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

Alibori River located in northwestern Benin is subject to contamination by trace metal elements (TME: Zn, Cu, Pb, Cd) due to the use of agricultural inputs in its vicinity. This study focuses on the speciation of TME elements in the sediments of this river. The sediments were sampled during the rainy and dry seasons, dried, crushed and then sieved. The sediments were then mineralized and subjected to sequential fractionation. The total extraction and sequential extractions were analyzed using a spectrophotometer UV. The sediments of Alibori River had an acid pH and were contaminated by TME during the dry season. The zinc and copper had an affinity with the different fractions with a high proportion in the fractions F1 and F2 during the rainy season and a high proportion in the F5 fraction during the dry season. The lead and cadmium had an affinity with the F5 fraction during the rainy season, and the F3 and F4 fractions during the dry season. The calculated contamination index, individual contamination factor and risk assessment code (RAC) demonstrated that the river presented a potential risk of water contamination. The aforementioned parameters also showed that the river induced risk of bioavailability ranging from medium to very high for organisms. The TMEs found in the sediments of the Alibori River were linked to the exchangeable and acid-soluble fractions which made them more mobile and bioavailable to organisms.   Key words: Speciation, Alibori River, trace metal elements (TME), bioavailability, fraction.