Determination of Cu2+ by N,N-dichromone-p-phenylenediamine modified carbon paste electrode

In this work, carbon paste electrode (CPE) is chemically modified with Schiff base N,N-dichromone - p-phenylenediamine (L2) and used for the determination of copper(II) in water. The measurements are carried out using differential pulse voltammetry (DPV). The obtained results show that Cu (II) ions are chemically accumulated onto the surface of CPE/L2 in acidic medium at open circuit potential. Moreover, it is shown that the peak current increases linearly with the concentration of Cu (II) in the range of 0.1 to 10 nM and 0.096 nM can be obtained as detection limit with relative standard deviation of 2.1% for 10 successive determinations of 1 nM. These results suggest that CPE/L2 should be an excellent tool for the detection of Cu (II) ions at trace level in aqueous media.Keywords: Carbon paste electrode, L2 Schiff base, copper (II) ions, differential pulse voltammetry (DPV), characterization

Inhibitive effects of 2-mercaptobenzimidazole (MBI) and 2-thiobenzylbenzimidazole (TBBI) on copper corrosion in 1 M nitric acid solution

The inhibitive actions of 2-mercaptobenzimidazole (MBI) and 2-thiobenzylbenzimidazole (TBBI) on copper corrosion in 1M HNO3 medium were studied, using weight loss method, at 25 to 65°C and concentrations of 5.10-5M to 10-3M. The results showed that the two compounds had fairly good inhibiting properties for copper corrosion in the medium, with efficiencies of 90.0% for TBBI and 87.7% for MBI at 25°C and concentration of 10-3M. Modified Langmuir isotherm was found to provide an accurate description of the behavior of the two compounds. The thermodynamic functions of adsorption (ΔG°ads,Qads) and the activation energy (Ea) were calculated. Negative values of changes in free energies were obtained, indicating the spontaneity of the adsorption process. From thermodynamic adsorption and dissolution functions, both physisorption and chemisorption were proposed. Quantum chemical parameters such as highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), energy gap (ΔE) and dipole moment (μ) were calculated for these compounds, using DFT/B3LYP/6-31G (d,p) method in order to discuss the correlation between theoretical data and experimental results. It was found that theoretical data support the experimental results.Key words: Corrosion Inhibitor, inhibition efficiency, adsorption isotherm, free adsorption energy, adsorption heat, theoretical calculation, dipole moment

Evaluation of the risk of contamination by pesticides

Pesticides have the particularity of accumulating mainly in aquatic  ecosystems. The concentration of pesticides in such contaminated  ecosystems appears to be a potential health risk resulting from the human consumption of fish from these ecosystems. The aim of this study is to determine the pesticide residue levels of Chrysichthys nigrodigitatus and Tilapia zilli × Tilapia guinensis. 120 samples of each species, distributed from 96 samples for sector IV and 24 samples for sector V, were collected from February 2014 to January 2015. These were analyzed by gas chromatography coupled to a spectrometer of mass (GC / MS), after extraction and purification respectively by accelerated solvent extraction (ASE) and by adsorption chromatography on Oasis HLB Plus cartridges. Pesticide concentrations detected in fish muscle ranged from 0 to 40.66 ìg / kg in the study area. All values found for the health risk index (HI) in Chrysichthys nigrodigitatus and Tilapia hybrid muscles are well below 1 (HI < 1). Pesticide residues detected in both fish species do not pose a potential risk to human health.Keywords: Contamination, pesticides, Chrysichthys nigrodigitatus, Tilapia, risk. French Title: Evaluation du risque de contamination par les pesticidesLes pesticides ont la particularité de s’accumuler principalement dans les écosystèmes aquatiques. La concentration de pesticides dans de tels écosystèmes contaminés apparaît comme un risque potentiel pour la santé résultant de la consommation humaine de poissons de ces écosystèmes. Cette étude a pour objectif de déterminer la concentration de résidus de pesticides chez Chrysichthys nigrodigitatus et Tilapia zilli × Tilapia guinensis. 120 échantillons de chaque espèce, repartis en raison de 96 échantillons pour le secteur IV et 24 échantillons pour le secteur V, ont été collectés de février 2014 à janvier 2015. Ceux-ci ont été analysés par chromatographie en phase gazeuse couplée à un spectromètre de masse (GC / MS), après Extraction et purification respectivement par ExtractionAccélérée par Solvant (ASE) et par chromatographie d’adsorption sur cartouches Oasis HLB Plus. Les concentrations de pesticides quantifiés et non détectés dans les muscles des poissons variaient entre 0 et 40,66 ìg/kg dans la zone d’étude. Toutes les valeurs trouvées pour l’indice de risque pour la santé (HI) dans les muscles de Chrysichthys nigrodigitatus et de Tilapia hybride sont nettement inférieures à 1 (HI <1). Les résidus de pesticides détectés chez les deux espèces de poisson ne présentent pasde risque potentiel pour la santé humaine.Mots-clés : Contaminations, pesticides, Chrysichthys nigrodigitatus, Tilapia, risque

Distribution of Polycyclic Aromatic Hydrocarbons (PAHs) in a tropical coastal lagoon (Grand-Lahou lagoon, Côte d’Ivoire)

The distribution of 8 polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the Grand-Lahou lagoon (Côte d’Ivoire) was investigated using a high performance liquid chromatography (HPLC). The total concentrations of PAHs were between 1.55 and 437.52 μg/g in the dry season. Pyrene, benzo (b) fluoranthene and fluoranthene have the highest concentrations. In the rainy season, the total PAHs concentrations varied between 46.35 and 1222.73 μg/g. Pyrene, benzo (a) pyrene and benzo (a) anthracene were the most present in the sediments of the lagoon of Grand-Lahou during the wet season. Possible sources of PAHs in the  lagoon of Grand-Lahou are oil and fuel spills from ships and fishing boats, combustion of waste, domestic waste disposal and especially the production of charcoal on the Grand-Lahou lagoon shores. A clear dominance of high molecular weight (HMW) PAHs (pyrene, Benzo (k) fluoranthene, Benzo (a) pyrene, indeno (1,2,3-cd) pyrilène, Benzo (g, h, i) pyrilene, Benzo (a) anthracene , Benzo (b) fluoranthene) was observed compared to low molecular weight (LMW) PAHs (fluoranthene).Keywords: Polycyclic Aromatic Hydrocarbon (PAH), coastal lagoon, pollution, West Africa

Study of adsorption of imidacloprid onto two different textures of soils

The main goal of this research is to evaluate the potential for imidacloprid to contaminate water and ground water. For this purpose, the adsorption of imidacloprid on two different soils is investigated. Physicochemical  properties such as texture, organic matter, pH of the two soils are investigated. Both soils have high organic matter and the same pH but different textures. The kinetic study of adsorption on these soils over 90 days yielded a mean half-life of 60 days. Furthermore, adsorption kinetics of imidacloprid was studied and the rate of sorption was found to conform to pseudo-second-order kinetics with 3.10 mg/g/h and 10.204 mg/g/h for soils of banana field and cocoa field respectively. Equilibrium isotherm data were analyzed according to Langmuir, Freundlich and Redlich–Peterson equations. The Redlich–Peterson isotherm gave the best correlation for the adsorption of imidacloprid adsorption on soils. The maximum adsorption capacities were determined to be 4.139 mg/g and 5.74 mg/g of soils from banana field and cocoa field respectively.The differences in adsorption capacities may be due to the effect of soils textures.Keywords: Imidacloprid, soils textures, adsorption, Redlich-Peterson model, Freundlich model, HPLC

Evaluation de la pollution métallique des eaux souterraines et de surface dans un environnement minier aurifère à Hiré (Côte d’Ivoire)

Cette étude a pour objet l’évaluation du taux de pollution métallique des eaux souterraines et de surface dans un environnement minier. Pour y parvenir, des prélèvements d’eaux ont été effectués au cours de deuxcampagnes d’échantillonnage (mois décembre 2012 et mois de février 2013) dans la Sous-préfecture de Hiré (centre ouest de la Côte d’Ivoire). Les résultats ont montré des concentrations élevées pour tous les paramètres métalliques dans la majorité des stations. En effet, les teneurs d’arsenic, de cadmium, de mercure, de nickel, de plomb sont largement supérieures aux valeurs limites fixées par l’OMS pour les eaux de consommation et  d’irrigation. En outre, elles pourraient constituer des risques sanitaires pour la population de la zone d’étude. Nos résultats serviront de base aux politiques environnementales nationales visant à protéger les populations vivant dans un environnement minier.Mots clés : Pollution, métaux, sols, Hiré, Côte d’Ivoire

Study of lead adsorption on activated carbons

In this study, the removal of lead (II) from water using commercial  activated carbons from wood and coconut shell were investigated in acidic medium (pH = 4). Atomic absorption spectrometer (AAS) was used to investigate initial (C0) and (equilibrium) (Ce) solution concentrations. Powder and granular activated carbons showed different adsorption capacity. The amount of Pb2+ adsorbed reached44.58, 38.96 and 39.06 mg/g for CPA, CGA 830 and CGA 1230 respectively at 25 °C. Langmuir and Freundlich adsorption models were used to represent the equilibrium data. Despite the high value of coefficient (R2) from Freundlich model, the best interpretation for the experimental data was given by the Langmuir model. The work showed that using powder activated carbon from wood exhibited relatively high adsorption capacity than activated carbon from coconut shell.Keywords: Lead, activated carbon, adsorption, Langmuir, isotherm

Preliminary assessment of cadmium mobility in surface sediments of a tropical estuary

Cadmium is a toxic metal often found with a strong enrichment factor in coastal sediments. The sequential extraction procedure proposed by the BCR (Community Bureau of Reference) was applied for partitioning of Cd in tropical estuary sediments. The method showed satisfactory recoveries. The repartition of Cd in different phases of sediment was controlled by the residual phase (50.32 to 67.45 %). However, the exchangeable and acid soluble fraction (F1) was in general found to be the second most abundant fraction in the surface sediments (11.14 to 15.24 %), indicating that an important portion of Cd could be remobilized, thus becoming available to aquatic biota. Cd also showed different distribution patterns in the sediment phases due to the heterogeneity of the sediments, as well as the physical and chemical conditions along with the different sources of Cd in the bays. The risk assessment code investigation showed a medium risk of Cd in the estuary. KEY WORDS: Cadmium, Mobility, Sediment toxicity, Sequential extraction Bull. Chem. Soc. Ethiop. 2014, 28(2), 245-254. DOI: http://dx.doi.org/10.4314/bcse.v28i2.

La pollution des eaux de la zone urbaine d’une lagune tropicale par les matières oxydables (lagune Ebrié, Côte d’Ivoire)

Suite à l’explosion démographique et au déversement de déchets hautement toxiques dans la métropole d’Abidjan, la qualité physico-chimique de cinq baies fermées de la lagune Ebrié en face d’Abidjan a étéévaluée de 2006 à 2008. Plusieurs paramètres (température, pH, salinité, oxygène dissous, matières oxydables et sels nutritifs) ont été mesurés. Il apparaît que les quatre premières baies, soumises aux rejets d’eauxrésiduaires, possèdent de très fortes charges en particules en suspension, DBO5, et DCO, et sont le siège de mortalités de la faune aquatique et d’une accumulation de sédiments riches en matières organiques. Enrevanche, la cinquième, éloignée des rejets, a enregistré des concentrations deux à trois fois plus faibles ; elle est bien oxygénée et présente des signes d’un dépôt des particules minérales. Les résultats des teneurs en sels nutritifs révèlent que les teneurs en ammonium de certaines zones affectent la vie aquatique et que les principales sources de sels nutritifs sont les rejets domestiques et industriels, les eaux de ruissellement et l’érosion des sols du bassin versant du fleuve Comoé. Ces résultats permettront de dépolluer les baies de la lagune Ebrié et de surveiller l’utilisation des engrais dans la région d’Abidjan.Mots clés: Pollution, lagune, matières oxydables, nutriments