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Trace Metal Leachability of Land-Disposed Dredged Sediments

Soil and Water Science Dep., Univ. of Florida, Gainesville, FL 32611-0290.

Filip M. G. Tack and Marc G. Verloo

Vakgroep Toegepaste Analytische en Fysische Chemie, Universiteit Gent, Coupure Links-653, B-9000 Gent, Belgium.

^* Corresponding author (spsingh{at}gnv.ifas.ufl.edu).

ABSTRACT

The potential risk of surface and ground water contamination by trace metals leached from contaminated land-disposed dredged sediment is a major environmental concern. The objective of this study was to evaluate trace metal leachability, leachate quality, and environmental effects of land-disposed dredged sediments (LDDS). In addition to chemical characterization and determination of potential and actual leachability, dredged sediments were also subjected to solid phase fractionation using a sequential extraction procedure. Potential leachability, defined as the maximum metal pool that may become available for leaching at a constant pH 4, decreased in the following order: Zn Cd > Mn > Ni > Co > Cu As > Pb > Cr. Potential metal leachability was controlled mainly by solid phase distribution of metals in sediments. The acid-extractable fraction of most metals correlated well with the potentially leachable metals extracted with a solution of pH 4 (r² > 0.67), except for Pb. The kinetics of metal release were determined using the cascade leaching test (CLT) with water at pH 4. Except for Ni and Zn in the first fraction, metal concentrations in all consecutive leaching fractions remained below the maximum permissible level in water for human consumption. Actual metal leachability expressed as a percentage of potential leachability varied widely among trace metals and decreased in the order: As > Cu > Cr > Ni > Zn > Cd > Co > Pb. Our results indicate low risk of surface and ground water contamination resulting from land disposal of dredged sediments.

Approved for publication as Florida Agricultural Experiment Station Journal Series no. R-06940.

Received for publication June 11, 1999.