Distribution of Total Mercury in the Sedimentary Environment in Lake Ahémé, Southern Benin (West Africa)

This study focuses on the spatio-temporal assessment of mercury pollution of the sedimentary environment of Lake Ahémé in southwestern Benin Republic. Sediment samples were taken from 32 sites in July 2018 and then in December 2019, covering the two major climatic seasons of the southern area of the country. Sampling was done according to a grid design of the entire area of the ecosystem. The surface sediment samples were collected at a depth between 0 and 5 cm in three takes at each site with a Van Veen grab. Samples were frozen, lyophilized at -40°C, crushed, sieved and homogenized. The fraction less than 63 µm in size was collected for the mercury determination by a Direct Mercury Analyser (DMA) operating by atomic absorption according to the US EPA 7473 method. The results obtained reveal that, in 2018, mercury is more concentrated in the northern and central part of the lake varying from 109 μg/Kg (center) to 132 μg/Kg (north) while in 2019, the central and southern zones of the lake were more concentrated in mercury, with 162 and 87 μg/Kg respectively. However, the values of the geo-cumulation index Igéo varies from 0 to 1, showing that Lake Ahémé is slightly polluted at these sites.