Seasonal and spatial variations of heavy metals in water and sediments from mainland and maritime areas of Ebrie lagoon (Côte d’Ivoire, Western Africa)

Abstract

This study has been conducted to assessment the contamination level of the water and sediment by heavy metals of the both mainland and maritime areas in western part of Ebrie lagoon. Water and sediments samples were collected in eleven stations in mainland and maritime areas from February 2014 to January 2015. Water quality parameters such as temperature, pH, conductivity, transparency, salinity and dissolved oxygen were measured in situ and suspended matter in a laboratory. The concentration levels of mercury (Hg), lead (Pb), Cadmium (Cd) and Arsenic (As) in water and sediments were determined using Atomic Absorption Spectrophotometer. The results showed that seasonal mean values of heavy metals varied slightly during the dry, rainy and swelling seasons in both the maritime and mainland areas. The highest average values of heavy metals were recorded in the mainland area. Seasonal concentration levels of mercury and cadmium in the both maritime and mainland areas were above the safe limit for human consumption. The Pearson correlation between heavy metals and physico-chemical parameters showed a relationship between these parameters. The contamination factor (CF) in mainland and maritime areas showed that the sediments were moderately contaminated for Hg, Pb, and Cd and As during all seasons, except Cd in maritime area. Maritime sediment is low contamination for Cd. The PLI value (PLI˃1) indicates polluted sediment from mainland and maritime areas. However, generally, the mainland area is more polluted.

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Keywords: Physico-chemical parameters, exchange factor, contamination factor, pollution load index