Baseline trace element concentrations in marine sediment from the West African coast

Abstract

Baseline studies play a crucial role as tools for environmental reconstructions and assessments, and guide future actions aimed at the restoration and preservation of marine ecosystems. Major and trace elements (TE) were determined in five sediment cores collected in the Angolan and Namibian coastal waters. Predominantly homogeneous vertical profiles indicate that natural sources control levels of TE in sediments. Enrichment Factors (EF) and the Geo Accumulation Index corroborate this hypothesis. Nevertheless, among potentially toxic elements, Cr was found in high concentrations in sediment (up to 640 mg kg⁻¹), surpassing sediment benchmarks in almost all samples. This is likely ascribable to naturally occurring minerals rather than anthropogenic inputs, based on our current knowledge. In the cores near the Namibian coast, shale-normalized rare earth elements (REE) were slightly enriched in heavy rare earth elements (HREE), while in Angola the pattern was enriched in the light REE (LREE). The Pb isotopic composition of sediment was found to resemble that measured in uncontaminated sediments from Namibia (average ²⁰⁶Pb/²⁰⁴Pb = 18.98, ²⁰⁸Pb/²⁰⁴Pb = 39.3) and are indicative of carbon-rich minerals from the region, further underscoring the natural sources of Pb.