Multivariate analysis of potentially toxic metals in sediments of a tropical coastal lagoon.

Surface sediments collected from the Lagos Lagoon, Nigeria, and three adjoining rivers were analysed for their physicochemical properties and pseudo-total concentration of the potentially toxic metals (PTM) Cd, Cr, Cu, Pb and Zn. The concentration of the PTM varied seasonally and spatially. Odo-Iyaalaro was observed to be the most polluted river, with highest concentrations of 42.1 mg kg(-1), 102 mg kg(-1), 185 mg kg(-1), 154 mg kg(-1) and 1040 mg kg(-1) of Cd, Cr, Cu, Pb and Zn, respectively, while Ibeshe River was the least contaminated, apart from a site affected by Cu from the textile industry. Some of the sediments were found to be above the consensus-based probable effect concentrations and Dutch sediment guideline for metals. Overall metal concentrations were similar to those reported for other tropical lagoon and estuarine systems affected by anthropogenic inputs as a result of rapid urbanisation. Due to the large number of samples, principal component analysis was used to examine relationships within the data set. Generally, sediments collected during the dry season were observed to have higher concentration of PTM than those collected during the rainy season. This means that PTM could accumulate over a prolonged period and then be released relatively rapidly, on an annual basis, into tropical lagoon systems.

Correlation studies of heavy metals concentration with sediment properties of some rivers surrounding the Lagos Lagoon

Lagos lagoon is a highly polluted water body; which receives enormous amount of domestic and industrial wastes from rivers and streams. In this study; two main Lagos urban rivers Odo-Iyaalaro and Shasha rivers that receive industrial effluents and empty into the Lagos Lagoon were examined. The sediments at the bottom of waters play a role in the study of pollution in the rivers. Upstream of Odo-Iyaalaro River (Point 1) receives the largest volume of effluents and showed the highest level of heavy metals in sediments with concentrations of 108.3mg/l for Pb; 805mg/l for Zn; 94.5mg/l for Cu; 31mg/l for Cr and 42.1 mg/l for Cd. Down the river; the levels decreased to 25mg/l for Pb; 64.5 mg/l for Zn; 22mg/l for Cu; 15.9 mg/l for Cr and 1.9 mg/l for Cd. A good correlation was found to exist between the level of Zn in water and sediment; and also between the CEC andsilt-clay of sediments. Shasha River receives relatively fewer amounts of industrial effluents; but is relatively the main receptacle for municipal and land-based waste. The levels of heavy metals in Shasha River were lower compared with that of Odo-Iyaalaro River; with the upstream points showing concentrations of 20.5mg/l for Pb; 25.3mg/l for Zn; 7.9mg/l for Cu; 30.8 mg/l for Cr and 1.5mg/l for Cd. A good correlation exists between the CEC and all the metals determined; and between theorganic carbon and all the metals determined. Compared with literature data; the results of heavy metals gave an indication of pollution