Environmental Encyclopedia

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Environmental Encyclopedia 3

Photoperiod

in which plastics are used in everyday life. Suffice to say

that, in the early 1990s, more than 60 billion pounds (27

billion kg) of plastics were produced in the United States

alone each year.

For their many advantages, plastics also create some

serious environmental problems. About one third, 20 billion

pounds (9 billion kg), of all plastics now produced are used

for short-term purposes, such as shopping bags and wrapping

material. These plastics are used once, briefly, and then

discarded.

Current estimates are that plastic materials make up

about 7 percent by weight and 18 percent by volume of

all municipal wastes. Since most plastics do not degrade

naturally, they will continue to be a part of the nation’s (and

the world’s)

solid waste

problem for decades.

One solution to the accumulation of plastics is to do

a better job of

recycling

them. Technical, economic, and

social factors have limited the success of this approach so

far, and no more than 1 percent of all discarded plastics are

ever recycled. Another solution is to fabricate plastics in such

a way that they will degrade. Addition of starch as a filler

in plastics, for example, tends to make them more

biode-

gradable

, that is, degradable by naturally-occurring

organisms.

Yet another approach is photodegradable plastics,

plastics that will decompose when exposed to sunlight. The

process of photodegradation is well understood by chemists.

In general, when light strikes a molecule, it may initiate any

number of reactions that result in the destruction of that

molecule. For example, light may dislocate one or more

electrons that make up a

chemical bond

in the molecule.

When the bond is broken, the molecule is destroyed.

On a practical level, that means that light can cause

certain materials to decompose. Among the plastics, aro-

matic-based polymers (those that have benzene-like ring

structures) are particularly susceptible to photodegradation.

Those that lack an aromatic structure are less susceptible to

the effects of light. Polyethylene, polypropylene,

polyvinyl

chloride

, polymethyl methacrylate, polyamides, and polysty-

rene--some of the most widely used plastics--fall into that

latter category.

In addition to the type of plastic, the kind of light

that falls on a material affects the rate of photodegradation.

Ultraviolet (UV) light is more effective, in general, in degrad-

ing all plastics than are most other forms of light.

The chemist’s task, then, is to find a mechanism for

converting a substance that is normally non-photodegradable

(like

polystyrene

) into a form that is decomposed by light.

In principle, that challenge is rather easily met. Certain

metallic ions and organic groups are known to absorb visible

light strongly. If these ions or groups are included in a plastic

1087

material, their

absorption

of light will contribute to the

decay of the plastic.

Photodegradable plastics are not a new market item.

Webster Industries, of Peabody, Massachusetts, has been

making photodegradable plastic bags since 1978. And Mobil

Chemical focused some of its advertising in 1990 on Hefty

trash bags that were designed to photodegrade.

But critics raise a number of points about photode-

gradable (as well as biodegradable) plastic materials. For one

thing, most plastics are disposed of in sanitary landfills where

they are rapidly covered with other materials. The critics

question the good of having a photodegradable plastic that

is not exposed to sunlight after it is discarded.

Questions have also been raised about the possible by-

products of photodegradation. It is possible that the very

additives used to make a plastic photodegradable may have

toxic or other harmful environmental effects, critics say.

Finally, photodegradable plastics take so long to decay

(typically two months to two years) that they will still pose

a hazard to

wildlife

and contribute to solid waste volume.

The “false promise” of photodegradability may, in fact, actu-

ally encourage the use of more plastics and add to the present

problem, rather than helping to solve it. See also Decomposi-

tion; Green packaging; Green products; Ultraviolet radiation

[David E. Newton]

ESOURCES

OOKS

Denison, R. A., and J. Wirka. Degradable Plastics: The Wrong Answer to

the Right Question. New York: Environmental Defense Fund, 1989.

ERIODICALS

Thayer, A. M. “Degradable Plastics Generate Controversy inSolid Waste

Issues.” Chemical & Engineering News (25 June 1990): 7–14.

“The Problem with Plastics.” Horticulture (August 1989): 18–19.

Donnelly, J. “Degradable Plastics.” Garbage 2 (May-June 1990): 42–47.

Photoperiod

The light phase in a cycle of alternating periods of light and

dark. Changes in light-dark cycles, such as changes in day-

length, are the most dependable external time cues (zeitgeb-

ers). The physiological response to the length of the day or

night, known as photoperiodism, is mediated by an internal

or biological clock that synchronizes daily activities with

external light-dark cycles. Most

species

studied show a

circadian or daily rhythm set to a 24-hour cycle. Organisms

also show long-term photoperiodism where their seasonal

activities, such as courtship, mating, reproduction,

migra-

tion

, flowering, and seed production, are coordinated with

others in the population and within the community.

Environmental Encyclopedia 3

Photosynthesis

Photosynthesis is the process by which green plants capture

sunlight and convert its kinetic energy into chemical energy

by manufacturing complex sugar molecules or carbohydrates.

The plants use

carbon dioxide

from the air and water as

the source materials for photosynthesis. Both

carbon

diox-

ide and water store relatively small amounts of energy. The

carbohydrates manufactured are rich in energy. Later, during

the process of

respiration

, the plant breaks down these

carbohydrates, and the energy that is then released is used

to fuel the growth and

metabolism

of the plant. The photo-

synthetic process also releases oxygen along with the forma-

tion of the carbohydrates. The water (H

O) that is used in

the photosynthetic reaction contributes its

hydrogen

to the

formation of the carbohydrate. The oxygen that is released

comes from the remaining, unused portion of the water

molecule. Therefore, water is just as essential a component

as carbon dioxide to the photosynthetic process. The entire

reaction is carried out with the help of green, light-sensitive

pigments within the plant, known as chlorophylls.

Photosynthesis is vital to the earth in two ways. It is

the process by which plant life is established, thereby provid-

ing food and supporting all the other consumers in the

food

chain/web

. The release of oxygen also ensures a livable,

breathable

atmosphere

for all other oxygen-dependent life

forms. The maintenance of a stable balance between the

processes of photosynthesis (which produces oxygen) and

respiration (which consumes oxygen) is critical to the

envi-

ronment

. For example, a large amount of organic matter

goes into a lake receiving sewage. This organic matter will

be used as a food source by bacteria which break it down

by the process of respiration just as humans do. During the

respiration process, the oxygen that is dissolved in the water

is used up. If there is insufficient plant material in the lake

to restore this used-up oxygen by photosynthesis, the total

supply of

dissolved oxygen

in the waters of the lake may

drop dangerously. Since fish are completely dependent on

the dissolved oxygen for their breathing requirements, severe

drops in the concentration of dissolved oxygen may kill the

fish, leading to sudden, and sometimes massive,

fish kills

Another aspect of environmental

pollution

are the

effects on the process of photosynthesis itself. A number of

contaminants have been shown to affect plant growth and

metabolism by inhibiting the plant’s ability to photosynthe-

size. Frequently, as in the case of metals like

copper

lead

and

cadmium

, the mechanism of inhibition is due to the

contaminant’s effect on the chlorophyll pigment. Copper

replaces the necessary magnesium in the chlorophyll mole-

cule, and the copper-substituted chlorophyll cannot effec-

tively capture light energy. Therefore, the effectiveness of

the photosynthetic process is greatly diminished, which leads

1088

Photosynthesis. (McGraw-Hill Inc. Reproduced by per-

mission.)

to a stunting of plant growth and a depletion of oxygen in

the environment. The maintenance of a healthy level of

photosynthesis is thus essential to the life of the planet, both

on the global and the micro-environmental scales.

[Usha Vedagiri]

ESOURCES

OOKS

Weier, T. E., et al. Botany: An Introduction to Plant Biology. New York:

Wiley, 1982.

Connell, D. W., and G. J. Miller. Chemistry and Ecotoxicology of Pollution.

New York: Wiley, 1984.

Photovoltaic cell

Photovoltaics is the direct conversion of sunlight into electri-

cal energy using solar cells. All energy on earth is received

from the sun through its electromagnetic spectrum. At any

one instant, the sun delivers 1,000 watts (kw) per square

meter to the earth’s surface. Most of this energy is absorbed

as heat by the lithosphere (

soil

), hydrosphere (water), and

atmosphere

but photovoltaic cells (PVC) are capable of

converting it into a non-polluting, ecologically sound, and

dependable source of electrical power. Although the photo-

Environmental Encyclopedia 3

Photovoltaic cell

voltaic effect was discovered 150 years ago, economically

viable applications were not possible until the recent develop-

ment of efficient semiconductor material and processing

methods.

The physics of converting sunlight into electricity is

simple. Most photovoltaic cells are a standard negative/posi-

tive type with attached leads. The negative terminal

lead

soldered on the light sensitive side of the cell, and the positive

lead is attached to the back side of the cell. When simply

exposed to light, each cell produces about the same voltage

between the two terminals. But if the cell is exposed to light

when a load such as a discharged battery or an electric

motor is connected between the two terminals, the voltage

difference causes a flow of electrons. This current is caused

by the formation of hole-electron pairs by the absorbed light

photons, and the amount of current is dependent on the

amount of absorbed light, which is dependent in turn on the

incident light intensity and the surface area of the absorbing

photovoltaic cell.

There are two main types of solar cells: thick-film cells

with a thickness greater than 25 microns of crystalline silicon

and thin-film cells with a thickness of less than 10 microns.

Thin-film cells are made of various materials, including

amorphous silicon and

copper

indium diselenide, and by

combining several varieties of these in tandem, each with

unique absorbing characteristics, the solar flux can be more

efficiently utilized. Because these cells use less material, they

are less costly to produce and will probably replace thick-

film cells.

Both thick-film and thin-film cells are classified by

the materials from which they are made—as crystalline (a

wafer sliced from a large ingot), amorphous (The condensed

gaseous form of a semi-conductor material such as silicon),

and polycrystalline. Material combinations known as com-

pound semiconductors have been investigated in the 1990s.

These are cell materials whose active layers are comprised

of various semiconductor materials, such as gallium arsenide,

copper sulfide, and

cadmium

telluride.

To increase voltage, multiple cells are connected in a

series by attaching the positive lead of one cell to the negative

lead of another. The series most commonly used for both

commercial and domestic applications is known as a module

and usually consists of 36 cells. One or more modules can

be connected directly to a load, such as a battery, a water

pump, or an exhaust fan. A typical photovoltaic system con-

sists of the modules, a storage battery, a charge and voltage

regulator, and a suitable load. Some compact high perform-

ance modules are designed to charge 12-volt batteries or

directly power a 12-volt DC motor.

Photovoltaic modules may be installed on a standard

ground mount or on a tracker. When installed on a standard

1089

The operation of a photovoltaic cell. (McGraw-

Hill Inc. Reproduced by permission.)

ground mount, the modules can be adjusted from 15–65

degrees at 5 degree increments. Ground mounts can support

two to eight modules. The tracker utilizes a variable thermal

expansion of gas, due to the changing solar exposure, and

actually follows the sun at approximately 15 degrees plus

latitude valve. To maximize efficiency, several modules are

mounted on a tracker supported by a single pole.

The net cost per kilowatt hour is the most important

factor in the future of photovoltaic cell production and appli-

cation. In industrialized countries, the economic viability of

this form of

solar energy

is determined by their cost relative

to competitive energy sources, particularly

fossil fuels

and

nuclear power

, and the environmental impact of each

source. The world market price for solar cells in 1993 was

four dollars a watt, based on rated output, and prices are

expected to drop 50% by the end of the decade, when most

photovoltaic cells will be manufactured with thin-film tech-

nology.

Decentralized single dwellings, cattle ranches and tree

farms remote from electric power lines, and small villages

with limited power demands are one of the three market

segments where photovoltaic cells can be utilized competi-

tively. The consumer and leisure market is another, and solar

cells are already widely used in boats, motor homes, and

camp sites, as well as in calculators and other electronics.

The third market is in industrial applications such as offshore

buoys, lighthouses, illuminated road signs, and railroad and

traffic signals.

The market for photovoltaic cells is increasing at an

overall annual rate of about 10%. Current worldwide demand

is estimated at about 100 megawatts of electrical power, and

predictions for the year 2000 estimate a demand of several

times this size. Growth is the fastest in the remote market;

rural consumer applications are increasing at an annual rate

Environmental Encyclopedia 3

Phthalates

of approximately 35%. There are millions of people around

the world who are not served by

electric utilities

due to their

remote location and the high cost of electrical transmission.

These populations generally depend on a 12-volt

automo-

bile

battery powered by a generator for their electrical needs,

which include water pumping, lighting, and radio and televi-

sion reception. The initial cost of a photovoltaic kit offsets

the cost of owning and operating a generator within three

years. As the life span of a module is usually 15 years, this

option is much more economical in many of these situations.

Prior to 1989, the largest manufacturer of photovoltaic

cells was ARCO Solar, a division of Atlantic Richfield Oil

Company. In 1989, Siemens Solar Industries (SSI), which

already had a joint manufacturing enterprise in Munich,

Germany, with ARCO, had purchased ARCO Solar. SSI

has manufacturing plants in Camarillo, California, and Mu-

nich, Germany.

Converting sunlight into electricity with photovoltaic

cells is a versatile and simple process. Unlike diesel or

gaso-

line

generators, all-weather modules have no moving parts

to wear out or break down, and they produce electricity

without contributing to

air pollution

. Solar cells do not

produce any noise and they do not require alternating-cur-

rent power lines, since photovoltaic electricity is direct cur-

rent. Maintenance is minimal and requires little technical

skill; systems are easy to expand and there are no expensive

fuels to purchase on a continuous basis. Photovoltaic cells

are a cheap and dependable source of power for a variety of

uses. See also Alternative energy sources; Alternative fuels;

Energy and the environment; Energy policy

[Muthena Naseri and Douglas Smith]

ESOURCES

OOKS

Lasnier, F., and T. Ang. Photovoltaic Engineering Handbook. New York:

American Institute of Physics, 1990.

ERIODICALS

Edelson, E. “Solar Cell Update.” Popular Science 240 (June 1992): 95–99.

Lewis, N. S. “More Efficient Solar Cells.” Nature 345 (May 24, 1990):

293–94.

Spinks, P. “Plug Into the Sun.” New Scientist 127 (September 22, 1990):

48–51.

Phthalates

Phthalates are aromatic compounds that are found through-

out the

environment

and are used in some

plastics

, sol-

vents,

detergents

, lubricating oils, and cosmetics. There is

concern that phthalates can cause

cancer

or reproductive

problems in people and animals. In 1998, the U.S. Consumer

Product Safety Commission (CPSC) conducted a study of

1090

the amount of one type of phthalate, diisononyl phthalate

(DINP) that can leach from children’s products such as

teethers, rattles, and toys. This study set an international

standard concentration for DINP in children’s products that

is 10 times higher than the level found to cause health

problems in laboratory animals. The results of a study re-

leased in 2000 by the

Centers for Disease Control and

Prevention

(CDC) and the National Toxicology Program

(NTP) found four types of phthalates in the urine of more

than 75% of test subjects, indicating that the phthalates that

humans are exposed to in the environment are metabolized.

The study was not designed to provide information on the

health risks of phthalates or on the degree of exposure of

the United States population, and follow-up studies by the

CDC are measuring phthalate concentrations in a larger part

of the population, including children six years old and older.

[Marie H. Bundy]

Phytoplankton

Photosynthetic

plankton

, including microalgae, blue-green

bacteria, and some true bacteria. These organisms are pro-

duced in surface waters of aquatic ecosystems, to depths

where light is able to penetrate. Sunlight is necessary since,

like terrestrial plants, phytoplankton use solar radiation to

convert

carbon dioxide

and water into organic molecules

such as glucose. Phytoplankton form the base of nearly all

aquatic food chain/webs, directly or indirectly supplying the

energy needed by most aquatic protozoans and animals.

Temperature,

nutrient

levels, light intensity, and consumers

(grazers) are among the factors that influence phytoplankton

community structure.

Phytoremediation

Phytoremediation combines the Greek word phyton, “plant,”

with the Latin word remediare, “to remedy,” to describe a

system whereby certain plants, working together with

soil

organisms, can transform contaminants into harmless and

often, valuable, forms. This practice is increasingly used to

remediate sites contaminated with

heavy metals

and toxic

organic compounds.

Phytoremediation takes advantage of plants’

nutrient

utilization processes to take in water and nutrients through

roots, transpire water through leaves, and act as a transforma-

tion system to metabolize organic compounds, such as oil

and pesticides. Or they may absorb and bioaccumulate toxic

trace elements, such as the heavy metals,

lead

cadmium

and selenium. In some cases, plants contain 1,000 times

more metal than the soil in which they grow. Heavy metals

Environmental Encyclopedia 3

Phytoremediation

are closely related to the elements plants use for growth. In

many cases, the plants cannot tell the difference, according

to Ilya Raskin, Professor of Plant Sciences in the Center for

Agricultural Molecular Biology at Rutgers University.

Phytoremediation is an affordable technology that is

most useful when contaminants are within the root zone of

the plants (top 3-6 ft [1-2 m]). For sites with contamination

spread over a large area, phytoremediation may be the only

economically feasible technology. The process is relatively

inexpensive because it uses the same equipment and supplies

used in agriculture.

Soil

microorganisms

can degrade organic contami-

nants. This is called

bioremediation

and has been used for

many years both as an in situ process and in land farming

operations with soil removed from sites.

Ilya Raskin and his interdisciplinary team at Rutgers

AgBiotech Center were first to demonstrate the utility of

certain varieties of mustard plants in removing such metals

as chromium, lead, cadmium, and zinc from

contaminated

soil

. Related technology developed by Raskin’s group used

hydroponic plant cultures to remove toxic metals from aque-

ous waste streams.

Plants can accelerate bioremediation in surface soils

by their ability to stimulate soil microorganisms through the

release of nutrients from and the transport of oxygen to their

roots. The zone of soil closely associated with the plant root,

the rhizosphere, has much higher numbers of metabolically

active microorganisms than unplanted soil. The rhizosphere

is a zone of increased microbial activity and

biomass

at the

root-soil interface that is under the interface of the plant

roots. It is this symbiotic relationship between soil

microbes

that is responsible for the accelerated degradation of soil

contaminants.

The interaction between plants and microbial commu-

nities in the rhizosphere is complex and has evolved to

the mutual benefit of both organisms. Plants sustain large

microbial populations in the rhizosphere by secreting sub-

stances such as carbohydrates and amino acids through root

cells and by sloughing root epidermal cells. Also, root cells

secrete mucigel, a gelatinous substance that is a lubricant

for root penetration through the soil during growth. Using

this supply of nutrients, soil microorganisms proliferate to

form the plant rhizosphere.

In addition to this rhizosphere effect, plants them-

selves are able to passively take up a wide range of organic

wastes from soil through their roots. One of the more impor-

tant roles of soil microorganisms is the

decomposition

organic residues with the release of plant nutrient elements

such as

carbon

nitrogen

, potassium, phosphate, and sulfur.

A significant amount of the

carbon dioxide

(CO

) in the

atmosphere

is utilized for organic matter synthesis primar-

ily through

photosynthesis

. This transformation of carbon

1091

dioxide and the subsequent sequestering of the carbon as

root biomass contributes to balancing the effect of burning

fossil fuels

on global warming or cooling.

Compounds are frequently transformed in the plant

tissue into less toxic forms or sequestered and concentrated

so they can be removed (harvested) with the plant. For

example, mustard greens were used to remove 45% of the

excess lead from a yard in Boston, Massachusetts, to ensure

the safety of children who play there. The sequestered lead

was carefully removed and safely disposed of. Besides mus-

tard greens, pumpkin vines were used to clean up an old

Magic Marker factory site in Trenton, New Jersey. Hydro-

ponically grown sunflowers were used to absorb radioactive

metals near the Chernobyl nuclear site in the Ukraine and a

uranium

plant in Ohio. The mustard’s hyper-accumulation

results in much less material for disposal. The

composting

of plant material can be another highly efficient stage in the

breakdown of contaminants removed from the soil.

When trees are used, such as poplars, the idea is to

move as much water through them as possible, so that they

take up as much of the contaminants as possible. Once the

heavy metals are absorbed, they are sequestered in the trees’

roots. Any organic compounds that are absorbed are metabo-

lized.

Absorption

of large amounts of nutrients by plants

and only a small amount of plant

toxins

that might be

harmful to them, is the key factor. Plants generally absorb

large amounts of elements they need for growth and only

small amounts of toxic elements that could harm them.

Therefore, phytoremediation is a cost-effective alternative

to conventional

remediation

methods. Cleaning the top 6

in (15 cm) of contaminated soil with phytoremediation costs

an estimated $2,500-$15,000 per hectare (2.5 acres), com-

pared to $7,500-$20,000 per hectare for on-site microbial

remediation. If the soil is moved, the costs escalate, but

phytoremediation costs are still far below those of traditional

remediation methods, such as stripping the contaminants

from the soil using physical, chemical, or thermal processes,

according to Dr. Scott Cunningham, a scientist at Dupont

Central Research for Environmental Biotechnology.

Plants are effective at remediating soils contaminated

with organic chemical wastes, such as solvents, petrochemi-

cals, wood preservatives, explosives, and pesticides. The con-

ventional technology for soil clean-up is to remove the soil

and isolate it in a

hazardous waste landfill

or incinerate it.

Phytoremediation, says Dr. Ray Hinchman, botanist

and plant physiologist at Argonne National Laboratory, is

“an in situ approach,” not reliant on the transport of contami-

nated material to other sites. Organic contaminants are, in

many cases, completely destroyed (converted to CO

and

O) rather than simply immobilized or stored.

Environmental Encyclopedia 3

Phytotoxicity

Salt-tolerant plants, called halophytes, have reduced

the salt levels in soils by 65% in only two years in one project

involving brine-damaged land from run-off from oil and gas

production in Oklahoma. After the salt was reduced, the

halophytes died and native grasses, which failed to thrive

when too much salt entered the soil, naturally returned,

replacing the salt-converting plants.

The establishment of vegetation on a site also reduces

soil

erosion

by wind and water, which helps to prevent the

spread of contaminants and reduces exposure of humans and

animals.

Classes of organic compounds that are more rapidly

degraded in rhizosphere soil than in unplanted soil include:

total

petroleum hydrocarbons

;

polycyclic aromatic hy-

drocarbons

; chlorinated pesticides (PCP,

2,4-D

); other

chlorinated compounds (PCBs, TCE); explosives (TNT,

DNT);

organophosphate

insecticides (diazanon and para-

thion); and surfactants (

detergents

Some plants used for phytoremediation are: alfalfa,

symbiotic with hydrocarbon-degrading bacteria; arabidopsis,

carries a bacterial gene that transforms

mercury

into a gas-

eous state; bladder campion, accumulates zinc and

copper

;

brassica juncea (Indian mustard greens), accumulates sele-

nium, sulfur, lead, chromium, cadmium,

nickel

, zinc, and

copper; buxaceae (boxwood), accumulates nickel; compositae

family (symbiotic with arthrobacter bacteria), accumulates

cesium and strontium; euphorbiaceae (succulent), accumu-

lates nickel; ordinary tomato, accumulates lead, zinc, and

copper; poplar, used in the absorption of the

pesticide

atrazine

; and thlaspi caerulescens (alpine pennycress), accu-

mulates zinc and cadmium.

[Carol Steinfeld]

ESOURCES

OOKS

Elliott, L. F., and F. J. Stevenson. Soils for the Management of Wastes and

Waste Waters. Madison, WI: Soil Science Society of America, 1977.

ERIODICALS

Anderson, G., and W. “Bioremediation, Environmental Science and Tech-

nology.” American Chemical Society 27, no. 13 (1993).

Howe, P. “Plants Doing the Dirty Work in Cleanup of Toxic Waste,”

Boston Globe, March 10, 1997.

Phytotoxicity

Phytotoxicity refers to the damage to plants caused by expo-

sure to some toxic stressor. Phytotoxicity can be evidenced

by acute injury such as obviously damaged, necrotic tissues.

Chronic phytotoxicity does not present such obvious sym-

toms and may result in such “hidden injuries” as a decrease

in productivity or a change in growth form. Plants can be

1092

poisoned by naturally occurring

toxins

, such as

nickel

serpentine-influenced soils. Humans also release phytotoxic

chemicals

into the

environment

. Such emissions occur

when, for example, gaseous and/or metal pollutants around

smelters damage vegetation. Deliberate use of phytotoxic

chemicals includes the use of herbicides in agriculture or

forestry to decrease the abundance of unwanted plants or

weeds.

Gifford Pinchot (1865 – 1946)

American conservationist and forester

Pinchot was born in Simsbury, Connecticut, to a prosperous

business and industrial family, part of whose wealth came

from timber holdings in several states. The Pinchots, like

other lumber investors of their day, practiced

clear-cutting

on forests to maximize their profits, shipped the logs to

market, and with the returns, repeated the cycle. Young

Gifford was pressured by his grandfather to enter the family

business, but his father James was beginning to dislike the

deforestation

of his area, and he encouraged his son to

pursue forestry.

Pinchot was educated at Exeter and then Yale, gradu-

ating in 1889. After graduation, his family supported further

education at L’Ecole nationale forestiere in Nancy, France,

where he studied silviculture, or forest

ecology

. It was in

Nancy that he learned “le coup d’oeil forestier—the forester’s

eye, which sees what it looks at in the woods.” In his 1947

book, Breaking New Ground, Pinchot noted that it was in

France that he began to think of “the forest as a crop,” that

forests could sustain human use by a “fixed and annual supply

of trees ready for the axe.”

Returning to the United States in 1892, Pinchot en-

gaged in “the first scientific forestry in America” on the

Vanderbilt estate in North Carolina, hoping to prove that

“trees could be cut and the forest preserved at one and the

same time.” Pinchot figured out how to sustain the forest

while maintaining its yield, and thus its income. He called

his first successful year “a balance on the side of practical

forestry.”

Pinchot then worked as a consulting forester in New

York City, where he attracted increasing attention for his

ideas. The National Academy of Science appointed him to

the new National Forest Commission, organized by the

U.S. Department of the Interior

. On the Commission’s

recommendation, President Grover Cleveland added 13

more forest reserves totaling 21 million acres (8.5 million

ha). Pinchot, voicing a minority opinion on the Commission,

Environmental Encyclopedia 3

Gifford Pinchot

Gifford Pinchot. (Corbis-Bettmann. Reproduced by per-

mission.)

saw the reserves as property for public use, not as a way to

lock up the nation’s

natural resources

In 1898 Pinchot became head of the U.S. Department

of Agriculture’s Division of Forestry. The division did not

operate the nation’s forest reserves, which were then admin-

istered by the Department of the Interior’s General Land

Office. Pinchot lobbied hard to have the reserves transferred

to his division, but his efforts were unsuccessful until William

McKinley’s assassination moved

Theodore Roosevelt

into

the White House. Pinchot and Roosevelt together mustered

enough support in Congress to approve the transfer to the

renamed Bureau of Forestry in 1905, marking the beginning

of the national forest system and what became the U.S.

Forest Service

Pinchot’s long-time collaboration with Roosevelt was

one of the benchmarks of the

conservation

movement,

which culminated in the creation of what have been called

the “midnight forests.” These 16 million acres of forest were

set aside as reserves late in the night before a Congressional

bill to limit the President’s power to do so took effect. After

Roosevelt left office, Pinchot’s association with President

William Howard Taft soured quickly, climaxing in a feud

with Richard Ballinger, Taft’s Secretary of the Interior and

ending in 1910, when Pinchot was fired by the President.

1093

Despite leaving before he had accomplished all that

he wished, Pinchot left his mark on the Forest Service.

Ironically, both are often criticized by modern environmen-

talists for their utilitarian policies. Yet this early conserva-

tionist was one of first to protect national forest lands from

the industrial powers who sought to destroy them com-

pletely.

Pinchot still generates controversy today. Most writers

trace the conflict between conservationists and preserva-

tionists to his falling-out with

John Muir

over the Hetch-

Hetchy Reservoir in California. Pinchot, with his pragmatic

approach, argued that the river valley served the greatest

public good as a dependable source of water for the people

of San Francisco. Muir maintained that Hetch Hetchy was

sacred and too beautiful to flood. He also believed the dam

would betray the

national park

ideal, since Hetch Hetchy

was in

Yosemite National Park

As he grew older, Pinchot did become less utilitarian,

creating what he called the “new conservationism,” but even

his “new” approach was an extension of his long-held convic-

tion that the forests of the nation belonged first to the

people, to be used by them wisely and in perpetuity. To

Pinchot, conservation meant “the greatest good to the great-

est number for the longest time.” Pinchot’s beliefs, which

have been revived in recent years, make sense both ecologi-

cally and economically. He claimed that “the central thing

for which Conservation stands is to make this country the

best possible place to live in, both for us and our descen-

dants.”

Pinchot was active on many fronts of the struggle

for conservation. The

Society of American Foresters

professional association and major force in resource manage-

ment and conservation today was created in 1900, due in

part to his efforts. He served two terms as Governor of

Pennsylvania (1923–27; 1931–35), and his efforts to relieve

the effects of the Great Depression led to the creation of

emergency work camps there, providing a model for the

Civilian Conservation Corps started by President Franklin

Roosevelt.

Pinchot recognized that people must live off the re-

sources of land where they live. In The Fight for Conservation

(1910), he stated bluntly that “the first principle of conserva-

tion is development, the use of the natural resources now

existing on the continent for the benefit of the people who

live here now.” But, he also recognized that use of resources

could quickly turn into abuse of resources, especially by

exploitation for the few. He believed that destruction of

forest resources was detrimental to the

environment

and

to the many who depended on it.

Pinchot’s ideas and his national forests are still with

us today. His concern with producing the greatest totality

land use

produced the

wilderness

that is preserved but

Environmental Encyclopedia 3

Placer mining

accessible and forest that is logged and renewed. Pinchot, a

giant of the conservation and the environmental movements,

leaves his legacy of a vast forest domain that belong to the

American people.

[Gerald L. Young Ph.D.]

ESOURCES

OOKS

McGeary, M. N. Gifford Pinchot: Forester-Politician. Princeton, NJ:

Princeton University Press, 1960.

Nash, R. “Gifford Pinchot.” In From These Beginnings: A Biographical

Approach to American History. Vol. 2. 2nd ed. New York: Harper &

Row, 1978.

Norton, B. G. “Moralists and Aggregators: The Case of Muir and Pinchot.”

In Toward Unity Among Environmentalists. New York: Oxford University

Press, 1991.

Pinchot, G. Breaking New Ground. Covelo, CA: Island Press, 1947.

ERIODICALS

Miller, C. “The Greening of Gifford Pinchot.” Environmental History

Review 16 (Fall 1992): 1–20.

Watkins, T. H. “Father of the Forests.” American Heritage 42 (February–

March 1991): 86–98.

PIRG

see

U.S. Public Interest Research Group

Placer mining

Placer deposits are collections of some mineral existing in

discrete particles, mixed with sand, gravel, and other forms

of eroded rock. Some of the minerals most commonly found

in placer deposits are diamond, gold, platinum, magnetite,

rutile, monazite, and cassiterite. These deposits are formed

by the action of wind, water, and chemical changes on more

massive beds of the mineral. Placer deposits can be classified

according to the method by which they are produced. Some

examples include stream placers, eolian placers (formed by

the action of winds), beach placers, and moraine placers

(formed by glacial action).

Placer deposits are important sources of some minerals

that are more dense than the sand or gravel around them.

For example, the gold in a placer deposit tends to settle

out and accumulate in a stream as surrounding materials

wash away.

With few exceptions, the mining of placer deposits is

carried out by traditional surface (compared to underground)

mining. Four general methods are in use. The oldest and

perhaps most familiar to the general public is the hand

method. Placerville, California, commemorates by its name

the type of mining that was done during the Gold Rush of

1094

1849. As the worker rocks his or her box or pans back and

forth, clay and sand are washed away, and the heavier gold

(or other minerals) settles to the bottom. This method is

less used today since deposits with which it works best have

been largely depleted.

Artificial streams of water are used in a second method

of placer mining--hydraulic mining. In this process, intense

streams of water are directed with large hoses at a placer

deposit. The water washes away the overlying sand and clay,

leaving behind the desired mineral.

A number of variations of this procedure exists. In

some cases, a natural stream is diverted from its course and

directed against a placer deposit. The action of the stream

substitutes for that of a hose in the traditional hydraulic

method. In another variation, a stream may be dammed

rather than diverted. When the dam is broken, the penned-

up water is released all at once with a force that can tear

apart a placer deposit. This technique is known as “booming”

a deposit and although it is no longer used in the United

States, the method is used around the world.

An increasingly popular approach to placer mining

makes use of familiar

surface mining

machinery used to

extract

coal

and other minerals. This machinery is often

very large and efficient. It removes

overburden

, extracts

mineral-containing earths with streams of water and then

separates and processes the extracted material by gravity

methods.

A fourth method of mining is used with deposits un-

derwater, as in a lake or along the seashore. In this process,

a large machine somewhat similar to a surface mining excava-

tor is placed on a barge. The machine then scoops materials

off the lake, stream, or ocean bottom and carries them to a

processing area on another part of the barge. This type of

dredging

machine might be thought of as a very large,

mechanized version of the old prospector’s gold pan and

rocker box.

Placer mining poses two kinds of environmental prob-

lems. The first is one that is common to all types of surface

mining, the disturbance of land. Federal law now requires

that land disturbed by surface mining such as placer mining

be restored to a condition that approximates its original state.

The extensive use of water during placer mining is a

second source of concern. By its nature, placer mining pro-

duces huge flows of water that have become contaminated

with mud, sand, and other suspended solids. As this water

is dumped into natural waterways, these solids may damage

aquatic plant and animal life and, as they settle out, create

new navigational hazards. In the United States, the Clean

Water Acts and other environmental laws carry provisions

to reduce the potential harm posed by placer mining.

[David E. Newton]

Environmental Encyclopedia 3

Plague

ESOURCES

OOKS

Sinclair, J. Quarrying, Opencast and Alluvial Mining. New York: Elsev-

ier, 1969.

ERIODICALS

“Mining Companies Urged to Provide for Wildlife Habitats.” Engineering

and Mining Journal 194 (April 1993): 16.

Pynn, L. “The Legacy of Klondike Gold: Strange Things Done to the

Landscape by the Men and Women Who Moil for Gold.” Canadian Geo-

graphic 112 (May-June 1992): 52–61.

Wuerthner, G. “Hard Rock and Heap Leach.” Wilderness 55 (Summer

1992): 14–21.

Plague

For centuries past, plague was the scourge of the earth,

killing at least an estimated 163 million people during three

major worldwide pandemics. Today, plague still exists in the

world although the number of cases and deaths is much

lower. Plague still infects several thousand people a year and

kills several hundred. Most cases are in southern Africa,

Asia, and central South America.

Plague is an infectious disease that affects animals and

humans. It is caused by the bacterium Yersinia pestis and is

usually found in rodents and their fleas. When released into

the air, the bacterium can survive for up to an hour. People

usually contract the disease after being bitten by an infected

flea or after handling an infected animal. To reduce the risk

of death, antibiotics must be given within 24 hours after the

first symptoms occur.

There are three types of plague and they can occur

separately or in combination. The types are:

Bubonic plague, the most common form of the disease. It

does not spread from person to person but is transmitted

when an infected flea bites a person or when material

contaminated with the bacterium enters through a cut in

a person’s skin. Symptoms include swollen lymph glands,

fever, headache, chills, and weakness.

Pneumonic plague, which infects a person through the

lungs. It can be spread in the air from person to person.

Symptoms include fever, headache, weakness, shortness of

breath, chest pain, cough, and pneumonia.

Septicemic plague, which occur when plague bacteria mul-

tiply in the blood. It can occur by itself or be a complication

of pneumonic or bubonic plague. It is not spread from

person to person. Symptoms include fever, chills, exhaus-

tion, abdominal pain, shock, and bleeding into the skin

and other organs.

To reduce the chance of death, people with plague

must receive antibiotics within 24 hours after the first symp-

toms appear. Effective antibiotics include streptomycin, gen-

1095

tamicin, and tetracycline. Early treatment allows most people

with plague to be cured if diagnosed in time. There is no

vaccine against plague available.

From 1954 to 1997, there were 80,613 reported plague

cases in 38 countries, of which 6,587 people died, according

to the World Health Organization (WHO). The highest

number of cases, 6,004, occurred in 1967, and the lowest

number, 200, occurred in 1981. These numbers likely repre-

sent only about a third of the actual number of cases, due

to inadequate surveillance and reporting methods, according

to WHO.

Plague has been around since the dawn of civilization

and probably existed in animals before humans inhabited

the earth. The first recorded plague epidemic occurred in

1320

and is described by its symptoms in the Bible (I

Samuel, V and VI). It is not known how many people were

infected. The first known pandemic, or severe worldwide

epidemic, occurred in Asia, Africa, and Europe between

542 and 546

. It was named Justinian’s plague, after the

emperor of the Byzantine Empire at the time, and killed an

estimated 50 million to 100 million people.

The first pandemic is believed to have started in Egypt,

spreading north through the eastern Mediterranean. The

plague struck at a critical time. In Constantinople, the capital

of the Byzantine empire, Justinian and his generals were in

the midst of battles to rejoin Byzantium to the remains

of Western Roman Empire. Justinian’s dream was to re-

establish the former Roman Empire; and he might have

succeeded if not for the plague. Procopius, a historian living

in Constantinople at the time, vividly described the plague

and its effects. His writings also include an accurate descrip-

tion of what would later be called the bubonic plague. He

wrote about agitated, feverish disease victims with painfully

enlarged lymph nodes (buboes) under their arms and in their

groins. According to Procopius, 300,000 people died within

the city alone. It is impossible to verify whether that figure

is accurate, but it is certain that the plague had a dramatic

effect on history. Justinian’s plans to re-establish the Roman

Empire were very likely derailed because of the loss of man-

power. In the west, the remnants of the Western Roman

Empire collapsed into the Dark Ages.

Following the initial outbreak in 542, the plague disap-

peared and reappeared at intervals over the next 200 years.

The years 542 to 600 were the most intense plagues years,

but local epidemics flared up throughout the Mediterranean

region through the mid-eighth century. The population of

Europe wasn’t able to recover between outbreaks and some

historians estimate that the population dropped by half be-

tween 542 and 700. After the late-eighth century, plague

disappeared from Europe for nearly 600 years.

The second pandemic is the infamous “Black Death”

from 1347 to 1350

. It killed from 25 million to 50 million

Environmental Encyclopedia 3

Plague

people, half in Asia and Africa and half in Europe (a quarter

of the population). Its entry into Europe was through Kaffa,

a small Italian trading colony on the shore of the Black Sea

in Crimea. Kaffa was besieged by an army and during the

siege, plague broke out among the soldiers. According to

some sources, the soldiers threw the corpses of those who

died over the town walls to spread plague among the men

defending the town. Whether that caused plague to break

out in the town is unknown, but the defenders were afflicted.

They managed to get to their boats and flee to Italy, unknow-

ingly carrying the disease with them.

By late 1347, plague was widespread in the Mediterra-

nean region, and in 1348 it spread throughout Italy, France,

and England. The Middle East and the Far East were also

severely affected. Medieval physicians were at a loss to ex-

plain the disease. Some claimed it was due to person-to-

person infection, while others said it arose from a poisonous

atmosphere

. Other explanations put forth by panicked citi-

zens blamed astrological influences, divine punishment, and

the Jewish community. Tens of thousands of Jewish citizens

were burned in Spain, Germany, Switzerland, and France

despite protests by Pope Clement VI, Emperor Charles IV,

and medical experts who said that they were innocent. How-

ever, the authorities were powerless to stop the spread of

plague, and they were not believed. Quarantines of plague

victims were ordered, but they were largely ineffective.

The Black Death was the beginning of a number of

plague outbreaks that ravaged Europe and Africa in subse-

quent centuries. In England alone, there were plague out-

breaks in 1361, 1369, 1390, 1413, 1434, 1439, and 1464.

Additional outbreaks occurred in Scotland in 1401–1403,

1430–1432, and 1455. The epidemics cut England’s popula-

tion of about seven million in half from 1300 to 1380. The

last major outbreaks of the Black Death pandemic occurred

in London in 1665–1666 and in Marseilles in 1720–1722.

Each of these outbreaks resulted in approximately 100,000

deaths.

In a controversial 2001 book, “Biology of Plagues,”

authors and epidemiologists Susan Scott and Christopher

Duncan write they believe the plague of 1347–1351 was not

caused by the bubonic plague, but rather by a still unknown

disease. They say the quick spread of the disease and the

fact that bubonic plague is not transmitted person to person,

as the Black Death was, points to another cause. Another

possibility, however, is that the ship trade of that time would

have allowed for disease-infested rats to move from location

to location rapidly and thus, spread the disease quickly

through various populations.

The world’s third plague pandemic began in 1894 in

China and Hong Kong. Called the Modern Pandemic, it

quickly spread throughout the world, carried by rats aboard

steamships. From 1894 through 1903, plague-infested ships

1096

had brought the disease to 77 ports in Asia, Africa, Europe,

North America,

Australia

, and South America. In India

alone, plague killed about 13 million people. In the year

the pandemic started, scientists discovered the cause of the

disease, and established that rats and their fleas were the

carriers.

According to most sources, the Modern Pandemic

continues to the present time. Epidemics linked to the Mod-

ern pandemic were reported in San Francisco, New Orleans,

and other coastal cities throughout the world and millions

died. The Modern pandemic also established in areas that

previously had been plague free, including North America,

South America, and southern Africa. With the advent of

antibiotics and the understanding of how plague spreads,

the Modern pandemic has been contained and the plague

no longer claims millions of victims. However, health au-

thorities remain vigilant because the plague has not been

eradicated.

At the turn of the twentieth century, plague outbreaks

twice hit San Francisco. The first outbreak was from 1900

to 1904, and the second from 1907 to 1909. Several hundred

infections were confirmed but health officials believe hun-

dreds of cases went unreported. More recently, an outbreak

of bubonic plague occurred in the African nation of Malawi

in early 2002, infecting at least 10 people

The decrease in the incidence of plague today is due

primarily to improved living standards and health services

in many underdeveloped nations. In India, plague epidemics

have stopped altogether. The reasons for this are not clear,

according to WHO scientists. The Government of India,

however, has taken a number of stringent measures to pre-

vent spread of the disease. These include mandatory screen-

ing at airports of every airline passenger intending to travel

abroad for signs and symptoms of plague,

fumigation

aircraft, including both the passenger cabin and the cargo

hold. Additionally, all aircraft are inspected for the presence

of rats. At all major sea ports, all out-going vessels are being

inspected for the presence of rats and insects. Ships are

required to have a certificate, issued by the port health officer,

showing that they have been deratted, before they can leave

port. All these measures are in accordance with the WHO

International Health Regulations.

Plague is often mentioned as a potential biological

weapon of terrorists. When released into the air, the bacte-

rium can survive for up to an hour. Of the three types of

plague (pneumonic, bubonic, and septicemic), pneumonic

is they one most likely to be used by terrorists since large

stockpiles were developed by the United States and Soviet

Union in the 1950s and 1960s. Much of the Soviet supply

is now in the hands of several of its former republics, now

independent nations. The U.S. government believes several

so-called “rogue” nations, such as Iran, Iraq, and North