Assessment of metal levels and pollution indices of the Songor Wetland, Ghana

Abstract

Sediment, soil and fish samples collected from the Songor Wetland were assessed for the spatial distributions of metal (Al, Fe, Zn, Cr, Ni, Cu, Pb, As, Cd and Hg) levels and contamination loads, using pollution indices and multivariate analysis. The samples were processed through microwave digestions (Soil and Sediment: [HNO3, HCl, HF, H2O2]; Fish: [HNO3, H2O2]), followed by the analysis of extracts using ICP-MS. The results displayed patchiness of metal levels in the sediment and soil samples, and in some cases, defying the established trend that levels of metals in sediments are generally higher than in soils. The differences in the results were ascribed to geological dominance and anthropogenic impacts. The finfish species displayed relatively higher bioaccumulation patterns of the metal levels than crustaceans. Aluminium (Al) and Zn levels were moderately enriched in sediment and soil samples. Overall enrichment factors ([EF {Al} and EF {Fe}]) suggested low to minimal enrichment except in a few cases. Pollution Load Index (PLI) based on Contamination Factor (CF) suggested that metal loads were less than baseline levels. On the other hand, Pearson Correlation Coefficient demonstrated that the metals present in the wetland were more lithogenic with remarkable inputs of biogenic and anthropogenic components. Principal Component Analysis revealed an association of Zn to the western section of the wetland, Cd, and Hg to the eastern part while the remaining metals were concentrated at the mid-section of the wetland. Lead (Pb) levels (1.10 ± 0.70 mg/kg) in finfishes exceeded the EU Regulation 1881/2006/EU (0.05 mg/kg) for fish tissues and could pose public health concerns.