females Comparatively the hazard quotient and hazard index indicate that the psammiticsandflats might pose a health risk to children in future

1 Introduction

Pollution investigations in coastal ecosystems of Niger Deltahave revealed that human mediated activities can adverselyalter the ecological integrity of fragile aquatic systems in theregion resulting in bioaccumulation of chemical contami-nants by zoobenthos [1ndash4] sediment enrichment [5] andimpact on species abundance and biomass [6 7] Most equa-torial wetlands and ultisol systems in the Niger Delta serveas primary recipients of petroleum exploration-exploitationwastes and domestic and industrial wastes generated bymultinational oil companies that are found in the regionStudies have indicated enhanced levels of trace metals in soilsurface water sediments and biota from aquatic ecosystemsin the area [8ndash11] In the wetlands and soil environment

trace metals are naturally ubiquitous [12 13] Although sometrace metals are present as natural nutrient componentsof the soil environment introduced through weatheringprocesses most however originate from a variety of humanmediated activities [14ndash18] In the Niger Delta crude oilpollution and petrochemical activities have been identifiedas major anthropogenic activities that significantly promotethe introduction of trace metals into both the terrestrial andaquatic environments [5 19 20]

Wetland soils act as both sinks and carriers for tracemetals and could provide valuable information on the pol-lution pattern and history of such ecosystems [21 22] Tracemetals present in the soil are capable of undergoing chem-ical transformation from solids to ionic species or throughbiomethylation into organometallic moieties [23] Also they

Hindawi Publishing CorporationApplied and Environmental Soil ScienceVolume 2016 Article ID 8178901 14 pageshttpdxdoiorg10115520168178901

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2 Applied and Environmental Soil Science

NigeriaN

W E

S

SettlementsSampling points

Mangrove swampWater

(Kilometers)30201050

8∘09984000998400998400E 8

∘10

9984000998400998400E 8

∘20

9984000998400998400E 8

∘30

9984000998400998400E7

∘50

9984000998400998400E

4∘30

9984000998400998400N

4∘40

9984000998400998400N

4∘50

9984000998400998400N

5∘09984000998400998400N

5∘10

9984000998400998400N

Figure 1 Qua Iboe Estuary mangrove ecosystem showing the sampling location along Douglas Creek Insert map of Nigeria showing thelocation of the study area

could be released in both particulate and dissolved forms andare known to have high affinities for fine-grained sedimentand soil particulates [24ndash27] However the fate transportand pollution characteristics of trace metals in the wetlandsoils have become an important problem due to their toxiceffects accumulation and bioconcentration through the foodchain [28 29]

Tracemetals introduced into the environment are capableof having toxicological implications on terrestrial inver-tebrates humans and the natural environment [30ndash32]Adverse health effects such as lung and skin cancer prostaticproliferative lesions peripheral neuropathy kidney dysfunc-tion dermal lesions and peripheral vascular disease havebeen attributed to trace metals pollution However metaltoxicitymainly depends on themetal speciation and bioavail-ability as well as on the means of uptake accumulation andexcretion rates of the organisms [24 28 33ndash35] Thereforeelucidating the potential sources ionic forms ecosystemvari-ability pollution status and environmental risks assessmentof trace metals in wetland soil environment is a criticaltool in understanding the contamination characteristics ofsuch ecosystems It also provides expository information forenvironmental pollution prevention and control

The present study was initiated with the following objec-tives (a) to determine the levels of trace metals accumulationand distribution in coastal sandflats flora and fauna from anestuarine ecosystem (b) to evaluate potential ecological risksfrom metal pollution using different indices such as metalpollution index (MPI) and transfer factors (TFs) (c) to assessthe degree of trace metal pollution using contaminationindices such as pollution load index (PLI) contamination

factor (Cf) modified contamination degree (mCD) andgeoaccumulation index (119868geo) (d) to evaluate the coastalsoil quality and environmental risks of investigated tracemetals by comparison with soil quality guidelines (SQGs)(e) to identify the possible sources of trace metal pollutionand to assess their ecotoxicological significance and (f) toassess potential noncarcinogenic and carcinogenic risks dueto inhalation dermal contact and oral ingestion exposurepathways

2 Materials and Methods

21 Study Area The Douglas Creek is a major tributary ofQua Iboe Estuary (Figure 1) The estuary is characterized byshallow intertidalmudflats that are surrounded bymangrovesand is perennially subjected to sediment deposition fromQua Iboe River and marine sand from the Atlantic OceanIt is located close to several coastline settlements within anoil producing area in Southeastern Nigeria The Qua IboeEstuary and Douglas Creek lie within latitude 4∘301015840 to 4∘451015840Nand longitude 7∘301015840 to 8∘001015840E It serves as the receivingwater body for residential agricultural and petrochemicalwastes generated frommultinational oil companies located inthe oil producing communities The estuary is characterizedby fine sandy beaches fringed with mangrove swamps andtidal mudflats on which Nypa palm vegetation dominatesThe study area is characterized by a humid tropical climatewith an annual rainfall of about 4021mm average humidityof 80 and mean minimum and maximum temperaturesof 22∘C and 30∘C respectively There are two predominantseasons dry and wet seasonsThewet season begins inMarch

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Applied and Environmental Soil Science 3

Table 1 Reference (SRM 8704) concentration values analytical results and percentage recovery

Metals SRM 8704 reference values AAS results Accuracy ( recovery)(mgkg) (mgkg) (119899 = 3)

Cadmium 294 plusmn 029 303 plusmn 004 10296Chromium 12190 plusmn 380 11947 plusmn 164 9801Nickel 4290 plusmn 370 4086 plusmn 018 9523Lead 15000 plusmn 1700 15604 plusmn 695 10423Zinc 40800 plusmn 1500 39860 plusmn 1054 9767

or April and is usually characterized by heavy storms of shortdurationThe dry season which normally lasts 3ndash5months iscomparatively short beginning in November and extendingto February Tidal currents are strong especially during thewet seasons along estuary upper reaches and creek and thisplays an important role in sedimentation biota distributiontrace metal laden waste transportation and industrial anddomestic waste transportation

22 Sampling A total of 30 plant and soil samples wereeach collected from the study area along a marked transectPlant and soil samples were collected during two separatetrips from five designated grids DC-V DC-W DC-X DC-Y and DC-Z mapped out along the stretch of Douglas Creekextending into Qua Iboe Estuary At each sampling stationtriplicates of the plants and soil samples were obtained andcarefully transferred into clean polyethylene glass containersA short core sampler was used to collect the soil from thetop 0 to 15 cm of the soil surface and homogenized andthe subsamples were stored in labeled black polythene bagsPlant samples were also handpicked along the tidal shores ofDouglas Creek and thoroughly cleanedwith freshwater to getrid of soil before transferring them into labeled aluminiumfoil The samples were all stored in ice-packed coolers andtransported to the laboratory They were further refrigeratedin the laboratory at 4∘C to inhibit microbial activities andpreserve the integrity of the samples prior to analysis

23 Analytical Procedures for Sample Pretreatment and Chem-ical Analysis The soil samples were air-dried by exposureto ambient air for 48 hours and manually sorted to removestones sticks organic matter and shells from the air-driedsamples pulverized using porcelain pestle and mortar andsieved through a 2mm mesh and sieved to collect lessthan 63 120583m grain sizes 20 g of each sample was digestedwith a solution of concentrated HCl (60mL) and HNO3(03mL) to near dryness and allowed to cool before 20mLof 50MHNO3 solution was added The digested soil samplesolution was allowed to stay for about 12 hours before theywere filtered The filtrates were subsequently transferred into100mL volumetric flask and made up to the mark with05MHNO3 prior to elemental analysis A reagent blank wasalso prepared using a mixture of HCl and HNO3 followingthe stepwise analytical procedure described for the samplepreparation

On the other hand the plant samples were oven driedat 80∘C for 24 hours to prevent microbial decomposition

pulverized into fine powder and stored in well-labeled Ziplocbags Precisely 10 g of each plant sample was accuratelyweighed into 10mL conical flask and 1mL HClO4 and 7mLof 40 HF were added and digested slowly for 2 hours usinga modified method of Vanek et al [36] After digestion theywere allowed to cool and later were heated and the contentwas evaporated until fumes of HClO4 appeared The residuewas allowed to cool and 1mL H2SO4 added and heatedagain to drive off HClO4 After cooling all samples werediluted with a little water and filtered into 25mL volumetricflasks fitted with a glass funnel and Whatman number 1filter paper The filtrates were later made up to 25mL markwith distilled water Also blanks were prepared following theabove procedure with all reagents excluding the sample Thesolutions were used for the determination of trace metalsAcid eluates desorbed from the filter and 30 digested soiland plant sample solutions and the reagent blanks wereanalysed for the concentrations of Zn Pb Cd Ni and Crusing an atomic absorption spectrometer (S Series S4 AASystem Thermo Electron Corporation) In order to evaluatethe precision of each method of digestion for soil and plantsamples the trace metal analyses were run in duplicates

24 Quality Assurance Buffalo River Sediment ReferenceMaterial (SRM 8704) sourced from National Institute ofStandards and Technology (US) intended primarily for usein the analysis of sediments soils or materials of a similarmatrix was analysed with the soil samples for quality assur-ance purposes Reference values and the analytical results forthe concentrations of five trace metals are given in Table 1The recoveries of the AAS analytical results for Cd CrNi Pb and Zn ranged between 9767 and 10423 Theconcentrations of certified materials SRM 8704 indicatedresults within the range of the reference values Therefore themethod employed for this work is reliable and reproducibleBlanks were also monitored throughout the analysis of thesoil samples and blank subtractions were employed to correctmetal concentrations obtained for soil samples

25 Statistical Analysis The data were analysed using theXLSTAT-Pro software (AddinSoft Inc NY USA) Pearsonrsquoscorrelation analysis and factor analysis were employed toexplore the interrelationship among trace metals in soilsamples and also attempt to identify their probable originThe various statistical analyses were performed with a 95confidence interval (significance 119901 lt 005)

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4 Applied and Environmental Soil Science

26 Pollution Indicators On the basis of observed data therelative gradation of contamination levels by trace metals inultisols can be achieved using pollution indices (PIs) andefficient risks assessment approaches However the evalua-tion of pollution loading status and the estimation of impactsassociated with human induced events on coastal wetlandsoils could be attained through geochemical approaches suchas geoaccumulation index and enrichment factor [16 37]

27 Soil Contamination Indices and Potential Ecological RisksTheunder listed contamination indices were adopted to eval-uate trace metals contamination assessment in soil samplescollected from the study area (i) degree of contamination(CD) (ii) modified contamination degree (mCD) (iii) con-tamination factor (Cf) (iv) pollution load index (PLI) (v)pollution index (PI) andNemerow integrated pollution index(NIPI) and (vi) geoaccumulation index (119868geo) [37]The singlemetal and multimetal potential ecological risk indices werealso calculated for Cd Cr Ni Pb and Zn

The CD was calculated to assess the holistic impactof multimetals on the environment [22 38] The formuladeveloped by Hakanson [39] was used for the calculation ofCD

CD = 119899sum119894=1

Cf 119894 (1)

Cf 119894 = [119862119894mconc119862119894bkg ] (2)

where Cf 119894 is contamination factor of metal 119894 119862119894mconc is meanconcentration and 119862119894bkg is background value of individualmetal The degree of contamination is classified into lowdegree of contamination (CD le 6) moderate degree ofcontamination (6 lt CD le 12) considerable degree ofcontamination (12 lt CD le 24) and very high degree ofcontamination (CD gt 24) The Cf is derived by dividingthe concentration of selected trace metal by the backgroundvalue The gradation of Cf is as follows Cf lt 1 indicateslow degree of contamination 1 le Cf lt 3 indicatesmoderate contamination 3 le Cf lt 6 indicates considerablecontamination and Cf ge 6 shows very high degree ofcontamination

ThemCD is an empirical assessment of the overall degreeof contamination by pollutants in a designated ecosystem andis mathematically expressed as follows

mCD = sum119899119894=1 Cf 119894119899 (3)

where Cf is contamination factor 119899 is the number of analysedtrace metals and 119894 is 119894th metal

The following classifications and descriptions are avail-able for modified degree of contamination in soil mCD lt15 refers to nil to very low degree of contamination 15 lemCD lt 2 indicates low degree of contamination 2 le mCD lt4 implies moderate degree of contamination 4 le mCD lt 8indicates high degree of contamination 8 le mCD lt 16

means very high degree of contamination 16 le mCD lt 32implies extremely high degree of contamination and mCD ge32 refers to ultrahigh degree of contamination

PLI was evaluated using Tomlinsonrsquos pollution load index(PLI) [40] and is expressed as the 119899th root of the product of119899 Cf as

PLI = [Cf1 times Cf2 times sdot sdot sdot times Cf119899]1119899 (4)

where 119899 is the number of metals and Cf119899 is the Cf valueof metal 119899 PLI is classified as follows according to thecontamination degree background concentration (PLI = 0)unpolluted (0 lt PLI le 1) unpolluted to moderately polluted(1 lt PLI le 2) moderately polluted (2 lt PLI le 3)moderately to highly polluted (3 lt PLI le 4) highly polluted(4 lt PLI le 5) or very highly polluted (PLI gt 5) [16 41]

Additionally the pollution index (PI) was used to eval-uate soil pollution by comparing the metal concentrationsobtained in this study with Dutch soil guidelines [42]According to Lee et al [37] PI is expressed as

PI = 119862119899119879119899 (5)

where119862119899 is the concentration of an individual tracemetal and119879119899 is the corresponding target concentration of Dutch soilguidelines which consider different land-use types and arebased on extensive studies of both the human and ecotoxico-logical effects of soil contaminants [43] Nemerow integratedpollution index (NIPI) was also employed for the assessmentof the overall pollution integrity of the investigated ecosystem[44] The NIPI was calculated using the following equation

NIPI = [05 times (1198682mean + 1198682max)]12 (6)

where 119868mean is the mean value of all pollution indices of themetals considered and 119868max is the maximum value AccordingtoCheng et al [45] the classification of NIPI is as follows safe(NIPI le 07) precaution (07 lt NIPI le 1) slightly polluted(1 lt NIPI le 2) moderately polluted (2 lt NIPI le 3) orheavily polluted (NIPI gt 3)

The index of geoaccumulation (119868geo) is a commonapproach employed to estimate metals enrichment abovebackground or baseline concentrations in soil or sedimentThe 119868geo values for the studied trace metals were calculatedusing the following equation developed by Muller [46]

119868geo = log2 ( 11986211989915119861119899) (7)

where 119862119899 is the measured concentration of selected metal(119899) in the soil sample and 119861119899 is the geochemical backgroundin average shale of metal (119899) In this study the geochemicalbackground soil concentrations of Cd CrNi Pb andZnwere03 90 68 20 and 95mgkg respectively and were used incalculating the 119868geo values [47] The coefficient 15 is used todetect variations in the background data due to lithogenic[48 49] and anthropogenic influences [50] 119868geo consists ofseven grades According to Muller [46] 119868geo consists of 7classes The corresponding relationships between 119868geo and

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Applied and Environmental Soil Science 5

Table 2 Summary statistics of tracemetal concentrations (mgkg) in sandflats andCommelina africana L from the sandy beaches of DouglasCreek

Trace metals Min Max Mean Std deviation CV

Soil

Zn 7143 77850 7451 2553 342Pb 0019 0030 0024 0004 1667Cd 0695 0900 0759 0090 1184Ni 1750 2600 2278 0346 1491Cr 6100 8120 7392 0875 1177

C africana L

Zn 22590 2522 23926 11801 493Pb 0050 0080 0058 0013 2241Cd 0150 0750 0304 0250 8224Ni 1065 26750 19152 7289 3807Cr 7879 13824 9642 2383 2469

the degree of metal pollution level are as follows unpolluted(119868geo le 0) unpolluted to moderately polluted (0 lt 119868geo le 1)moderately polluted (1 lt 119868geo le 2) moderately to heavilypolluted (2 lt 119868geo le 3) heavily polluted (3 lt 119868geo le 4)heavily to extremely polluted (4 lt 119868geo le 5) or extremelypolluted (119868geo gt 5)

The overall toxicity and potential ecological hazardsposed by metals in soil were assessed using a methodproposed by Hakanson [39] The potential ecological riskindex (PERI) primarily evaluates the probable degree of tracemetal contamination taking into consideration the relativetoxicity of the overall metals and the short-to-long-termresponse of the environment The risk index (119877119868) is calculatedbased on the following equation

119864119894119891 = sum119879119894119903 (119862119894119904119862119894119899)

119877119868 = sum119864119894119891(8)

where 119877119868 is the sum of individual risk factors for all tracemetals 119864119894119891 is the monomial PERI for individual metal119862119894119904 and 119862119894119899 are the observed and background values ofconcentrations of metals respectively and 119879119894119903 is the toxicresponse factor for a single trace metal 119879119894119903 for Cd Cr Ni Pband Zn are 30 2 5 5 and 1 respectively [39 51]The potentialecological risk 119877119868 is classified as follows 119877119868 lt 95 low risk95 le 119877119868 lt 190 moderate risk 190 le 119877119868 lt 380 high riskand 119877119868 ge 380 very high risk while the potential ecologicalrisk index associated with an individual metal 119864119894119891 is rankedas follows 119864119894119891 lt 40 low risk 40 le 119864119894119891 lt 80 moderate risk80 le 119864119894119891 lt 160 considerable risk 160 le 119864119894119891 lt 320 high riskand 119864119894119891 ge 320 very high risk [18 52]

28 Assessment of Pollution and Bioaccumulation Index inCommelina africana L Bioaccumulation index can be usedto provide a relative evaluation of the degree of contaminationthrough uptake or exposure This is sometimes referred toas a plant uptake factor or transfer factors (TFs) of heavy

metals from soil to plants In this study the transfer factorwas determined using

TF119901 = 119862119894119901119862119894119904 (9)

where 119862119894119901 is the 119894 metal concentration in the plant material(dry weight basis) and 119862119894119904 is the total concentration of the 119894metal in the soil (dry weight basis) [53 54] In addition metalpollution index (MPI)was employed as ameans of comparingthe total metal concentration of Commelina africana L withthe respective sampling sites MPI is expressed according tothe following equation [55 56]

MPI = [1198621 times 1198622 times 1198623 times sdot sdot sdot times 119862119899]1119899 (10)

where 119899 is the number of metals and 119862119899 is the concentrationof metal 119899 in Commelina africana L on dry weight basis

3 Results and Discussion

31 Trace Metal Content Metal levels in the Commelinaafricana L and soil samples have been assessed for zinc (Zn)lead (Pb) cadmium (Cd) nickel (Ni) and chromium (Cr)and the results are presented in Table 2 The results showthat mean concentration of most trace metals in the coastalsandflats exceeded the recommended guideline values Themean concentrations of Cd Cr Ni Pb and Zn in sandflatsoil samples were 076 plusmn 90 times 10minus2 739 plusmn 87 times 10minus1 228 plusmn035 0024 plusmn 40 times 10minus3 and 7451 plusmn 255mgkg respectivelyNotably the metal levels indicate strong variability withsampling sites The observed variability and enhanced metallevels could have been influenced by changes in transport andsedimentation modes from surrounding intertidal ecosys-tem Additionally these variations may be attributed todifferences in the rates of metal solubility in soils which ispredominantly controlled by pH amount of metals cationsexchange capacity organic carbon content and oxidationstate of the system [57] The order of mean concentrationsin the C africana L samples was Zn gt Ni gt Cr gtPb gt Cd However Cd level (075mgkg) in C africana L

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6 Applied and Environmental Soil Science

Table 3 Pollution indicators for trace metals in sandflats fromDouglas Creek

Pollution indices Sample sitesDC-V DC-W DC-X DC-Y DC-Z

Cf

Zn 077 078 082 080 075Pb 0001 0001 0001 0001 0001Cd 234 233 231 267 300Ni 003 003 004 003 004Cr 009 008 007 009 007

119868geoZn 0512 0520 0546 0535 0508Pb 0001 0001 0001 0001 0001Cd 1558 1556 1544 1778 2000Ni 0017 0021 0025 0023 0025Cr 0059 0059 0051 0060 0045

Cd 3219 3234 3251 3595 3859mCD 0644 0647 0650 0719 0772

from location DC-W was far above FAOWHO maximumlevel of 02mgkg [58]

Although there is no authoritative reference detailing theregulated background values of trace metals in Nigeria itis obvious that observed metal levels except Cd in sandflatsoil samples did not exceed background values or regulatorystandards of heavy metals from other parts of the world[59 60] Trace metals in soils have been shown to bevery useful indicators of environmental pollution [61ndash63]Thus the environmental quality of this sandflat soil raisesserious health concerns especially considering its usage as arecreational area where people come into direct contact withcontaminant soil and dust particles Some of the dominantsources of trace metal loadings to the sandflat soil may be dueto wastes deposited from localised or diffused sources such ascrude oil spill fuel combustion (gas flaring) wastes disposaltraffic emission petrochemicals fertilizers and pesticides

32 Evaluation of Soil Pollution Indices The contaminationfactor values were calculated using (2) and are listed inTable 3 The mean Cf values calculated for studied tracemetals in psammitic sandflat soil samples were in the fol-lowing order Cd (253) gt Zn (078) gt Cr (008) gt Ni (003)gt Pb (0001) (Figure 2) Cf values less than 1 (one) andthose between 1 and three are considered to pose low andmoderate degree of contamination respectively Thereforethe results of the present study at the various sites showedthat the soil samples taken from the beach of Douglas Creekwere moderately contaminated by Cd whereas Cr Ni Pband Zn indicated low degree of contamination Cadmiumcould be introduced to soil air and aquatic environmentthrough anthropogenic inputs such as fossil fuel combustionapplication of phosphate fertilizers and waste dumpingand incineration [43 64] Cd is a known carcinogen thatcan potentially cause adverse effects to human kidneyslungs and bones Thus the relatively high Cf value of Cdindicating moderate contamination is significant Howeverconsiderable contamination is likely through uncontrolled

Cd Cr Ni Pb Zn

Cr Ni Pb

01020304050607080

Indi

vidu

al ec

olog

ical

risk

inde

x

Igeo

Cf

Ef

0

05

1

15

2

25

3

0004008012016

02

Mea

n Cf

Ige

o

Figure 2 Individual ecological risk index and mean Cf119868geo valuesof trace metals for sandflats soil samples of Douglas Creek

fossil fuel combustion (excessive gas flaring) and untreatedwaste disposal and carcinogenic risk associated with Cd ispotentially of health and environmental concerns

The degree of contamination (CD) and modified degreeof contamination (mCD) were calculated using (1) and(3) respectively and the derived contamination values arepresented in Table 3 Results indicate that the CD and mCDat all sites generally showed low degree of contaminationInterestingly both values did not exhibit correlative variabil-ity with the selected sites and may be considered to be in therange of unperturbed variability This might be a functionof the hydrodynamic conditions of the aquatic ecosystemat the period of obtaining the soil samples However thecontamination ranking of trace metals on the basis of percentcontribution to CD and mCD is Cd gt Zn gt Cr gt Ni gt Pb

Table 3 shows the results of the calculated 119868geo values andFigure 2 presents the mean 119868geo values for each trace metalin the sandflats soil samples of the investigated sites The 119868geovalues for Cr Ni Pb and Zn indicated less variability amongthe sampling sites and were within 0 lt 119868geo le 1 implyingthat the soil samples were unpolluted to moderately pollutedThe calculated 119868geo values for Cd showed that the soil sampleswere moderately polluted (1 lt 119868geo le 2) at all sites It isimperative to emphasize that the average 119868geo values for Cdwere relatively higher than other trace metals suggesting thatthe soil samples from the Douglas sandy beach must havebeen contaminated by Cd due to anthropogenic activities

The pollution load index provides an integrated con-tamination assessment based on the Cf of each trace metalThe PLI values for Cd Cr Ni Pb and Zn are presented inFigure 3 and ranged between 0086 and 0097 at DC-W andDC-Z sites respectively As indicated by these PLI valuesthe sandflat samples of the present study are unpollutedwith PLI values between zero and one for all sites Howeverit must be noted that the present day PLI values obtainedfor soil samples were dominated by individual contributionsof Cd and Zn The calculated pollution index (PI) and theNemerow integrated pollution index (NIPI) values of tracemetals in foreshore psammitic soil samples of Douglas Creekare presented in Table 4 Results indicate that the sandy beachof this aquatic ecosystem was not polluted but contaminationranking is precautionary (07 lt NIPI le 1)

Page 7

Applied and Environmental Soil Science 7

Table 4 Comparison of pollution indices (PIs) of trace metals in sandflat soils of Douglas Creek and other studies

Cd Cr Ni Pb Zn 119868mean 119868max NIPIMean 076 739 228 002 7451Target valuea 08 100 35 85 140This study 095 0074 0065 00003 053 032 095 071Odewande and Abimbola [76] 02 06 05 06 07 05 09 07Dutch soil guidelines [42]a

Table 5 Soil-to-plant transfer factors of studied trace metals

Sample ID Cd Cr Ni Pb ZnDC-V 029 110 1326 200 313DC-W 107 109 1085 263 305DC-X 030 133 1057 261 309DC-Y 026 097 447 200 331DC-Z 017 227 463 267 348

33 Evaluation of Pollution and Bioaccumulation Index MPIresults indicated that the calculated values varied with sam-pling sites and were a function of the total concentration ofindividual trace metals The highest MPI value (442) wasobtained at DC-W site followed by 375 at DC-X and then346 atDC-Z siteThe lowestMPI value of 295 forCommelinaafricana L was recorded at downstream of the creek at DC-Y site Moreover transfer factor is one way through whichthe mobility of metal by plants can be assessed The soil-to-plant transfer factor (TF) values recorded for differentsamples sites are presented in Table 5 The results revealedthat Ni (1326) in DC-V and Zn (348) in DC-Z soil had thehighest transfer factor value while Cd (017) and Cr (097) insoils from DC-Z and DC-Y stations respectively reportedthe lowest transfer factor value in the study area The metalbioavailability from soil to the plant as indicated by thetransfer factor values for the five sample stations decreasedin the order TFNi gt TFZn gt TFPb gt TFCr gt TFCd A highervalue of transfer factor implies the tendency of more mobileand available metals [53] Generally Ni element exhibitedhigher valves of TF at all the sampling sites as shown on thetable when compared with the results of other trace metalsunder investigation

34 Evaluation of Potential Ecological Risks The potentialecological risks assessment of trace metals in sandflat soilsamples of the investigated ecosystem were calculated basedon (8) Results of average potential ecological risk index ofeach trace metal are presented in Figure 2 Calculated 119864119894119891values for Cr (016) Ni (017) Pb (0006) and Zn (078)indicated low degree of risk while Cd 119864119894119891 value indicatedmoderate risk (40 le 119864119894119891 lt 80) This result again highlightspossible contamination concerns associated with Cd whichis likely due to fossil fuel burning in the region over theyears Interestingly other researchers have reported thatCd contribution to potential ecological risk index of theenvironment is very significant [61 65] The contamination

DC-V DC-W DC-X DC-Y DC-ZSampling sites

008

0085

009

0095

01

Pollu

tion

load

inde

x

Figure 3 Pollution load index ofmetals at sampling sites of DouglasCreek

ranking of trace metals in line with the mean PERIs forindividual metal stressors is Cd gt Zn gt Ni gt Cr gt PbHowever on the basis of the calculated 119877119868 value (119877119868 = 77) alow ecological risk (119877119868 lt 95 low risk) was indicated for themultielements considered in this study

35 Principal Component Analysis (PCA) The principalcomponent analysis (PCA) of variables was performed toextract significant principal components (PCs)The results of119899-Pearson PCA performed further explored the relationshipsbetween the trace metals and also clarify their possiblesources Table 6 summarises the factor loadings of tracemetals for sandflat and Commelina africana L grouped intothree principal component models The loading plots of thePCs are presented in Figure 4 The Eigen values of PC1and PC2 associated with sandflat soil were greater than 1and in general accounted for 8663 of the variability inconcentrations of trace metals PC1 indicated that 5988 ofthe total variance was positively related to Cd Pb and Niwith Cd and Pb showing relatively high factor loadings whileCr indicated a strong negative relationship On the otherhand PC2 which explained 2676 of the total varianceindicated strong positive interrelationships for Ni and Zn

It is worthy of note that the positive loading of Cd Niand Pb with PC1 could possibly suggest that contaminationof the sandflat soil samples might have been influenced byanthropogenic pollution sourcesTheEigen values of PC1 andPC2 derived for Commelina africana L samples indicate theywere greater than 1 and accounted for 8332 of the variabilityin trace metal levels PC1 was the most significant principalcomponent and was dominated by Cd Cr Ni Pb and Zn

Page 8

8 Applied and Environmental Soil Science

Table 6 PCA factor loadings of the concentrations of trace metalsfor sandflat soil and C africana L samples

Factor components1198651 1198652 1198653

Sandflat

Zn minus0477 0830 0207Pb 0880 minus0223 0212Cd 0923 minus0107 0308Ni 0663 0724 0038Cr minus0837 minus0251 0475

Eigenvalue 2994 1338 0410Variability () 59879 26755 8207Cumulative 59879 86634 94841

C africana L

Zn 0833 minus0470 0037Pb 0849 0516 minus0021Cd minus0690 0304 0637Ni minus0724 0430 minus0500Cr 0791 0600 0083

Eigenvalue 3042 1124 0664Variability () 60838 22483 13285Cumulative 60838 83321 96606

High factor loadings for each principle component are highlighted with boldtype

which accounted for 6084 of the total variance A veryhigh loading of Cr (0791) Pb (0849) and Zn (0833) in thePC1 component and the investigated trace metals indicated asignificantly positive interrelationship Additionally the highloading of Cd (0690) and Ni (0724) on the first principalcomponent indicated strong negative correlation

36 Potential Health Risk Assessment The health effectsthat might be attributed to noncarcinogenic trace metals insoilsanddust could be evaluated by comparing an exposurevia oral ingestion over a specified timeperiodwith a referencedose (RfD) for each metal over a similar exposure periodThis noncancer risk assessment ratio is termed target hazardquotient (THQ) [66]The RfD is the toxicity threshold valuewhich is specific for each chemical contaminant However inorder to evaluate the overall exposure potential for combinedchronic effects caused by all the metal contaminants a hazardindex (HI) approach was adopted The HI is equal to thearithmetic sum of individual metal THQs [66]The estimateddaily dose exposure through oral ingestion (EDDing) dermal(EDDdermal) and inhalation absorption (EDDinh) THQ andHI is determined by the following equations respectively[66ndash68]

EDDinh = 119862metal times EF times ED times IRinhBw times AT times PEF

EDDing = 119862metal times EF times ED times IRing

Bw times AT times 10minus6

EDDdermal = 119862metal times AF times EF times ED times SA times ABSBw times AT

times 10minus6THQ119894 = [ EDIRfD119894

]

HI = 119899sum119894=1

THQ119894(11)

where 119862metal is the concentration (mgkg) of trace metal insandflat sample EF is the exposure frequency (365 dyear)ED is the exposure duration equal to 6 y and 18 y for childrenaged between 1 and 6 years and 6 and 18 years respectivelyand 524 years for adults (World Bank 2013 estimate foraverage life expectancy in Nigeria) [69] IRing is the ingestionrate (100 and 50mgday for children and adults resp) IRinhis inhalation rate [70] Bw is the average body weight (70 48and 19 kg for adults and children resp) and AT is the averageexposure time for noncarcinogens (2190d age 1ndash6 y 6570 dage 6ndash18 y 191625 d adults) PEF is the particulate emissionfactor (m3kg) = 136times 109 SA is the exposed skin surface area(cm2) AF is the adherence factor (kgcm2-day) ABS is thedermal absorption factor and RfD is the oral reference dose(mg kgminus1 dayminus1) The variable 119894 denotes the 119894th trace metalThe RfDs for Cd Cr Ni Pb and Zn are 0001 0003 00200035 and 03mg kgminus1 dminus1 respectively [71] However targethazard quotient or hazard index le 1 indicates that potentialadverse health impacts from ingestion are unlikely whileTHQ or HI gt 1 suggests that adverse chronic effects arelikely fromdirect oral ingestion of contaminated sandflats soil[66] Moreover to assess the carcinogenic effects the averagedaily dose is multiplied by the corresponding slope factor(SF) to produce a level of cancer risk [16 72] However theaggregate carcinogenic risk was evaluated as a summation ofthe individual cancer risk across inhalation exposure pathwayas

Risk = sumEDD119894 times SF119894 (12)

Tables 7 and 8 present the calculated results for noncar-cinogenic hazard index for children and adults (males andfemales) in Nigeria assessed by considering the exposureto trace metal contaminated sandflat soils via ingestioninhalation and dermal contact pathways The potential risksin terms of the minimum maximum and average hazardindices of trace metals in sandflat soil samples for childrenand adult males and females were less than 1 Thus thesepopulations are unlikely to face any potential health risks [73]

As presented inTable 8 Cd Cr andNimay pose relativelysignificant noncarcinogenic health risks to the selected pop-ulation compared to Pb and Zn For instance considering thetotal hazard quotients (THQs) for inhalation of sandflat soilsin children Cd Cr and Ni accounted for 3355 3267and 3356of the calculated hazard index respectively whilePb and Zn contributed the relatively insignificant 022

Page 9

Applied and Environmental Soil Science 9

Table 7 Noncarcinogenic effects due to oral ingestion exposure to sandflat soil trace metals

Cd Cr Ni Pb ZnEstimated daily dose (EDDing)

Children (1ndash6 years)Min 00035 00307 00088 00001 03756Max 00045 0041 00131 00002 03929Mean 00038 00373 00115 00003 03761

Children (6ndash18 years)Min 00014 00122 00035 000004 01487Max 00018 00162 00052 000006 01555Mean 00015 00148 00046 000005 01489

AdultsMin 00004 00043 00012 000001 00524Max 00006 00057 00018 000002 00548Mean 00005 00052 00016 000002 00525

Target hazard quotient (THQ)

Children (1ndash6 years)Min 00035 00103 00004 000002 00012Max 00045 00137 00007 000004 00013Mean 00038 00124 00006 000003 00012

Children (6ndash18 years)Min 00014 00041 00002 000001 00004Max 00018 00054 00003 000002 00005Mean 00015 00049 00002 000001 00004

AdultsMin 00005 00014 000006 0000003 00002Max 00006 00019 000009 600E minus 06 00002Mean 00005 00017 000008 400E minus 06 00002

Hazard index (HI) Min Max Mean1ndash6 years 0015 002 00186ndash18 years 0006 0008 0007Adults 0002 0003 0003

Zn

PbCd

Ni

Cr

Sandflat soil (F1 and F2 8663)

Zn

Pb

Cd

Ni

Cr

C africana L (F1 and F2 8332)

minus08

minus06

minus04

minus02

0

02

04

06

08

1

F2 (2

248

)

minus1

minus08

minus06

minus04

minus02

0

02

04

06

F2 (2

675

)

minus12 minus08 minus04 0 04 08 12F1 (5988)

minus12 minus08 minus04 0 04 08 12F1 (6084)

Figure 4 Factor loadings of principal components 1 and 2 for trace metals concentration in sandflat and C africana L samples showing thetotal variance explained by each component

Results for potential exposure through dermal contact inchildren showed that Cd and Cr concentrations accountedfor 7331 and 2549 respectively towards the total hazardindex value while Ni Pb and Zn represent about 119 Pre-vious studies on health risks assessment of soil trace metalsindicated that Cd Cr and Ni exposure could pose relatively

higher noncarcinogenic effects on children and adults dueto their low RfD values or enhanced concentrations in soils[16] Similarly in adult females the THQs of Cd and Crrepresented 7331 and 2549 of the total hazard index(HItot) value for exposure due to inhalation while both tracemetals accounted for about 9881 of the HItot value for risks

Page 10

10 Applied and Environmental Soil Science

Table8Non

carcinogenichazard

indexforc

hildrenandadultfor

inhalatio

nandderm

alexpo

sure

pathways

Metal

Child

ren(1ndash

6years)

Adultfem

ales

Adultm

ales

Con

clevels

Con

c(m

gkg)

Inhalatio

nDermalcontact

Inhalatio

nDermalcontact

Inhalatio

nDermalcontact

EDD

inh

(mgkg-day)

THQ

EDD

derm

al(m

gm3-day)

THQ

EDD

inh(m

gkg-day)

THQ

EDD

derm

al(m

gm3-day)

THQ

EDD

inh(m

gkg-day)

THQ

EDD

derm

al(m

gm3-day)

THQ

Cd

Min

069

197Eminus10

197Eminus09

112Eminus08

157Eminus01

791Eminus11

791Eminus08

501Eminus06

501Eminus01

109Eminus10

109Eminus07

419Eminus06

419Eminus01

Max

090

255Eminus10

849Eminus06

145Eminus08

203Eminus01

102Eminus10

102Eminus07

649Eminus06

649Eminus01

142Eminus10

142Eminus07

543Eminus06

543Eminus01

Mean

076

215Eminus10

717Eminus06

123Eminus08

172Eminus01

864

Eminus11

864

Eminus08

547Eminus06

547Eminus01

120Eminus10

120Eminus07

458Eminus06

458Eminus01

CrMin

610

173Eminus09

576Eminus07

985Eminus08

493Eminus02

694Eminus10

231Eminus07

941Eminus06

157Eminus01

994Eminus10

321Eminus07

788Eminus06

131Eminus01

Max

812

230Eminus09

575Eminus05

131Eminus07

656Eminus02

924Eminus10

308Eminus07

125Eminus05

208Eminus01

128Eminus09

428Eminus07

105Eminus05

175Eminus01

Mean

739

209Eminus09

698Eminus06

119Eminus07

597Eminus02

841Eminus10

280Eminus07

114Eminus05

190Eminus01

117Eminus09

389Eminus07

955Eminus06

159Eminus01

Ni

Min

175

496Eminus10

184Eminus05

989Eminus06

183Eminus03

199Eminus10

996Eminus09

315Eminus05

583Eminus03

277Eminus10

138Eminus08

264

Eminus05

488Eminus03

Max

260

736Eminus10

248Eminus08

147Eminus05

272Eminus03

296Eminus10

148Eminus08

468Eminus05

867Eminus03

411Eminus10

206Eminus08

392Eminus05

726Eminus03

Mean

228

645Eminus10

717Eminus06

129Eminus06

238Eminus03

259Eminus10

129Eminus08

410Eminus05

760Eminus03

259Eminus10

180Eminus08

343Eminus05

635Eminus03

PbMin

002

538Eminus12

154Eminus09

184Eminus09

351Eminus06

216Eminus12

618Eminus10

587Eminus09

112Eminus05

360Eminus12

858Eminus10

490Eminus09

935Eminus06

Max

003

849Eminus12

243Eminus09

291Eminus09

554Eminus06

341Eminus12

976Eminus10

926Eminus09

176Eminus05

300Eminus12

136Eminus09

775Eminus09

148Eminus05

Mean

002

691Eminus12

197Eminus09

236Eminus09

450Eminus06

278Eminus12

793Eminus10

754Eminus09

144Eminus05

474Eminus12

110Eminus09

631Eminus09

120Eminus05

ZnMin

7443

210Eminus08

702Eminus08

240

Eminus05

400

Eminus04

847Eminus09

282Eminus08

766Eminus05

127Eminus03

118Eminus08

392Eminus08

641Eminus05

106Eminus03

Max

7785

220Eminus08

110Eminus04

251Eminus05

419Eminus04

886Eminus09

295Eminus08

801Eminus05

133Eminus03

123Eminus08

410Eminus08

671Eminus05

112Eminus03

Mean

7451

211Eminus08

440

Eminus08

241Eminus05

401Eminus04

848

Eminus09

282Eminus08

767Eminus05

128Eminus03

118Eminus08

393Eminus08

642Eminus05

107Eminus03

Cumulativerisk

form

invalues

234Eminus08

384Eminus05

945Eminus09

123Eminus04

131Eminus08

103Eminus04

Cumulativerisk

form

axvalues

253Eminus08

458Eminus05

102Eminus08

146Eminus04

142Eminus08

122Eminus04

Cumulativerisk

form

eanvalues

240

Eminus08

422Eminus05

967Eminus09

134Eminus04

134Eminus08

113Eminus04

HIm

invalue

869Eminus07

207Eminus01

349Eminus07

665Eminus01

485Eminus07

556Eminus01

HIm

axvalue

194Eminus04

272Eminus01

456Eminus07

867Eminus01

633Eminus07

725Eminus01

HIm

eanvalue

214Eminus05

234Eminus01

409Eminus07

746Eminus01

568Eminus07

624Eminus01

Page 11

Applied and Environmental Soil Science 11

associated with dermal contact The total hazard quotients ofCd and Cr indicated a relatively high percentage contributionof 8972 and 9881 of the overall HItot for adult malesexposed to sandflat soils via inhalation and dermal contactpathways respectively However the THQs of trace metalsfor children adult males and adult females decreased in theorder of Cd gt Cr gt Ni gt Zn gt Pb for exposure due todermal contact while the risks ranking following inhalationpathway decreased in the order Cr gt Cd gt Ni gt Zn gt Pband Cd gt Ni gt Cr gt Zn gt Pb for adult (males andfemales) and children respectively In general the probabilitythat noncarcinogenic effectmay likely occur varied accordingto the three groups considered in this study The rankingfollowed the decreasing order children gt adult males gt adultfemales indicating that children are the most vulnerablegroup to noncarcinogenic risks Comparatively the hazardquotient and hazard index indicated that the sandflats mightpose a health risk to children Similar conclusion byOlawoyinet al [11] on the vulnerability of Niger Delta children has beenreported

In this study the carcinogenic risks associated with oralingestion and dermal contact exposures were not considereddue to unavailability of corresponding carcinogenicity slopefactors for Cd Cr Ni Pb and Zn However the carcinogenicrisks for Cd Cr and Ni were estimated only throughinhalation pathways while Pb and Zn were not considereddue to lack of unit risk values [74] Results for the averagecarcinogenic risk values were 898 times 10minus8 501 times 10minus8 and361 times 10minus8 for children adult males and adult femalesrespectively The 25 percentile of carcinogenic risks forchildren adult males and adult female was 742 times 10minus8 414 times10minus8 and 298 times 10minus8 respectively while the 75 percentileof cancer risk values for children adult males and adultfemales was estimated as 988 times 10minus8 552 times 10minus8 and 397times 10minus8 respectively According to Hu et al [75] estimatedcarcinogenic risk values less than 10times 10minus8 are not consideredas capable of posing adverse health effects and risks above10 times 10minus4 are identified as unacceptable In this study thecalculated carcinogenic risks were below 10 times 10minus6 and thesandflat soils are not considered to pose significant healtheffects to the three groups However the carcinogenicityranking obtained in the present study decreased following theorder children gt adult males gt adult females

4 Conclusion

The present study confirms the occurrence and variability inthe levels of carcinogenic trace metals in sandflat soils andC africana L of an important coastal ecosystem in NigerDelta Nigeria Results provide qualitative information on thepollution status of Cd Cr Pb Ni and Zn using pollutionindices and ecological and health risks approaches Basedon the pollution indicators employed the trace metals wereconsidered to pose low tomoderate degree of contaminationAvailable assessments indicate that anthropogenic activitiessuch as petrochemical operations fuel combustion andindustrial wastes dump are very likely sources of metalburden to the C africana L and sandflat soils Results of

the present study confirmed the dominant role of Cd inpotential toxicity and in potential ecological risk Noncar-cinogenic and carcinogenic health risks assessments of soiltrace metals may pose no adverse effects to children andadults However long-term health risks to children beingthe most vulnerable population in the region raise a lot ofconcernTherefore stringent measures should be put in placeto limit children exposure risks to trace metals In additionfrequent monitoring study by relevant government agenciesindependent researchers and health safety and environmentdepartments of multinational oil companies operating in theNiger Delta region is recommended Also safe disposal ofdomestic sewage and industrial effluents should be practicedand where possible recycled to minimize the level of metalsintroduced into coastal water ecosystems

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] N U Benson and J P Essien ldquoPetroleum hydrocarbons con-tamination of sediments and accumulation in Tympanotonusfuscatus var radula from the Qua Iboe Mangrove EcosystemNigeriardquo Current Science vol 96 no 2 pp 238ndash244 2009

[2] N U Benson W U Anake J P Essien P A Enyong and AA Olajire ldquoDistribution and risk assessment of trace metals inLeptodius exarata surface water and sediments from DouglasCreek Qua Iboe estuaryrdquo Journal of Taibah University ForScience 2016

[3] J P Essien N U Benson and S P Antai ldquoSeasonal dynamicsof physicochemical properties and heavy metal burdens inMangrove sediments and surfacewater of the brackishQua IboeEstuary Nigeriardquo Toxicological and Environmental Chemistryvol 90 no 2 pp 259ndash273 2008

[4] NU Benson J P Essien A BWilliams andD E Bassey ldquoMer-cury accumulation in fishes from tropical aquatic ecosystems inthe Niger Delta of Nigeriardquo Current Science vol 96 no 2 pp781ndash785 2007

[5] N U Benson E D Udosen and O Akpabio ldquoInterseasonaldistribution and partitioning of heavy metals in subtidal sed-iment of Qua Iboe Estuary and associated Creeks Niger Delta(Nigeria)rdquo Environmental Monitoring and Assessment vol 146no 1ndash3 pp 253ndash265 2008

[6] J P Essien S P Antai and N U Benson ldquoMicroalgae biodiver-sity and biomass status in Qua Iboe Estuary Mangrove SwampNigeriardquo Aquatic Ecology vol 42 no 1 pp 71ndash81 2008

[7] J Liu H Wu J Feng Z Li and G Lin ldquoHeavy metal contam-ination and ecological risk assessments in the sediments andzoobenthos of selected mangrove ecosystems South ChinardquoCatena vol 119 pp 136ndash142 2014

[8] N U Benson andUM Etesin ldquoMetal contamination of surfacewater sediment and Tympanotonus fuscatus var radula of IkoRiver and environmental impact due toUtapete gas flare stationNigeriardquo Environmentalist vol 28 no 3 pp 195ndash202 2008

[9] J P Essien V Essien and A A Olajire ldquoHeavy metal burdensin patches of asphyxiated swamp areas within the Qua Iboeestuarymangrove ecosystemrdquo Environmental Research vol 109no 6 pp 690ndash696 2009

Page 12

12 Applied and Environmental Soil Science

[10] E D Udosen and N U Benson ldquoSpatio-temporal distributionof heavymetals in sediments and surfacewater in Stubbs CreekNigeriardquo Trends in Applied Sciences Research vol 1 no 3 pp292ndash300 2006

[11] R Olawoyin S A Oyewole and R L Grayson ldquoPotential riskeffect from elevated levels of soil heavymetals on human healthin the Niger deltardquo Ecotoxicology and Environmental Safety vol85 pp 120ndash130 2012

[12] NU Benson ldquoLead nickel vanadium cobalt copper andman-ganese distributions in intensely cultivated floodplain ultisol ofCross River Nigeriardquo International Journal of Soil Science vol1 no 2 pp 140ndash145 2006

[13] YHu andHCheng ldquoApplication of stochasticmodels in identi-fication and apportionment of heavymetal pollution sources inthe surface soils of a large-scale regionrdquo Environmental Scienceand Technology vol 47 no 8 pp 3752ndash3760 2013

[14] E D Udosen NU Benson J P Essien andG A Ebong ldquoRela-tion between aqua-regia extractable heavy metals in soil andmanihot utilissima within a municipal dumpsiterdquo InternationalJournal of Soil Science vol 1 no 1 pp 27ndash32 2006

[15] J O Nriagu ldquoA history of global metal pollutionrdquo Science vol272 no 5259 pp 223ndash224 1996

[16] H Chen Y Teng S Lu Y Wang and J Wang ldquoContaminationfeatures and health risk of soil heavy metals in Chinardquo Scienceof the Total Environment vol 512-513 pp 143ndash153 2015

[17] X-W Fu D-G Wang X-H Ren and Z-J Cui ldquoSpatialdistribution patterns and potential sources of heavy metals insoils of a crude oil-polluted region in Chinardquo Pedosphere vol24 no 4 pp 508ndash515 2014

[18] X Yang X Yuan A Zhang et al ldquoSpatial distribution andsources of heavy metals and petroleum hydrocarbon in thesand flats of Shuangtaizi Estuary Bohai Sea of Chinardquo MarinePollution Bulletin vol 95 no 1 pp 503ndash512 2015

[19] L C Osuji and C M Onojake ldquoField reconnaissance andestimation of petroleumhydrocarbon and heavymetal contentsof soils affected by the Ebocha-8 oil spillage in Niger DeltaNigeriardquo Journal of Environmental Management vol 79 no 2pp 133ndash139 2006

[20] M C Onojake and O Frank ldquoAssessment of heavy metals in asoil contaminated by oil spill a case study inNigeriardquoChemistryand Ecology vol 29 no 3 pp 246ndash254 2013

[21] M A Addo H A Affum B O Botwe et al ldquoAssessment ofwater quality and heavy metal levels in water and bottom sed-iment samples from Mokwe Lagoon Accra Ghanardquo ResearchJournal of Environmental and Earth Sciences vol 4 no 2 pp119ndash130 2012

[22] X Li L Liu Y Wang et al ldquoHeavy metal contamination ofurban soil in an old industrial city (Shenyang) in NortheastChinardquo Geoderma vol 192 no 1 pp 50ndash58 2013

[23] L Madrid E Dıaz-Barrientos and F Madrid ldquoDistributionof heavy metal contents of urban soils in parks of SevillerdquoChemosphere vol 49 no 10 pp 1301ndash1308 2002

[24] N U Benson W U Anake and I O Olanrewaju ldquoAnalyticalrelevance of trace metal speciation in environmental andbiophysicochemical systemsrdquo American Journal of AnalyticalChemistry vol 04 no 11 pp 633ndash641 2013

[25] C Mario D Valeria H Georg and P Stefano ldquoGuidance forsediment and biota monitoring under the Common Imple-mentation Strategy for the Water Framework Directiverdquo TrACTrends in Analytical Chemistry vol 36 pp 15ndash24 2012

[26] J J Vicente-MartorellM D Galindo-Riano M Garcıa-Vargasand M D Granado-Castro ldquoBioavailability of heavy metalsmonitoring water sediments and fish species from a pollutedestuaryrdquo Journal of Hazardous Materials vol 162 no 2-3 pp823ndash836 2009

[27] S Qiao Z Yang Y Pan and Z Guo ldquoMetals in suspendedsediments from the Changjiang (Yangtze River) and Huanghe(Yellow River) to the sea and their comparisonrdquo EstuarineCoastal and Shelf Science vol 74 no 3 pp 539ndash548 2007

[28] S Gotze A Bose I M Sokolova D Abele and R SaborowskildquoThe proteasomes of two marine decapod crustaceans Euro-pean lobster (Homarus gammarus) and Edible crab (Cancerpagurus) are differently impaired by heavy metalsrdquo Compara-tive Biochemistry and Physiology C Toxicology and Pharmacol-ogy vol 162 no 1 pp 62ndash69 2014

[29] S Rahmanpour N F Ghorghani and S M Lotfi AshtiyanildquoHeavy metal in water and aquatic organisms from differentintertidal ecosystems Persian Gulfrdquo Environmental Monitoringand Assessment vol 186 no 9 pp 5401ndash5409 2014

[30] J P Essien S P Antai andNU Benson ldquoMicrobial populationdynamics as a function of sediment salinity gradients in theQuaIboe Estuary Mangrove Swamp (Nigeria)rdquo Research Journal ofMicrobiology vol 1 no 3 pp 255ndash265 2006

[31] M Nummelin M Lodenius E Tulisalo H Hirvonen andT Alanko ldquoPredatory insects as bioindicators of heavy metalpollutionrdquo Environmental Pollution vol 145 no 1 pp 339ndash3472007

[32] F Talarico P Brandmayr P G Giulianini et al ldquoEffects of metalpollution on survival and physiological responses in Carabus(Chaetocarabus) lefebvrei (Coleoptera Carabidae)rdquo EuropeanJournal of Soil Biology vol 61 pp 80ndash89 2014

[33] N Alkan M Aktas and K Gedik ldquoComparison of metalaccumulation in fish species from the Southeastern Black SeardquoBulletin of Environmental Contamination and Toxicology vol88 no 6 pp 807ndash812 2012

[34] M E Goher H I Farhat M H Abdo and S G Salem ldquoMetalpollution assessment in the surface sediment of Lake NasserEgyptrdquo Egyptian Journal of Aquatic Research vol 40 no 3 pp213ndash224 2014

[35] P Vrhovnik J P Arrebola T Serafimovski et al ldquoPotentiallytoxic contamination of sediments water and two animal speciesin Lake Kalimanci FYR Macedonia relevance to humanhealthrdquo Environmental Pollution vol 180 pp 92ndash100 2013

[36] A Vanek L Boruvka O Drabek M Mihaljevic and MKomarek ldquoMobility of lead zinc and cadmium in alluvialsoils heavily polluted by smelting industryrdquo Plant Soil andEnvironment vol 51 no 7 pp 316ndash321 2005

[37] C S-L Lee X Li W Shi S C-N Cheung and I ThorntonldquoMetal contamination in urban suburban and country parksoils of Hong Kong a study based on GIS and multivariatestatisticsrdquo Science of the Total Environment vol 356 no 1ndash3 pp45ndash61 2006

[38] G Qingjie D Jun X Yunchuan W Qingfei and Y LiqiangldquoCalculating pollution indices by heavy metals in ecologicalgeochemistry assessment and a case study in parks of BeijingrdquoJournal of China University of Geosciences vol 19 no 3 pp 230ndash241 2008

[39] L Hakanson ldquoEcological risk index for aquatic pollutioncontrol A sedimentological approachrdquoWater Research vol 14pp 975ndash1001 1980

[40] D C Tomlinson J G Wilson C R Harris and D WJeffrey ldquoProblems in the assessment of heavy metals levels

Page 13

Applied and Environmental Soil Science 13

in estuaries and the formation of pollution indexrdquo HelgolandMarine Research vol 33 pp 566ndash575 1980

[41] C Zhang Q Qiao J D A Piper and B Huang ldquoAssessment ofheavy metal pollution from a Fe-smelting plant in urban riversediments using environmental magnetic and geochemicalmethodsrdquo Environmental Pollution vol 159 no 10 pp 3057ndash3070 2011

[42] VROM Circular on Target Values and Intervention Valuesfor Soil Remediation Annex A Dutch Ministry of HousingSpatial Planning and Environment (VROM) The Hague TheNetherlands 2000

[43] G Suresh V Ramasamy M Sundarrajan and K ParamasivamldquoSpatial and vertical distributions of heavy metals and theirpotential toxicity levels in various beach sediments from high-background-radiation area Kerala Indiardquo Marine PollutionBulletin vol 91 no 1 pp 389ndash400 2015

[44] N L Nemerow Stream Lake Estuary andOceanPollution VanNostrand Reinhold Publishing New York NY USA 1985

[45] H ChengM Li C Zhao et al ldquoOverview of tracemetals in theurban soil of 31 metropolises in Chinardquo Journal of GeochemicalExploration vol 139 pp 31ndash52 2014

[46] GMuller ldquoIndex of geoaccumulation in sediments of the RhineRiverrdquo GeoJournal vol 2 pp 108ndash118 1969

[47] K K Turekian and K H Wedepohl ldquoDistribution of theelements in some major units of the earthrsquos crustrdquo GeologicalSociety of America Bulletin vol 72 no 2 pp 175ndash192 1961

[48] N U Benson F E Asuquo A B Williams et al ldquoSource evalu-ation and tracemetal contamination in benthic sediments fromequatorial ecosystems using multivariate statistical techniquesrdquoPLoS ONE vol 11 no 6 Article ID e0156485 2016

[49] W Zhuang and X Gao ldquoIntegrated assessment of heavy metalpollution in the surface sediments of the Laizhou Bay and thecoastal waters of the Zhangzi Island China comparison amongtypical marine sediment quality indicesrdquo PLoS ONE vol 9 no4 Article ID e94145 2014

[50] K Loska D Wiechulła and I Korus ldquoMetal contamination offarming soils affected by industryrdquo Environment Internationalvol 30 no 2 pp 159ndash165 2004

[51] Y Wang L Yang L Kong E Liu L Wang and J ZhuldquoSpatial distribution ecological risk assessment and sourceidentification for heavy metals in surface sediments fromDongping Lake Shandong East Chinardquo CATENA vol 125 pp200ndash205 2015

[52] S Wu S Peng X Zhang et al ldquoLevels and health riskassessments of heavy metals in urban soils in DongguanChinardquo Journal of Geochemical Exploration vol 148 pp 71ndash782015

[53] M Intawongse and J R Dean ldquoUptake of heavy metals byvegetable plants grown on contaminated soil and their bioavail-ability in the human gastrointestinal tractrdquo Food Additives andContaminants vol 23 no 1 pp 36ndash48 2006

[54] E T Idowu N H Amaeze P I Adie and O A OtubanjoldquoHeavy metal bioaccumulation and biomarkers of oxidativestress in the wild African tiger frogHoplobatrachus occipitalisrdquoAfrican Journal of Environmental Science and Technology vol 8no 1 pp 6ndash15 2014

[55] A Khaled A Hessein A M Abdel-Halim and F M MorsyldquoDistribution of heavy metals in seaweeds collected alongMarsa-Matrouh beaches Egyptian Mediterranean Seardquo Egyp-tian Journal of Aquatic Research vol 40 no 4 pp 363ndash371 2014

[56] J Usero E Gonzalez-Regalado and I Gracia ldquoTrace metalsin the bivalve molluscs Ruditapes decussatus and Ruditapesphilippinarum from the Atlantic Coast of Southern SpainrdquoEnvironment International vol 23 no 3 pp 291ndash298 1997

[57] M Ghosh and S P Singh ldquoA review on phytoremediation ofheavy metals and utilization of its byproductsrdquo Applied Ecologyand Environmental Research vol 3 no 1 pp 1ndash18 2005

[58] FAOWHO ldquoReport of the sixth session of the Codex Commit-tee on contaminants in foodsrdquo Tech Rep CF6 INF1 CodexAlimentarius Commission The Hague The Netherlands 2012

[59] State Environmental Protection Administration of China(SEPAC) ldquoEnvironmental quality standard for soilsrdquo Tech RepGB15618-1996 State Environmental Protection Administrationof China (SEPAC) Beijing China 1995

[60] United States Environmental Protection Agency (USEPA)Supplemental Guidance for Developing Soil Screening Levels forSuperfund Sites Office of SolidWaste andEmergencyResponseWashington DC USA 2002

[61] X-S Luo S Yu Y-G Zhu and X-D Li ldquoTracemetal contami-nation in urban soils of Chinardquo Science of the Total Environmentvol 421-422 pp 17ndash30 2012

[62] Y Sun Q Zhou X Xie and R Liu ldquoSpatial sources andrisk assessment of heavy metal contamination of urban soilsin typical regions of Shenyang Chinardquo Journal of HazardousMaterials vol 174 no 1ndash3 pp 455ndash462 2010

[63] Z P Yang W X Lu Y Q Long X H Bao and Q CYang ldquoAssessment of heavy metals contamination in urbantopsoil from Changchun City Chinardquo Journal of GeochemicalExploration vol 108 no 1 pp 27ndash38 2011

[64] Agency for Toxic Substances and Disease Registry (ATSDR)Division of Toxicology and Environmental MedicineAppliedToxicology Branch 2012 httpwwwatsdrcdcgovToxPro-filestpaspid=48amptid=15

[65] X Qing Z Yutong and L Shenggao ldquoAssessment of heavymetal pollution and human health risk in urban soils ofsteel industrial city (Anshan) Liaoning Northeast ChinardquoEcotoxicology and Environmental Safety vol 120 pp 377ndash3852015

[66] USEPA (United States Environmental Protection Agency) RiskAssessment Guidance for Superfund Human Health EvaluationManual (Part A) vol 1 Office of Emergency and RemedialResponse Washington DC USA 1989 EPA5401-89002

[67] A O W Leung N S Duzgoren-Aydin K C Cheung and MHWong ldquoHeavymetals concentrations of surface dust from e-waste recycling and its human health implications in southeastChinardquoEnvironmental Science and Technology vol 42 no 7 pp2674ndash2680 2008

[68] P Li C Lin H Cheng X Duan and K Lei ldquoContaminationand health risks of soil heavy metals around a leadzincsmelter in southwestern ChinardquoEcotoxicology and Environmen-tal Safety vol 113 pp 391ndash399 2015

[69] World Bank Data Catalogue Life Expectancy at Birth Total(Years) 2015 httpdataworldbankorgindicatorSPDYNLE00INcountriesNGdisplay=graph

[70] United States Environmental Protection Agency (USEPA)Exposure Factors Handbook 2011 Edition EPA600R-090052F2011

[71] United States Environmental ProtectionAgency (USEPA) Inte-grated Risk Information System (IRIS) 2014

[72] L Ferreira-Baptista and E De Miguel ldquoGeochemistry and riskassessment of street dust in Luanda Angola a tropical urban

Page 14

14 Applied and Environmental Soil Science

environmentrdquo Atmospheric Environment vol 39 no 25 pp4501ndash4512 2005

[73] USEPA (United States Environmental Protection Agency)ldquoSupplemental guidance for developing soil screening levels forsuperfund sitesrdquo OSWER 93554-24 Office of Solid Waste andEmergency Response Washington DC USA 2001

[74] USEPA (United States Environmental Protection Agency)Integrated Risk Information System 2007 httpscfpubepagovnceairis2atozcfm

[75] X Hu Y Zhang Z Ding et al ldquoBioaccessibility and health riskof arsenic and heavymetals (Cd Co Cr CuNi Pb Zn andMn)in TSP andPM25 inNanjing ChinardquoAtmospheric Environmentvol 57 pp 146ndash152 2012

[76] A A Odewande and A F Abimbola ldquoContamination indicesand heavy metal concentrations in urban soil of Ibadanmetropolis southwestern Nigeriardquo Environmental Geochem-istry and Health vol 30 no 3 pp 243ndash254 2008

Page 15

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