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).