Ife Journal of Science

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Two issues of

Ife Journal of Science vol. 14, no. 1 (2012) 1

ATMOSPHERIC TRACE METAL CONCENTRATIONS IN SUSPENDEDPARTICULATE MATTER (SPM) OF A RURAL RESIDENTIAL AREA IN SOUTHERN

NIGERIA

Ukpebor, J. E., *Ukpebor, E. E., Kadiri, V. I., Odiase, J. I., Okuo, J. M. and Ogbeifun, D.1 2 2 3 2 2

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Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UKAir Pollution Research Group, Department of Chemistry, University of Benin, Nigeria

Department of Mathematics and Statistics, University of Benin, Benin City, Nigeria(Received: 9 November, 2011; Accepted: 13 March, 2012)

Trace metals are one of the most toxic constituents of atmospheric particulates. The baseline concentrations ofPb, Cd, Zn and Cr in airborne particulates collected at a rural community in southern Nigeria have beenevaluated. The particulate samples from where the metals were characterized and quantified, were collectedbetween December 2007 and March 2008, using a Gravimetric technique a portable SKC 506673 High volumeGravimetric sampler. The air particulate samples were collected from the kitchens, living rooms and outdoorenvironment of five households in the community. The quantification of the trace metals was done usingAtomic Absorption spectrometry method, employing HNO based wet digestion. High baseline concentration

of SPM were obtained with an outdoor range of 240.74 555.55 µgm , living room range of 546.30 955.56 µgmand kitchen range of 425.92 1444.00 µgm . However, relatively low concentrations of the trace metals weremeasured in the samples with Zn and Cr being the most abundant. The outdoor and kitchen Zn concentrationranged from < 0.0001 0.0603 µgm and 0.0185 0.1171 µgm respectively, while the Cr levels were < 0.00010.0252 µgm (outdoor) and < 0.0001 0.0204 µgm (kitchen). The correlation matrix analysis showed a strongpositive correlation between the kitchen, living room and outdoor sites, suggesting identical sources of the tracemetals. Principal component analysis (PCA) identified two fundamental sources of the metals, which was furtherconfirmed by the hierarchical cluster analysis.

Heavy Metals, Suspended Particulate Matter, Rural Area

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Keywords:

ABSTRACT

INTRODUCTIONUnderstanding the composition of atmosphericparticulate matter is crucial for so many reasons.Trace metals are however one of the most toxicconstituents of atmospheric particulates. The sizeand composition of airborne particulates play animportant role in determining their health effects(Radojevic and Bashkin, 2007). The particle sizefor instance relates to how deeply the particles willreact in the respiratory system. It also relates to thedeposition velocity, which in turn, relates to theresidence time in the atmosphere and hence thepotential for long range transport in theatmosphere (Radojevic and Bashkin, 2007).Specific components of suspended particulatematter (SPM) include combustion particles(particles of elemental and organic carbon);secondary particles (particles of ammoniumsulphate/sulphuric acid and ammonium nitrate);and lastly coarse particles (surface dust re-suspended by traffic activity and made up mainlyof inorganic mineral components) (Harrison,2001).

The components of airborne particleswhich raise the most health concerns are the tracemetals and trace organic compounds. Interest in

trace metals relates primarily to their potentialtoxicity. Metals have a variety of effects upon thehuman body, mostly at the cellular level. Whilesome metals disrupt biochemical reactions othersblock essential biological processes, including theabsorption of nutrients. Some accumulate in thebody giving rise to toxic concentrations aftermany years of exposure and yet others such asArgon, Beryllium, Cadmium and Chromium arecarcinogens (Friberg et al., 1986). Among thetrace metals which have stimulated the greatestinterest in relation to public health is lead. Thehealth effects of lead have been studiedextensively and are well documented (EPA, 1986;Krewski et al., 1989). Young children areespecially vulnerable; lead poisoning of childrenleads to permanent brain damage, causinglearning disabilities, hearing loss, and behaviouralabnormalities. In adults, lead absorption causeshypertension, blood pressure problems and heartdisease (EPA, 1986; Krewski et al., 1989). Themain sources of airborne lead are motor vehiclesusing leaded gasoline, industrial processes such asferrous and non ferrous metallurgy and coalcombustion.

2 Ukpebor et al.: Atmospheric Trace Metal Concentrations

Studies and data on trace metal content ofatmospheric particulate matter in Nigeria arescanty. A study conducted around cementfactories in Nigeria reported Pb, Zn and Cu rangesof 2.30 9.40 µgm , 0.10 14.00 µgm and 0.100.90 µgm respectively (Akeredolu et al., 1994).Furthermore, in a recent study, in Benin City,Nigeria using andto assess the levels of trace metals in theatmosphere (Ukpebor et al., 2010), a Pb range of20.00 70.00 µg/g was reported. Some of thesereported trace metal levels in Nigeria urbancentres are worrisome, as they tend to violateexisting regulatory standards. However, in therural communities, limited studies have beenconducted on air quality assessment despite thefact that ~ 63% of Nigeria's over 140 millionpeople live in these rural communities (NPC,2006; NDHS, 2008). Within these communitiesthere exist a very high degree of vulnerability to airquality impairment because of the abundant useof firewood and the re suspension of dustparticles from the daily sweepings of these earthroads. Ideriah et al., (2001) reported highlyelevated levels of airborne particles in both indoorand outdoor environments in some ruralcommunities in south eastern Nigeria.Furthermore, an observational study by Edet(2003) relying on proxies such as fuel and stovetype and time spent near the fire inferred that thesignificance of air pollution to health was a majorhealth challenge in rural communities in Nigeria.

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Delonix regia Casuarina equisetifolia

The scant information on trace metalcontent of airborne particles from ruralcommunities makes assessing their contributionsto the high mortality and morbidity difficult toascer tain. In this study, the basel ineconcentrations of Pb, Cd, Zn and Cr in particulatematters from outdoors, kitchen and living roomsof a rural community in Nigeria were evaluated.The data obtained were further compared withavailable regulatory standards to ascertain theircompliance and lastly, the data would be madeavailable to government agencies for effectivepolicy formulation and epidemiological studies.

This study was conducted at Iyowa Community inOvia Northeast Local Government of Edo State,southern Nigeria (Fig. 1). The community iscompletely rural, sparsely populated; thesettlement is linear with a majority of the housesmade of mud and a few block houses roofed withrusted iron sheets. The climate is typically humid(39.0 77.5%), with high tropical ambienttemperature (28.2 35.8 C) and low wind speed(0.4 2.9 m/s) (Table 11). There are two distinctseasons (wet and dry) and an average rainfall ofabout 1898.0 mm with two distinguishing peaks inJuly (3313.0 mm) and September (3621.0 mm)(Iyamu, 2004).

EXPERIMENTAL DATA AND METHODS

Study area

o

Boundary

State Capital

Local Govt HQ

Legend

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5’0’0’E 5’30’0’E 6’0’0’E 6’30’0’E

5’0’0’E 5’30’0’E 6’0’0’E 6’30’0’E

5’30’0’N

6’0’0’N

6’30’0’N

7’0’0’N

7’30’0’N

8’0’0’N

5’30’0’N

6’0’0’N

6’30’0’N

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8’0’0’N

ONDO

STAT

E

KOGI STATE

DELTA STATE

IGARRA

AUCHIFUGA

AGENEGBODE

AFUZE

SABOGIDOA-ORA

EKPOMA IRRUA UROMI

UBIAJA

IGUEBENEHOR

ISSELE-UKU

ABUDUAGBOR

IDOGBO

BENIN CITY

OKADA

IGUOBAZUWA

IYOWA

SAPELE

Ukpebor et al.: Atmospheric Trace Metal Concentrations 3

Figure 1: Edo State Map Showing Iyowa Community

Ukpebor et al.: Atmospheric Trace Metal Concentrations4

The vegetation is natural and predominantly rainforest and the main source of water are streamsand rain. Electricity supply is erratic and the meansof transportation include motor cycles andbicycles. The predominant occupation is farmingwhile cooking in this community is doneexclusively by the use of firewood and cropresidues. Lighting in the night is more by the use ofkerosene lamps.Remarkably, health records from the communityhealth centre, reveals a high prevalence of airpollution related health problems (e.g. catarrh,cough, asthma and emphysema).

Selection of households for this study was basedcompletely on voluntary participation. Fivehouseholds were selected to represent the five

Selection of Homes/Sites

quarters of the community. Characteristics of thehouse and its occupants were collected using astandard environmental inventory questionnaire(Lebowitz et al., 1989). Household levelparameters collected included kitchen type, fueltype, household ventilation, cooking duration andother potential sources of particulates insidehomes such as outdoor combustion sources,cigarette smoking and mosquito coils.Information on sex, age, and smoking habits werereported in a daily diary. It provided informationabout the daily activity pattern (number of hoursspent in cooking at home, and time spent on otheractivities).

Table 1 represents the description of thecharacteristics of the homes and kitchen. Theoutdoor sites were geo referenced by usingGARMIN GPS MAP 765 chart plotting receiver.

Table 1: Description and Characteristics of the Households and Kitchens Assessed.

Household Code Coordinates Kitchen type andconfiguration

Fueltype

Buildingtype

Ventilation

A AKAPAO

N06o28.494E005o36.155

Detached kitchen madeof bamboo and palmleaf

Wood Cement wallhouse withzinc roof

Good withdoors andwindows

B BKBPBO

N06o28.357E005o36.195

Detached kitchen madeof wood andclay

Wood mud housewithunceiledroof

Poorlyventilatedapartment

C CKCPCO

N06o28.349E005o36.172

Detached kitchen madeof palm leavesand bamboo sticks

Wood Mud housewithzinc roof

Fairly good

D DKDPDO

N06o28.309E005o36.176

In built and attachedkitchen

Wood Mud houseWith zincroof

Poor

E EKEPEO

N06o28.419E005o36.161

Detached kitchen madeof wood andClay

Wood Cement wallhouse withzinc roof

Well ventilatedwithdoors andwindows

K = Kitchen, P = Living room O = Outdoor

Data Collection

SPM High Volume Gravimetric SamplerAirborne particles were collected on Whatmanglass fibre filters using a portable high volumegravimetric sampler (SKC UK Model no.506673). The sampler was placed on a tripod withheight of ~ 1.5 and 2.0 m at each sampling spot.The sampling unit consists of a gas pump, a filterholder manifold connected to the sampling pumpby a Teflon tube. A gas flow rate meter with a rateof 0 5 Lmin was used to measure the air flow rateduring sampling. Before sampling, all unloadedglass fibre filters were dried in a desiccator at roomtemperature and their initial weights were taken.

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The particulates were collected on the preweighed filter by pumping 2.5 Lmin volume ofair through it for 8 hrs. Sampling was donebetween December 2007 and March 2008 onalternate days at the sampling sites (1 m from thefire source, 0.8 m from the front of the house andat the centre of the living room). After sampling,the loaded filter was again dried in a desiccator andreweighed to determine the final weight. Theconcentration of the airborne particles in the airwas determined gravimetrically. The duration ofsampling and the average flow rate were recorded(Shaw, 1987; UNEP/WHO, 1994). Thismeasuring approach was done according to

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EN12341 (CEN, 1999), the reference methoddefined in EU Directive 1999/30/EC. Thecollection efficiency of this technique under fieldconditions in the tropics, has recently beenascertained (Ukpebor et al., 2006).

After sampling, the glass fiber filters weretransferred into containers brought to thelaboratory and stored in the dark prior toextraction/analysis for heavy metals. The filterswere placed in a beaker to which 20 mL of 0.25 MHNO was added (Bagiroz, 2002; Bozlaker, 2002).The solution was then concentrated to about 5 mLon a hot plate at 150 C to 180 C. After this, 10 mLof 1:1 HNO was further added and the extractwas filtered through a Whatman filter paper. Thebeaker and filter paper was washed with successivealiquot of 0.25 M HNO . The filtrate andwashings were finally transferred into a 50 mLvolumetric cylinder and made up to the mark withthe dilute HNO . Unused filters from the samebatch were extracted in the same way to determinethe blank values (Basha et al., 2010). Samples wereanalyzed using Flame Atomic AbsorptionSpectrophotometer (AA 6701 Shimadzu) andstandard quality control solutions were used(USEPA, 2001). Detection limits for the metalswas 0.0001 µgm .

The rural community ofIyowa has no weather station, consequently airtemperatures, relative humidity and wind speedswere measured simultaneously during thesampling duration. These parameters significantlyaffect the ambient concentrations and spatialdistributions of SPM and therefore would berelevant in the interpretations of the measureddata.Measurements were taken every half hour from8.00 a.m. to 8.00 p.m. on alternate days. The airtemperature/humidity was measured using RShumidity/Temperature meter with resolution of0.1% RH and 0.1 C (Model RS 1364, RSComponent Ltd UK). Wind speeds were alsomeasured using an LM 8000 Anemometer(Heatmiser UK) with a resolution of 0.1 ms .

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Meteorological Data:

Statistical analysis: The results of pollutantconcentrations obtained were subjected to intercorrelation matrix, principal component factoranalysis and cluster analysis using Microsoft officeExcel 2007 and SPSS 16.0.

Heavy metals concentration in airborneparticulate matter is of serious environmentalconcern, because of the health implications oftheir high doses in the atmospheric environment.The baseline levels of Pb, Cd, Zn and Cr obtainedat Iyowa village during the study are summarizedin Tables 2, 3 and 4.

The outdoor par t iculate matterconcentration used for the quantification of thetrace metals ranged from 240.74 - 555.55 µgm .These values clearly violated the WHO regulatorylimit of 150 230 µgm (WHO, 2000); while someof the values obtained violated the NigeriaFederal Ministry of Environment statutory limitof 250 µgm (FEPA, 1991).However, relatively low baseline concentrationsof the trace metals were measured in the front ofthe homes examined. Lead was not found inmeasurable quantities in households A, B and D.In locations C and E, the mean Pb concentrationswere 0.0015 µgm and 0.0029 µgm respectively.Zinc gave the highest concentration of the tracemetals studied with a range of < 0.0001 0.0603µgm . The highest Cd mean concentration of0.0039 µgm was measured in household B. Inlocation C, Cd was not detected. Chromium wasalso present at very low levels with the highestmean concentration of 0.0252 µgm measured insite E. The concentrations of the characterizedmetals were within the typical rural concentrationranges (Table 5) and also within the availableWHO limits for Pb (0.5 µgm ) and Cd (0.005 µgm) (WHO, 2000). The typical rural Pb, Cd and Znconcentration ranges are 0.02 2.0 µgm , 0.00011.0 µgm and 0.003 0.1 µgm respectively. Thereare no national limits for trace metals in Nigeria.

RESULTS AND DISCUSSION

Outdoor Heavy Metals Concentration

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Ukpebor et al.: Atmospheric Trace Metal Concentrations 5

However, WHO has regulatory limits for Pb andCd and they are 0.5 µgm and 0.005 µgmrespectively. Pb and Cd data from this study alsocomplied with the above limits. There are nostandards for Cr and Zn.

Spatial variations were not evident in thetrace metal distributions, with identicalconcentrations reported in all the outdoorsampling sites. Factors responsible for spatial andambient concentrations of air pollutants whichcould also be responsible for the trend in thiscommunity, include emission strength, emissionrate, emission conditions and atmosphericdispersion conditions (Baumbach et al., 1995). Atall the sites, dispersion conditions were similarcharacterized by low wind speed, high ambienttemperature and moderately humid atmosphere(Table 6). Anthropogenic sources of trace metalswere observed to be low in the community. The

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main anthropogenic sources of trace metalsinclude metal manufacturing industries, fossil fuel(petroleum, coal, gas) combustion, burning ofsolid waste and incinerators. At Iyowa, theseanthropogenic trace metal sources are notprevalent, especially motor vehicles which havepreviously been indicted (Ukpebor et al., 2010) asbeing responsible for the high Pb concentrations inurban centres in Nigeria. Instead, what is rife atIyowa is the abundant combustion of biomass(firewood) for cooking and frying cassava which isthe economic mainstay of the inhabitants of thisvillage. Other likely trace metal sources in thecommunity include emissions from very fewmotorcycles, cassava milling machine and the re-suspension of dust particles while sweeping andfugitive harmattan dust from the trans saharadesert.

Table 2: Concentration of Outdoor Heavy Metals and Particulate Matter at Iyowa (µgm )-3

Table 3: Kitchen Concentration of Heavy Metals and Particulate Matter at Iyowa (µgm )-3

Table 4: Living Room Concentration of Particulate Heavy Metals and Particulate Matter at Iyowa (µgm )-3

Table 5: Typical Concentrations of Some Trace Metals in Air

Ukpebor et al.: Atmospheric Trace Metal Concentrations6

A similar study of trace elements in airparticulate in the rural village of Bagauda, northernNigeria (Beavington and Cawse, 1978), reported asimilar trend of low metals levels. Just as observedin location CO, Cd was not detected in the Baguadastudy, but Pb, Cr and Zn mean concentrations were0.012 µgm , 0.007 µgm and 0.015 µgmrespectively and they came basically from re-suspended dust. In comparison to the study byRizzio et al (1999) in the rural - residential area ofIspra (Italy), higher levels of Pb (0.098 µgm ) andZn (0.149 µgm ) were reported. However, Cd(0.0005 µgm ) and Cr (0.0065 µgm ) mean valueswere identical to the values reported in our study.The Pb, Cr and Zn concentration obtained from arelated study at rural location of Delhi (India)(Shridhar et al., 2010), were several orders of

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magnitude higher than the values measured atIyowa. Just as reported in location CO in our study,Cd was not detected in their study. The bulk of themetallic burden in Delhi, came from resuspendedand wind blown dust (Shridhar et al., 2010).

The sampling was done between December 2007and March 2008, dry season period of the year. Asexpected therefore, high ambient temperatureswere recorded at all the sampling locations with arange of 28.2 - 35.8 C (Table 6). Relative humiditywhich measures the degree of wetness and drynessof the atmosphere was found to be moderate withan average range of 49.2 - 58.6%. Low wind speedswere measured at all the sites with a range of 0.4 -2.9 ms .

Meteorology During the Sampling Period

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Table 6: Ambient Temperature, Relative Humidity and Wind Speed During Sampling

Indoor Concentrations of Trace Metals

Kitchen AreaTable 3 represents the particulate mass and thetrace metals concentration measured in thekitchens of households A, B, C, D and E. The SPMmass ranged from 425.93 - 1444.00 µgm and thesevalues are a factor of between 2 and 7 greater thanthe available WHO and FMENV limits. In contrastto the above trends, the elemental concentrationswere found to be low. Pb was not detected in any ofthe kitchen's air samples while Cr was only found inmeasurable quantities in locations BK, CK and EKwith mean concentrations of 0.0224 µgm , 0.0065µgm and 0.0121 µgm respectively. Zinc again wasthe highest with a range of 0.0185 - 0.1171 µgm .Cd gave a range of 0.0013 - 0.0043 µgm . Therewas no difference in their spatial distribution andthe measured values when compared with theWHO limits for Pb and Cd, can be safely inferredto be low. The metal levels were also within theirtypical rural concentration ranges (Table 5). Mostof the reported studies on the rural levels of tracemetals, were outdoor investigations (Beavingtonand Cawse, 1978; Purghart-Galli et al., 1990;Ayrault et al., 2010; Shridhar et al., 2010),

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consequently, the data from this study could not becompared with previous literature values.Nevertheless, data generated here would form thebasis for future assessment.

Most people spend a large amount of their timeindoors, which makes indoor spaces importantmicro-environments when addressing risks fromair pollution (WHO, 2000). Consequently, theliving room concentrations of these metals werequantified. The trace metal data from this exercise(Table 4) were found to be relatively low. However,the particulate matter data measured in these livingrooms depicted enhanced concentrations, withSPM range of 546.30 - 955.56 µgm obtainedwhich exceeded by a factor of 2- 3 the availableWHO and FMENV regulatory limits. Pb wasfound in measurable quantities only in locationsAP and EP, with the same mean value of 0.0003µgm . The mean Zn, Cd and Cr concentrations forthe rooms, were 0.0478 µgm , 0.0003 µgm and0.0135 µgm respectively. These values are oncemore within their typical rural concentration range(Table 5) and the available WHO limits.As observed for the outdoor and kitchen trace

Living Room

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Ukpebor et al.: Atmospheric Trace Metal Concentrations 7

metals data, there was no remarkable differences inthe spatial distributions of the measured metals.This of course suggests similarities in their sourcesand strength. Some of the identified sources ofthese metals indoors, include outdoor sources re-suspended dust, firewood smoke, motorcycles andcassava milling engine exhaust emissions. Some ofthe metals are also envisaged to have come fromindoor sources which include emissions fromtobacco smoke, soot from hurricane lanterns andlocally made naked lamps and particles from thewalls of the mud houses. Ideriah et al., (2001) intheir study on indoor and outdoor concentrationsof SPM in rural areas, observed that mud wallscontributed significantly to indoor SPM levels(152.6 1037.2 µgm ) and by extrapolation indoorlevels of trace metals. Comparative analysis of the

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measured living room data with literature, wasdifficult as a result of scanty relevant data.

Ratios obtained from the calculations of thekitchen and living room levels are shown in Table 7.There was no observed distinct trend in theirdistributions. Pb was not detected in most of thekitchens and living rooms assessed. In householdsA and B, Zn was higher in the living room. Inlocation C, it was evenly distributed in both kitchenand living room. In apartment D, the kitchen Znlevel was now higher than the living roomconcentration. Cd was higher in the kitchens ofhouseholds B and C. In apartments A and E, theliving room values were slightly higher.

Comparison of kitchen and living room tracemetals concentrations

Table 7: Comparison of Kitchen and Living Room Heavy Metals Levels (µgm )-3

For most of the homes, Cr was present at levelslower than the detection limits of the equipmentused. A possible explanation for this trend is thatboth microenvironments contributed evenly to thetrace metal levels in the community.

The living room/outdoor ratio of Zn ranged from0.9 - 1.7. In household A, the ratio was 1, whichimplies an even distribution at both locations. Inapartments B and C, the living room Zn values

Comparison of Living Room and OutdoorTrace Metal Concentration.

slightly exceeded the outdoor values (Table 8),while in house E, the metal was not detected.Except for household E, where the outdoorconcentration of Pb was higher than the livingroom, Pb was either not present or randomlydistributed in the other homes. The living roomconcentration of Cd was higher than the livingroom levels for most of the homes. The erratictrend in the living room/outdoor levels of thetrace metals once again reflects the probable variedsources of trace metals in this community.

Ukpebor et al.: Atmospheric Trace Metal Concentrations8

Table 8: Comparison of Living Room and Outdoor Heavy Metals Levels (µgm )-3

Ukpebor et al.: Atmospheric Trace Metal Concentrations 9

Table 9: Correlation Matrix for Heavy Metals

Table 10: Communalities of Heavy Metals at all the Sampling Locations (Indoor and Outdoor)

Initial Extraction

AK1 1.000 1.000AK2 1.000 0.981AP1 1.000 0.861AP2 1.000 1.000AP3 1.000 1.000AO1 1.000 1.000AO2 1.000 0.996BK1 1.000 0.997BK2 1.000 0.999BP1 1.000 1.000BP2 1.000 0.997BO1 1.000 0.989BO2 1.000 0.995CK1 1.000 0.997CK2 1.000 0.974CP1 1.000 0.993CP2 1.000 0.994CO1 1.000 0.990CO2 1.000 0.997DK1 1.000 1.000DK2 1.000 1.000DP1 1.000 1.000DP2 1.000 1.000DO1 1.000 0.995DO2 1.000 0.999EK1 1.000 0.963EK2 1.000 0.982EP1 1.000 0.992EP2 1.000 0.988EO1 1.000 0.919

Extraction method: Principal Component Analysis

Ukpebor et al.: Atmospheric Trace Metal Concentrations10

Multivariate Analysis of the Trace MetalsThe concentrations of the trace metals (Zn, Cd,Cr, Pb) obtained from all the sampling sites(outdoor, living room and kitchen) were combinedand subjected to inter correlation, principalcomponent analysis and factor analysis using SPSS16.0. This was done to elucidate relationshipsamong the sampling sites and to identify thesources contributing to trace metal levels in thiscommunity. The strong positive correlationobtained in the distribution of the trace metalsbetween the kitchen, living room and outdoor ofhouseholds A, B, C and D (Table 9), suggestsimilarities in the source(s) of the metals. Howeverthere was a weak correlation between the kitchen,living room and outdoor of household E,indicative of a different trace metal source. Inorder to identify the source(s) contributing to tracemetals emissions at the sampling locations, theobtained data were further subjected to factoranalysis with varimax rotation and only sampling

locations with high extraction communalities(Table 10) were retained for the analysis. Toascertain the number of factors to be retained inour study, only factors with eigenvalues = 1 wereconsidered significant as suggested by Roscoe etal., (1982). Three factors were identified (Figs 2and 3) as the main sources of the trace metalswhich were further confirmed by the hierarchicalcluster analysis (Table 11). Cluster 1 comprises thekitchen, living room and outdoor of householdsA, B, C, and E and the outdoor of household D.Cluster 2 is made up of kitchen and living roomof household D. The identified trace metalssources in the community are emissions fromfirewood combustion, harmattan dust, re-suspended dust during sweepings, particles fromdeteriorating roofing sheets and emissions frommotorcycles and cassava milling machineexhausts. Re-suspended and wind blown dustappeared to be the dominant sources of tracemetals in the community.

Case 2 Clusters

AK1 1AK2 1AP1 1AP2 1AP3 1AO1 1AO2 1BK1 1BK2 1BP1 1BP2 1BO1 1BO2 1CK1 1CK2 1CP1 1CP2 1CO1 1CO2 1DK1 1DK2 2DP1 2DP2 2DO1 1DO2 1EK1 1EK2 1EP1 1EP2 1EO1 1

Table 11: Cluster Membership

Ukpebor et al.: Atmospheric Trace Metal Concentrations 11

Ukpebor et al.: Atmospheric Trace Metal Concentrations12

Figure 2: Dendrogram Using Average Linkage (between Groups) for Heavy Metals at DifferentSampling Locations.

0 5 10 15 20 25

Rescaled Distance Cluster Combine

C A S E

Label Num

AO2

DO1

AP2

AK2

7

24

4

2

CK2 15

BP1 10

DK1 20

DO2 25

BK1 8

CO2 19

BO1 12

CO1 18

BP2

EK2

BO2

CK1

CP2

CP1

AP1

BK2

EK1

EP2

EP1

EO1

AK1

AO1

AP3

DP1

DP2

DK2

11

27

13

14

17

16

3

9

26

29

28

30

1

6

5

22

23

21

Figure 3: Principal Component Analysis Plot of Heavy Metals Concentration at the Different Sampling Locations

CONCLUSION

ACKNOWLEDGEMENT

This study on the trace metal content of airparticulate matter collected from a ruralcommunity in Nigeria, revealed a high particulatemass but relatively low baseline levels of Pb, Zn,Cd and Cr. Spatial variability in the measured datawas not apparent, while the outdoor, kitchen andliving room concentrations were similar. Theconcentration ranges of the metals were typical ofrural concentration ranges and re-suspended andwindblown dust was identified as the dominantsources of trace metals in the community.

The authors acknowledge the co operation of thecommunity head and the occupants of thehouseholds assessed. We also wish to express outprofound gratitude to Edo State Ministry ofEnvironment which through its laboratoryprovided the samplers and instrument for theanalysis.

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