| I | INTRODUCTION |
There are two main categories of polluting
materials, or pollutants. Biodegradable pollutants are materials, such as
sewage, that rapidly decompose by natural processes. These pollutants become a
problem when added to the environment faster than they can decompose (see
Sewage Disposal). Nondegradable pollutants are materials that either
do not decompose or decompose slowly in the natural environment. Once
contamination occurs, it is difficult or impossible to remove these pollutants
from the environment.
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Nondegradable compounds such as
dichlorodiphenyltrichloroethane (DDT), dioxins, polychlorinated biphenyls
(PCBs), and radioactive materials can reach dangerous levels of accumulation as
they are passed up the food chain into the bodies of progressively larger
animals. For example, molecules of toxic compounds may collect on the surface of
aquatic plants without doing much damage to the plants. A small fish that grazes
on these plants accumulates a high concentration of the toxin. Larger fish or
other carnivores that eat the small fish will accumulate even greater, and
possibly life-threatening, concentrations of the compound. This process is known
as bioaccumulation.| II | IMPACTS OF POLLUTION |
Because humans are at the top of the food
chain, they are particularly vulnerable to the effects of nondegradable
pollutants. This was clearly illustrated in the 1950s and 1960s when residents
living near Minamata Bay, Japan, developed nervous disorders, tremors, and
paralysis in a mysterious epidemic. More than 400 people died before authorities
discovered that a local industry had released mercury into Minamata Bay. This
highly toxic element accumulated in the bodies of local fish and eventually in
the bodies of people who consumed the fish. More recently research has revealed
that many chemical pollutants, such as DDT and PCBs, mimic sex hormones and
interfere with the human body’s reproductive and developmental functions. These
substances are known as endocrine disrupters. See Occupational and
Environmental Diseases.
Pollution also has a dramatic effect on
natural resources. Ecosystems such as forests, wetlands, coral reefs, and rivers
perform many important services for Earth’s environment. They enhance water and
air quality, provide habitat for plants and animals, and provide food and
medicines. Any or all of these ecosystem functions may be impaired or destroyed
by pollution. Moreover, because of the complex relationships among the many
types of organisms and ecosystems, environmental contamination may have
far-reaching consequences that are not immediately obvious or that are difficult
to predict. For instance, scientists can only speculate on some of the potential
impacts of the depletion of the ozone layer, the protective layer in the
atmosphere that shields Earth from the Sun’s harmful ultraviolet rays.
Another major effect of pollution is the
tremendous cost of pollution cleanup and prevention. The global effort to
control emissions of carbon dioxide, a gas produced from the combustion of
fossil fuels such as coal or oil, or of other organic materials like wood, is
one such example. The cost of maintaining annual national carbon dioxide
emissions at 1990 levels is estimated to be 2 percent of the gross domestic
product for developed countries.
In addition to its effects on the economy,
health, and natural resources, pollution has social implications. Research has
shown that low-income populations and minorities do not receive the same
protection from environmental contamination as do higher-income communities.
Toxic waste incinerators, chemical plants, and solid waste dumps are often
located in low-income communities because of a lack of organized, informed
community involvement in municipal decision-making processes.
| III | TYPES OF POLLUTION |
Pollution exists in many forms and affects
many different aspects of Earth’s environment. Point-source pollution
comes from specific, localized, and identifiable sources, such as sewage
pipelines or industrial smokestacks. Nonpoint-source pollution comes from
dispersed or uncontained sources, such as contaminated water runoff from urban
areas or automobile emissions.
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The effects of these pollutants may be
immediate or delayed. Primary effects of pollution occur immediately after
contamination occurs, such as the death of marine plants and wildlife after an
oil spill at sea. Secondary effects may be delayed or may persist in the
environment into the future, perhaps going unnoticed for many years. DDT, a
nondegradable compound, seldom poisons birds immediately, but gradually
accumulates in their bodies. Birds with high concentrations of this pesticide
lay thin-shelled eggs that fail to hatch or produce deformed offspring. These
secondary effects, publicized by Rachel Carson in her 1962 book, Silent
Spring, threatened the survival of species such as the bald eagle and
peregrine falcon, and aroused public concern over the hidden effects of
nondegradable chemical compounds.| A | Air Pollution |
Human contamination of Earth’s atmosphere
can take many forms and has existed since humans first began to use fire for
agriculture, heating, and cooking. During the Industrial Revolution of the 18th
and 19th centuries, however, air pollution became a major problem. As early as
1661 British author and founding member of the British Royal Society John Evelyn
reported of London in his treatise Fumifugium, “… the weary Traveller, at
many Miles distance, sooner smells, than sees the City to which he repairs. This
is that pernicious Smoake which fullyes all her Glory, superinducing a sooty
Crust or Furr upon all that it lights.…”
Urban air pollution is commonly known as
smog. The dark London smog that Evelyn wrote of is generally a smoky mixture of
carbon monoxide and organic compounds from incomplete combustion (burning) of
fossil fuels such as coal, and sulfur dioxide from impurities in the fuels. As
the smog ages and reacts with oxygen, organic and sulfuric acids condense as
droplets, increasing the haze. Smog developed into a major health hazard by the
20th century. In 1948, 19 people died and thousands were sickened by smog in the
small U.S. steel-mill town of Donora, Pennsylvania. In 1952, about 4,000
Londoners died of its effects.
A second type of smog,
photochemical smog, began reducing air quality over large cities like Los
Angeles in the 1930s. This smog is caused by combustion in car, truck, and
airplane engines, which produce nitrogen oxides and release hydrocarbons from
unburned fuels. Sunlight causes the nitrogen oxides and hydrocarbons to combine
and turn oxygen into ozone, a chemical agent that attacks rubber, injures
plants, and irritates lungs. The hydrocarbons are oxidized into materials that
condense and form a visible, pungent haze.
Eventually most pollutants are washed out
of the air by rain, snow, fog, or mist, but only after traveling large
distances, sometimes across continents. As pollutants build up in the
atmosphere, sulfur and nitrogen oxides are converted into acids that mix with
rain. This acid rain falls in lakes and on forests, where it can lead to the
death of fish and plants, and damage entire ecosystems. Eventually the
contaminated lakes and forests may become lifeless. Regions that are downwind of
heavily industrialized areas, such as Europe and the eastern United States and
Canada, are the hardest hit by acid rain. Acid rain can also affect human health
and man-made objects; it is slowly dissolving historic stone statues and
building facades in London, Athens, and Rome.
One of the greatest challenges caused by
air pollution is global warming, an increase in Earth’s temperature due to the
buildup of certain atmospheric gases such as carbon dioxide. With the heavy use
of fossil fuels in the 20th century, atmospheric concentrations of carbon
dioxide have risen dramatically. Carbon dioxide and other gases, known as
greenhouse gases, reduce the escape of heat from the planet without blocking
radiation coming from the Sun. Because of this greenhouse effect, average global
temperatures are expected to rise 1.4 to 5.8 Celsius degrees (2.5 to 10.4
Fahrenheit degrees) by the year 2100. Although this trend appears to be a small
change, the increase would make the Earth warmer than it has been in the last
125,000 years, possibly changing climate patterns, affecting crop production,
disrupting wildlife distributions, and raising the sea level.
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Air pollution can also damage the upper
atmospheric region known as the stratosphere. Excessive production of
chlorine-containing compounds such as chlorofluorocarbons (CFCs) (compounds
formerly used in refrigerators, air conditioners, and in the manufacture of
polystyrene products) has depleted the stratospheric ozone layer, creating a
hole above Antarctica that lasts for several weeks each year. As a result,
exposure to the Sun’s harmful rays has damaged aquatic and terrestrial wildlife
and threatens human health in high-latitude regions of the northern and southern
hemispheres.| B | Water Pollution |
The demand for fresh water rises
continuously as the world’s population grows. From 1940 to 1990 withdrawals of
fresh water from rivers, lakes, reservoirs, and other sources increased
fourfold. Of the water consumed in the United States in 1995, 39 percent was
used for irrigation, 39 percent was used for electric power generation, and 12
percent was used for other utilities; industry and mining used 7 percent, and
the rest was used for agricultural livestock and commercial purposes.
Sewage, industrial wastes, and
agricultural chemicals such as fertilizers and pesticides are the main causes of
water pollution. The U.S. Environmental Protection Agency (EPA) reports that
about 37 percent of the country’s lakes and estuaries, and 36 percent of its
rivers, are too polluted for basic uses such as fishing or swimming during all
or part of the year. In developing nations, more than 95 percent of urban sewage
is discharged untreated into rivers and bays, creating a major human health
hazard.
Water runoff, a nonpoint source of
pollution, carries fertilizing chemicals such as phosphates and nitrates from
agricultural fields and yards into lakes, streams, and rivers. These combine
with the phosphates and nitrates from sewage to speed the growth of algae, a
type of plantlike organism. The water body may then become choked with decaying
algae, which severely depletes the oxygen supply. This process, called
eutrophication, can cause the death of fish and other aquatic life. Agricultural
runoff may be to blame for the growth of a toxic form of algae called
Pfiesteria piscicida, which was responsible for killing large amounts of
fish in bodies of water from the Delaware Bay to the Gulf of Mexico in the late
1990s. Runoff also carries toxic pesticides and urban and industrial wastes into
lakes and streams.
Erosion, the wearing away of topsoil by
wind and rain, also contributes to water pollution. Soil and silt (a fine
sediment) washed from logged hillsides, plowed fields, or construction sites,
can clog waterways and kill aquatic vegetation. Even small amounts of silt can
eliminate desirable fish species. For example, when logging removes the
protective plant cover from hillsides, rain may wash soil and silt into streams,
covering the gravel beds that trout or salmon use for spawning.
The marine fisheries supported by ocean
ecosystems are an essential source of protein, particularly for people in
developing countries. Yet pollution in coastal bays, estuaries, and wetlands
threatens fish stocks already depleted by overfishing. In 1989, 260,000 barrels
of oil spilled from the oil tanker Exxon Valdez into Alaska’s Prince
William Sound, a pristine and rich fishing ground. In 1999 there were 8,539
reported spills in and around U.S. waters, involving 4.4 billion liters (1.2
billion gallons) of oil.
| C | Soil Pollution |
Soil is a mixture of mineral, plant, and
animal materials that forms during a long process that may take thousands of
years. It is necessary for most plant growth and is essential for all
agricultural production. Soil pollution is a buildup of toxic chemical
compounds, salts, pathogens (disease-causing organisms), or radioactive
materials that can affect plant and animal life.
Unhealthy soil management methods have
seriously degraded soil quality, caused soil pollution, and enhanced erosion.
Treating the soil with chemical fertilizers, pesticides, and fungicides
interferes with the natural processes occurring within the soil and destroys
useful organisms such as bacteria, fungi, and other microorganisms. For
instance, strawberry farmers in California fumigate the soil with methyl bromide
to destroy organisms that may harm young strawberry plants. This process
indiscriminately kills even beneficial microorganisms and leaves the soil
sterile and dependent upon fertilizer to support plant growth. This results in
heavy fertilizer use and increases polluted runoff into lakes and streams.
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Improper irrigation practices in areas
with poorly drained soil may result in salt deposits that inhibit plant growth
and may lead to crop failure. In 2000 bc, the ancient Sumerian cities of the
southern Tigris-Euphrates Valley in Mesopotamia depended on thriving
agriculture. By 1500 bc, these
cities had collapsed largely because of crop failure due to high soil salinity.
The same soil pollution problem exists today in the Indus Valley in Pakistan,
the Nile Valley in Egypt, and the Imperial Valley in California.| D | Solid Waste |
Solid wastes are unwanted solid materials
such as garbage, paper, plastics and other synthetic materials, metals, and
wood. Billions of tons of solid waste are thrown out annually. The United States
alone produces about 200 million metric tons of municipal solid waste each year
(see Solid Waste Disposal). A typical American generates an average of 2
kg (4 lb) of solid waste each day. Cities in economically developed countries
produce far more solid waste per capita than those in developing countries.
Moreover, waste from developed countries typically contains a high percentage of
synthetic materials that take longer to decompose than the primarily
biodegradable waste materials of developing countries.
Areas where wastes are buried, called
landfills, are the cheapest and most common disposal method for solid wastes
worldwide. But landfills quickly become overfilled and may contaminate air,
soil, and water. Incineration, or burning, of waste reduces the volume of solid
waste but produces dense ashen wastes (some of which become airborne) that often
contain dangerous concentrations of hazardous materials such as heavy metals and
toxic compounds. Composting, using natural biological processes to speed the
decomposition of organic wastes, is an effective strategy for dealing with
organic garbage and produces a material that can be used as a natural
fertilizer. Recycling, extracting and reusing certain waste materials, has
become an important part of municipal solid waste strategies in developed
countries. According to the EPA, more than one-fourth of the municipal solid
waste produced in the United States is now recycled or composted. Recycling also
plays a significant, informal role in solid waste management for many Asian
countries, such as India, where organized waste-pickers comb streets and dumps
for items such as plastics, which they use or resell.
Expanding recycling programs worldwide can
help reduce solid waste pollution, but the key to solving severe solid waste
problems lies in reducing the amount of waste generated. Waste prevention, or
source reduction, such as altering the way products are designed or manufactured
to make them easier to reuse, reduces the high costs associated with
environmental pollution.
| E | Hazardous Waste |
Hazardous wastes are solid, liquid, or gas
wastes that may be deadly or harmful to people or the environment and tend to be
persistent or nondegradable in nature. Such wastes include toxic chemicals and
flammable or radioactive substances, including industrial wastes from chemical
plants or nuclear reactors, agricultural wastes such as pesticides and
fertilizers, medical wastes, and household hazardous wastes such as toxic paints
and solvents.
About 400 million metric tons of hazardous
wastes are generated each year. The United States alone produces about 250
million metric tons—70 percent from the chemical industry. The use, storage,
transportation, and disposal of these substances pose serious environmental and
health risks. Even brief exposure to some of these materials can cause cancer,
birth defects, nervous system disorders, and death. Large-scale releases of
hazardous materials may cause thousands of deaths and contaminate air, water,
and soil for many years. The world’s worst nuclear reactor accident took place
near Chernobyl’, Ukraine, in 1986 (see Chernobyl’ Accident). The accident
killed at least 31 people, forced the evacuation and relocation of more than
200,000 more, and sent a plume of radioactive material into the atmosphere that
contaminated areas as far away as Norway and the United Kingdom.
Until the Minamata Bay contamination was
discovered in Japan in the 1960s and 1970s, most hazardous wastes were legally
dumped in solid waste landfills, buried, or dumped into lakes, rivers, and
oceans. Legal regulations now restrict how such materials may be used or
disposed, but such laws are difficult to enforce and often contested by
industry. It is not uncommon for industrial firms in developed countries to pay
poorer countries to accept shipments of solid and hazardous wastes, a practice
that has become known as the waste trade. Moreover, cleaning up the careless
dumping of the mid-20th century is costing billions of dollars and progressing
very slowly, if at all. The United States has an estimated 217,000 hazardous
waste dumps that need immediate action. Cleaning them up could take more than 30
years and cost $187 billion.
Hazardous wastes of particular concern are
the radioactive wastes from the nuclear power and weapons industries. To date
there is no safe method for permanent disposal of old fuel elements from nuclear
reactors. Most are kept in storage facilities at the original reactor sites
where they were generated. With the end of the Cold War, nuclear warheads that
are decommissioned, or no longer in use, also pose storage and disposal
problems.
| F | Noise Pollution |
Unwanted sound, or noise, such as that
produced by airplanes, traffic, or industrial machinery, is considered a form of
pollution. Noise pollution is at its worst in densely populated areas. It can
cause hearing loss, stress, high blood pressure, sleep loss, distraction, and
lost productivity.
Sounds are produced by objects that
vibrate at a rate that the ear can detect. This rate is called frequency and is
measured in hertz, or vibrations per second. Most humans can hear sounds between
20 and 20,000 hertz, while dogs can hear high-pitched sounds up to 50,000 hertz.
While high-frequency sounds tend to be more hazardous and more annoying to
hearing than low-frequency sounds, most noise pollution damage is related to
the intensity of the sound, or the amount of energy it has. Measured in
decibels, noise intensity can range from zero, the quietest sound the human ear
can detect, to over 160 decibels. Conversation takes place at around 40
decibels, a subway train is about 80 decibels, and a rock concert is from 80 to
100 decibels. The intensity of a nearby jet taking off is about 110 decibels.
The threshold for pain, tissue damage, and potential hearing loss in humans is
120 decibels. Long-lasting, high-intensity sounds are the most damaging to
hearing and produce the most stress in humans.
Solutions to noise pollution include
adding insulation and sound-proofing to doors, walls, and ceilings; using ear
protection, particularly in industrial working areas; planting vegetation to
absorb and screen out noise pollution; and zoning urban areas to maintain a
separation between residential areas and zones of excessive noise.
| IV | HISTORY |
Much of what we know of ancient
civilizations comes from the wastes they left behind. Refuse such as animal
skeletons and implements from stone age cave dwellings in Europe, China, and the
Middle East helps reveal hunting techniques, diet, clothing, tool usage, and the
use of fire for cooking. Prehistoric refuse heaps, or middens, discovered by
archaeologists in coastal areas of North America reveal information about the
shellfish diet and eating habits of Native Americans who lived more than 10,000
years ago.
As humans developed new technologies, the
magnitude and severity of pollution increased. Many historians speculate that
the extensive use of lead plumbing for drinking water in Rome caused chronic
lead poisoning in those who could afford such plumbing. The mining and smelting
of ores that accompanied the transition from the Stone Age to the Metal Age
resulted in piles of mining wastes that spread potentially toxic elements such
as mercury, copper, lead, and nickel throughout the environment.
Evidence of pollution during the early
Industrial Revolution is widespread. Samples of hair from historical figures
such as Newton and Napoleon show the presence of toxic elements such as antimony
and mercury. By the 1800s, certain trades were associated with characteristic
occupational diseases: Chimney sweeps contracted cancer of the scrotum
(the external sac of skin enclosing the testes, or reproductive glands) from
hydrocarbons in chimney soot; hatters became disoriented, or “mad,” from
nerve-destroying mercury salts used to treat felt fabric; and bootblacks
suffered liver damage from boot polish solvents.
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By the 21st century, pollution had evolved
from a mainly localized problem to one of global consequences in which
pollutants not only persisted in the environment, but changed atmospheric and
climatic conditions. The Minamata Bay disaster was the first major indication
that humans would need to pay more attention to their waste products and waste
disposal practices, in particular, hazardous waste disposal. In the years that
followed, many more instances of neglect or carelessness resulted in dangerous
levels of contamination. In 1976 an explosion at a chemical factory in Seveso,
Italy, released clouds of toxic dioxin into the area, exposing hundreds of
residents and killing thousands of animals that ate exposed food. In 1978 it was
discovered that the Love Canal housing development in New York State was built
on a former chemical waste dump. The development was declared uninhabitable. The
world’s worst industrial accident occurred in Bhopal, India, in 1984. A deadly
gas leaked from an American chemical plant, killing more than 3,800 people and
injuring more than 200,000.
The 1986 Chernobyl’ nuclear reactor accident
demonstrated the dangerous contamination effects of large, uncontained
disasters. In an unprecedented action, pollution was used as a military tactic
in 1991 during the conflict in the Persian Gulf. The Iraqi military
intentionally released as much as 1 billion liters (336 million gallons) of
crude oil into the Persian Gulf and set fire to more than 700 oil wells, sending
thick, black smoke into the atmosphere over the Middle East.
| V | CONTROLLING POLLUTION |
Because of the many environmental tragedies
of the mid-20th century, many nations instituted comprehensive regulations
designed to repair the past damage of uncontrolled pollution and prevent future
environmental contamination. In the United States, the Clean Air Act (1970) and
its amendments significantly reduced certain types of air pollution, such as
sulfur dioxide emissions. The Clean Water Act (1977) and Safe Drinking Water Act
(1974) regulated pollution discharges and set water quality standards. The Toxic
Substances Control Act (1976) and the Resource Conservation and Recovery Act
(1976) provided for the testing and control of toxic and hazardous wastes. In
1980 Congress passed the Comprehensive Environmental Response, Compensation, and
Liability Act (CERCLA), also known as Superfund, to provide funds to clean up
the most severely contaminated hazardous waste sites. These and several other
federal and state laws helped limit uncontrolled pollution, but progress has
been slow and many severe contamination problems remain due to lack of funds for
cleanup and enforcement.
International agreements have also played a
role in reducing global pollution. The Montréal Protocol on Substances that
Deplete the Ozone Layer (1987) set international target dates for reducing the
manufacture and emissions of the chemicals, such as CFCs, known to deplete the
ozone layer. The Basel Convention on the Control of Transboundary Movements of
Hazardous Wastes and Their Disposal (1989) serves as a framework for the
international regulation of hazardous waste transport and disposal.
Since 1992 representatives from more than 160
nations have met regularly to discuss methods to reduce greenhouse gas
emissions. In 1997 the Kyōto Protocol was devised, calling for industrialized
countries to reduce their gas emissions by 2012 to an average 5 percent below
1990 levels. The Kyōto Protocol went into force in February 2005 with more than
130 countries having ratified it. Under the administration of President George
W. Bush, however, the United States, a major producer of greenhouse gases,
refused to submit the treaty for ratification. In 2006 the Global Carbon Project
reported that carbon dioxide emissions were increasing at an annual rate of 2.5
percent in the first five years of the 21st century, compared with an annual
increase of 1 percent in the 1990s.
Regulations and legislation have led to
considerable progress in cleaning up some air and water pollution in developed
countries. Vehicles in the 21st century emit fewer nitrogen oxides than those in
the 1970s did; power plants now burn low-sulfur fuels; industrial stacks have
scrubbers to reduce emissions; and lead has been removed from gasoline.
Developing countries, however, continue to struggle with pollution control
because they lack clean technologies and desperately need to improve economic
strength, often at the cost of environmental quality. The problem is compounded
by developing countries attracting foreign investment and industry by offering
cheaper labor, cheaper raw materials, and fewer environmental restrictions. The
maquiladoras, assembly plants along the Mexican side of the Mexico-U.S.
border, provide jobs and industry for Mexico but are generally owned by
non-Mexican corporations attracted to the low-wage labor and lack of pollution
regulation. As a result, this border region, including the Río Grande, is one of
the most heavily polluted zones in North America. To avoid ecological disaster
and increased poverty, developing countries will require aid and technology from
outside nations and corporations, community participation in development
initiatives, and strong environmental regulations.
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Nongovernmental citizen groups have formed at
the local, national, and international level to combat pollution problems
worldwide. Many of these organizations provide information and support for
people or organizations traditionally not involved in the decision-making
process. The Pesticide Action Network provides technical information about the
effects of pesticides on farmworkers. The Citizen’s Clearinghouse for Hazardous
Waste, established by veterans of the Love Canal controversy, provides support
for communities targeted for hazardous waste installations. A well-organized,
grassroots, environmental justice movement has arisen to advocate equitable
environmental protections. Greenpeace is an activist organization that focuses
international attention on industries and governments known to contaminate land,
sea, or atmosphere with toxic or solid wastes. Friends of the Earth
International is a federation of international organizations that fight
environmental pollution around the world.
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