Ecological Risk Link to Trace Metals Levels in Surface Sediments from Fresco Lagoon, Côte d’Ivoire, West Africa

Sediment contamination with trace metals remains a current problem for aquatic ecosystems management worldwide. Surface sediments from Fresco Lagoon (Côte d'Ivoire) were analyzed to assess the contamination degree of the area. Concentrations of five selected trace metals (Pb, As, Mn, Zn, and Fe) and organic matter content were determined in samples collected from ten (10) stations, from June 2019 to March 2020. Trace metals concentrations were determined using an ICP-OES Instrument, while the organic matter contents were determined by the mass loss on ignition. The results revealed organic matter contents ranged from 5.28 to 28.31% and concentrations of trace metal (in mg.kg-1 dry weight) in the following ranges: 3.68 to 38.2 for Pb, 0.98 to 19.1 for As, 19.79 to 325 for Mn, 13.78 to 461.18 for Zn, and 1269.21 to 59862.37 for Fe. Organic matter showed a positive and significant correlation with Pb and Fe. To assess the metal pollution status in the studied area, four pollution indices were also calculated: Geoaccumulation Index (Igeo), Enrichment Factor (EF), Degree of Contamination (DC), and Pollution Load Index (PLI). Based on Igeo values, the sediments of Fresco Lagoon were in the range of unpolluted to moderately polluted with As, but unpolluted with Zn, Pb, Mn, Fe. The Enrichment factors of Pb, Zn, As, Mn, and Fe were: 64.22±52.32, 107.04±111.88, 227.29±203.06, 10.25±8.76, and 52.04±47.44 respectively, suggesting that the source of those metals was more likely to be anthropogenic. The falling trend of enrichment factors was as follows: As > Zn > Pb > Fe > Mn. Moreover, the PLI values (PLI>1) showed higher values at the stations closed to the urban area, due to the influence of direct external sources such as agricultural runoff, and other anthropogenic inputs. The comparison of trace metals concentrations in sediments from Fresco Lagoon with the sediment quality guidelines showed that there was no toxic risk for benthic organisms regarding arsenic, lead, and zinc. In conclusion, the results obtained for the present work have revealed the need for the best management of anthropogenic activities regarding trace metals in general, and more particularly Pb and As.