Environmental Encyclopedia

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Environmental Encyclopedia 3

Ozone layer depletion

cules to form O

. When it absorbs

ultraviolet radiation

that would otherwise reach the earth, ozone is, in turn,

broken down into O

+ O. The elemental oxygen generated

then finds another O

molecule to become O

once again.

In 1974, chemists F. Sherwood Rowland and Mario

J. Molina realized that

chlorine

from chlorofluorocarbon

(CFC) molecules was capable of breaking down ozone in

the stratosphere. In time, evidence began accumulate that

the ozone layer was indeed being broken apart by these

industrial

chemicals

, and to a lesser extent by

nitrogen

oxide emissions from jet airplanes as well as

hydrogen

chloride emissions from large volcanic eruptions.

When released into the

environment

, CFCs slowly

rise into the upper atmosphere, where they are broken apart

by solar radiation. This releases chlorine atoms that act as

catalysts, breaking up molecules of ozone by stripping away

one of their oxygen atoms. The chlorine atoms, unaltered by

the reaction, are each capable of destroying ozone molecules

repeatedly. Without a sufficient quantity of ozone to block

its way, ultraviolet radiation from the sun passes through

the upper atmosphere and reaches the surface of the earth.

When damage to the ozone layer first became apparent

in 1974,

propellants

aerosol

spray cans were a major

source of CFC emissions, and CFC aerosols were banned

in the United States in 1978. However, CFCs have since

remained in widespread use in thermal insulation, as cooling

agents in refrigerators and air conditioners, as cleaning sol-

vents, and as foaming agents in

plastics

, resulting in contin-

ued and accelerating depletion of stratospheric ozone.

The Antarctic ozone hole

The most dramatic evidence of the destruction of the

ozone layer has occurred over

Antarctica

, where a massive

“hole” in the ozone layer appears each winter and spring,

apparently exacerbated by the area’s unique and violent cli-

matological conditions. The destruction of ozone molecules

begins during the long, completely dark, and extremely cold

Antarctic winter, when swirling winds and ice clouds begin

to form in the lower stratosphere. This ice reacts with chlo-

rine compounds in the stratosphere (such as hydrogen chlo-

ride and chlorine nitrate) that come from the breakdown of

CFCs, creating molecules of chlorine.

When spring returns in August and September, a sea-

sonal vortex—a rotating air mass—causes the ozone to mix

with certain chemicals in the presence of sunlight. This

helps break down the chlorine molecules into chlorine atoms,

which, in turn, react with and break up the molecules of

ozone. A single chlorine,

bromine

, or nitrogen molecule

can break up literally thousands of ozone molecules.

During December, the ozone-depleted air can move

out of the Antarctic area, as happened in 1987, when levels

of ozone over southern

Australia

and New Zealand sank

by 10% over a three week period, causing as much as a 20%

1047

increase in ultraviolet radiation reaching the earth. This may

have been responsible for a reported increase in skin cancers

and damage to some food crops.

The seasonal hole in the ozone layer over Antarctica

has been monitored by scientists at the National Aeronautics

and Space Administration’s (NASA) Goddard Space Flight

Center outside Washington, D.C. NASA’s NIMBUS-7 sat-

ellite first discovered drastically reduced ozone levels over

the Southern Hemisphere in 1985, and measurements are

also being conducted with instruments on aircraft and bal-

loons. Some of the data that has been gathered is alarming.

In October 1987, ozone levels within the Antarctic

ozone hole were found to be 45% below normal, and similar

reductions occurred in October 1989. A 1988 study revealed

that since 1969, ozone levels had declined by 2% worldwide,

and by as much as 3% or more over highly populated areas

of North America, Europe, South America, Australia and

New Zealand.

In September 1992, the NIMBUS-7 satellite found

that the depleted ozone area over the southern polar region

had grown 15% from the previous year, to a size three times

bigger than the area of the United States, and was 80%

thinner than usual. The ozone hole over Antarctica was

measured at approximately 8.9 million mi

(23 million km

as compared to its usual size of 6.5 million mi

(17 km

The contiguous 48 states is, by comparison, about 3 million

(7.8 million km

), and all of North America covers 9.4

million mi

(24.3 million km

). Researchers attributed the

increased thinning not only to industrial chemicals but also

to the 1991 volcanic eruptions of

Mount Pinatubo

in the

Philippines and Mount Hudson in Chile, which emitted

large amounts of

sulfur dioxide

into the atmosphere.

Dangers Of ultraviolet radiation

The major consequence of the thinning of the ozone

layer is the penetration of more solar radiation, especially

Ultraviolet-B (UV-B) rays, the most dangerous type, which

can be extremely damaging to plants,

wildlife

, and human

health. Because UV-B can penetrate the ocean’s surface, it

is potentially harmful to marine life forms and indeed to the

entire chain of life in the seas as well.

UV-B can kill and affect the reproduction of fish,

larvae, and other plants and animals, especially those found

in shallow waters, including

phytoplankton

, which forms

the basis of the oceanic

food chain/web

. The National

Science Foundation reported in February 1992 that its re-

search ship, on a six week Antarctic cruise, found that the

production of phytoplankton decreases at least 6–12% during

the period of greatest ozone layer depletion, and that the

destructive effects of UV radiation could extend to depths

of 90 ft (27 m).

A decrease in phytoplankton would affect all other

creatures higher on the food chain and dependent on them,

Environmental Encyclopedia 3

Ozone layer depletion

including

zooplankton

, microscopic ocean creatures that

feed on phytoplankton and are also an essential part of the

ocean food chain. And marine phytoplankton are the main

food source for

krill

, tiny Antarctic shrimp that are the

major food source for fish, squid, penguins,

seals

whales

and other creatures in the Southern Hemisphere.

Moreover, phytoplankton are responsible for ab-

sorbing, through

photosynthesis

, great amounts of

carbon

dioxide

(CO

) and releasing oxygen. It is not known how

a depletion of phytoplankton would affect the planet’s supply

of life-giving oxygen, but more CO

in the atmosphere

would exacerbate the critical problem of global warming,

the so-called

greenhouse effect

There are numerous reports, largely unconfirmed, of

animals in the southern polar region being harmed by ultravi-

olet radiation. Rumors abound in Chile, for example, of

pets, livestock, sheep, rabbits, and other wildlife getting

cataracts, suffering reproductive irregularities, or even being

blinded by solar radiation. Many residents of Chile and

Antarctica believe these stories, and wear sunglasses, protec-

tive clothing, and sun-blocking lotion in the summer, or

even stay indoors much of the day when the sun is out. If

the ozone layer’s thinning continues to spread, the lifestyles

of people across the globe could be similarly disrupted for

generations to come.

Particularly frightening have been incidents reported

to have taken place in Punta Arenas, Chile’s southernmost

city, at the tip of Patagonia. After several days of record

low levels of ozone were recorded in October 1992, people

reported severe burns from short exposure to sunlight. Sheep

and cattle became blind, and some starved because they

could not find food. Trees wilted and died, and melanoma-

type skin cancers seem to have increased dramatically. Simi-

lar stories have been reported from other areas of the south-

ern hemisphere. And malignant melanoma, once a rare dis-

order, is now the fastest rising

cancer

in the world.

Ozone thinning spreads

Indeed, ozone layer depletion is spreading at an

alarming rate. In the 1980s, scientists discovered that an

ozone hole was also appearing over the Arctic region in the

late winter months, and concern was expressed that similar

thinning might begin to occur over, and threaten, heavily

populated areas of the globe. These fears were confirmed in

April 1991, when the

Environmental Protection Agency

(EPA) announced that satellite measurements had recorded

an ominous decrease in atmospheric ozone, amounting to an

average of 5% over the mid-latitudes (including the United

States), almost double the loss previously thought to be

occurring.

The data showed that ozone levels measured in the

late fall, winter, and early spring over large areas of the

1048

United States, Europe, and the mid-latitudes of the North-

ern and Southern Hemisphere had dropped by 4–6% over

the last decade—twice the amount estimated in earlier years.

The greatest area of ozone thinning in the United States

was found north of a line stretching from Philadelphia to

Denver to Reno, Nevada. One of the most alarming aspects

of the new findings was that the ozone depletion was contin-

uing into April and May, a time when people spend more

time outside, and crops are beginning to sprout, making

both more vulnerable to ultraviolet radiation.

The new findings led the EPA to project that over

the next 50 years, thinning of the ozone layer could cause

Americans to suffer some 12 million cases of skin cancer,

200,000 of which would be fatal. Several years earlier, the

agency had calculated that over the next century, there could

be an additional 155 million cases of skin cancers and 3.2

million deaths if the ozone layer continued to thin at the

then current rate. Another EPA projection made in the

1980s was that the increase in radiation could cause Ameri-

cans to suffer 40 million cases of skin cancer and 800,000

deaths in the following 88 years, plus some 12 million eye

cataracts.

No one can say how accurate such varying projections

will turn out to be, but evidence of ozone layer thinning

is well-documented. In October 1991, additional data of

spreading ozone layer destruction were made public. Dr.

Robert Watson, a NASA scientist who co-chairs an 80-

member panel of scientists from 80 countries, called the

situation “extremely serious,” saying that “we now see a

significant decrease of ozone both in the Northern and

Southern Hemispheres, not only in winter but in spring and

summer, the time when people sunbathe, putting them at

risk for skin cancer, and the time when we grow crops.”

In February 1992, a team of NASA scientists an-

nounced that they had found record high levels of ozone-

depleting chlorine over the Northern Hemisphere. This

could, in turn, lead to an ozone “hole” similar to the one

that appears over Antarctica developing over populated areas

of the United States, Canada, and England. The areas over

which increased levels of

chlorine monoxide

were found

extended as far south as New England, France, Britain, and

Scandinavia.

Action to protect The ozone layer

As evidence of the critical threats posed by ozone layer

depletion has increased, the world community has begun to

take steps to address the problem. In 1987, the United States

and 22 other nations signed the Montreal Protocol, agreeing,

by the year 2000, to cut CFC production in half, and to

phase out two ozone-destroying gases, Halon 1301 and Ha-

lon 1211.

Halons

are man-made bromine compounds used

mainly in fire extinguishers, and can destroy ozone at a rate

10 to 40 times more rapidly than CFCs. Fortunately, these

Environmental Encyclopedia 3

Ozone layer depletion

restrictions appear to already be having an impact. In 1992,

it was found that the rate at which these two Halon gases

were accumulating in the atmosphere had fallen significantly

since 1987. The rate of increase of levels of Halon 1301 was

about 8% a year from 1989 to 1992, about half of the average

annual rate of growth over previous years. Similarly, Halon

1211 was increasing at only 3% annually, much less than

the previous growth of 15% a year.

Since the Montreal Protocol, other international trea-

ties have been signed limiting the production and use of

ozone-destroying chemicals. When alarming new evidence

on the destruction of stratospheric ozone became available

in 1988, the world’s industrialized nations convened a series

of conferences to plan remedial action. In March 1989,

the 12-member European Economic Community (EEC)

announced plans to end the use of CFCs by the turn of the

century, and the United States agreed to join in the ban. A

week later, 123 nations met in London to discuss ways to

speed the CFC phase-out. The industrial nations agreed

to cut their own domestic CFC production in half, while

continuing to allow exports of CFCs, in order to accommo-

date

third world

nations.

Ironically, the large industrial nations, which have cre-

ated the CFC problem, are now much more willing to take

effective action to ban the compounds than are many devel-

oping nations, such as India and China. The latter nations

resist restrictions on CFCs on the grounds that the chemicals

are necessary for their own economic development.

After the meeting in London, leaders and representa-

tives from 24 countries met in an environmental summit at

The Hague, and agreed that the United Nations’ authority

to protect the world’s ozone layer should be strengthened.

In May 1989, members of the EEC and 81 other

nations that had signed the 1987 Montreal Protocol decided

at a meeting in Helsinki to try to achieve a total phase-out

of CFCs by the year 2000, as well as phase-outs as soon as

possible of other ozone-damaging chemicals like

carbon

tetrachloride, halons, and methyl chloroform. In London in

June 1990, most of the Montreal Protocol’s signatory nations

formally adopted a deadline of the year 2000 for industrial

nations to phase out the major ozone-destroying chemicals,

with 2010 being the goal for developing countries.

Finally, in November 1992, 87 nations meeting in

Copenhagen decided to strengthen the action agreed to un-

der the Montreal Protocol and move up the phase-out dead-

line from 2000 to January 1, 1996, for CFCs, and to January

1, 1994, for halons. A timetable was also agreed to for

eliminating

hydrochlorofluorocarbons

(HCFCs) by the

year 2030. HCFCs are being used as substitutes for CFCs

even though they also deplete ozone, albeit on a far lesser

scale than CFCs. The conference failed to ban the produc-

1049

tion of the

pesticide

methyl bromide, which may account

for 15% of ozone depletion by the year 2000, but did freeze

production at 1991 levels.

Environmentalists were disappointed that stronger ac-

tion was not taken to protect the ozone layer. But Environ-

mental Protection Agency (EPA) Administrator William

K. Reilly, who headed the U.S. delegation, estimated that

the reductions agreed to could, by the year 2075, prevent a

million cases of cancer and 20,000 deaths.

Although the restrictions apply to developed nations,

which produce most of the ozone-damaging chemicals, it

was also agreed to consider moving up a phase-out of such

compounds by developing nations from 2010 to 1995. A

month after the Copenhagen conference, the nations of the

European Community agreed to push bans on the use of

CFCs and carbon tetrachloride to 1995 and to cut CFC

emissions by 85% by the end of 1993.

The private sector has also taken action to reduce

CFC production. The world’s largest manufacturer of the

chemicals, DuPont Chemical Company, announced in 1988

that it was working on a variety of substitutes for CFCs,

would phase out production of them by 1996, and would

partially replace them with HCFCs. Environmentalists

charge that DuPont has been moving too slowly to eliminate

production of these chemicals.

There are many ways that individuals can help reduce

the release of CFCs into the atmosphere, mainly by avoiding

products that contain or are made from CFCs, and by

recycl-

ing

CFCs whenever possible. Although CFCs have not

generally been used in spray cans in the United States since

1978, they are still used in many consumer and industrial

products, such as styrofoam. Other products manufactured

using CFCs include solvents and cleaning liquids used on

electrical equipment,

polystyrene

foam products, and fire

extinguishers that use halons.

Refrigerants in cars and home air conditioning units

contain CFCs and must be poured into closed containers

to be cleaned or recycled, or they will evaporate into the

atmosphere. Using foam insulation to seal homes also re-

leases CFCs. Many alternatives to foam insulation exist,

such as cellulose fiber, gypsum, fiberboard, and fiberglass.

Unfortunately, whatever steps are taken in the next

few years, the problem of ozone layer depletion will continue

even after the release of ozone-destroying chemicals is lim-

ited or halted. It takes six to eight years for some of these

compounds to reach the upper atmosphere, and once there,

they will destroy ozone for another 20–25 years. Thus, even

if all emissions of destructive chemicals were stopped, com-

pounds already released would continue to damage the ozone

layer for another quarter century.

Environmental Encyclopedia 3

Ozone layer depletion

Understanding ozone depletion

As detailed collection of data about interactions in the

stratosphere progresses, the observational support for the

ozone depletion theory continues to grow more compelling.

Yet atmospheric scientists are beginning to realize that their

understanding of the upper atmosphere is still quite crude.

While certain key reactions which maintain and destroy

ozone are theoretically and observationally supported, scien-

tists will have to comprehend the interaction of dozens, if

not hundreds, of reactions between natural and artificial

species

of hydrogen, nitrogen, bromine, chlorine and oxy-

gen before a complete picture of ozone-layer dynamics

emerges. The recent eruption of

Mount Pinatubo

, for exam-

ple, made scientists aware that heterogenous processes—those

reactions which require cloud surfaces to take place—may

play a far greater role in causing ozone depletion than origi-

nally believed. Such reactions had previously been observed

taking place only at the earth’s poles, where stratospheric

clouds form during the long winter darkness, but it is now

thought that sulfur aerosols ejected by Pinatubo may be

serving as a catalyst to speed ozone depletion at nonpolar

latitudes.

Ironically, ozone-depleting reactions are best under-

stood around the thinly inhabited polar regions, where stable

and isolated conditions over the winter allow scientists to

understand stratospheric changes most easily. In contrast, at

the temperate latitudes where constantly moving air masses

undergo no seasonal isolation, it is difficult to determine

1050

whether a fluctuation in a given chemical’s density is a result

of local reactions or atmospheric turbulence. In 1995, the

Nobel Prize for Chemistry was awarded to F. Sherwood

Roland, Mario Molina and Paul Crutzen for their work on

the formation and destruction of the ozone layer. It is hoped

that increasingly detailed measurements using a new genera-

tion of equipment (such as NASA’s Perseus remote-control

aircraft) will begin to shed more light on the processes oc-

curring away from the poles. Joe Waters of NASA’s Jet

Propulsion Laboratory summarizes the urgent task: “We

must be able to lay out the catalytic cycles that are destroying

ozone at all altitudes all over the globe—from its production

region in the tropics to the higher latitudes and the polar

regions.” See also Photochemical reaction

[Lewis G. Regenstein]

ESOURCES

OOKS

Benedick, R. E. Ozone Diplomacy: New Directions in Safeguarding the Planet.

Washington, DC: World Wildlife Fund, 1991.

Clark, S. L. Protecting the Ozone Layer: What You Can Do. New York:

Environmental Information Exchange, 1988.

ERIODICALS

Lyman, F. “As the Ozone Thins, the Plot Thickens.” Amicus Journal 13

(Summer 1991): 20–28, 30.

Monastersky, R. “Ozone Layer Shows Record Thinning.” Science News 143

(April 24, 1993): 260.

Zurer, P. S. “Ozone Depletion’s Recurring Surprises Challenge Atmo-

spheric Scientists.” Chemical and Engineering News (May 24, 1993): 8–18.

PAHs

see

Polycyclic aromatic hydrocarbons

Paleoecology/paleolimnology

Paleoecology, the scientific study of ancient environments

and the interrelationships of their plants and animals, and

paleolimnology, the scientific study of evidence of ancient

inland waterways, including lakes, ponds, freshwater

marshes, and streams, were both established at the end of

the nineteenth century. The roots of both disciplines can be

traced to early nineteenth-century botanical and chemical

studies, and later, geological studies of the consolidated sedi-

ments of ancient lake beds, in which their organisms and

environments were examined in relationship to both the

lakes and the surrounding uplands.

By the early 1920s, limnologists began to collect

sedi-

ment

cores from lakes and to interpret stratigraphic data

from plant and animal fossils as a record of a lake’s history.

This provided clues to how lakes had changed over time as

a result of either natural events or human activities. Data

collected from lakes and

wetlands

provide baselines to com-

pare the impacts of a activities such as land clearance,

drain-

age

water pollution

, and

air pollution

. They can also be

used to assess the rate of recovery from the activities once

they have ended.

Lake and wetland sediments contain detailed archeo-

logical records of how the overlying ecosystems have been

affected over time. It is in many ways equivalent to archeo-

logical reconstruction of past civilizations by examining their

stratified remains. Lake sediments and wetland peat deposits

form a selective trap for a variety of plant and animal remains

and elements such as

carbon

phosphorus

, sulfur, iron,

and manganese that are stored at varying concentrations

depending on the activities that were occurring at the time

the sediment layer was formed. Changes in this profile record

not only the history of the lake or peatland but also what

happened in the surrounding

watershed

. Initially, limnolo-

1051

gists collected core samples from lakes and interpreted them

on the basis of plant and animal fossils. The limnologists

observed that in some lakes there were thin laminated sedi-

ments. These were shown to result from an annual deposition

cycle which involves summer deposition of calcium carbonate

and deposition of organic matter during the rest of the year.

These alternating light and dark layers represent a yearly

cycle. Using these bands, or laminae, scientists can count

back in time and date individual strata of sediment cores.

Studying plant and animal microfossil remains (such

as pollen, diatom shells, and remains of

zooplankton

bod-

ies) in the sediment cores and knowing the environments

in which these organisms occur today allow a limnologist

to reconstruct historical conditions in a lake as well as in its

drainage basin. Such wetland studies were limited, however,

until the development of

radioisotope

dating methods in

the 1950s and 1960s. Today radioisotopes such as carbon-

14 and lead-210 can be used to date the time a sediment

was deposited.

Other methods limnologists use include the pollen,

which indicates what types of land vegetation were present.

They also examine plant and animal fossil remains, including

cell fragments and molecules such as plant pigments, all

of which provide clues about vegetation and aquatic life.

Limnologists also search for organic pollutants and certain

trace elements, whose presence indicates the result of human

activities.

Analysis of the layers in sediment cores from lakes

and wetlands has provided information about regional varia-

tions in past climatic conditions and watershed vegetation

patterns which indicates the causes of environmental change.

Studies on recently deposited lake sediments have provided

evidence for the timing and causes of lake

pollution

, includ-

ing the effects of excess nutrients on lake

ecology

and

information about atmospheric transport of various pol-

lutants.

These techniques have also been applied to address

basic plant ecology questions regarding plant

succession

on which there are two major schools of thought. The first

Environmental Encyclopedia 3

Paleoecology/paleolimnology

is the community concept which has three basic attributes:

vegetation occurs in recognizable and characteristic commu-

nities; community change through time occurs because of

the vegetation; and the changes occur in a sequence that

leads to a mature stable climax

ecosystem

. The community

explanation can be contrasted with the continuum concept.

Here, the distribution of vegetation is determined by the

environment

. Since each plant

species

adapts differently,

no two occupy the exact same location. Additionally, the

observed replacement sequence is influenced by the chance

occurrence of viable seeds that allows a certain plant to grow

on the site. This results in a continuum of overlapping sets

of species. In this scenario although ecosystems change, it

is not directed toward a particular climax community.

One of the areas where these two concepts directly

collide is in the study of wetlands and

peatlands

. The

classical community view of succession is that wetlands are

a transitional stage in the progression from shallow lake to

terrestrial forested climax community. This view requires

that lakes gradually fill in as organic material from dying

plants accumulates and minerals are carried down from up-

slope into the water. At first change is slow, but it accelerates

when the lake becomes shallow enough to support rooted

aquatic plants. When the water becomes even more shallow,

it supports the development of a peat mat, allowing trees

and shrubs to grow which further modifies the site by not

only adding organic matter but also by drying the site

through

evapotranspiration

. According to the community

version, in the final stages a climax forest occupies the site.

This sequence implies that most of the change is caused by

plants and not external environmental changes.

Paleoecological analyses of peat beds have provided

information refuting the validity of the community concept’s

explanation. Fossil records including analysis of pollen in

northern peat lands provide two generalizations: in some

sites the present vegetation has existed for several thousand

years and climatic change and

glaciation

had a large impact

on plant species and distribution. Generally, bogs expanded

during warm, wet periods and contracted during cool, drier

periods although the influence of local topographic and

drainage conditions often mask climatic shifts.

While this evidence supports the continuum assump-

tions that other environmental factors overwhelm the vegeta-

tion effects, there is evidence within the bogs that says that

vegetation can have a large impact on the character of the

landscape. In particular, this is evidenced by the patterned

landscape of these peatlands as the water flow is changed

due to the vegetation. It seems that in the wetlands or bogs

themselves there can be changes in vegetation that occur

over time as a result of succession. However, these changes

do not necessarily point toward a terrestrial climax. In fact,

pollen profiles indicate that a bog, not some type of terrestrial

1052

forest, is the endpoint. These studies confirmed conclusions

from a classical study on the Lake Aggassiz Plain (Minnesota

and south-central Canada) that indicates most of the peat-

lands developed during a moist

climate

about 4,000 years

ago when surface water levels rose about 12 ft (4 m). This

implies that while there may be changes within the peatlands,

they are stable, so the central concepts of succession in this

case are not supported.

Examples of the findings and results of some signifi-

cant types of paleolimnological studies show how they are

useful in evaluating changes and as indicators of potential

problems due to human activities. The Red Lake peatland

in northwestern Minnesota has been used as a study site to

document the occurrence of

acid rain

and global warming.

Based on past changes in the type of vegetation and changes

, future impacts on the bog surface can be evaluated.

acid deposition

were to lower the pH of the bog signifi-

cantly, different types of mosses would be evident. Likewise,

if global warming were to lower the water tables’ moss types,

characteristics of drier conditions would occur.

Using sediment cores from lakes and observing the

changes in

flora

fauna

, and chemistry allows the evaluation

of impacts of human settlement on lakes in the upper Mid-

west of the United States. A lake studied in northern Minne-

sota on the iron range shows these changes. There was a

distinct increase in hematite (iron) grains in the sediments

as mining began and a decrease as it declined. Settlement

was also marked by a rise in the concentration or ragweed

pollen which reflects the replacement of the forests with

agricultural fields. There were also changes in the type of

diatom shells reflecting the

nutrient

enrichment of the lake

due to the

discharge

of sewage directly to the lake. By

analyzing the pH preferences of individual species of diatoms

and algae the past pH conditions in a lake can be determined.

Using the results of these studies it has been demonstrated

that lakes in the

Adirondack Mountains

were not naturally

acidic. Current monitoring suggests that these lakes that

were acidified due to

acid

rain have not yet responded reduc-

tions in the amount of sulfate deposition.

[James L. Anderson]

ESOURCES

OOKS

Freshwater Ecosystems: Revitalizing Educational Programs in Limnology.

Washington, DC: National Academy Press, 1996.

Mitsch, W.J., and J.G. Gosselink. Wetlands. New York: Van Nostrand

Reinhold, 1993.

PAN

see

Peroxyacetyl nitrate

Environmental Encyclopedia 3

Pareto optimality (Maximum social welfare)

Panda

see

Giant panda

Panther

see

Florida panther

Panthera tigris

see

Tigers

Paper mills

see

Pulp and paper mills

Parasites

Organisms that live in or upon the body of a host organism

and are metabolically dependent on the host for completion

of their life cycle. Parasites may be plants, animals, viruses,

bacteria, or

fungi

. Parasites feed either on their host directly

or upon its surplus fluids. Some parasites, known as endopar-

asites, live inside their host, while ectoparasites live on the

outside of their host. Organisms in which parasites reach

maturity are called definitive hosts, and hosts harboring para-

site stages are called intermediate hosts. Organisms which

spread parasite stages between hosts are known as vectors.

Full-time, or obligatory, parasites have an absolute depen-

dence on their hosts. Examples of this type are viruses, which

can only live and multiply inside living cells, and tapeworms,

which can only live and multiply inside other

species

. Part-

time, or facultative, parasites, such as wood ticks, have para-

sitic and free-living stages in their life cycle and are only

temporary residents of their hosts.

The effects of parasites on their hosts depend on the

health of the host, as well as the severity of the infestation.

In diseased, old, or poorly-fed individuals, parasite infesta-

tions can be fatal, but parasites do not typically kill their

hosts, though they can slow growth and cause weight loss.

Some plant parasites do kill their host and then live on its

decomposing remains, and certain species of hymenopteran

insect are parasitoids, whose larva feeds within the living

body of the host, eventually killing it. Some parasites, such

as Sacculina, castrate their host by infecting its reproductive

organs. Cuckoos are brood parasites, and they lay their eggs

in the nest of another bird species, evicting the eggs that

were there and leaving the young cuckoos to be raised by

the parents of the host species.

community ecology

, parasites are often grouped

together with predators, since both feed directly upon other

organisms, either harming them or killing them. Ecologi-

1053

cally, small disease-causing organisms (viruses, bacteria, pro-

tozoans) are regarded as microparasites, while larger parasites

(flatworms, roundworms, lice, fleas, ticks, rusts, mistletoe)

are macroparasites. Together with predators and diseases,

parasites are one of the natural components of environmental

resistance

which serves to limit

population growth

. Mi-

croparasites that are transmitted directly between infected

hosts, such as rabies or distemper, target herd animals with

a high host density and can significantly reduce population

levels. Macroparasites that employ one or more intermediate

hosts, such as flukes, tapeworms, or roundworms, have

highly effective transmission stages but usually have only a

limited effect on the population of the host.

Parasites can play a larger role in altered ecosystems.

In the eastern United States parasitic infections have held

populations of cottontail rabbits well below the

carrying

capacity

of the

habitat

. Parasitic insects have been used

to control populations of the olive scale insect, a serious

pest

of olive trees in California. Accidentally introduced parasites

have negatively impacted populations of commercial species

by altering the balance of the

ecosystem

. For example, a

protozoan parasite infecting California oysters was intro-

duced to French oyster beds, wiping out the native European

oysters and seriously damaging

commercial fishing

there.

See also Population biology; Predator-prey interactions

[Neil Cumberlidge Ph.D.]

ESOURCES

OOKS

Bullock, W. L. People, Parasites, and Pestilence: An Introduction to the Natural

History of Infectious Disease. Minnesota: Burgess Publishing Company, 1982.

Crew, W., and D. R. W. Haddock. Parasites and Human Disease. London:

Edward Arnold, 1985.

Despommier, D. D., and J. W. Karapelou. Parasite Life Cycles. New York:

Springer-Verlag, 1987.

Noble, E. R., and G. A. Noble. Parasitology: The Biology of Animal Parasites.

6th ed. Philadelphia: Lea & Febiger, 1989.

Schmidt, G. D., and L. S. Roberts. Foundations of Parasitology. 4th ed. St.

Louis: Times Mirror/Mosby College Pub., 1989.

Smith, R. L. Elements of Ecology. 3rd ed. New York: Harper Collins, 1991.

Pareto optimality (Maximum social

welfare)

Usually, one thinks of efficiency as not being wasteful or

getting the most out of the resources one has available.

Economists offer the Pareto optimum—“a situation where

no one can be better off without making someone worse

off.” Derived from the work of the Italian economist and

sociologist Vilfredo Pareto, whose late nineteenth-century

writings on political economy inspired much thinking about

what made an economy efficient, Pareto optimality has come

Environmental Encyclopedia 3

Parrots and parakeets

to mean making at least one person better off without making

anyone else worse off. For an economy, it means that the

allocation of resources is optimal if no other allocation exists

wherein a person is better off and everyone is at least as well

off. Economic theory holds that these conditions are met

if consumers maximize utility, producers maximize profits,

competition prevails, and information is adequate for the

making of rational decisions. A free market unconstrained by

government involvement, it is assumed, will achieve Pareto

optimality by an invisible hand, that is, automatically, pro-

vided that production and consumption decisions do not

entail substantial environmental disamenities. Imperfect

market conditions, which include environmental disame-

nities on a large scale, challenge the assumptions of Pareto

optimality and call for remedial measures such as

pollution

taxes or

emission

rights to restore market efficiency. See

also Externalities

Parrots and parakeets

These intelligent, brightly colored, affectionate birds are

found mainly in warm, tropical regions and have long been

popular as pets, in large part because many of them can

learn to talk. But capture of wild parrots for the

pet trade

along with the destruction of forests, have decimated popula-

tions of these birds, and many

species

are now threatened

with

extinction

About half of the approximately 315 species of parrots

in the world are native to Central and South America. Mem-

bers of the parrot order (Psittaciformes) include the macaws

of Central and South America, which are the largest parrots,

with bright feathers; cockatoos of

Australia

with white

feathers and crests on their heads; lorikeets of Australia with

orange-red bills and brightly-colored feathers; cockatiels,

which are small, long-tailed, crested parrots also from Aus-

tralia; and parakeets, which are small, natural acrobats, usu-

ally with green feathers. Parakeets include lovebirds from

Africa and budgies from Australia. Budgies are the most

common type of pet parakeet, and they can be trained to

say many words. Most parakeets sold as pets are bred for

that purpose, thus their trade does not usually threaten wild

populations.

Part of the attraction of parrots is their high intelli-

gence, but this can make them unsuitable pets. The birds

are often loud and they demand a great deal of attention,

and many people who buy parrots give them up because of

the frustrations of owning one of these complex birds. In

addition, parrots often carry a disease called psittacosis which

can be transmitted to humans and commercially raised poul-

try. For this reason, parrots must be examined by officials

from the

U.S. Department of Agriculture

(USDA) before

1054

entering the United States, and hundreds of thousands of

parrots have been destroyed to prevent the spread of psitta-

cosis.

The large scale capture of parrots for the legal and

illegal pet trade has been a major factor in the depletion of

these beautiful birds. The world trade in wild birds has been

estimated at over seven million annually, and the United

States is the world’s largest consumer of exotic birds. Over

1.4 million wild birds were imported into this country during

1988–1990, and half of these were parrots and other birds

supposedly protected under the

Convention on Interna-

tional Trade in Endangered Species of Wild Fauna and

Flora

(CITES). The

mortality

rate for birds transported

in international trade is massive. For every wild bird that

makes it to the pet store, at least five may have died on the

way, and USDA

statistics

show that 79,192 birds perished

in transit to the United States from 1985 to 1990, and

258,451 died while in quarantine or because they were re-

fused entry due to Newcastle disease. In 1991 one airline

shipment alone included 10,000 dead birds. Moreover, the

shock of capture and caging the birds before shipment may

cause even greater mortality rates.

As a species becomes rare or endangered, it often

becomes more valuable and sought-after, and some parrots

have been sold for $10,000 or more. In October 1992, shortly

before being named Secretary of the Interior, former Arizona

governor Bruce Babbitt addressed the annual meeting of the

Humane Society of the United States

. Expressing dismay

at “the looming extinction of tropical parrots and macaws

in South America,” he described their exploitation in the

following terms: “These birds are captured for buyers in the

United States who will pay up to $30,000 for a hyacinth

macaw. You can stand on docks outside Manaus, Brazil,

and other towns in the Amazon and see confiscated crates

with blue and yellow macaws, their feet taped, their beaks

wired, stacked up like cordwood in boxes. They have a fatality

rate of 50% by the time they’re smuggled into Miami.”

Some progress has been made in restricting the inter-

national trade in parrots. By the end of 1992 over 100 airlines

had agreed to forbid the carrying of wild birds. The Wild

Bird Conservation Act, signed into law on October 27, 1992,

bans trade immediately for several severely exploited bird

species and, within a year of passage, outlaws commerce in

all parrots and other birds protected under CITES. The act

requires exploiters to prove that a species can withstand

removal from the wild. This has greatly reduced the number

of birds imported into the United States. Conservation

groups, such as the Humane Society of the United States

and the

Animal Welfare Institute

, have worked for years

to secure passage of this legislation.

Nevertheless, the persistence of smuggling as well as

the legal trade in some species of these birds will continue

Environmental Encyclopedia 3

Partnership for Pollution Prevention

to threaten wild populations. This is especially true when

the trees in which parrots nest are cut down to provide

collectors access to chicks in the nest. As of 2002, 16 parrot

species, 10 parakeet species, and three macaw species were

listed as endangered by the

U.S. Department of the Interior

and all species of parrots, parakeets, macaws, lories, and

cockatoos are listed in the most endangered categories of

CITES. IUCN—The World Conservation Union—in-

cludes 69 members of the parrot order in its 2000 list of

threatened animals.

Nine parrots are listed as extinct by IUCN. One is

the beautiful orange, yellow, and green Carolina parakeet

(Conuropsis carolinensis) once ranged in large numbers from

Florida to New York and Illinois, but the demand for its

feathers by the millinery trade was so great that the species

was hunted into extinction between 1904 and 1920. Conser-

vationists fear that several other species of the parrot family

may soon join the Carolina parakeet on the list of extinct

birds.

[Lewis G. Regenstein]

ESOURCES

OOKS

Beissinger, S. R., and E. H. Bucher. New World Parrots in Crisis: Solutions

From Conservation Biology. Washington, DC: Smithsonian Institution

Press, 1991.

ERIODICALS

Beissinger, S. R., and E. H. Bucher. “Can Parrots Be Conserved Through

Sustainable Harvesting?” BioScience 42 (March 1992): 164–73.

Defreitas, M. “Feathering a Nest in the Windwards. (Saving the Santa

Lucian parrot).” Americas 43 (March–April 1991): 40–45.

Particulate

An adjective describing anything that consists of, or relates

to, particles. The term was formerly used in laboratory slang

to stand for “particulate matter,” but this use has nearly

disappeared since its repudiation by the

Environmental Pro-

tection Agency

(EPA). The term particulate matter, which

often means the particle content of a given volume of air,

is used as a more inclusive variant of “particles.”

Typical atmospheric particulate matter may comprise

three populations of particles according to size. The smallest

of these is found only near sources, since the particles rapidly

aggregate to larger sizes. The upper size limit for these

particles is near 0.1 micrometer (1 micrometer = 1 ␮m=

0.001 mm). Number concentrations can be quite high. This

population is referred to as the nuclei mode of particles. The

next larger size class, which begins at a diameter of about 0.1

␮m and extends to about 2.0 ␮m, is called the accumulation

mode, since once in the air it tends to remain for days;

1055

number concentrations have become low enough that

ag-

glomeration

is slow, and settling velocities are very small.

The sum of the nuclei mode and the accumulation mode is

called the fine particles. These are characteristically formed

by condensation from the gas phase, or by agglomeration

of particles formed from the gas phase. The final particle

population in air is called the coarse mode, or simply the

coarse particles. These are of any size larger than about 2

␮m (about 1/10,000 inch), and are formed by mechanical

grinding of larger masses of matter. Coarse particles are

usually particles of local

soil

or rocks.

Partnership for Pollution Prevention

The Partnership for

Pollution

Prevention (Ppp) is an inter-

national cooperative effort to ensure the environmental sus-

tainability of the Western Hemisphere. Pollution prevention

requires the efficient utilization of raw materials and energy,

as well as modifications in products and manufacturing pro-

cesses to minimize environmental impact. The Ppp promotes

technical and financial cooperation and information ex-

change among nations. It also promotes the adoption of

strict, internationally compatible environmental laws and

regulations and the implementation of international environ-

mental agreements. The Ppp works toward improving tech-

nologies for environmental protection and increasing public

awareness and participation in environmental issues, particu-

larly among indigenous groups and other affected communi-

ties. Finally, the Ppp encourages the inclusion of sustainabil-

ity objectives in other developmental and national policies.

The Ppp is Action Initiative 23 of the Plan of Action

developed at the First Summit of the Americas, held in

Miami, Florida, in 1994. It is based on the policies formu-

lated at the 1992 United Nations Conference on Environ-

ment and Development and the 1994 Global Conference on

the

Sustainable Development

of Small Island Developing

States. The initial Ppp priorities were formulated at a meet-

ing in San Juan, Puerto Rico, in November 1995. The meet-

ing also addressed issues of financing, public-private partner-

ships, new legislation, compliance and enforcement, and

public participation. Sponsored by the Organization of

American States (OAS), the U.S.

Environmental Protec-

tion Agency

(EPA), and the Pan American Health Organi-

zation (PAHO), this meeting included representatives from

20 countries, as well as members of international organiza-

tions, non-governmental organizations, and development

banks.

The initial Ppp priorities are health and environmental

problems stemming from

lead

contamination and the mis-

use of pesticides. The Ppp also addresses problems of waste,

air and

water quality

marine pollution

, and urbanization.

Environmental Encyclopedia 3

Parts per billion

Under the Ppp, 10 nations have made formal political com-

mitments in the areas of health and the environment. Fur-

thermore, under the Ppp, the environmental policies of the

North American Free Trade Agreement

(NAFTA) are

being integrated with its trade and economic policies, and

NAFTA is confronting issues of

pesticide

registration and

chemical

pollution control

An OAS meeting in 1996 that included the Inter-

American Development Bank, the

World Bank

, the

PAHO, the EPA, and the United States Agency for Interna-

tional Development (USAID) formed a task force for Ppp

implementation. In October 1997 the task force merged

with a similar task force from the 1996 Santa Cruz (Bolivia)

Summit on Sustainable Development. This new task force

established a number of working groups to address cleaner

production, innovative financing for sustainable develop-

ment, improved access to drinking water, and the networking

of environmental experts. The working group on energy

infrastructure has obtained funding for a gas pipeline being

constructed between Santa Cruz and Sa

o Paolo, Brazil. The

working group for sustainable cities and communities initi-

ates projects to strengthen local governments, promote local

involvement in planning, and improve access to capital and

to low-income housing.

The Ppp working group to phase out leaded

gasoline

has served as a model for other working groups. The EPA,

PAHO, and the World Health Organization (WHO) have

held lead phase-out training workshops. The World Bank

works with individual countries to finance refinery upgrades

and conversions. As a result of these efforts, a number of

nations have banned the sale of leaded gasoline. Leaded

gasoline is expected to be eliminated from the Western

Hemisphere by 2007. The World Bank, USAID, and the

EPA also have developed a lead-monitoring program for

children and adults in Latin America and the Caribbean.

Under the auspices of the Ppp, the Cleaner Production

Conference of the Americas was held in Sa

o Paulo in 1998.

It established the Cleaner Production Roundtable of the

Americas, a formal network of cleaner production prac-

titioners who share ideas and promote the benefits of cleaner

production for sustainable development. The conference also

set up a communications network and identified priority

needs for cleaner production and pollution controls.

Under the Ppp, the USAID’s Regional Environmental

Project for Central America, in collaboration with the EPA

and the Central American Commission on Environment and

Development, has established regional pollution prevention

networks to address

solid waste

and wastewater manage-

ment and the safe use of pesticides. Wastewater and air-

contamination regulations, municipal pollution prevention

and environmental action plans, and a training network in

environmental law

have been established in Central Amer-

1056

ican countries. As part of the Ppp, the USAID has carried

out projects for pollution prevention, clean industrial tech-

nologies, and coastal and marine management throughout

Latin America and the Caribbean.

[Margaret Alic Ph.D.]

ESOURCES

OOKS

Bureau of Inter-American Affairs.Words Into Deeds, Progress Since the Miami

Summit: Report on the Implementation of the Decisions Reached at the 1994

Miami Summit of the Americas. Washington, DC: United States Department

of State, 1998.

THER

First Summit of the Americas: Plan of Action. Secretariat for Legal Affairs,

Organization of American States. 2001 [cited May 29, 2002]. <www.oas.-

org/Juridico/english/PlanI.html>.

Office of the Summit Follow-Up.Words Into Deeds: Progress Since the Miami

Summit. Organization of American States. 1998 [cited May 28, 2002].

<www.summit-americas.org/WordsintoDeeds-eng.htm>.

RGANIZATIONS

Free Trade Area of the Americas “FTAA” Administrative Secretariat,

Apartado Postal 89-10044, Zona 9, Ciudad de Panama

, Republica de

Panama

(507) 270-6900, Fax: (507) 270-6990, , www.ftaa-alca.org/

alca_e.asp

National Pollution Prevention Roundtable, 11 Dupont Circle, NW, Suite

201, Washington, DC, USA 20036 (202) 299-9701, Fax: (202) 299-9704,

Email: talk@p2.org, www.p2.org

Organization of American States, 17th Street and Constitution Ave., NW.,

Washington, DC, USA 20006 (202) 458-3000, , <http://www.oas.org>

United States Environmental Protection Agency, 1200 Pennsylvania

Avenue, NW, Washington, D.C. USA 20460 Toll Free: (800) 490-9198,

Email: public-access@epa.gov, <http://www.epa.gov>

Parts per billion

A means of expressing minute concentrations, often of an

element, compound, or particle that contaminates

soil

water, air, or blood. The expression may be on either a mass

or a volume basis, or a combination of the two, such as

micrograms of a chemical per kilogram of soil, or micrograms

of chemical per liter of water. In the United States, one

billion equals 1x10

Dioxin

, a contaminant associated with

the

herbicide 2,4,5-T

and implicated in the formation of

birth defects

, can cause concern at concentrations measured

in ppb.

Parts per million

A means of expressing small concentrations, usually of an

element, compound, contaminant, or particle in water or a

mixed medium such as

soil

and normally on a mass basis.

Units that are equivalent to ppm include micrograms per

gram, milligrams per kilogram, and milligrams per liter.