The Lake Togo-Lagoon of Aného is located in the coastal zone where phosphorite mining is carried out. This mining discharges all kinds of waste such as fuel oil into the surrounding environment without prior treatment. Moreover, the hydrosystem receives runoff and river inputs after having crossed and leached from mining and urban soils. This study aims to determine the polycyclic aromatic hydrocarbons (PAHs) contamination in commercially consumed fish species (Chrysichthys nigrodigitatus) from that hydrosystem and the associated health risks for consumers. For that, fish sample collection was performed during the dry season. Afterwards, their muscles, gills, and livers were cut and 12 PAHs were analyzed using gas chromatography coupled with a mass spectrometer (GC-MS). The total PAHs (tPAHs) concentrations in fish tissues ranged from 5.24 to 48.40 µg/kg with average concentration of 14.51 ± 8.95 µg/kg in muscles, from 5.90 to 28.20 µg/kg averaging 14.90 ± 5.19 µg/kg in gills, and from 43.20 to 149.00 µg/kg with an average of 80.74 ± 27.08 µg/kg in livers. The average concentrations of low molecular weight PAHs (LMW PAHs) were 10.82 ± 9.61 µg/kg in muscles, 8.25 ± 5.43 µg/kg in gills, and 47.97 ± 22.56 µg/kg in livers whereas those of high molecular weight of PAHs (HMW PAHs) were 4.10 ± 2.14 µg/kg in muscles, 7.98 ± 3.96 µg/kg in gills, and 32.77 ± 8.66 µg/kg in livers. An overall trend of decreasing concentrations with increasing fish size classes was observed for some PAHs (Naphtalene, Pyrene in muscles, for Pyrene, Benzo(a)Anthracene, Chrysene in gills and for Naphtalene, Phenanthrene in livers). The PAHs in these fish might have pyrogenic and petrogenic sources, with the dominance of pyrogenic, and all of the total hazard quotients (THQ) are less than 1. This situation must not be neglected for better planning sustainable management of the target ecosystem.

The concentrations of major, trace (TE), and rare earth (REE) elements and their seasonal and spatial distribution were studied on the fine fraction (<63 µm) of the sediments of the Lomé lagoons (West Lake, East Lake, and Lake Bè). The sediments were collected on a total of nine sampling sites (three per Lake) during two campaigns (dry season and rainy season). The quality of the sediments was assessed on the basis of the enrichment factor (EF) and the labile or non-residual fraction (NRF) in relation to the values recommended for the quality of the sediments (Sediment Quality Guidelines, SQG). The distribution of rare earth elements shows enrichments in light rare earths superior to those of heavy rare earth elements during any season. Positive Ce anomalies are less noticeable and less variable between seasons than Eu anomalies. La/Yb ratios are positively correlated with the percentage of Al and Fe oxides and with the percentage of fine fractions. The main bearing phases of rare earth elements are, therefore, Al and Fe oxides and the finest fractions of the sediments. The concentrations of trace elements vary little, according to the seasons, but show strong variations from one element to another. The degrees of enrichment obtained are moderate for Bi, Cr, Ga, Mo, Pb, Sn, and Zn (1.5 < EF < 5) to significant for As, Cd, and Sb (5 < EF < 20) for all sites of Lake Bè. For the sites of West Lake, the degrees of enrichment obtained are moderate for As, Cd, Cu, Mo, and Pb (1.5 < EF < 5) to a significance for As, Bi, Cd, Pb, Sb, Sn, and Zn (5 < EF < 20). Only the East Lake sites show high degrees of enrichment for elements such as Sb and Sn (20 < EF < 40). Trace elements (TE) such as As, Cd, Cu, and Ni have total concentrations within the range of variation of the SQG concentrations (particularly Probable Effect Level (PEL) and Effect Range Median (ERM)), whereas Cr, Pb, and Zn total concentrations are higher. The ranking of priority sites with respect to the sediment contamination is determined according to ERM and PEL quotients in relation to the probability of toxicity for benthic organisms. For almost all the sites, the priority is lowest to medium-low with regard to As, Cd, and Cu and medium-high (Cr and Ni) to highest (Pb and Zn), particularly for the East and West Lakes. Moreover, the NRF can represent significant percentages of the total TE concentrations: 5% to 15% for As, Bi, Ni, V, Mo, and Sc, 15% to 25% for Co, Cu, and Sr, 25% to 40% for Pb and Zn and, lastly, 47% to 55% for Cd.

La bioaccumulation du cadmium, du plomb et de l’arsenic par les poissons et bivalves couramment pêchés dans le système lagunaire togolais a été évaluée afin d’en estimer les risques sanitaires liés à leur consommation. Il ressort des résultats que tous les poissons analysés sont pollués. Les moyennes des teneurs en cadmium (0,33 mg/kg pour Caranx hippos à 0,98 mg/kg pour Hemichromis fasciatus), en plomb (1,17 mg/kg pour Liza falcipinnis à 2,89 mg/kg pour Lutjanus goreensis) et en arsenic (9,41 mg/kg pour C. hippos à 22,54 mg/kg pour Pomadasys jubelini) sont supérieures aux normes fixées par l’OMS. Les Facteurs de Bioconcentration (FBC) varient de 6,94 à 20,36 pour le Cd, de 9,58 à 23,67 pour le Pb et de 2,30 à 5,52 pour l’As. Quant aux bivalves les teneurs moyennes indiquent une forte concentration en Arsenic (56,06 mg/kg pour Senilia senilis et 47,76 mg/kg pour Crassostrea gasar) suivie du plomb (2,83 mg/kg pour S. senilis et 2,95 mg/kg pour C. gasar) et enfin le cadmium (0,97 mg/kg pour S. senilis et 0,83 mg/kg pour C. gasar). Les FBC varient de 16,6 à 19,14 pour le Cd, de 39,86 à 41,55 pour le Pb et de 19,10 à 34,42 pour l’As. En outre, il a été montré que la bioaccumulation de ces trois éléments varie en fonction de l’espèce considérée ainsi que de son habitat. La consommation de ces poissons et bivalves pourrait avoir des impacts négatifs sur la santé humaine en général et celle des enfants en particulier.

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.

The hydrosystem composed of Lake Togo, Lagoon of Togoville, and Lagoon of Aného is located in the coastal zone of Togo and receives important and different kinds of mining waste that cause its degradation. This study aims to evaluate the physicochemical and metallic quality of these waters and determine the possible sources of these contaminants using geostatistical, multivariate, and special analysis methods. These waters were very mineralized according to the average conductivity (15.51 mS/cm). Average contents (μg/L) in trace elements varied from 2.46 μg/L for As to 141.63 μg/L for Pb. Average levels of Cd, Pb, Cr, and Ni were significantly higher than the WHO standards. Trace elements and physicochemical parameters showed strong spatial variations with the highest values recorded downstream of the hydrosystem. The main possible source of trace element pollution was the intrusion of seawater loaded with phosphate effluent, followed by atmospheric deposition and soil leaching. This hydrosystem, therefore, deserves special attention for better planning its management.