Environmental Encyclopedia

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Environmental Encyclopedia 3

Pollution control

larly, natural soils with large concentrations of selenium

support plants that can hyperaccumulate this element to

concentrations greater than one percent. These plants are

poisonous to livestock, causing a toxic syndrome known as

blind staggers.

Of course, there are many well-known cases where

pollution is caused by anthropogenic emissions of chemicals.

Some examples include:

Emissions of sulfur dioxide and metals from smelters can

cause damage to surrounding terrestrial and aquatic ecosys-

tems. The sulfur dioxide and metals are directly toxic. In

addition, the deposition of sulfur dioxide can cause an

extreme acidification of soil and water, which causes metals

to be more bio-available, resulting in important, secondary

toxicity. Because smelters are point sources of emission,

the spatial pattern of chemical pollution and ecological

damage displays an exponentially decreasing intensity with

increasing distance from the source.

The use of pesticides in agriculture, forestry, and around

homes can result in a non-target exposure of birds and

other

wildlife

to these chemicals. If the non-target biota

are vulnerable to the

pesticide

, then ecological damage

will result. For example, during the 1960s urban elm trees

in the eastern United States were sprayed with large quanti-

ties of the insecticide DDT, in order to kill beetles that

were responsible for the transmission of Dutch elm disease,

an important

pathogen

. Because of the very large spray

rates, many birds were killed, leading to reduced popula-

tions in some areas. (This was the “silent spring” that was

referred to by Rachel Carson in her famous book by that

title.) Birds and other non-target biota have also been killed

by modern insecticide-spray programs in agriculture and

in forestry.

The deposition of acidifying substances from the

atmo-

sphere

, mostly as acidic precipitation and the

dry deposi-

tion

of sulfur dioxide, can cause an acidification of surface

waters. The acidity solubilizes metals, most notably alumi-

num, making them bio-available. The acidity in combina-

tion with the metals causes toxicity to the biota, resulting

in large changes in ecological communities and processes.

Fish, for example, are highly intolerant of acidic waters.

Oil spills from tankers and pipelines can cause great ecolog-

ical damage. When oil spilled at sea washes up onto coast-

lines, it destroys seaweeds, invertebrates, and fish, and their

communities are changed for many years. Seabirds are very

intolerant of oil and can die of hypothermia if even a small

area of their feathers is coated by petroleum.

Most of the

lead shot

fired by hunters and skeet shooters

miss their target and are dispersed into the environment.

Waterfowl and other avian wildlife actively ingest lead shot

because it is similar in size and hardness to the grit that

they ingest to aid in the mechanical abrasion of hard seeds

1107

in their gizzard. However, the lead shot is toxic to these

birds, and each year millions of birds are killed by this

source in North America.

Humans can also cause pollution by excessively fertiliz-

ing natural ecosystems with nutrients. For example, freshwa-

ters can be made eutrophic by fertilization with

phosphorus

in the form of phosphate. The most conspicuous symptoms

of eutrophication are changes in species composition of the

phytoplankton

community and, especially, a large increase

in algal

biomass

, known as a bloom. In shallow waterbodies

there may also be a vigorous growth of vascular plants. These

primary responses are usually accompanied by secondary

changes at higher trophic levels, including arthropods, fish,

and waterfowl, in response to greater food availability and

other

habitat

changes. However, in the extreme cases of

very eutrophic waters, the blooms of algae and other

micro-

organisms

can be noxious, producing toxic chemicals and

causing periods of oxygen depletion that kill fish and other

biota. Extremely eutrophic waterbodies are polluted because

they often cannot support a fishery, cannot be used for

drinking water, and have few recreational opportunities and

poor esthetics.

Pollution, therefore, is associated with ecological deg-

radation, caused by environmental stresses originating with

natural phenomena or with human activities. The prevention

and management of anthropogenic pollution is one of the

greatest challenges facing modern society. See also Cultural

eutrophication

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Ehrlich, P. R., A. H. Ehrlich, and J. P. Holdren. Ecoscience. Population,

Resources, Environment. San Francisco: W. H. Freeman & Co., 1977.

Freedman, Bill. Environmental Ecology. 2nd edition, San Diego: Academic

Press, 1995.

Speth, J. G. Environmental Pollution: A Long-Term Perspective. Washington,

DC: World Resources Institute, 1988.

Pollution control

Pollution

control is the process of reducing or eliminating

the release of pollutants into the

environment

. It is regu-

lated by various environmental agencies which establish pol-

lutant

discharge

limits for air, water, and land.

Air pollution control

strategies can be divided into

two categories, the control of

particulate

emissions and

the control of gaseous emissions. There are many kinds of

equipment which can be used to reduce particulate emissions.

Physical separation of the particulates from the air using

settling chambers,

cyclone

collectors, impingers, wet

Environmental Encyclopedia 3

Pollution control

scrubbers

, electrostatic precipitators, and

filtration

devices,

are all processes that are typically employed.

Settling chambers use gravity separation to reduce par-

ticulate emissions. The air stream is directed through a set-

tling chamber, which is relatively long and has a large cross

section, causing the velocity of the air stream to be greatly

decreased and allowing sufficient time for the settling of

solid particles.

cyclone collector

is a cylindrical device with a coni-

cal bottom which is used to create a tornado-like air stream.

A centrifugal force is thus imparted to the particles, causing

them to cling to the wall and roll downward, while the

cleaner air stream exits through the top of the device.

An impinger is a device which uses the inertia of the

air stream to impinge mists and dry particles on a solid

surface. Mists are collected on the impinger plate as liquid

forms and then drips off, while dry particles tend to build

up or reenter the air stream. It is for this reason that liquid

sprays are used to wash the impinger surface as well, to

improve the collection efficiency.

Wet scrubbers control particulate emissions by wetting

the particles in order to enhance their removal from the air

stream. Wet scrubbers typically operate against the current

by a water spray contacting with the gas flow. The particulate

matter becomes entrained in the water droplets, and it is

then separated from the gas stream. Wet scrubbers such as

packed bed, venturi, or plate scrubbers utilize initial im-

paction, and cyclone scrubbers use a centrifugal force.

Electrostatic precipitators are devices which use an

electrostatic field to induce a charge on dust particles and

collect them on grounded electrodes. Electrostatic precipita-

tors are usually operated dry, but wet systems are also used,

mainly by providing a water mist to aid in the process of

cleaning the particles off the collection plate.

One of the oldest and most efficient methods of partic-

ulate control, however, is filtration. The most commonly-

used filtration device is known as a

baghouse

and consists

of fabric bags through which the air stream is directed.

Particles become trapped in the fiber mesh on the fabric

bags, as well as the filter cake which is subsequently formed.

Gaseous emissions are controlled by similar devices

and typically can be used in conjunction with particulate

control options. Such devices include scrubbers,

adsorption

systems, condensers, flares, and incinerators.

Scrubbers utilize the phenomena of adsorption to re-

move gaseous pollutants from the air stream. There is a wide

variety of scrubbers available for use, including spray towers,

packed towers, and venturi scrubbers. A wide variety of

solutions can be used in this process as absorbing agents.

Lime, magnesium oxide, and sodium hydroxide are typi-

cally used.

1108

Adsorption can also be used to control gaseous emis-

sions. Activated

carbon

is commonly used as an adsorbent in

configurations such as fixed bed and fluidized bed adsorbers.

Condensers operate in a manner so as to condense

vapors by either increasing the pressure or decreasing the

temperature of the gas stream. Surface condensers are usually

of the shell-and-tube type, and contact condensers provide

physical contact between the vapors, coolant, and condensate

inside the unit.

Flaring and

incineration

take advantage of the com-

bustibility of a gaseous pollutant. In general, excess air is

added to these processes to drive the

combustion

reaction

to completion, forming

carbon dioxide

and water.

Another means of controlling both particulate and

gaseous air pollutant

emission

can be accomplished by mod-

ifying the process which generates these pollutants. For ex-

ample, modifications to process equipment or raw materials

can provide effective source reduction. Also, employing fuel

cleaning methods such as desulfurization and increasing fuel-

burning efficiency can lessen air emissions.

Water pollution

control methods can be subdivided

into physical, chemical, and biological treatment systems.

Most treatment systems use combinations of any of these

three technologies. Additionally,

water conservation

is a

beneficial means to reduce the volume of

wastewater

gen-

erated.

Physical treatment systems are processes which rely

on physical forces to aid in the removal of pollutants. Physical

processes which find frequent use in water pollution control

include screening, filtration,

sedimentation

, and

flotation

Screening and filtration are similar methods which are used

to separate coarse solids from water. Suspended particles are

also removed from water with the use of sedimentation

processes. Just as in

air pollution

control, sedimentation

devices utilize gravity to remove the heavier particles from

the water stream. The wide array of sedimentation basins

in use slow down the water velocity in the unit to allow time

for the particles to drop to the bottom. Likewise, flotation

uses differences in particle densities, which in this case are

lower than water, to effect removal. Fine gas bubbles are

often introduced to assist this process; they attach to the

particulate matter, causing them to rise to the top of the

unit where they are mechanically removed.

Chemical treatment systems in water pollution control

are those processes which utilize chemical reactions to re-

move water pollutants or to form other, less toxic, com-

pounds. Typical chemical treatment processes are chemical

precipitation, adsorption, and disinfection reactions. Chemi-

cal precipitation processes utilize the addition of

chemicals

to the water in order to bring about the precipitation of

dissolved solids

. The solid is then removed by a physical

process such as sedimentation or filtration. Chemical precip-

Environmental Encyclopedia 3

Pollution credits

itation processes are often used for the removal of

heavy

metals

and

phosphorus

from water streams. Adsorption

processes are used to separate soluble substances from the

water stream. Like air pollution adsorption processes, acti-

vated carbon is the most widely used adsorbent. Water may

be passed through beds of granulated activated carbon

(GAC), or powdered activated carbon (PAC) may be added

in order to facilitate the removal of dissolved pollutants.

Disinfection processes selectively destroy disease-causing

organisms such as bacteria and viruses. Typical disinfection

agents include

chlorine

ozone

, and

ultraviolet radiation

Biological water pollution control methods are those

which utilize biological activity to remove pollutants from

water streams. These methods are used for the control of

biodegradable

organic chemicals, as well as nutrients such

nitrogen

and phosphorus. In these systems,

microorgan-

isms

consisting mainly of bacteria convert carbonaceous

matter as well as cell tissue into gas. There are two main

groups of microorganisms which are used in biological treat-

ment,

aerobic

and

anaerobic

microorganisms. Each re-

quires unique environmental conditions to do its job. Aerobic

processes occur in the absence of oxygen. Both processes

may be utilized whether the microorganisms exist in a sus-

pension or are attached to a surface. These processes are

termed suspended growth and fixed film processes, respec-

tively.

Solid pollution control methods which are typically

used include landfilling,

composting

, and incineration. San-

itary landfills are operated by spreading the

solid waste

compact layers which are separated by a thin layer of

soil

Aerobic and anaerobic microorganisms help to break down

the biodegradable substances in the

landfill

and produce

carbon dioxide and

methane

gas which is typically venter

to the surface. Landfills also generate a strong wastewater

called leachate which must be collected and treated to avoid

groundwater

contamination.

Composting of solid wastes is the microbiological bio-

degradation of organic matter under either aerobic or anaero-

bic conditions. This process is most applicable for readily

biodegradable solids such as sewage

sludge

, paper,

food

waste

, and household

garbage

, including garden waste

and organic matter. This process can be carried out in static

pile, agitated beds, or a variety of reactors.

In an incineration process, solids are burned in large

furnaces thereby reducing the volume of solid wastes which

enter landfills, as well as reducing the possibility of ground-

water contamination. Incineration residue can also be used

for metal

reclamation

. These systems are typically supple-

mented with air pollution control devices. See also Air pollu-

tion index; Air quality criteria; Clean Air Act; Clean Water

Act; Emission standards; Heavy metals and heavy metal

poisoning; Industrial waste treatment; Primary standards;

1109

Secondary standards; Sewage treatment; Water quality stan-

dards

[James W. Patterson]

ESOURCES

OOKS

Advanced Emission Control for Power Plants. Paris: Organization for Eco-

nomic Cooperation and Development, 1993.

Handbook of Air Pollution Technology. New York: Wiley, 1984.

Jorgensen, E. P., ed. The Poisoned Well: New Strategies for Groundwater

Protection. Washington, DC: Island Press, 1989.

Kenworthy, L., and E. Schaeffer. A Citizen’s Guide to Promoting Toxic

Waste Reduction. New York: INFORM, 1990.

Wentz, C. A. Hazardous Waste Management. New York: McGraw-Hill,

1989.

Pollution credits

Pollution

credits emerged from the federal

Clean Air Act

of 1990 (CAA) as a way for businesses to deal with the

regulations that attempt to lower

air pollution

. The

Envi-

ronmental Protection Agency

(EPA) and individual states

have created a “cap and trade” system (in practice since 1995)

allowing utilities and manufacturers allowances to emit a

certain amount of specific pollutants. This system offers

companies some flexibility in their compliance while helping

to maintain the standards required for cleaner air.

A company can earn pollution credits by voluntarily

reducing polluting emissions below limits dictated by the

EPA. Earned credits can then be sold to another company

that has trouble keeping its emissions within permissible

limits, or saved for future use. According to Dean S. Sommer

writing for The Albany (New York) Business Review in March

1999, “The ‘cap’ portion of the system refers to the specific

amount of emissions that may be discharged within a state,

region or the nation as set forth by the EPA and the CAA.

The ’trade’ portion refers to a participant’s ability to buy or

sell the allowances. States, or the EPA, allocate

emission

allowances to affected sources in specified amounts to ensure

that the cap is not exceeded by emissions from all partici-

pants.”

Different “cap and trade” allowances apply to the most

common pollutants,

sulfur dioxide

and

nitrogen oxides

which contribute to

acid rain

smog

, and

ozone

depletion.

Each allowance, or credit, is a trading unit equivalent to one

ton of air emissions. The EPA exacts annual penalties to

those companies whose emissions exceed the number of

allowances.

According to the EPA, the practice of pollution credits

bartering has proven beneficial not only in reducing air pollu-

tion, but in providing an incentive for companies to meet

Environmental Encyclopedia 3

Pollution Prevention Act (1990)

environmental goals. For example, the EPA’s national

acid

rain program to reduce sulfur dioxide resulted in a decrease

of six million tons of emissions a year compared to 1980

levels.

Nitrogen

oxide levels were reduced by 50% compared

to 1990 levels as a result of a program undertaken by numer-

ous northeastern states.

Critics of the trading program, however, have sug-

gested that the system is flawed. They contend that although

it was meant to be a way of encouraging industry to find

ways of producing less pollution, the system provides a way

of merely transferring responsibility—the one polluting is

not held responsible for the poor quality of air it has affected.

In 2000, for example, the state of New York identified

several midwestern and southeastern states—Delaware, Illi-

nois, Indiana, Ohio, Michigan, Kentucky, Maryland, New

Jersey, North Carolina, Pennsylvania, Tennessee, Virginia,

West Virginia, and Wisconsin—as the major sources of its

acid rain, a serious problem undermining

natural resources

and

wildlife

. Between 1995 and 2000, the state had accumu-

lated more than 700,000 pollution credits—providing the

New York businesses selling them with a total of approxi-

mately $37.5 million. The result was that pollution within

New York had declined only to be blown back over state lines

by other states that had purchased the credits. According to

a May 2, 2000 report of the Environment News Service

(ENN) by writer Cat Lazaroff, “Despite the state’s efforts

to reduce sulfur dioxide emissions, many high altitude lakes

in New York’s

Adirondack Mountains

remain too acidic

to support many native

species

. Some government studies

estimate about half of the region’s 3,000 lakes and ponds

may become too acidic to support life if acid rain is not

reduced.” The state fought back with legislation authorizing

the fining of utility companies that sell their pollution credits

to the polluting states.

Attempts to regulate less and provide more incentives

have been met with suspicion by program critics, who fear

an increase in pollution, and applause by businesses, who

view the reduction in standards as a possible financial relief.

In any case, pollution credits had become a valuable com-

modity on the open market by the early twenty-first century,

in the United States and throughout the world.

[Jane E. Spear]

ESOURCES

ERIODICALS

“Big Cities a Headache U.N. Summit wants to Address.” Environmental

News Network June 6, 2002 [cited July 7, 2002]. <http://www.enn.com/

news/wire-stories/2002/06/06062002/reu_47462.asp>.

Borenstein, Seth. “Bush Vows to Cut Pollution with more Incentives,

Fewer Regulations.” Knight Rider Newspapers, February 14, 2002.

“Environmentalists, EPA Disagree Whether Current Law or Bush Plan

would Help Air More.” Environmental News Network, February 21, 2002

1110

[cited July 7, 2002]. <http://www.enn.com/news/wire-stories/2002/02/

02212002/ap_46452.asp>.

“Industry Still Failing on Environment, says U.N. Report.” Environmental

News Network, May 16, 2002 [cited July 7, 2002]. <http://www.enn.com/

news/wire-stories/2002/05/05162002/reu_47235.asp>.

Kahn, Joseph. “Whitman Begins to Consider Streamlining Pollution

Checks.” New York Times, July 28, 2001.

Kranish, Michael. “The Politics of Pollution.” Boston Globe Magazine,

February 18, 1998.

Lazaroff, Cat. “New York Fights Acid Rain Through Curb on Pollution

Credits.” Environment News Service, May 2, 2000.

Max, Arthur. “Pollution Trading a Contentious Issue at Climate Talks.”

Associated Press, November 15, 2000.

“Oil Spills in the Sky.” December 9, 1997 [cited July 7, 2002]. <http://

www.enn.com/features/1997/12/120997/1209fea_20122.asp>.

“Pollution Credits: The Science Isn’t In Yet.” Environmental News Network,

February 2, 1999 [cited July 7, 2002]. <http://www.enn.com/news/enn-

stories/1999/02/020299/co2findings_1423.asp>.

Sommer, Dean S. “’Retiring’ Pollution Credits helps both Business and

Environment.” The Business Review, March 22, 1999.

“States Ready to Trade Air Pollution Credits.” Environmental News Net-

work, January 3, 2001 [cited July 7, 2002]. <http://www.enn.com/news/

enn-stories/2001/01/01032001/pollution_41007.asp>.

“Trading for Clean Air just got Easier.” December 5, 2001 [cited July 7,

2002]. <http://www.enn.com/news/enn-stories/2001/12/12052001/

s_45776.asp>.

“Trading Credits Does not cut Pollution.” Houma Today, November 28,

2001.

“U.S. EPA Proposes Pollution Credits to Clean Up Rivers.” Environmental

News Network. May 16, 2002 [cited July 7, 2002]. <http://www.enn.com/

news/wire-stories/2002/05/05162002/reu_47230.asp>.

THER

Environmental Protection Agency. “The Plain English Guide to the Clean

Air Act.” May 13, 2002 [cited July 7, 2002]. <http://www.epa.gov/oar/

oaqps/peg_caa/pegcaain.html>.

RGANIZATIONS

U.S. Environmental Protection Agency, 1200 Pennsylvania Avenue, NW,

Washington, DC USA 20460 (202) 260-2090, <http://www.epa.gov>

Pollution Prevention Act (1990)

The

Pollution

Prevention Act of 1990 is a piece of legislation

intended to limit the creation of pollution. As part of the

Omnibus Budget Reconciliation Act of 1990, the Pollution

Prevention Act differed from previous legislation, which

had generally treated pollution after it had been created.

Environmental Protection Agency

(EPA) administrator

William K. Reilly strongly supported the act, believing that

much hazardous or toxic pollution can be more effectively

and economically controlled, and the

environment

pro-

tected more fully, if the pollution never occurs.

The impetus for this act lies in a 1986 EPA report

to Congress entitled “Minimization of Hazardous Wastes.”

Based on this report, the agency began to take actions de-

signed to reduce pollution. According to a subsequent report

by the Office of Technology Assessment (OTA), however,

Environmental Encyclopedia 3

Nicholas Polunin

the EPA needed to do more. The two reports identified four

main approaches to prevent pollution: (1) manufacturing

changes, (2) equipment changes, (3) product reformulations

and substitutions, and (4) improved industrial housekeeping.

By using such approaches, companies (and individuals) can

both save money by reducing

pollution control

costs and

have a cleaner environment because certain pollution will be

prevented. The corporation 3M, for instance, has saved over

$300 million since 1975 by reducing air, water, and

sludge

pollutants at the source. The OTA estimated that a ten

percent reduction in hazardous wastes per year for five years

could be achieved through source reduction. The reports

also found that pollution prevention is primarily hindered

not by a lack of technology but rather by a lack of knowledge

and awareness due to institutional hurdles. The Pollution

Prevention Act was designed to help overcome these hurdles

through information collection, assistance in technology

transfer, and financial assistance to state pollution prevention

programs.

In addition to developing a general strategy to promote

the reduction of pollution at its source, the act crated a new

EPA office to administer the program. The major provisions

of the law are as follows: a state grant program to aid states

in establishing similar pollution prevention programs; EPA

technical assistance for business; the development of a Source

Reduction Clearinghouse, administered by the EPA and

available for public use, to help in the collection and distribu-

tion of source reduction information; the establishment of

an advisory committee on the issue; the creation of a training

program on pollution prevention; and the creation of annual

awards to businesses that achieve outstanding source reduc-

tion. Businesses using toxic substances were required to meet

special standards--to report on how many and the amount

of toxic substances released into the environment, how much

recycled, how they attempted to prevent the generation of

toxic pollutants, and how they learned of source reduction

techniques. Lastly, the EPA is to report biennially on the

effectiveness of the new program and its components. The

Act authorized $16 million each year for three years for the

EPA to implement this program.

[Christopher McGrory Klyza]

ESOURCES

OOKS

Environmental Quality: 21st Annual Report. Council on Environmental

Quality. Washington, DC: Government Printing Office, 1990.

ERIODICALS

“Budget Reconciliation Act Provisions.” Congressional Quarterly Almanac

46 (1990): 141–163.

1111

THER

“Pollution Prevention Act of 1990.” Senate Committee on Environment

and Public Works, Senate Report 101-526, 1990, 101st Congress, 2d

Session.

“Waste Reduction Act.” House Committee on Energy and Commerce,

House Report 101-555, 1990, 101st Congress, 2d Session.

Nicholas Polunin (1909 – 1997)

English environmentalist

Nicolas Polunin will be long remembered for two unusual

achievements. First, he founded and was first editor of not

one but two influential journals, Biological Conservation

(founded in 1967 and edited from that year to 1974) and

then Environmental Conservation (founded in 1974 and ed-

ited from its inception through 1995 when he was in his

mid-eighties). Second, the readers of either journal, but

particularly the latter, will remember the vivid language Po-

lunin used in numerous editorials and other articles and texts

to urge readers to start paying attention to the impact of

human activities on other species on earth and on the natural

environment.

Polunin credited his very public concern about such

issues to a small UNESCO Conference in Finland in 1966,

where he “had a sudden realization, amounting to a kind of

vision, that if the world’s populations went on growing and

acting as profligately as they had been doing in recent de-

cades, more and more ecodisasters would be inevitable and

ultimately there would be an end to much of what was best

in our civilization and conceivably to all life on Earth.” He

went on to say that “thereupon we decided that it was our

solemn duty to do all we could henceforth to warn humanity

of these grave dangers.” That “quite shocking realization”

led to his founding and editing of the international journal

on conservation, and after he considered it “sufficiently es-

tablished,” a “more predominately environmental journal.”

Biological Conservation has become a mainstay for scientists

investigating the vast range and significance of biological

diversity on the planet and on the possibilities for sustainable

use by humans of the biosphere. Environmental Conservation

tries to reach a wider readership, one well outside the com-

munity of research biologists and is much more activist in

tone and content. Establishment of two such influential

journals is a significant accomplishment and they remain

Polunin’s enduring legacy, one matched by few other ecolo-

gists.

On the cover of the first issue of Biological Conserva-

tion, Polunin listed 30 subject headings as “the content of

our subject.” These included the history and development of

conservation, a focus on “man and environment,” disturbance

and maintenance of ecosystems and the biosphere, popula-

tion dynamics, threatened species and nature reserves and

Environmental Encyclopedia 3

Polybrominated biphenyls

parks, legislation and enforcement, education and training,

fresh waters and wetlands, and a list of chemical, physical

and biological threats to wildlife and environment. Those

30 topics were listed only on the first six issues, but the

editorial description of topics for papers (as noted on an

inside cover sheet in most science journals) are almost identi-

cal in the latest issues (2002) with those Polunin stated in

the first issue. Typically, however, Polunin’s topical editorial

in that first issue was titled “Some Warnings,” suggesting

that “our world is beset with many threats,” including his

concern about the rapid increase in human population, a

concern he voiced many times in editorials in both journals.

In a still relevant and prescient voice, he called for a “severe

limitation of human breeding and cognate desecrating tend-

encies.” When he stepped down as editor, the publishers

noted his energy and enthusiasm as reflected in “the great

wealth of material published under his guidance.”

While the stated purpose in the first journal was, and

remains, the widest possible dissemination of original papers

on “the preservation of wildlife and all nature,” Polunin’s

editorial directions to authors in the first issue of Environ-

mental Conservation differed quite radically, stating that the

journal “advocates timely action for the protection and ame-

lioration of the environment of Man and Nature throughout

the world...for the lasting future of Earth’s fragile biosphere.”

Polunin’s editorial language remained strong, continuing to

warn about the plagues human actions were visiting on each

other, on other organisms, and on the earth. Words and

phrases like ’faustian bargain,’ ’ecodisasters,’ ’our world men-

aced’ and ’rays of hope’ were common in his editorial pleas

for sanity.

He published longer statements, such as his “Thoughts

on Some Conceivable Ecodisasters” in the Autumn, 1974,

issue of Environmental Conservation, he organized major

international conferences on the environmental future and

edited the proceedings, all evidence of his world-wide influ-

ence on thinking about human-environment issues and

problems. He also never lost hope, claiming in 1991 (Au-

tumn issue of Environmental Conservation) that there had

been “recent changes for the better in the prospect of an

improved future for the global environment” and listing

twelve rays of hope, including “a growing realization that

there are coming to be far too many human beings on our

limited Planet Earth.”

Nicholas Polunin was born in England to a Russian

father and an English mother. He earned a First Class

Honours degree in botany and ecology from Oxford in 1932,

a Masters from Yale, and returned to Oxford for a PhD in

1935. One of his mentors was Arthur Tansley. He traveled

widely with a number of scientific expeditions while still an

undergraduate and published his first book (Russian Waters,

1931) before he completed his degree. He was a member

1112

of the party that discovered Prince Charles Island, the “last

major island to be marked on the world’s map.” He held

academic positions at McGill University, and at universities

in Iraq and Nigeria, among others.

Perhaps unknown to general readers more familiar

with his visible roles as editor, writer, and environmental

activist, Polunin was a productive research biologist, special-

izing in arctic vegetation and plant ecology and, later, on

marine ecosystems. His 1960 text on plant geography is one

of the best known in that field and still in print over forty

years later.

Myers remembered Polunin as a “scientist in the

round,” an appropriate epitaph for one whose legacy includes

two influential international journals, ever renewed encour-

agement to scientists to focus more clearly on global issues

of conservation and environmental science, a better informed

and more aware public around the world, and more realistic

hopes for a better quality of life for all humanity and for

continued maintenance of the diversity of Earth’s natural

biota.

[Gerald L. Young Ph.D.]

URTHER

EADING

ERIODICALS

Bataille, A. “Nicholas Polunin C.B.E., M.S., M.A., D.Phil., D.Sc., F.L.S.,

F.R.G.S. (1909–1997). Watsonia 22, no. 2 (August 1998): 203&ndahs;205.

Myers, Norman. “Nicholas Polunin: A Scientist in the Round.” Environ-

mental Conservation 25, no. 1 (March 1998): 8–10.

Polybrominated biphenyls

A mixture of compounds having from one to ten

bromine

atoms attached to a biphenyl ring, analogous to polychlori-

nated biphenyl (PCB)s. Manufactured as fire retardants,

PBBs were banned after a 1973 Michigan incident when

pure product was accidently mixed with cattle feed and dis-

tributed throughout the state. PBBs were identified as the

cause of weight loss, decreased milk production, and

mortal-

ity

in many dairy herds. Approximately 30,000 cattle, 1.5

million chickens, 1,500 sheep, 6,000 hogs, 18,000 pounds

(8,100 kg) of cheese, 34,000 pounds (15,300 kg) of dried

milk products, 5 million eggs, and 2,700 pounds (1,215 kg)

of butter were eventually destroyed at an estimated cost

of $1 million. Although human exposures have been well-

documented, long term epidemiological studies have not

shown widespread health effects.

Environmental Encyclopedia 3

Polycyclic organic compounds

Polychlorinated biphenyls

Mixture of compounds having from one to ten

chlorine

atoms attached to a biphenyl ring structure. There are 209

possible structures theoretically; the manufacturing process

results in approximately 120 different structures. PCBs resist

biological and heat degradation and were used in numerous

applications, including dielectric fluids in capacitors and

transformers, heat transfer fluids, hydraulic fluids, plasticiz-

ers, dedusting agents, adhesives, dye carriers in carbonless

copy paper, and

pesticide

extenders. The United States

manufactured PCBs from 1929 until 1977, when they were

banned due to adverse environmental effects and ubiquitous

occurrence. They bioaccumulate in organisms and can cause

skin disorders, liver dysfunction, reproductive disorders, and

tumor formation. They are one of the most abundant or-

ganochlorine contaminants found throughout the world. See

also Organochloride

Polycyclic aromatic hydrocarbons

Polycyclic aromatic

hydrocarbons

are a class of organic

compounds having two or more fused

benzene

rings. While

usually referring to compounds made of

carbon

and

hydro-

gen

, PAH also may include fused aromatic compounds

containing

nitrogen

, sulfur, or cyclopentene rings. Some

of the more common PAH include naphthalene (2 rings),

anthracene (3 rings), phenanthrene (3 rings), pyrene (4

rings), chrysene (4 rings), fluoranthene (4 rings), benzo(a)-

pyrene (5 rings), benzo(e)pyrene (5 rings), perylene (5 rings),

benzo(g,h,i)perylene (6 rings), and coronene (7 rings).

PAH are formed by a variety of human activities in-

cluding incomplete

combustion

fossil fuels

, wood, and

tobacco

; the

incineration

garbage

;

coal gasification

and liquefaction processes; smelting operations; and coke,

asphalt, and

petroleum

cracking; they are also formed natu-

rally during forest fires and volcanic eruptions. Low molecu-

lar-weight PAH (those with four or fewer rings) are generally

vapors while heavier molecules condense on submicron,

breathable particles. It is estimated that more than 800 tons

of PAH are emitted annually in the United States. PAH

are found worldwide and are present in elevated concentra-

tions in urban aerosols, and in lake sediments in industrial-

ized countries. They also are found in developing countries

due to

coal

and wood heating, open burning, coke produc-

tion, and vehicle exhaust.

The association of PAH with small particles gives

them atmospheric residence times of days to weeks, and

allows them to be transported long distances. They are re-

moved from the

atmosphere

by gravitational settling and

are washed out during precipitation to the earth’s surface,

where they accumulate in soils and surface waters. They also

1113

directly enter water in discharges,

runoff

, and

oil spills

They associate with water particulates due to their low water

solubility, and eventually accumulate in sediments. They do

not bioaccumulate in biota to any appreciable extent, as they

are largely metabolized.

Many but not all PAH have carcinogenic and muta-

genic activity; the most notorious is benzo(a)pyrene, which

has been shown to be a potent

carcinogen

. Coal tar and

soot were implicated in the elevated skin

cancer

incidence

found in the refining, shale oil, and coal tar industries in

the late nineteenth century. Subsequent research led to the

isolation and identification of several carcinogens in the early

part of this century, including benzo(a)pyrene. More recent

research into the carcinogenicity of PAH has revealed that

there is significant additional biological activity in urban

aerosols and soot beyond that explained by known carcino-

gens such as benzo(a)pyrene. While benzo(a)pyrene must be

activated metabolically, these other components have direct

biological activity as demonstrated by the

Ames test

. They

are polar compounds, thought to be mixtures of mono-

and dinitro-PAH and hydroxy-nitro derivatives. Tobacco

smoking exposes more humans to PAH than any other

source.

[Deborah L. Swackhammer]

ESOURCES

OOKS

Dias, J. R. Handbook of Polycyclic Aromatic Hydrocarbons. New York: Elsev-

ier, 1987.

Harvey, R. G. Polycyclic Aromatic Hydrocarbons: Chemistry and Carcinogenic-

ity. New York: Cambridge University Press, 1991.

Polycyclic organic compounds

In organic chemistry, a cyclic compound is one whose mole-

cules consist of three or more atoms joined in a closed ring.

A polycyclic compound is one whose molecules contain two

or more rings joined to each other. Environmentally, the

most important polycyclic organic compounds are the

poly-

cyclic aromatic hydrocarbons

, also known as polynuclear

aromatic

hydrocarbons

(PAHs). Some examples of polycy-

clic organic compounds include naphthalene, anthracene,

pyrene, and the benzopyrenes. A number of polycyclic hy-

drocarbons pose hazards to human health. For example,

benzo(a)pyrene from

automobile

exhaust and

tobacco

smoke

is known to be a

carcinogen

. See also Cigarette

smoke

Polynuclear aromatic hydrocarbons

see

Polycyclic aromatic hydrocarbons

Environmental Encyclopedia 3

Polystyrene

Polystyrene is a lightweight transparent plastic derived from

petroleum

by-products and

natural gas

. It is widely used

in the packaging industry, but most polystyrene is used to

make durable goods such as television cabinets, appliances,

and furniture. Polystyrene also has excellent insulating prop-

erties. As packaging, polystyrene is used both in foam and

solid forms. Solid polystyrene is used in yogurt, sour cream,

and cottage cheese containers, cutlery, clear clamshells used

at salad bars, and video and audio cassette containers. As

foam, polystyrene is used in cups, bowls, plates, trays, clam-

shell containers, meat trays, egg cartons, and packaging for

electronics and other delicate items. Polystyrene foam is

manufactured by processing solid polystyrene resin pellets

with a gaseous expansion agent. In the past, about 30% of

polystyrene foam products were made with

chlorofluoro-

carbons

(CFCs), which were identified as contributors to

the deterioration of the

ozone

layer in the Earth’s upper

atmosphere

. By 1990, manufacturers had phased out the

use of CFCs as a polystyrene expansion agent. Some manu-

facturers switched to the use of hydrochlorofluorocarbon-

22 (HCFC-22), which reduced

ozone layer depletion

po-

tential by about 95% over CFCs. By 1994, as required by

federal law, polystyrene foam manufacturers phased out the

use of HCFC-22 and by 1997 were using alternative expan-

sion agents, most commonly pentane gas. Pentane does not

affect the ozone layer, but because it can contribute to

smog

formation some manufacturers recycle pentane emissions.

Carbon dioxide

(CO

) is also used by manufacturers as a

polystyrene expansion agent. CO

is nontoxic, nonflamma-

ble, does not contribute to smog, and has no atmospheric

ozone depletion potential, but it has been implicated in

global warming.

Polystyrene packaging accounts for about 1.2 % (by

weight) of the total solid

waste stream

in the United States,

and polystyrene makes up from about 2-10% of materials

thrown away as litter. However, polystyrene can be recycled

and used to make new polystyrene products such as wall

insulation, packing filler, and cafeteria trays. Polystyrene has

an energy content of 17,000 Btu/pound, about four times

that of average

municipal solid waste

, and can be burned

with other solid wastes in an incinerator that has appropriate

emission

controls to contain potentially toxic

combustion

products. Another potential environmental concern is the

release of toxic metals such as

cadmium

and

lead

from

combustion of inks used to tint the polystyrene. The polysty-

rene manufacturing industry is developing source reduction

techniques, including improving resin properties to make

stronger products with less material and making lighter-

weight foam products.

1114

Polystyrene is manufactured from

styrene

, which is

a hazardous chemical. When styrene is heated to 392°F

(198°C), it is converted into the polymer polystyrene. Health

concerns have been raised about styrene residues remaining

in polystyrene products, especially those that are used to

contain food for consumption. Styrene is soluble in oil and in

ethanol

, substances commonly found in foods and alcoholic

beverages. A U.S. EPA National Human Adipose Tissue

Survey in 1986 identified styrene in 100% of the 46 human

fat samples collected.

[Judith Sims]

ESOURCES

THER

Expansion Agents for Polystyrene Foam. Washington, DC: Polystyrene Pack-

aging Council, 1997.

Polystyrene in the Solid Waste Stream. Washington, DC: Polystyrene Packag-

ing Council, 1997.

Uses and Benefits of Polystyrene. Washington, DC: Polystyrene Packaging

Council, 1997.

Polyvinyl chloride

Polyvinyl chloride, also known as PVC, is a plastic produced

by the polymerization of

vinyl chloride

. It is used with

plasticizers to make packaging films, boots, garden hose,

etc. Without plasticizers, PVC is used to make pipe, siding,

shingles, window frames, toys, and other items. An attractive

aspect of PVC for industry is its ability to withstand

weath-

ering

and its

resistance

chemicals

and solvents. How-

ever, this attractive aspect is the major environmental con-

cern for PVC and many other

plastics

. The great bulk of

such plastic (about 98%) is neither reused nor recycled but

occupies ever dwindling

landfill

space.

Pongo pygmaeus

see

Orangutan

POPs

see

Persistent Organic Pollutants

Population biology

Population biology is the study of the factors determining

the size and distribution of a population, as well as the ways

in which populations change over time. The discipline of

population biology dates back to the 1960s, when researchers

merged aspects of population

ecology

with aspects of popu-

lation genetics. It employs a traditional empirical approach

Environmental Encyclopedia 3

Population Council

which consists of observation of the numbers of individuals

in a population and the variation in those numbers over time

and space, and the measurement of physical (abiotic) factors

and the living (biotic) factors that may affect population

numbers.

Given optimum conditions, the populations of most

organisms grow at a constant rate of increase, doubling in

size at regular intervals, which is known as

exponential

growth

. Exponential

population growth

is explosive but

it is usually opposed by factors that reduce numbers, such

as disease, predation, or harsh climates. The result is

logistic

growth

, where the rapidly growing population slows and

reaches a stable but dynamic equilibrium at or near the

carrying capacity

of the

environment

. The populations

of some

species

such as migratory locusts show boom and

bust cycles: in these cases explosive growth produces vast

numbers of individuals that eventually overwhelm the car-

rying capacity and a catastrophic

dieback

follows.

The rate of growth of a population is the net result

of the gains and losses from a number of intrinsic factors

operating within the population. These include natality,

fe-

cundity

, life span, longevity,

mortality

, and immigration

and emigration. Patterns of

survivorship

and age structure

created by these interacting factors show how a population

is growing and indicate what general role a species plays

in the

ecosystem

. Density-dependent biotic factors that

decrease natality or increase mortality include the numbers

of competitors both interspecific and intraspecific, as well

as predators, prey,

parasites

, and other interactive species.

Stress and overcrowding are other density-dependent biotic

factors that limit population size through excessive intraspe-

cific

competition

for limited resources.

The local distribution pattern of populations of most

species is limited by physical factors such as temperature,

moisture, light,

soil

quality, and

salinity

. Within their

areas of distribution, animals occur in varying densities (ei-

ther scattered thinly or crowded) and in varying dispersal

patterns (either spaced evenly or clumped into herds). Popu-

lation density and dispersion are often studied together,

and are important in ecology and management. Density is

measured by direct visual count, and by

trapping

, collecting

fecal pellets, using pelt records, monitoring vocalization fre-

quencies, and so on. Life tables constructed from these data

show precisely how a population is age-structured.

Population genetics recognizes two important attri-

butes of a population--its gene frequencies and its total

gene

pool

. Population size exerts some influence on the genetic

composition of its members, since the number of sexually

interbreeding individuals influences the transfer of genes

within a population. It also affects the kinds of genotypes

that are available, and the survival and reproductive capacity

of individuals with certain genes. The application of the

1115

principles of population genetics is vital to the success of

programs to improve the breeds of animals and plants for

agricultural use, and for the captive breeding of

endangered

species

. See also Captive propogation and reintroduction;

Gene bank; Genetic engineering; Predator-prey interactions;

Sustainable development; Wildlife management

[Neil Cumberlidge Ph.D.]

ESOURCES

OOKS

Begon, M., J. L. Harper, and C. R. Townsend. Ecology: Individuals, Popula-

tions, and Communities. 2nd Edition. Boston: Blackwell Scientific Publica-

tions, 1990.

Emmel, T. C. Population Biology. New York: Harper and Row, 1976.

Hendrick, P. W. Population Biology: The Evolution and Ecology of Popula-

tions. Boston: Jones and Bartlett, 1984.

Ricklefs, R. E. The Economy of Nature. 3rd ed. New York: W. H. Free-

man, 1993.

Smith, R. L. Elements of Ecology. New York: HarperCollins, 1991.

Stiling, P. D. Introductory Ecology. Englewood Cliffs, NJ: Prentice Hall,

1992.

Population control

see

Family planning; Male contraceptives

Population Council

The Population Council was established in 1952 to find

solutions to the world’s population problems. Although

based in New York, the Council is an international non-

profit organization with regional offices in Bangkok, Cairo,

Dakar, Mexico City, and Nairobi. In conducting research

in health, social, and biomedical sciences, the Council has,

among other accomplishments, broken ground in contracep-

tive devices, explored male fertility, and analyzed the social

position of women and its concurrent effect on the popu-

lation.

The Council seeks to use science and technology to

provide relief to the population problems of developing

countries. Governed by a board of 20 trustees from 16 coun-

tries who meet twice a year, the Council has programs in

50 countries throughout Latin America, the Caribbean,

Asia, and Africa. It receives funding from world govern-

ments, United Nations agencies, foundations, and individu-

als for its research and programs. The major programs and

institutions of the Population Council are the Center for

Biomedical Research, the Research Division, and the Pro-

grams Division.

The Center for Biomedical Research investigates new

ways to regulate human fertility, primarily through develop-

ment of new methods of contraception. For example the

Environmental Encyclopedia 3

Population growth

Center invented the Norplant levonorgestrel implant and a

copper-bearing T-shaped intrauterine device (IUD). Both

methods are for long-term protection and are reversible.

Other methods include a hormone-releasing IUD, Norplant

II (with two implants instead of six), and contraceptive vagi-

nal rings. Another idea in progress includes a vaginal contra-

ceptive that provides protection from the human immunode-

ficiency

virus

(HIV). These methods are designed for

women, but the Center for Biomedical Research also con-

centrates on controlling male fertility through research into

male physiology. With particular interest in creating a con-

traceptive to block sperm production without dampening

the male sex drive, the Center is working on a “nonsurgical”

or “no-scalpel” vasectomy and male subdermal implants, akin

to women’s Norplant.

The Population Council does not restrict its research

to the biomedical domain, however. Through its Research

Division, it looks for solutions to population problems

through social research. A small interdisciplinary group of

demographers, economists, sociologists, and anthropologists

make up the Research Division. Among notable studies is

an ongoing project examining the consequences of high

fertility in a family. For instance, early research indicates

that in Maharashtra, India, the advantages associated with

growing up in a small family exist for boys but not for girls.

Apparently in many smaller families in India, girls have

a proportionately heavier burden of labor. The Research

Division also conducts many studies in China, where the

state is heavily involved in regulating its population. Through

research into

family planning

and fertility, child survival,

and women’s roles and status—a subject that has taken prece-

dence in the Council’s research since 1976—the Research

Division provides theories that the Population Council puts

to use in controlling worldwide population problems.

The Council applies the research conducted by the

Center for Biomedical Research and the Research Division

through its Programs Division. The Programs Division col-

laborates with governments, organizations, and scientific in-

stitutions of developing countries to formulate population

policy. Many of the programs set forth by this division

parallel studies being conducted by the Research Division.

For example, the Programs Division conducts family plan-

ning and fertility counseling; works to insure reproductive

health and child survival; and seeks to improve women’s

roles and status in developing countries. The contraceptive

introduction program is also an important part of the Pro-

grams Division.

In addition to its programs and research, the Council

publishes two scholarly journals: Population and Development

Review and Studies in Family Planning. Both contain studies

of current ideas and theories in population control. The

Population Council also sponsors outstanding scholars and

1116

scientists to further research into the technology needed to

control the world’s populations.

[Andrea Gacki]

ESOURCES

RGANIZATIONS

Population Council, 1 Dag Hammarskjold Plaza, New York, NY USA

10017 (212) 339-0515, Fax: (212) 755-6052, Email: pubinfo@

popcouncil.org, http://www.popcouncil.org

Population growth

A population is the number of individuals of a given

species

usually within a specified

habitat

or area. Within the science

ecology

, the study of population dynamics, or the ways

in which the number of individuals in a community expands

and contracts, makes up an important subfield known as

population biology

. While ecologists and

wildlife

biolo-

gists rely on understanding the nature of population change

and the factors that influence population size, one of the

main ways population studies have been used is in projecting

the growth of the human population. Since the 1960s human

population growth has been an issue of fierce theoretical

debate. Many scientists and social planners predict that the

human population, like animal populations frequently ob-

served in nature, is growing at a perilous rate that will ulti-

mately lead to a catastrophic

die-off

in which billions of

people will perish. Other scholars and planners argue that

current trends may not lead to disaster and that we may yet

find a reasonable and stable population level. Both sides of

the debate use ecological principles of population biology in

predicting human population dynamics and their effect upon

the conditions in which we may live in the future.

The extent of population growth is based on fertility,

or the number of offspring that individuals of reproductive

age successfully produce. In some animal and plant species

(flies, dandelions) every individual produces a great number

of offspring. These populations grow quickly, as long as

nutrients and space are available. Other species (

elephants

pandas) produce few offspring per reproductive adult; popu-

lations of these species usually grow slowly even when ample

food and habitat are available. The maximum number of

offspring an organism can produce under ideal conditions

is known as the biotic potential of that organism. For in-

stance, if an individual housefly can produce 120 young in

her lifetime, and each of those successfully produces 120

young, and so on, the fly’s biotic potential in one year (seven

generations) is nearly six trillion flies. Clearly biotic poten-

tials are rarely met: reproductive failures and life hazards

usually prevent the majority of houseflies, like other species,

from achieving their theoretical reproductive potential.