• Air pollution is the modification of the natural characteristics of the
atmosphere by a chemical, particulate matter, or biological agent.
The atmosphere is a complex, dynamic natural gaseous system that
is essential to support life on planet Earth. Stratospheric ozone
depletion due to air pollution has long been recognized as a threat to
human health as well as to the Earth's ecosystems.
• Worldwide air pollution is responsible for large numbers of deaths 
and cases of respiratory disease. While major stationary sources
are often identified with air pollution, the greatest source of
emissions is actually mobile sources, mainly automobiles. Gases
such as carbon dioxide, which contribute to global warming, have
recently gained recognition as pollutants by climate scientists, while
they also recognize that carbon dioxide is essential for plant life
• Before flue gas desulfurization was installed, the emissions from this power plant in New Mexico contained excessive amounts of sulfur dioxide.
• There are many substances in the air which may impair the health of plants and animals (including humans), or reduce visibility. These arise both from
natural processes and human activity. Substances not naturally found in the air or at greater concentrations or in different locations from usual are
referred to as pollutants.
• Pollutants can be classified as either primary or secondary. Primary pollutants are substances directly emitted from a process, such as ash from a
volcanic eruption or the carbon monoxide gas from a motor vehicle exhaust.
• Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary
pollutant is ground level ozone - one of the many secondary pollutants that make up photochemical smog.
• Note that some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.
• Major primary pollutants produced by human activity include:
• Sulfur oxides (SOx) especially sulfur dioxide are emitted from burning of coal and oil.
• Nitrogen oxides (NOx) especially nitrogen dioxide are emitted from high temperature combustion. Can be seen as the brown haze dome above or plume
downwind of cities.
• Carbon monoxide is colourless, odourless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas,
coal or wood. Vehicular exhaust is a major source of carbon monoxide.
• Carbon dioxide (CO2), a greenhouse gas emitted from combustion.
• Volatile organic compounds (VOC), such as hydrocarbon fuel vapors and solvents.
• Particulate matter (PM), measured as smoke and dust. PM10 is the fraction of suspended particles 10 micrometers in diameter and smaller that will
enter the nasal cavity. PM2.5 has a maximum particle size of 2.5 µm and will enter the bronchies and lungs.
• Toxic metals, such as lead, cadmium and copper.
• Chlorofluorocarbons (CFCs), harmful to the ozone layer emitted from products currently banned from use.
• Ammonia (NH3) emitted from agricultural processes.
• Odors, such as from garbage, sewage, and industrial processes
• Radioactive pollutants produced by nuclear explosions and war explosives, and natural processes such as radon.
• Secondary pollutants include:
• Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog, such as nitrogen dioxide.
• Ground level ozone (O3) formed from NOx and VOCs.
• Peroxyacetyl nitrate (PAN) similarly formed from NOx and VOCs.
• Minor air pollutants include:
• A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework
• A variety of persistent organic pollutants, which can attach to particulate matter.
• The World Health Organization states that 2.4 million people die each year from
causes directly attributable to air pollution. Many of these mortalities are
attributable to indoor air pollution. Worldwide more deaths per year are linked to air
pollution than to automobile accidents. Published in 2005 suggests that 310,000
Europeans die from air pollution annually. Direct causes of air pollution related deaths
include aggravated asthma, bronchitis, emphysema, lung and heart diseases, and
respiratory allergies. The US EPA estimates that a proposed set of changes in diesel
engine technology could result in 12,000 fewer premature mortalities, 15,000 fewer
heart attacks, 6,000 fewer emergency room visits by children with asthma, and 8,900
fewer respiratory-related hospital admissions each year in the United States.
• The worst short term civilian pollution crisis in India was the 1984 Bhopal
Disaster. Leaked industrial vapors from the Union Carbide factory, belonging to
Union Carbide, Inc., U.S.A., killed more than 2,000 people outright and injured
anywhere from 150,000 to 600,000 others, some 6,000 of whom would later die from
their injuries The United Kingdom suffered its worst air pollution event when the
December 4 Great Smog of 1952 formed over London. In six days more than 4,000
died, and 8,000 more died within the following months. An accidental leak of anthrax
spores from a biological warfare laboratory in the former USSR in 1979 near
Sverdlovsk is believed to have been the cause of hundreds of civilian deaths. The
worst single incident of air pollution to occur in the United States of America occurred
in Donora, Pennsylvania in late October, 1948, when 20 people died and over 7,000
• Water pollution is a large set of adverse effects upon water bodies such as lakes, rivers, oceans,
and groundwater caused by human activities.
• Although natural phenomena such as volcanoes, algae blooms, storms, and earthquakes also
cause major changes in water quality and the ecological status of water, water is only called
polluted when it is not able to be used for what one wants it to be used for. Water pollution has
many causes and characteristics. Increases in nutrient loading may lead to eutrophication.
Organic wastes such as sewage impose high oxygen demands on the receiving water leading to
oxygen depletion with potentially severe impacts on the whole eco-system. Industries discharge a
variety of pollutants in their wastewater including heavy metals, resin pellets, organic toxins, oils,
nutrients, and solids. Discharges can also have thermal effects, especially those from power
stations, and these too reduce the available oxygen. Silt-bearing runoff from many activities
including construction sites, deforestation and agriculture can inhibit the penetration of sunlight
through the water column, restricting photosynthesis and causing blanketing of the lake or river
bed, in turn damaging ecological systems.
• Pollutants in water include a wide spectrum of chemicals, pathogens, and physical chemistry or
sensory changes. Many of the chemical substances are toxic. Pathogens can produce waterborne
diseases in either human or animal hosts. Alterations of water’s physical chemistry include acidity,
electrical conductivity, temperature, and eutrophication. Eutrophication is the fertilization of
surface water by nutrients that were previously scarce. Even many of the municipal water supplies
in developed countries can present health risks. Water pollution is a major problem in the global
context. It has been suggested that it is the leading worldwide cause of deaths and diseases,
and that it accounts for the deaths of more than 14,000 people daily.
• Contaminants may include organic and inorganic substances.
• Some organic water pollutants are:
• Insecticides and herbicides, a huge range of organohalide and other chemicals
• Bacteria, often is from sewage or livestock operations
• Food processing waste, including pathogens
• Tree and brush debris from logging operations
• VOCs (volatile organic compounds), such as industrial solvents, from improper storage
• DNAPLs (dense non-aqueous phase liquids), such as chlorinated solvents, which may fall at the bottom of
reservoirs, since they don't mix well with water and are more dense
• Petroleum Hydrocarbons including fuels (gasoline, diesel, jet fuels, and fuel oils) and lubricants (motor oil) from oil
field operations, refineries, pipelines, retail service station's underground storage tanks, and transfer operations.
Note: VOCs include gasoline-range hydrocarbons.
• Various chemical compounds found in personal hygiene and cosmetic products
• Some inorganic water pollutants include:
• Heavy metals including acid mine drainage
• Acidity caused by industrial discharges (especially sulfur dioxide from power plants)
• Pre-production industrial raw resin pellets, an industrial pollutant
• Chemical waste as industrial by products
• Fertilizers, in runoff from agriculture including nitrates and phosphates
• Silt in surface runoff from construction sites, logging, slash and burn practices or land clearing sites
• Most water pollutants are eventually carried by the rivers into the oceans. In some areas of the world the influence can be traced hundred
miles from the mouth by studies using hydrology transport models. Advanced computer models such as SWMM or the DSSAM Model
have been used in many locations worldwide to examine the fate of pollutants in aquatic systems. Indicator filter feeding species such as
copepods have also been used to study pollutant fates in the New York Bight, for example. The highest toxin loads are not directly at the
mouth of the Hudson River, but 100 kilometers south, since several days are required for incorporation into planktonic tissue. The Hudson
discharge flows south along the coast due to coriolis force. Further south then are areas of oxygen depletion, caused by chemicals using
up oxygen and by algae blooms, caused by excess nutrients from algal cell death and decomposition. Fish and shellfish kills have been
reported, because toxins climb the foodchain after small fish consume copepods, then large fish eat smaller fish, etc. Each successive
step up the food chain causes a stepwise concentration of pollutants such as heavy metals (e.g. mercury) and persistent organic
pollutants such as DDT. This is known as biomagnification which is occasionally used interchangeably with bioaccumulation.
• The big gyres in the oceans trap floating plastic debris. The North Pacific Gyre for example has collected the so-called Great Pacific
Garbage Patch that is now estimated at two times the size of Texas. Many of these long-lasting pieces wind up in the stomachs of marine
birds and animals. This results in obstruction of digestive pathways which leads to reduced appetite or even starvation.
• Many chemicals undergo reactive decay or chemically change especially over long periods of time in groundwater reservoirs. A
noteworthy class of such chemicals are the chlorinated hydrocarbons such as trichloroethylene (used in industrial metal degreasing and
electronics manufacturing) and tetrachloroethylene used in the dry cleaning industry (note latest advances in liquid carbon dioxide in dry
cleaning that avoids all use of chemicals). Both of these chemicals, which are carcinogens themselves, undergo partial decomposition
reactions, leading to new hazardous chemicals (including dichloroethylene and vinyl chloride).
• Groundwater pollution is much more difficult to abate than surface pollution because groundwater can move great distances through
unseen aquifers. Non-porous aquifers such as clays partially purify water of bacteria by simple filtration (adsorption and absorption),
dilution, and, in some cases, chemical reactions and biological activity: however, in some cases, the pollutants merely transform to soil
contaminants. Groundwater that moves through cracks and caverns is not filtered and can be transported as easily as surface water. In
fact, this can be aggravated by the human tendency to use natural sinkholes as dumps in areas of Karst topography.
• There are a variety of secondary effects stemming not from the original pollutant, but a derivative condition. Some of these secondary
• Silt bearing surface runoff from can inhibit the penetration of sunlight through the water column, hampering photosynthesis in aquatic
• Thermal pollution can induce fish kills and invasion by new thermophilic species
• Land pollution is the degradation of earth's land
surfaces often caused by human activities and its
misuse. Haphazard disposal of urban and industrial
wastes, exploitation of minerals, and improper use of soil
by inadequate agricultural practices are a few of the
contributing factors. Also, increasing urbanization,
industrialization and other demands on the environment
and its resources is of great consequence to many
• The Industrial Revolution set in motion a series of events
which impinged on the countryside destroying many
natural habitats, and introduced pollution causing
disease in both human and animal alike.
• Pesticides are any chemical used to remove pests whether they are plants or animals. They are used to kill wire worms and slugs that attack cereal crops and to kill ergot
- Claviceps purpurea - a fungus that attacks crops and may get into human food.
• Herbicides are used to kill weeds, especially on pavements and railways. They are similar to auxins and most are biodegradable by soil bacteria. However one group
derived from trinitrophenol (2:4 D and 2:4:5 T) have the impurity dioxin which is very toxic and causes fatality even in low concentrations. It also causes spontaneous
abortions, haemorraging and cancer. Agent Orange (50% 2:4:5 T) was used as a defoliant in Vietnam. Eleven million gallons were used and children born since then to
American soldiers who served in this conflict, have shown increased physical and mental disabilities compared to the rest of the population. It affects the head of the
sperm and the chromosomes inside it.
• Another herbicide, much loved by murder story writers, is Paraquat. It is highly toxic but it rapidly degrades in soil due to the action of bacteria and does not kill soil fauna.
• Fungicides are the group used to stop the growth of smuts and rusts on cereals, and mildews and molds like Mucor on plants. The problem is that they may contain
copper and mercury. Copper is very toxic at 1ppm to water plants and fish and can enter the skin if being sprayed to reduce mildew and accumulate in the central nervous
system. Organomercury compounds have been used to get rid of sedges which are insidious and difficult to remove. However it also can accumulate in birds’ central
nervous system and kill them.
• Insecticides are used to rid farmers of pests which damage crops. The insects damage not only standing crops but also stored ones and in the tropics it is reckoned that
one third of the total production is lost during food storage. As with fungicides, the first used in the nineteenth century were inorganic e.g. Paris Green and other
compounds of arsenic. Nicotine has also been used since the late eigtheenth century. There are now two main groups of synthetic ones -
• Organochlorines include DDT, Aldrin, Dieldrin and BHC. They are cheap to produce, potent and persistent. DDT was used on a massive scale from the 1930s, with a
peak of 72,000 tonnes used 1970. Then usage fell as the environmental problems were realized. It was found worldwide in fish and birds and was even discovered in the
snow in the Antarctic. It is only slightly soluble in water but is very soluble in the bloodstream. It affects the nervous and enzyme systems and causes the eggshells of
birds to lack calcium and be so fragile that they break easily. It is thought to be responsible for the decline of the numbers of birds of prey like ospreys and peregrine
falcons in the 1950s - they are now recovering.
• As well as increased concentration via the food chain, it is known to enter via permeable membranes, so fish get it through their gills. As it has low solubility it tends to stay
at the surface, so organisms that live there are most affected. DDT found in fish that formed part of the human food chain caused concern but the levels found in the liver,
kidney and brain tissues was less than 1ppm and in fat was 10 ppm which was below the level likely to cause harm. However DDT was banned in Britain and America to
stop the further building up of it in the food chain. However, the USA exploited this ban and sold DDT to developing countries who could not afford the expensive
replacement chemicals and who did not have such stringent regulations governing the use of pesticides.
• Some insects have developed a resistance to insecticides - e.g. the Anopheles mosquito which carries malaria.
• Organophosphates, e.g. parathion, methyl parathion and about 40 other insecticides are available nationally. Parathion is highly toxic, methyl-parathion is less so and
Malathion is generally considered safe as it has low toxicity and is rapidly broken down in the mammalian liver. This group works by preventing normal nerve transmission
as cholinesterase is prevented from breaking down the transmitter substance acetylcholine, resulting in uncontrolled muscle movements.
• Entry of a variety of pesticides into our water supplies causes concern to environmental groups, as in many cases the long term effects of these specific chemicals is not
• Limits came into force in July 1985 and were so frequently broken that in 1987 formal proceedings were taken against the British government. Britain is still the only
European state to use Aldrin and organochlorines, although it was supposed to stop in 1993. East Anglia has the worst record for pesticide contamination of drinking
water. Of the 350 pesticides used in Britain, only 50 can be analyzed - this is a worrying thought for many people.
• In some areas more metal ores had to be extracted out of the ground, melted and cast using coal out of the ground and cooled using
water, which raised the temperature of water in rivers. (This reduces the oxygen carrying capacity of the water and affects all the living
things there.) The excavation of metal ores, sand and limestone led to large scale quarrying and defacing of the countryside. To a large
extent this has stopped or is more closely controlled, and attempts have been made to use the holes profitably i.e. sand pits have been
turned into boating lochs and quarries have been used as landfill waste sites. Central Scotland bears the scars of years of coal mining,
with pit bings and visible from the motorways.
• As the demand for labor grew, the areas round the factories and mines were given over to housing. This took up former agricultural land,
caused sewage and waste problems, increased the demands for food and put pressure on farmers to produce more food.
• The demand for more housing meant the need to use more raw materials to make bricks, slates for roofing and timber for joists, etc. Once
again this led to quarrying and to the destruction of forests. The houses also needed running water and a supply of energy. Initially this
water would have been supplied directly from a stream but as demand increased the need for reservoirs increased. This again led to the
loss of land as valleys were flooded to meet the demands. The main fuels used would have been coal and wood but as time progressed,
hydro electric, coal, oil and nuclear power stations were built which again became features or eyesores on the landscape. Associated with
this was the radiating network of pylons forming the National Grid, as well as, the sub stations and transformers. Until the late 1970s little
attempt was made to hide these metal structures but now more care is taken in their siting and underground cables are often used -
although these are not popular with repair crews who have to find faults and service them, often in very remote areas.
• This increase in the concentration of population into cities, along with the internal combustion engine, led to the increased number of
roads and all the infra structure that goes with them. Roads cause visual, noise, light, air and water pollution, as well as using up land.
The visual and noise areas are obvious, however light pollution is becoming more widely recognised as a problem. From space large
cities can be picked out at night by the glow of their street lighting, so city dwellers seldom experience total darkness. On a smaller scale
lights along roads can cause people living there to have interrupted sleep patterns due to the lack of darkness.
• The contribution of traffic to air pollution is dealt with in another article, but, suffice to say that sulfur dioxide, nitrogen oxides and carbon
monoxide are the main culprits. Water pollution is caused by the run off from roads of oil, salt and rubber residue, which enter the water
courses and may make conditions unsuitable for certain organisms to live.