Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 9 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET ENVIRONMENTAL IMPACT OF MINING IN SOUTHWEST BURKINA FASO: A COMPREHENSIVE ANALYSIS Marie-Claire Diarra École Nationale Supérieure Université Ouagadougou Canada ABSTRACT: The intensification of mining activities in Burkina Faso, driven by increased global demand for minerals and metals, particularly gold, has raised significant economic prospects for the nation. This transformation from a traditionally agrarian economy to a burgeoning mining hub has positioned Burkina Faso among the leading gold-producing countries in Africa. This transition is marked by the operation of seven active gold mines within the country, ushering in newfound opportunities and challenges. One notable player in this landscape is the Poura Gold mine, historically the pioneer industrial gold mine in Burkina Faso. This mine, managed by the state-owned mining company SOREMIB from 1985 to 1999, played a pivotal role in shaping the country's mining sector. During its operational years, Poura Gold mine contributed significantly, yielding approximately 15 tons of gold. In 2012, an American mining company, Newmont, reopened the Poura Gold mine, primarily focusing on exploration and prospection activities. However, the remnants of the earlier mining era (1985-1999) still linger, manifesting as substantial volumes of mine wastes accumulated at the site. This study delves into the evolving dynamics of Burkina Faso's mining landscape, with a particular focus on the Poura Gold mine's historical significance and its implications for the present and future of mining in the region. It explores the environmental and socioeconomic ramifications of mining activities in Burkina Faso, shedding light on the challenges and opportunities that come with this transition. Keywords: Burkina Faso, mining, Poura Gold mine, gold production, environmental impact. INTRODUCTION Due to the high mineral and metal demand of emerging economies such as India and China, the prices of these commodities have increased on the international market, leading to intensive mining worldwide. Burkina Faso, a landlocked country, has been long considered as a least developed backward agricultural country that may benefit from the "mining boom". Since 2010, the country has become the fourth largest African gold producing country after South Africa, Ghana and Mali. Nowadays Burkina Faso has seven active gold mines (Taparko, Essakane, Mana, Youga, Inata, Kalsaka, Sabcé). The Poura Gold mine (Figure 1) was the first industrial gold mine of the country. The mine was operated from 1985 to 1999 by the state owned mining company "Société de Recherches Minières du Burkina Faso (SOREMIB)". During this period, Poura Gold mine produced approximately 15 tons of mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 10 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET gold. In 2012 the mine was reopened by Newmont, an American mining company, but the activities are currently limited to exploration and prospection. The previous mining (i.e., 1985-1999) has generated several tons of mine wastes which are still piled up on the site. These mine wastes consist of overburden, waste rock dumps, tailings and usually various sulfide and iron minerals. In the nature the interaction between these minerals and oxygen and/or water lead to their oxidation, a process known as acid rock drainage (ARD). However, an exacerbated ARD through mining is known as acid mine drainage (AMD). AMD is characterized (Kawatra and Natarajan, 2001) by high acidity (low pH) and high concentrations of sulfate and metals and metalloids such as iron (Fe), manganese (Mn), aluminum (Al), zinc (Zn), copper (Cu), nickel (Ni), lead (Pb), cadmium (Cd) and arsenic (As). As a result, AMD represents, by far, the most serious threat to the ecosystem adjacent to mining sites. Thus, AMD acidifies the receiving environment through a release of sulfuric acid, and also maintains in solution highly reactive and toxic metals (US-EPA, 2000; Naicher 2003; Galvez-Cloutier and Lefrancois 2005). Thus, AMD enhances the mobility and bioavailability of potentially toxic metals in the ecosystem. The main metals released into the environment due to mining are: Fe, Mn, Pb, Zn, Cd, Cr and Ni. Increased solubilization of these metals following AMD generation can enter food web, and pose serious threats to human health through consumption, for example, of contaminated seafood. In humans, the metals are stored in most soft tissues, particularly the liver and kidneys as well as in the bone, Collon (2003). The ingested metals are therefore bioaccumulative and non-biodegradable in human body, and thus highly toxic even at very low doses (trace amounts). The aim of this paper is to assess the spread of potentially harmful elements (PHE), e.g. heavy metals associated to mine wastes and tailings, and its impacts on the environment. mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 11 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET Figure 1: Geological map of Burkina Faso with the location of Poura gold mine. Acid Mine Drainage (AMD) By definition, acid mine drainage is an effluent produced during mining or after the mine closure which physic-chemical characteristics differ from the original water (Collon, 2003). In the deposits and in particular metalliferous deposits, minerals are usually associated with sulfur or iron minerals (pyrite, chalcopyrite, arsenopyrite, galena, sphalerite, pyrrothite, covelite). Consequently, these sulfide minerals are found in tailings or waste rock piles. Exposure of tailings to air and water leads to sulfate and iron oxidation and production of acid mine drainage known as AMD. The kinetics of this oxidation reaction is enhanced in the presence of thiobacillus ferrooxidan bacteria, that can speed up the reaction rate about 105 time compared to abiotic reaction. The acidification will impact the release of metals from various minerals. An orange-brown color of insoluble Fe (OH)3 usually characterizes this acidic drainage. Assuming the presence of pyrite in tailings (Kleinman et al., 1981; Aubertin et al., 2002a; Bussière et al., 2005), interaction between tailing seeping or highly acidic process waters and a receiving environment (e.g., surface water) with a pH close to neutral (5 4), the ferric iron precipitates as ferric hydroxide releasing more acid in water (reaction 3). Fe3+ + 3H2O → Fe(OH)3 + 3H+ [3] The ferrous iron can also be precipitated as iron hydroxide and produce acid as shown in reaction 4. Fe2+ +1/4O2 + 3/2H2O → FeOOH + 2H+ [4] When the pH is sufficiently low (pH <4), ferric iron remains in solution, and thus playing the role of a highly reactive oxidant (the so-called indirect reaction). The indirect oxidation of pyrite produces more protons, and thus exacerbates acidification of the receiving environment (reaction 5). FeS2 + 14Fe3+ + 8H2O → 15Fe2+ + 2SO42- + 16H+ [5] The overall pyrite oxidation reaction can be expressed as follows: FeS2 +15/4O2 + 7/2H2O → Fe (OH)3 + 2H2SO4 [6] These equations show that the oxidation of one mole of pyrite produces two moles of sulfuric acid in the environment. METHODOLOGY Samples of surface water, groundwater (hand-pumped boreholes and wells), soil and mine wastes were collected at Poura old gold mine.Water concerned surface water and groundwater to assess their chemical parameters. The pH and water temperature have been measured in the field; geographic coordinates of sampling site have been recorded. For ground water, the depth (of the well) is recorded. Each sample of mine wastes and soil is a composite of three sub-samples collected from sampling sites located at the distance of 10-20 m from each other. About, 3 kg have been dried, sieved and homogenized. The < 2mm fraction (about 5g), have been taken for analysis. All samples (water, mine wastes, and soil) were shipped to Johannesburg (South Africa) to the laboratory "Acmelabs" for analysis. Water samples have been the subject of the determination of F, pH, conductivity, alkalinity and Hg. Samples of mine waste, and soil were subjected to aqua regia digestion and a full suite of 36 elements have been analyzed. RESULTS Sampling All collected samples are reported in Figure 2. A total of 10 groundwater samples, 14 of surface water, 16 of soil and 11 of mine wastes were collected. mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 13 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET Figure 2: Location of sampling sites on the satellite map (Google imaging © 2014) Groundwater and surface water Results of chemical analyses of the groundwater and surface water are given in Tables 1a and 1b. Table 1a: Chemical analyses of groundwater Physical parameters Miscellaneous inorganics (mg/l) Sample Depth (m) Temperature Conductivity (°C) (µS/cm) pH Fluoride Alkalinity Bicarbonate Carbonate Total HCO3 CO3 CaCO3 Hydroxide OH GW1 *HPB 31.50 340 8.45 0.190 189 221 4.82 <0.50 GW2 *HPB 32.30 239 8.35 0.120 133 158 2.22 <0.50 GW3 25 23.40 157 8.02 0.096 78.6 95.9 <0.50 <0.50 GW4 *HPB 30.70 357 8.39 0.250 197 232 4.03 <0.50 GW5 30 28.60 169 7.73 0.098 58.9 71.9 <0.50 <0.50 GW6 *HPB 30.80 365 8.37 0.240 155 184 2.87 <0.50 GW7 *HPB 30.80 339 8.38 0.200 145 170 3.04 <0.50 GW8 *HPB 31.00 455 8.32 0.063 193 230 2.42 <0.50 GW9 10 29.40 153 7.49 0.045 17.8 21.7 <0.50 <0.50 mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 14 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET GW10 *HPB 28.40 456 8.67 0.130 244 271 13.10 <0.50 *HPB: Hand-pumped borehole Table 1b: Chemical analyses of surface water Physical parameters Miscellaneous inorganics (mg/l) Sample Temperature (°C) Conductivity (µS/cm) pH Fluoride Alkalinity Total CaCO3 Bicarbonate HCO3 Carbonate CO3 Hydroxide OH SW1 28.3 234 8.03 0.076 60.70 74.10 <0.50 <0.50 SW2 29.1 233 7.88 0.065 61.80 75.40 <0.50 <0.50 SW3 29.0 454 8.33 0.380 165 197 2.12 <0.50 SW4 27.6 60.4 6.61 0.064 8.29 10.10 <0.50 <0.50 SW5 34.2 146 8.07 0.110 70.00 85.40 <0.50 <0.50 SW6 28.3 45.6 7.44 0.058 16.30 19.80 <0.50 <0.50 SW7 32.2 45.7 7.54 0.072 16.70 20.30 <0.50 <0.50 SW8 29.3 225 7.95 0.059 59.50 72.60 <0.50 <0.50 SW9 28.6 287 8.13 0.670 150 183 <0.50 <0.50 SW10 27.9 624 8.51 0.400 290 336 8.99 <0.50 SW11 30.2 112 8.06 0.090 47.10 57.50 <0.50 <0.50 SW12 27.9 556 8.27 0.160 191 233 <0.50 <0.50 SW13 34.2 8810 2.23 0.027 <0.50 <0.50 <0.50 <0.50 SW14 32.2 48.0 7.23 0.076 15.50 18.90 <0.50 <0.50 Mine wastes and soil The contents of some potentially harmful elements are shown in Table 2a and 2b. This table shows for arsenic, copper, nickel, lead and zinc relatively much higher contents in the mine wastes than in soils. Concentrations in mine wastes are: arsenic (4 to more than 10000 ppm), lead (2 to 1339.6 ppm), zinc (14 to 604 ppm), copper (7 to 534.8 ppm), cobalt (3 to 40 ppm), chromium (5 to 304 ppm), nickel (3 to 101.3) and cadmium (0.1 to 5 ppm). These contents in the soil are: arsenic (0.5 to 335.2 ppm), lead (3.8 to 49 ppm), zinc (7 to 130 ppm), copper (7 to 49.7 ppm), cobalt (4 to 35.8 ppm), and chromium (41 to 299 ppm), nickel (6 to 133.6 ppm) and cadmium (for the most less than the detection limit). Table 2a: Contents of some potentially harmful elements in the mine waste samples Element As Cd Co Cr Cu Pb Zn Ni Hg Fe Unit PPM PPM PPM PPM PPM PPM PPM PPM PPM % *LOD 0.5 0.1 0.1 1 0.1 0.1 1 0.1 0.01 0.01 W1 198.6 <0.1 3.4 5 7.7 21.9 21 5.8 0.24 0.70 mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 15 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET W2 4.2 <0.1 39.0 87 80.9 2.3 84 68.3 <0.01 7.23 W3 563.7 0.1 35.6 39 41.6 11.9 69 47.4 0.05 3.37 W4 44.0 <0.1 4.7 14 17.8 1.3 14 3.2 <0.01 1.50 W5 4025.5 5.2 38.1 70 534.8 948.0 588 75.0 2.25 5.12 W6 549.8 <0.1 6.3 18 11.4 10.9 24 10.9 0.04 1.92 W7 151.5 <0.1 38.5 64 44.3 4.9 42 33.8 0.09 3.75 W8 141.8 <0.1 19.7 10 26.6 2.6 23 13.8 0.06 1.84 W9 309.6 1.7 28.7 304 253.8 804.0 604 101.3 0.26 12.88 W10 >10000.0 0.9 24.4 15 251.3 1339.6 107 60.2 4.08 9.24 W11 >10000.0 2.8 40.0 24 329.1 1069.8 364 83.3 3.68 10.97 *LOD: Li mit of detectio n Table 2b: Contents of some potentially harmful elements in the soil sampl es Element As Cd Co Cr Cu Pb Zn Ni Hg Fe Unit PPM PPM PPM PPM PPM PPM PPM PPM PPM % *LOD 0.5 0.1 0.1 1 0.1 0.1 1 0.1 0.01 S1 1.3 <0.1 16.3 52 23.7 11.8 28 24.4 2.92 S2 335.2 0.2 35.8 51 49.7 49.0 130 28.7 1.04 4.36 S3 9.9 <0.1 16.2 83 29.0 4.4 20 36.6 <0.01 3.37 S4 7.3 <0.1 25.8 141 27.1 5.6 34 74.6 0.01 3.86 S5 0.5 <0.1 4.8 25 7.6 6.8 7 6.6 <0.01 1.37 S6 3.6 <0.1 16.8 67 17.7 4.6 16 36.8 <0.01 2.23 S7 20.8 <0.1 17.9 55 19.0 4.9 11 11.7 0.02 2.38 S8 11.5 <0.1 22.0 299 23.8 3.8 21 133.6 0.01 3.63 S9 64.2 <0.1 24.6 70 31.5 16.2 73 21.4 0.84 4.16 S10 33.9 <0.1 20.3 50 23.9 4.6 35 25.2 0.05 3.52 S11 105.6 <0.1 30.7 283 42.0 30.2 47 22.5 1.18 12.89 S12 4.5 <0.1 16.6 103 18.1 4.8 17 30.8 <0.01 2.55 S13 19.0 <0.1 18.5 41 18.9 4.9 12 14.8 <0.01 2.17 S14 5.2 <0.1 14.1 57 11.6 5.6 15 12.1 0.02 2.92 S15 4.5 <0.1 12.2 43 14.3 4.1 13 16.7 <0.01 2.67 SNC1 17.7 <0.1 20.0 70 15.7 5.9 13 15.2 <0.01 2.43 *LOD: Limit of detection DISCUSSION All samples were collected in August (rainy season), which justifies the relatively high temperatures of water samples. Ground water is characterized by a pH close to neutrality (7.49-8.67) and relatively low conductivity values compared to the surface water (153-456 µS/cm). The surface water samples SW4 and SW13 show lower values of pH which are respectively 6.61 and 2.23. Sample SW13 with high conductivity (8810 uS / cm) and high acidity (low pH) confirms the presence of AMD resulting from the mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 16 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET oxidation of tailings stored there. These values indicate that oxidation is local and very advanced in that the pH value is below the minimum 6.5 required for the protection of aquatic life and even below the acute toxicity of 5.0 (Berryman et al. 2003). According to the standards in force in Burkina Faso guideline values for fluoride are 0.07 to 1.5 mg/l. Concentrations of fluoride are higher in groundwater than in surface water. However, these values are consistent with the guideline values. The alkalinity values are highly variable from one sample to another, and are higher in groundwater than in surface water. The acidification of SW13 is confirmed by its alkalinity which is less than the detection limit (0.50 mg /l CaCO3). According to the "Ministère du développement durable, de l’environnement, de la faune et des parcs" (MDDEFP, 2013) the sensitivity of a medium to the acidification varies with alkalinity: high sensitivity, alkalinity < 10 mg /l CaCO3; mean sensitivity, alkalinity ranges from 10 to 20 mg /l CaCO3; low sensitivity alkalinity > 20 mg /l CaCO3. The anions HCO3 -, CO3 2- and OH- have also been analyzed. Bicarbonate, carbonate and hydroxide form alkalinity, however, natural waters usually contain no carbonate or hydroxide. The results given in Tables 2a and 2b show that the concentrations of various analyzed elements are higher in mine tailings than in soils. This is due to the mineralogy of the host rocks of the mineralization. Indeed, at Poura geology comprise mainly volcanic rocks (andesite-dacite), volcano- sedimentary (tuffs, agglomerates) and detrital sedimentary rocks (pelitic to conglomerate rocks) which are intruded by mafic to felsic intrusions (granites gabbroic). Gold is associated with quartz veins whose cracks are filled by sulfides: pyrite (FeS), arsenopyrite (FeAsS), sphalerite (ZnS), galena (PbS), chalcopyrite (CuFeS). High levels in some soil samples (arsenic: S2, S11; lead: S2 and zinc: S2) would come from contamination through leaching, solubilization (due to the decline in pH) and migration of elements from tailings stockpiles. This means enrichment for these elements. Sampling site S2 is the most contaminated and mainly by arsenic, lead and zinc. For soils there are no guideline values from Burkina Faso. But according to Canadian soil quality guidelines for the protection of environmental and human health (Canada, ATSDR, 2005), and taking into account the fact that these soils used for agriculture, some sites are polluted by arsenic, chromium, copper, lead, nickel and zinc. To assess the level of contamination, the index of geo-accumulation (Igeo), (Muller, 1969; Krzysztof et al, 2003) was calculated for soil samples and mine wastes, to assess the presence and levels of contamination (Table 3a, 3b). Igeo Cm = concentration of a given element in the tested soil; BV = concentration of the element in the Earth’s crust (background value); the background values after Levinson (1974) after Lar et al. (2003). 1.5 = a constant accounting for fluctuations in the content of a given substance in the environment. The negative of geo-accumulation indexes for some elements indicates the absence of contamination. mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 17 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET The use of the index of geo-accumulation is based on seven descriptive classes for increasing Igeo values shown in Table 4. Table 3a: Igeo values for some elements in the soil Element Igeo As Co Cr Cu Pb Zn Ni S1 -0.24 1.04 0.84 1.20 0.90 -0.03 0.51 S2 2.17 1.38 0.83 1.52 1.51 0.04 0.58 S3 0.64 1.03 1.04 1.29 0.47 -0.18 0.69 S4 0.51 1.24 1.27 1.26 0.57 0.05 1.00 S5 -0.65 0.51 0.52 0.70 0.66 -0.63 -0.06 S6 0.20 1.05 0.95 1.07 0.49 -0.27 0.69 S7 0.97 1.08 0.87 1.10 0.51 -0.44 0.19 S8 0.71 1.17 1.60 1.20 0.40 -0.15 1.25 S9 1.46 1.21 0.97 1.32 1.03 0.39 0.46 S10 1.18 1.13 0.82 1.20 0.49 0.07 0.53 S11 1.67 1.31 1.58 1.45 1.30 0.19 0.48 S12 0.30 1.04 1.14 1.08 0.51 -0.25 0.61 S13 0.93 1.09 0.74 1.10 0.51 -0.40 0.30 S14 0.36 0.97 0.88 0.89 0.57 -0.30 0.21 S15 0.30 0.91 0.76 0.98 0.44 -0.36 0.35 SNC1 0.90 1.12 0.97 1.02 0.59 -0.36 0.31 Table 3b: Igeo v alues for some elements in th e mine wastes Element As Igeo Co Cr Cu Pb Zn Ni W1 1.95 0.36 -0.18 0.71 1.16 -0.15 -0.11 W2 0.27 1.41 1.06 1.73 0.19 0.45 0.96 W3 2.40 1.38 0.72 1.44 0.90 0.36 0.80 W4 1.29 0.50 0.27 1.07 -0.06 -0.33 -0.37 W5 3.25 1.40 0.97 2.55 2.80 1.29 1.00 W6 2.39 0.62 0.38 0.88 0.86 -0.10 0.16 W7 1.83 1.41 0.93 1.47 0.51 0.15 0.65 W8 1.80 1.12 0.12 1.25 0.24 -0.12 0.26 W9 2.14 1.28 1.61 2.23 2.73 1.30 1.13 W10 >3.65 1.21 0.30 2.22 2.95 0.55 0.90 W11 >3.65 1.43 0.51 2.34 2.85 1.08 -0.11 Table 4: Igeo classes with ct to soil quality mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 18 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET res pe Igeo value Igeo class Designation of soil quality > 5 6 Extremely contaminated 4-5 5 Strongly to extremely contaminated 3-4 4 Strongly contaminated 2-3 3 Moderately to strongly contaminated 1-2 2 Moderately contaminated 0-1 1 Uncontaminated to moderately contaminated 0 0 Uncontaminated According to these classes, soils are uncontaminated to moderately contaminated (class 1) by arsenic, cobalt, chromium, copper, lead, zinc and nickel. They are moderately contaminated (class 2) by arsenic, cobalt, chromium, copper, lead and nickel. The Igeo class 3, i.e. moderately to strongly contaminated sites concerns only arsenic. Concerning mine wastes, Igeo classes 1 and 2, i.e. respectively uncontaminated to moderately contaminated and moderately contaminated concern both element in table 4 (arsenic, cobalt, chromium, copper, lead, zinc and nickel). The highest degrees of contamination are caused by arsenic, copper and lead (class 3: moderately to strongly contaminated sites) and by arsenic (class 4: strongly contaminated sites). So, in soils and mine wastes, the most harmful element is arsenic. Arsenic, copper and lead are the main constituents of sulfides (arsenopyrite: FeAsS, chalcopyrite: CuFeS, galena: PbS) encountered in the mineralized host rocks at Poura. This explains their high concentrations in mine wastes that resulted from the ore treatment or waste rocks. According to Smedley et al (2007), the source of arsenic in Burkina Faso, is likely to be the oxidized sulfide minerals and secondary iron oxides in the mineralized zones. For these authors, high-As groundwater observed derive from zones of gold mineralization in Birimian (Lower Proterozoic) volcano-sedimentary rocks, the gold occurring in vein structures along with quartz and altered sulfide minerals (pyrite, chalcopyrite, arsenopyrite). This is consistent with the assumption mentioned above. Therefore, the high arsenic concentrations in soils and groundwater would be the host rocks of gold mineralization. At Poura, soil contamination in arsenic would come from mine wastes stockpiles stored for many years. Indeed, in the problems of environmental pollution, the main parameters to consider are the source, intensity, extent and vulnerability. If the source (oxidation of mine waste or AMD), the intensity (Igeo and Igeo classes) and extent (contaminated sites) can be established, it is not the same the vulnerability without analyzes e.g. of plants, crops, blood, urine or hair. So, concerning vulnerability, despite the lack of analysis of plants and crops, heavy metals released into the environment through the oxidation of mine wastes can be absorbed by plants. Indeed, several studies mailto:topacademicjournals@gmail.com Academic Journal of Science, Engineering and Technology Vol.8, Issue 3; May - June 2023; ISSN: 2837-2964 Impact Factor: 6.67 1252 Columbia Rd NW, Washington DC, United States https://topjournals.org/index.php/AJSET/index; mail: topacademicjournals@gmail.com 19 | A c a d e m i c J o u r n a l o f S c i e n c e , E n g i n e e r i n g a n d T e c h n o l o g y | https://topjournals.org/index.php/AJSET e.g. Álvarez et al (2003), Huang (2007), Zhang et al (2009), Lar et al (2013), Park and Choi (2013), Kalagbor and Diri (2014) have shown that plants can absorb heavy metals that will be eventually encountered in their fruits, leaves and tubers. In addition, heavy metals and potentially harmful element released by the oxidation of mine wastes can be transported in the Mouhoun River which is the main river in the region. The populations will be contaminated as a result in the consumption of fishes that have ingested these different toxic elements. CONCLUSIONS This study shows that mine wastes stockpiles at Poura, are oxidized in some places, due to their exposure during several years to water and atmospheric agents. This oxidation is the source of acidic pH of surface water or acidic effluents known as acid mine drainage (AMD). This acid mine drainage results in the solubilization of potentially harmful elements (arsenic, cobalt, chromium, copper, lead, zinc and nickel) that are subsequently released into the environment. The index of geo-accumulation (Igeo) and the descriptive classes for increasing Igeo values indicate that arsenic, copper and lead are the most harmful elements. The soil is moderately contaminated (class 2) by arsenic, cobalt, chromium, copper, lead and nickel, then moderately to strongly contaminated (class 3) by arsenic. For mine wastes, moderately contaminated sites (class 2) are due to arsenic, cobalt, chromium, copper, lead, zinc and nickel; moderately to strongly contaminated (class 3) by arsenic copper and lead; strongly contaminated (class 4) by arsenic which appears to be the most polluting element. The source of these elements that cause the phenomenon of contamination would be sulfides and other metallic minerals which constitute the host rocks of the mineralization and are encountered in mine wastes. REFERENCES Álvarez, E. et al. (2003). Heavy metals in the dump of an abandoned mine in Galicia (NW Spain) and in the spontaneously occurring vegetation. The Science of the Total Environment 313, 185-197. ATSDR (2005). ToxGuide for Arsenic, U.S. Department of Health and Human Service. Canadian Environmental Council of Ministers of the Environment (1999): Soil Quality Guidelines for the Protection of Environmental and Human Health, updated 2006. Aubertin, M., Bussière, B., et Bernier L. (2002a). 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