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الانجليزيه
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What is
pollution?
Pollution is
the presence of a substance or substances that would not normally be found or
that are not present in normal amounts. Pollutants can be in solid, liquid or
gaseous form.
The
consequences of pollution can be direct, by the toxic effect of a substance.
For example, an accidental spill of a pesticide spilled into a river may very
well have an immediate effect and be very harmful to aquatic life. The
consequences of pollution can be indirect. Nitrogen and phosphorus are
essential for plant growth, but excessive growth of plants can be dangerous for
water. For example, phosphorus levels in improved surface waters (which
adequately contain nitrogen) can stimulate excessive growth of algae. Over
time, the decomposition process of algae reduces the oxygen available in the
water, fish and harms aquatic life.
Our use of
water can cause pollution, not only because of the substances we accidentally
or deliberately put into the water, but also because of intensive use of water
and groundwater. Therefore, the reduction of water pollution is based not only
on the prevention of potentially polluting substances, but also on reducing the
amount of water we use.
Before going
further you can consult our soil pollution diagnosis page.
Some useful
definitions related to pollution
Pollutants -
a contaminant present in the environment or entering the environment which,
because of its properties or the quantity or concentration, causes harm.
Contaminant
- substance, material or agent that is undesirable in the environment.
Risk - the
combination of the probability of occurrence of damage and the severity of
damage.
Dose - the
amount received by the receiver: this is an essential consideration "the
dose makes the poison".
Nature of
pollution sources
Pollution is
often described as a point or diffuse source of pollution.
Point
pollution on a body of water or at a specific location, it is usually easily
identifiable. Potential point sources of pollution are effluent discharges from
wastewater treatment plants and industrial sites, power plants, landfills, fish
farming and oil spills via a pipeline of industrial sites for example.
Point
pollution is usually easily avoided as it is possible to identify the source.
Polluters can take preventive action through immediate corrective action, or
long-term investments in treatment and control facilities.
Diffuse
pollution occurs when substances are widely used and dispersed over an area as
a result of intensive land use, such as urban development, agriculture and
forestry.
These
activities may be recent or have been conducted in the past. It is often
difficult to identify specific sources of pollution and therefore take
immediate action to prevent it, since prevention often requires major changes
to land use and management practices.
Examples of
diffuse pollution are leaching into surface water and groundwater from roads,
fertilizers, nutrients and pesticides used in agriculture and forestry,
atmospheric deposition of contaminants from industry. A special case arises
when, for example, a power plant emits sulfur dioxide and nitrous oxide into
the air. Although it is a point source, the deposition (fallout) will result in
a large area of diffuse pollution.
Substances
that can cause pollution
Some of the
main substances that can cause pollution are described below.
nutrients
The main
potentially polluting nutrients in water are nitrogen, ammonia (a gas
containing nitrogen and hydrogen), phosphorus and sulfur. They come from the
natural decomposition of crop residues and soil organic matter, precipitation,
fertilizer, urine and manure, landfills, industrial effluents and effluents,
electricity generation and other fuel activities.
For example,
nutrients are the main cause of eutrophication which is the enrichment of
lakes, rivers and the marine environment that leads to plant growth. This has
the effect of increasing the appearance of algae.
pesticides
These
include herbicides, insecticides and fungicides that are used in gardens,
agriculture, roadsides and on the ground (railway) and in parks and golf
courses.
Heavy
metals
Heavy metals
are commonly used ingredients for chemical compounds in the industry.
Contaminated industrial land can be a source of leaching of heavy metals into
the environment. They also exist naturally in low concentration soils. They can
be present in fuels, chemicals, waste and batteries. At high concentrations,
they are toxic to humans, animals, fish and plants.
Suspended
solids
Suspended
solids are inorganic or organic particles that remain in suspension in water.
They sink very slowly or are easily resuspended by the turbulence of the water.
Suspended matter can erode the soil. Wastewater from sewage treatment plants
and industry can also transport suspended solids into the water. Solids
suspended in water also reduce light levels. The murky waters can also be a
sign of pollution, pesticides and metals can be attached to suspended
particles.
Pathogens
They are
present in faeces of human and animal origin, including wildlife. They can
enter the water due to poor wastewater management or improper handling of
manure, slurry and other agricultural waste. They can also be spread directly
on the fields during heavy rains or on water bodies.
Temperature
Temperature
is not strictly a pollutant in the general sense of the word, but is included
here because it can affect the health of the aquatic environment. Shallow water
tends to be warmer than deep water because it is heated more easily by the sun.
Treated effluents from wastewater treatment and industry and cooling water from
power plants are generally warmer than the receiving waters in which they are
discharged, which can lead to temperature stress as well as stress due to
reduced oxygen content in the water because hot water has less oxygen than cold
water.
hydrocarbons
These
include vegetable and mineral oils (including gasoline, diesel, white spirit,
heating and lubricating oil) and chlorinated solvents such as dry cleaning
fluids.
Persistent
organic pollutants (POP)
These are
chemicals that are able to be transported over long distances. They accumulate
in human and animal tissues, and have a significant impact on human health and
the environment, even at low concentrations. They include substances such as
dioxins and PCBs.
More details
on some sources of pollution
Landfills
Landfills
can be a source of pollution in the aquatic environment through several
mechanisms. Waste containing water releases the polluting substances during the
run-off process after landfilling. The landfill directive requires that the
amount of unstabilized organic waste sent to landfill must be significantly
reduced in order to reduce the risk of water pollution and emissions of
methane, which is a significant greenhouse gas. However, it will take time to
be fully effective and there are many older landfills that continue to generate
leachate for many years. Otherwise the leachate (residual liquid that comes
from the percolation of water through a material) can be partially treated on
site and then discharged into a sewer for further treatment in a sewage
treatment plant.
Contaminated
land
Contaminated
land is largely a legacy of historic industrial activity, when there was
little, if any, environmental regulation. The nature of the contamination can
vary considerably. Contamination of water from these sites occurs mainly due to
rain, contaminated sediment and dissolved compounds run down to streams or
groundwater beneath a site and groundwater. Contamination of groundwater and
surface water can also occur when there is poor storage and when handling
chemicals such as solvents or spill oils.
Mining
The main
source of water contamination from mining is acid mine drainage. For example,
rock layers contain pyrite (iron sulphide) which oxidizes in contact with air
and in the presence of bacteria to form sulfuric acid. Therefore, the drainage
of a mine has a very low pH (acidity) and contains high concentrations of
sulfur, iron and a range of heavy metals such as arsenic and cadmium. This
process also depletes the water of its oxygen, this has an impact on the
fishing and the life of the insects.
fish
farming
Fish farming
is the intensive production of fish in a small area. It can be carried out in
specifically constructed basins, or in cages in sheltered lakes and coastal
waters.
Fish farming
can have a variety of effects on the marine environment, through the release of
nutrients, solid waste, drugs. Nitrogen and phosphorus from fish feed released
into the marine environment in a soluble form can enhance the growth of marine
plants and algae. Food waste can be deposited on the seabed under the fish
cages. This increase in organic matter can have an impact on the environment,
which affects the nature and chemistry of sediments, and can reduce the
diversity of animals that live there.
Intensive
fish farming can increase the disease because of the proximity of a large
number of fish. As a result, a number of drugs are used in fish farms to
maintain fish health. Farmed salmon is susceptible to pest infestations that
cause considerable stress. Sea lice on farmed fish can potentially be
transferred to wild salmon and sea trout by reducing the health of the wild
stock. Treatment chemicals may be toxic to marine invertebrates, although the
use of antibiotics to treat bacterial diseases has declined in recent years
because of effective vaccination programs.
Fish farming
is monitored and regulated by the authorities, supported by good practice
guides. For example, the manual of the Scottish Environmental Protection Fish
Farming Agency provides advice on legislation, policies and procedures relevant
to the marine cage farming industry.
Road and
runoff, urban stormwater discharges
Roads and
car parks produce runoff in urban areas. This runoff is often contaminated by
sediment, oil, gasoline and toxic metals from motor vehicles. These
contaminants are flowing in sewers and nearby waterways. Most surface water is
directly connected to streams, so any spills of chemicals tend to drain into
rivers.
Unit sewage
systems transport both wastewater and runoff. Unit sewers are common in urban
areas. Normally, the entire flow goes to a wastewater treatment plant, but
during a heavy rainstorm the flow into the sewers may be greater than it can
accommodate and the excess flow must be redirected to a receiving watercourse
via an overflow (called overflow of combined sewers) to avoid severe flooding
near urban areas and the treatment plant.
Sustainable
urban drainage systems are increasingly adopted to ensure that urban areas
behave more like natural basins through the use of porous pavement surfaces and
by diverting potentially polluted water from rivers . The goal is to reduce the
risk of pollution caused by direct runoff and reduce the volume of water
flowing through the drainage system, thus avoiding flooding and sewer
overflows.
