Heavy metal contents in surface soils along the Upper Scheldt river (Belgium) affected by historical upland disposal of dredged materials.

For several decades, periodical dredging of river sediments has been necessary to allow for shipping traffic on the river Scheldt. Sediments were disposed along the shores in the alluvial plain without concern for the potential presence of contaminants. The aim of this study was to survey the alluvial plains of the Upper Scheldt river in Belgium for the presence of old dredged sediment landfills, and to appraise the heavy metal contamination at these sites. Up to 82% of the areas that were affected by dredged sediment disposal was found to be polluted by at least one of the metals Cd, Cr, Zn or Pb. Concentrations of Cd, Cr and Zn were, in 10% of the cases, higher than 26, 1900 and 2800 mg/kg, respectively. Cu and Ni concentrations were of no environmental concern on any site. Trends in metal concentrations as a function of location and time were explored and discussed. The highest average concentrations of Cd, Cr, Cu, Pb and Zn were found in the most downstream quarter of the Upper Scheldt. Contents of Pb and Cu were significantly lower for sediments disposed after 1965, but no indication for improvement of the sediment quality with time was observed for Cd, Cr and Zn. The pollution levels encountered warrant for caution as most of the soils affected by historical dredged sediment disposal are currently in use for agriculture, nature development or forestry.