Contamination and risk assessment of heavy metals, and uranium of sediments in two watersheds in Abiete-Toko gold district, Southern Cameroon

Abstract

In this investigation, the level of toxic metals (Cd, Pb, Hg, Cu, Ni, Al, Zn and U) was determined in sediment samples from two watersheds (Kienké and Tchangué) in the Abiete-Toko gold district, southern Cameroon. The potential contamination and toxicity of studied metals was determined by evaluating enrichment factor (EF), geo-accumulation index (Igeo) and ecological risk assessment (ERA). Considering the spatial distribution patterns, metal concentrations were lower than the average shale values, except for Cu and Ni of site 4 in the Kienké watershed and only Ni in the Tchangué watershed. In this study, the EF and Igeo values revealed that sediments were moderately polluted by Ni and Cu and unpolluted by other metals. The evaluation of the ERA based on ecological risk index (RI), ecological risk factor (Er), contamination factor (CF) and pollution load index (PLI) revealed that the sediments from the Abiete-Toko watersheds have significant to very high ecological risk assessment and are generally unpolluted by trace metals and U, except for Ni and Cu. Little quantities of heavy metals with low U levels and distribution were found at the sites close to the vicinity of artisanal mining and peri-urban areas. This proximity reveals that artisanal gold mining activities, agricultural runoff, and other anthropogenic inputs in the study area are probable sources of slight metal contamination. However, the non-use of toxic effluents for gold mining and pesticides for agriculture can be an advantage of the unpolluted status of the watersheds. The physical degradation of the ecosystem through excavations, wells and other stream diversion methods is expanding in the zone. Appropriate measures should be taken by artisans to rehabilitate the gold mining sites, to ensure appropriate treatment of wastewater and non-use of toxic effluents into nearby tributaries.

Contaminated aquatic sediments

“…Although the carcinogenic risk index was ranged from 1.46 * 10 −6 to 232.62 * 10 −6 and target hazard quotient (THQ) was varied from 0.0036 to 1.08, rigorous monitoring of source and overall effective management is necessary to control notorious fate and transport of the above mention metals. Mandeng et al (2019) used enrichment factor (EF), geo-accumulation index (I geo ), ecological risk index (ERI), and pollution load index (PLI) to identify the contamination level and risk potential of sediments after analyzing 13 composite samples from two watersheds, that is, Kienké and Toko contaminated by heavy metals and uranium (U) in Southern-Cameroon where average metal concentrations were within the range of 8,501.08-9,590.01 (Al), 0.099-0.128 (Cd), 5.85-5.976 (Pb), 0.068-0.106 (Hg), , and 0.534-0.78 mg/kg (U). Although the watersheds were moderately enriched by heavy metals and U with very high ER factor, the sites were considered as unpolluted.…”

Mine Waste and Heavy Metal Pollution in Betare-Oya Mining Area (Eastern Cameroon)

“…The volume of this waste rock resulting from the sinking process often depends on the depth at which this level is located. This depth often varies from a few meters to more than ten meters [15,36]. When the depth of the pit becomes significant, the stripping is done in successive steps (Figure 4b) and the different levels of the ground thus stripped are placed on these bearings for easy evacuation.…”

“…Gold mining could also be the cause of soil infertility, as a result of the erosion of the organo-mineral layer. The soils are then destroyed, and therefore not suitable for agriculture ( Figure 4d) [36][37][38].…”

“…Similar results are obtained for average Cr (192.5 mg/kg) and Ni (64 mg/kg) values in soil at Bedobo site (Table 1). Low concentrations of heavy metals and radioactive elements can be linked to leaching of source rocks [16,36,38]. According to the WHO and UNICEF [39], the mean heavy metal concentrations in the Betare-Oya soils and tailings are under the agricultural, residential and industrial limits for environmental health.…”

Characteristics and Assessment of Toxic Metal Contamination in Surface Water and Sediments Near a Uranium Mining Area

“…and radionuclides (e.g., U, Th, Ra, etc.) in mining ecosystems have been widely reported [17][18][19][20]. Radionuclides pollution and toxic metals loading in shallow tailings, discharge water, surface water, groundwater, and paddy soil around the study uranium mining area were found and recognized [21][22][23][24].…”