WSN 158 (2021) 22-58 EISSN 2392-2192
Heavy metals concentration and distribution in soils
around Oshiri and Ishiagu lead – zinc mining areas,
southeastern Nigeria
Ezekiel Obinna Igwe1,*, Christian Ogobuchi Ede1, Moses Oghenenyoreme Eyankware1,2
1Department of Geology, Ebonyi State University, Abakaliki, Nigeria
2Geomoses Consultancy Limited Warri, Delta, Nigeria
*E-mail address: ezekieloigwe@gmail.com
ABSTRACT
The study area is characterized by ubiquitous ore deposits within the underlying Asu River Group of the southern Benue Trough of Nigeria. The extensive mineralization resulted in widespread artisan and unlawful mining activities, necessitating the need for the assessment of the effects on soils in the area. Careful evaluation of the soils was undertaken to give account of heavy metals concentrations and distribution, and pollution level in soils across the lead – zinc mines. The soil samples were digested and chemically analysed using Atomic Absorption Spectrophotometer (AAS). Results showed concentrations of heavy metals of the soil samples in the order trend Zn>Pb>Mn>Cd>Cu>Fe>
Ni>Co>Cr and Pb>Zn>Mn>Fe>Cu>Cd>Ni>Cr>Co in both Oshiri and Ishiagu areas. Cd showed high contamination in the soils with higher amount of contamination occurring in Oshiri. Findings also revealed Co, Fe Cu, Mn, Zn, Pb and Ni whose Igeo’s values indicated uncontaminated to moderate contamination have an insignificant contribution to the pollution in the study area while Cd showed highest Igeo with moderate contamination. Co, Cr, Ni, Pb and Zn show deficiency to minimal enrichment while Cd recorded very high enrichment 23.95 – 37.48 and 25.66 – 34.21 mk/kg in the Oshiri and Ishiagu areas respectively. Cd showed high index of contamination ranging from 7.21 – 13.89, while other metals showed no index of contamination in the area. Pollution load index indicates that only few sites in Oshiri area require urgent rectification measures. The food chain in the area is not safe due to possible biomagnifications; hence arable soil around the mines is not suitable for production of food crops.
Keywords: Lead, zinc, Mining activities, Heavy metals, Soil pollution, Southeastern Nigeria
1. INTRODUCTION
Soil, as a multi-component system, comprises of solid, liquid and gaseous phases along with living organisms (Brandy and Weil 1999). Soil responds to environmental modifications as a result of anthropogenic activities such as mining. Such changes produce a steady modification of soil characteristics until another balance is attained. Heavy metals are considered essential elements (Goorzadi et al. 2009; Igwe et al. 2020; Chang et al. 2014; Clarke 2011) which if starved of, the biochemical activities in living organisms would not be achievable; however, when they surpass normal concentrations, they become toxic. Varying concentrations of the heavy metals can be introduced into the soil either through geogenic or anthropogenic sources. Though heavy metals occur naturally in rocks, most of its occurrences emanate from anthropogenic sources (Eyankware et al. 2016; Igwe et al. 2020) such as mining activity. The occurrence and exploitation of Pb-Zn sulphide deposits (galena and sphalerite) in Nigeria have span across decades with its attendant environmental deterioration in the mining regions with study area chiefly among.
Heavy metal pollution of soil and/or water has recently become a major concern confronting humans (Namaghi et al. 2011; Igwe et al. 2020) and is commonly related with variables of concealment, persistency and irreversibility (Zhu et al. 2012). Sharma et al. (2009) were of the view that heavy metals, whilst non-biodegradable and continuing in the environment; can attain toxic levels in plants on arable soils, thus reducing both yield and quality. As such when plants are harvested from these arable soils, the problem of enlarging input of daily intake of heavy metals by human has to be considered as studied by some authors (e.g. Ye et al. 2015; Sharma et al. 2009). Sajn and Gosar (2008); Eyankware and Ephraim, (2021) were of the view that heavy metals are beneficial to plant, animal and human health at low concentrations but can be toxic at higher concentrations.
These potentially toxic elements are of particular interest in addition to the range of contaminants that occur in soils (Ulakpa, et al., 2021). Mining and associated activities are the most significant anthropogenic sources of heavy metals that damagingly affect the nearby environment (Boussen et al. 2010). Lakatusu et al. (2001) documented the pollution of soil by heavy metals including Pb, Zn, Cu and Cd in the Zlatna area of Western Carpathian Region of Romania, known for its old polymetallic mining and ore processing activities. More so, Plakaki (2006) studied the mobility of potential toxic elements in soils of the Stratoni mining area, Chalkidiki in Western Greece and found elevated concentrations for some heavy metals such as Pb, Zn and Cd. There is much evidence that Pb-Zn mining and processing usually lead to severe soil contamination (Dudka and Adriano 1999). Notably, Sajn and Gosar (2008) carried out a geochemical investigation on pollution in Slovenia due to mining and metallurgy and noted enrichment of Cd, Cu, Hg, Mn, Pb and Zn in soil exceeding the limit. Johnson et al.
(2000) noted that the level and intensity of heavy metal contamination around mines differ, and depend on geochemical characteristics and level of mineralization of the tailings. The metals discharged by sulfide oxidation are gradually reduced by precipitation, co-precipitation and sorption reactions (McGregor et al. 1998; Berger et al. 2000) in and around the mines. Such metals dispersion and their contributions into soil, sediment and water systems have been the focus of many studies (Eyankware, et al., 2020; Lee et al. 2001; Kim et al. 2002).
The results of studies carried out by Liao and Li (2008) on the heavy metals contamination characteristics in soil of different mining activity zones in Pb-Zn mines in Hunan Province, China showed that the soil is seriously polluted by heavy metals. In a study of heavy metal
contamination around the abandoned base metal mine sites in Korea carried out by Chon et al.
(2005), three Pb-Zn mines were investigated and the results showed significant levels of Cd, Cu, Pb and Zn in soils around the mines.
Adewara and Akinolu (2008) assessed soils of Ibadan metropolis in Nigeria for heavy metal concentrations and recorded heavy contamination of the environment in the area by Pb, Cu and Zn. Nweke et al. (2008) conducted a detailed study of lead, zinc and pH concentrations of soils in Enyigba in southeastern Nigeria and reported high level of lead and zinc in the soil which affects the agricultural yield. Ezeonu, et al. (2002) reported high level of lead and zinc concentration in the soils of Itakpe north-central Nigeria when compared to those of Enyigba area in the southeastern Nigeria.
High level of concentration of lead in crops harvested from Ihetutu, Amaeze and Amaeke localities of the present study region was due to nearness of these localities to the mining sites (Ehosum 2002). The heavy metals have the potential to bio-accumulate in food crops in contaminated environment and may be toxic to plants and animals even at low exposure levels (Louttfy et al. 2006; Khan et al. 2008; Liu et al. 2008; Garg et al 2014). Food chain contaminated with heavy metals is the major contributing pathway (accounting for more than 90%) to human contact more than inhalation and dermal exposure pathways (Cai et al. 2015;
Dikioye et al. 2018; Ibraheem et al. 2018; Srikanta, 2018; Rizal et al. 2021).
Kloke et al. (1984) reported that heavy metals have distinct transfer rates from soil to plant, based on transfer coefficients of metals viz: Cd, TI and Zn are readily taken up by plants as a result of higher transfer coefficient, whereas Cu, Co, Cr, and Pb are firmly bound to the soil structures and display lowest transfer to plants from soils due to lower transfer coefficient.
The food crops store these heavy metals in their harvestable parts (through root uptake, foliar adsorption and accumulation of certain elements in leaves) and degree of this uptake process affects the overall chemical composition of the plant (Omene, et al., 2015). Heavy metal contamination when ingested by humans is a known causative of many health disorders such as neurotoxicity, cardiotoxicity, teratogenesis, mutagenesis, immune disorders, carcinogenicity, and reproductive malfunction (Jarup 2003; Dyer 2007; Moses and Ruth 2015;
Pattnaik et al 2016). This study seeks to account for the occurrence, distribution of heavy metals and pollution level in the arable soils around the lead – zinc mines of Oshiri and Ishiagu region of southeastern Nigeria using geochemical approach.
2. PHYSIOGRAPHY AND GEOLOGIC SETTING
Santonian tectonic activities deformed the rocks underlying the study region and resulted in considerable folding of the sediments (Kogbe 1975), which subsequently affected the general topography. The intrusives are widely distributed from Ishiagu through Zurak and beyond and places such as Lokpanta, Abakaliki, Lafia, Egbede Hills and Aghila areas all in the Benue Trough of Nigeria. Topographically, the study is characterized by hills and valleys, with most of them occurring in NW-SE direction, same trend with the folds in the Benue Trough.
Dendritic drainage pattern which represents the argillaceous and other fine grained sediments characterize the study area. Oshiri and Ishiagu areas are well drained with the major river flow trending NE – SW (Fig. 1). Most of the draining rivers return in the northern and southern parts forming tributaries to the Asu and Eze-inyiaku rivers in Okposi and Akaeze respectively. The overall surface water flow configuration also conforms to the fold axes. Majority of the rivers
in Ishiagu area follow that same direction except those of the northwestern part which flow in NE-SW. Oshiri area hosts thick and dense vegetation typical of the tropical rainforest. The nature of the superficial deposits in the area support luxuriant growth of plants and trees. This explains the abundance of dense vegetation in the area. The vegetation is notably denser in areas overlain by sediments of Asu-River Group, especially in Ishiagu.
The Asu River and Eze-Aku groups (Fig. 2) which are parts of the several Cretaceous sedimentary units of the southern Benue Trough of Nigeria, underlie the area (Murat, 1972).
The Benue Trough formed as the failed arm of a trilate fracture system during the break-up of the Gondwana supercontinent and subsequent opening up of the southern Atlantic and Indian oceans (Burke et al. 1972; Olade 1975; Burke 1976; Hoque and Nwajide 1984; Fairhead 1988;
Benkhelil 1989). Thickness of sediments between 4000 to 6000 m deposited in the Benue Trough in an 800 km stretch from the northern parts of the Niger Delta Basin in the southwest to the fringes of the Chad Basin in the north east. The Asu-River Group is the oldest lithostratigraphic unit in the study area, and comprises of dark grey shale, indurated/baked shale with subordinate sandstones lenses, mudstones, sandy limestones, volcanoclastics and intrusives. Whiteman (1982) reported that minor basic and intermediate rocks intruded the Asu- River Group during the Santonian Orogeny and these rocks are found around Ishiagu and Abakaliki areas.
Fig. 1. Topographic map of the study area.
Nwachukwu (1975) noted that Pb-Zn mineralization characterized the Albian Asu-River Group sediments. He noted that the mineralization predominantly occur as open fillings within steeply dipping fracture system. Ezepue and Odigi (1993) noted a low temperature
hydrothermal source for the Pb-Zn mineralization in the study area, with the anticlines which were transacted by N and NW trending fractures acting as main controls for Pb-Zn mineralization.
The sediments of Asu-River Group are extensively fractured, folded and faulted with numerous joints system which created secondary porosity in the shale-sandstone units (Obi et al. 2001; Nwajide 1985; Todd 1980). Other associated minerals are pyrite, siderite, quartz, and chalcopyrite which occurred together with the Pb - Zn as the gangue minerals (Ferguson 1990).
The Pb-Zn mineralization in the trough occurs in NE-SW trending 600 km long belt of the dominantly deformed Albian sediments. The Asu-River Group is unconformably overlain by the Eze-Aku Group (late Cenomanian – Turonian) around Abaomege (Igwe and Okoro 2016) near Oshiri.
Igwe and Okoro, (2016) noted that the Eze-Aku Shale of the group is as same as the shale described by Reyment (1965) in Akaeze which also extends to Ohana area and surrounds entire Abakaliki Anticlinorium. The Eze-Aku Group consists of flaggy, calcareous shale, siltstones, mudstones, limestones and sandstone ridges designated as Amasiri Sandstone (Igwe and Okoro 2016; Reyment 1965; Whiteman 1982) which outcrops around Oshiri.
Fig. 2. Geologic map showing the lithostratigraphic units underlying the area and soil sample collection points
3. MATERIALS AND METHODS 3. 1. Sampling and Laboratory Analysis
Representative soil samples were randomly collected at different locations in the study area (Figs. 3a – d). They were sampled from soil around the mine dumps where mine water is being into the farm land (Fig. 3a and c), while others were sampled on soil several meters away from the dumpsites, all around and beyond the derelict of Oshiri and Ishiagu mine areas. At each sample point, samples were collected at depths of 10 – 15 cm after removal of solid waste covering the natural soil to avoid undue contamination as carried out by Nyangababo and Hamya (1986); Eddy et al. (2006) and Odai et al. (2008). The Global positioning System (GPS) was used for georeferencing of the sampled locations. A total of thirty (30) samples of soil were collected for this study. Soil samples collected were stored in fresh plastic labeled bags and tightly sealed.
The collected samples were sun-dried for seventy two (72) hours, and were disaggregated and then homogenized using agate mortar and pestle. This was followed by sieving to obtain required optimum grain size and to achieve best geochemical contrast is the 120 mesh as noted by Ukpong (1991) for Benue Trough, Nigeria. The use of nylon screen was adopted to prevent contamination. The screening was followed by weighing 2.0 g of each sample for digestion.
Aqua regia prepared by the mixture of HF, HNO3 and HCl in the ratio 1:1:3 was used for the digestion. The extract from each digested sample was subjected to chemical analysis using Varian AA240 Atomic Absorption Spectrophotometer (AAS) for determination of heavy metal in the soil samples in line with guideline given by the American Public Health Association (APHA 1998). Heavy metals analyzed include Pb, Zn, Cu, Fe, Ni, Co, Mn, Cd and Cr. The pH samples of soil were taken in situ. Configuration of the heavy metals concentration and distribution in the study area were modeled using Microsoft Excel and Sufer 12 software. The results were compared with the World Health Organization (WHO) permissible (standards) limits.
Table 1. Concentrations of heavy metals in soil (mg/kg) of Oshiri area.
Sample no pH Cd Co Cr Cu Fe Mn Ni Pb Zn
EC/O/016 6.2 2.41 0.70 0.57 1.24 0.84 1.60 0.81 12.80 2.54
EC/O/017 5.8 2.16 0.28 0.41 2.12 1.19 3.53 0.60 0.84 11.14
EC/O/018 7.4 0.94 0.14 0.80 1.01 0.82 0.54 0.00 0.00 1.80
EC/O/019 6.4 0.84 1.36 1.61 0.15 0.42 6.19 1.11 3.11 6.19
EC/O/022 6.7 0.27 0.04 0.18 0.52 0.00 2.31 0.82 6.24 1.16
EC/O/023 6.8 0.54 0.92 1.11 1.16 0.01 4.42 1.18 3.87 0.01
EC/O/026 5.6 1.51 1.14 0.00 0.16 1.51 1.19 0.54 0.00 1.60
EC/O/051 6.4 0.82 0.31 0.00 1.51 0.57 4.92 0.00 4.18 7.01
Minimum 5.6 0.27 0.04 0.18 0.15 0.01 0.54 0.60 0.84 0.01
Maximum 7.4 2.41 1.36 1.61 2.12 1.51 6.19 1.18 12.80 11.14
Mean 6.43 1.21 0.63 0.63 1.01 0.69 3.14 0.62 4.38 4.26 WHO(1996)
Standards 0.8 Ngl 100 36 Ngl Ngl 35 85 50
Ngl = No permissible limits
… …
Fig. 3. (a) Food crops in Amankalu farm land affected by effluent discharge from mines in Oshiri, (b) Temporarily abandoned lead – zinc mine at Ihetutu in Ishiagu, (c) Arable land around lead – zinc mine in Oshiri, (d) Mine water being pumped out into farm land at Amaokpara in Oshiri
Table 2. Concentrations of heavy metals in soil (mg/kg) of Ishiagu area.
Sample no pH Cd Co Cr Cu Fe Mn Ni Pb Zn
EC/I/048 6.3 0.67 0.51 0.81 1.70 0.27 2.70 0.87 9.21 14.27
EC/I/049 6.9 2.09 1.04 0.53 1.10 0.81 5.70 0.72 1.56 4.63
EC/I/050 7.4 1.54 0.58 1.11 1.17 1.60 3.56 1.48 0.34 0.06
EC/I/052 4.3 0.61 0.27 0.00 1.59 0.06 1.04 0.58 0.00 10.88
EC/I/057 8.0 0.38 0.00 0.12 1.84 0.86 0.06 0.91 14.96 5.76
c d
a b
EC/I/058 6.9 0.00 0.55 0.62 1.88 1.74 3.61 0.54 8.10 6.34
EC/I/062 6.8 2.02 0.39 0.17 0.00 0.59 4.60 0.00 1.86 4.81
EC/I/076 6.8 0.52 0.00 0.54 1.17 0.47 1.64 0.31 3.08 3.18
EC/I/080 7.8 0.00 1.57 0.79 0.29 0.41 3.13 0.81 7.28 3.60
EC/I/090 6.2 2.20 1.16 0.00 1.50 6.31 4.31 1.48 11.14 4.51
EC/I/091 7.6 0.94 0.34 1.94 1.30 1.46 2.18 1.80 2.58 3.64
EC/I/095 7.0 1.62 0.00 0.56 0.00 0.08 0.00 0.44 4.89 2.34
Minimum 4.3 0.94 0.27 0.12 0.29 0.06 0.06 0.31 0.34 0.06
Maximum 8.0 2.20 1.57 1.94 1.88 6.30 5.70 1.80 14.96 14.27
Mean 6.73 1.05 0.57 0.65 1.10 1.50 2.73 0.83 5.71 5.59
WHO(1996)
Standards 0.8 Ngl 100 36 Ngl Ngl 35 85 50
Ngl = No permissible limits
3. 2. Data Analysis
The data analysis involved the evaluation of concentration of the heavy metals load using the following parameters: geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (CF), contamination index (PI), integrated contamination index (PC), pollution load index (PLI) and effect range median (ERM) and effect range low (ERL).
(a) Geoaccumulation Index (Igeo)
Table 3. Index of geoaccumulation (Igeo) of heavy metals in soil of Oshiri area.
Muller (1979) introduced Igeo and it has been extensively used since 1960’s for the evaluation and quantification of heavy metals in assessing pollution level. The assessment of
Igeo contamination involves comparing the levels of heavy metals gotten at a site to the background level in the environment. The empirical formula for deducing it as proposed by Muller (1979) and Yu et al. (2011),
Igeo = log2(Cn 1.5⁄ × Bn) (1)
while Cn represents measured concentration of different assessed metals, Bn denotes the geochemical background values of the same metal (average shale) in the crust. 1.5 is multiplying factor used to minimize the outcome of possible differences in the background or control values which may be ascribed to lithogenic effects (Mesiolla et al., 2008; Kumar and Edward 2009; Elueze et al. 2009).
Table 4. Index of geoaccumulation (Igeo) of heavy metals in soil of Ishiagu area.
(b) Enrichment Factor (EF)
The determination of enrichment factor of heavy metals normalizes measured metal content from each location with respect to a reference metal such as Fe or Zn (APHA 1998).
This study selected Fe as reference metal because of its abundance, wide usage as reference element. The heavy metal enrichment factor was calculated based on the standardization of the tested metal against reference factors (Kumar and Edward 2009). The formula for the contamination and/or pollution of the various metals (Zoller 1974; Birch 2003; Zhang and Liu 2002) is given in Equation 2:
EF = Cn(sample)/Cref(sample)
Bn(background)/Bref(background) (2) Cn = concentration of the analysed metal,
Cref = mean content of the metal
Bn = content of the metal in the reference environment, Bref = mean content of the metal in the environment (c) Contamination index (Pi)
It is mathematically expressed as:
𝑃𝑖𝐶𝑛
𝑆𝑖 (4) (Hong − gui et al. 2012; Yan et al. 2015 ) where Cn = represent concentration of heavy metal, n while 𝑆𝑖 = represents standard value for the metal.
(d) Integrated Contamination Index (Pc) is mathematically expressed as
𝑃𝐶 = ∑(𝑃𝑖 − 1)
𝑛
𝑖=1
(5)
where 𝑃𝑖 = total concentration of each metal measured from the sampling area.
Table 5. Enrichment factor (EF) of heavy metals in soils of Oshiri area.
Sample no Ag EF Cd EF Co EF Cr EF Ni EF Pb EF Zn EF
EC/O/016 0.84 0.02 2.41 37.48 0.70 0.38 0.57 0.32 0.81 0.05 12.80 2.84 2.54 0.12
EC/O/017 1.19 0.05 2.16 33.59 0.28 0.15 0.41 0.37 0.60 0.04 0.84 0.23 21.14 1.03
EC/O/018 0.82 0.02 0.94 14.62 0.14 0.08 0.80 0.72 0.00 0.00 0.00 0.00 1.80 0.09
EC/O/019 0.42 0.01 0.84 13.06 1.16 0.62 1.61 1.25 1.11 0.21 3.11 0.85 41.19 2.01
EC/O/022 0.00 0.00 0.27 4.20 1.04 0.57 0.18 0.26 0.82 0.05 6.24 1.70 13.16 0.64
EC/O/023 0.01 0.00 0.54 `8.40 0.92 1.13 1.11 1.95 1.18 0.05 03.89 0.88 0.01 0.00
EC/O/026 2.51 0.05 1.51 24.48 1.14 0.71 0.00 0.00 0.54 0.03 0.00 0.00 1.60 0.08
EC/O/051 0.57 0.01 0.82 23.95 1.31 0.71 0.00 0.00 0.00 0.00 4.18 1.07 4.01 2.32
Table 6. Enrichment factor (EF) of heavy metals in soils of Ishiagu area.
Sample no Ag EF Cd EF Co EF Cr EF Ni EF Pb EF Zn EF
EC/I/048 0.27 0.01 0.67 2.75 0.51 0.28 0.81 0.53 0.87 0.03 9.21 2.50 14.27 0.69
EC/I/049 0.81 0.02 2.09 32.50 1.04 1.37 0.53 0.48 0.72 0.03 1.56 0.42 4.63 0.23
EC/I/050 1.60 0.05 1.54 31.41 0.58 0.32 1.11 1.25 1.48 0.09 0.34 0.09 0.06 0.00
EC/I/058 1.74 0.02 0.00 14.62 0.55 0.30 0.62 0.56 0.54 0.02 8.10 2.20 6.34 0.50
EC/I/062 0.59 0.01 2.02 25.66 0.39 0.21 0.17 0.95 0.00 0.00 1.86 0.51 4.81 0.43
EC/I/090 0.31 0.01 2.20 34.21 1.16 0.63 0.00 0.00 1.48 0.05 11.14 3.75 4.51 0.35
EC/I/091 1.46 0.03 0.94 10.42 0.34 0.18 1.94 1.75 1.80 0.03 2.58 0.70 3.64 0.18
Table 7. Concentration index (Pi) and integrated contamination index (Pc) for soil of Oshiri area.
Sample No Fe Pi Cd Pi Co Pi Cr Pi Cu Pi Ni Pi Pb Pi Zn Pi PC
EC/O/016 1.81 0.38 2.41 1.39 0.70 0.04 0.57 0.01 1.24 0.02 0.81 0.17 12.80 0.44 2.54 0.03 4.54
EC/O/017 0.14 0.03 2.16 7.21 0.28 0.01 0.41 0.01 2.12 1.06 0.60 0.06 0.84 0.04 11.14 0.04 3.11
EC/O/018 1.25 0.12 0.94 3.14 0.14 0.01 0.80 0.02 1.01 0.82 0.00 0.00 0.00 0.00 1.80 0.02 0.87
EC/O/019 0.00 0.00 0.84 2.81 1.36 0.05 1.61 0.08 0.15 0.00 1.11 0.07 3.11 0.16 6.19 0.19 0.96
EC/O/022 2.18 0.42 0.27 0.90 0.04 0.07 0.18 0.05 0.52 0.01 0.82 0.01 6.24 0.31 1.16 0.02 0.01
Table 8. Concentration index (Pi) and integrated contamination index (PC) for soil of Ishiagu area.
Sample No Fe Pi Cd Pi Co Pi Cr Pi Cu Pi Ni Pi Pb Pi Zn Pi PC
EC/I/049 2.40 0.24 2.09 7.00 1.04 0.40 0.53 0.01 1.10 0.28 0.72 0.02 1.56 0.08 4.63 0.05 7.77
EC/I/050 0.39 0.04 1.54 5.14 0.58 0.03 1.11 0.09 1.17 0.12 1.48 0.02 0.34 0.02 0.06 0.00 6.08
EC/I/062 1.01 0.20 2.02 6.75 0.39 0.02 0.17 0.05 0.00 0.00 0.00 0.00 1.86 0.09 4.81 0.55 5.47
EC/I/090 1.18 0.32 2.20 13.89 1.16 0.06 0.00 0.00 1.50 0.03 1.48 0.19 11.14 1.05 4.51 0.26 9.32
EC/I/038 12.11 1.21 0.54 1.80 3.92 0.20 7.11 0.16 10.16 0.20 10.18 0.13 13.89 0.69 0.01 0.00 3.51
EC/I/039 8.50 0.85 1.51 5.04 2.04 0.10 0.00 0.00 19.16 0.38 9.54 0.12 0.00 0.00 1.60 0.02 5.53
EC/I/051 0.59 0.06 0.82 2.74 1.31 0.07 0.00 0.00 29.57 0.59 0.00 0.00 4.18 0.15 98.01 1.16 6.70
Pi ≤ 1 1 – 2 2 – 3 ≥ 3
No contamination Low contamination Moderate contamination High contamination
PC ≤ 1 0 – 7 7 – 21 ≥ 21
No contamination Low contamination Moderate contamination High contamination EF < 1 EF = 1 - 2 EF = 2 – 5 EF = 5 – 20 EF = 20 – 40 EF = > 40
Deficient Minimal Low Significant Very high Extremely high
(e) Pollution load index (PLI)
Pollution load index was developed by Tomlinson et al. (1980) to measure the degree of soil pollution for each metal in a single site. Pollution load index gives comparative means for assessment of site quality and thus suggests further necessary action to be taken.
Mathematically, pollution load index (PLI) (Tomlinson et al. 1980; Mohiuddin et al. 2010;
Barakat et al. 2012) is expressed as:
PLI = √𝐶𝐹𝑛 1× 𝐶𝐹2× 𝐶𝐹3× … … 𝐶𝐹𝑛. (6)
CF = C metal/C background, where CF = contamination factor, n = number of metals, C metal
= metal concentration in polluted environment, C background = background value of the metal Table 9. Pollution load index (PLI) of heavy metal in soil of Oshiri area
Table 10. Pollution load index (PLI) of heavy metal in soil of Ishiagu area.
(f) Effect range low (ERL) and effect range median (ERM)
The Effect range low (ERL) represents lowest metals concentration in soils/ stream sediments which produced negative effects in 10% of organisms, while the effect range median (ERM) indicates 50% of the organisms assessed showed harmful effects as evaluated by US
Sample No Fe Cd Co Cr Cu Mn Ni Pb Zn PLI
EC/I/049 2.40 2.09 1.04 0.53 1.10 5.70 0.72 1.56 4.63 0.06
EC/I/050 0.39 1.54 0.58 1.11 1.17 3.56 1.48 0.34 0.06 0.27
EC/I/062 1.01 2.02 0.39 0.17 0.00 4.60 0.00 1.86 4.81 0.31
EC/I/090 1.18 2.20 1.16 0.00 1.50 4.31 1.48 11.14 4.51 0.09
EC/I/037 12.11 0.54 3.92 7.11 10.16 100.19 10.18 13.89 0.01 0.24
EC/I/039 8.50 1.51 2.04 0.00 19.16 19.16 9.54 0.00 1.60 0.11
EC/I/046 0.59 0.82 1.31 0.00 29.57 10.57 0.00 30.18 5.81 0.47
Sample No Fe Cd Co Cr Cu Mn Ni Pb Zn PLI
EC/O/016 1.81 2.41 0.70 0.57 1.24 1.60 0.81 12.80 2.54 0.23
EC/O/017 0.14 2.16 0.28 0.41 2.12 3.53 0.60 0.84 11.14 1.02
EC/O/018 1.25 0.94 0.14 0.80 1.01 0.54 0.00 0.00 1.80 0.09
EC/O/019 0.00 0.84 1.36 1.61 0.15 6.19 1.11 3.11 6.19 0.18
EC/O/022 2.18 0.27 0.04 0.18 0.52 2.31 0.82 6.24 1.16 0.04
EPA-MAIA (1988). Based on values of ERL and ERM, concentration of metals below the ERL values are not expected to provide any adverse effects, while those above the ERM values are will be very toxic and pose negative effects. The three categories of assessment for evaluating effects of metals concentration in soil in the study area using ERL and ERM analysis are: (i) Good contamination, indicating values of metal concentration are below ERL value (ii) Intermediate contamination, indicating values of metals concentration are higher than values of ERL (iii) It is poor contamination, when values of metals concentration are above the ERM values.
Table 11. Quality of soils in Oshiri using effective range low (ERL) and effective range median (ERM)
Table 12. Quality of soils in Ishiagu using effective range low (ERL) and effective range median (ERM)
Sample No Ag Fe Cd Co Cr Cu Mn Ni Pb Zn
EC/I/46 0.87 1.82 3.90 11.07 1.17 2.00 2.61 2.78 0.00 3.78
EC/I/052 0.24 10.11 21.50 1.80 3.51 21.14 14.80 11.24 16.61 7.98
EC/I/058 0.06 3.16 1.64 0.00 0.54 8.26 27.64 3.41 11.81 7.52
EC/I/083 0.00 1.27 18.90 1.66 1.24 1.54 26.14 0.00 21.18 53.52
EC/I/095 10.61 1.81 18.94 4.92 1.72 18.27 17.00 14.16 12.84 16.80
Sample No Ag Fe Cd Co Cr Cu Mn Ni Pb Zn
EC/O/03 1.61 0.92 52.00 0.00 0.88 8.54 10.80 4.51 16.11 18.38
EC/O/07 2.50 1.32 0.76 2.04 1.14 4.62 21.60 12.60 13.81 1.89
EC/O/018 14.86 13.04 18.54 9.14 0.24 21.86 43.54 9.92 11.84 62.17
EC/O/019 18.89 1.27 4.68 3.35 3.54 9.24 39.81 2.98 61.50 46.86
EC/O/026 4.62 27.28 36.19 4.36 1.82 51.19 27.84 15.72 6.84 38.24
EC/O/029 6.71 12.64 6.10 10.11 9.14 34.50 50.16 4.54 49.56 54.08
EC/O/039 19.80 32.56 9.10 2.61 0.00 0.38 11.27 1.89 1.54 6.48
EC/O/051 9.50 0.00 34.56 7.21 0.00 10.53 21.87 20.18 3.68 25.60 US-EPA-MAIA (1988)
Limits:
ERL (mg/kg) 1.00 8.20 1.20 7.00 81.00 34 29.00 4.90 47.00 150
ERM (mg/kg) 37 70 96 94 370 270 140 40 220 410
GI ≥ 5 Extremely contaminated
EC/I/100 0.24 3.54 19.81 0.00 11.12 12.16 2.64 2.80 07.54 10.89
EC/I/101 7.19 0.08 27.50 4.02 8.26 0.00 9.70 0.89 53.50 25.28
EC/I/104 10.42 11.19 31.40 12.18 6.43 06.51 26.52 12.81 17.88 34.41
EC/I/107 7.32 18.26 4.61 0.34 24.12 7.87 22.11 2.26 2.54 72.50
EC/I/108 10.83 9.62 10.11 29.52 12.57 12.04 16.50 3.37 34.16 74.21 US-EPA-MAIA (1988)
Limits:
ERL (mg/kg) 1.00 8.20 1.20 7.00 81.00 34 29.00 4.90 47.00 150
ERM (mg/kg) 37 70 96 94 370 270 140 40 220 410
4. RESULTS AND DISCUSSION
4. 1. Heavy Metals Concentration and Distribution
Tables 1 and 2 showed concentration values in mg/kg for the heavy metals in the investigated soil, while Figs. 4 and 5 showed the modeled distribution maps of contaminants in the soils of the study area. The concentration and distribution of the heavy metals are presented as follows:
4. 1. 1. Cadmium (Cd)
Cadmium is a naturally occurring element in mineral soils (Segura et al. 2006). Song et al. (1999) and Li et al. (2015) noted that background amount of cadmium is dependent on geologic parent materials, but soil cadmium concentrations typically are less than 1 mg/kg which is in agreement with WHO (1996) permissible limit of 0.8 mg/kg. Cd mobility in soil is influenced by soil pH. The total concentration of cadmium in a soil consists of inputs from parent rock materials and contributions from extraneous sources and in some cases; Cd contamination in soil is related with anthropogenic activities such as mining works (Ciftci et al.
2005; Eyankware et al. 2016; Wirnkor et al. 2017).
The widespread concentration of cadmium in the soils of the southern Benue Trough of Nigeria is as results of release of heavy metals often via erosion, dissolution, rock and water interaction (Usoro et al. 2015; Obiora et al. 2016; Nganje et al. 2010). Mining activity constitutes one of the sources of Cd and other heavy metals to the environment (Dolenec et al.
2005; Wang et al. 2008; Kar et al. 2008). As such, since anthropogenic activity is the main source of Cd contamination; mining may have influenced the high percentage of Cd in the soils of the study area. Cd present in soil is intensely adsorbed to organic matter and it can be exceedingly harmful as their uptake through food will increase (Nnabo 2015). Alysson and Fabio (2014) opined that Cd has highest tendency to contaminate soil bearing food crops and its subsequent release to animals and humans that feed on these contaminated food crops.
The spatial distribution map of Cd showed that it ranges from 0.27 to 2.41 mg/kg at Oshiri axis with mean value of 1.21 mg/kg (see Table 1 and Fig. 4a). The values obtained in locations:
EC/O/016, EC/O/017, EC/O/018, EC/O/019, EC/O/026 and EC/O/051 exceeded permissible (standards) limits specified in WHO (1996) for soil. The concentration of Cd in the soil can be attributed to mine wastes discharge and dispersion into nearby agricultural soils (Esshaimi et
al. 2013). While the concentration of Cd in soil within Ishiagu axis ranges from 0.00 to 2.2 mg/kg with mean value of 1.05 mg/kg; the highest concentration of Cd within Ishiagu was seen at location EC/I/062 with concentration value of 2.2 mg/kg (see Fig. 4a). High concentrations of Cd in Ishiagu that exceeded permissible (standards) limits occur in locations: ECO/I/049, EC/I/050, EC/I/062, EC/I/090, EC/O/091 and EC/I/095 (see Table 2).
4. 1. 2. Cobalt (Co)
Cobalt is a naturally occurring element that has properties related to those of iron and nickel. Cobalt naturally occurs in soil in small amounts (Obasi and Akudinobi 2020). The concentration of Co within Oshiri ranges from 0.04 to 1.36 mg/kg with mean value of 0.63 mg/kg (see Table 1). Heavy metals such as Co under certain conditions when released by lead- zinc mining may stimulate, transfer and buildup in various target media such as soil thereby directly or indirectly affecting plants, animals and humans (Grattan et al. 2002; Liu et al. 2005;
Pusapukdepob et al. 2009; Bai and Yan 2008; Kim et al. 2008). The concentration of Co showed ranges between 0 to 1.57 mg/kg with mean value of 0.57 mg/kg in Ishiagu (see Fig. 4b and Table 2). High concentration of Co in soil was seen around EC/I/049, EC/I/080 and EC/I/090, the high concentration could be attributed to active mining activities that is current ongoing within the area
4. 1. 3. Chromium (Cr)
The concentration of Cr in soil differs significantly and, depends on the composition of the parent geological materials upon which the soil was formed (Jankiewicz and Ptaszyñski 2005). Moreover, anthropogenic activities such as mining may significantly trigger the concentrations of Cr in soil, especially around active mines. In most cases when plant absorb this heavy metal from the soil, and is consumed by man it may lead to kidney and liver disease (Harendra et al. 2017). The concentration of Cr in soil within Oshiri ranges from 0 to 1.61 mg/kg with mean value of 0.63 mg/kg (see Table 1). The concentration of Cr within Ishiagu axis ranges from 0 to 1.94 with mean value of 0.65 mg/kg (see Fig. 4c and Table 2). Previous workers have reported moderate/high concentrations of Cr within Ishiagu mines (Obiora et al.
2016; Nganje et al. 2010). The concentrations of Cr in soil at Oshiri and Ishiagu are within permissible (standards) limits specified in WHO (1996) (see Table 1 and 2).
4. 1. 4. Copper (Cu)
Copper is one of the few metals to occur naturally as an un-compounded mineral. The most vital natural source of Cu is the geological parent material. When copper is discharged into soil, it can become strongly attached to the organic and geological materials and may not disperse very far when it is released. Excess effect of Cu could be felt within surrounding areas where high concentration of Cu is observed or plant produce that absorbed high concentration of Cu are transported to other locations. Zhuang et al. (2009) stated that Cu in soil can be linked to mining and processing of copper ores. Cu contributes majorly to environmental pollution;
thus influencing environmental quality and ecosystem services. However, some metal contaminants such as Cu may escape either during ore mining or processing and are dispersed for much longer distances, affecting the quality of soil sediment.
The concentration of Cu in soil within Oshiri area ranges from 0.15 to 2.12 mg/kg with mean value of 1.01 mg/kg (see Table 1). While the concentration of Cu in soil within Ishiagu
area ranges from 0 to 1.88 mg/kg with mean value of 1.10 mg/kg. The highest concentration of Cu in soil was observed at Oshiri EC/O/017 (see Table 2 and Fig. 4d). Findings from the study showed that the concentrations of Cu in soil at Oshiri and Ishiagu are within permissible (standards) limits specified in WHO (1996) (Table 1 and 2).
4. 1. 5. Iron (Fe)
Iron is a metal commonly present in most soil (Zabowski et al. 2001). The concentration of Fe in soil at Oshiri area ranges from 0 to 1.51 mg/kg with mean value of 0.69 mg/kg (see Table 1). The concentration of Fe in soil while in Ishiagu area ranges from 0.06 to 6.31 mg/kg with mean value of 1.50 mg/kg (see Table 2). The highest concentration of Fe in soil was observed around Ishiagu axis of the study area at sample location at EC/I/090 (see Fig. 5a and Table 2). This could be due to Fe stored in mine tailings which in turn can be dispersed to nearby soils, streams via erosion, leaching and weathering activities (Marques et al. 2001; Lee at al. 2005; Lintnerova et al. 2008; Rodriguez et al. 2009).
4. 1. 6. Manganese (Mn)
Manganese is a naturally occurring and abundant metal that is vital in biological systems, with its chemical behavior dominated by pH, reduction and oxidation reactions. This naturally occurring element is also abundant in the environment, both in soil and sediment systems. The concentration of Mn within the Oshiri area ranges from 0.54 to 6.19 mg/kg with mean value of 3.14 mg/kg (see Table 1). Table 2 shows that Mn concentration values range from 0 to 5.7 mg/kg with a mean value of 2.73 mg/kg within Ishiagu area. Significant concentration of Mn was observed in soil sample at locations EC/I/049 (Fig. 5b). A detailed analysis of the mineralization in the area would be necessary to substantiate clearly that these heavy metals are indeed coming from the mining activities, slope runoff, rainwater leaching and wind, and its negative effects on the surrounding environments (Lu et al. 2017).
4. 1. 7. Nickel (Ni)
Nickel is a somewhat abundant and naturally occurring element, commonly distributed in the earth‟s crust. The status in soils relies strongly on its concentration in the parent geological materials, but in surface soils, however its content is an indication of processes associated with soil formation and pollution (Ayodele and Mohammed 2011; Hseu 2006; Rao et al. 2007).
Nickel can also occur in different forms in soils such as adsorption or complex on organic cation surfaces or on inorganic cation exchange surfaces, inorganic crystalline minerals or precipitates, water soluble, free-ion or chelated metal complexes in soil solution (Eyankware et al. 2016). The concentration of Ni in soil within the Oshiri area ranges from 0 to 1.18 mg/kg with mean value of 0.62 mg/kg (Table 1). The highest concentration of Ni in soil was observed at location EC/O/023 (see Fig. 5c).
Table 2 shows that Ni values vary from 0 to 1.8 mg/kg with mean value of 0.83 mg/kg within Ishiagu area. Findings revealed that highest concentration of Ni in soil was seen at sample location EC/I/091 (Fig. 5c Table 2). Horvath and Gruiz (1996), Yang et al. (2003), and Li et al. (2007) reported Pb-Zn mining works as one of the primary sources of nickel in soil and environment.
4. 1. 8. Lead (Pb)
Lead is nonessential element, regarded to be toxic and its effects have been more significantly evaluated than the effects of other trace metals (Raikwar et al. 2008; SON 2015;
Egbueri and Mgbenu 2020; Egbueri 2020). The pH of all the soil samples whose Pb concentrations have been investigated were determined so as to understand the ease of accessibility of Pb in soil. Pb is strongly bound to soil particles with soil pH of 6–8 (near-neutral soils) and may not be available for plant uptake. It becomes more soluble in acidic soils (pH <
5) as in location EC/I/052 (see Table 2). Pb is the least mobile heavy metal in soils, especially under non-acidic conditions (Rodríguez et al. 2009; Harendra et al. 2017; Li et al. 2015). The concentration of Pb in soil within the Oshiri ranges from 0 to 12.8 mg/kg with mean value of 4.38 mg/kg (see Table 1). From the study, it was observed that the highest concentration of Pb within Ishiagu area was seen at location EC/I/057 and this could be attributed to low pH in addition to easy dissolution of Pb in the environment; hence making them to occur at high concentrations in the mine waste substrates (Ciftci et al. 2005). Result from Table 2 shows that Pb values vary from 0 to 14.96 mg/kg with mean value of 5.71 mg/kg within Ishiagu area. It was observed that location EC/I/057 has the highest Pb concentration in soil (Fig. 5d and Table 2). Previous study within the southern Benue Trough of Nigeria showed concentration of Pb in soil (Obiora et al. 2016; Nnabo 2015). Results obtained from Table 1 and 2 showed that the concentrations of Pb in soil at Oshiri and Ishiagu were within permissible (standards) limits specified in WHO (1996). Though Pb is nonessential element for the human body, too much intake of it can lead to severe damage to nervous, endocrine, skeletal, enzymatic, circulatory, and immune systems. Pb also has significant effects on intelligence quotients and physical development in children (Dariusz et al. 2012).
4. 1. 9. Zinc (Zn)
The concentration of Zn in soil within the Ishiagu area ranges from 0.06 to 14.27 mg/kg with mean value of 4.26 mg/kg. The highest concentration Zn within that axis was observed at location EC/1/048 with value of 14.27 mg/kg (see Table 2). While the concentration of Zn within the Oshiri axis of the study area ranges from 0.01 to 11.14 mg/kg with mean value of 5.59 mg/kg, the highest concentration of Zn around that axis was seen at location EC/O/017 with value of 11.14 mg/kg (Fig. 5e, Tables 1 and 2). It was observed that value of Zn concentration in soil within Oshiri and Ishiagu were within permissible (standards) limits specified in WHO (1996).
4. 2. Soil pH
The pH of a normal soil is considered as an index of its exchangeable cations saturation.
Soil pH affects all other properties of soil both physicochemical and biological; cation exchange capacity, organic carbon and soil texture; which influence metal bioavailability for plant uptake (Naidu et al. 2008). Soil pH, most importantly influences metal mobility and availability in soil.
The concentration of pH within the Oshiri ranges from 5.8 to7.4 with mean value of 6.5 (see Table 1). Table 2 shows that pH values vary from 4.3 to 8 with a mean value of 6.73 within Ishiagu axis of the study area. Table 2 showed that pH values fell within basic except for location EC/I/052 that tends to be acidic with value of 4.3 this could be attributed to Pb-Zn mining within the study area.
a
b
Fig. 4. Modeled distribution maps of: (a) Cadmium, (b) Cobalt, (c) Chromium, (d) Copper.
c
b
a
b
c
d
Fig. 5. Modeled distribution maps of: (a) Iron, (b) Manganese, (c) Nickel, (d) Lead, (e) Zinc.
4. 3. Assessment of Pollution Levels and Enrinchment 4. 3. 1. Index of geoaccumulation (Igeo)
Geoaccumulation index (Igeo) (Eq. 1) as proposed by Muller, (1979) has been applied to assess the degree of metal contamination or pollution in soil, aquatic and marine environment (Tijani and Onodera 2001; Wei et al. 2019). The quality of soil in Oshiri and Ishiagu areas calculated with Igeo is shown in Tables 3 and 4. The degree of metal pollution using Igeo is evaluated on the basis of seven (7) classes of contamination using increasing numerical values of the index (Muller 1979) as follows: Igeo≤0 implies practically uncontaminated, 0<Igeo<1 implies uncontaminated – moderately contaminated, 1<geo<2 implies moderately contaminated, 2<Igeo<3 represents moderately – heavily contaminated, 3<Igeo<4 represents heavily contaminated, 4<Igeo<5 implies heavily – extremely contaminated and Igeo<5 represents extremely contaminated.
Based on the limits of Muller (1979), the values of indices of geo-accumulation for Co, Fe, Mn, Ni, Zn and Cu show absence of significant contamination for the soil in the study area. Co, Fe Cu, Mn, Zn, Pb and Ni whose Igeo’s values indicated uncontaminated to moderate contamination have an insignificant contribution to the pollution in the study area (Fig. 6).
However, Cr is moderately contaminated in Oshiri (EC/O/019) but shows no significant contamination in other locations in the area. Cd recorded highest Igeo with moderately
e
contaminated in EC/O/016 (1.48), EC/O/017(1.45), EC/O/026 (1.01) and EC/1/062 (1.35), EC/I/049 (1.05), EC/I/050 (1.03), EC/I/090 (1.04), EC/I/095 in Oshiri and Ishiagu respectively and uncontaminated to moderately uncontaminated in many other locations (Tables 3 and 4, Fig. 6). These locations still host aggregates of sphalerite, and galena oxides which have not been dispersed by weathering activities.
Fig. 6. Ageoaccumulationindex chart showing concentration levels of soil in the study area
4. 3. 2. Enrichment Factor (EF)
Enrichment Factor (EF) (Eq. 2) has been deployed as a standard approach to assess the anthropogenic impact of heavy metals for concentrations higher than uncontaminated background levels (Lacatuso 1998; Fagbote and Olanipekun 2010). Fe has been employed successfully to normalize heavy metal (Muncah et al. 2003, Pere-Neto et al. 2006; Mediolla et al. 2008). Thus heavy metals enrichment factor (EF) in soil was evaluated using Fe as reference metal as showed by Kumar and Edward (2009) because of its abundance occurrence and its wide usage as reference element. Results of EF in the study area are presented in Tables 5 and 6. The five contamination categories of the EF of Sutherland (2000) and, Zhang and Liu (2002) were used in this study: EF <2 shows deficiency to minimal enrichment, EF = 2 – 5 represents moderate enrichment, EF = 5 – 20 shows significant.
Sample No Ag Igeo
Fe Igeo
Cd Igeo
Co Igeo
Cr Igeo
Cu
Igeo MnIgeo Ni Igeo
Pb Igeo
Zn Igeo
EC/O/016 + +
EC/O/017 +
EC/O/018 + + + + + +
EC/O/019 + +
EC/O/022 + +
EC/O/023 + + +
EC/O/026 + + + + +
EC/I/048 +
EC/I/049 +
EC/I/050 + +
EC/O/051 + +
EC/I/057 + + + +
EC/I/058 + + + +
EC/I/062 + + + + + + +
EC/I/080 + + + + +
EC/I/090 + +
EC/I/091 + + + +
EC/I/095 + + + + +
+ Practically uncontaminated
uncontaminated to moderately contaminated
Moderately contaminated
Moderately to heavily contaminated
Heavily contaminated
Heavily to extremely contaminated
Extremely contaminated
The outcome of results analysis of EF indicates that Co, Cr, Ni, Pb and Zn show deficiency to minimal enrichment with Ni and Zn having most deficiency enrichment. Very high enrichments were observed for Cd in EC/0/016 (37.48), EC/O/017 (33.59), EC/O/026 (24.28), EC/O/051 (23.95), and EC/I/049 (32.50), EC/I/050 (31.41), EC/I/0/062 (25.66), EC/1/090 (34.21) in Oshiri and Ishiagu area respectively (Tables 5 and 6, Fig. 7). Cd is also significantly enriched in EC/O/018 (14.62), EC/O/019 (13.06) in Oshiri and EC/1/058 (14.62), EC/1/091 (10.41) in Ishiagu.
Fig. 7. Enrichment factor of cadmium and lead in soils of Oshiri and Ishiagu area.
4. 3. 3. Contamination index (Pi) and integrated contamination index (PC)
Assessment of soil contamination in Oshiri and Ishiagu areas was carried out using indices of contamination (Pi) (Eq. 4) and integrated contamination (Pc) (Eq. 5) as tools of contamination assessment of heavy metal concentrations in the soil samples. Pi and Pc contamination levels were categorized into four grades as classified by Bai et al. (2008) were used in this study: Pi ≤ 1 indicates no contamination, Pi = 1 – 2 denotes low contamination, Pi
= 2 – 3 represents moderate contamination, Pi ≥ 3 means high contamination, and Pc ≤ 1 represents no contamination, Pc = 0 – 7 implies low contamination, Pc = 7 – 21 indicates moderate contamination, Pc ≥ 21 means high contamination. Results of contamination index (Pi) and integrated contamination index (Pc) in the study area are presented in Tables 7 and 8.
There were noticeable high contamination in some sampling locations in both Oshiri and Ishiagu areas. Cd showed high contamination in EC/O/017 (7.21), EC/O/018 (3.14) and EC/I/090 (13.89), EC/I/049 (7.00), EC/I/062 (6.75), EC/I/050 (5.14) in Oshiri and Ishiagu respectively (Tables 7 and 8). Cd also recorded moderate contamination in Oshiri EC/O/019 (2.81) and Ishiagu EC/I/051(2.74). Cu, Co, Cr, Ni, Pb, Zn and Fe showed no index of contamination in the study. However, Fe and Pb recorded low index of contamination in
0 5 10 15 20 25 30 35 40
Enrichment Factor (EF)
Sample Locations
Cd Pb
