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.
Highlights
Contamination by trace metals is a serious threat in aquatic systems due to their level of toxicity, abundance, persistence in the environment and subsequent accumulation in aquatic milieu (Bessa et al, 2018; Ekoa Bessa et al, 2018)
The main aim of the present study is to evaluate the levels of trace metals and U in the sediments from the Abiete-Toko watersheds in order to identify their naturally enriched or anthropogenic sources using heavy metal indices as well as to assess the environmental risk of heavy metal in the investigated area
The present study quantified and assessed the natural enrichment or anthropogenic sources, contamination levels and toxicity of some heavy metals and U in sediment samples from two watersheds of the AbieteToko gold complex. It shows that the distribution of these metals in sediments is not uniform over the watersheds and the change in concentration is due to the release of these metals from different anthropogenic sources
Summary
Contamination by trace metals is a serious threat in aquatic systems due to their level of toxicity, abundance, persistence in the environment and subsequent accumulation in aquatic milieu (Bessa et al, 2018; Ekoa Bessa et al, 2018). Nuclear fission in connection with atomic weapons testing and nuclear power generation provides some of the sources of sediment and water contamination, the major part of radionuclides released into the environment will accumulate in either the upper layer of soils or interstitial system of sediments in aquatic systems (Igwe et al, 2005; Carvalho et al, 2014; Xiang et al, 2016; Ma et al, 2019). Once the uranium enters in the organism, it is transferred to extracellular fluids and transported through the blood to other organs
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