Study of the overall toxicity, water quality and microplastics of the peninsula of Cape Verde, Senegal [résumé]
Résumé
Currently only thirteen percent (13 %) of domestic wastewater produced daily in Dakar is being treated. Industrial and agricultural activities and domestic waste are the source of significant pollution of the marine and coastal environment in Senegal. Our work focuses on assessing the overall toxicity of sediments, the microbiological and chemical quality of water, and the quantification of microplastics around the Cape Verde Peninsula. Physicochemical measurements are carried out in situ and the sampling points correspond to effluent outlets, compared to two reference stations that are assumed to have little or no contamination. A total of 15 sites were collected: Cambéréne, Yoff Tonghor, Ngor, Almadie-Vivier, Ouakam, Magdalen Islands, Soumbédioune, Dakar Dantec, Hann1, Hann2, Port of Dakar, Lac rose, Guédiawaye, Mamelles and UCAD. High sediment toxicity [100% ADL (Larval Development Anomalies)] was demonstrated at sixty percent (60%) of the sites. Twenty percent (20%) of sites have intermediate toxicity ranging from 30% to 60% ADL). Sites with the lowest toxicity (up to 30% ADL) accounted for only 20% and no ADL values were reported as nil. Mercury levels in sediments are very low, with a notable variation between sites in the north and those in the south of the peninsula. Coliforms (Escherichia coli) and enterococci are present in large quantities at most sites (64%). The presence of Salmonella is noted only in Cambéréne. The results of mass spectrometry analyzes also show overall high concentrations of heavy metals (Al, Cd, Cr, Co, Cu, Hg, Ni and Zn) with the exception of Fe and Mn, which are below the criteria for "Protection of acute and chronic aquatic life". Microplastic analysis revealed high mean values: 25,864 mpts / km2 (42 g / km2) for microplastics (300 µm and 5 mm) and 37,441 MPTS / km2 (97.33 g / km2) for macroplastics > 5 mm and < 200 mm). All the results obtained show, according to the pollutants, the importance of the sediment granulometry, the nature of the pollution, the size of the effluents, the anthropic contributions, the atmospheric falls like that of the behaviors of the populations. Our results are discussed with a view to environmental monitoring at the local, regional or national level. They will also allow this approach to be extended to other contaminants (hydrocarbons, metals, pesticides, megaplastics) as well as bio-trials in the various compartments of the marine and coastal environment (sediments, waters, fauna and flora ). An in-depth statistical analysis will also allow optimization of ecotoxicological monitoring, sampling and analysis strategies.