Assessment of groundwater to pollution by the toxic metals in the municipality of Kerou (Benin) in watershed of the Niger

Abstract

This case study has assessed the vulnerability of boreholes water to pollution by toxic metals in the cotton zone of Kerou, in northern Benin. Toxic metals (lead, copper, cadmium, zinc, nickel and iron) were analyzed by atomic absorption spectrophotometry. The results show high values for lead, nickel and iron, which means that 7 out of 18 boreholes are contaminated. Only the lead level exceeds the standard for the boreholes of Ganbore and Korigourou (0.0613 and 0.098 mg/l against 0.04 mg/l) The level of contamination of Cadmium, zinc and copper is very irregular, but however one must notice that the two aforementioned boreholes are contaminate with the concentration of cadmium above the permitted limit (0.0234 and 0.0244 mg/l against 0.005 mg/l). These findings allow us to say that, apart from the two boreholes of the localities of Ganbore and Korigourou located in cotton farm, most of the boreholes are resistant to pollution. So the responsible factors, of the noticed contamination are defined. It is above all due to the cultivation of cotton in this area. The assays witness of the Mekrou River has revealed high contamination by lead (0.060 mg/l) and the iron (1.4341 mg/l): this result can highlight the ongoing relationship of surface water with groundwater.

Keywords: Vulnerability, groundwater, contamination, toxic metals, cotton culture