Speciation and spatial distribution of trace metals in sediments around gold mining areas in northern Côte

The purpose of this study was to investigate the spatial distribution, possible sources, and potential ecological risks 15 associated with traces metals Cu, Mn and Ni in sediments around gold mine areas in northern Côte d’Ivoire. The 16 sampling was conducted in industrial and artisanal and small-scale gold mining sites in Korhogo and Tengrela. 17 Analysis of variance was performed to ascertain spatial differences. The possible sources of pollution were 18 identified using the enrichment factor, principal component, and hierarchical cluster analysis. Trace metals Cu, Ni 19 and Mn concentrations in sediments did not vary across the stations. The same spatial mapping distribution trend 20 was observed for Ni, while those of Cu and Mn differed among the stations. The geoaccumulation index indicated 21 low to moderate contamination of Cu, Mn and Ni at Korhogo and Tengrela. The results of principal component 22 and hierarchical cluster analysis indicated that Cu, Ni, and Mn were generated both by anthropogenic and natural 23 inputs, which were confirmed by the enrichment factor. The potential ecological risks indicated that Cu, Mn and 24 Ni could pose low risk to organisms at Korhogo and Tengrela. This study provides first trace metals data in 25 sediments across Korhogo and Tengrela gold mine areas. The sequential extraction procedure proposed by the 26 Community Bureau of Reference (BCR) showed that a major portion (between 59.68 to 79.22 %) of Cu, Ni and 27 Mn is highly associated with the residual fraction, showing their low mobility.


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Traces metals are among the most serious pollutants in the aquatic environment and have attracted global 3 indications of mobility, biological availability and potential risks related to metal content in aquatic ecosystems.

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This study aimed to (1) study the spatial distribution of trace metals (Cu, Ni and Mn) in surface sediments; (2) 81 identify the possible sources of pollution using the enrichment factor (EF) and the principal component and 82 hierarchical cluster analyses, (3) assess pollution levels and potential ecological risks associated with these heavy 83 metals using the geoaccumulation index (Igeo), the potential ecological risk factor (Er), the potential ecological

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The savannah district is well known through activities such as livestock, cotton, cashew and food activities (Yapo

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Sampling campaigns took place in 2016 during the dry season. The collection of the sediment samples, 122 digestion, and total metal concentration measurements have been described by Kinimo et al. (2018). A total of 5 123 surface sediment samples (0-5 cm) were collected from each site (Fig.1). In order to take the local variability into 124 account, each sample (300 g) was made of five subsamples collected using a Van Veen stainless steel grab (with 125 an area of 0.02 m 2 ) (Saleem et al.2015). Without emptying the grab, a sample was taken from the center with a 126 polyethylene spoon (acid washed) to avoid contamination by the metallic parts of the dredge. Samples were then 127 put into ice bags and transported to the laboratory, stored in a deep-freeze unit before the drying procedure.

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Trace metals (Fe, Al, Cu, Mn, and Ni) were measured using an inductively coupled plasma-optical emission 142 spectrometer (ICP OES Icap 6200, Thermo Fisher, Cambridge, UK). Three replicates of each sample analysed 143 presented an error that was within 6%. Accuracy of the analytical procedures were evaluated through the analysis 144 of the certified reference material CRM CNS 301-04-050 (Sigma-Aldrich; Missouri, U.S.A) for freshwater 145 sediment. The measured concentrations fell within the range of certified values (Table 1) (Kinimo et al.2018).

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The pH of the sediments was measured with a pH meter (HANNA HI.9828). For determination of pH, 10 g of the 147 air-dried sample was mixed with 25 mL distilled water (sediment: water at a ratio of 1:2.5) and was stirred for 1 148 hour (Islam et al.2000;Halim et al.2013). The mixture was allowed to stand for 30 min for allowing it to settle.

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The slurry was decanted and pH was measured with a calibrated pH meter.

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showed that Fe (92 %) was relatively present in the residual fraction relative to Al (87 %

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Following equations were used to calculate Er and IR (Hakanson 1980): Where Ci is the average content for metal i in the sediment, C0 is the background concentration of metal in the

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The distributions mapping trend of Ni in artisanal mining areas at Korhogo were the same indicated by the red and concentration (60 ± 11 μg/g) was found at Tongon.

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The spatial distribution mapping of Ni in the sediments of Tengrela was almost similar in all stations except the 299 stations T10 and T5 which correspond to the lowest values (2 -13 µg/g, red and orange colours). However, no 300 spatial variability (p < 0.05) of Ni was observed at Tengrela.

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One-way ANOVA analysis (p < 0.05) showed no significant difference between artisanal sites at Korhogo and 302 artisanal site at Tengrela. Nonetheless, the highest concentration (25 ± 8 μg/g) was found at Taoura.       The results of the ecological risk indices (Er) and (IR) for all sampling areas are shown in Table 3. It

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showed that all sampling areas were considered to have a very low level of ecological risk (Er< 40 and IR < 80).

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The highest IR was found in Tongon industrial zone sediments, and the lowest IRs was reported in Tengrela 342 sediments.      392 Table 6 gives

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For comparison purposes, the trace metals concentrations in this study and in some other mining areas are 447 summarized in Table 5. Although the different geological settings and difference in analytical methods may 448 influence metal concentrations in sediments, it can be seen that the environmental contamination with Cu, Mn and

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Ni by mining activities found in the present study is consistent with previous investigations in Ghana (Klubi et

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The results of PCA also revealed that sediment texture is an important carrier for Ni both through sand and silt and 490 clay fractions. However further studies should be conducted to better understand high association of Ni with the 491 sands revealed by PCA, but not by AHC in the sediments.

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The grouping of pH, Cu and Ni on factor 3 suggests that pH drives the distribution of Cu and Ni. The pH has an 493 impact on the mobility and solubility of metals in sediments. In acidic conditions, the mobility of trace metal is 494 pronounced, while high pH leads to the metal adsorption in sediment (Halim et al.2013

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The results indicated that the potential risk was low at all sites, where the IR values were below 80. Based 514 on the IR values (Table 3), the trend of the potential ecological risk of trace metals in surface sediments was:

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Tongon > Bevogo >Taoura > Badenou > Kanakono > Sissingue. This indicates that Cu, Ni and Mn in the sediments 516 of the Tongon industrial areas could pose higher risks than those in the artisanal areas. Therefore, the monitoring 517 of the Tongon area should be stepped up to prevent pollution of drinking water sources in the future. Local 518 communities could be exposed through pathways such as consumption of contaminated vegetables, fish and fruits.

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Therefore, bioaccumulation studies are needed to understand human potential health risks.

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Result from RAC show that trace metals present a low toxicity risk to the environment and biota in the areas