Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 4(8), 33-41, August (2014) Res. J. Chem. Sci. International Science Congress Association 33 Evaluation of the state of pollution of complex Aheme Lake -lagoon of Ouidah by trace metals Zn, Cu, Cd, Pb and Cu speciation in sedimentComlan AchilleDEDJIHO1,2*, Aristide B. AKPO, Coffi Justin NOUMONMarielle Yasmine AGBAHOUNGBATA,Parfait HOUNSINOUDaouda MAMA1,2, Moussa BOUKARI et Dominique C. K. SOHOUNHLOUELaboratoire d’Hydrologie Appliquée (LHA), Faculté des Sciences et Techniques (FAST), Université d’Abomey-Calavi 01 BP : 526 Cotonou, BENIN Laboratoire de Chimie Inorganique et de l’Environnement (LACIE), Faculté des Sciences et Techniques (FAST), Université d’Abomey-Calavi 01 BP : 526 Cotonou, BENIN Laboratoire de la Physique du Rayonnement, Faculté des Sciences et Techniques (FAST), Université d’Abomey-Calavi 01 BP : 526 Cotonou, BENIN Laboratoire d’Etude et de Recherche en Chimie Appliquée (LERCA), Ecole Polytechnique d’Abomey-Calavi (EPAC), Université d’Abomey-Calavi, BENIN Available online at: www.isca.in, www.isca.me Received 6th July 2014, revised 27th July 2014, accepted 14th August 2014 Abstract The objective of this work is the evaluation of the state of pollution of the complex Aheme lake -Lagoon of Ouidah by trace metals elements (TME) such as zinc, copper, cadmium and lead, and speciation copper in sediments. This study reveals that the TME are much more concentrated in sediments [Cu: 46-356 mg/kg; Zn: 2.91 to 323 mg/kg; Pb: 1.53 to 4.17 mg/kg; Cd: 0 to 1.14 mg/kg], and in fish [Cu: 19 mg/kg; Zn: 10.36 mg/kg; Pb: 0.56 mg/kg; Cd: 0 mg/kg] and in the water column: [Cu: from 0.1 to 0.44 mg/L; Zn: 0.3 to 1.1 mg/L; Pb: from 0.013 to 0.33 mg/L; Cd: 0.067 to 0.009 mg/L]. Speciation of copper metal, the most abundant in sediments (average 171.44 mg/kg) for all sampling points, reveals that it is much more present in the oxide (29.83%) and the acid-soluble fraction (25.70%) at Guézin against 35.23% acid-soluble fraction and 30.92% in the reducible fraction Tohonou. Keywords: Aheme lake, TME, speciation, sediment, water, fish. IntroductionThe Republic of Benin has tremendous potential in aquatic natural resources. Various anthropogenic pressures on the environment caused over the years, an advanced degradation of these resources. Moreover, contamination of aquatic ecosystems by metals remains a serious environmental problem of increasing concern. Water, fish species and sediments from Nokoue Lake and those of the lagoon of Porto-Novo in Benin are contaminated by heavy metals3-5. Sediments are micro traps; they give an indication of the historical pollution of watercourses5,6. Indeed, the contaminants are adsorbed to the particles in suspension and then accumulated in the sediments; most contaminants are on the clay, the hydroxides of Mn and Fe, carbonates, organic materials and biologic materials and five fractions such as Exchangeable fractions, carbonates, oxides Fe and Mn, the organic matter and sulfides. In the case of shallow lakes, resuspension of sediments enriched and leaching of nutrients help maintain high concentrations in the water masse. The present study aims to assess the state of pollution of complex the lake Aheme and lagoon of Ouidah by trace metals (zinc, copper, cadmium, lead), and speciation of copper in sediments. Material and Methods Environment Study: The study was conducted on the periphery of the Aheme lake in Benin (West Africa). Aheme lake (78 km) is situated in a sub-equatorial climate. It connects the Couffo River and the coastal lagoon of Ouidah in the watershed Mono-Couffo. Around it is developed agriculture, livestock and especially fishing. Methods: The pH and the sediment pHKCl: The pH was measured in situ in the water with the pH/Oxi 340i WTW meter previously calibrated. Regarding pHKCl we weighed 10 grams fine sediment sieved to 0.2 mm in a beaker. We added 25 mL of distilled water and was then stirred with a magnetic stirrer for 60 min at room temperature of 20 ± 2°C. This allows to suspend the whole of the sample and thereby to obtain a balance between the aqueous and solid phase. The mixture is then allowed to stand for two hours in airtight then pHKCl is always measured in the supernatant using the pH meter WTW pH/Oxi 340i. Total Organic Matter in Sediments: Determination of organic material by incineration. We followed the following steps: i. Drying of the sample of ground for 16 hours at 150°C., ii. Clean the crucible by heating to red, and then cool in a desiccator for 10 minutes. iii. Take the weight of the empty crucible. Add 10 g of dried soil. Record the final weight. iv. Calcine the soil in a Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 4(8), 33-41, August (2014) Res. J. Chem. Sci. International Science Congress Association 34 mitten furnace at 375 °C for 16 hours. v. Allow to cool in a desiccator and weigh the crucible containing the ashes. vi. The calculation formula of MOT: MOT =  MOT: total organic material: P1: final weight, P0: the weight of the empty crucible P2: weight of the crucible containing the ashes. Figure-1 Location of the Environment study and sampling points rrrrrrrrr AC A ALLADASAVALOUDJIDJALOKOSSAATHIEMEGRAND-POPODOGBODJAKOTOMEBOPACOMEHOUEYOGBEOUIDAHKPOMASSETOVIKLINKLOUEKANMEZOGBODOMELALOABOMEYAGBANGNIZOUNTOUKOUNTOUNANATITINGOUBOUKOUMBEMATERIKOBLITANGUIETATCHAOUROUBANTEDJOUGOUOUAKECOPARGOKOUANDEPEHONKOKEROUGLAZOUETOFFOZETORI-BOSSITOABOMEY-CALAVICOTONOUCOVEBOHICONZA-KPOTADASSAZANGNANADOSAVESEMESO-AVAAGUEGUESDANGBOPORTO-NOVOADJARAMISSERETEAVRANKOUIFANGNIADJOHOUNOUINHIBONOUKETOUSAKETEADJA-OUEREPOBEKARIMAMAN'DALIOUESSESINENDEBANIKOARAGOGOUNOUKALALEPARAKOUBEMBEREKEPERERENIKKIKANDISEGBANAMALANVILLEAPLAHOUE                     AFRIQUEBurkFaNigeriaTogo LEGENDE Source: Fond topographique IGN, 1992Travaux de terrain, Février 2013 Reproduction de 2014: DEDJIHO Comlan Achille 1012Km       \n                   \n \n           \n \n \n \n \r                        Océan AtlantiqueLagune côtièrePlan d'eauLimites communesCours d'eau temporaireCours d'eau permanentPiste principaleRoute principaleRoute bituméeSite d'échantillonnageAdjatokpaTokpa-DomèGuézinTohonouKpétouGbèzounmèDékanmèBopaPossotomè