1. Introduction
Geophagy among humans dates to several centuries ago, it is widely practiced in various parts of the world [1,2]. It has been reported in several countries in Africa such as Nigeria, South Africa, Kenya, Ghana, Cameroon, etc. [3,4,5]. The first documentation of geophagic practice in Nigeria dates to the 1960s among TIV pregnant women in Benue State [6,7]. It is prevalent among the Yoruba, Hausa, and Igbo tribes in Nigeria [8]. There are several reasons why people from diverse age groups, gender, status, and background practice geophagia. Some of these reasons could be cultural, as people feel it is a blessing from their ancestors and eating it will allow fertility in women [9]. For religious reasons, people practice geophagia as a form of spiritual ritual [10]. For example, children suck cakes with Christ impressions around the United States–Mexican border towns [11]. Often, medical reasons prevail most, either for supplementary mineral nutrients (such as calcium (Ca), iron (Fe), and magnesium (Mg)) [12] or detoxifying poisonous substances because of the high cationic exchange capacity of the clays [13]. Women in Africa believe that eating earth material could reduce nausea and vomiting during pregnancy [14]. Geophagic practice could be passed from parents to children or unintentionally by ingesting earth materials while playing on the ground or floor by hand to mouth movements [15].
Kaolin minerals dominate the clay minerals in geophagic materials with various concentrations of major and trace elements which have health implications [16]. Quartz occurring with kaolinite in most geophagic materials could cause dental enamel damage, abrasion of the gastrointestinal tract, and rupturing of the colon [17]. The red colour of the geophagic soils commonly consumed is usually due to the presence of Fe [18] which may not be bioavailable [19]. The genesis and properties of the geophagic material determines its influence on human health. In recent times, health risks associated with trace elements present in several geophagic materials have drawn the attention of medical geologists and environmental health scientists. The impact of trace elements toxicity levels on human health depends on the type of element and its concentration in the material [5]. For example, higher concentrations of Fe in the human body are known to cause hepatic failure and arthritis [20,21], whereas renal dysfunction, nausea, and diarrhea have been linked to excessive copper (Cu), cadmium (Cd), and arsenic (As) [21]. Toxicity of lead (Pb) means it is harmful for babies in the womb and after birth because it can result in birth defects and brain damage [8]. In addition, high levels of chromium (Cr) tend to cause kidney failure, dermatitis, and pulmonary cancer [22,23].
Previous studies on the health risks associated with the consumption of geophagic materials have only reported the concentrations of trace elements and its health implications relative to global averages and World Health Organisation (WHO) standards [3,4,24,25]. This approach does not examine potential non-carcinogenic and carcinogenic risks to humans [26]. However, few studies have assessed the non-carcinogenic and carcinogenic health risks associated with trace elements in geophagic samples [5,8,27,28] through direct oral ingestion, inhalation, and dermal absorption based on the guidelines put forward by the United States Environmental Protection Agency [29]. Lar et al. [8] is one of the few studies on geophagic clay materials in Nigeria that assessed the potential health risks associated with trace elements present in them. They reported high risk to human health particularly pregnant women and children due to the presence of As, Cd, Pb, selenium (Se), and antimony (Sb). Okunlola and Owoyemi [4] concluded that manganese (Mn), Cr, nickel (Ni), and cobalt (Co) concentrations were higher when compared to global occurrences in some geophagic clays from Southern Nigeria. More studies are required to assess the statuses of several other geophagic materials and report potential health risk associated with human consumption for a healthier populace. Hence, this study aimed at establishing the concentrations of selected trace elements in Cretaceous and Paleogene/Neogene geophagic kaolinitic clays from Eastern Dahomey and Niger Delta Basins, Nigeria as well as estimating the possible associated health risks to humans.
2. Materials and Methods
A total of thirteen (13) geophagic kaolinitic clays comprising of six (6) Cretaceous and seven (7) Paleogene/Neogene were collected from Lakiri and Ubulu-Uku deposits within Eastern Dahomey and Niger Delta Basins, Nigeria, respectively (Figure 1 and Figure 2). The dominance of kaolins in the clays have been established through a separate study [30], hence, the term ‘kaolinitic clays’ is used to define rocks rich in kaolins without particle size connotation [31].
Fresh samples were collected at 2 m and 1 m intervals from Lakiri (LP) and Ubulu-Uku (UL) deposits within Ise (Abeokuta Group) and Ogwashi-Asaba Formations from outcrop faces dug to 60 cm (Figure 1 and Figure 2). Detailed geologic descriptions of the formations have been published earlier by Oyebanjo et al. [32]. The samples were air-dried and gently pulverised to a finer homogenous grain size prior to analyses. No sieving was carried out to have the samples in the state in which they are consumed [3].
The trace elemental concentrations of vanadium (V), Cr, zinc (Zn), Cu, Pb, Ni, and Co in the geophagic samples were determined using an Excimer laser with 193 nm resolution attached to an agilent 7700 series inductively coupled plasma mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) at the Central Analytical Facilities (CAF), Stellenbosch University (SU), South Africa (SA). Certified reference Basaltic Hawaiian Volcanic Observatory (BHVO) glass and powder by United States Geological Survey (USGS) were used as standards [33,34]. The limit of detection (LOD) and limit of quantification (LOQ) for each element in mg kg−1 were 0.015 and 0.20, 0.148 and 1.99, 0.011 and 0.23, 0.101 and 1.52, 0.130 and 1.56, 0.004 and 0.06, and 0.008 and 0.11 for V, Cr, Cu, Ni, Zn, Pb, and Co, respectively. The analytical procedures and processing followed those described by Adebayo et al. [35]. Glitter software [36], distributed by Access Macquarie Ltd., Macquarie University, New South Wales, was used for data processing. A PANalytical Axios Wavelength Dispersive X-ray Fluorescence Spectrometer (Malvern Panalytical Ltd, Malvern, United Kingdom) at CAF, SU, SA equipped with a 2.4 kW Rhodium tube was used to determine Fe concentrations (detection limit of 0.5 mg kg−1) in fused glass disks. Theoretical alpha and measured line overlap factors to the raw intensities measured with the SuperQ PANalytical software were used to correct for matrix effects in the samples. The NIM-G (Bushveld Granite from the Council for Mineral Technology, South Africa) and BE-N (Basalt from the International Working Group) were used as standards. The analytical procedures and processing followed those described by Fitton [37].
Pollution levels and risk evaluation due to the consumption of the geophagic kaolinitic clays were conducted using the index of geoaccumulation (Igeo), hazard index (HI), and carcinogenic risk index (CRI), respectively.
The Igeo developed by Muller [38] was computed following the formula:
Igeo = log2 [(Cn/1.5Bn)]
where Cn is the concentration of the trace element, Bn is the background of the element using the upper continental crust (UCC) values [39], and the factor 1.5 was used to minimise the possible variations in Bn due to lithogenic influence. The Igeo descriptive classes for the contamination level are as follows: uncontaminated (Igeo ≤ 0), uncontaminated to moderate (0 < Igeo ≤ 1), moderate (1 < Igeo ≤ 2), moderate to heavy (2 < Igeo ≤ 3), heavy (3 < Igeo ≤ 4), heavy to extremely (4 < Igeo ≤ 5), and extremely (Igeo > 5) [38].
The HI and CRI were used to estimate the non-carcinogenic and carcinogenic risks associated with the individual trace elements through direct oral ingestion, inhalation of particulate elements through mouth and nose, and dermal absorption of the elements on exposed skin [24,41,42]. HI is the sum of hazard quotients (HQ) for each of the pathways (ingestion (HQing), inhalation (HQinh), and dermal (HQderm)) whereas, CRI is the sum of the chronic daily intake (CDI, mg kg−1 d−1) for each of the pathways (ingestion (CDIing), inhalation (CDIinh), and dermal (CDIderm). The CDI, HI, and CRI values for the individual elements through the pathways were computed as follows:
CDIing=C×IngR×EF×ED×CFBW×AT
CDIinh=C×InhR×EF×EDPEF×BW×AT
CDIderm=C×SA×AF×ABS×EF×ED×CFBW×AT
HI=∑i=nnHQ=∑i=1n(CDIingiRfDingi)+∑i=1n(CDIinhiRfDinhi)+∑i=1n(CDIdermiRfDdermi)
CRI=∑i=1n(CRIingi+CRIinhi+CRIdermi)
=∑i=1n(CDIingi×SFingi)+∑i=1n(CDIinhi×SFinhi)+∑i=1n(CDIdermi×SFdermi)
Details of the parameters used in Equations (2)–(6) are presented in Table 1. HI values < 1 suggest no significant risk of non-carcinogenic effects, whereas HI > 1 suggest potential risk of non-carcinogenic effects [42,43]. In addition, CRI values > 1 × 10−4 is considered unacceptable with potential adverse carcinogenic risk to human health, whereas values between 1 × 10−6 and 1 × 10−4 are generally acceptable [42,44].
A T-test was used to assess the differences in the trace element concentrations between the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays using IBM Statistical Package for Social Sciences (SPSS) version 25.0. 3. Results and Discussion
The results of trace element concentrations in the geophagic kaolinitic clays are presented in Table 2. In the Cretaceous geophagic kaolinitic clays, the mean Fe, V, Cr, Co, Ni, Cu, Zn, and Pb were 15,560.22, 149.82, 143.54, 7.92, 62.42, 26.17, 39.91, and 35.16 mg kg−1, respectively. No unique trace element concentration variations with depth was observed except for LP2 0m having the highest concentrations (except for Pb) (Figure 3a). Mean values for Fe, V, Cr, Co, Ni, Cu, Zn, and Pb were 90,685.70, 155.08, 113.45, 3.77, 21.68, 43.80, 69.85, and 30.96 mg kg−1, respectively in the Paleogene/Neogene geophagic kaolinitic clays. Samples from UL2 1m and 3m had higher trace element concentrations relative to others (Figure 3b).
Based on the trace element concentrations, the order of trace elements in the Cretaceous geophagic kaolinitic clays was Fe > V > Cr > Ni > Zn > Pb > Cu > Co, whereas in the Paleogene/Neogene geophagic kaolinitic clays was Fe > V > Cr > Zn > Cu > Pb > Ni > Co (Figure 4). Iron is the most abundant element in the geophagic kaolinitic clays which could be attributed to its abundance in the upper continental crust and the presence of hematite, goethite, and anatase minerals in them [30,51]. In addition, some of the Fe were present in the structure of the kaolinites [52,53].
Comparison between the trace elements in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays showed that the differences in the concentrations were not statistically significant (p > 0.05) except for Fe (Table 3 and Figure 4). The mean concentrations of V, Cr, Co (except geophagic clays from Asaba, Ibadan, and Free State), Ni (except geophagic clays from Geita), and Cu were higher and Fe (except geophagic clays from Taraba), Zn (except geophagic clays from Ibadan and Benin), and Pb (except geophagic clays from Free State and Geita) were lower in the Cretaceous geophagic kaolinitic clays than those reported for geophagic clays from Asaba, Ekiti, Ibadan, Benin (Nigeria: [4]), Free State (South Africa: [49]), and Geita (Tanzania: [50]) (Table 2 and Figure 4). Paleogene/Neogene geophagic kaolinitic clays have a higher average Fe, V, Cr (except geophagic materials from Geita), Cu (except geophagic clays from Geita), Zn (except geophagic clays from Taraba), and a lower average Co, Ni (except geophagic clays from Taraba and Free State), and Pb (except geophagic clays from Free State and Geita) relative to those reported from Asaba, Ekiti, Ibadan, Benin (Nigeria: [4]), Free State (South Africa: [49]), and Geita (Tanzania: [50]) (Table 2 and Figure 4).
The elements present in the geophagic kaolinitic clays consumed determine the nutritional value. The recommended dietary intake (RDI) contributions for Cr, Cu, Zn, and Fe are presented in Table 4 for the various age groups. The average contributions for Cr, Cu, Zn, and Fe were 0.34 and 0.43, 0.13 and 0.08, 0.21 and 0.12, and 272.06 and 46.68 mg/30 g, respectively for Cretaceous and Paleogene/Neogene geophagic kaolinitic clays (Table 4). The contributions from Cr and Fe were more than the RDI, whereas Cu and Zn were less than the RDI for all the various groups [54] (Table 4). This suggests that the consumption of the geophagic kaolinitic clays will not contribute to the nutrient demands for Cu and Zu of the geophagic individual.
3.1. Pollution and Risk Assessment
The average Igeo values (Table 2) for the individual trace elements in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays were generally below zero for V, Cr (except for Cretaceous geophagic kaolinitic clays), Co, Ni, Cu, Zn, and Fe (except for Paleogene/Neogene geophagic kaolinitic clays) indicating no contamination. However, the average Igeo values above zero for Fe (except for Cretaceous geophagic kaolinitic clays), Pb, and Cr (except Paleogene/Neogene geophagic kaolinitic clays) for Cretaceous and Paleogene/Neogene geophagic kaolinitic clays, respectively, indicates moderate contamination levels (Figure 5). The order of the average Igeo values follow Pb > Cr > V > Ni > Cu > Zn > Co > Fe and Fe > Pb > Cu > V > Cr > Ni > Zn > Co for Cretaceous and Paleogene/Neogene geophagic kaolinitic clays, respectively. Apart from the earlier reasons stated for occurrence of Fe in the geophagic kaolinitic clays, the Paleogene/Neogene geophagic kaolinitic clays have higher Fe concentrations relative to the Cretaceous geophagic kaolinitic clays because of the leaching of Fe from the overlying ferricitic layer above the profiles (Figure 1) [53,55]. Lead can occur naturally in kaolinitic clays by inheritance from parent material through weathering, whereas anthropogenic sources for Pb are from mining and industrial activities. Atmospheric Pb deposition from the burning of leaded gasoline is very likely to account for the Pb in the kaolinitic clays [56].
3.1.1. Non-Carcinogenic Risk
The hazard index (HI) values for the trace elements in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays through ingestion, inhaling, and dermal contact with children and adults are presented in Table 5. The HQ through the three pathways did not exceed 1 for children (except HQ ingestion in children) and adults.
This result showed that health risk associated with the consumption of the geophagic kaolinitic clays are higher through ingestion for children. The HQing of Cr and Fe accounted for 56.44% and 26.73%, and 20.99% and 72.30% of total HQing for children exposed to the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays, respectively. From the total non-carcinogenic HI, children are in higher risk relative to adults with HI > 1 as stipulated by USEPA [57] (Table 5 and Figure 6a) when they consume the geophagic kaolinitic clays. This observation is like previous reports from other studies in Australia [58], Malaysia [59], South China [42], and Iran [26]. The consumption of the Paleogene/Neogene geophagic kaolinitic clays is riskier for the children than Cretaceous geophagic kaolinitic clays (Figure 6a). This can be attributed to the variations in the physiological parameters between the children and adult population [42,47].
The HI values of the trace elements were in the following increasing order: Cr > Fe > Pb > Ni > Cu > Co > Zn and Fe > Cr > Pb > Cu > Ni > Zn > Co for both children and adults consuming the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays, respectively. It is obvious that Cr and Fe are the most hazardous elements that pose non-carcinogenic risk. This is consistent with the previous observation in this study, that Cr and Fe were present in the geophagic kaolinitic clays above the RDI. The utilisable fraction of trace elements by children and adults consuming the geophagic material will be dependent on their bioavailability and absorption in the gastrointestinal tract [5]. Excessive dosages of Fe can cause vomiting and diarrhea at low overdosage and could eventually lead to systemic toxicity at high overdosage [54]. The toxicity level of hexavalent chromium (IV) (Cr6+) is higher relative to trivalent chromium (Cr3+). In addition, Cr6+ is believed to become reduced into Cr3+ in the human body [26,60]. Evidence for the carcinogenicity of Cr3+ in humans is lacking, but it could cause skin rashes [54].
3.1.2. Carcinogenic Risk
The carcinogenic risk associated with the Cr, Ni, and Pb in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays are presented in Table 5. CRI values from ingestion (CRIing) and inhalation (CRIinh) for children and adults in Cretaceous geophagic kaolinitic clays were 7.40 × 10−5 and 4.49 × 10−7 and 4.23 × 10−5 and 5.14 × 10−7, respectively. In the Paleogene/Neogene geophagic kaolinitic clays, the CRIing and CRIinh were 5.85 × 10−6 and 3.54 × 10−7 for children, and 3.35 × 10−5 and 4.04 × 10−7 for adults, respectively. The CRIing contributed about 99.40% and 98.80% to the total CRI (TCRI) values relative to CRIinh contributing about 0.6% and 1.19% for children and adults, respectively. The TCRI for children and adults were 7.45 × 10−5 and 4.28 × 10−5 for Cretaceous geophagic kaolinitic clays and 5.89 × 10−5 and 3.39 × 10−5 for Paleogene/Neogene geophagic kaolinitic clays, respectively. The children have higher TCRI values relative to the adults (Figure 6b) which further suggests higher susceptibility of children to potential risk associated to the trace elements present in the geophagic kaolinitic clays. Risk level ranges from previous study are as follows: very low (<10−6), low (10−6–10−5), medium (10−5–10−4), high (10−4–10−3), and very high (>10−3) [47,61]. This suggests low to medium carcinogenic risk to the children and adult health consuming the geophagic kaolinitic clays. However, the TCRI values obtained are within the tolerable CRI, i.e., 10−6 < CRI < 10−4 [43,48].
4. Conclusions The potential health risks due to selected trace elements in Cretaceous and Paleogene/Neogene geophagic kaolinitic clays within Eastern Dahomey and Niger Delta Basins, Nigeria have been assessed. The average trace elements concentrations in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays were 15,560.22 and 90,685.70, 149.82 and 155.08, 143.54 and 113.45, 7.92 and 3.7, 62.42 and 21.68, 26.17 and 43.80, 39.91 and 69.85, 35.16 and 30.96 ppm, for Fe, V, Cr, Co, Ni, Cu, Zn, and Pb, respectively. No significant statistical differences were observed between their concentrations except for Fe. This was attributed to the leaching of Fe down to the underlying Paleogene/Neogene geophagic kaolinitic clays from the overlying ferricretic layer. The average nutritional values for Cu and Zn were lower than RDI, whereas Cr and Fe were higher relative to the RDI in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays. The contamination levels for the trace elements were generally low except for Cr, Pb, and Fe with moderate contaminations. The Paleogene/Neogene geophagic kaolinitic clays (average HI = 2.21) pose higher non-carcinogenic risk to children relative to the Cretaceous geophagic kaolinitic clays (average HI = 1.10), particularly due to Cr and Fe (through ingestion). The carcinogenic risk to children and adults consuming the geophagic kaolinitic clays is low and generally within the tolerable limit (10−6 < CRI < 10−4). The study therefore recommends the processing of the geophagic kaolinitic clays by reducing the trace elements to acceptable levels prior to ingestion to minimise the potential human health risk particularly to children.
![View Image - Figure 1. Vertical profiles showing sampling spots and lithologic units of the studied geophagic kaolinitic clay deposits (Modified from [30]).](https://media.proquest.com/media/hms/THUM/2/auayG?_a=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%2BgIBWYIDA1dlYooDHENJRDoyMDI1MDUyMzA1MjgwODY4MDo4OTQxMTY%3D&_s=fJDjVQ9tjxd%2F2PUnrnMJhqVSSWg%3D "View Image - Figure 1. Vertical profiles showing sampling spots and lithologic units of the studied geophagic kaolinitic clay deposits (Modified from [30]).")
Enlarge this image.Figure 1. Vertical profiles showing sampling spots and lithologic units of the studied geophagic kaolinitic clay deposits (Modified from [30]).
![View Image - Figure 2. Geologic Maps of (a) Eastern Dahomey and (b) Niger Delta Basins showing the study areas (Modified after [30,40]).](https://media.proquest.com/media/hms/THUM/4/auayG?_a=ChgyMDI1MDUyMzA1MjgwODY4MDo0ODk0ODISBzEzODMzMjMaCk9ORV9TRUFSQ0giDjIxNi43My4yMTYuMjA3KgU1NDkyMzIKMjQyMTUyNTk4MDoLSW5saW5lSW1hZ2VCATBSBk9ubGluZVoDSUxJYgRUSFVNagoyMDIwLzAxLzAxcgoyMDIwLzEyLzMxegCCASBQLTEwMDAwODQtMjAxMzk1LVNUQUZGLW51bGwtbnVsbJIBBk9ubGluZcoBZ01vemlsbGEvNS4wIEFwcGxlV2ViS2l0LzUzNy4zNiAoS0hUTUwsIGxpa2UgR2Vja287IGNvbXBhdGlibGU7IENsYXVkZUJvdC8xLjA7ICtjbGF1ZGVib3RAYW50aHJvcGljLmNvbSnSARJTY2hvbGFybHkgSm91cm5hbHOaAgdQcmVQYWlkqgIbT1M6RU1TLUZ1bGxUZXh0LWdldEZ1bGxUZXh0ygIPQXJ0aWNsZXxGZWF0dXJl4gIA8gIA%2BgIBWYIDA1dlYooDHENJRDoyMDI1MDUyMzA1MjgwODY4MDo4OTQxMTY%3D&_s=i9yVyQNgmUubDOxm2z5yvOtZgcY%3D "View Image - Figure 2. Geologic Maps of (a) Eastern Dahomey and (b) Niger Delta Basins showing the study areas (Modified after [30,40]).")
Enlarge this image.Figure 2. Geologic Maps of (a) Eastern Dahomey and (b) Niger Delta Basins showing the study areas (Modified after [30,40]).
Enlarge this image.Figure 3. Trace element variations in Cretaceous (a) and Paleogene/Neogene (b) geophagic kaolinitic clays from Eastern Dahomey and Niger Delta Basins, Nigeria.
Enlarge this image.Figure 4. Plot of average trace element concentrations in Cretaceous and Paleogene/Neogene geophagic kaolinitic clays from Eastern Dahomey and Niger Delta Basins, Nigeria (this study) and from other studies.
Enlarge this image.Figure 5. Plot of the average geoaccumulation index (Igeo) for trace elements in the Cretaceous and Paleogene/Neogene geophagic kaolinitic clays within Eastern Dahomey and Niger Delta Basins, Nigeria.
Enlarge this image.Figure 6. Plot of average total non-carcinogenic risk (a) and carcinogenic risk (b) for children and adults for trace elements in Cretaceous and Paleogene/Neogene geophagic kaolinitic clays within Eastern Dahomey and Niger Delta Basins, Nigeria.
| (a) | |||
|---|---|---|---|
| Parameters | Definition | Unit | Values Used |
| C | Element content in soil | mg kg−1 | |
| CF a | Conversion factor | kg mg−1 | 10−6 |
| EF a | Exposure frequency | d yr−1 | 350 |
| ED a | Exposure duration | yr | 6 for children, 30 for adults |
| BW a | Body weight | kg | 16 for children, 70 for adults |
| ATnc b | Average time for non-carcinogenic effects | d | 2190 for children, 10,950 for adults |
| ATca b | Average time for carcinogenic effects | d | 25,550 |
| Ingestion | |||
| IngR b | Ingestion rate | mg d−1 | 200 for children, 100 for adults |
| Inhalation | |||
| InhR b | Respiratory rate | m3 d−1 | 20 |
| PEF b | Particulate emission factor | m3 kg−1 | 1.39 × 109 |
| Dermal contact | |||
| SA b | Skin Surface Area | cm2 | 2800 for children, 5700 for adults |
| AF b | Adherence factor | mg cm−2 d−1 | 0.2 for children, 0.07 for adults |
| ABS c | Absorption factor | Unitless | 0.001 for all metals |
a [24,41]; b [43]; c [45,46].
| (b) | |||||||
|---|---|---|---|---|---|---|---|
| Fe d | Cr e | Co d | Pb e | Cu e | Zn e | Ni e | |
| RfDing (mg kg d−1) | 0.7 | 3.00 × 10−3 | 0.02 | 3.50 × 10−3 | 0.04 | 0.3 | 0.02 |
| RfDderm (mg kg d−1) | - | 6.00 × 10−5 | - | 5.25 × 10−4 | 0.12 | 0.06 | 5.40 × 10−3 |
| RfDinh (mg kg d−1) | - | 2.86 × 10−5 | - | 3.52 × 10−3 | 0.04 | 0.3 | 9.00 × 10−5 |
| SF for ingestion (kg d mg−1) | - | 0.5 | - | 8.50 × 10−3 | - | - | - |
| SF for inhalation (kg d mg−1) | - | 42 | - | - | - | - | 0.84 |
RfD—reference dose; SF—slope factor; d [47]; e [48]; (-) not available.
| Fe | V | Cr | Co | Ni | Cu | Zn | Pb | |
|---|---|---|---|---|---|---|---|---|
| Cretaceous | ||||||||
| LP1 0 m | 10,580.00 | 87.16 | 91.66 | 5.69 | 31.14 | 16.95 | 36.59 | 40.20 |
| LP1 2 m | 9722.16 | 172.13 | 136.80 | 12.18 | 52.32 | 49.86 | 42.64 | 18.97 |
| LP1 4 m | 38,602.70 | 114.00 | 138.81 | 8.61 | 50.13 | 15.84 | 51.76 | 23.96 |
| LP2 0 m | 17,442.70 | 305.35 | 218.84 | 7.85 | 164.23 | 44.95 | 46.49 | 28.23 |
| LP2 2 m | 8578.38 | 114.86 | 144.15 | 5.91 | 40.39 | 11.09 | 30.74 | 18.93 |
| LP2 4 m | 8435.40 | 105.44 | 131.02 | 7.31 | 36.36 | 18.36 | 31.27 | 80.69 |
| Min | 8435.40 | 87.16 | 91.66 | 5.69 | 31.14 | 11.09 | 30.74 | 18.93 |
| Max | 38,602.70 | 305.35 | 218.84 | 12.18 | 164.23 | 49.86 | 51.76 | 80.69 |
| Average | 15,560.22 | 149.82 | 143.54 | 7.92 | 62.42 | 26.17 | 39.91 | 35.16 |
| Average Igeo | −1.75 | −0.24 | 0.16 | −1.74 | −0.34 | −0.75 | −1.44 | 0.25 |
| Paleogene/Neogene | ||||||||
| UL1 0 m | 66,196.48 | 99.94 | 100.86 | 2.47 | 16.14 | 22.96 | 37.60 | 25.66 |
| UL1 1 m | 109,374.31 | 177.19 | 124.39 | 3.89 | 30.33 | 37.36 | 48.19 | 41.14 |
| UL1 2 m | 74,774.85 | 136.42 | 93.17 | 2.73 | 16.46 | 27.64 | 63.23 | 25.13 |
| UL2 0 m | 71,200.53 | 161.91 | 127.05 | 2.79 | 20.97 | 17.13 | 32.09 | 36.36 |
| UL2 1 m | 95,648.90 | 214.78 | 163.06 | 3.12 | 23.52 | 102.97 | 38.73 | 42.69 |
| UL2 2 m | 98,937.28 | 113.50 | 88.97 | 4.13 | 16.60 | 46.49 | 132.30 | 19.63 |
| UL2 3 m | 118,667.55 | 181.83 | 96.66 | 7.25 | 27.73 | 52.08 | 136.83 | 26.10 |
| Min | 66,196.48 | 99.94 | 88.97 | 2.47 | 16.14 | 17.13 | 32.09 | 19.63 |
| Max | 118,667.55 | 214.78 | 163.06 | 7.25 | 30.33 | 102.97 | 136.83 | 42.69 |
| Average | 90,685.70 | 155.08 | 113.45 | 3.77 | 21.68 | 43.80 | 69.85 | 30.96 |
| Average Igeo | 0.79 | −0.09 | −0.16 | −2.85 | −1.65 | −0.01 | −0.84 | 0.23 |
| Other studies | ||||||||
| Asaba (n = 8) 1 | 58,618.91 | 102.12 | - | 13.56 | 33.16 | 19.88 | 40.40 | 46.30 |
| Ekiti (n = 2) 1 | 30,167.29 | 95.00 | - | 4.90 | 21.85 | 18.56 | 42.30 | 39.53 |
| Ibadan (n = 6) 1 | 29,881.35 | 115.17 | - | 21.57 | 38.13 | 22.04 | 38.32 | 49.69 |
| Benin (n = 4) 1 | 36,172.16 | 97.50 | - | 6.55 | 24.08 | 26.89 | 29.10 | 64.62 |
| Taraba (n = 20) 2 | 13,153.65 | - | 86.57 | 5.54 | 7.76 | 32.31 | 600.65 | 36.78 |
| Free State, SA (n = 8) 3 | 56,617.29 | 83.62 | 58.62 | 83.30 | 18.86 | 17.24 | 64.00 | 27.38 |
| Geita, Tanzania (n = 14) 4 | 49,771.00 | - | 129.00 | - | 69.10 | 67.70 | 43.70 | 6.50 |
(-) Not detected; 1 [4]; 2 [8]; 3 [49]; 4 [50].
| Element | Mean | SD | t-Value | p-Value | |
|---|---|---|---|---|---|
| Fe | Cretaceous | 15,560.22 | 11,771.95 | −8.32 | 0.01 |
| Paleogene/Neogene | 90,685.70 | 20,238.24 | |||
| V | Cretaceous | 149.82 | 81.35 | −0.14 | 0.89 |
| Paleogene/Neogene | 155.08 | 40.69 | |||
| Cr | Cretaceous | 143.54 | 41.44 | 1.53 | 0.16 |
| Paleogene/Neogene | 113.45 | 26.51 | |||
| Co | Cretaceous | 7.92 | 2.37 | 3.61 | 0.06 |
| Paleogene/Neogene | 3.77 | 1.65 | |||
| Ni | Cretaceous | 62.42 | 50.52 | 1.98 | 0.11 |
| Paleogene/Neogene | 21.68 | 5.76 | |||
| Cu | Cretaceous | 26.17 | 16.69 | −1.37 | 0.20 |
| Paleogene/Neogene | 43.80 | 28.94 | |||
| Zn | Cretaceous | 39.91 | 8.49 | −1.71 | 0.13 |
| Paleogene/Neogene | 69.85 | 45.34 | |||
| Pb | Cretaceous | 35.16 | 23.65 | 0.41 | 0.70 |
| Paleogene/Neogene | 30.96 | 8.99 | |||
SD—standard deviation.
| Group | Range in Years | RDI (mg/d) | |||
|---|---|---|---|---|---|
| Cr | Cu | Zn | Fe | ||
| Childhood | 0–8 | 0.0002–0.015 | 0.2–0.44 | 2–5 | 0.27–11 |
| Adolescent | 9–18 | 0.025–0.035 | 0.7–0.89 | 8–11 | 8–11 |
| Adult | >19 | 0.03–0.035 | 0.9 | 11 | 8 |
| Average Nutritional Value (mg/30 g) * | |||||
| Cretaceous (n = 6) | 0.43 | 0.08 | 0.12 | 46.68 | |
| Paleogene/Neogene (n = 7) | 0.34 | 0.13 | 0.21 | 272.06 | |
* Average nutritional value = average conc. of element (wt %) × 30 g [24].
| Non-Carcinogenic Hazard Index | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cretaceous | Paleogene/Neogene | |||||||||||||||
| Children | Adult | Children | Adult | |||||||||||||
| HQ ing | HQ derm | HQ inh | HI | HQ ing | HQ derm | HQ inh | HI | HQ ing | HQ derm | HQ inh | HI | HQ ing | HQ derm | HQ inh | HI | |
| Cr | 5.74E−1 | 8.03E−2 | 4.33E−3 | 6.58E−1 | 6.55E−2 | 1.31E−2 | 9.89E−4 | 7.96E−2 | 4.53E−1 | 6.35E−2 | 3.42E−3 | 5.20E−1 | 5.18E−2 | 1.03E−2 | 7.82E−4 | 6.29E−2 |
| Ni | 3.74E−2 | 3.88E−4 | 5.98E−4 | 3.84E−2 | 4.28E−3 | 6.32E−5 | 1.37E−4 | 4.48E−3 | 1.30E−2 | 1.35E−4 | 2.08E−4 | 1.33E−2 | 1.48E−3 | 2.19E−5 | 4.75E−5 | 1.55E−3 |
| Zn | 1.59E−3 | 2.23E−5 | 1.15E-07 | 1.62E−3 | 1.82E−4 | 3.64E-06 | 2.62E−8 | 1.86E−4 | 2.79E−3 | 3.91E−5 | 2.01E−7 | 2.83E−3 | 3.19E−4 | 6.36E−6 | 4.59E−8 | 3.25E−4 |
| Pb | 1.20E−1 | 2.25E−3 | 8.61E-06 | 1.23E−1 | 1.38E−2 | 3.66E−4 | 1.97E−6 | 1.41E−2 | 1.06E−1 | 1.98E−3 | 7.58E−6 | 1.08E−1 | 1.21E−2 | 3.22E−4 | 1.73E−6 | 1.24E−2 |
| Co | 4.75E−3 | 4.75E−3 | 5.42E−4 | 5.42E−4 | 2.26E−3 | 2.26E−3 | 2.58E−4 | 2.58E−4 | ||||||||
| Cu | 8.46E−3 | 7.32E−6 | 5.64E−7 | 8.46E−3 | 9.66E−4 | 1.19E−6 | 1.29E−7 | 9.68E−4 | 1.42E−2 | 1.23E−5 | 9.44E−7 | 1.42E−2 | 1.62E−3 | 1.995E−6 | 2.16E−7 | 1.62E−3 |
| Fe | 2.66E−1 | 2.66E−1 | 3.05E−2 | 3.05E−2 | 1.55E+ | 1.55E+ | 1.77E−1 | 1.77E−1 | ||||||||
| Total | 1.01E+ | 8.30E−2 | 4.93E−3 | 1.10E+ | 1.16E−1 | 1.35E−2 | 1.13E−3 | 1.30E−1 | 2.14E+ | 6.56E−2 | 3.64E−3 | 2.21E+ | 2.45E−1 | 1.07E−2 | 8.31E−4 | 2.57E−1 |
| Carcinogenic Risk Index | ||||||||||||||||
| Cretaceous | Paleogene/Neogene | |||||||||||||||
| Children | Adult | Children | Adult | |||||||||||||
| CRI ing | CRI inh | CRI ing | CRI inh | CRI ing | CRI inh | CRI ing | CRI inh | |||||||||
| Cr | 7.37E−5 | 4.46E−7 | 7.42E−5 | 4.21E−5 | 5.09E−7 | 4.26E−5 | 5.83E−5 | 3.5E−7 | 5.86E−5 | 3.33E−5 | 4.03E−7 | 3.37E−5 | ||||
| Ni | 3.88E−9 | 3.88E−9 | 4.43E−9 | 4.43E−9 | 1.3E−9 | 1.35E−9 | 1.54E−9 | 1.54E−9 | ||||||||
| Pb | 3.07E−7 | 3.07E−7 | 1.75E−7 | 1.75E−7 | 2.7E−7 | 2.7E−7 | 1.54E−7 | 1.54E−7 | ||||||||
| Total | 7.4E−5 | 4.49E−7 | 7.45E−5 | 4.23E−5 | 5.14E−7 | 4.28E−5 | 5.85E−5 | 3.5E−7 | 5.89E−5 | 3.35E−5 | 4.04E−7 | 3.39E−5 | ||||
Author Contributions
Investigation, O.O.; Writing-original draft, O.O.; Writing-review & editing, G.-I.E. and J.O. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the National Research Foundation (South Africa), grant number UID 91559 and the University of Venda's Research and Publication Committee, grant number S 677.
Acknowledgments
The financial support received from the Research and Publication Committee (RPC), University of Venda is highly appreciated. Staff of the Central Analytical Facilities, Stellenbosch University Riana Roussouw and Mareli Grobbelaar) are appreciated for the trace element analysis.
Conflicts of Interest
The authors declare no conflict of interest.
1. Hunter, J.M. Geophagy in Africa and United States: A culture-nutrition hypothesis. Geogr. Rev. 1973, 63, 170-195.
2. Young, S.L.; Sherman, P.W.; Lucks, J.B.; Pelto, G.H. Why on earth? Evaluating hypotheses about the physiological functions of human geophagy. Q. Rev. Biol. 2011, 86, 97-120.
3. Ekosse, E.G.; Jumbam, N.D. Geophagic clays their mineralogy, chemistry and possible human health effects. Afr. J. Biotechnol. 2010, 9, 6755-6767.
4. Okunlola, O.A.; Owoyemi, K.A. Compositional characteristics of geophagic clays in parts of Southern Nigeria. Earth Sci. Res. 2015, 4, 1-15.
5. Ngole-Jeme, V.M.; Ekosse, G.E.; Songca, S.P. An analysis of human exposure to trace elements from deliberate soil ingestion and associated health risks. J. Expo. Sci. Environ. Epidemiol. 2016, 28, 55-63.
6. Vermeer, D.E. Agricultural and Dietary Practices among the Tiv, Ibo and Birom Tribes, Nigeria. Ph.D. Thesis, University of Berkeley, Berkeley, CA, USA, 1964.
7. Vermeer, D.E. Geophagy among the Tiv of Nigeria. Ann. Assoc. Am. Geogr. 1966, 56, 197-204.
8. Lar, U.A.; Agene, J.I.; Umar, A.I. Geophagic clay materials from Nigeria: A potential source of heavy metals and human health implications in mostly women and children who practice it. Environ. Geochem. Health 2015, 37, 363.
9. Ghorbani, H. Geophagia, a soil-Environmental related disease. In International Meeting on Soil Fertility, Land Management and Agroclimatology, Special Issue; Adnan Menderes Üniversitesi Ziraat Fakültesi Dergisi: Aydin, Turkey, 2009; pp. 957-967.
10. van Wyk, M. The Investigation of Iron and Mineral Deficiency Associated with the Practice of Geophagia. Ph.D. Thesis, Central University of Technology, Bloemfontein, South Africa, unpublished. 2013.
11. Ferrell, R.E. Medicinal clay and spiritual healing. Clays Clay Miner. 2008, 56, 751-760.
12. Abrahams, P.W. Geophagy and the involuntary ingestion of soil. In Essentials of Medical Geology: Impacts of the Natural Environment on Public Health; Selinus, O., Alloway, B., Centeno, J.A., Finkelman, R.B., Fuge, R., Lindh, U., Smedley, P., Eds.; Elsevier: Amsterdam, The Netherlands, 2005; pp. 435-458.
13. Tateo, F.; Summa, V.; Gianossi, M.L.; Ferrero, G. Healing clays: Mineralogical and geochemical constraints on the preparation of clay-water suspension ("argillic water"). Appl. Clay Sci. 2006, 33, 3-4.
14. Hunter-Adams, J. Interpreting habits in a new place: Migrants' descriptions of geophagia during pregnancy. Appetite 2016, 105, 557-561.
15. Bisi-Johnson, M.A.; Obi, C.L.; Ekosse, G-I.E. Microbiological and health related perspectives of geophagia: An overview. Afr. J. Biotechnol. 2010, 9, 5784-5791.
16. Kutalek, R.; Wewalka, G.; Gundacker, C.; Haluza, D.; Huhulescu, S.; Hillier, S.; Sager, M.; Prinz, A.; Auer, H.; Wilson, J. Geophagy and potential health implications: Geohelminths, microbes and heavy metals. Trans. R. Soc. Trop. Med. Hyg. 2010, 104, 787-795.
17. Ekosse, G.E.; Ngole, V.M. Mineralogy, geochemistry, and provenance of geophagic soils from Swaziland. Appl. Clay Sci. 2012, 57, 25-31.
18. Ekosse, G.E.; De Jager, L.; Ngole, V.M. Traditional mining and mineralogy of geophagic clays from Limpopo and Free State provinces, South Africa. Afr. J. Biotechnol. 2010, 9, 8058-8067.
19. Ngole, V.M.; Ekosse, G.I.E.; De-Jager, L.; Songca, S.P. Physicochemical characteristics of geophagic clayey soils from South Africa and Swaziland. Afr. J. Biotechnol. 2010, 9, 5929-5937.
20. Andrews, N.C. The iron transporter DMT1. Int. J. Biochem. Cell Biol. 1999, 31, 991-994.
21. Prashanth, L.; Kattapagari, K.K.; Chitturi, R.T.; Baddam, V.R.; Prasad, L.K. A review on role of essential trace elements in health and disease. J. Ntr. Univ. Health Sci. 2015, 4, 75-85.
22. Adriano, D.C. Trace Elements in Terrestrial Environments: Biochemistry, Bioavailability and Risks of Metals, 2nd ed.; Springer: New York, NY, USA, 2001.
23. Cefalu, W.T.; Hu, F.B. Role of chromium in human health and in diabetes. Diabetes Care 2004, 27, 2741-2751.
24. Kamau, T.W. Quantification of Selected Essential and Toxic Minerals in Geophagic Materials in Kiambu County, Kenya. Master's Thesis, Kenyatta University, Nairobi, Kenya, unpublished. 2016.
25. Woode, A.; Hackman-Duncan, S.F. Risks associated with geophagia in Ghana. Can. J. Pure Appl. Sci. 2014, 8, 2789-2794.
26. Alibadi, H.; Sany, S.; Oftadeh, B.; Mohamad, T.; Shamszade, H.; Fakhari, M. Health risk assessments of arsenic and toxic heavy metal exposure in drinking water in northeast Iran. Environ. Health Prev. Med. 2019, 24, 1-17.
27. Nkansah, M.A.; Korankye, M.; Darko, G.; Dodd, M. Heavy metal content and potential health risk of geophagic white clay from the Kumasi Metropolis in Ghana. Toxicol. Rep. 2016, 3, 644-651.
28. Kortei, N.K.; Koryo-Dabrah, A.; Akonor, P.T.; Manaphraim, N.Y.B.; Ayim-Akonor, M.; Boadi, N.O.; Essuman, E.K.; Tettey, C. Potential health risk assessment of toxic metals contamination in clay eaten as pica (geophagia) among pregnant women of Ho in the Volta Region of Ghana. BMC Pregnancy Childbirth 2020, 20, 160.
29. U.S. Environmental Protection Agency (USEPA). Risk Assessment Guidance for Superfund: Human Health Evaluation Manual (Part. A): Interim Final; U.S. Environmental Protection Agency: Washington, DC, USA, 1989.
30. Oyebanjo, O.M.; Ekosse, G.E.; Odiyo, J.O. Mineral constituents and kaolinite crystallinity of the <2 µm fraction of Cretaceous-Paleogene/Neogene Kaolins from Eastern Dahomey and Niger Delta Basins, Nigeria. Open Geosci. 2018, 10, 157-166.
31. Murray, H.H. Applied Clay Mineralogy. Ocurrences, Processing and Application of Kaolins, Bentonites, Palygorskite-Sepiolite, and Common Clays, 1st ed.; Elsevier: Oxford, UK, 2007; p. 189.
32. Oyebanjo, O.; Ekosse, G.; Odiyo, J. Hydrogen and oxygen isotope composition of selected Cretaceous and Paleogene/Neogene kaolins from Nigeria: Paleoclimatic inferences. Appl. Clay Sci. 2018, 162, 375-381.
33. Jochum, K.P.; Nohl, U.; Herwig, K.; Lammel, E.; Stoll, B.; Hofmann, A.W. GeoReM: A new geochemical database for reference materials and isotopic standards. Geostand. Geoanal. Res. 2005, 29, 333-338.
34. Jochum, K.P.; Weis, U.; Schwager, B.; Stoll, B.; Wilson, S.A.; Haug, G.H.; Andreae, M.O.; Enzweiler, J. Reference values following ISO guidelines for frequently requested rock reference materials. Geostand. Geoanal. Res. 2016.
35. Adebayo, O.F.; Akinyemi, S.A.; Madukwe, H.Y.; Aturamu, A.O.; Ojo, A.O. Geochemical characterization and palynological studies of some Agbada Formation deposits of the Niger Delta basin: Implications for paleodepositional environments. Turkish J. Earth Sci. 2016, 25, 573-591.
36. Griffin, W.L.; Powell, W.J.; Pearson, N.J.; O'Reilly, S.Y. GLITTER: Data reduction software for laser ablation ICP-MS. In Laser Ablation-ICP-MS in the Earth Sciences: Current Practices and Outstanding Issues; Sylvester, P., Ed.; Mineralogical Association of Canada Short Course: Quebec, Canada, 2008; Volume 40, pp. 308-311.
37. Fitton, G. X-ray fluorescence spectrometry. In Modern Analytical Geochemistry: An Introduction to Quantitative Chemical Analysis Techniques for Earth, Environmental and Material Sciences; Gill, R., Ed.; Addison Wesley Longman: Harlow, UK, 1997; pp. 135-153.
38. Muller, G. Die Schwermetallbelstang der sediment des Neckarars und seiner N ebenflusseeine estandsaufnahme. Chem. Ztg. 1981, 105, 157-164.
39. McLennan, S.M. Relationships between the trace element composition of sedimentary rocks and upper continental crust, Geochem. Geophys. Geosyst. 2001, 2, 1021.
40. Nwajide, C.S. Geology of Nigeria's Sedimentary Basins; CSS Press: Lagos, Nigeria, 2013; p. 565.
41. Luo, X.S.; Ding, J.; Xu, B.; Wang, Y.J.; Li, H.B.; Yu, S. Incorporating bioaccessibility into human risk assessments of heavy metals in urban park soils. Sci. Total. Environ. 2012, 424, 88-96.
42. Gao, L.; Wang, Z.; Zhu, A.; Liang, Z.; Chen, J.; Tang, C. Quantitative source identification and risk assessment of trace elements in soils from Leizhou Peninsula, South China. Hum. Ecol. Risk Assess. Int. J. 2019, 25, 1832-1852.
43. U.S. Environmental Protection Agency (USEPA). Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites, OSWER 9355; Office of Emergency and Remedial Response: Washington, DC, USA, 2002.
44. U.S. Environmental Protection Agency (USEPA). Integrated Risk Information System of the US Environmental Protection Agency; US Environmental Protection Agency (USEPA): Washington, DC, USA, 2012.
45. Chabukdhara, M.; Nema, A.K. Heavy metals assessment in urban soil around industrial clusters in Ghaziabad, India: Probabilistic health risk approach. Ecotoxicol. Environ. Saf. 2013, 87, 57-64.
46. Qing, X.; Yutong, Z.; Shenggao, L. Assessment of heavy metal pollution and human health risk in urban soils of steel industrial city (Anshan), Liaoning, Northeast China. Ecotoxicol. Environ. Saf. 2015, 120, 377-385.
47. Weissmannová, H.D.; Mihočová, S.; Chovanec, P.; Pavlovský, J. Potential ecological risk and human health risk assessment of heavy metal pollution in industrial affected soils by coal mining and metallurgy in Ostrava, Czech Republic. Int. J. Environ. Res. Public Health 2019, 16, 1-19.
48. Chen, H.; Teng, Y.; Lu, S.; Wang, Y.; Wu, J.; Wang, J. Source apportionment and health risk assessment of trace metals in surface soils of Beijing metropolitan, China. Chemosphere 2016, 144, 1002-1011.
49. Ekosse, G.E.; Ngole, V.M.; Diko, M.L. Environmental geochemistry of geophagic materials from Free State province in South Africa. Open Geosci. 2017, 9, 1-12.
50. Nyanza, E.C.; Joseph, M.; Premji, S.S.; Thomas, S.K.; Mannion, C. Geophagy practices and the content of chemical elements in the soil eaten by pregnant women in artisanal and small scale gold mining communities in Tanzania. Bmc Pregnancy Childbirth 2014, 14, 144.
51. Wedepohl, K.H. The composition of the continental crust. Geochim. Cosmochim. Acta 1995, 59, 1217-1232.
52. Wilson, M.J. Rock-Forming Minerals, Sheet Silicates-Clay Minerals, 2nd ed.; The Geological Society: London, UK, 2013; Volume 3c, p. 724.
53. Oyebanjo, O.M. Paleo-environmental conditions and tectonic settings of Cretaceous-Tertiary kaolins in the Eastern Dahomey and Niger Delta Basins in Nigeria. Ph.D. Thesis, University of Venda, Thohoyandou, South Africa, unpublished. 2018.
54. Institute of Medicine. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc; National Academy Press: Washington, DC, USA, 2001.
55. Emofurieta, W.O.; Kayode, A.A.; Coker, S.A. Mineralogy, geochemistry and economic evaluation of the kaolin deposits near Ubulu-Uku, Awo-Omama and Buan in Southern Nigeria. J. Min. Geol. 1992, 28, 211-220.
56. Barbieri, M. The importance of enrichment factor (EF) and geoaccumulation index (Igeo) to evaluate the soil contamination. J. Geol. Geophys. 2016, 5, 4.
57. U.S. Environmental Protection Agency (USEPA). Risk Assessment Guidance for Superfund: Volume III-Part. A, Process. For Conducting Probabilistic Risk Assessment; U.S. Environmental Protection Agency: Washington, DC, USA, 2001.
58. Saha, N.; Rahman, M.S.; Ahmed, M.B.; Zhou, J.L.; Ngo, H.H.; Guo, W. Industrial metal pollution in water and probabilistic assessment of human health risk. J. Environ. Manage. 2017, 185, 70-78.
59. Kusin, F.M.; Azani, N.M.; Hasan, S.N.; Sulong, N. Distribution of heavy metals and metalloid in surface sediments of heavily mined area for bauxite ore in Pengerang, Malaysia and associated risk assessment. Catena 2018, 165, 454-464.
60. Cuong, A.M.; Le Na, N.T.; Thang, P.N.; Diep, T.N.; Thuy, L.B.; Thanh, N.L.; Thang, N.D. Melanin-embedded materials effectively remove hexavalent chromium (Cr VI) from aqueous solution. Environ. Health Prev. Med. 2018, 23, 9.
61. Rapant, S.; Fajčíková, K.; Khun, M.; Cvečková, V. Application of health risk assessment method for geological environment at national and regional scales. Environ. Earth Sci. 2010, 64, 513-521.
Olaonipekun Oyebanjo1,2,*, Georges-Ivo Ekosse2 and John Odiyo3
1Natural History Museum, Obafemi Awolowo University, Ile-Ife 220282, Osun State, Nigeria
2Directorate of Research and Innovation, University of Venda, Thohoyandou 0950, Limpopo Province, South Africa
3School of Environmental Sciences, University of Venda, Thohoyandou 0950, Limpopo Province, South Africa
*Author to whom correspondence should be addressed.
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