Geochemical Composition of the Lomé Lagoon Sediments, Togo: Seasonal and Spatial Variations of Major, Trace and Rare Earth Element Concentrations

Abstract

The concentrations of major, trace (TE), and rare earth (REE) elements and their seasonal and spatial distribution were studied on the fine fraction (<63 µm) of the sediments of the Lomé lagoons (West Lake, East Lake, and Lake Bè). The sediments were collected on a total of nine sampling sites (three per Lake) during two campaigns (dry season and rainy season). The quality of the sediments was assessed on the basis of the enrichment factor (EF) and the labile or non-residual fraction (NRF) in relation to the values recommended for the quality of the sediments (Sediment Quality Guidelines, SQG). The distribution of rare earth elements shows enrichments in light rare earths superior to those of heavy rare earth elements during any season. Positive Ce anomalies are less noticeable and less variable between seasons than Eu anomalies. La/Yb ratios are positively correlated with the percentage of Al and Fe oxides and with the percentage of fine fractions. The main bearing phases of rare earth elements are, therefore, Al and Fe oxides and the finest fractions of the sediments. The concentrations of trace elements vary little, according to the seasons, but show strong variations from one element to another. The degrees of enrichment obtained are moderate for Bi, Cr, Ga, Mo, Pb, Sn, and Zn (1.5 < EF < 5) to significant for As, Cd, and Sb (5 < EF < 20) for all sites of Lake Bè. For the sites of West Lake, the degrees of enrichment obtained are moderate for As, Cd, Cu, Mo, and Pb (1.5 < EF < 5) to a significance for As, Bi, Cd, Pb, Sb, Sn, and Zn (5 < EF < 20). Only the East Lake sites show high degrees of enrichment for elements such as Sb and Sn (20 < EF < 40). Trace elements (TE) such as As, Cd, Cu, and Ni have total concentrations within the range of variation of the SQG concentrations (particularly Probable Effect Level (PEL) and Effect Range Median (ERM)), whereas Cr, Pb, and Zn total concentrations are higher. The ranking of priority sites with respect to the sediment contamination is determined according to ERM and PEL quotients in relation to the probability of toxicity for benthic organisms. For almost all the sites, the priority is lowest to medium-low with regard to As, Cd, and Cu and medium-high (Cr and Ni) to highest (Pb and Zn), particularly for the East and West Lakes. Moreover, the NRF can represent significant percentages of the total TE concentrations: 5% to 15% for As, Bi, Ni, V, Mo, and Sc, 15% to 25% for Co, Cu, and Sr, 25% to 40% for Pb and Zn and, lastly, 47% to 55% for Cd.

Major Factors Controlling the Elemental Composition of Al-Kharrar Lagoon Bottom Sediments, Rabigh, Saudi Arabia

“…With future changes in the pH, redox potential, salinity, and dissolved organic carbon of the lagoon, heavy metals trapped in sediments can be released into the water column and become bioavailable and posing a negative effect on biota. If the pH of bottom water drops to 5 and 5.5, Cu, and Zn can be rapidly bio-available in the aquatic environment, respectively [43,44]. In addition, the warm and dry climate and the construction of dams reduced the freshwater supply to the lagoon allowing increasing water salinity.…”

Multi-Indices Assessment of Origin and Controlling Factors of Trace Metals in River Sediments from a Semi-Arid Carbonated Basin (the Sebou Basin, Morocco)

“…The total concentration is not sufficient to evaluate the potential risk of metal availability to living organisms [16,67]. The distribution of TMs between the residual and non-residual fractions was determined using widely used simple EDTA and HCl extractions in order to extract the maximum possible fraction of trace elements more or less weakly adsorbed on organic and inorganic complexes [35,68].…”

Physicochemical and Microbiological Quality of Shallow Groundwater in Lomé, Togo

“…Groundwater mixing with the lagoon system is a potential source of groundwater contamination in addition to on-site sanitation facilities, leakage of municipal and industrial wastewater. Therefore, water resources interactions deserve considerations for future investigation with emphasis on additional contaminants such as pesticides, organic matter, polycyclic aromatic hydrocarbons, and trace elements including As, Cd, and Pb, which were determined in coastal surface water and sediments (Gnandi et al, 2011;Ayah et al, 2015;Badassan et al, 2020). The consideration of the impact of the seasonal rainfall with hydrogeological conditions as well as the risk factors associated with each sampling point (the type of boreholes, boreholes drilling technic, borehole construction and maintenance, boreholes lining, proximity to and density of contamination sources, boreholes depth, static level, etc.)…”