“…The investigated sites show oxidizing environments, with pH values ranging from 5.3 to 6.1. Such conditions are suitable for solubility and mobility of metals in the soil, especially Pb, Cr, Cd and Hg [59][60][61][62]. It should be noted that the Pawara area has a savanna climate with two seasons.…”
Section: Heavy Metal Concentration In the Pawara Soilsmentioning
confidence: 99%
“…Site B shows the highest Pb concentration probably due to the use of big machinery in mining operations leading to a deeper and larger excavation of the soil right to the bedrock; thus, exposing a larger waste material for weathering and leaching to take place. The authors of [62] indicated that areas around abandoned mines commonly show a high pollution index. In the Pawara area, the pollution load index values are exceptionally higher.…”
Section: Heavy Metal Concentration In the Pawara Soilsmentioning
Pawara area is a mining district in the eastern region of Cameroon. Mining in the area is generally artisanal and semi-mechanized, practiced by the local miners and immigrants from neighboring African countries and China. The lack of strict regulations and control of mining activities permits the miners to use illegal substances, especially Hg in gold separation. These expose the area to toxic and heavy metals pollution. This study highlights the source of heavy metals concentration in the Pawara soils and the potential adverse effects of Hg on gold separation to the environment and health. Three mining sites and one control site were investigated, namely Site A, Site B and Site C. The control Site 0 (background) is an area where no mining and agricultural activities have taken place. Soil samples were collected at depth of 20 cm, with six from each site (24 samples). Samples were analyzed for Al, Cd, Cr, Cu, Fe, Hg, Pb, Cd and Zn content using atomic absorption spectrophotometry in a graphite furnace. The metals, except for Fe, show high values for all three sites exceeding the background levels in the soils. Hg shows the highest concentration on Site A with a value of 1590 mg kg−1. Pb is highest on Site B with a concentration of 12,274 mg kg−1. The contamination degree was assessed with the help of contamination indices (Igeo—index of geo-accumulation; PLI—pollution load index; RI—potential ecological risk; Eri—ecological risk; Pi—single pollution index; CF—contamination factor) and all parameters show a high degree of contamination on all three sites compared to the control site. Hg, Pb, Cd, Cr and Cu as single pollutants show the highest ecological risk on Site A and Site B where intense mining is taking place. The absence of industrial and large-scale agricultural activities in the Pawara area, the nonexistence of contaminants on the control site and the presence of contaminants on Site C where farming is high and mining is low jointly show that the discharge of mine wastes onto the soils and stream channels are the main source of contaminants and potential pollutants of the Pawara ecological environment.
“…The investigated sites show oxidizing environments, with pH values ranging from 5.3 to 6.1. Such conditions are suitable for solubility and mobility of metals in the soil, especially Pb, Cr, Cd and Hg [59][60][61][62]. It should be noted that the Pawara area has a savanna climate with two seasons.…”
Section: Heavy Metal Concentration In the Pawara Soilsmentioning
confidence: 99%
“…Site B shows the highest Pb concentration probably due to the use of big machinery in mining operations leading to a deeper and larger excavation of the soil right to the bedrock; thus, exposing a larger waste material for weathering and leaching to take place. The authors of [62] indicated that areas around abandoned mines commonly show a high pollution index. In the Pawara area, the pollution load index values are exceptionally higher.…”
Section: Heavy Metal Concentration In the Pawara Soilsmentioning
Pawara area is a mining district in the eastern region of Cameroon. Mining in the area is generally artisanal and semi-mechanized, practiced by the local miners and immigrants from neighboring African countries and China. The lack of strict regulations and control of mining activities permits the miners to use illegal substances, especially Hg in gold separation. These expose the area to toxic and heavy metals pollution. This study highlights the source of heavy metals concentration in the Pawara soils and the potential adverse effects of Hg on gold separation to the environment and health. Three mining sites and one control site were investigated, namely Site A, Site B and Site C. The control Site 0 (background) is an area where no mining and agricultural activities have taken place. Soil samples were collected at depth of 20 cm, with six from each site (24 samples). Samples were analyzed for Al, Cd, Cr, Cu, Fe, Hg, Pb, Cd and Zn content using atomic absorption spectrophotometry in a graphite furnace. The metals, except for Fe, show high values for all three sites exceeding the background levels in the soils. Hg shows the highest concentration on Site A with a value of 1590 mg kg−1. Pb is highest on Site B with a concentration of 12,274 mg kg−1. The contamination degree was assessed with the help of contamination indices (Igeo—index of geo-accumulation; PLI—pollution load index; RI—potential ecological risk; Eri—ecological risk; Pi—single pollution index; CF—contamination factor) and all parameters show a high degree of contamination on all three sites compared to the control site. Hg, Pb, Cd, Cr and Cu as single pollutants show the highest ecological risk on Site A and Site B where intense mining is taking place. The absence of industrial and large-scale agricultural activities in the Pawara area, the nonexistence of contaminants on the control site and the presence of contaminants on Site C where farming is high and mining is low jointly show that the discharge of mine wastes onto the soils and stream channels are the main source of contaminants and potential pollutants of the Pawara ecological environment.
“…This analytical approach helps identify two sources of surface water pollution: the fixed anthropic pollution source, represented by direct mining discharge into surface waters following extractive activities enriched with metallic elements (Pb, Cd, Cr). The second source is diffusive anthropogenic pollution, corresponding to a likely mobile source linked to river sediments with a high geo-accumulation of harmful elements, such as metallic elements, considered a secondary source of pollution [ 53 ]. Fig.…”
“…Statistical analysis also showed that there was a positive correlation between Fe/Mn with the heavy metals (Table ). This fraction of the heavy metals may release to groundwater and eventually to river water in response to the changes of environmental conditions, such as redox condition, during and after river restoration. ,, The association of the heavy metals with residual fraction (mineral structures, F5) was another important fraction in both river-bed and river-side sediments for As, Cr, Co, Ni, Pb, and Zn (Figure ). In the river-side sediments, the structural fraction of these heavy metals occupied nearly 50% or more of the total heavy-metal concentrations in the sediments (Figure ).…”
This study investigated the accumulation and release risks of heavy metals As, Cd, Co, Cr, Cu, Ni, Pb, and Zn in representative contaminated river-bed and river-side sediments from a groundwater−river water interaction zone (GRIZ) currently under restoration. The results revealed different accumulation and release risk behaviors of the heavy metals in the river-bed and river-side sediments that are a complex function of contamination history, local hydrogeological and chemical properties, and metal-specific chemistry. In the river-bed sediments, the concentrations of all the metals first increased and then decreased with depth, reflecting the histories of metal-containing wastewater discharges and sedimentation of metal-containing particles in river water. In the river-side sediments, the concentrations of As, Cd, Co, and Pb were higher in finer grain materials, while those of Cr, Cu, Ni, and Zn were higher in coarser materials, reflecting the combined effects of stronger sorption capacity in finer materials and preferential water flow in coarser materials that carried metals from contaminated river. Speciation analysis indicated that Cd was mainly controlled by surface complexation, Cu was mainly controlled in complexation with organics, and other metals dominantly associated with iron-oxide and structural fractions with a higher structural fraction in the river-side sediments. Risk analysis indicated that release potentials were metal-specific, following an order of Cd > Cu > Ni > Cr > Co > Zn > As > Pb. The results have a strong implication for understanding heavy-metal distribution and accumulation in GRIZ sediments and for the management of contaminated sediments during and after watershed restoration.
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