Interrelationship between Ecological Risk Assessment with Trace Metals Levels in Surface Sediments from Fresco Lagoon, Côte d’Ivoire, West Africa

The objective of the present study was to determine the trace elements concentrations in the sediments on one hand, and on the other hand, to identify their main sources of contamination. This study will allow an updating of data, understanding of the origin and the extent of contamination of these trace metals through their spatial distribution in the aquatic environment of the Fresco Lagoon. Contamination of aquatic environment by trace metals has been intensively studied in recent years, due to the fact that metals are persistent, toxic, tend to bioaccumulate, and that they induce a risk for humans and ecosystems.

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. 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 (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. There was no hazardous danger for benthic creatures in the sediments from Fresco Lagoon when the trace metal concentrations were compared to the sediment quality standards. In conclusion, the findings of the current study have demonstrated the necessity of the best management of anthropogenic activities with regard to trace metals in general, and Pb and As in particular.