Algae samples from Dakar coast (Senegal) and Galician Rias (Spain) were analyzed by cold vapor atomic absorption spectrometry (CV-AAS) to assess the bioaccumulation of mercury in the two aquatic systems. In this work, the contents of inorganic mercury and total mercury were determined. Simplified analytical procedures (microwave digestion and ultrasonic assisted extraction) were used for sample preparation. A reference material (BCR-60) was used to validate the analytical procedures used for sample preparation. The results of the analysis show that the total mercury contents found in algae samples from the Galician Rias are relatively similar to those found in algae samples from the Dakar coast. However, the inorganic mercury content of the algae from Pontevedra Ria was considerably higher than that found in the algae samples from Vigo Ria. The distribution was observed for inorganic mercury and total mercury, indicating that inorganic mercury is the major mercury species that bioaccumulates in marine algae. The inorganic mercury contents were always approximately equal to those of total mercury in the algae samples and a satisfactory correlation (p <0.0001; r = 0.9997) was obtained between them. Finally, the ANOVA analysis indicates that no significant difference (F = 0.165; p = 0.809) was found between the algae of the two aquatic systems (Dakar coast and Galician Rias).

Mussel samples from the Dakar coast (Senegal) were analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Microwave acid digestion was also employed for metals (Mn, Pb, Cd, As) determination. Dakar coast usually receives numerous domestic and industrial discharges without prior treatment. The contents of Arsenic were, in all cases, higher than other metals. However, the bivalve molluscs present themselves as effective bio-monitors when assessing marine aquatic pollution by contaminants in the Dakar coast. The ANOVA analysis allows concluding that significant differences were found between mussels from different sampling points. In all cases, the February samples have in all cases a higher content than those collected in October.

Au Sénégal, les eaux usées constituent les principales sources de pollutions des milieux aquatiques. Ce travail étudie la répartition des paramètres physico-chimiques et métalliques des eaux usées drainées par le canal Est d'évacuation de la baie de Hann, en milieu marin. La commune de Hann, située le long du littoral dakarois, a été choisie pour les nombreuses activités, surtout industrielle qui s'y déroulent. L'Office Nationale de l'Assainissement du Sénégal (ONAS) estime à près de 180 000 mètres cubes d'eaux usées par jour jetées en mer. Ainsi, l'environnement de la baie est agressé par les rejets industriels et domestiques sans traitement préalable. A cela, s'ajoute l'apport des effluents provenant du port de pêche, des petites industries de transformation, des habitats de type traditionnel et des décharges sauvages d'ordures. Les échantillons des mesures sont prélevés au point de chute des eaux du canal et à une distance de 40 mètres dans l'océan. Les paramètres physiques (pH, température et conductivité) sont mesurés in situ à l'aide d'un appareil HANNA instruments pH/conductivity de marque HI 98129. Les paramètres chimiques (ammonium, chlorure, nitrate, phosphate, sulfate, fluorure) et métalliques (chrome 6, fer, potassium) ont été dosés par un spectrophotomètre de marque PF-11. Les résultats obtenus dans les eaux usées montrent la présence de tous les paramètres étudiés, notamment (Cl-, PO 4 3-, NO 3-, NH 4 + et SO 4 2-) de concentrations en moyennes respectives (223.33, 44.33, 7.33, 108.33 et 161). Les teneurs notées en profondeur sont plus élevées que celles contenues dans l'eau de mer naturelle. Les valeurs maximales sont, cependant, observées près du point de rejet des eaux. Ainsi, ces eaux usées modifient la composition physico-chimique des eaux salines des côtes dakaroises jusqu'à 40 m du point de rejets.

No abstract

The region of Dakar is characterized by a high population density often leading to a problem of development of the sewage network not equipped with a treatment station. The ejection of these raw untreated waters on the Dakar coast continually causes pollution of bays, seawater and threatens life in the aquatic environment and human health. The objective of this study is to assess the physicochemical quality of the wastewater discharged at the beaches of Hann, Mbao and Soumbédioune by the UV-visible spectrophotometry method. The physicochemical parameters show that the temperature varies between 21.7 and 34.8°C and the pH ranged from 6.73 to 7.93. Results are European standards for the water quality. However, the conductivity ranged from 1569 to 86500 (μS/cm) and exceeds the European standard. In addition, water results obtained show that the wastewater derived from the Dakar coast is rich in nitrites (2.3 mg/L) and phosphates (65 mg/L) which clearly exceed the standards established by the legislation, WHO (2017) reference guideline. Thus, it becomes important to establish sewage treatment plants in the study areas to improve the state of the coastal environment of the Dakar coast.