Page 18 - Soil and water contamination, 2nd edition

General introduction 5

loads of nutrients in fertilisers leads to the eutrophication of soil and surface waters: the
excessive enrichment of nutrients, associated with rapid growth of vegetation. In the past
four decades, excessive nutrient loading has emerged as one of the most important direct
drivers of ecosystem change in terrestrial, freshwater, and marine ecosystems (Millennium
Ecosystem Assessment, 2005). In many cases, groundwater polluted by excess fertiliser
application is endangering supplies of drinking water . This is of particular concern in the
countries in which groundwater is the main source of drinking water.
The pressure on the natural environment is clearly highest in urbanised regions. Cities
and urban areas with their concentrated population, large energy consumption, transport
and industrial activities, generally display the worst environmental pollution problems.
Some industrial and commercial activities in urban areas may have brought about local
soil contamination through spillage or dumping of chemicals. If these activities have
been abandoned and the contaminated or potentially contaminated land is available for
building development, the land is generally referred to as a brownfield site or, simply, a
brownfield. Examples of brownfields are the sites of abandoned factories, petrol stations,
and dry-cleaning establishments. The redevelopment of such sites may be complicated by
the actual or potential contamination. Urbanised areas also typically consume more energy
and other natural resources and produce more waste per capita than rural areas. Industrial
emissions of polluting substances to the atmosphere or into surface water and the dumping
of industrial and domestic wastes on waste disposal sites cause environmental pollution
problems far beyond the city limits. Furthermore, the exploitation of natural resources
required to maintain the standard of living in urban areas brings about spills and emissions
of environmental pollutants elsewhere, for example during the mining and smelting of metal
ores.
How far an emitted pollutant spreads in the environment depends on the physical and
chemical characteristics of the pollutant itself, the soil’s ability to retain it, and the nature and
transport rate of the medium by which it is transported (air, water). The complex behaviour
of pollutants in the environment is primarily caused by the variation of processes at or near
the Earth’s surface in both space and time. Nevertheless, they can be elucidated by the basic
principles of physics and chemistry.

1.3 ENVIRONMENTAL POLLUTANTS
1.3.1 Classification of pollutants

In general, there are two basic types of pollutants. Primary pollutant s cause harmful effects
in the form in which they are released into the environment and secondary pollutant s
are formed as a result of a chemical process in the environment, often from less harmful
precursors (Alloway and Ayres, 1997). As defined above, substances become pollutants if
they are harmful or poisonous and have been introduced into the environment by humans,
or as a result of human activities. There are many substances that are not commonly
considered as pollutants but may cause pollution if they are released into the environment
in excessive amounts or in an unfortunate place and time. Milk, fruit juice, and sugar, for
example, are generally not considered as pollutants, but if directly released into surface
water they are harmful to aquatic life, since the oxidation of the organic substances depletes
dissolved oxygen in the water. On the other hand, many substances that are generally
thought of as pollutants may occur naturally in soil and water: heavy metals , nitrate , and
polycyclic aromatic hydrocarbons (PAHs), for example.
Pollutants can be classified in numerous ways based on their physical and chemical
properties, abundance, persistence in the environment, effect on ecosystems, or toxicity .

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