Page 303 - Soil and water contamination, 2nd edition

290 Soil and Water Contamination
Y m
Y L b OM c a (16.4)
st st st
Y r
-1
-1
where Y = standardised concentration (mg kg ), Y = measured concentration (mg kg ),
st m
-1
Y = regression prediction of concentration (mg kg ), L = clay content of standard soil (%),
r st
and OM = organic matter content of standard soil (%). In the Netherlands, the standard
st
soil is usually defined as a soil with 25 percent clay and 10 percent organic matter. However,
different percentages of clay and organic matter content may also be assumed for the
standard soil.
16.4 LATERAL VARIATION
16.4.1 Introduction
The principal cause of lateral spatial variation of contaminants in the soil and vadose
zone is spatial differences in inputs and losses of contaminants at the soil surface or from
groundwater. As noted, the transport processes in the soil and vadose zone are generally
vertically oriented, so lateral dispersal of contaminants from a point source contamination is
of minor importance. Therefore, point source pollution in soil and vadose zone can usually

be considered to be horizontally confined . Conversely, diffuse inputs of contaminants
extend over much larger areas. Examples of important diffuse source s that contribute to
soil contamination are applications of agricultural fertiliser and pesticide, atmospheric
deposition , and the deposition of contaminated sediment . In contrast to the direct
anthropogenic immissions of fertiliser and pesticide application, contaminant immissions
into soil due to atmospheric deposition and deposition of contaminated sediment are
controlled by natural transport processes driven by wind or water flow.
16.4.2 Effects of fertiliser and pesticide application

As a consequence of anthropogenic inputs of fertilisers and pesticides , the topsoil
of agricultural soils is enriched with a wide range of contaminants such as nitrogen ,
phosphorus , heavy metals , and chlorinated hydrocarbons. These contaminants comprise
the persistent organic and inorganic residues of the agrochemicals. Ferguson et al. (2003)
demonstrated that the application of agrochemicals (including livestock manure, inorganic
fertilisers and lime, pesticides, sewage sludge, irrigation water, industrial by-product ‘wastes’
and composts) is the second most important source of heavy metals in agricultural soils in
England and Wales. In these soils, these inputs contribute to an estimated 51% of the total
annual Zn input, 61% of the total Cu input, 22% of the total Pb input, and 47% of the
total Cd input. However, in individual fields where livestock manure and sewage sludge are
extensively applied, they could be the major source of heavy metals (Ferguson et al., 2003).
Consequently, differences in present and past land use and management between different
fields or agricultural areas are likely to be reflected in the spatial pattern of contaminants in
the topsoil.
The contaminant concentrations in soil resulting from application of agrochemicals may
have a strong seasonal variation. This seasonal variation will be influenced by the times of
application and crop harvest, the crop uptake rate, and the rates of transport and chemical
transformation processes (e.g. leaching , decomposition , and retention ). In the long term,
persistent impurities in agrochemicals (e.g. heavy metals) or other residues may build up in
the topsoil of farmland. Many residues (for example, phosphorus and heavy metals ) exhibit
a great adsorptive affinity for soil solids. Others (for example, nitrate and some pesticide

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