LEVELS AND DISTRIBUTION OF TRACE-METALS IN SEDIMENTS OF LAGUNA LAKE (PHILIPPINES) AND ITS TRIBUTARY RIVERS

Trace metal levels in bottom sediments of Laguna Lake (Luzon, Philippines) and of five of its tributary rivers, and in lakeshore samples were compared. Total metal analyses by flame atomic absorption spectrophotometry indicate relatively low (Cu, Zn, and Pb) to moderate (Fe, Mn, Hg, and Cd) metal contamination in the sediments. Using the Tessier et al. sequential chemical extraction scheme, the order of remobilizability was Mn > Cu > Zn » Fe for lake sediments; similar trends were observed in tributary river sediments and lakeshore soil samples, except that Zn was more extractable than Cu. Organic matter bound significant amounts of Cu, Zn, and Fe in lake sediments and of Cu in river sediments. Mn was distributed rather evenly across all fractions in all samples. The largest fraction of all metals in lakeshore soil was associated with reducible Fe/Mn oxides. The non-available or residual fraction (relative to the total metal content) in all samples ranged as follows: Fe, 85-94%; Zn, 40-81%; Cu, 39-78%; Mn, 9-74%. © 1991, Taylor & Francis Group, LLC. All rights reserved.