The Nangbéto hydroelectric dam lake, which is a spillway for agricultural input residues, urban and industrial effluents present in the Mono basin, is exposed to all forms of pollution. The aim of this work is to estimate the content of seven trace elements present in the sediments of the aforementioned lake in order to assess the ecological risk incurred by the aquatic biocenosis and therefore by man. Forty-two sediment samples (21 per season) are realized in different areas of the Lake. Cd, Pb, Ni, Cu, Cr, As and Hg are measured out in the sediments by the flame atomic absorption spectrophotometer in these pre-mineralized samples. The results show average contents varying from the lowest level 0.04 mg / kg for Hg to the highest 12.15 mg / kg for Cu in the rainy season and from 0.03 mg / kg for Hg and for As to 9.14 mg/kg for Cu in the dry season. All of these values are below Canadian sediment quality standards. The strongest average geoaccumulation indices (Igeo) are obtained for Pb with values less than 2. The mean values of the contamination factor (FC) are less than 1. The mean indices of contamination (Im) are less than 2, threshold d 'an onset of polymetallic contamination. The ecological risk (Ri) in relation to the contamination of the sediments of the Lake with trace elements is low in any season (Ri <40) and this implies a low risk of contamination of the biocenosis. However, the present study only deals with metallic trace elements. It does not take into account other pollutants, nor the potential "cocktail" effects between them. Additional work should therefore be continued in this direction to consolidate the low risk recorded for the biocenosis. Le Lac du barrage hydroélectrique de Nangbéto qui constitue un déversoir des résidus des intrants agricoles, des effluents urbains et industriels présent dans le bassin du Mono est exposé à toutes formes de pollution. Le but de ce travail est de quantifier les teneurs de sept (7) éléments traces dans les sédiments dudit Lac afin d’évaluer le risque écologique encouru par la biocénose aquatique et partant par l’homme.Quarante-deux (42) échantillons de sédiments (21 par saison) sont échantillonnés dans différentes zones du Lac. Le Cd, Pb, Ni, Cu, Cr, As et Hg sont dosés dans les sédiments par le spectrophotomètre d’absorption atomique à flamme dans ces échantillons minéralisés. Les résultats montrent des teneurs moyennes variant de la plus faible teneur 0,04mg/kg pour le Hg à la plus forte (12,15mg/kg) pour le Cu en saison pluvieuse et de 0,03 mg/kg pour le Hg et pour l’As à la plus forte (9,14 mg/kg) pour le Cu en saison sèche. Toutes ces valeurs sont inférieures aux normes canadiennes de qualité des sédiments. Les plus forts indices de géoaccumulation (Igeo) moyens sont obtenus chez le Pb avec des valeurs inférieures à 2. Les valeurs moyennes de facteur de contamination (FC) sont inférieures à 1. Les indices moyens de contamination (Im) sont inférieurs à 2, seuil d’un début de contamination polymétallique. Le risque écologique (Ri) par rapport à la contamination des sédiments du Lac en éléments traces est faible en toute saison (Ri < 40) et cela implique un faible risque de contamination de la biocénose. La présente étude ne porte toutefois que sur les éléments traces métalliques. Elle ne tient compte ni des autres polluants, ni des effets "cocktail" potentiels entre eux. Un travail complémentaire devra donc être poursuivi dans ce sens pour consolider le faible risque enregistré pour la biocénose.

The objective of this study was the evaluation of the health risks of the pesticides use and their bioaccumulation by the vegetables grown in Lomé gardens. Pesticide residues levels were assessed in vegetable samples collected in Lomé areas by Gaz chromatography-mass spectrometry or liquid chromatography-mass spectrometry in order to know their concentrations. Data obtained were used for estimating the potential health risks associated with the exposures to these pesticides.The results showed that all of the samples contain pesticide residues with high levels of Dithiocarbamates (7.79 ppm) in carrots, Chlorpyriphos ethyl (0.445 ppm) in spinach, cucumbers (0.239 ppm), peppers (0.032 ppm), and turnips. Levels above the maximum residue limits (MRLs) of chlorothalonil, and carbendazime were found in peppers, prothioconazole and pendimethalin in turnips, cypermethrin in pepper (0.254 ppm) and in eggplant (0.037 ppm). The pepper has concentrated 5 residues, leek and turnip 4 residues each other, African eggplant 3, lettuce 2 residues and spinach 2 residues. The health risks indices show that the detected pesticides could not be considered as a serious public health problem in the studied conditions, but there is the need to increase their monitoring to reduce their misuse on the vegetables.

Background. Phosphorites in the mining area of Hahotoé-Kpogamé contain high levels of fluoride that can cause illness among people living close to the mining and processing sites. Objectives. To assess the distribution of fluoride in the different areas around the phosphorite mining areas in Togo. Methods. Analyses were performed by molecular absorption spectrometer (HACH DR3800) according to the procedure manual at the geochemical laboratory of the University of Lomé. The sodium 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonate (SPADNS) method was used to determine fluoride contents and the PhosVer® 3 with acid persulfate digestion method was used to measure phosphorus pentoxide (P 2 O 5). GraphPad Prism version 3.0 software was used for the data processing. Results. The surface water of the mining sites had a fluoride content ranging from 0.38 to 3.52 mg/l (average = 1.33 mg/l; n = 10, n is the number of samples). Groundwater in this area had a fluoride content between 0.15 mg/l and 1.39 mg/l (average = 0.58 mg/l, n = 15). In the groundwater in the villages around the phosphorite processing plant, the fluoride content ranged between 0.15 and 0.63 mg/l (average = 0.41 mg/l; n = 22). The fluoride content in the water of the phosphorite mining area was higher than in Gbodjomé (reference area). Meanwhile, assessment of the effluents discharged into the ocean had a fluoride content ranging from 12 to 20 mg/l. In dusts, the P 2 O 5 and fluoride contents were 36.02% and 1.85%, respectively. Vegetables from the local market garden produce showed levels of fluoride up to 2.06%. The average contents of P 2 O 5 and fluoride in one of the phosphorite profiles were 32.38% and 3.00%, respectively. A significant correlation was observed between P 2 O 5 and fluoride. Conclusions. The correlation between P 2 O 5 and fluoride in phosphorites shows that phosphorite mining is the main source of fluoride pollution in this area.

The hydrosystem Lac Togo-Lagoon of Aného is located in a watershed where phosphate mining of trace element-rich phosphorites takes place. This activity generates various types of wastes that are dumped into the environment without prior treatment. In addition, there are contributions of its tributaries after leaching of agricultural and urban soils. All this contributes to the degradation of the water quality of this ecosystem. The aim of this study is to assess the level of trace elements contamination of the waters from the hydrosystem Lake Togo-Lagoon of Aného and its spatio-seasonal variations. In the dry and rainy season, the physicochemical parameters of waters were measured according to French standards (AFNOR). The trace elements were determined by atomic absorption spectrometer coupled to a hydride and cold vapour generator. The spatial distribution was evaluated using maps which were performed by ordinary kriging interpolation method of ArcGIS 10.2.2 software. The results showed that the average dry season concentrations were significantly higher (p < 0.0001) than those of the rainy season except that of Zn. The average concentrations (in μg/l) observed for Cd: (39.28; 24.63), Pb: (216.82; 66.44), Cr: (197.00; 69.05) and Ni: (100.06; 66.50), respectively, in dry and rainy season were significantly higher than the WHO standards. However, overall trace elements contamination has been noted with polymetallic contamination indices which reached 4.14 in the dry season and 2.41 in the rainy season. This contamination is mainly of anthropogenic origin and comes from the intrusion of seawater loaded with phosphate effluents in the dry season and the leaching of mining and agricultural soils in the rainy season. The results proved that this lagoon ecosystem is polluted by trace elements mainly caused by phosphate mining. Thus, it deserves special attention for its better management for a sustainable development.

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