Heavy Metals Speciation and Human Health Risk Assessment at an ...

Research

Heavy Metals Speciation and Human Health Risk Assessment at an Illegal Gold Mining Site in Igun, Osun State, Nigeria Olanrewaju Olusoji Olujimi1, Ogheneochuko Oputu2, Olalekan Fatoki2, Oluwabamise Ester Opatoyinbo1, Oladokun Ali Aroyewun1, Judith Baruani2 1 Department of Environmental Management & Toxicology, College of Environmental Resources Management, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria 2 Department of Chemistry, College of Applied Sciences, Cape Peninsula University of Technology, Cape Town Campus, Cape Town, South Africa

Corresponding Author: Olanrewaju Olusoji Olujimi [email protected] [email protected]

Background. There is increasing global concern over the health effects of heavy metals arising from various anthropogenic activities, especially mining. Mining activities in developing countries are often carried out at an artisanal level using a variety of extraction methods with human health and environmental consequences. Objectives. The broad objective of this study is to assess the chemical forms, distribution pattern, and health risks due to mining and processing techniques at a gold mining site in Igun, Osun State, Nigeria. Methods. Samples were collected from 28 active mine pits and sequentially extracted using standard methods. Extracts were analyzed for metals using inductively coupled plasma optical emission spectrometer (ICP/OES), while health risk was assessed using United States Environmental Protection Agency (USEPA) and Dutch methods. Chemical speciation of heavy metals and health risk assessment was calculated using mobile phase fraction summation. Results. Metals were exclusively present in the residual fractions, indicating that these metals are strongly bound to the resistant components of the soil matrix. The percentage in the residual fraction ranged from 9.41% (tin) to 99.42% (aluminium). The heavy metals geoaccumulation index for the site ranged from 0 (no contamination) to 6 (extremely contaminated). The cancer risk ranged from 6.17E-13 to 7.77E-05 and 2.73E-12 to 4.64E-04 for adults and children, respectively. Discussion. Cancer risk and non-cancer risk (hazard index) assessment showed that arsenic poses a higher risk in adults and children compared to other metals through the dermal exposure route. Competing Interests. The authors declare no competing financial interests. Keywords. Heavy metals pollution, chemical speciation, Igun gold mine, human health risk. J Health Pollution 8: 19-32 (2015)

Introduction Metals such as lead (Pb), cadmium (Cd), mercury (Hg), zinc (Zn), and chromium (Cr) are known for their persistent behavior in the environment with consequent environmental, human and animal damage.1,2 Some of these metals are known to act as human mutagens and carcinogens and are associated with various human ailments such as cardiovascular, nervous system, blood and bone diseases, kidney failure, gingivitis, and tremors, among others.3,4 These metals are easily released into the environment via anthropogenic activities, e.g. metal plating facilities, mining, and agricultural activities.5 Gold mining is often associated with 19

Journal of Health & Pollution Vol. 5, No. 8 — June 2015

positive economic benefits such as job creation and increased standard of living; however, mining activities may also have negative impacts on the environment and human health. Recently, gold mining activities in two villages in Zamfara State in northwestern Nigeria resulted in the death of over 100 children. This is the first documentation of an outbreak of childhood lead poisoning associated with artisanal gold mining in Nigeria.6 Artisanal gold mining is dangerous to human health, as heavy metals, mainly Hg, Pb, and arsenic (As) are often released into the environment. The Igun gold mine is located in the southwestern schist belt of Nigeria.

Gold is known to occur with pyrite, pyrrhotite and minor chalcopyrite, galena, sphalerite, magnetite and ilmenite.7 There have been reported cases of gold mining at the Igun secondary mine which have resulted in the release of acid mine drainage (AMD).8,9 AMD is water with a low pH, high electrical conductivity, elevated concentrations of iron, aluminum and manganese and raised concentrations of other toxic heavy metals. The acid produced dissolves salts and mobilizes heavy metals from mine workings. Dark, reddish-brown water and pH values as low as 2.5 persist at the site.10 Previous studies at the site only

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Research assessed the levels of heavy metals without attention to the chemical forms, distribution pattern, pollution indexing, and human health risk of classified toxic metals by the International Agency for Research on Cancer (IARC).11 The main objective of this study is to assess the chemical forms, distribution pattern, and health risks due to mining and processing techniques adopted by workers at the Igun artisanal gold mining site.

Methods Study Area, Sample Collection and Preparation The study site is located in the Atakumosa Local Government Area of Osun State. The sampling location is shown in Figure 1. At the site, the sluicing extraction technique was adopted (gravity concentration technique). Sluices use water to wash ore or alluvium down a series of angled platforms. As water washes sediment down a sluice, gold particles sink and are captured by material covering the bottom of the sluice. Sluices are usually inclined at a 5 to 15 degree angle. As moving water travels down a sluice, it generates greater force and keeps gold particles from easily sinking.12 Soil samples were collected from 28 hand-dug pits which were pooled into 7 sampled areas based on pit closeness and grouping of artisanal miners operating at the site. Figure 2 shows the mining pits, artisans, and the processed sample. Soil samples were collected at different depths from which sand was collected and processed for gold extraction by the artisans. The samples were stored in sealed polyethylene bags, labeled, and then transported to the laboratory. Soil samples were air-dried, grinded using mortar and pestle, and then sieved through a 1-mm mesh sieve to remove refuse and small stones. The samples were then transferred into a zip-lock bag for further analysis.

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Heavy Metals Speciation and Human Risk Assessment in Igun, Osun State, Nigeria

Abbreviations

ABS Al ANOVA

Dermal absorption factor Aluminum Analysis of variance

As

Arsenic

AT

Averaging time

Ba

Barium

BW C

Average body weight Exposure-point concentration

Ca

Calcium

Cd

Cadmium

Co

Cobalt

Cr

Chromium

CR

Carcinogenic risk

Cu

Copper

Ddermal

Dose from dermal contact

ICP/OES

Inductively coupled plasma optical emission spectrometer

IngR

Ingestion rate

IUR

Inhalation unit risk

K Mn n

Potassium Manganese Number of samples

Na

Niacin

Ni

Nickel

P Pb PEF RC

Phosphorus Lead Particle emission factor Risk characterization

RfCi

Inhalation reference concentration

RfDo

Reference dose

s

Standard deviation of the log-transformed data

Ding

Dose from ingestion

Dinh

Dose from inhalation

SA

Skin surface area

Dvapour

Dose from inhalation of vapour

Sb

Antimony

Se

Selenium

ED

Exposure duration

EF

Exposure frequency

Fe

Iron

GIABS H HI

Gastrointestinal absorption factor Value from the h-statistic table Hazard index

HQ

Non-carcinogenic effect

IARC

International Agency for Research on Cancer

ICP-MS

Inductively coupled plasma-mass spectrometer

SFo

Oral slope factor

Si

Silicon

SL

Skin adherence factor

Sn

Tin

SPSS ∑ USEPA X Zn

Statistical Package for the Social Sciences sum United States Environmental Protection Agency Arithmetic mean of the log-transformed data Zinc


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Figure 1 — Sampling location2

Reagents and Chemicals All reagents were analytical grade and were obtained from Sigma Aldrich, South Africa. The reference material (BCR-277R) was purchased from the European Community Bureau of Reference, IRMM, Belgium. Sequential Extraction Procedure Sequential extraction of metals in collected soil samples was performed using a modified 4-stage extraction procedure previously applied in similar studies.13, 14 A schematic presentation of the extraction procedure is shown in Figure 3. Soil samples were (1) acid soluble/exchangeable fraction (F1, exchangeable metal and carbonated associated fractions); (2) reducible 21


fraction (F2, fraction associated with iron (Fe) and manganese (Mn) oxides); (3) oxidizable fraction (F3, bound to organic matter) and (4) residual fraction (F4). Samples were rinsed twice with 10 mL deionized water, centrifuged, and decanted between each extraction step. Extracts were analyzed for trace and heavy metals using an inductively coupled plasma optical emission spectrometer (ICP/OES) running on a smart analyzer equipped with a CETAC ASX-520 auto sampler. Working and calibration standards were prepared daily by proper dilution from 50 mgL-1 of trace elements and 10,000 mgL-1 of calcium (Ca), potassium (K), niacin (Na) and phosphorus (P) in 10% nitric

acid. External calibration curves were constructed for the quantification of the elements, while instrument calibration was checked with icalizing solution supplied by Spectro Genesis. Contamination Assessment Using the Geoaccumulation Index (Igeo) A common approach for estimating the degree of enrichment of metal concentrations above background or baseline concentrations in soil, sediment, and dust is to calculate the geoaccumulation index (Igeo), as proposed by Muller.15 This method assesses the degree of metal pollution in terms of seven enrichment classes based on the increasing numerical values of the index. This index is

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A

B

C

D

E

F

G

H

I

Figure 2 — A) Abandoned mine pit; B) Active mine pit; C) Illegal miners collecting soil sample for processing; D–G) Illegal miners washing mined soil; H) Extracted gold samples; I) Villager fetching water for domestic usage.

calculated as follows: Equation 1:

Igeo = log2 (Cn /1.5 Bn) Where Cn is the concentration (µgg1 ) of the element in the enriched samples, and Bn is the background or pristine concentration of the element (µgg-1), i.e. the background content of the element in the crust.16,17 A factor of 1.5 is introduced to minimize the effect of possible variations in background values which may be attributed to lithologic variations in the sediments.18 Muller15 proposed the following descriptive classes for increasing Igeo values: >5 = Olujimi et al

extremely contaminated, 4–5 = strongly to extremely contaminated, 3–4 = strongly contaminated, 2–3 = moderately to strongly contaminated, 1–2 = moderately contaminated, 0–1 = uncontaminated to moderately contaminated and 0 = uncontaminated.

analyzed in triplicate. All statistical analyses were carried out using the Statistical Package for the Social Sciences (SPSS) Software. Analysis of variance (ANOVA) and Pearson’s correlation index were used to test for significant differences (95% confidence level).

Quality Control and Statistical Analysis For each batch of 10 field samples, a procedural blank, certified reference material, and sample triplicate were processed. In order to check for the accuracy of the sequential extraction procedure, reference sediment materials BCR-277R were extracted using the above procedure and

Health Risk Assessment Model Daily exposure dose and exposure point concentration The model used for health risk assessment for estimating human exposure to metals in this study is based on criteria of the United States Environmental Protection Agency19 (USEPA) and the Dutch National Institute of Public Health


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g dust samples 0.5

20 mL 0.11M acetic acid, shake 16 hours at 25 oC, centrifuge 10,000 rpm 10 minutes.

Equation 2:

Extract analyzed for exchangeable metal F1

Ding = C x (IngRBWx EFx ATx ED) x 10-6

Equation 3:

Residue dust sample

20 mL 0.1 M hydroxyl ammonium chloride (pH2), shake 16 hours at 25oC, centrifuge 10,000 rpm 10 minutes.

Extract analyzed for reducible metals F2 Residue dust sample

5 mL 8.8 M H2O2 (pH2), digested for 1 hr. Repeated twice.

25 mL 1 M ammonium acetate (pH 2), shake 16 hours at 25oC, centrifuge 10,000 rpm 10 minutes.

Cool digested dust sample

Extract analyzed for organic bound metal F3 Residue dust sample

10 mL aqua regia, 1mL HF, digested for 2 hr, 85oC.

Cool digested dust sample

Dissolved in 20 mL 5% HNO3

Solution analyzed for residual metals F4 Figure 3. Sequential extraction procedure for trace metals in soil sample Figure 3 — Sequential Extraction Procedure for Trace Metals in Soil Sample

and Environmental Protection.20 The health risk assessment focused on two separate sets of people, children and adults. Exposure to metals can occur through three main paths: (a) 23

in particles adhered to exposed skin. Exposure calculation for daily estimation was achieved using the following equations:


ingestion of atmospheric particulates due to their deposition, (b) direct inhalation of atmospheric particulates through the mouth and nose, and (c) dermal absorption of trace elements

InhR x EF x ED Dinh = C x (PEF x BW x AT)

Equation 4:

x ABS x EF x ED Ddermal = C x (SL x SA BW ) x 10-6 x AT

Where D (mg kg-1 day-1) is the dose contacted through ingestion (Ding), inhalation (Dinh), dermal contact (Ddermal) and inhalation of vapour (Dvapour). For this study, ingestion rate (IngR) was 200 mg day-1 for children and 100 mg day-1 for adults.21 The ingestion rate (IngR) was 7.6 m3 for children and 20 m3 for adults,20 and the exposure frequency (EF) was 180 days per year-1.13, 22 The exposure duration (ED) was 6 years for children and 24 years for adults (USEPA, 2001). Average body weight (BW) was 15 kg for children and 70 kg for adults.23 Averaging time (AT) for non-carcinogens was ED x 365 days and AT for carcinogens was 70 x 365 = 25,550 days. Skin surface area (SA) was 2800 cm2 for children and 3300 cm2 for adults.24 The skin adherence factor (SL) was 0.2 mg cm-2 d-1 for children and 0.7 mg cm-2 d-1 for adults, the dermal absorption factor (ABS) was 0.03 for As and 0.001 for Cd; no values were available for other elements, therefore 1.0% was used. The particle emission factor (PEF) was 1.36 x 109 m3 kg-1. The exposure-point concentration, µg g-1 (C) in Equations 2–5 is an estimate of reasonable maximum exposure4,14, 22, 24, 25 and was calculated as the upper limit of the 95% confidence limit for

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the mean using Equation 5. Also, this was based on the assumption that the mobile fractions (F1 + F2 + F3) of the trace metals are potentially labile and bioavailable due to physical activities once they enter the complex internal environment of the human body.14 Equation 5:

C95% UCL = exp {X + 0.5 x S2 + Snx- H1 } Where X is the arithmetic mean of the log-transformed data, s is the standard deviation of the log-transformed data, H is the value from the H-statistic table26 and n is the number of samples. Risk Characterization Risk characterization (RC) was assessed separately from noncarcinogenic effect (HQ) using Equations 6 and 7: Equation 6:

HQ =

Ding RfDo

D

= (RfDo xdermal = GIABS)

Dinh (RfCi x 100ug mg-1)

Equation 7: CR = Ding x SFo = Ddermal x (SFo | GIABS) = IUR x Dinh The values for SFo (oral slope factor, mg kg-1 day-1), RfDo (reference dose), RfCi (inhalation reference concentration, mg m-3), GIABS (gastrointestinal absorption factor) and IUR (inhalation unit risk (µg m-3)), were obtained from the USEPA website.27 The hazard index (HI) was estimated to be equal to the sum of HQs. HI was used to assess the overall potential for non-carcinogenic effects from different pathways. Risk surpassing 1 x 10-4 is viewed as unacceptable, risk below 1 x 10-6 is not considered to pose significant health effects, while risk in the range of 1 x 10-4 to 1 x 10-6 is generally considered acceptable depending on the circumstances of exposure.24,28

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However, it should be noted that in some countries, 1 x 10-5 is considered to be acceptable risk.29 Uncertainty in Risk Assessment Uncertainty is pervasive in risk assessment, especially when it arises due to lack of precise knowledge, variability in environmental systems, and variability of individual systems and characteristics.31,32 It should be noted that there were no studies on health risk modeling of heavy metals in soil or dust in Nigeria before the previous study by Olujimi et al.5 Therefore, the model parameters might contain some uncertainty due to different geographical locations and human genetic variation. Additionally, the number of Nigerians living with cancer and cancer-related diseases has been on the rise, with approximately 100,000 new cases recorded annually.32,33 Consequently, parameters for toxicity of heavy metals were derived from USEPA guidelines and the relevant literature (Equations 2-7). In adopting the models for dermal absorption, mechanisms via metal-ions complex formation (with carboxylic (-COOH), amine (-NH2) and thio (-SH) of proteins) provided the basis on which the assumption proposed by the USEPA and other literature was based.34,35

Results and Discussion Quality Control The recovery efficiencies for all of the metals ranged between 92.05% and 101.01% for ICP-MS (inductively coupled plasma-mass spectrometer) with a deviation of less than 10% in all cases. The drift in instrumentation measurement ratio was also minimal at 0.89 to 1.01. Chemical Partitioning and Distribution of Metals in Soil Chemical partitioning and concentrations of the four fractions

for the 16 metals obtained by the sequential extraction procedure are presented in Table 1. Eight of these metals: aluminum (Al), As, copper (Cu), Fe, Mn, nickel (Ni), antimony (Sb) and Se were exclusively present in the residual fractions, indicating that these metals are strongly bound to the resistant components of the soil matrix. Barium (Ba) and Cd were also present mainly in the residual fraction with mean proportions of 45.2794.48% and 45.95-78.82%, respectively. These results are in line with previously published data.36 In all of the soil samples, tin (Sn) was present as mobile extractable Sn ranging from 69.13-90.59%. With the exception of sample 7, all other samples showed high proportions of mobile Pb, ranging from 56.69-79.80%. The major contribution to the mobile fraction of these metals (Sn and Pb) in the soils was from the oxidizable fraction of the soil, representing 56.16-81.63% and 45.32-73.55% of the sample, respectively. The total metal concentration and fractional percent as presented in Tables 1 and 2 shows that the general distribution pattern for the pooled mine pits is Al > Fe > Sn > silicon (Si) > Se > Pb > Mn > cobalt (Co) > As > Ba > Zn > Cr > Cd > Sb. The order reported in this study differs from the distribution pattern reported in other studies in Niger and Zamfara states in Nigeria and Malaysia.37-39 The mean concentration of Pb, Zn, Cd, and Cu at the mine site was lower than values reported in tailings and soil around a Pb-Zn mine in Spain.40 In addition, the mine pit trace metal concentrations could be arranged in the order of IGUN 5 > IGUN 3 > IGUN2 > IGUN 4 > IGUN 6 >IGUN 1 > IGUN 7. The levels and distribution of Pb differs from previous values reported for gold mine pits in Luku, Niger State.41


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Al

As

Ba

Cd

Co

Cr

Cu

Fe

Ph

Mn

Ni

Sh

Si

Se

Sn

Zn

F1

182.44

3.24

17.2

0.92

1.84

2.56

1.12

12.96

16.24

10.08

0.64

1.04

153.76

1.16

265.2

0.32

F2

275.04

3.08

19.6

1

5.04

3.24

0.72

115.12

11

55.36

0.4

1.72

53.32

2.24

112

0

619.9

13.95

3.95

1.3

1.2

19.25

2.1

214.4

108.55

5.95

1.8

4.1

439

60.9

1633.35

1.85

8.6

68.52

556.92

78.12 49366.4 103.72 422.68

87.32

90.24

6588.44 1082.68 897.92

101.6

11.82

76.6

581.97

82.06 49708.88 239.51 494.07

90.16

97.1

7234.52 1146.98 2908.47 103.77

11.88

1.08

1.16

5.28

1.36

11.64

12.24

11.36

0.68

1.84

257.84

11.2

234.44

3.64

5.08

37.2

0.52

12.4

100.44

10.24

38.2

2.76

5.35

1.7

5.45

232.35

92.55 2407.25

Location

1

F3 R

71781.2 448.28 160.28

MP 72858.58 468.55 201.03

2

F1

44.52

F2

218.36

1.84

14

1.8

1.8

2

0.56

113.32

F3

486.05

42.55

4.45

1.3

0.8

28.25

1.2

215.25 144.25

82976.4 527.48

130.4

10.32

66.56

581.6

62.64 55029.2

227.24

57.52

105.44

MP 83725.33 573.79 160.73

65.76 55369.41 251.77 281.15

60.42

125.13 1200.11 1391.59 3139.09 86.09

R

3

1.92

14.5

70.32

617.13

137.2

1

3.96

6.36

1.52

171.2

16.48

16.28

0.8

1.8

170

12.48

278.6

1.72

F2

194.04

2,84

19.04

0.96

118.64

2.44

3.04

213.2

8.6

535.04

1.36

1.72

62.04

2.28

103.88

2.52

F3

226.95

12.65

2.2

1.3

5.85

19.8

16.95

124

112.75

27.2

1.35

4.5

136

69.15

1800.4

R

52062.4

324

131.08

7

51.2

375.96

571.32

62.8

F1

14.84

F2 F3

10.26

179.65 404.56

71.56 39927.88 84.92

67.88 10915.64 810.96 932.16

93.07 40436.28 222.75 1149.84 66.31

75.9

4.84

0.64

5

1.88

8.48

1.04

1.04

149.56

1.56

9.52

0.96

8.64

1.32

1.04

378.15

37.25

4.95

1.3

1.2

30.15

1.25

93238.8 618.28 159.64

12.28

83.36

675.72

MP 93781.35 658.97 182.59

5.3 79.28

11283.68 894.87 3115.04 88.82

11.68

4.24

0.4

1.28

203.8

11.88

188.28

2.56

114.96

4.6

55.04

1.04

1.32

63.36

211.55

157.3

6.2

2.15

5.4

199.65

4.76

27.4

5.88

95.95

2573.4

6.8

85.04 64932.8 119.44 309,64

66.04

121.76

504.72 1546.64 616.96 125.92 971.53 1659.23 3406.04 141.16

15.58

94.24

712.03

87.97 65264.31 293.02 375.12

69.63

129.76

F1

201.24

3.04

3.732

1.08

1.92

7.4

0.56

24.56

12.64

128.32

0.88

1.6

166.08

17.32

235.28

6.2

F2

231.6

2.28

17.32

1

3.68

2.68

2.12

260.84

3.72

187.68

0.44

1.48

35.04

5.92

58.28

4.48

241.65 170.25

165.9

F3

611.4

39

8.25

1.3

0.85

28.05

4.35

20.05

1.9

5.9

96.15

2674.6

5.55

R

49412

298.44

404.4

6.24

23.44

298.84

25.36 20982.16 79.8

125.32

16.64

61.36

369.32 710.76

308.4

55.88

9.62

29.89

336.97

32.39 21509.21 266.41 461.37

19.86

70.34

736.34 830.15 3276.56 72.11

5.36

0.88

0

F1

49.96

2.56

21.68

1.12

2

F2

35.52

0.96

7.32

0.96

1.28

1

0.12

F3

227.7

37.4

5.65

1.3

1.55

29.35

2.9

11150.6 104.72 194.56

4.04

11.72

72.24

6.4

MP 11463.78 145.64 229.21

R

7

76.64

4.12

MP 50456.24 342.76 433.702

6

459.2

213.72

R

5

609.48 1277.6

F1

MP 52697.11 343.61 289.52

4

90.2

3.05

0

0

0.88

0

108.96

13.24

241.84

12.76

601.92

0.08

26.48

0.32

1.44

1220.6

173.3

12.65

1.5

5.4

42.56

3.36

41.08

1.28

123.65

100.5 2694.55

8975.8 1045.68 77.44

7.12

29

264.72 178.04

321.2

4.05 50.92

7.42

16.55

107.95

10.3 10798.32 1219.06 116.57

9.,82

35.84

539.89 295.14 3298.67 69.01

F1

47.92

2.24

14.48

1.08

1.4

6.88

1.64

233.68

11.64

44.28

0.68

1.64

74.12

18.64

199.56

10.44

F2

46.64

0.84

2.36

0.96

1.24

0.52

0.16

792.52

0.92

5.56

0.36

1.28

70.32

4.44

23.52

11.6

F3

75.8

30.6

411.4

3.4

1.3

0.55

21.1

0.15

147.95

3.15

0.7

4.55

84.7

81.6

2441.7

1.5

346.28

2.84

11.24

109.08

5.16

5167.44 40.64

68.44

6.24

22.04

293.56

233.6

368.72

16.76

1705.48 132.64 366.52

6.18

14.43

137.58

7.11

6605.04 201.15 121.43

7.98

29.51

522.7

338.28 3033.5

40.3

R 16884.12 98.96 MP

Table 1 — Concentrations of Trace Metals Using the BCR SEP Method (mg/kg) F1 = acid soluble/exchangeable fraction; F2 = reducible fraction with Fe and Mn oxides; F3 = oxidizable fraction bound to organic matter; R = residual fraction and MP = ∑ F1 + F2 + F3 + R. Relative standard deviation ranged from 4.76 to 9.22%

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%Al

%As

%Ba

%Cd

%Co

%Cr

%Cu

%Fe

%Ph

%Mn

%Ni

%Sh

%Si

%Se

%Sn

%Zn

F1

0.25

0.69

8.56

7.78

2.40

0.44

1.36

0.03

6.78

2.04

0.71

1.07

2.13

0.10

9.12

0.31

F2

0.38

0.66

9.75

8.46

6.58

0.56

0.88

0.23

4.59

11.20

0.44

1.77

0.74

0.20

3.85

0.00

Location

1

2

3

4

5

6

7


F3

0.85

2.98

1.96

11

1.57

3.31

2.56

0.43

45.32

1.20

2.00

4.22

6.07

5.31

56.16

1.78

R

98.52

95.67

79.73

72.76

89.45

95.70

95.20

99.31

43.31

85.55

96.85

92.94

91.07

94.39

30.87

97.91

MP

1.48

4.33

20.27

27.24

10.55

4.30

4.80

0.69

56.69

14.45

3.15

7.06

8.93

5.61

69.13

2.09

F1

0.05

0.33

7.39

7.45

1.65

0.86

2.07

0.02

4.86

4.04

1.13

1.47

21.48

0.80

7.47

4.23

F2

0.26

0.32

8.71

12.41

2.56

0.32

0.85

0.20

2.02

13.23

0.86

9.91

8.37

0.74

1.22

3.21

F3

0.58

7.42

2.77

8.97

1.14

4.58

1.82

0.39

57.29

1.90

2.81

4.36

19.36

6.65

76.69

3.54

R

99.11

91.93

81.13

71.17

94.65

94.24

95.26

99.39

35.83

80.83

95.20

84.26

50.79

91.81

14.63

89.02

MP

0.89

8.07

18.87

28.83

5.35

5.76

4.74

0.61

64.17

19.17

4.80

15.74

49.21

8.19

85.37

10.98

F1

0.41

1.20

47.39

9.75

2.20

1.57

1.63

0.42

7.40

1.42

1.21

2.37

1.51

1.39

8.94

1.94

F2

0.37

0.83

6.58

9.36

66.04

0.60

3.27

0.53

3.86

46.53

2.05

2.27

0.55

0.25

3.33

2.84

F3

0.43

3.68

0.76

12.67

3.26

4.89

18.21

0.31

50.62

2.37

2.04

5.93

1.21

7.73

57.80

5.97

R

98.80

94.29

45.27

68.23

28.50

92.93

76.89

98.74

38.12

49.69

94.71

89.43

96.74

90.62

29.92

89.26

MP

1.20

5.71

54.73

31.77

71.50

7.07

23.11

1.26

61.88

50.31

5.29

10.57

3.26

9.38

70.08

10.74

F1

0.02

0.29

4.64

6.68

1.10

0.68

0.73

0.01

3.99

1.13

0.57

0.99

20.98

0.72

5.53

1.81

F2

0.16

0.24

5.21

6.16

9.17

0.19

1.18

0.18

1.57

14.67

1.49

1.02

6.52

0.29

0.80

4.17

F3

0.40

5.65

2.71

8.34

1.27

4.23

1.42

0.32

53.68

1.65

3.09

4.16

20.55

5.78

75.55

4.82

R

99.42

93.83

87.43

78.82

88.46

94.90

96.67

99.49

40.76

82.54

94.84

93.83

51.95

93.21

18.11

89.20

MP

0.58

6.17

12.57

21.18

11.54

5.10

3.33

0.51

59.24

17.46

5.16

6.17

48.05

6.79

81.89

10.80

F1

0.40

0.89

0.86

11.23

6.42

2.20

1.73

0.11

474

27.81

4.43

2.27

22.55

2.09

7.18

8.60

F2

0.46

0.67

3.99

10.40

12.31

0.80

6.55

1.21

1.40

40.68

2.22

2.10

4.76

0.71

1.78

6.21

F3

1.21

11.38

1.90

13.51

2.84

8.32

13.43

1.12

63.91

4.35

9.57

8.39

22.53

11.58

81.63

7.70

R

97.93

87.07

93.24

64.86

78.42

88.68

78.30

97.55

29.95

27.16

83.79

87.23

50.16

85.62

9.41

77.49

MP

2.07

12.93

6.76

35.14

21.58

11.32

21.7

2.45

70.05

72.84

16.21

12.77

49.84

14.38

90.59

22.51

F1

0.44

1.76

9.46

15.09

12.08

4.97

8.54

0.00

0.00

0.00

8.96

0.00

20.18

4.49

7.33

18.49

F2

0.31

0.66

3.19

12.94

7.73

0.93

1.17

5.57

0.01

22.72

3.26

4,02

7.88

1.14

1.25

1.85

F3

1.99

25.68

2.46

17.52

9.37

27.19

28.16

11.3

14.22

10.85

15.27

15.07

22.9

34.05

81.69

5.87

R

97.27

71.9

84.88

54.45

70.82

66.92

62.14

83.12

85.78

66.43

72.51

80.92

49.03

60.32

9.74

73.79

MP

2.73

28.1

15.12

45.55

29.18

33.08

37.86

16.88

14.22

33.57

27.49

19.08

50.97

39.68

90.26

26.21

F1

0.28

1.69

3.95

17.48

9.7

5

23.07

3.54

5.79

36.47

8.52

5.56

14.18

5.51

6.58

25.91

F2

0.27

0.63

0.64

15.53

8.59

0.38

2.25

12

0.46

4.58

4.51

4.34

13.45

1.31

0.78

28.78

F3

0.44

23.07

0.93

21.04

3.81

15.34

2.11

6.23

73.55

2.59

8.77

15.42

16.20

24.12

80.49

3.72

R

99

74.61

94.48

45.95

77.89

79.28

72.57

78.23

20.2

56.36

78.2

74.69

56.16

69.06

12.15

41.59

MP

1

25.39

5.52

54.05

22.11

20.72

27.43

21.77

79.8

43.64

21.8

25.31

43.84

30.94

87.85

58.41

Table 2 — Distribution of Trace Metals Bound to Each Fraction in Soil Samples from Different Site Locations F1 = acid soluble/exchangeable fraction; F2 = reducible fraction with Fe and Mn oxides; F3 = oxidizable fraction bound to organic matter; R = residual fraction and MP = ∑ F1 + F2 + F3 + R

Olujimi et al


26

Research

1

2

3

4

5

6

7

Average

Igeo Class

Al

-0.73

-0.53

-1.19

-0.36

-1.26

-3.40

-2.82

-1.47

0

As

7.70

7.99

7.25

8.19

7.25

6.02

5.88

7.18

6

Ba

-2.04

-2.36

-1.51

-2.18

-0.93

-1.85

-1.17

-1.72

0

Cd

6.33

6.62

6.13

6.73

6.03

5.66

5.39

6.13

6

Co

2.35

2.23

3.58

2.65

0.99

0.14

-0.06

1.70

0-4

Cr

3.47

3.56

2.95

3.76

2.68

1.04

1.39

2.69

1-4

Cu

1.13

0.81

1.31

1.23

-0.21

-1.86

-2.40

0.00

0

Fe

-0.08

0.08

-0.38

0.31

-1.29

-2.28

-2.99

-0.95

0

Pb

3.00

3.07

2.89

3.29

3.15

5.34

2.75

3.36

3-6

Mn

-0.87

-1.68

0.35

-1.26

-0.96

-2.95

-2.89

-1.47

0

Ni

1.59

1.01

1.14

1.21

-0.60

-1.61

-1.91

0.12

0-2

Sb

8.34

8.70

7.98

8.76

7.87

6.90

6.62

7.88

6

Si

-6.00

-8.59

-5.36

-8.89

-9.29

-9.74

-9.79

-8.24

0

Metal/Locations

Se

3.93

4.21

3.58

4.47

3.47

1.98

2.17

3.40

2-5

Sn

8.46

8.57

8.56

8.69

8.63

8.64

8.52

8.58

6

Zn

-0.04

-0.31

-0.26

0.41

-0.56

-0.63

-1.40

-0.40

0

Table 3 — Geoaccumulation Index (Igeo) in Soil

27

The mobility sequence of the trace metals is based on the sum of acidextractable, reducible and oxidizable fractions for all of the soil samples (Table 2). The mobility sequence is in the order of Sn (82.17%) > Pb (58.01%) > Si (36.01%) > Mn (35.92%) > Cd (34.82%) > Co (24.54%) > Zn (20.25%) > Ba (19.12%) > Cu (17.57%) > Se (16.42%) > Sb (13.81%) > Cr (12.48%) > Ni (11.99%) > Fe (6.31%) > Al (1.42%). Notably, Sn and Pb were more than 50% present in mobile phases and therefore could be considered to be more readily mobilized and bioavailable in the soil samples.

contaminated). Al, Ba, Cu, Fe, Si and Zn were found in the uncontaminated class, while Ni ranged from uncontaminated to moderately contaminated. Cr and Co ranged from uncontaminated to strongly contaminated, while As, Cd, Pb and Sn were found to be extremely contaminated at the site. As, Cd, Pb, Cr and Co are included in the IARC list of probable carcinogenic compounds. The negative Igeo values obtained for some of the metals (Table 3) is an indication of relatively low levels of contamination of these metals in the soil samples and the background variability factor (1.5) used in the Igeo equation.42

Pollution Index The geoaccumulation index (Igeo) for the 16 elements investigated is presented in Table 3. The mean Igeo levels ranged from -8.24 (Si) to 8.58 (Sn) while the Igeo class ranged from 0 (uncontaminated) to 6 (extremely

Non-cancer and Cancer Profiling Using Mobile Fraction Concentrations for Adults The results of the carcinogenic and non-carcinogenic risk assessment for children and adults using the summation of mobile fractions are


presented in Table 3 and 4, while Figures 4 and 5 show the percentage contribution of each metal to both the cancer and non-cancer effects. For the non-cancer effects for adults, dermal exposure to Ni (2.30E-01) was the major exposure route, followed by the ingestion route for Co (1.44E01), Al (1.22E-01) and As (1.02E01), respectively. The non-cancer distribution pattern for the ingestion route was: Co > Al > As > Mn > Ni > Cr > Cd > Pb >Cu > Zn; dermal route: Ni > As > Cr > Al > Co > Cd > Pb > Mn > Cu > Zn, while the distribution pattern for the inhalation route was Al > Co > Ni > Mn > As > Cd > Cr. The hazard index summation for the sites using mobile fractions (F1+F2+F3) shows that arsenic poses a higher risk of non-cancer effects among the studied elements (Table 2; Figure 4). This is followed by Co and Al, respectively, while Zn poses the lowest

Olujimi et al

Research

Element


Concentration C(95%UCL) mg/kg

Ding

Dinh

Ddermal

Al 172483.3 1.22E-01 1.79E-05 2.81E-03

derRfd

ingRfd

inhRfd

HQing

HQdermal

HQinh

HI

CR

1

1

1.57E-03

1.22E-01

2.81E-03

1.14E-02 1.36E-01

—

Cr

33.96

2.39E-05 3.52E-09 5.53E-07

7.5E-05

3E-03

1E-01

7.98E-03

7.37E-03

3.52E-08 1.53E-02

2.3E-05

Mn

6391.77

4.50E-03 6.62E-07 1.04E-04

1.4E-01

1.4E-01

5E-02

3.22E-02

7.43E-04

1.32E-05 3.29E-02

—

Co

61.19

4.31E-05 6.34E-09 9.96E-07

3E-04

3E-04

4.92E-05

1.44E-01

3.32E-03

1.29E-04 1.47E-01 5.71E-11

Ni

62.2

4.38E-05 6.44E-09 1.01E-06

4.4E-04

1.1E-02

7.66E-05

3.98E-03

2.30E-01

8.41E-05 6.37E-03 1.55E-12

Cu

10.87

7.66E-06 1.13E-09 1.77E-07

4E-02

4E-02

—

1.91E-04

4.42E-06

Zn

21.43

1.51E-05 2.22E-09 3.49E-07

3E-01

0.3

—

5.03E-05

As

43.42

3.06E-05

3E-04

3E-04

1.5E-02

1.02E-01

Cd

3.6

2.54E-06 3.73E-10 5.86E-08

2.5E-05

1E-01

1E-02

2.54E-03

2.34E-03

Pb

166.95

1.18E-04 1.73E-08 2.72E-06

35E-03

3E-01

—

3.92E-04

7.76E-04

—

HQinh

4.5E-09

2.12E-05

—

1.96E-04

—

1.16E-06

—

5.15E-05

—

7.07E-02

3E-07

1.73E-01 7.77E-05

3.73E-08 4.88E-03 6.71E-13 1.17E-03 3.37E-05

Table 4 — Cancer and Non-cancer Risks for Adults

Element

Concentration C(95%UCL) mg/kg

Cr

33.96

Mn

6391.77

Al 172483.3

Ding

Dinh

Ddermal

2.23E-04 6.24E-09 6.25E-07 4.2E-02

1.17E-06 1.18E-04

1.134

3.17E-05 3.18E-03

derRfd

ingRfd

inhRfd

HQing

HQdermal

HI

CR

0.000075

0.003

0.1

7.44E-02

8.34E-03

6.24E-08 8.28E-02 1.24E-04

0.14

0.14

0.05

3E-01

8.41E-04

2.35E-05

3.01E-1

—

1

1

3.175583

1.13

3.18E-03

9.98E-06

1.14

—

Co

61.19

4.02E-04 1.12E-08 1.13E-06

0.0003

0.0003

0.001127

1.34

3.76E-03

9.98E-06

1.34

1.01E-10

Ni

62

4.08E-04 1.14E-08 1.14E-06

0.00044

0.011

0.001141

3.71E-02

2.59E-03

9.98E-06

3.9E02

2.73E-12

Cu

10.87

7.15E-05

0.04

0.04

—

1.79E-03

5E-06

—

1.79E-02

—

Zn

21.43

1.41E-04 3.94E-09 3.95E-07

0.3

0.3

—

4.7E-04

1.32E-06

—

4.71E-04

—

As

43.42

2.86E04

0.0003

0.0003

0.015

9.52E-01

7.99E-02

5.32E-07

1.03

4.64E-04

6.61E-08 2.63E-02 1.19E-12

2E-09 7.98E-09

2E-07 2.4E-05

Cd

3.6

2.37E-05 6.61E-10 6.63E-08

0.000025

0.001

0.01

2.37E-02

2.65E-03

Pb

166.95

1.09E-03 3.07E-08 3.07E-06

0.0035

0.3

—

3.66E-03

8.78E-04

—

4.54E-03 3.08E-04

Table 5 — Cancer and Non-cancer Risks for Children

risk. The sum (∑)HI for all of the metals and all routes is 5.16E-01. Individually and collectively, the values were lower than 1, and this is an indication that the soil poses no non-cancer threat to adults. The range reported for the non-cancer effects in the present study is consistent with previous studies in China and Nigeria,5,14,24 but lower than values reported by Zheng et al.22,25 and Shi et al.29 Arsenic contributed 34% of the non-cancer effects (Figure 4), while

Olujimi et al

other major contributors are Co, Al and Mn with contributions of 29%, 26% and 6%, respectively. It is important to note that the overall non-cancer effect for all routes of exposure and all metals were in the 50th percentile of the acceptable limit of 1. This is an indication of potential side effects, as some miners might be more affected depending on their underlying health conditions and particular body chemistries.

The carcinogenic risk (CR) for As, Cd, Co, Cr, Ni and Pb was considered. The cancer risk ranged from 6.17E-13 to 7.77E-05 for Cd and As, respectively, while ∑CR for all the metals and routes was 1.34E-04. The percentage contribution for each metal to CR is presented in Figure 5. This shows that As contributed 58%, while Pb and Cr contributed 25% and 17%, respectively. The metals distribution pattern reported in this study differs


28

Research

Figure 4 — 1) Percentage Contribution of Metals to HI in Adults; 2) Percentage Contribution of Metals to HI in Children

Figure 5 — 1) Percentage Contribution of Metals to Cancer Risk in Adults; 2) Percentage Contribution of Metals to Cancer Risk in Children

from previous work on dust reported by Shi et al.29 and Olujimi et al.5 The range for all of the metals is within the acceptable limit for no probable cancer effect, at 1.0E-04 to 1.0E-06. However, it is noteworthy that the ∑CR for the metals considering all routes (1.34E04) was higher than the 10-5 risk factor acceptable by some authorities.29

29


Non-cancer and Cancer Profiling Using Mobile Fraction Concentrations in Children Children are highly susceptible to environmental pollutants due to their unique developmental stage. As presented in Table 4, the non-cancer distribution pattern for the studied metals was Co > Al > As > Mn > Cr > Ni > Cd > Pb > Cu > Zn; As > Cr > Al

> Ni > Cd > Pb > Mn > Cu > Zn; and Mn > Al ≈ Co ≈ Ni > As > Cd > Cr for the ingestion, dermal and inhalation routes, respectively. The distribution pattern for the ∑HI of the metals for all routes was Co > Al > As > Mn > Cr > Cd > Cu > Pb > Zn. Individually, Co, Al, and As exceeded the acceptable limit of 1 for non-cancer effects in children. This suggests that these

Olujimi et al

Research metals could cause or contribute to non-cancer effects in children. This finding is similar to the trend reported by Zheng et al.22,25 and Li et al.43 However, the values reported here are higher than findings elsewhere.5,24,29,42 The non-cancer effects due to mining activities may be more significant in children because the mine site is less than 100 m from the village and children usually follow their parents to the site. As shown in Figure 4, Co had a 34% contribution to the HI, followed by Al, As and Mn at 29%, 26% and 7% respectively. The overall non-cancer effect (∑HI) was 3.97 for all metals, considering all routes of exposure. This is about 4 times higher than the acceptable limit of 1 and suggests that children who are exposed to the mining site have a risk of non-cancer effects. The carcinogenic risk for children ranged from 2.73E-12 to 4.64E-04 for Ni and As, respectively. The ∑CR for the six studied metals was 8.97E-04. As depicted in Figure 5, As presented the highest risk for cancer development at 52%, followed by Pb and Cr at 34% and 14% respectively. The impacts from other metals were negligible. Furthermore, the cancer risk assessment showed that Cd, Co, Ni and Pb were generally below the acceptable limit range of 1.0E-04 to 1.0E-06, while As and Cr were within the stipulated range. The risk factor for these two metals was higher than the regulated limits in other countries.29 In addition, the ∑CR (8.97E04) for the site indicates that there is probability of cancer development due to exposure to these metals over all routes of exposure.

Conclusion The impact of anthropogenic heavy metal pollution at the Igun mine site was evaluated using geoaccumulation indices (Igeo) and human health risk. The indices varied at each location, suggesting that the soil ranged

Olujimi et al


from uncontaminated to extremely contaminated with respect to the metal analyzed. The chemical forms of soil samples at the Igun mine site differed slightly from each other, with most of the metals exclusively present in the residual fractions, while Sn was mainly present in the mobile form. Health risk assessment of the metals indicated that the dermal route was the major form of exposure for both adults and the children and presented the most probable route for risk of cancer development. Non-cancer effects were more likely in children due to Al, Co and As, as the values for these metals and metalloid exceeded acceptable limits. The present study confirms that both adults and children are at risk of cancer development, with children having a higher risk considering all exposure routes.

Nov [cited 2015 May 25];36(10-11):850-7. Available from: http://onlinelibrary.wiley.com/doi/10.1002/ clen.200800062/epdf 4. Sun G, Li Z, Bi X, Chen Y, Lu S, Yuan X. Distribution, sources and health risk assessment of mercury in kindergarten dust. Atmospheric Environ [Internet]. 2013 Jul [cited 2015 May 25];73:169-76. Available from: http://www.sciencedirect.com/science/ article/pii/S1352231013001830 Subscription required to view. 5. Olujimi O, Steiner O, Goessler W. Pollution indexing and health risk assessments of trace elements in indoor dusts from classrooms, living rooms and offices in Ogun State, Nigeria. J Afr Earth Sci [Internet]. 2015 Jan [cited 2015 May 25];101:396-404. Available from: http://www.sciencedirect.com/science/ article/pii/S1464343X14003495 Subscription required to view. 6. Dooyema CA, Neri A, Lo YC, Durant J, Dargan PI, Swarthout T, Biya O, Gidado SO, Haladu S, Gwarzo NS, Nguku PN, Akpan A, Idris S, Bashir AM, Brown MJ. Outbreak of fatal childhood lead poisoning related to artisanal gold mining in

Acknowledgements. This work was funded in part by a grant from Pure Earth. The authors also want to thank Cape Peninsula University of Technology, Cape Town for support given during the analysis.

northwestern Nigeria, 2010. Environ Health Perspect [Internet]. 2012 Apr [cited 2015 May 25];120(4):6017. Available from: http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC3339453/ 7. Ogola JS, Mitullah WV, Omulo MA. Impact of gold mining on the environment and human health: a case study in the Migori gold belt, Kenya. Environ Geochem Health [Internet]. 2002 Jun [cited 2015 May 25];24(2):141-58. Available from: http://link.springer.

References

com/article/10.1023%2FA%3A1014207832471 Subscription required to view.

1. Zheng J, Chen KH, Yan X, Chen SJ, Hu GC, Peng

8. Adler R, Rascher J. A Strategy for the

XW, Yuan JG, Mai BX, Yang ZY. Heavy metals in

management of acid mine drainage from gold mines

food, house dust, and water from an e-waste recycling

in Gauteng. Pretoria, South Africa: Water Resource

area in South China and the potential risk to human

Governance Systems Research Group; 2007. Report No.:

health. Ecotoxicol Environ Safety [Internet]. 2013 Oct

CSIR/NRE/PW/ER/2007/0053/C.

1 [cited 2015 May 25];96:205-12. Available from:

9. Ekwue YA, Gbadebo AM, Arowolo TA,

http://www.sciencedirect.com/science/article/pii/

Adesodun JK. Assessment of metal contamination

S0147651313002595 Subscription required to view.

in soil and plants from abandoned secondary and

2. Zhu Z, Sun G, Bi X, Li Z, Yu G. Identification

primary goldmines in Osun State, Nigeria. J Soil Sci

of trace metal pollution in urban dust from

Environ Management [Internet]. 2012 Nov [cited 2015

kindergartens using magnetic, geochemical and lead

May 26];3(11):262-74. Available from: http://www.

isotopic analyses. Atmospheric Environ [Internet].

academicjournals.org/article/article1380038873_

2013 Oct [cited 2015 May 25];77:9-15. Available from:

Ekwue%20et%20al.pdf


10. Akcil A, Koldas S. Acid mine drainage


(AMD): causes, treatment and case studies. J

3. Rashed MN. Total and extractable heavy metals

Cleaner Production [Internet]. 2006 [cited 2015

in indoor, outdoor and street dust from Aswan

May 26];14(12-13):1139-45. Available from:

City, Egypt. Clean – Soil, Air, Water [Internet]. 2008



30

Research

31


conmedia/soil/toc.htm

28. Freyer M, Collins CD, Ferrier H, Colvile RN,

11. Agents Classified by the IARC Monographs. 1 vol.

20. Berg RV. Human exposure to soil contamination:

Nieuwenhuijsen MJ. Human exposure modelling

Lyon, France: International Agency for Research on

a qualitative and quantitative analysis towards

for chemical risk assessment: a review of current

Cancer; 2011. 102 p.

proposals for human toxicological intervention

approaches and research and policy implications.

12. Styles MT, Amankwah RK, Hassan SA, Nartey

values [Internet]. Bilthoven, The Netherlands:

Environ Sci Policy [Internet]. 2006 May [cited

RS. The identification and testing of a method for

National Institute of Public Health and

2015 May 27];9(3):261-74. Available from: http://

mercury-free gold processing for artisanal and

Environmental Protection; [revised 1995; cited 2015

www.sciencedirect.com/science/article/pii/

small-scale gold miners in Ghana. Int J Environ Pollut

May 27]. 93 p. Report No.: 725201011. Available

S1462901106000141 Subscription required to

[Internet]. 2010 [cited 2015 May 26];41(3-4):289-

from: http://rivm.openrepository.com/rivm/

view.

303. Available from: http://nora.nerc.ac.uk/9990/1/

bitstream/10029/10459/1/725201011.pdf

29. Shi G, Chen Z, Bi C, Wang L, Teng J, Li Y, Xu

IJEP_0010_Styles_et_al_final_.pdf

21. Supplemental guidance for developing soil

S. A comparative study of health risk of potential

13. Delgado J, Brioso CB, Nieto JM, Boski T.

screening levels for superfund sites. Washington, D.C.:

toxic metals in urban and suburban road dust in the

Speciation and ecological risk of toxic elements

United States Environmental Protection Agency; 2001.

most populated city of China. Atmospheric Environ

in estuarine sediments affected by multiple

Report No.: 9355.4e24.

[Internet]. 2011 Jan [cited 2015 May 27];45(3):764-71.

anthropogenic contributions (Guadiana saltmarshes,

22. Zheng N, Liu J, Wang Q, Liang Z. Health

Available from: http://www.sciencedirect.com/science/

SW Iberian Peninsula): I. Surficial sediments.

risk assessment of heavy metal exposure to street

article/pii/S1352231010007247 Subscription required

Sci Total Environ [Internet]. 2011 Sep 1 [cited

dust in the zinc smelting district, Northeast of

to view.

205 May 26];409(19):3666-79. Available from:

China. Sci Total Environ [Internet]. 2010 Jan 15

30. Mari M, Nadal M, Schuhmacher M, Domingo

http://www.sciencedirect.com/science/article/

[cited 2015 May 27];408(4):726-33. Available from:

JL. Exposure to heavy metals and PCDD/Fs by the

pii/S0048969711006346 Subscription required to


population living in the vicinity of a hazardous

view.


waste landfill in Catalonia, Spain: health risk

14. Li H, Qian X, Hu W, Wang Y, Gao H. Chemical

23. Risk assessment guidance for superfund:

assessment. Environ Int [Internet]. 2009 Oct

speciaition and human health risk of trace metals in

human health evaluation manual [Internet]. Vol.

[cited 2015 May 27];35(7):1034-9. Available from:

urban street dusts from a metropolitan city, Nanjing,

l. Washington, D.C.: United States Environmental


SE China. Sci Total Environ [Internet]. 2013 Jul 1

Protection Agency; 1989 Dec [cited 2015 May 27].


[cited 2015 May 26];456-457:212-21. Available from:

Report No.: EPA/540/1-89/002. Available from: http://

31. Frias MM, Chalabi Z, Vanni T, Foss AM.


www.epa.gov/oswer/riskassessment/ragsa/pdf/rags_a.

Uncertainty in environmental health impact


pdf

assessment: quantitative methods and perspectives.

15. Muller G. Index of geoaccumulation in sediments

24. Hu X, Zhang Y, Ding Z, Wang T, Lian H,

Int J Environ Health Res [Internet]. 2013 [cited 2015

of the Rhine River. Geol J. 1969;2(3):108-18.

Sun Y, Wu J. Bioaccessibility and health risk of

May 27];23(1):16-30. Available from: http://www.

16. Taylor SR, Mclennan SM. The geochemical

arsenic and heavy metals (Cd, Co, Cr, Cu, Ni,

tandfonline.com/doi/abs/10.1080/09603123.2012.67

evolution of the continental crust. Rev Geophysics

Pb, Zn and Mn) in TSP and PM2.5 in Nanjing,

8002?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.

[Internet]. 1995 May [cited 2015 May 26];33(2):241-

China. Atmospheric Environ [Internet] 2012 Sep

org&rfr_dat=cr_pub%3dpubmed Subscription

65. Available from: http://onlinelibrary.wiley.com/

[cited 2015 May 27];57:146-52. Available from:

required to view.

doi/10.1029/95RG00262/abstract Subscription

http://www.sciencedirect.com/science/article/

32. Ezeome ER, Anarado AN. Use of complementary

required to view.

pii/S1352231012004281 Subscription required to

and alternative medicine by cancer patients at the

17. Hawkesworth CJ, Kemp AI. Evolution of the

view.

University of Nigeria Teaching Hospital, Enugu,

continental crust. Nature [Internet] 2006 Oct 19 [cited

25. Zheng N, Liu, J, Wang Q, Liang Z. Heavy metals

Nigeria. BMC Complement Altern Med [Internet]. 2007

2015 May 27];443(7113):811-7. Available form: http://

exposure of children from stairway and sidewalk

Sep 12 [cited 2015 Feb 14];7:28. Available from: http://

www.nature.com/nature/journal/v443/n7113/abs/

dust in the smelting district, northeast of China.

dx.doi.org/10.1186/1472-6882-7-28

nature05191.html Subscription required to view.

Atmospheric Environ [Internet]. 2010 Sep [cited

33. Agba EJ, Curado MP, Ogunbiyi O, Oga E,

18. Stoffers P, Glasby GP, Wilson CJ, Davis KR,

2015 May 27];44(27):3239-45. Available from:

Fabowale T, Igbinoba F, Osubor G, Otu T, Kumai

Walter P. Heavy metal pollution in Wellington


H, Koechlin A, Osinubi P, Dakum P, Blattner W,

Harbour. New Zealand J Marine Freshwater Res


Adebamowo CA. Cancer incidence in Nigeria: a

[Internet]. 1986 [cited 2015 May 27];20:495-512.

26. Gilbert RO. Statistical methods for environmental

report from population-based cancer registries.

Available from: http://www.tandfonline.com/doi/pdf/1

pollution monitoring. 1 ed. Hoboken, New Jersey: John

Cancer Epidemiol [Internet]. 2012 Oct [cited 2015

0.1080/00288330.1986.9516169

Wiley & Sons, Inc.; 1987 Feb 1. 320 p.

May 27];36(5):e271-8. Available from: http://www.

19. Soil screening guidance: technical background

27. Regional screening level: pacific southwest,

cancerepidemiology.net/article/S1877-7821(12)00060-

document [Internet]. Washington, D.C.: United

region 9 [Internet]. Washington, D.C.: United States

4/abstract Subscription required to view.

States Environmental Protection Agency; 1996 Jul

Environmental Protection Agency; [updated 2015 Jan;

34. Moody RP, Joncas J, Richardson M, Petrovic

[cited 2015 May 27]. Report No.: EPA/540/R-95/128.

cited 2015 May 27]. Available at: http://www.epa.gov/

S, Chu I. Contaminated soils (II): in vitro dermal

Available from: http://www.epa.gov/superfund/health/

region9/superfund/prg/index.html.

absorption of nickel (Ni-63) and mercury (Hg-203)


Olujimi et al

Research


in human skin. J Toxicol Environ Health A [Internet].

from: https://www.peregrinefund.org/subsites/

2009 [cited 2015 May 27];72(8):551-9. Available

conference-lead/PDF/0213%20Rodriguez-Ramos.

from: http://www.tandfonline.com/doi/abs/10.108

pdf

0/15287390802706322?url_ver=Z39.88-2003&rfr_

41. Ako TA, Onoduku US, Oke SA, Adamu IA, Ali

id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed

SE, Mamodu A, Ibrahim AT. Environmental impact

Subscription required to view.

of artisanal gold mining in Luku, Minna, Niger

35. Ullah H, Noreen S, Fozia, Rehman A, Waseem

State, North Central Nigeria. J Geoscience Geomatics

A, Zubair S, Adnan M, Ahmad I. Comparative

[Internet]. 2014 Jan [cited 2015 May 27];2(1), 28-37.

study of heavy metals content in cosmetic products

Available from: http://pubs.sciepub.com/jgg/2/1/5/

of different countries marketed in Khyber

index.html

Pakhtunkhwa, Pakistan. Arabian J Chem [Internet].

42. Abrahim, GM, Parker RJ. Assessment of

2013 Sep 20 [cited 2015 Feb 14];Special Issue:1-9.

heavy metal enrichment factors and the degree of


contamination in marine sediments from Tamaki

S1878535213003195

Estuary, Auckland, New Zealand. Environ Monit Assess

36. Okoro HK, Fatoki OS, Adekola FA, Ximba BJ,

[Internet]. 2008 Jan [cited 2015 May 27];136(1-3):227-

Snyman RG. Fractionation, mobility and multivariate

38. Available from: http://link.springer.com/article/10

statistical evaluation of metals in marine sediments

.1007%2Fs10661-007-9678-2 Subscription required to

of Cape Town, Harbour, South Africa. Chem

view.

Speciation Bioavailability [Internet]. 2014 Aug [cited

43. Li Z, Ma Z, Kuijp TJ, Yuan Z, Huang L. A review

2015 May 27];26(3):126-38. Available from: http://

of soil heavy metal pollution from mines in China:

www.tandfonline.com/doi/pdf/10.3184/09542291

pollution and health risk assessment. Sci Total Environ

4X14038001068544

[Internet]. 2014 Jan 15 [cited 2015 May 27];468-

37. Tsafe AI, Hassan LG, Sahabi DM, Alhassan Y,

469:843-53. Available from: http://www.sciencedirect.

Bala BM. Evaluation of heavy metals uptake and

com/science/article/pii/S0048969713010176

risk assessment of vegetables grown in Yargalma of

Subscription required to view.

Northern Nigeria. J Basic Appl Sci Res [Internet]. 2012 [cited 2015 May 27];2(7):6708-14. Available from: http://textroad.com/Old%20version/pdf/JBASR/J.%20 Basic.%20Appl.%20Sci.%20Res.,%202(7)67086714,%202012.pdf 38. Ashraf MA, Maah MJ, Yusoff I. Chemical speciation and potential mobility of heavy metals in the soil of former tin mining catchment. Sci World J [Internet]. 2012 [cited 2014 Sep 14]; 2012: 1-11. Available from: http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC3330713/pdf/TSWJ2012-125608.pdf 39. Lar UA, Chika CS, Ashano EC. Human exposure to lead and other potentially harmful elements associated with galena mining at New Zurak, central Nigeria. J Afr Earth Sci [Internet]. 2013 Aug [cited 2015 May 27];84:13-9. Available from: http://www.sciencedirect.com/science/article/ pii/S1464343X13000538 Subscription required to view. 40. Ramos JR, Gutierrez V, Hofle U, Mateo R, Monsalve I, Crespo E, Blanco JM. Lead in griffon and cinereous vultures in Central Spain: correlations between clinical signs and blood lead levels. In: Watson RE, Fuller M, Pokras M, Hunt G, editors. Ingestion of spent lead ammunition: implications for wildlife and humans [Internet]. Boise, Idaho: The Peregrine Fund; 2009 [cited 2015 May 27]. Available

Olujimi et al


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