Abstract
Tanzania is at advance stages in the preparation to start uranium mining at Mkuju River Deposit. In order to implement best practice in environmental management in uranium mining as required by national and international regulations and standards, a set of site specific baseline data have to be established prior the mining operation. In order to establish heavy metal baseline data for this purpose, a total of 84 soil samples were collected from clustered area of about 1,300 km 2 at two depths: 0-15 cm and 15-30 cm. Analysis of the data using EDXRF showed a total metal concentration ranges of 3570-19400 for Al, 15200-58600 Fe, 400-1400 Mn, 15.2-54.9 Cr, 13.5-51.0 Zn, 2.2-45.3 Pb, 2.1-37.3 Cd, 0.2-23.0 Hg, 1.8-25.1Cu, 2.1-22.7 Ni and 0.8-9.1 mgkg -1 for Co. Since the spatial distributions of heavy metals in the vicinity of the planned uranium mine are comparable to established global concentration ranges in soils, it is an indication that the distribution is natural. By virtue of their strong association with uranium and immobility in soil, spatial distributions of lead and copper concentrations would be more sensitive indicators for monitoring uranium related soil contaminants when the uranium mine become operational.
Highlights
The toxicity and tolerance limits of heavy metals are well documented and in many cases they have been used in formulation of national or international standards (Tricopoulos, 1997; European Union (EU), 2002; United State Environmental Protection Agency (USEPA), 2002; Cheng et al, 2006; Tanzania Bureau of Standards (TBS), 2007; Momodu & Anyakora, 2010; Jintao et al, 2011; Lokeshappa et al, 2012)
Since this study aims at establishing baseline data whose distribution varies slowly with distance, the grid was increased to 100 m x 100 m to reduce the sampling points without sacrificing representation of heavy metal distributions
Establishment of baseline data for such a vast area, about 1300 km2 in this case, can be a very challenging undertaking because it requires an enormous amount of sampling points, sample transport, preparation and elemental concentration measurements
Summary
The toxicity and tolerance limits of heavy metals are well documented and in many cases they have been used in formulation of national or international standards (Tricopoulos, 1997; EU, 2002; USEPA, 2002; Cheng et al, 2006; TBS, 2007; Momodu & Anyakora, 2010; Jintao et al, 2011; Lokeshappa et al, 2012). For data to be a good representative of a point, soil sampling is done by taking samples at least two layers. This approach makes it possible to establish data base for mobile and immobile heavy metals (Swenson et al, 1984). For the sake of accuracy, duplicates or triplicates of analyses have to be made for each sample taken If all these requirements are taken into consideration, establishment of baseline data can be costly and time consuming. In this work a method to reduce sampling points without sacrificing spatial and temporal distribution representation of concentration of heavy metals in soil at Mkuju river basin is presented
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