Physico-Chemical Characterization of Waters and Sediments of Basins in the Cotton Area in Benin: Case of the Alibori Basin in the Commune of Banikoara North of Benin

Abstract

The Alibori Basin, with an area of 13,400 km 2 , is a tributary of the Niger River in Benin. It is a river that passes through the potentially agricultural area of Benin. The waters of the river are useful for wildlife and are used for various purposes (drinking water, laundry, domestic activities). They regularly receive the discharges and drainage of the residues of the chemical fertilizers and pesticides not used by crops during the cultivation of the river and watershed bank. This study aims to assess the impact of the agricultural inputs on the quality of the waters from Alibori river on the basis of its physico-chemical characteristics and concentrations in Trace Metal Elements such as Zn, Pb, Cd and Cu. Seven (7) sites were selected along the river. Concentrations of 3 NO − , 2 NO − , 4 NH + , 2 4 SO − 3 4 PO − , Cu and Zn were measured using a spectrophotometer Spectrophotometer DR 2800 and that of Pb and Cd by Metalyse. The Metal Trace Elements were measured in the Alibori river sediments after being treated and mineralized using aqua regia. The results revealed that Alibori river characteristics varied with seasons and its waters and sediments were polluted by metals, phosphates and nitrites. The pollution of waters of the Alibori River was due to the intensive use of the chemical fertilizers and pesticides for agricultural purposes.

Speciation of trace metal elements in sediments of Alibori River, North-West of Benin

“…Zinc, copper and lead were more concentrated in the sediments during the rainy season, which is a cultivation period, than the dry season, unlike cadmium. This observation is in agreement with Chitou et al (2019) who reported similar variation for TMEs concentrations in Alibori River's sediments between the dry season and the rainy season in 2018.In accordance with Chitou et al (2019), it could be concluded that the high values of TME during the cultivation period were due to the use of fertilizers and pesticides since the river is located in a rural area dominated by agricultural activities (Chitou et al, 2019). The concentration of Zinc and copper in the sediments has increased compared to that obtained in the 2018 during the dry season (Max: 15.6 mg.kg-1 for zinc, 19.1 for copper) and the rainy season (Max: 175 mg.kg -1 for zinc, 231 mg.kg -1 for copper) using a metalyser (Chitou et al, 2019).…”

“…However, the pH being inversely proportional to the temperature, therefore the decrease in pH suggest to the increase in temperature of the medium, thus causing the decrease in the absorption of copper and zinc. There was likely a phenomenon of chemical release as shown in reaction Scheme 2, which explains the increase in the concentrations of the latter (TME) observed in the water in previous work in this period (Chitou et al, 2019). There is a great affinity between organic matter and metallic trace elements (Zhao et al, 2012), which explain the strong correlation observed between the oxidizable fraction of copper, zinc and organic matter during the rainy season as shown by the circle of correlation.…”

“…There is a dearth of information on the effects of human activities on the Alibori River (Thierry et al, 2016;Chitou et al, 2019). Our previous study showed that sediments of the Alibori River were contaminated by TMEs (Zn, Cu, Pb, Cd) due to the use of agricultural inputs in its surroundings (Chitou et al, 2019).…”

“…Alibori River's waters are used by the populations for daily needs (drink, cooking, laundry, dishes) and the processing of agricultural products as adequate local water supply facilities are not available in the region (PEA) (Tachégnon and Ibrahim, 2012;Chitou et al, 2019). Intensive agriculture is also developed around the river and is dominated by cash and food crops such as cotton, and corn (Agagbé, 2008;Thierry et al, 2016;Tachégnon and Ibrahim, 2012).…”

“…One of the consequences of the use of these products (chemical fertilizers and phytosanitary products) is the contamination of waterways by various pollutants such as pesticides and trace metal elements (TME). These TMEs can lead to morphological abnormalities and neurophysiological disorders, and affect enzymatic and hormonal activities in living organisms (Chitou et al, 2019;Wang et al, 2017).…”