T HE STUDY aims at evaluating the quality of the water in the Ouémé River basin. Data were collected from October 2014 through September 2015. Physico-chemical parameters were assessed and the concentrations of dissolved heavy metals were determined. The results show both physical and chemical pollutions of the water according to a nonlinear pollution gradient. The middle basin up to the height of the city of Kaboua appears to be the most polluted segment. The Delta region, near the coast, is the second most polluted segment, and the remaining parts of the basin are the least polluted. Pollutant concentrations are highest during the low flow season. Cluster analysis and Principal Component Analysis (PCA) of sampled sites reveals that Atchakpa-Rejet and Kaboua have high concentrations of nitrite, nitrate, ammonium, orthophosphate, conductivity, TDS, pH, calcium, magnesium, and total hardness. Kpassa, Bétérou, and Atchakpa-Bethel have high dissolved oxygen and high transparency values. All other sites have high alkalinity. During the low flow season, Cd, Pb, Zn and Cu were detected at concentrations exceeding ecological standards in most of the sites. The Water Quality Index (WQI) ranged from 52.7 to 80.9, meaning that water in that river basin can be classified either as marginal quality, moderately polluted, or good quality for aquatic life. Overall, water in the Oueme River basin is under high and increasing influence of human activities.
Ostracoda species are indicators of their current and past environment (paleoenvironment). The study aims to evaluate the acute and chronic sensitivities of a freshwater ostracod species (Eucypris sp.) to agricultural pesticides (a cypermethrin-based insecticide and a glyphosate herbicide-based formulation). Lethal concentrations (LC50) of each pesticide for the species at 24 and 48 h were determined. The chronic exposure allowed assessing the effects of low concentrations of both pesticides; firstly, on the parthenogenetic reproduction of Eucypris sp., and, secondly, on its population growth. Then, individuals of Eucypris sp. were exposed to 0.536 ppb and 1.072 ppb of cypermethrin and 4.51 ppm and 9.03 ppm of glyphosate. These concentrations are respectively the 10%, and the 20% of the 48-h LC50 (median lethal concentration) of both pesticides for the species. The estimated 24-h LC50 of cypermethrin was 7.287 ppb. At 48-h, it was 5.361 ppb. For glyphosate, the 24-h LC50 was 50.521 ppm, while at 48-h it was 45.149 ppm. After 10 days of exposure to low concentrations of cypermehrin, only 30% of females reproduced parthenogenetically with 10% and 20% of LC50-48-h. For the control treatment, reproduction in 80% of females was observed. Eucypris sp. population growth after 28 days of exposure to low concentrations of cypermethrin showed significant retardation. Regarding glyphosate chronic exposure, 60%, 50%, and 90% of individuals were able to reproduce at 10% of LC50-48-h, 20% LC50-48-h, and the control treatment, respectively. The population growth was also affected by the tested low concentrations of glyphosate. The study showed high sensitivity of Eucypris sp. to cypermethrin compared to glyphosate. However, low concentrations of both pesticides affected the species at individual and population level.
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