Characteristics of Natural and Urban Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 110

Excessive phosphorus, if plant-available, that is more soluble, can create defi-
ciencies of iron, manganese and zinc for plants by forming poorly soluble
phosphates of these important trace nutrients.
The global nitrogen cycle has been grossly altered by industry and agriculture
(Vitousek et al. 1997 ). Much increased nitrogen inputs into the soil system has
caused serious soil acidification, loss of calcium and magnesium and increases of
nitrogen in the groundwater and open water bodies.
Excessive plant-available nitrogen, for example as nitrate, tends to accelerate the
oxidation of organic matter in soils and reduce the quality of the soil as well as pro-
ducing more greenhouse carbon dioxide. In ecosystems where the nitrogen content
of the soil is limiting plant growth, adding nitrogen can lead to more sequestration
of carbon through increased photosynthesis. Nitrogen toxicity often leads to stunted
growth and abnormal deep green foliage. Specific ammonium toxicity causes roots
to become affected and brown with necrotic tips, while leaves can develop necrotic
lesions and chlorosis (Wong 2005 ).
In Australia, large regions have been adversely affected by the use of super-
phosphate to promote the growth and productivity of clovers, especially subclover
( Trifolium subterraneum ) on soils with low cation exchange capacity and low cal-
cium. The increased production of nitrogen by the clover, and its conversion to
nitrate when organic matter decomposes, led to increased loss of calcium when the
nitrate is leached out. The soils in these regions often became so acid that the clovers
would cease to grow and pasture productivity dropped dramatically, while the cost
of liming vast areas became a limitation. The process of soil acidification that is
affecting millions of hectares in Australia became a prominent agricultural issue in
the 1980s and 1990s (Coventry 1992 ; Coventry and Slattery 1991 ; Helyar 1991 ;
Helyar and Porter 1989 ). In terms of many metals, increased soil acidity tends to
increase their mobility.
Britto and Kronzucker ( 2002 ) discovered that many plants are sensitive to very
high ammonium concentrations in the soil and that these plants are pumping out the
NH 4 + after having at first absorbed it at high rates. The removal of the NH 4 + from
the cells requires a great amount of energy and this energetic cost is the cause of a
toxic shock.
2.3.1.6 Contaminants from Hospital Effluents and Sludges Discharged on Soil
A special but probably widespread type of soil contamination occurs when either
treated hospital wastewater or sludge from hospital and municipal sewage treat-
ments plants is discharged on the soil. The application can occur in rural and urban
areas. Accordingly, it should be taken into account in relation to the urbanized areas
as well.
Kümmerer ( 2001 ) reviewed the range of pharmaceuticals that are excreted by
patients and unused medicines that are disposed of in wastewater in hospitals. To this
should be added the personal care products like shampoos and soaps that likewise
find their way into the wastewater and other segments of the environment (Klaschka