Spatial Variability of Total Mercury and Methyl Mercury Concentrations in Coastal Sediments from Five African Countries in the Gulf of Guinea Region

Anthropogenic activities, such as untreated sewage disposal and mining, contribute to metal pollution in coastal marine environments. Toxic metals (e.g., mercury) are detrimental, even in small amounts,tal and can be transferred through the aquatic food chain via bioaccumulation and biomagnification. Mercury is a naturally abundant element and a potentially toxic industrial metal, mostly released into the environment via drinking water, dietary intake, and industrial activities (Charkiewicz et al., 2025; Genchi et al., 2017; Li et al., 2024). Therefore, there is a need to investigate the status of mercury contamination in the coastal marine environment. Mercury occurs in different forms, including inorganic elemental mercury, monovalent mercury, divalent mercury, and organic forms such as methylmercury (MeHg)(Tian et al., 2023). There are mainly three forms: elemental mercury (Hg0), inorganic mercury (IHg: Hg+ and Hg2+), and organic mercury(methyl—MeHg; ethyl—EtHg; and phenyl—PhHg), with the MeHg form being the most dangerous and harmful to human health or even life (Genchi et al., 2017; Hu et al., 2021)'. The study assessed spatial distribution of total mercury (THg) and methyl mercury (meHg) in coastal sediments from five African countries covering five coastal water bodies, mainly, Ebrié Lagoon (E.L., Côte d'Ivoire), Volta Estuary (V.E., Ghana), Lake Togo (L.T., Togo), Lake Nokoué (L.N., Benin), and Lagos Lagoon (L.L., Nigeria) within the Gulf of Guinea region to understand the spatial dynamics and transboundary mercury pollution for protection of life below water (SDG14), promote good health and well-being (SDG3), promote clean water and sanitation (SDG6), and building partnerships to advocate for reforms in mercury pollution policies in the sub Saharan Africa region. Sediment is a source of environmental contamination and a permanent component of aquatic ecosystems. Forty-eight surficial coastal sediment samples (0–10 cm) were collected from the five selected coastal systems based on their ecological significance and human impacts in the dry season (November 2022, February, and March 2023) using bottom sampling gear ( Eckman and Van Veen grabs) based on the depth of the waterbodies. Wet coastal sediment (the uppermost oxidised portion, 0 –2 cm) was air-dried immediately after collection for preservation. Before the analytical procedures, all sediments were oven-dried at 60°C and sieved to obtain particle-size fractions. The Direct Mercury Analyser (Model DMA-80, Milestone) was used to determine total mercury (THg) and methyl mercury (MeHg) in the <63 μm size fraction of sediment according to the standard methods (e.,g US-EPA 1998).