Abstract
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.
Highlights
Like most aquatic ecosystems, Lake Ahémé is influenced by human activities
Given that lake Ahémé presents a certain richness in muddy faces and is subject to multiple pollution (Dimon et al, 2014; Chouti et al, 2017), its sedimentary environment becomes an interesting subject to study
These representations show that the distribution of mercury in the sediment depends on the period of the year
Summary
Lake Ahémé is influenced by human activities. It receives pollutants from the leaching of agricultural land located upstream (Amoussou, 2010; Dédjiho, 2014) and from domestic wastewater from neighboring villages (Dèdjiho, 2014). Previous studies on the environment have revealed metallic contamination (Cu, Zn, Pb and Cd) of water and sediment matrices (Dimon et al, 2014; Chouti et al, 2017) They revealed the beginning of lead, zinc and arsenic contamination of the sediments of the lakeside village of Agonsa (Dimon et al, 2014). The present work is a continuation of the work already carried out and those in progress, to broaden the fields of investigation towards other metallic trace elements just as toxic such as mercury This will involve (i) evaluating the distribution of total mercury over the entire extent of the lake, (ii) evaluating the influence of environmental parameters on the mercury content and (iii) identifying areas with probable Eco toxicological risk
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