To improve understanding in the area of the fundamental physical and chemical processes governing pollutant behaviour in the soil system using a combination 
of new and existing knowledge applied to soil samples, soil solutions and transport in soil columns and aquifers. 
            

he effect of calcium competition on cadmium binding on humic acids has been measured using voltammetric methods. Adsorption of humic acids on the mercury aqueous 
solution interface has been studied. Copper binding to humic acids was measured by ion selective electrode at pH 4, 6 and 8 with copper activities varying from 
1E-3 to 1E-14 M. 10 different types of iron oxides were synthesized and characterized for specific surface area and porosity. Binding of cadmium on several 
of these oxides was measured as a function of pH and metal ion activity. The charging characteristics of these same oxides were determined as a function of pH 
and ionic strength. Although the charging properties varied considerably for the various materials, the cadmium binding behaviour was quite similar. Adsorption 
of humic acid on hematite was studied as a function of pH, indicating increased adsorption with decreasing pH. Cadmium binding on 2 different soils was measured 
using pH stat and a cadmium selective electrode, allowing the exchange stochiometry between hydrogen and cadmium ions to be established. A collection of 28 
different soils was intensively characterized and the soil extracts analyzed for approximately 50 elements. A theoretical analysis was made on wetting front 
instability leading to fingering wetting, profiles. This type of water movement can also affect solute transport in the field. The combination of physical 
and chemical heterogeneity on solute transport was analysed. A new analytical mathematical solution for this type of problem was derived and results were 
compared with those of numerical methods. The longitudinal spreading of the retarded plumes is greatly affected by the interplay of physical and chemical 
heterogeneity. Transverse spreading is unaffected by chemical heterogeneity.  
In the research project 6 major parts can be distinguished as follows.   
  
Measurement and modelling of the interaction of cadmium, zinc, hydrogen and calcium with several purified soil humic and fulvic acids. Measurement and 
interpretation of the metal speciation in soil extracts using water and 0.01 M calcium chloride as extractants.   
  
Preparation and characterization of iron oxides with different surface structures. Measurement and modelling of specific ion adsorption (both cations 
and anions) on these iron oxides. Characterization of iron oxides in soils, measurement and modelling of ion adsorption to iron oxides in soils.   
  
Measurement and interpretation of the interaction of purified humic and fulvic acids with mineral surfaces (metal oxides, clay) in the presence of variable 
concentrations of metal ions under a series of environmental conditions (eg pH, salt level). Measurement and modelling of metal speciation in these systems. 
  
  
Development of methods to determine the type and number of reactive sites in soils. Measurement of metal adsorption to soils under a series of conditions, 
test of the applicability of physical chemical adsorption models for estimating metal speciation in soils.   
  
Integration of existing and newly developed knowledge with respect to chemical processes in soil (adsorption to several reactive phases, complexation, 
ion exchange, precipitation) in a multi component chemical model that can be coupled to a transport algorithm.   
  
Finally, measurement of heavy metal transport (cadmium and zinc) through soil and aquifer materials. Modelling with the multicomponent transport model 
to validate parameter sets obtained in the second, third and fourth parts. Extension of measurements and modelling using heterogeneous columns. In situ measurement 
of tracer and reacting chemical transport in unsaturated soil and in aquifers to characterize preferential flow in natural heterogeneous systems. Modelling 
with deterministic and stochastic models for soil and aquifers. 
            

Lead Institution: 
Wageningen Agricultural University, Wageningen, The Netherlands 
Partner Institutions: 
Instituto Superior Tecnico (PT)  
Technische Universitat Munchen, Munich, Germany  
Natural Environment Research Council, Swindon, UK  
Universita degli Studi di Trento, Italy  
Junta de Andalucia, Spain  
 
This information was taken from a source other than the project site: European Commission (1993) STEP and REWARD project synopses from the Second Framework 
Programme (1987-1991). No EUR 14849 EN