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

Abstract

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.

Assessment of the Pollution Status of Alluvial Plains: A Case Study for the Dredged Sediment-Derived Soils Along the Leie River

“…In 99 of the 139 samples (72%) with soil pollution, Cr, Cd as well as Zn concentrations are above the pollution criterion for agriculture, nature and forestry. Cd pollution is lower than in the Upper Scheldt area (Vandecasteele et al 2002a) and similar to the Sea Scheldt (Vandecasteele et al 2003). In comparison with the Upper and Sea Scheldt, Cr levels are lowest while the Zn, Cu and Pb levels are highest for the Leie DSDS.…”

“…Along the Leie river, sediments have mostly been disposed close to the location where they were dredged, this in contrast to the Upper (Vandecasteele et al 2002a) and Sea Scheldt (Vandecasteele et al 2003). This greatly facilitates detection of spatial and temporal trends in sediment disposal and sediment quality for the river Leie.…”

“…The pre-requisite of metal stabilization in the sediment for temporal comparison of sediment data (Christiansen et al 2002) is largely met for these calcareous landfilled sediments because of the very low mobility of metals (Vandecasteele et al 2002a). It is evident from the data that sediment pollution was occurring since long before 1970, especially for the area downstream from Deinze.…”

“…the destroyed meandering pattern, the levellingup of the wetter parts during the river broadening works (Defoort and Roggeman 1996), the intensive urbanization pressure on the open areas (upstream from the canal Roeselare-Leie), and both pollution status and geographical distribution of DSDS especially in the vicinity and downstream from Deinze. Landfilling of dredged sediments caused a pollution of the alluvial plains with a more permanent character than the in situ sediment pollution itself (Vandecasteele et al 2002a). River sediment quality is expected to improve gradually once input of pollutants into the river system has been reduced.…”

“…Temporal trends may also be affected by diagenetic processes (Zwolsman et al 1993). Besides the use of sediment and suspended matter samples taken directly from the river bed (Ollivon et al 2002, Belzunce et al 2001, sediment cores from floodplain lakes (Winter et al 2001), landfilled dredged sediments (Vandecasteele et al 2002a) and salt marshes (Zwolsman et al 1993, Christiansen et al 2002 were used to identify temporal trends in sediment quality.…”