1. Introduction

JEP

Journal of Environmental Protection

2152-2197

Scientific Research Publishing

10.4236/jep.2022.139039

JEP-119953

Articles

Earth&Environmental Sciences

Exposure of Mercury from Gold Ming Area: A Case Study in Tendo and Aby Lagoon in Côte d’Ivoire

Stéphane

Jean Claon

¹Serge

Kouakou Kouassi

²^*Séka

Arsène M’bassidje

³Laurent

Kipré Séri

⁴Luc

Kouakou Kouadio

⁵Joseph

Allico Djaman

⁴

Water Quality Control and Analysis Laboratory, National Drinking Water Office, Abidjan, C&ocirc;te d’Ivoire

Department of Medical and Fundamental Biochemistry, Institut Pasteur of C&ocirc;te d’Ivoire, Abidjan, C&ocirc;te d’Ivoire

Environmental Sciences Laboratory, Nanguy Abrogoua University, Abidjan, C&ocirc;te d’Ivoire

Biology and Health Laboratory, Félix Houphou&euml;t-Boigny University, Abidjan, C&ocirc;te d’Ivoire

Public Health and Hydrology Laboratory, Félix Houphou&euml;t-Boigny University, Abidjan, C&ocirc;te d’Ivoire

08092022

130961362723, July 202218, September 2022 21, September 2022

2014

This work is licensed under the Creative Commons Attribution-NonCommercial International License (CC BY-NC).http://creativecommons.org/licenses/by-nc/4.0/

Lagoons of West African countries are seriously threatened by rapid artisanal and small-scale gold mining (ASGM) that exposes lagoons to mercury pollution. In this study, the mercury level in the sediments of the Tendo and Aby lagoons in Côte d’Ivoire had been evaluated. A total of 87 samples from 25 stations located on Tendo and Aby lagoons were analyzed by atomic fluorescence spectrometry. The mean Hg concentrations obtained in the sediments of Tendo and Aby lagoons were 0.89 ± 0.26 mg⋅kg ^-1 and 0.70 ± 0.18 mg⋅kg ^-1, respectively. Hg concentrations evaluated in the bays of Tendo and Aby during the dry season were 1.38 ± 0.45 mg⋅kg ^-1 and 1.07 ± 0.31 mg⋅kg ^-1, respectively. The minimum and maximum total Hg concentrations in the sediments from 25 stations were 0.04 and 3.56 mg⋅kg ^-1, respectively. Mercury contamination in lagoons during ASGM poses risks of pollution for the lagoon ecosystem and also poses health risks for the population living near these lagoons.

ASGM Mercury Sediments Côte d’Ivoire Pollution

1. Introduction

Mercury (Hg) is a recognized ubiquitous contaminant in aquatic ecosystems [1] [2]. Methylmercury (MeHg) is the Hg species of particular interest due to its propensity to bioaccumulate and potentiality to cause health problems to humans and wildlife when exposed at high levels [3]. Hg pollution is a worldwide problem that has got severed during the past few decades because of its toxicity, extensive sources, non-biodegradable characteristics, and capacity to accumulate in aquatic environments [4] [5].

More than 99% of the heavy metals can be stored in the sediments indifferently [6] [7]. Sediments constitute a habitat for many aquatic organisms and often serve as effective reservoirs for pollutants [8] [9]. These toxic elements can be found in the water during favorable environmental conditions and degrade the quality of the water [10] [11]. Recent studies showed that mercury (Hg) released into the atmosphere from artisanal and small-scale gold (Au) mining (ASGM; approximately 880 Mg/year) activities is one of the primary emissions to the atmosphere [5]. It currently accounts for an estimated 37% of global Hg emissions into the atmosphere [12] [13]. Indeed, the amalgam is heated to vaporize the mercury and separate the gold. In “open burning”, all of the mercury vapour is emitted into the air [14]. After elemental mercury is vaporized, it can enter into aquatic ecosystems, where it may be biomethylated by bacteria into an organic form, methylmercury [15]. Fish and macroinvertebrates in aquatic ecosystems accumulate methylmercury in their tissues, with increasing concentrations in higher trophic levels [16].

The sediments were also contaminated by the activities of ASGM with up to 78% of THg of anthropogenic origin. This anthropogenic Hg, more than half (66% - 74%) comes from the liquid Hg (0) which is released during ASGM [17]. Gold miners usually add larger amounts of mercury to ensure that all available gold is amalgamated. Mercury is generally used in ASGM without any type of capture system to reduce chemical releases into the environment including soil and water [18]. The remaining anthropogenic Hg was from ASGM-induced erosion of Hg-rich soils in the river [17].

ASGM occurs in over 70 developing countries [13]. It is estimated to employ 13 million people globally, and an additional 80 - 100 million people are directly reliant upon or impacted by ASGM [19] [20]. This concerns most of the West African countries [21]. A recent investigation conducted in West Africa suggested in general that artisanal-mining activities are a source of trace metals to wetlands, with negative consequences on human health [22] [23].

In Côte d’Ivoire, ASGM has been increasingly developed since the outbreak of the sociopolitical crisis of September 19, 2002. Although ASGM attracts rural populations through the incomes it provides, however, documentation of its environmental consequences remains more fragmented. A few studies have investigated metal contaminations in lagoons during gold-mining activities [21] [23].

The aim of this study was to determine accumulations of mercury in the sediments during ASGM activities along Aby and Tendo lagoons in Côte d’Ivoire. Indeed, Aby and Tendo lagoons are under the influence of the Bia and Tanoe rivers, respectively, and these rivers constitute many ASGM industries. However, ASGM activities that have gradually developed over the years around the rivers Bia and Tanoe fear that these rivers will serve as a vector of pollution for heavy metals, including mercury from gold-mining areas to the estuary of Aby and Tendo lagoons. Assessment of the exposure of Aby and Tendo lagoon sediments to pollutants resulting directly or indirectly from gold-mining activities is a relevant indicator of this pollution.

2. Materials and Methods2.1. Study Areas

Aby lagoon (5˚05'N-5˚22'N and 3˚16'W-2˚55'W) is located in West Africa, on the coast of the Gulf of Guinea between Côte d’Ivoire and Ghana. Aby lagoon covers 24.5 km and 56 km, respectively, from east to west with an estimated area of 420 km², while the Tendo lagoon is formed by the band from west to east and has a width of about 20 km. Aby and Tendo lagoons are located in an equatorial climate region with a climate composed of 4 successive seasons: 2 rainy seasons from May to July and from October to November and 2 dry seasons from August to September and from December to March/April [24].

We indicated successively from north to south for Aby north and south lagoons, and from west to east for Tendo (Figure 1). The 2 north and south Aby lagoons will simply be called Aby throughout this study. Several towns, villages,

and seasonal fishing camps exist around the Aby and Tendo lagoons. The population estimated to 30,000 [25] are living around Aby and Tendo lagoons that constitute and provide a real source of food and living for these populations through fishing activities. Aby and Tendo lagoons are under the influence, respectively, of the Bia river whose watershed is estimated at about 10,000 km² with an average flow estimated at 300 m³/s during rainy floods and the Tanoe river whose watershed is at about 16,074 km² with an average flow estimated at 142 m³/s [26]. These rivers are home to numerous gold deposits that have gradually developed over the years. Thus, artisanal and industrial gold mining around the Bia and Tanoe rivers fears that these rivers will serve as a pollution vector for heavy metals, especially mercury from gold-mining areas to its outlets in Aby and Tendo lagoons. Assessment of Aby and Tendo lagoon sediments’ exposure to pollutants resulting directly or indirectly from gold-mining activities, namely, mercury, is a relevant indicator of this pollution. In addition to spatial, bathymetric, and hydrological variations, Aby and Tendo lagoons were influenced by the Bia and Tanoe rivers, respectively. Aby and Tendo lagoons are the estuaries of the Bia and Tanoe rivers, respectively.

2.2. Sampling Method

The study was conducted on the Aby and Tendo lagoons during the rainy and dry seasons. Two sampling periods were carried out during the rainy season from May to July and from October to November and two others during the dry season from August to September and from December to March/April based on the climatic variations.

Sampling was carried out on four sites: Aby lagoon where in samples A1 and A2 correspond to the estuary of Bia river, Tendo lagoon channel, bay of Tendo lagoon, and estuary of Tanoe river. Sediment samples of Aby and Tendo lagoons were sampled at stations preselected by the research team according to spatial, bathymetric, and hydrological variations. The sediment samples were collected in borosilicate glass vials (50 mL), previously washed in order to avoid adsorption and desorption reactions of the vessel walls. Wearing polyethylene gloves was adopted in all washing steps and while using equipment. Sampling equipment and sample containers were cleaned and kept clean according to the protocol described by Quémerais et al. [27]. A total of 87 sediment samples (0 - 5 cm) from 25 stations located on Aby and Tendo lagoons were collected (Table 1).

2.3. Sample Preparation and ICP Analysis

Samples were stored in polyethylene bags after being perfectly homogenized and kept in the dark in a cooler. Sediment samples were transported to the laboratory 24 hours after collection. As soon as it reached the laboratory, the sediments were immediately dried in an oven at 40˚C until a constant weight was obtained and then sieved. The fraction inferior to 63 μm was collected in hermetic polyethylene

Table 1 Distribution of sampling points and locations on Aby and Tendo lagoon

Sites	n	Stations	GPS coordinates	Location
Aby lagoon	9	A1	05˚21' (15.6˚)N 003˚12' 04.9˚)W	Bia river
		A2	05˚20’ (59.5˚)N 003˚1' (08.6˚)W	Estuary of Bia
		A3	05˚20' (00.8˚)N 003˚15' (01.7˚)W	Opposite side of A3
		A4	05˚20' (06.8˚)N 003˚10' (01.9˚)W	Estuary of Eholie (village of Eboué)
		A5	05˚17' (31.8˚)N 003˚15' (07.0˚)W	Channel of Adiaké
		A6	05˚17’ (32.0˚)N 003˚11’ (02.9˚)W	Abiaty
		A7	05˚15' (06.0˚)N 003˚15' (00.0˚)W	Ettueboué
		A8	05˚12' (31.1˚)N 003˚15' (00.1˚)W	Proximity switches to sea
		A9	05˚10' (00.0˚)N 003˚10' (00.0˚)W	Akounougbé
Tendo lagoon channel	7	TC1	05˚07' (42.6˚)N 002˚57' (08.6˚)W	Crest of Frambo
		TC2	05˚06’ (57.6˚)N 002˚57’ (41.4˚)W	Channel of N’zobenou
		TC3	05˚07' (26.8˚)N 003˚00' (36.8˚)W	Channel of Assué
		TC4	05˚07' (33.6˚)N 003˚02' (29.6˚)W	Channel of Tiapoum
		TC5	05˚08’ (20.0˚)N 003˚05’ (00.0˚)W	Eboko
		TC6	05˚08' (00.5˚)N 003˚07' (36.0˚)W	Channel of Eboinda
		TC7	05˚07' (42.6˚)N 002˚57' (08.6˚)W	Toward Ehy lagoon
Bay of Tendo lagoon	4	TB1	05˚07' (46.7˚)N 002˚59' (55.6˚)W	Bay of Mohoua village
		TB2	05˚08' (11.5˚)N 003˚01’ (42.8˚)W	Bay of Tiapoum village
		TB3	05˚09' (06.1˚)N 003˚03' (36.8˚)W	Bay of N’Guiémé village
		TB4	05˚08' (54.7˚)N 003˚06' (35.6˚)W	Bay of Eboinda village
Estuaries of river Tanoé	5	E1	05˚06' (16.3˚)N 002˚54' (19.3˚)W	Tanoé river (south of Ghana’s border)
		E2	05˚05' (55.2˚)N 002˚54' (34.7˚)W	South-side estuary extension 1
		E3	05˚06' (32.4˚)N 002˚55' (03.5˚)W	South-side estuary extension 2
		E4	05˚06' (17.3˚)N 002˚55' (55.6˚)W	Connection to the channel
		E5	05˚07' (19.5˚)N 002˚56' (01.4˚)W	Tanoé river (north of Ghana’s border)

tubes and stored in a clean, dry place. The mineralization was made in Montpellier in the Department of Environmental Sciences and Public Health by the faculty of pharmaceutical sciences [28] [29].

The microwave mineralization method (301 Prolabo^® and Microdigest Prolabo^®) was used [30]. Sediment samples were taken up in a nitric acid and hydrogen peroxide (HNO₃ and H₂O₂) mixture according to the protocol described by Tseng et al. [31]. About 0.25 g of dried, homogenized sediment was weighed into a container added with 8 mL of concentrated nitric acid, and the container was closed using a reflux column. A plastic seal was placed between the reflux column and the container to avoid evaporation. The tube and its contents were subjected to the first phase of microwave heating at 20 W for 5 minutes; after cooling for 5 minutes, 2 mL of H₂O₂ were added; and they were subjected to the second heating phase at 20 W for 5 minutes. Finally, the mineralization was diluted with Milli-Q water in a 50 ± 0.06 mL borosilicate glass volumetric flask and then stored in the refrigerator in a polyethylene tube until analysis.

Analyses were performed on the PerkinElmer^® ICP/MS Elan 6000 with Baffled Quartz Cyclonic Spray chamber. The methodology described by US EPA was used for instrument optimization and the analytical procedure [32]. The analysis was carried out with an RF power of 1100 W, a plasma gas flow of 15 L/min, an auxiliary gas flow of 1.2 L/min, and with nebulizer gas flow of 0.96 L/min. Peak scanning mode and an integration time are 1625.0 ms. Dwell time was fixed at 50 ms and 3 replicates were performed per sample.

2.4. Statistical Analysis

The statistical analysis of the data was carried out using the GraphPad Prism 5.0 software. Quantitative variables are summarized as the mean value and standard deviation in the tables and figures. For statistical analysis, quantitative data were analyzed using the Mann-Whitney U test, according to their distribution evaluated by the Shapiro-Wilk test. All tests were two-tailed and viewed as indicating statistical significance at a p-value of less than 0.05.

3. Results and Discussions

A total of 87 samples were analyzed in this study: 16 from Tanoe river, 23 from the channel of Tendo lagoon, 16 from bays of Tendo, and 32 from Aby north lagoon.

3.1. Mercury Accumulation in Selected Sediments

The highest concentrations of mercury were obtained in the bays of Tendo with an average of 0.89 ± 0.26 mg·kg⁻¹ and extremes ranging from 0.23 to 3.56 mg·kg⁻¹ and in Aby with an average of 0.70 ± 0.18 mg·kg⁻¹ and extremes ranging from 0.07 to 4.16 mg·kg⁻¹ (Table 2).

As shown in Table 2, sediment bays of Tendo and Aby north lagoons were the most contaminated. The results of the bays in this study were significantly higher than that of Bietri Bay. Indeed, in sediments of Bietri Bay, Hg ranged from 0.35 to 1.33 μg·kg⁻¹ [33]. The Hg concentrations in these sediments were similar to those reported by Kehrig et al. [34] (ranged from 0.50 to 2.38 mg·kg⁻¹). According to Veeck et al. [35], mercury accumulation was reported in bays, and sediment composition in these bays is strongly influenced by fluvial inputs of mercury.

3.2. Mercury Accumulation during Seasons

In this study, two sediment collections were carried out during the rainy season (RS) and two others during the dry season (DS). RS was characterized by a significant (p < 0.05) mercury accumulation in bays of Tendo (0.40 ± 0.08 mg·kg⁻¹) with extremes between 0.23 and 0.94 mg·kg⁻¹ compared with other sampling sites. DS was characterized by significant (p < 0.05) mercury accumulation in bays of Tendo (1.38 ± 0.45 mg·kg⁻¹) with concentrations ranging from 0.30 to 3.56 mg·kg⁻¹ and in the Aby lagoon (1.04 ± 0.31 mg·kg⁻¹) with extremes ranging from 0.13 to 4.16 mg·kg⁻¹ compared with other sampling sites. However, Hg concentrations were significantly elevated (p < 0.05) in the dry season than the rainy season at all sampling sites as shown in Figure 2, with high rates at the bays of Tendo and Aby, precisely during the first dry season (DS1) compared with the second dry season (DS2) (Table 3 and Table 4). The results of this study were higher than those of Kouamenan et al. [36] in the mainland (0.44 ± 0.19 mg·kg⁻¹) and maritime (0.39 ± 0.13 mg·kg⁻¹) sediments of the Ebrié lagoon

Table 2 Mean sediment Hg by site

Sites	Tanoe river	Channel of Tendo	Bays of Tendo	Aby
n	16	23	16	32
Mean ( mg·kg⁻¹)	0.35	0.44	0.89	0.70
Median	0.27	0.30	0.40	0.31
Min.-Max.	0.04 - 0.96	0.10 - 1.50	0.23 - 3.56	0.07 - 4.16
Standard Deviation	0.05	0.08	0.26	0.18

Table 3 Hg concentrations between RS1/RS2 for different sites of Tanoe river, Tendo lagoon, and Aby lagoon

Sites		RS1	RS2	p-value
Tanoe river	Mean ± SD	0.18 ± 0.02	0.30 ± 0.03	0.04
	Median	0.19	0.27
	Min.-Max.	0.14 - 0.22	0.27 - 0.43
Channel of Tendo	Mean ± SD	0.21 ± 0.04	0.35 ± 0.06	0.23
	Median	0.20	0.30
	Min.-Max.	0.10 - 0.38	0.26 - 0.60
Bays of Tendo	Mean ± SD	0.36 ± 0.02	0.43 ± 0.17	0.69
	Median	0.36	0.28
	Min.-Max.	0.31 - 0.42	0.23 - 0.94
Aby	Mean ± SD	0.27 ± 0.09	0.29 ± 0.05	0.85
	Median	0.19	0.26
	Min.-Max.	0.08 - 0.59	0.07 - 0.50

Note: RS1—First Rainy Season, RS2—Second Rainy Season.

in Côte d’Ivoire during the dry season. Like Tomiyasu et al. [37], a difference was observed in mercury concentrations between the rainy and dry seasons in this study. Koffi et al. [33] also reported higher Hg mean concentrations in the dry season. In addition, the concentrations of mercury in the sediments of the study areas exceeded the standard concentration levels (Hg = 0.04 mg·kg⁻¹) as recommended by INERIS [38]. This high level of Hg in bays could be explained by the fact that in the rainy season, there was a greater distribution of Hg, while in the dry season, the predominant process was the remobilization of Hg due to

Table 4 Hg concentrations between DS1/DS2 for different sites of Tanoe river, Tendo lagoon, and Aby lagoon

Sites		DS 1	DS2	p-value
Tanoe river	Mean ± SD	0.55 ± 0.12	0.28 ± 0.04	0.061
	Median	0.47	0.26
	Min.-Max.	0.40 - 0.96	0.22 - 0.43
Channel of Tendo	Mean ± SD	0.61 ± 0.18	0.58 ± 0.20	0.924
	Median	0.48	0.47
	Min.-Max.	0.13 - 1.25	0.13 - 1.50
Bays of Tendo	Mean ± SD	2.29 ± 0.63	0.46 ± 0.07	0.028
	Median	2.53	0.47
	Min.-Max.	0.54 - 3.56	0.30 - 0.59
Aby	Mean ± SD	1.77 ± 0.50	0.37 ± 0.07	0.018
	Median	1.68	0.28
	Min.-Max.	0.13 - 4.16	0.19 - 0.70

Note: DS1—First Dry Season, DS2—Second Dry Season.

the resuspension of bottom sediments [39]. Tendo and Aby lagoons are the estuaries of the Tanoe and Bia rivers, respectively. Mirlean et al. [40] reported concentrations of 0.02 - 17.84 mg·kg⁻¹ in sediments of the Patos estuarine lagoon in southern Brazil. The Tendo and Aby lagoons receive freshwater from the Bia and the Tanoé rivers, respectively. During the rainy season, these rivers are home to numerous gold deposits that have gradually developed over the years. Thus, artisanal gold mining around the Bia and Tanoe rivers fears that these rivers will serve as a pollution vector for heavy metals, especially mercury from gold-mining areas to its outlet in lagoons Aby and Tendo. Moreover, the Bia river sampling site was downstream of mining activities in Ghana [41] [42], and the samples in the other locations were all near commercial or artisanal gold-mining activities. Moreover, estuaries are the meeting place of saltwater from the sea and freshwater from rivers and are dynamic environments characterized by large fluctuations in environmental conditions [43]. The mercury is then transferred from lower to higher trophic levels, from plankton to fish [44], which consumption is the main source of exposure to mercury (Hg) through diet in humans [45]. The health risks associated with increased Hg levels in reservoir fish, which impact communities that rely on fish as a traditional food [46].

3.3. Spatial Distribution of Mercury

A wide range of Hg levels were captured in estuarine sediments with concentrations varying across regions and between sites and subsites [47]. As shown in Figure 3, during the DS1, all sites in the bay of Tendo exhibited the highest concentrations of mercury. However, no spatial evolution of Hg in the sediments could be observed

between sites TB1 (close to the outlet of the river) and TB4 (near the inflow to the sea). Site TB2 was an exception to this evolution because unlike the other bays, it was the outlet of a tributary of the Tendo lagoon; the sedimentation could have been disrupted. Moreover, mercury was accumulated along the Aby lagoon, as well as at the mouth of the Bia river during the DS1 with high concentrations at Abiaty (A6) and Ettueboué (A7). These two sampling points are located in the central part of the lake that constitutes the deepest region, so the removal of Hg may be more difficult [39]. In the DS1, Hg concentrations in the sediments of the Aby north lagoon showed a positive gradient at the Bia river estuary where it runs to the sea. This phenomenon was not observed in other sampling operations (DS2, RS1, and RS2). The distribution pattern of Hg in the bottom sediment demonstrates that an expansion of the area occurs in relation to the area of distribution of Hg in the dry season [39]. Bełdowski et al. [48] suggested that despite the decrease in mercury emissions to the environment in recent years, local weather conditions intensified by climate change seriously affect the bioavailability of past mercury deposits in coastal sediments. Indeed, global mineralization of the waters of the Aby lagoon caused by significant evaporation due to high temperatures during the dry season [22] [49] could explain this accumulation of mercury. Temperatures at all sites in the Aby lagoon are higher in the dry season (29˚C - 31˚C) than in the rainy season (25˚C - 27˚C) [50] [51]. Indeed, physic-chemical parameters such as temperature (T), pH, DO, salinity, conductivity (EC), total suspended solids (TSS) and total phosphorus (TP) in surface water, AVS and TOC in sediments are important factors affecting the concentrations, migration and transformation of heavy metals in rivers [52].

This accumulation of mercury could also be due to the limited exchanges between the lagoon and the sea due to the shrinkage of the Assinie pass over time [50] [51].

4. Conclusion

This study showed mercury accumulation in sediments of Aby north and Tendo lagoons. It increases in the dry season, particularly in the Aby north lagoon and in the bays of the Tendo lagoon, where its distribution in the sediments was subject to spatial variations. In this study, sediment concentrations of Hg were higher than normal with some contaminated sites. The risk to the preservation of the Aby lagoon ecosystem linked to the presence of Hg in the sediments is not negligible. The highest levels of Hg found in sediments were mainly due to the anthropogenic input around these lagoons.

Acknowledgements

This work was supported by funding from the French Development Agency. We would like to thank Montpellier and Pau and Pays de l’Adour teams for supervising this work.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

Cite this paper

Claon, S.J., Kouassi, S.K., Séka, A.M.,Séri, L.K., Kouadio, L.K. and Djaman, J.A. (2022) Exposure of Mercury from Gold Ming Area: A Case Study in Tendo and Aby Lagoon in Côte d’Ivoire. Journal of Environmental Protection, 13, 613-627. https://doi.org/10.4236/jep.2022.139039

References1

Guédron, S. and Acha, D. (2021) Mercury and Methylmercury Contamination of Terrestrial and Aquatic Ecosystems. Applied Sciences, 11, Article No. 4807. https://doi.org/10.3390/app11114807

Mergler, D. (2021) Ecosystem Approaches to Mercury and Human Health: A Way toward the Future. Ambio, 50, 527-531. https://doi.org/10.1007/s13280-020-01455-0

Chen, C.Y., Driscoll, C.T., Lambert, K.F., Mason, R., Rardin, L., Serrell, N. and Sunderland, E. (2012) Marine Mercury Fate: From Sources to Seafood Consumers. Environmental Research, 119, 1-2. https://doi.org/10.1016/j.envres.2012.10.001

Kocman, D., Wilson, S.J., Amos, H.M., Telmer, K., Steenhuisen, F., Sunderland, E., Mason, R., Outridge, P. and Horvat, M. (2017) Toward an Assessment of the Global Inventory of Present-Day Mercury Releases to Freshwater Environments. International Journal of Environmental Research and Public Health, 14, Article No. 138. https://doi.org/10.3390/ijerph14020138

Obrist, D., Kirk, J.L., Zhang, L., Sunderland, E.M., Jiskra, M. and Selin, N.E. (2018) A Review of Global Environmental Mercury Processes in Response to Human and Natural Perturbations: Changes of Emissions, Climate, and Land Use. Ambio, 47, 116-140. https://doi.org/10.1007/s13280-017-1004-9

Salomons, W. (1995) Long-Term Strategies for Handling Contaminated Sites and Large-Scale Areas. In: Salomons, W. and Stigliani, W.M., Eds., Biogeodynamics of Pollutants in Soils and Sediments, Springer, Berlin, Heidelberg, 1-30. https://doi.org/10.1007/978-3-642-79418-6_1

Hossain, M.S., Ahmed, M.K., Liyana, E., Hossain, M.S., Jolly, Y.N., Kabir, M.J., Akter, S. and Rahman, M.S. (2021) A Case Study on Metal Contamination in Water and Sediment Near a Coal Thermal Power Plant on the Eastern Coast of Bangladesh. Environments, 8, Article No. 108. https://doi.org/10.3390/environments8100108

Zan, F., Huo, S., Zhang, J., Zhang, L., Xi, B. and Zhang, L. (2014) Arsenic Fractionation and Contamination Assessment in Sediments of Thirteen Lakes from the East Plain and Yungui Plateau Ecoregions, China. Journal of Environmental Sciences (China), 26, 1977-1984. https://doi.org/10.1016/j.jes.2014.07.010

Lintern, A., Leahy, P., Deletic, A., Heijnis, H., Zawadzki, A., Gadd, P. and McCarthy, D. (2018). Uncertainties in Historical Pollution Data from Sedimentary Records from an Australian Urban Floodplain Lake. Journal of Hydrology, 560, 560-571. https://doi.org/10.1016/j.jhydrol.2018.03.055

Mrozińska, N. and B&aogon;kowska, M. (2020) Effects of Heavy Metals in Lake Water and Sediments on Bottom Invertebrates Inhabiting the Brackish Coastal Lake &Lstrok;ebsko on the Southern Baltic Coast. International Journal of Environmental Research and Public Health, 17, Article No. 6848. https://doi.org/10.3390/ijerph17186848

Hong, Z., Zhao, Q., Chang, J., Peng, L., Wang, S., Hong, Y., Liu, G. and Ding, S. (2020) Evaluation of Water Quality and Heavy Metals in Wetlands along the Yellow River in Henan Province. Sustainability, 12, Article No. 1300. https://doi.org/10.3390/su12041300

Telmer, K.H. and Veiga, M.M. (2009) World Emissions of Mercury from Artisanal and Small Scale Gold Mining. In: Mason, R. and Pirrone, N., Eds., Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models. Springer, US, 131-172. https://doi.org/10.1007/978-0-387-93958-2_6

Telmer, K.H. and Veiga, M.M. (2009) World Emissions of Mercury from Artisanal and Small Scale Gold Mining. In: Mason, R. and Pirrone, N., Eds., In Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models, Springer, Boston, 131-172. https://doi.org/10.1007/978-0-387-93958-2_6

United Nations Environment Programme (2013) Global Mercury Assessment 2013 Sources, Emissions, Releases and Environmental Transport.https://wedocs.unep.org/handle/20.500.11822/12325

United Nations Environment Programme and Global Mercury Partnership (2017) Developing a National Action Plan to Reduce and, Where Feasible, Eliminate Mercury Use in Artisanal and Small-Scale Gold Mining - Guidance Document. https://wedocs.unep.org/20.500.11822/25473

Graham, E.B., Knelman, J.E., Gabor, R.S., Schooler, S., McKnight, D.M. and Nemergut, D.R. (2017) Trends in Dissolved Organic Matter Cycling, Sediment Microbiomes, and Methylmercury Production across Vegetation Heterogeneity in a Great Lakes Wetland. PeerJ, 7, Article No. e4575. https://doi.org/10.7717/peerj.4575

Martinez, G., McCord, S.A., Driscoll, C.T., Todorova, S., Wu, S., Araújo, J.F., Vega, C.M., and Fernandez, L.E. (2018) Mercury Contamination in Riverine Sediments and Fish Associated with Artisanal and Small-Scale Gold Mining in Madre de Dios, Peru. International Journal of Environmental Research and Public Health, 15, Article No. 1584. https://doi.org/10.3390/ijerph15081584

Goix, S., Maurice, L., Laffont, L., Rinaldo, R., Lagane, C., Chmeleff, J., Menges, J., Heimbürger, L., Maury-Brachet, R. and Sonke, J.E. (2019) Quantifying the Impacts of Artisanal Gold Mining on a Tropical River System using Mercury Isotopes. Chemosphere, 219, 684-694. https://doi.org/10.1016/j.chemosphere.2018.12.036

Rajaee, M., Obiri, S., Green, A., Long, R., Cobbina, S., Nartey, V., Buck, D., Antwi, E. and Basu, N. (2015) Integrated Assessment of Artisanal and Small-Scale Gold Mining in Ghana—Part 2: Natural Sciences Review. International Journal of Environmental Research and Public Health, 12, 8971-9011. https://doi.org/10.3390/ijerph120808971

The World Bank (2013) Artisanal and Small-Scale Mining. https://www.worldbank.org/en/topic/extractiveindustries/brief/artisanal-and-small-scale-mining

Mensah, S.K., Siabi, E.K., Donkor, P. and Kurantin, N. (2022) Assessing the Safety and Health Practices in the Artisanal and Small-Scale Gold Mining Sector of Ghana: A Case of Ntotroso. Environ Challenges, 6, Article ID: 100443. https://doi.org/10.1016/j.envc.2022.100443

Klubi, E., Abril, J.M., Nyarko, E. and Delgado, A. (2018) Impact of Gold-Mining Activity on Trace Elements Enrichment in the West African Estuaries: The Case of Pra and Ankobra Rivers with the Volta Estuary (Ghana) as the Reference. Journal of Geochemical Exploration, 190, 229-244. https://doi.org/10.1016/j.gexplo.2018.03.014

Kinimo, K.C., Yao, K. M., Marcotte, S., Kouassi, N.L.B. and Trokourey, A. (2018) Preliminary Data on Arsenic and Trace Metals Concentrations in Wetlands around Artisanal and Industrial Mining Areas (Cote d’Ivoire, West Africa). Data in Brief, 18, 1987-1994. https://doi.org/10.1016/j.dib.2018.04.105

Chantraine, J.-M. (1980) La lagune Aby (Côte d’Ivoire). Morphologie, hydrologie, paramètres physico-chimiques. Doc. Sci. Centre Reche Océanogr, Abidjan, 39-70.

RGPH (Recensement Général de la Population et de l’Habitat) (2014) Résultats Généraux. http://www.ins.ci/n/RESULTATSGLOBAUX.pdf

Charles-Dominique, E. (1993) Exploitation de la lagune Aby (Côte d’Ivoire) par la pêche artisanal. Dynamique des ressources, de l’exploitation et des pêcheries. Biologie des populations et Ecologie, Université de Montpellier II - Sciences et Techniques du Languedoc, 403.

Quémerais, B., Cossa, D., Rondeau, B., Pham, T.T., Gagnon, P. and Fortin, B. (1999) Sources and Fluxes of Mercury in the St. Lawrence River. Environmental Science and Technology, 33, 840-849. https://doi.org/10.1021/es980400a

Morita, H., Tanaka, H. and Shimomura, S. (1995) Atomic Fluorescence Spectrometry of Mercury: Principles and Developments. Spectrochimica Acta Part B: Atomic Spectroscopy, 50, 69-84. https://doi.org/10.1016/0584-8547(94)00116-D

Cai, Y. (2000) Speciation and Analysis of Mercury, Arsenic, and Selenium by Atomic Fluorescence Spectrometry. TrAC Trends in Analytical Chemistry, 19, 62-66. https://doi.org/10.1016/S0165-9936(99)00180-6

Hamilton, E. (1991) Introduction to Microwave Sample Preparation Edited by H.M. Kingston and L.B. Jassie, American Chemical Society Professional Reference Book, American Chemical Society, Washington, DC, 1988, 263 pp. Price: ￡59.95. The Science of the Total Environment, 103, 245-246. https://doi.org/10.1016/0048-9697(91)90149-9

Tseng, C.M., Garraud, H., Amouroux, D. and Donard, O.F.X. (1998) Open Focused Microwave-Assisted Sample Preparation for Rapid Total and Mercury Species Determination in Environmental Solid Samples. Journal of Automatic Chemistry, 20, Article ID: 487680. https://doi.org/10.1155/S1463924698000145

U.S. Environmental Protection Agency (2007) Method 7471B. Mercury in Solid or Semisolid Waste (Manual Cold-Vapor Technique). United States Environmental Protection Agency, Washington DC. https://www.epa.gov/sites/default/files/2015-12/documents/7471b.pdf

Koffi, K.M., Coulibaly, S., Atse, B.C. and Paul, E. (2014) Survey of Heavy Metals Concentrations in Water and Sediments of the EStuary Betri Bay, Ebrie Lagoon, Cote d’Ivoire. International Journal of Research in Earth & Environmental Sciences, 1, 1-10.

Kehrig, H.A., Pinto, F.N., Moreira. I. and Malm, O. (2003) Heavy Metals and Methylmercury in a Tropical Coastal Estuary and a Mangrove in Brazil. Organic Geochemistry, 34, 661-669. https://doi.org/10.1016/S0146-6380(03)00021-4

Veeck, L., Wasserman, J.C., Sella, S.M., Santos, I.R. and Lacerda, L.D. (2007) Mercury Distribution in Sediments of a Sub-Tropical Coastal Lagoon, Sepetiba Bay, Se Brazil. Geochimica Brasiliensis, 21, 50-57.

Kouamenan, N.M., Coulibaly, S., Atse, B.C. and Goore, B.G. (2019) Seasonal and Spatial Variations of Heavy Metals in Water and Sediments from Mainland and Maritime Areas of Ebrie Lagoon (Côte d’Ivoire, Western Africa). International Journal of Biological and Chemical Sciences, 13, 2374-2387. https://doi.org/10.4314/ijbcs.v13i4.39

Tomiyasu, T., Hamada, Y.K., Baransano, C., Hidayati, N. and Rahajoe, J.S. (2019) Time Variation in Transfer Amounts of Mercury by a River System Near an Artisanal and Small-Scale Gold Mining Area in West Java, Indonesia. Environmental Earth Sciences, 78, Article No. 686. https://doi.org/10.1007/s12665-019-8727-9

Institut national de l’environnement industriel et des risques [INERIS] (2010) Qualité chimique des sédiments marins en France. Rapport d’étude 02/11/2010.

de Almeida, R., Bernardi, J.V.E., Oliveira, R.C., de Carvalho, D.P., Manzatto, A.G., de Lacerda, L.D. and Bastos, W.R. (2014) Flood Pulse and Spatial Dynamics of Mercury in Sediments in Puruzinho Lake, Brazilian Amazon. Acta Amazonica, 44, 99-105. https://doi.org/10.1590/S0044-59672014000100010

Mirlean, N., Andrus, V.E. and Baisch, P. (2003) Mercury Pollution Sources in Sediments of Patos Lagoon Estuary, Southern Brazil. Marine Pollution Bulletin, 46, 331-334. https://doi.org/10.1016/S0025-326X(02)00404-6

Mason, R.P., Baumann, Z., Hansen, G., Yao, K.M., Coulibaly, M. and Coulibaly, S. (2019) An Assessment of the Impact of Artisanal and Commercial Gold Mining on Mercury and Methylmercury Levels in the Environment and Fish in Cote d’Ivoire. Science of the Total Environment, 665, 1158-1167. https://doi.org/10.1016/j.scitotenv.2019.01.393

Miyittah, M.K., Tulashie, S.K., Tsyawo, F.W., Sarfo, J.K. and Darko, A.A. (2020) Assessment of Surface Water Quality Status of the Aby Lagoon System in the Western Region of Ghana. Heliyon, 6, Article ID: E04466. https://doi.org/10.1016/j.heliyon.2020.e04466

Bakri, B., Sumakin, A., Widiasari, Y. and Ihsan, M. (2020). Distribution Pattern of Water Salinity Analysis in Jeneberang River Estuary Using ArcGIS. IOP Conference Series: Earth and Environmental Science, 419, Article ID: 012116. https://doi.org/10.1088/1755-1315/419/1/012116

Teisserenc, R., Lucotte, M., Canuel, R., Moingt, M. and Obrist, D. (2014) Combined Dynamics of Mercury and Terrigenous Organic Matter Following Impoundment of Churchill Falls Hydroelectric Reservoir, Labrador. Biogeochemistry, 118, 21-34. https://doi.org/10.1007/s10533-013-9902-9

Ferreira-Rodríguez, N., Castro, A.J., Tweedy, B.N., Quintas-Soriano, C. and Vaughn, C.C. (2021) Mercury Consumption and Human Health: Linking Pollution and Social Risk Perception in the Southeastern United States. Journal of Environmental Management, 282, Article ID: 111528. https://doi.org/10.1016/j.jenvman.2020.111528

Moriarity, R.J., Liberda, E.N. and Tsuji, L.J.S. (2020) Subsistence Fishing in the Eeyou Istchee (James Bay, Quebec, Canada): A Regional Investigation of Fish Consumption as a Route of Exposure to Methylmercury. Chemosphere, 258, Article ID: 127413. https://doi.org/10.1016/j.chemosphere.2020.127413

Taylor, V.F., Buckman, K.L., Seelen, E.A., Mazrui, N.M., Balcom, P.H., Mason, R.P. and Chen, C.Y. (2019) Organic Carbon Content Drives Methylmercury Levels in the Water Column and in Estuarine Food Webs across Latitudes in the Northeast United States. Environmental Pollution, 246, 639-649. https://doi.org/10.1016/j.envpol.2018.12.064

Be&lstrok;dowski, J., Szubska, M., Be&lstrok;dowska, M., Jankowska, K., Kotlarska, E. and Graca, B. (2018) Seasonal Changes of Mercury Speciation in the Coastal Sediments. Journal of Soils and Sediments, 18, 3424-3436. https://doi.org/10.1007/s11368-018-1993-4

Kouassi, A.M. and Adingra, A.A. (2005) Surveillance hydrologique des eaux de la lagune Ebrié au niveau d’Abidjan, 1-18.

Wango, T.D. (2009) Modélisation de l’hydrodynamique, de la dispersion du sel et de l’eau douce dans le complexe lagunaire de côte d’ivoire (Grand-Lahou, Ebrié et Aby). Thèse, Université de Côte d’Ivoire (Cote d’Ivoire).

Kambiré, O., Adingra, A.A., Eblin, S.G., Aka, N., Kakou, A.C. and Koffi-Nevry, R. (2014) Caractérisation des eaux d’une lagune estuarienne de la Côte d’Ivoire: La Lagune Aby Characterization of an Estuarine Lagoon Waters of Ivory Coast: The Aby Lagoon. Larhyss Journal, 20, 1112-3680.

Zeng, J., Han, G. and Yang, K. (2020) Assessment and Sources of Heavy Metals in Suspended Particulate Matter in a Tropical Catchment, Northeast Thailand. Journal of Cleaner Production, 265, Article ID: 121898. https://doi.org/10.1016/j.jclepro.2020.121898