Chemical Fractionation and Soil-to-Plant Transfer Characteristics of Heavy Metals in a Sludge Deposit Field of the River Ruhr,Germany

The presented study assessed the heavy metal contamination risk in a former sludge deposit field of the River Ruhr in Essen, Germany. Therefore, the temporal and spatial distribution in soils and plants, chemical fractionation, mobilization potential, and transfer characteristics have been investigated. Soil samples, roots and shoots of rushes (Juncus sp.), and stem wood disks of willows (Salix sp.) were analyzed for Zn, Cu, Pb, Ni, Cr, and Cd. Plant available and mobile heavy metal portions have been determined using a sequential extraction procedure. The results show that the soils and the rushes are highly contaminated, although there is a considerable decrease compared to initial concentrations some 20 years ago. The willows show only small heavy metal enrichment. pH induced mobilization potential in soil is high for Cd, Zn and Ni. Additionally, these elements contain high portions of plant-available fractions. High transfer rates from soil to roots and very high rates from roots to shoots of rushes have been determined for Cd and Zn, indicating an accumulation of these elements in shoots of rushes. The rushes reflect the temporal and spatial heavy metal distribution in soil and might thus be used as a bioindicator or for phytoremediation.