Global Journal of Science Frontier Research, H: Environment & Earth Science, Volume 21 Issue 6

measurement and sampling were made at the artisan mines. For the purpose of accuracy the positions were marked with a portable hand held global positioning system (GPS). The horizontal profile soil sampling strategy was chosen for the present study, since the mine site is a virgin site. A total of 49 samples were collected all together. After removal of stones and vegetable matter, each soil sample were packed into its own secure water-tight polythene bag in order to prevent cross contamination and was taken to the laboratory for analysis. b) Sample Preparation and Analysis Samples were each dried at ambient laboratory temperature. For one week, ground, sieved 2.0mm with the aid of spatula and weighing bottle. 0.5g of each soil/mill tailing sample was obtained. The digestion was carried out using concentrated nitric (10ml) and concentrated perchloric acids in the ratio of 2:1 and the oven was maintained at 200oC. After one hour, the mixture was allowed to cool before leaching the residue with 5cm3 to 20% HNO3. Digested samples were then filtered and made up to 100ml with de-ionized water. A blank determination was treated in the atomic Absorption spectrometer, but without sample. Solution of samples were taken and aspirated into Unicom 969 Atomic Absorption spectrometer for analyzing metals. At least one reagent blank and one duplicate sample were run as described above for background correction and to verify the precision of the method. A calibration graph was plotted for each element using measured absorbance and the corresponding concentration. The calibration curve was used to determine the concentration of the metal. Accuracy was however assessed by analyzing two replicates of certified reference materials, Recoveries were satisfactory, average value being in excess of 90% for Pb, Cu, Zn, As, Mn, Fe, Cd, Cr, Co, Mn and Ni analyzed. c) Assessment of Heavy Metal Contamination i. The contamination factor (CF) The level of contamination of soil in metal is expressed in term of a contamination factor calculated as follows (Harikumar, et al. , 2009): = (1) Where represent the metal concentration in sample and represent metal concentration. If the contamination factor (CF) < 1 refers to low contamination; 1 ≤ < 3 means moderate contamination; 3 ≤ ≤ 6 indicates considerable contamination and > 6 indicates very high contamination. ii. The Pollution Load Index (PLI) The pollution Load Index (PLI) is obtained as contamination factors (CF), the CF is the quotient obtained by dividing the concentration of the metal related to the target area by reference area. The PLI also provide comprehensive information about the metal toxicity in the respective samples. This method was developed by Tomlison (Tomlison, et al., 1980). The PLI of the site are calculated by obtaining the n-root from the n-CFs that was obtained for all the metals as follows (Tomlison, et al., 1980): = ( 1 × 2 × 3 × … .× ) 1/ (2) Where represent number of metals studied, represent contamination factor and PLI represent pollution load index. The PLI value of >1 is polluted, where as <1 indicates no pollution (Harikumar, et al., 2009). iii. Degree of contamination (DC) The degree of concentration (DC) of one determined area is the sum of all contamination factors. = ∑ (3) If < 1 : indicates low concentration 1 ≤ < 3 : Indicates moderates contamination 3 ≤ < 6 : Indicates considerable contamination ≥ 6 : Indicates Very high contamination (Hakanson, 1980) III. Results And Discussion a) Heavy Metal Concentrations The mean concentrations in (ppm) of the heavy metals (Pb, Fe, Mn, Cu, Zn, As, Cr, Co, Ni, Cd) were analyzed for the mine, mill tailing and control samples respectively. Heavy metals were detected at varying concentrations in the samples. Table 1 presents the mean concentrations of the heavy metals in the mine, mill tailing and control sites with the WHO limit and its toxic response factor. The mean concentrations (ppm) of the studied heavy metals in mine site were calculated to be 429.76±26.202 1707.63±237.78, 181.61±82.38, 90.95±59.42, 37.41±33.30, 17.99±4.53, 93.19±47.39, 47.94±5.71 22.28±6.17, and 3.23±2.07 respectively. For the mill tailing site, the mean concentrations (ppm) of the heavy metals were calculated to be 846.87±100.27, 1914.99±89.06, 177.70±50.51, 739.33 ±337.57, 100.41±41.37, 43.52±7.97, 163.28±39.48, 53.48±2.79, 45.59±18.54, 5.83±0.48 respectively and for the control area, the mean and standard deviations of the concentrations of heavy metals were calculated to be21.40±6.11, 1331.00±142.75, 68.10±23.99, 35.72 ±16.45, 11.91±8.91, 5.73±2.71, 47.85±4.78, 18.17 ±5.65, 14.26±3.26, and 0.23±0.29 respectively. Determination of Heavy Metal Pollution in Soil Samples from Angwan Kawo Gold Mining Sites, Niger State, Nigeria © 2021 Global Journals 1 Global Journal of Science Frontier Research Volume XXI Issue VI Year 2021 72 ( H ) Version I