The environmental availability of heavy metals in soils and sediments : the influence of site specific factors
This thesis examines how the environmental availability and fractionation of arsenic,
cadmium, chromium and lead varies in soils and sediments of three sites in Walsall,
West Midlands. Two ofthe sites have historically received landfill whilst one is a
canal. The data indicates that the percentage of the four metals leachable represents a
very low percentage of the total flux present due to binding to components in the
substrates. The soils and sediments from the three sites underwent analysis for total
and leachable arsenic, cadmium, chromium and lead using rep-OES and rep-MS.
Analysis of other major and trace elements was carried out using rep-OES whilst the
soils and sediments were also characterised in terms of organic matter content,
particle size, and electrochemistry. Sequential extractions using the 3-stage BCR
method and principal components analysis enabled the association of the heavy metals
with different soil components on each site to be determined.
The results show that on the Slacky Lane landfill site arsenic is bound to aluminium
hydroxide/organic complexes, chromium is associated with the clay fraction, whilst
cadmium and lead are mainly associated with oxides of iron and manganese. On the
Walstead Road landfill site arsenic is mainly associated with aluminium
hydroxide/organic complexes whilst cadmium, chromium and lead are associated with
manganese oxides. By contrast, in the Walsall Canal sediments, arsenic and
chromium are associated with sulphides, lead with organic matter/silt size particles
/ and cadmium with both organic matter/silt and manganese oxide/calcium complexes.
The research enables models to be produced that show how the metals are fractionated
on those sites specifically which have been previously poorly characterised. This
enables a prediction to be made ofthe possible release scenarios of the metals under
changing environmental conditions.