Trace metals (Cd, Cr, Cu, Ni and Pb) concentrations in benthic sediments were analyzed through multi-step fractionation scheme to assess the levels and sources of contamination in estuarine, riverine and freshwater ecosystems in Niger Delta (Nigeria). The degree of contamination was assessed using the individual contamination factors (ICF) and global contamination factor (GCF). Multivariate statistical approaches including principal component analysis (PCA), cluster analysis and correlation test were employed to evaluate the interrelationships and associated sources of contamination. The spatial distribution of metal concentrations followed the pattern Pb>Cu>Cr>Cd>Ni. Ecological risk index by ICF showed significant potential mobility and bioavailability for Cu, Cu and Ni. The ICF contamination trend in the benthic sediments at all studied sites was Cu>Cr>Ni>Cd>Pb. The principal component and agglomerative clustering analyses indicate that trace metals contamination in the ecosystems was influenced by multiple pollution sources.

An analysis of the distribution and chemical forms of selected metals: cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb) in subtidal sediments of Qua Iboe Estuary and adjourning creeks, collected between June 2000 and January 2001, were studied using a sequential chemical extraction method. The concentration of metals in each extracted fraction was determined using inductively coupled plasma spectrometer (ICP-AES). Pb, Cd and Cu appear to be the most abundant metal in the sediments of the systems, and are predominantly associated with the residual, organic and oxidisable phases. Results indicate that there are also insignificant components that are bound to both the exchangeable and carbonates fractions. Ni is largely associated with bioavailable phases with insignificant bound to organic matter and residual fractions. In general, an insignificant component of Cd and Pb are bound to organic matter phase. Moreover, speciation results indicate that metal contamination in the ecosystems investigated primarily comes from human-mediated sources. Thus, based on index of geoaccumulation calculated, sediments of these ecosystems have been classified as uncontaminated by Cr, Cu and Ni, strongly contaminated by Pb and extremely contaminated by Cd.

The physicochemical properties, total metal, metal fractions, and related human health problems of metals in oil-bearing soils of Akwa Ibom State were appraised using standard procedures. The study aimed at assessing the effects of crude oil and related activities on the properties of soil including metals (Cd, Cr, Ni, Pb and V), their fractions and associated health problems. Results showed that, levels of parameters were higher in the soils examined than in the control. The entire metals examined, apart from Cd, were within their acceptable limits however; higher than the limits for agricultural soils. Cd and Cr existed mainly in the readily available fraction, while Ni, Pb, and V occurred mainly in the reducible fraction in the studied soils. Conversely, these metals, except Cd, occurred principally in the inert fraction in the control. V/Ni ratio confirmed the soils as oil-forming continents and of organic matter origin. The natural factor, crude oil, and oil-related activities were major sources of soil contaminants. Anthropogenic proportions of metals were more in the soils investigated than in the background soil. The locations were contaminated with metals. Daily intake rates of metals were within their recommended doses except for Pb. The pollution status of the oil-bearing soils and the related human health risks have been revealed.