Journal of Geochemical Exploration xxx (2014) xxx–xxx

GEXPLO-05370; No of Pages 6

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Journal of Geochemical Exploration

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Concentration levels of potentially harmful elements from gold mining in Lake VictoriaRegion, Kenya: Environmental and health implications

Veronica Ngure a,⁎, Theophilus Davies b, Geoffrey Kinuthia c, Noah Sitati d, Silvanus Shisia e, Elijah Oyoo-Okoth f

a Department of Biological Sciences, Laikipia University, P.O. BOX 1100-20300, Nyahururu, Kenyab Faculty of Natural Sciences, Mangosuthu University of Technology, 511, Mangosuthu Hwy, Umlazi 4031, South Africac Department of Biological Sciences, Daystar University, P.O. Box 44400-00100, Nairobi, Kenyad African Wildlife Foundation, Kilimanjaro Landscape, P.O. BOX 20-00207, 13, Nairobi, Kenyae Department of Chemistry, Laikipia University, P.O. BOX 1100-20300, Nyahururu, Kenyaf Department of Environmental Health, Karatina University, P.O. BOX 1957-10101, Karatina, Kenya

⁎ Corresponding author.E-mail addresses: vera_ngure@yahoo.com (V. Ngure),

(T. Davies), gkinuthia@daystar.ac.ke (G. Kinuthia), n_wasshisia2003@yahoo.com (S. Shisia), elijaoyoo2009@yahoo.

http://dx.doi.org/10.1016/j.gexplo.2014.04.0040375-6742/© 2014 Elsevier B.V. All rights reserved.

Please cite this article as: Ngure, V., et al., ConEnvironmental and health imp..., J. Geochem

a b s t r a c t

a r t i c l e i n f o

Article history:Received 7 October 2013Revised 1 April 2014Accepted 7 April 2014Available online xxxx

Keywords:EnvironmentHealthGold miningFishPotentially harmful elementsLake Victoria

Second only to the agricultural industry, mining is often considered to be the largest source of pollution in mostmineral-rich countries. Minewastes and tailings commonly generate large concentrations of effluents containinghigh levels of potentially harmful elements (PHEs) which migrate into various compartments of the ecosystemwith obvious undesirable health consequences. In this study, the concentrations of As Cd, Hg and Pb were deter-mined on samples of soil, stream water and fish (Rastrineobola argentea) collected from the Migori Gold Belt(MGB) in Kenya. Maximum total concentrations of Cd, Pb, As and Hg recorded in some samples in the studyarea were found to be far above the World Health Organization (WHO) and the Food and Agriculture Organisa-tion (FAO) maximum allowable concentrations (MAC), respectively, including some from the control site,150 km away from the MGB. The calculated geometric means showed that the PHE concentrations were signif-icantly above MAC levels (p b 0.05) in the three sample types.The PHE concentrations were as follows: in water, Cd: 1.5–10.5 μg l−1, Pb: 0.4–13.1 μg l−1, As: 0.06–23.0 μg l−1,and Hg: 0.36–52.1 μg l−1; in soil, Cd: 4.5–570 mg kg−1, Pb: 5.9–619 mg kg−1, As: 0.08–86.0 mg kg−1, and Hg:0.51–1830 mg kg−1; and in fish; Cd, 1.9–10.1 mg kg−1, Pb: 2.0–13.1 mg kg−1, As: 0.02–1.92 mg kg−1, and Hg:0.26–355 mg kg−1.Concentrations of PHEs were much higher in the area affected by gold mining than at point S4 which wassampled for comparison and was 70 km away from the gold mining area. We conclude that gold mining andother human activities in the MGB have led to the release of toxic levels of Cd, Pb, As and Hg, which may leadto serious environmental health consequences in humans. We recommend that the public health sectoraddresses in a timely fashion, these sources of contamination (gold mining and associated human activities),in order to obviate impending health problems.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

The distribution of potentially harmful elements (PHEs) in thegeological environment is governed by many geogenic factors in-cluding the chemical composition of bedrock, intensity of bedrockweathering, chemistry of the regolith, soil type and the intrinsicchemical properties of the PHEs themselves. Today, as a result ofrapid urbanisation in some mining centres, the role of anthropo-genic factors has also become important in controlling the

theo.clavellpr3@gmail.comilwa@yahoo.com (N. Sitati),com (E. Oyoo-Okoth).

centration levels of potential. Explor. (2014), http://dx.do

distribution of PHEs (Davies and Mundalamo, 2010; Khalifi andHamza-Chaffai, 2010). Human activities may drastically alterdynamics in the biochemical and geochemical cycles of PHEsin the environment. The study of PHEs in the environment is a sub-ject of increasing interest to ecologists, biologists, farmers andenvironmentalists.

An assessment of the environmental risks due to soil pollution byPHEs, is of particular importance in studying the fecundity of agricultur-al areas (Orisakwe et al., 2012; Oyoo-Okoth et al., 2013). Potentiallyharmful elements can persist in soils for a very long time (regardlessof their associated land use), and may enter the food chain in signifi-cantly elevated amounts under certain circumstances (Christensenand Moller, 1975; Davies, 2013; Khairiah et al., 2009; Liu et al., 2005;Oyoo-Okoth et al., 2013; Uwah et al., 2009).

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In Kenya, mining is known to provide a variety of socio-economicbenefits, but it is also regarded as the single largest source of pollutionafter agriculture. Gold mining is a process that generates large volumesof mine waste, tailings and effluents, with considerable amounts ofPHEs (AMAP/UNEP, 2013; Ogola et al., 2002; Telmer and Stapper,2012; Telmer and Veiga, 2009). This causes a great deal of environmen-tal and human health concerns, which may include land degradation,habitat alteration, and both soil and water contamination (Mol andOuboter, 2004; Veiga and Baker, 2004; Webb et al., 2004). There is evi-dence that the concentrations of PHEs continue to increase in LakeVictoria (Oyoo-Okoth et al., 2013). In this paper, we examine the distri-bution of As, Cd, Hg, and Pb in soil, stream water and fish in gold

Fig. 1. Map of the study area showing the four sampling sites

Please cite this article as: Ngure, V., et al., Concentration levels of potentialEnvironmental and health imp..., J. Geochem. Explor. (2014), http://dx.do

mining areas of the Lake Victoria basin in Kenya (Fig. 1), and reviewthe implications of elevated levels of PHE's to human health whenthese elements are incorporated into the food chain, and propose tangi-ble measures for obviating any health risks.

2. Study area

2.1. General information

The study area ofMacalder is within theMigori Gold Belt (MGB) andcovers part of the Lake Victoria Basin. This region is the centre of manyhuman activities, including agriculture, fishing and gold mining. Lake

(S1, S2, S3 and S4) along Gucha, Migori and Nzoia Rivers.

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Victoria (68,800 km2) is the second largest freshwater body in theworld, with a mean depth of 40 m. It lies in a catchment area of about84,000 km2 and is shared by three riparian states (Kenya, Tanzaniaand Uganda).

2.2. Physiography

The major landscape units of the study area reflect the differentclimatic zones present. These units include: the Stable Slopes, havingan altitude range of between 1500 and 2000 m, and an annual rainfallof about 1200 mm; the Ridges, with an altitude that varies from 1300to1600 m, and an annual rainfall of between 800 and 1300 mm; the‘Sediments’ which consist of alluvial fans and pediments, with slopesvarying from 2% to10%, altitude ranging from 1200 to1500 m, andwith annual rainfall of between 700 and 1200mm; the Flat area (slight-ly undulating, with maximum slopes of 5%), with an altitude rangingfrom 1200 to 1600 m; and, the Lacustrine Plain, with a lithology com-prised of sandy and clayey alluvial deposits, altitude of about 1200 m,and annual rainfall of between 700 and 800 mm.

2.3. Riverine deposits and soils

Alluvial sediments occur below the confluence of the Gucha andMigori rivers (North and South Kadem Locations). The texture is largelysilty, but lenses of sand and gravel occur. Black cotton soils, partly allu-vial in origin, occur in flat- bottomed valleys and drier parts of the area.They are characteristic of poor drainage.

2.4. Geology and gold mineralisation

The Migori granite–greenstone complex consists of Precambrianrocks of about 2.8 billion years old (Ogola et al., 2002). These rocks areintruded by doleritic dykes along the Migori River Valley. The complexcontains gold mineralisation in quartz veins that transect maficvolcanics.

3. Materials and methods

3.1. Sampling sites and sampling regime

Four sites were purposively selected for this study (Fig. 1). Sites S1,S2 and S3 are located within the area rich in gold deposits, with numer-ous artisanal mining activities taking place at these localities (Yager,2013). The control site, S4 is located close to Port Victoria where thereare no known gold deposits (Ogola, et al., 2002). Port Victoria marksthe entry point of Nzoia River into Lake Victoria and is located awayfrom MGB, at approximately 73 km from S1, and 60 km and 44 kmfrom S2 and S3, respectively (Fig. 1). Samples of soil, water and fishwere collected in triplicate, twice per month, for 9 months, giving atotal of 648 samples (Table 1). Timing of data collection between Janu-ary and September 2011, was done in such a way as to allow the detec-tion of variations in geochemical trends during thewet and dry seasons.

3.1.1. SoilUsing a soil auger, triplicate near-surface (10–30 cmbelowAo) com-

posite soil samples of about 250 g each, were taken from each of three

Table 1Total number of water, soil and fish samples from the sites 1–4 in the study area.

Type of sample Sampling points Total number of samples

S1 S2 S3 S4

Water 54 54 54 54 216Soil 54 54 54 54 216Fish 54 54 54 54 216Total 216 216 216 216 648

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farms in different topographical locations in agricultural fields. At eachfarm, a composite soil samplewas prepared by homogenising and quar-tering on a plastic sheet, four soil samples taken from each of the fourcorners of a 20 m by 20 m square, in accordance with IGCP 259 recom-mendations (Darnley et al., 1995). The composite soil sample was thentransferred, using a plastic trowel, to air tight plastic containers to retainthe moisture content (Fordyce et al., 2000).

The air dried soil samples were disaggregated to pass a 2 mm nylonsieve and then ground in an agatemortar to a fine powder. The sampleswere then lyophilised for 72 h. About 0.2 g of each sample was placed ina Teflon digestion vessel, with the addition of 7.0ml of ANALAR concen-trated nitric acid (65%), 1.0 ml ANALAR concentrated hydrochloric acid(30%) and 1.0 ml of ultra pure hydrogen peroxide (30%). The mixturewas then placed in an Ethos D microwave lab station (Milestone Inc ®Monroe, CT, USA) until digestion was complete.

3.1.2. Water samplingWater samples were collected in 500 mlmetal free Van Dorn plastic

bottles fromMigori River (S1) and Gucha River (S2), Lake Victoria (S3),and south of the Nzoia River (S4) (Fig. 1). The samples were then acid-ified to about pH1.5 to 2.0with ARISTAR grade concentratedhydrochlo-ric acid, to prevent adsorption of dissolved PHEs onto the interior wallsof the storage bottles, and to minimise microbial activity. As soon as thesamples were brought to the laboratory, they were filtered through0.45 μm pore filter paper with the aid of a vacuum pump, and storedin 125 ml plastic sample bottles at 4 °C until analysed.

3.1.3. FishA total of 216mature dry fish samples of R. argentea specieswere ob-

tained from local volunteers in three homesteads in each of the foursites (54 samples from each site) fromwhich the soil samples were ob-tained. The fish sampleswere packed in polyethylene bags and kept fro-zen until preparation for laboratory analysis. The 54 whole fish samplesfrom the three farms in each site were treated separately. The resultantsamples were treated with 20 ml of a 1:1 mixture of ANALAR concen-trated nitric acid, and water purified by the use of a MilliQ water purifi-cation system. The contents were boiled for 30 min and the filtrateevaporated to a moist residue (2–3 ml) and diluted to 50 ml by the ad-dition of 0.1% nitric acid. Potentially harmful elements in water, soil andfish samples were analysed at the Biochemical Laboratory of Moi Uni-versity, Eldoret, Kenya. Concentrations of Pb, Cd and Hg were deter-mined using Flame Atomic Absorption Spectroscopy (FAAS, PerkinElmer, Analytik Jena AG, Germany, AAS 5 FL model equipped with a

Fig. 2. Geometric mean value of PHEs in streamwater in sites S1, S2 and S3 located in thearea of artisanal gold mining and control site S4 is located outside the mining area.

ly harmful elements from gold mining in Lake Victoria Region, Kenya:i.org/10.1016/j.gexplo.2014.04.004

Table 2Summary of the ranges in mean PHE concentrations in samples compared with MAC levels set by FAO/WHO.

Potentially harmfulelements

Soil samples(mg kg−1) — DW

MAC in unpolluted soils(mg kg−1) FAO/WHO (1999)

Water samples(μg l−1)

MAC in water(μg l−1)FAO/WHO (1999)

Fish samples(mg kg−1) — DW

MAC in fish(mg kg−1)FAO/HO (1999)

Cd 4.5–570 0.1–1.0 1.5–10.5 0.005 1.9–10.095 b0.01Pb 5.5–619 10–70 0.4–13.1 0.050 2.3–13.095 b0.05As 0.08–86.0 3–12 0.05–23.0 0.010 0.015–1.92 b0.05Hg 0.51–1830 0.05–0.08 0.36–52.1 0.002 0.26–355 b0.05

DW= dry weight; MAC = maximum allowable concentration.

4 V. Ngure et al. / Journal of Geochemical Exploration xxx (2014) xxx–xxx

deuterium lamp, air-acetylene gas mixture and auto sampler AS51).Arsenic was determined by Hydride- Generation Atomic Absorptionspectrometry (HGAAS, Perkin Elmer, (USA) Model MHS-20).

3.2. Assessment of data quality

The quality control procedure involved analysis of reagent blanks,duplicate sampling of soil, water and fish, as well as the use of referencematerials. Analytical precision was determined by duplicate analyses ofrandomly selected samples and reference samples. Reliability of analysesdetermined by reference materials was ±24.8% for Cd, ±37.5% for Pb,0.007± 0.002% for As and±85% for Hg. The detection limits, for test por-tions of 1 and 5 g (wet products) were 0.5 to1 mg kg−1 for Cd and 5 to20 mg kg−1 for Pb.

3.2.1. Data analysisData analysis was performed using SPSS for Windows version 13.0

(SPSS Inc.). The statistical significance was set at p b 0.05. Comparisonof PHE concentrations in soil, water, and fish samples collected fromdif-ferent sites within the study areawas done by tests that employ ‘means’and ‘standard deviations’ functions.

4. Results

4.1. Soil

The concentrations of PHEs in the soil variedwithin and between thestudy sites, with the control site (S4) recording high concentrations ofCd and Hg. Details of these variations are shown in Fig. 2. Analysis ofthe soil data revealed that concentrations of As, Cd, Hg and Pb, exceededthe MAC set by the WHO (WHO, 1996) and FAO (FAO, 1999; Table 2),respectively.

Fig. 3. Geometric mean value of PHEs in soils in sites S1, S2 and S3 located in the area ofartisanal gold mining and control site S4 is located outside the mining area.

Please cite this article as: Ngure, V., et al., Concentration levels of potentialEnvironmental and health imp..., J. Geochem. Explor. (2014), http://dx.do

4.2. Water

Variation in concentration levels in water for all four PHEs studied(As Cd, Hg and Pb) is shown in Table 2 and Fig. 2, respectively. The con-trol site recorded high concentrations of all the four elements studied.The concentrations of all the four PHEs exceeded the MAC of WHO(WHO, 1996) and FAO (FAO, 1999), respectively (Table 1).

4.3. Fish

Variation in concentration levels in whole fish samples for all fourPHEs studied (As, Cd, Hg and Pb) is shown in Fig. 4. Some of these valuesare well beyond the WHO and FAO MACs (WHO, 1996; FAO, 1999;Table 2).

5. Discussion

The PHE concentration ranges in the three sampling media (soil,water and fish) are very variable. Water samples recorded the highestgeometrical means for Cd (11.1 μg l−1 in site S4); Pb (15.1 μg l−1 in site3); As (23.3 μg l−1 in site S3), and Hg (50.6 μg l−1 in site S3) (Fig. 3). Allof these values are above the MAC recommended by WHO (FAO/WHO,1999). The high concentrations of As, Hg and Pb in site S3, S1 and S2 areexplained as natural background values, and as possible additions fromPb and As associated with gold ores, as well as Hg used in the amalgam-ation of gold (Ogola et al., 2002). Gold is commonly associated with Asin greenstone belts, although in some gold deposits, themetal is associat-ed with Hg as well. However, the main source of Hg in surface water,stream sediments and in fish is from the amalgamation of gold concen-trate (Ogola et al., 2002; Oyoo-Okoth et al., 2010). High concentrationsof Cd and Pb in site S4 (Fig. 1) could be a result of additions from thefactories along the Yala and Nzoia River courses for example, from

0.1

1

10

100

1000

10000

S1 S2 S3 S4

PH

Es

in f

ish

mg

kg

−1

Sampling sites

CdPbAsHg

Fig. 4. Geometric mean value of PHEs in fish in sites S1, S2 and S3 located in the area byartisanal gold mining and control site S4 is located outside the mining area.

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theWebuye Pan PaperMill. Moreover, many urban centres in Kenya con-tribute PHEs into water systems through municipal urban wastes(Mwamburi, 2003; Oyoo-Okoth et al., 2010). Kimani (2007) for example,recorded up to 46.7 mg kg−1 Hg, 13,500 mg kg−1 Pb and 1058 mg kg−1

Cd, in soil samples in municipal dumpsites in Nairobi, Kenya. Theseelements are leached and washed to the rivers, increasing their pollutionload, and eventually entering food chains. Although PHE concentrationsin water were noted to be high, some of these high concentrations werenot reflected in the fish. The explanation could be a low availability ofthe PHEs for fish due to their immobilisation in stream sediments(Oyoo-Okoth et al., 2010). All samples analysed showed high concentra-tions of Cd and Hg with the lowest values recorded exceeding theMAC limits of WHO and FAO, respectively (WHO, 1996; JointFAO/WHO, 1999; Table 1). In a similar study on sediments inMigori gold mines in Kenya, Odumo et al. (2011),concentrationsof As (29.3–8246.6 mg kg−1); Pb (16.31–14,999.40 mg kg−1) andHg (16.1–149.9 mg kg−1), showed the average concentrations ofthe PHEs to be above the acceptable levels as recommended byWHO (1999).

In Kenya, studies of metal pollution due to their high content in geo-logical environments are rare (Banza et al., 2009; Oyoo-Okoth et al.,2013). There is however growing concern as evidence continues to indi-cate that PHE pollution stemming from mining and agricultural activi-ties poses increasing risks to residents on the continent (Nriagu, 1992;Oyoo-Okoth et al., 2010, 2013). The high concentrations of the PHEsreported in water, soil and fish samples in exposed sites could lead toentry of high environmental levels of Cd, Pb, As and Hg into food chains.These results complement previous studies (Mwamburi, 2003; Ogoyiet al., 2011; Onyari and Wandiga, 1989; Oyoo-Okoth et al., 2010; Toleand Shitsama, 2003; Wandiga et al., 1983), which indicate that metalconcentrations in waters of Lake Victoria have continued on an increas-ing trend in the last decades. Comparison of PHE concentrations in thewater samples with US EPA water quality guideline values (US EPA,2002) shows that PHE concentrations of the samples from some ofthe exposed sites are above the MAC levels. Whole fish samples ofR. argentea recorded total Hg concentration that was highest in sitesS3 and S2, respectively, and lowest in site S4, probably due to bioaccu-mulation of Hg from thewater and sediments. The fish has been report-ed to be a benthic feeder, normally foraging in the sediment, andtherefore likely to accumulate sediment bound PHEs (Mbabazi andWasswa, 2010). The increasedmetal concentrations in water are attrib-utable to both geogenic and anthropogenic sources, such as minewastes and tailings generated through increased artisanal mining activ-ities over the last few years (Ogola et al., 2002). Consumption ofRastrineobola argentea could result in significant intake of the PHEsstudied. The Rastrineobola argentea forms the main source of food forthe local inhabitants living adjacent to LakeVictoria, since it is affordableand easy to capture. According to Abila and Jansen (1997), these fishspecies comprise about 70% of the food of the local inhabitants, and as12 such imposing high health risks to the consumers.

6. Conclusion

In conclusion, there is clear evidence to support the notion thatresidents in metal enriched environments with widespread artisanalmining activities risk being exposed to high concentrations of PHEsthrough consumption of food andwater, and exposure to soils. Further-more, the investigated area is shown to be exposed tomulti-source con-tamination such as from the spread of industrial emissions, besides goldmining related activities, which are considered to be the principalsource. Therefore the challenge for future work would be firstly, to dif-ferentiate between individual sources of contamination, in order for theproblem to be more efficiently and economically tackled. There is needto mount awareness campaigns and educate miners (e.g., on the use ofprotective gear) on the dangers of Hg use in artisanal and small-scalegold mining. Water in Nzoia River, although far removed from the

Please cite this article as: Ngure, V., et al., Concentration levels of potentialEnvironmental and health imp..., J. Geochem. Explor. (2014), http://dx.do

goldmining belt, showed high levels of PHEs, which could be attributedto the discharge of effluents from the Pan PaperMill, and waste streamsfrom the urban centres (Fig. 1). It is recommended that the need for ad-dressing environmental contamination to alleviate the health problemsfrom themining of gold, should be incorporated into the national devel-opment agenda.

Acknowledgements

We are grateful to Joseph Maritim of Moi University for his rolein the analysis of the samples. We thank David Lubanga also of MoiUniversity for his help in sampling and analysis. We also thank thelocal community in the study area who provided their boats andassisted in other aspects of the sampling campaign in Lake Victoria.This study was carried out under the auspices of IGCP/UNESCO/SIDA/MUT Project 606

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