Assessment Of Heavy Metal Contamination In Irish Potatoes And Soils From An Abandoned Mining Site In Jos-South, Using AAS And XRF Techniques
This study was undertaken to assay the elemental concentration in some Irish potatoes and soils from farmlands in an ex-mining area at Dahwol-vwana village, Jos-south L.G.A, Plateau state, Nigeria. The total heavy metal concentrations (for Irish potato and soil samples) were obtained using Atomic Absorption Spectrometer. It was observed from the soil sample concentration values gotten at the end of the AAS analysis (Pb, ranges from 0.0445-3.9343ppm; Cd, from 0.0086- 0.1200ppm and Zn, from 0.0751-39.0302ppm) are higher than the concentration values obtained from control area (Pb- 0.0088ppm, Cd-0.0029ppm and Zn-0.0101ppm), but lesser than the international threshold values (EU:- Pb-300ppm, Cd-3.0ppm and Zn-300ppm. USA: – Pb- 300ppm, Cd-3.0ppm and Zn-250ppm. UK:- Pb-70ppm, Cd-1.4ppm and Zn-200ppm). While that of Irish potatoes: – Pb, ranges from 0.0741-1.5042ppm; Cd, from 0.0081-0.0931ppm and Zn, from 0.1038-88.0503ppm). A modified sequential extraction procedure of Tessier et. al., (1979) was used in separating the total metal concentrations into four operationally defined fractions (exchangeable and carbonate, Fe and Mn oxides, organic matter, and residual fractions). Where it was discovered that the bulk of metals were partitioned to the residual fraction (Zn- 138.85ppm, Pb-55.59ppm and Cd-2.5ppm) which implies that the soils of the farmland are not polluted by any of the metals studied. Pollution indices also as compared with Banat et. al., (2005) standards, indicated minimal contamination of the soils matrix with Cd, which had enrichment factor value of 15.4 and I-geo factor of 4. The bulk partitioning of the metals onto the residual fraction indicates a lithogenic origin of the heavy metals, i.e. the heavy metals were directly inherited from the parent material, and also a low risk of contaminant transfer under normal cultural practices. However, heavy perturbation of the soil, such as mining, would lead to significant pollution of soil, and water bodies as well enhanced Irish potatoes and other plants uptake of the metals, thereby resulting in a threat of biomagnifications.
Tin mining industry which is also the largest producer of columbite in Jos plateau state started in 1902 (Adegboye, 2012). The mining of tin has been largely responsible for profound changes in the landscape and in the social economic structure of study area (Adegboye, 2012). Limited arable land is experienced in Jos plateau area, according to (Patterson, 1986) this is due to the high rate of surface mining. (Scholar, 1979) revealed that mined soils are poorer in agricultural value compared to adjoining natural land. Crops grown on such mined land are of low agricultural value, quick maturing and low-nutrient demanding, such as acha, dauro, maize, millet and Irish potato. (Calvert, 1990) revealed that the indiscriminate mining on the Jos plateau, led to many parts of the area being exposed to erosion and reduces the available arable land for crop production. The volume of mineral tripped off during mining reduces the nutrient present in the soil (Adegboye, 2012). Jos South local government area is an extensively mined area, which was dominated by use of heavy earth – moving equipment and draglines. As a result, the zone is characterized by deep excavations and dumping of high over burden, mine ponds, mine tailings and slurry wash deposits (Olaniyan, 1998; Musa et. al., 2011). According to (Gyang et. al., 2010), the major problem of the area still remains the devastated and de-vegetated land and mine spoils; depriving the inhabitants of fertile farmland. The deep mining which is an excavation of underlying sand has created mining pits, man-made lakes, pools and ponds which have great effect on both the people and agricultural practices. Mining ponds have always been death traps for people and animals (Davis, 2001).
The ponds are always sources of erosion especially in rainy season when most of the ponds over flow their banks as was the case of a paddock behind the Amalgamated Tin Mines of Nigeria LTD (ATMN) stadium Bukuru. Fully mechanized mining activities as well as formal mining are still in operation around „rayfield‟ area of the local government. The early inhabitants of the present tin mining areas of the study area were aware of the existence of the mineral in their locality long time ago when the mining started on a small scale, which later extended to take over large area of arable land. As a result of the drastic loss of farmlands to mining activities, attention of most of the inhabitants has shifted to the mining rather than farming (Morrison, 1994).
1.1 Background of the Study
1.1.1 Toxicity History
The first considered toxicity-related description in the western literature is the biological weapon or poison from the “many-headed” sea serpent, Hydra, used in poisoning Hercules’s arrows. The knowledge on toxicity and poisonous substances is attributed to the earliest humans, who devised “poisonous” weapons using plant extracts and animal venom for hunting animals. (www.rsc.org/toxicology).
Further toxicological studies have led to the establishment of safety standards, maximum allowable dosages, and detailed toxicity levels of substances, which are the scientific bases of medical treatments, environmental and health care systems. (www.rsc.org/toxicology).
In a general sense, the toxicity of a substance could be defined as the capacity to cause injury to a living organism (NAS/NRC, 1970; Sanockij, 1970). A highly toxic substance will damage an organism if administered in very small amounts; a substance of low toxicity will not produce an effect unless the amount is very large. Thus, toxicity cannot be defined without reference to the quantity of a substance administered or absorbed (dose), the way in which this quantity is administered (e.g. inhalation, ingestion, injection) and distributed in time (e.g. single dose, repeated doses), the type and severity of injury, and the time needed to produce that injury.
There is no generally agreed definition of “hazard” associated with a chemical, but the term is used to indicate the likelihood that a chemical will cause an adverse health effect (injury) under the conditions in which it is produced or used (Goldwater, 1968; NAS/NRC, 1970, Pravdin, 1934).
Risk is a statistical concept and has been defined by the Preparatory Committee of the United Nations Conference on the Human Environment, as the expected frequency of undesirable effects arising from exposure to a pollutant. Estimates of risk may be expressed in absolute terms or in relative terms. The absolute risk is the excess risk due to exposure. The relative risk is the ratio between the risk in the exposed population and the risk in the unexposed population (BEIR, 1972; ICRP, 1966).
The principle behind toxicity is based on the prescient statement of Philippus Theophrastus Aureolus (Paracelsus), a Swiss physician and alchemist, that “all substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.”(www.rsc.org/toxicology).
There are important factors in determining the toxicity of a substance. These factors, according to Dr. Emily Monosson, a toxicologist and an editor of the Encyclopedia of Earth, include “dosage, exposure route, form and innate chemical activity, species, age, sex, ability to be absorbed, metabolism, distribution within the body, excretion and presence of other chemicals.” These factors may have significant impact on toxicity; however, the most critical factor is dosage (www.rsc.org/toxicology).
Toxicity, in general, is classified according to the site affected by the toxicant (toxic substance). The toxic effect may occur at only one site and this is called organ specific toxicity. Some of the common organ specific toxicity includes hepatotoxicity (liver), immunotoxicity (immune system), neurotoxicity (nervous system) and nephrotoxicity (kidney). On the other hand, if the toxic effect occurs on multiple organs or parts, it is called systemic toxicity. The systemic toxicity may be developmental (developing fetus), carcinogenic (abnormal cell growth), acute (occurs immediately) and chronic (occurs gradually or over time) (www.rsc.org/toxicology).
1.1.2 Heavy Metal Toxicity
Heavy metals are metallic elements which have a high atomic weight and a density much greater (at least 5 times) that ofwater. There are more than 20 heavy metals, but four are of particular concern to human health: lead (Pb), cadmium (Cd), mercury (Hg), and inorganic arsenic (As) (Victor, 2011). These four heavy metals are four of the top six hazards present in toxic waste sites. They are highly toxic and can cause damaging effects even at very low concentrations. They tend to accumulate in the food chain and in the body and can be stored in soft (e.g., kidney) and hard tissues (e.g., bone). Being metals, they often exist in a positively-charged form and can bind on to negatively-charged organic molecules to form complexes (Victor, 2011).
The body has need for approximately 70 friendly trace element heavy metals, but there are another 12 poisonous heavy metals, such as Lead, Mercury, Aluminum, Arsenic, Cadmium, Nickel, etc., that act as poisonous interference to the enzyme systems and metabolism of the body. No matter how many good health supplements or procedures one takes, heavy metal overload will be a detriment to the natural healing functions of the body. Some metals are naturally found in the body and are essential to human health. Iron, for example, prevents anemia, and zinc is a cofactor in
over 100 enzyme reactions. Magnesium and copper are other familiar metals that, in minute amounts, are necessary for proper metabolism to occur (Victor, 2011). They normally occur at low concentrations and are known as trace metals; for example, high levels of zinc can result in a deficiency of copper, another metal required by the body. Heavy or toxic metals are trace metals that are at least five times denser than water. As such, they are stable elements (meaning they cannot be metabolized by the body) and bio-accumulative (passed up the food chain to humans). These include: mercury, nickel, lead, arsenic, cadmium, aluminum, platinum, and copper (metallic form versus ionic form). Toxic heavy metals have no function in the body and can be highly toxic. Heavy metals are taken into the body via inhalation, ingestion, and skin absorption. If heavy metals enter and accumulate in body tissue faster than the body‟s detoxification pathways can dispose of them, a gradual buildup of these toxins will occur. High-concentration exposure is not necessary to produce a state of toxicity in the body tissues and, over time, can reach toxic concentration levels (Victor, 2011).
1.2 Statement of the Problem
Heavy metal contamination is one of the serious environmental problems limiting plant productivity and threatening human health (Luptakaet al 2002; Verma and Dubey,2003; Kadukova et. al., 2006 ). Inputs of heavy metals to agricultural soils can occur from a variety of sources. These include the application of biosolids, fertilisers, livestock manure, agrochemicals, and irrigation water and from atmospheric deposition. Some of the concerns about accumulation of heavy metals in agricultural soils stem from their possible negative impacts on soil fertility and in some case their potential to accumulate in the human chain (McLaugh et. al., 1999; Gray et. al., 2003). Among the substances that contribute anthropogenically to pollution of the biosphere, trace elements are the most toxic. Lead, Zinc and Cadmium are toxic metals of increasing environmental concern as they enter the food chain in significant amounts (Luptaka et. al., 2002; Verma and Dubey, 2003; Kadukova et. al., 2006).
Currently, majority of the soil dug from the mining holes in Dahwol-vwana village, Jos-south L.G.A. have been scattered on their farmlands. Farm inputs like fertilisers are also used in the farming of Irish potatoes and all these might contain Cd, Zn and Pb metals, for Irish potato crops intake on the farms. There is therefore the need for studies to establish the level of these metals in the Irish potato crop and soil on these farms.
1.3 Aim and Objectives
The aim of this thesis is to determine the amount of heavy metals and concentration of toxic elements in some selected soils and Irish potatoes samples in ex-mining areas of Jos and to analyze through the following objectives:-
- Assay the elemental concentration in both Irish potatoes and the soils in which they will be transplanted in ex-mining area at Dahwol-vwana village, Jos-south L.G.A Plateau state, Nigeria.
- To compare the concentration of the toxic elements both in the Irish potatoes and the soil used for their farming with concentration values from control and International threshold values.
- To determine and evaluate the geochemical species (fractions) of Pb, Cd, and Zn in some farmlands in an ex-mining area in dahwol-vwana village, Jos-south L.G.A Plateau state, Nigeria.
- Total enrichment factor and geo-index analyzed to assess the level of contamination.
1.4 Justification of Research
A comprehensive understanding that toxic elements are found within mining areas, in which farming around such areas need to be investigated. In this work Irish potatoes farmed in ex-mining area in Dahwol-vwana village, Jos south L.G.A Plateau state, Nigeria is to be investigated.
It is important to provide a necessary data required as baseline that will enable further study on the toxic elements in products farmed in mining areas.
In this study, Energy dispersive X-ray Fluorescence spectroscopy (EDXRF) and Atomic Absorption spectroscopy (AAS) techniques shall be employed for the analyses.
1.5 Scope and Limitation of Study
This work is to be carried out on some farms in an ex-mining site in Dahwol-vwana village, Kuru district, Jos-south L.G.A., Plateau state, to determine the amount of heavy metals and concentration of toxic elements in some selected soil and Irish potatoes samples. The samples‟ collections were done around three ex-mining hole areas (N09044.662‟E008050.590‟), (N09044.656‟E008050.591‟) and (N09044.638‟E008050.577‟). While for the control samples gotten in a virgin area (N09041.062‟E008045.003‟) in Trade-Centre village, along Vom road, in Kuru district, Jos-south L.G.A., Plateau state.
This site is an ex-mining site; mining activities took place last seven-eight years ago (Information; from some of the villagers).
The entire research will be conducted in raining season. Also, the short duration of the study period coupled with limited resources will force only one time sampling of the Irish potatoes and the soil for measurements and analyzes. This could reduce the sample number to have error margin.
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