Concentrations and ecological risks of metals in surface sediments of some coastal creeks in the Niger Delta, Nigeria

Abstract

The concentrations of nine metals were measured by atomic absorption spectrophotometry in surface sediments of three coastal creeks, namely, the Ifie, Egbokodo and Ubeji creeks, in the Niger Delta of Nigeria, from August 2012 to January 2013. The aim of the study was to provide information on the spatial and seasonal distribution patterns, degree of contamination, and ecological risks of metals in these sediments. The mean concentrations of the nine metals in these creek sediments ranged from 0.30 to 3.20 mg kg⁻¹ Cd; 10.7 to 24.7 mg kg−1 Pb, 125 to 466 mg kg⁻¹ Cr; 3.1.10 to 14.9 mg kg⁻¹ Cu; 4.7 to 14.3 mg kg⁻¹ Co; 61.1 to 115 mg kg−1 Ni; 106 to 183 mg kg⁻¹ Mn; 52.0 to 170 mg kg⁻¹ Zn and 5 469 to 20 639 mg kg⁻¹ Fe. In general, the metal concentrations were higher in the dry season than the wet season, except for Cr. The concentrations of Cd, Cr, Ni and Zn were above their regulatory control limits in sediment as specified by the Nigerian Regulatory Authority and Cd was identified as the main ecological risk factor. The enrichment factors for the studied metals followed the order: Cd > Cr > Ni > Zn > Pb > Co > Mn > Cu. The average multiple pollution index values indicated that these sediments were severely polluted with significant inputs from Cd, Ni and Cr.

Keywords: Contamination factors, distribution patterns, enrichment factors, pollution index, seasonal variations, soil quality