Analysis of the Pollution Level and Its Variation: A Case Study of Some Selected Sites within Kano State Nigeria

摘要

Aim: This research investigates the pollution level of heavy metals and their variation in five selected areas in Kano state, Nigeria. The heavy metals investigated are Cadmium (Cd), Chromium (Cr), Manganese (Mn), Zinc (Zn), Lead (Pb), Copper (Cu), Iron (Fe), and Nickel (Ni). Place and Duration of Study: The area under investigation is found to be associated with various activities (e.g. Industrialization, blacksmithing, metal scrap dump site, agriculture etc) for the past 40 years but due to increase in population, it is now a compact (Nucleated) settlement. In agricultural areas, some of the farmers use the polluted water released for their source of irrigation activities. The study covers a period of six months (November 2015 to April 2016), based on the period of activities in the selected sites (e.g. cultivation by the farmers, Industrial activities, Melting, Metal scraps etc). Methodology: Sample Preparation, Preservation and Digestion- The soil samples are collected for Three Months (February, March and April, 2016) after the sites were prepared for three months (November, December 2015 and January, 2016) for the experiment. Each time the sample was collected it was shade-dried for seven days on the plastic trays to avoid metal contact. The dried samples are grinded using ceramic coating, then sieved into refined powder and leveled into polythene bags, for storage under the ambient temperature [1]. Procedure: A beaker containing 1gm of soil sample and 30ml of Aqua regia (HNO3 +HCl) at 3:1 ratio was placed into mixer (vibrator) for one hour thirty minutes. Filter paper (Whiteman No.42) was used to filter the solution (suspension) on a separate beaker and distilled water was added to marked 50ml. Atomic absorption spectroscopy ((ASS)-Model 210 VGP) was used to determine the presence and concentration of; Pb, Cd, Ni, Cu, Cr, Zn, Mn and Fe with the corresponding wavelength of each metal; 248.3, 213.9, 232, 357.9, 228.8, 217, 279.5 and 324.8nm respectively. The result obtained was further analyzed using SPSS 20.0. Results: It is found that in all the five (5) sites (locations) of the study, there exist all the eight heavy metals (HMs) in varying concentrations. The slopes are deduced with the values as; Cd (0.109), Cr (0.119), Cu (0.022), Fe (0.026), Ni (0.013), Mn (0.02), Pb (0.022) and Zn (0.017). These values are used to compute the concentration of the eight metals identified, which gave the order of concentrations as: Zn>Ni>Mn>Fe>Cu>Pb>Cr>Cd (for February and March, 2016) but Ni>Cu>Pb>Mn>Fe>Cd>Cr>Zn (For April, 2016). The pollution load index for the five locations is obtained as: 1.2927 (BUK), 1.6249 (Naibawa), 1.6783 (KofarRuwa), 1.4197 (BUK Screen) and 1.559 (Sharada). Conclusion: The results obtained reveals that eight (8) HMs are determined - (Cr, Cd, Cu, Fe, Zn, Ni, Pb, and Mn). These HMs recorded different/varying concentrations (within the soil). The correlation matrix generated from the concentrations of samples obtained shows that in each site, there is group of HMs that originate from the same source(s) and others that emanate from another source (s). In Naibawa, Cd, Cr, Cu, Fe, Ni, Mn, and Pbhave high probability of originating from the same source while Zn might have originated from a different source But in KofarRuwa site, Fe and Zn recorded high probability of originating from the same source while Cd, Cr, Cu, Ni, Mn and Pb are from other source(s). In BUK – E; Cd, Cr, Cu, Fe and Pb are probably from the same source, while Ni, Mn and Znare from different source. In the control area (BUK C site), Cd, Ni, Mn, Pb recorded values have probabilities, indicating they are from the same source while Cr, Cu, Fe and Zn are contrary from the latter. In the overall sites, the data generated reveals that Cr and Cu are from the same source while Cd, Cr, Cu, Ni, Mn and Pb are from another source. From the soil pollution load index computed (before, during and after planting), the study indicates decrease in the level of contamination in all the sites.