Bervoets, L.

Blust, R.

de Deckere, E.

De Jonge, M.

Meire, P.

Teuchies, J.

Open Marine Archive

The effect of increasing surface water oxygen concentrations on 
metal mobility in sediments from the Schelde Estuary 
Teuchies J.1, M. De Jonge2, L. Bervoets2, E. de Deckere3, R. Blust2 and P. Meire1.  
1 ECOBE, Departement Biologie, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Wilrijk, Belgium 
E-mail: johannes.teuchies@ua.ac.be   
2 EBT, Departement Biologie, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, 
Belgium 
3 Port of Antwerp, Havenhuis 1, Entrepotkaai, B-2000 Antwerpen, Belgium 
 
Domestic and industrial waste water was untreated in many Belgian streams for decades. A high 
organic load resulted in low surface water oxygen concentrations while contaminants, including 
trace metals, were often concentrated in the sediments. Under these hypoxic conditions the 
formation of insoluble metal sulfides is found to reduce metal mobility and toxicity in sediments (Di 
Toro et al., 1992). However, after the implementation of waste water treatment plants last years, an 
increase in surface water oxygen concentrations was observed in many rivers, the Schelde and its 
tributaries included. Under these conditions, sulfides may be oxidized and associated metals can 
become more available in the sediment or migrate to the surface water. Then the risk exists that 
historically contaminated sediments will be turned from a trace metal sink into a trace metal source. 
In an experimental setup the effect of surface water aeration on trace metal mobility was 
investigated. Natural sediments from the Zenne and Moerbeek with high concentrations of metals 
and sulfides were exposed to aerated surface water (oxygen = 90%). This resulted in increasing 
sediment redox potential values and decreasing sulfide concentrations. Trace metals, precipitated 
with these sulfides, became more mobile. An increase in sediment metal availability, release to the 
surface water and higher toxicity to Daphnia magna were observed after 2 months exposure to the 
high oxygen surface water.  
 
Long term field data were used to explore the effects found in the experiments on a larger scale. 
Due to the implementation of a waste water treatment plant near Brussels in 2007, an abrupt 
increase in oxygen concentrations in the Zenne surface water was observed. However, this did not 
result in increasing metal concentrations in surface water of the Zenne, as could be expected based 
on the experimental results. Also in the Schelde Estuary oxygen concentrations raised the last 10 
years but differences concerning the effect on trace metal mobility may exist. The gradual decrease 
in surface water concentrations of most metals between 1960 and 2005 is followed by a recent 
increase of some metals in the river water. Additionally, surface sediment metal concentrations in 
freshwater tidal marshes of the Schelde showed a recent increase. Increasing oxygen concentrations 
in the Schelde resulting in higher metal mobility in the sediments can be one of the possible 
explanations. 
 
These results may indicate a large scale mobilization of trace metals from Schelde sediments which 
contain a huge amount of historically accumulated trace metals. Even when the migration towards 
the surface water may be negligible in terms of toxicity, a substantial increase in metal availability 
in the superficial sediment layer can be expected. Since this layer is of main importance for benthic 
invertebrates and consequently for feeding migrating birds, metal toxicity in this biologically 
important zone may have a large impact on the estuarine ecosystem.  
 
References  
Di Toro, D.M., J.D. Mahony, D.J. Hansen, K.J. Scott, A.R. Carlson and G.T. Ankley. 1992. Acid volatile 
sulfide predicts the acute toxicity of cadmium and nickel in sediments. Environ Sci Technol. 
26:96-101. 
 
 
 
 - 82 -


The effect of increasing surface water oxygen concentrations on metal mobility in sediments from the Schelde Estuary

Abstract

Similar works

Full text

Available Versions

Open Marine Archive