Heavy Metal Analysis of Soil Around Mine Sites in Ameri, Enyigba, and Ishiagu in Ebonyi State

Heavy metal contamination of soil, water and crops, and their health impact on residents, is a persistent social issue, and several studies have identified health risks of residents living near operational and abandoned mines. In this study, eight (8) homogenous soil samples were collected from mining sites in Enyigba, Ameri and Ishiagu in Ebonyi State, south-eastern Nigeria and analyzed for Pb, Zn, Ni, Co, Mn, and Ag. Metal concentration was determined using the Atomic Absorption Spectrometry (AAS) technique. Result for the heavy metals followed the trend: Mn > Zn > Pb > Ni > Ag > Co for the soil analyzed. However, lead (Pb) was only detected in Enyigba mining sites. Metal concentrations in some samples indicated soil contamination from Mn, Pb, Zn, Ni, and Ag, which showed high concentration than the United States Environmental Protection Agency (US EPA) (1986) permissible limit for heavy metals in agricultural soil; only Co was recorded at a concentration below the US EPA (1986) permissible limit for all samples analyzed. The variations observed for the heavy metals suggest that both geologic and anthropogenic activities may be responsible for their distribution.


MATERIALS AND METHODS Apparatus
Beakers, Whatman filter paper, Hot plate, Fume cupboard, Mortar and pestle, Sieve, sample bottles, Analytical weighing balance, Sample bags, Hand auger.

Study Area
The study area is located, between latitudes 6 0 09′N and 6 0 13′N and longitudes 8 0 04′E and 8 0 09′E, covering an area of 64km 2 . The area of study consists of cretaceous sediments of the Asu river group, dominantly shales, silty shales, limestones and volcanic rocks. The study area around Abakaliki is one of the well-known lead-zinc mineralized districts in Africa where soil and streams have developed from naturally enriched parent materials, including black shales, hydrothermally mineralized rocks and mine dumps (Itumohet al., 2013). In Ishiagu and Enyigba environs, lead and zinc mining has been going on for over fifty years, and in recent times its exploration has been intensified. The vegetation is dominated by grasses, shrubs and trees (e.g. palm trees, coconut, mango, and orange trees). The areas are leading producers of rice, yam, potatoes, cocoyam, maize, plantain and cassava.
Enyigba and Ameri districts are located within Abakaliki and Ikwo Local Government Areas while Ishiagu is situated in Ivo Local Government Area of Ebonyi State, South Eastern Nigeria. Ishiagu is located between latitudes 50 o 52' to 50 o 60' N and longitudes 70 o 30' to 70 o 37" and Enyigba is located at Latitude 6 o 10/ N -6 o 13/ N and Longitude 8 o 07/ E -8 o 10/ E and covers a surface area of 33.06 km 2 . The lead-zinc lode in the Enyigba district comprises of Enyigba, Ameri and Ameka (Onyeobi and Imeokparia, 2014). These lodes are located within the Abakaliki anticlinorium in the Lower 4 Benue Trough. The occurrences of lead-zinc in the study area are associated with saline water. Figure 1 below shows the lead-zinc lode in the Enyigba districts; Enyigba, Ameri and Ameka.  Apr. 2014 PP. 30-40 www.vkingpub.com © American V-King Scientific Publishing.

Sampling and Sample Preparation
A total of eight soil samples were collected with a soil hand auger at a depth of 5 cm and distances of 20 m away from mine sites (Ameri, Enyigba, and Ishiagu). At each sampling site, triplicate collections within a 2 m × 2 m grid were made from spots other than the first to ensure uniformity of soil samples from a site, out of which 1 kg was packaged in polyethylene bags. All the collected samples were properly marked and identified by their sampling locations using a Global Positioning System (GPS) receiver. The collected soil samples were taken to the laboratory for further processing.
The soil samples collected were sun-dried, grounded into fine powder using a mortar and pestle, and sieved through a 2 mm mesh to remove, residue stones and other plant materials to obtain a homogenous sample matrix. Close attention was paid to every sample to avoid cross-contamination. Sample Digestion 1g each of the pulverized samples was carefully weighed into a 200 mls digestion beaker upon which the addition Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.9, No.10, 2019 of acids was followed. Thirty (30) mls of Conc HCl and 10mls of Conc HNO3 acids were added in the ratio of 3:1 (aqua regia) to the beakers. The samples were then subjected to heat on a hotplate for digestion. As the volume of the content in the beaker dropped to about 5mls, aqua regia was added again and the samples were further digested a second time. That is, digestion was done twice on the samples, in order to ensure that the elements of interest are brought into solution. The digested samples were filtered into sample bottles and made up to mark with distilled water. Analysis of metals for Pb, Zn, Ni, Co, Mn, and Ag were performed using atomic absorption spectrometer (AAS), Thermo Scientific ICE 3000 series. A matrix standard and blank was also prepared in the analysis.

RESULT AND DISCUSSION
The result of the heavy metal content of soil samples collected from three different locations in the mining community are shown in table 1.  The graphical illustration shown in figure 2 revealed that the concentration of Cobalt (Co) in all the samples followed the order (B) < (C) < (D) < (F) < (A) < (E) < (H) < (G). All soil samples showed concentration above the Bowen (1986) standard, but fell below the 7.50 mg/l (750 mg/kg) of the United States Environmental Protection Agency (US EPA) limit permissible for domestic gardens, residential and agricultural areas. This suggests that the soil samples were not "in all contaminated" and could support agricultural activities, however, metal accumulation over a long period of time may occur leading to high metal level content. Similar studies by (Karaca A., 2004) showed that the concentration of cobalt in soil around mine sites fell below the 7.50 mg/l limit permissible set by the US EPA.   Figure 4 revealed that the Nickel (Ni) concentration for all the samples ranged from 1.894 mg/l -3.082mg/l (189.4 mgkg -1 -308.2 mgkg -1 ) in the order of (C) < (A) < (H) < (E) < (F) < (B) < (G) < (D). All samples from the three regions showed nickel concentration above the permissible limit of 1.5 mg/l (150 mgkg -1 ) for residential and agricultural lands set by the US EPA and CEC. This indicates that the soil suffers from nickel contamination and may affect plants lives cultivated on the soil. . All samples were above the tolerable limits of 1 mg/l -3 mg/l (100mgkg -1 -300mgkg -1 ) set by US EPA for agricultural lands except for sample (B) from Ameri mining site. Soil sample (F) from Enyigba and sample (B) from Ameri showed a considerably high Mn concentration of 9.703 mg/l and 10.802 mg/l respectively. The result suggest that the contamination of the soil could have resulted from the decay of shale, hence releasing more of the toxicity into the soil and rendering it unfit for agricultural practices as they may affect plant growth negatively. Figure 6: Lead concentrations in soil samples relative to US EPA permissible limits Lead was detected in only two samples (figure 6): sample (F) and (G) from Enyigba at concentration of 4.056 mg/l and 2.226 mg/l (405.6 mgkg -1 and 222.6 mgkg -1 ). The concentration of the metal analyzed for sample (F) was above the permissible limit of 0.3 mg/l -3 mg/l (30 mgkg -1 -300 mgkg -1 ) set by the US EPA while that of sample (G) fell below the limit. The rest of the soil samples from the other regions did not show the presence of lead quantifiable as it was not detected by the spectrometer. This suggests that the concentration of lead in the soil sample (F) from Enyigba could affect agricultural practices and plant lives negatively in the region (Obasi et al.,2012).  Figure 7 revealed that the silver (Ag) concentration in all the samples analyzed ranged from 0.788 mg/l -1.882 mg/l (78.8 mgkg -1 -188 mgkg -1 ). The silver (Ag) content was in the order of (D) < (F) < (H) < (E) < (G) < (C) < (A) < (B). It appeared that the silver content in all samples from the three regions was higher than the permissible limit in normal soil by Lindsay (1979). The soil sample (B) from Ameri harbored the highest silver content, which suggests a possible contamination of the soil as the mineral host rock decays gradually with time releasing its toxicity into the soil.

CONCLUSION
The total concentration of all the mobile heavy metals in soil revealed that mining activities in the Pb-Zn mineralization regions of Ameri, Enyigba and Ishiagu in Ebonyi State, South-East Nigeria, were above the normal soil composition based on Bowen (1979), and in the order Mn> Zn>Pb>Ni>Ag>Co. The high values may indicate both geologic and anthropogenic origin. Many of the soil samples contained heavy metals at levels that could cause toxicity and impact negatively on the environment through their introduction above the threshold limit to the soil and water thereby causing severe pollution of the water and soil.
The main conclusion that can be drawn from this study is that the risk level of heavy metal leaching and groundwater contamination from the soil is very high with considerable likelihood of heavy metal transport by water percolating through the soils/mine waste since the dumping of the mine wastes is practiced. The people of Abakaliki who are known producers of rice and yams in southeastern Nigeria, would need a management plan against the transfer of metals into the ecosystem in order to alleviate the possible metal related health problems. This can be done by reducing the solubility and concentration of metals in the soil to reduce metal intake through the consumption of contaminated forages and soil.