Sediment load and bioconcentration of heavy metals by shrimp (Peaneus notalis) from Epe Lagoon, Nigeria.

In many developing countries, surface waters, especially rivers and lagoons, have become deposition sites for all sorts of wastes. Three sampling sites located trigonally on Epe lagoon, Lagos, Nigeria were identified, and water, sediment, and commonly farmed shrimp, Peaneus notalis, were sampled and assessed for heavy metal concentrations. Zn, Pb, Ni, Cu, Cr, Cd, and Mn were determined in the aqua regia digests of the samples by means of Perkin Elmer AAnalyst 200 atomic absorption spectrophotometer. Heavy metals occurred above detection limits at all sites. The highest load of these trace elements was found in sediment samples followed by the water samples. The levels observed in the shrimp samples, however, were much lower than WHO levels. In the distribution, zinc was the highest metal found in the samples ranging from 17.94 +/- 2.60 mg/L in water to 37.85 +/- 9.35 microg/g in sediments. The least was Cd 0.03 +/- 0.01 mg/L in water and 0.28 +/- 0.04 microg/g in sediments. Lead was the most widely varied metal in shrimp with a 84.38% coefficient of variation. Apart from Cr, the metals appeared to be fairly and evenly distributed in the sediment, with coefficient of variation ranging from 14.29% (Cd) to 24.76% (Mn) The variations were between 14.49% (Zn) and 66.67% (Cr) in the water samples. The paired t test carried out between water and sediment, water and shrimp, and shrimp and sediment was significant at p = 0.05. Three-factor analysis of variance did not reveal any significant difference in metal burdens among the trigonally located sites under investigation. Shrimp samples showed evidence of bioaccumulation but are still below internationally established levels.