Monitoring Chemical Pollution in the Chenal's Waters of Cotonou

Abstract

The protection of estuarine aquatic ecosystems is essential to the ecological balance of fish species and to a healthy diet for local populations. The Cotonou Chenal in southern Benin is under the influence of several forms of pollution that result for most human activities. This work proposes to know the current state of chemical pollution of the aquatic ecosystem of the Chenal in order to limit the ecotoxicological risks. Monitoring indicators of physico-chemical quality (temperature, pH, conductivity, total dissolved solids, dissolved oxygen, transparency and depth) of organic pollution (COD) and total lead have been searched for in the different water and sediment samples of the channel. The inventory of the potential sources of chemical pollution of the Chenal, reveals that the garbage dumps littering the lagoon banks, the collectors and the drainage channels of the city of Cotonou, the road and maritime transport, and the dyers of Gbogbanou are the main sources. The physicochemical measurements of the Chenal water monitoring have shown that the values of the recorded temperature, pH, nitrate, nitrite and phosphate do not show statistically a sign of pollution of the studied area apart from some pockets of contamination like the mouth of the SOBEBRA and the Hotel du Lac at the time of wastewater rejection. Besides, the measured values reveal at the threshold of 5% a low transparency (0 to 0.875m), a low level of dissolved oxygen (0.00 to 4.33mg/L), a very high Chemical Oxygen Demand (COD) (669 ± 615 to 997 ± 337 mg O2/L) and a high contamination of the water column with ammonium ion (6.84 ± 3.43 at 13.80 mg/L) at the mouth of the SOBEBRA (lake Hotel). In water, the average lead content is 0.258 ± 0.29 mg/L.