Environmental Encyclopedia

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Environmental Encyclopedia 3

Trophic level

that countries adopt measures to restrict the use and release

rate of TBT-based antifouling paints. Since that recommen-

dation, many countries have prohibited the use of TBT anti-

fouling paints on small craft. New Zealand and Japan banned

the use of TBT anti-fouling paints on all ships. In 1998,

the IMO agreed to ban the application of TBT-based paints

by 2003 and their presence on ships by 2008. Due to the

ensuing reductions in the use of TBT-based paints, both

TBT contamination and its effects on organisms have been

decreasing worldwide.

Less toxic alternatives to TBT are being developed

quickly. In the animal and plant worlds, researchers have

found over 50 naturally-occurring substances that have the

same effects as TBT and other antifouling paints, keeping

organisms such as algae and some invertebrates from becom-

ing laden with other forms of algae and sea life. In addition,

other alternatives to TBT have been developed, and include

epoxy-copper flake paints, which may protect boats for up

to 10 years, but cannot be used on ships with aluminum

hulls. Ceramic-epoxy coats are also available, and can be

used on fiberglass and metal hulls. Other alternativess to

TBT are foulant-release coatings that contain silicone elasto-

mers that last as long as the copolymers in TBT. Finally,

researchers are studying eletrical current systems that can

sterilize the hulls of ships for up to four years as another

alternative.

[Judith L. Sims]

ESOURCES

OOKS

de Mora, S. J., ed.Tributyl Tin: Case Study of an Environmental Contami-

nant.Cambridge, UK: Cambridge University Press, 1997.

St. Louis, Richard.Tributyl Tin: The Case for Virtual Elimination in Canada.-

Toronto, Canada: World Wildlife Fund Canada, 1999.

THER

“Antifoulants.” Organotin Environmental Programme (ORTEP). Associa-

tion, The Hague, The Netherlands. [cited June 21, 2002]. <http://ortep-

a.org/pages/antifoulants.htm>.

Trihalomethanes

Trihalomethanes (THMs) are organic

chemicals

composed

of three halogen atoms (primarily

chlorine

and

bromine

)

and one

hydrogen

atom bound to a single

carbon

atom.

They are commonly used as solvents in a variety of applica-

tions, and trichloromethane (or chloroform) was once used

by medical doctors as an anesthetic. In 1974, Johannes Rook

of the Netherlands discovered the presence of THMs in

chlorinated drinking water. He and other researchers subse-

quently demonstrated that minute quantities of THMs are

formed during

water treatment

. Chlorine, when added to

1427

disinfect the water, reacts with naturally occurring organic

matter present in the water.

Groundwater

can also be con-

taminated with THMs if people use them improperly, re-

lease them accidentally, or dispose of them unsuitably. Since

high dosages of chloroform had been found to produce

can-

cer

in mice and rats, the United States

Environmental

Protection Agency

(EPA) amended the drinking water

standards in 1979 to limit the concentration of THMs to a

sum total of 100 parts ber billion, or 0.1 mg/l. In 1998, a

more stringent limit of 0.08 mg/l was introduced. See also

Carcinogen; Drinking-water supply; Water quality stan-

dards

Trophic level

One way of analyzing the biological relationships within an

ecosystem

is to describe who eats whom within the system,

also called a functional analysis. Each feeding level in an

ecosystem is called a trophic level. In the

grasslands

, for

example, plants are considered primary producers, forming

the first trophic level. The second trophic level consists of

primary consumers, such as deer, mice, seed and fruit-eating

birds, and other animals, depending completely on the pri-

mary producers for their food. Carnivores and predators,

such as hawks, are the secondary consumers. Often, the same

species

may fit into several categories. Bears, for example,

are considered both primary and secondary consumers be-

cause they feed on plant matter as well as meat. Bacteria

and

fungi

that decompose dead organic matter are called

the

decomposers

. Thus, on the basis of food source and

feeding behavior, a complex

food chain/web

exists within

any ecosystem and every species belongs to one or more of

several trophic levels.

environmental science

, the concept of trophic

levels is often used to assess the potential for transfer of

pollutants through an ecosystem. Since each trophic level is

dependent on all the other levels, positive or negative changes

in the composition or abundance of any one trophic level

will ultimately affect all other levels. In ecosystems that

normally have stable, complex trophic levels within the food

web,

pollution

can lead to fluctuations and simplification

of the trophic levels. Contaminants that are taken up by

plants from the

soil

may be transferred to primary and

secondary consumers through their feeding patterns. This

is known as trophic level transfer.

A classic example of trophic level transfer was the

release of DDT in the

environment

. DDT is an insecticide

commonly used in the United States during the 1950s and

early 1960s. DDT ran off treated fields into lakes and rivers,

where it accumulated in the fatty tissues of primary consum-

ers such as fish and shellfish. The

chemicals

were then

Environmental Encyclopedia 3

Tropical rain forest

transferred into secondary consumers, such as eagles, which

fed on the primary consumers. While the concentrations of

DDT were rarely high enough to kill the birds, it did cause

them to lay eggs with thin shells. The thin eggshells led to

decreased hatching success and thus caused a decline in the

eagle population.

Trophic level analysis is a commonly used method

of environmental assessment. A pollutant or disturbance is

assessed in terms of its effects on each trophic level. If

significant amounts of nutrients are brought into a lake

receiving

fertilizer runoff

from fields, a spurt in the growth

of algae (primary producers) in the lake may be triggered.

However the increased growth might actually be dominated

by certain algal groups, such as blue-green algae, which may

not constitute desirable food sources for the

zooplankton

and fish (primary consumers) which normally depend on

algae for food. In this case, even though the environmental

conditions might appear to stimulate increased growth in

one trophic level, the nature of the change does not necessar-

ily prove advantageous to other trophic levels within the

same system. See also Agricultural pollution; Algal bloom;

Aquatic weed control; Balance of nature; Bald eagle; Decom-

position; Environmental stress; Predator control; Predator-

prey interactions

[Usha Vedagiri]

ESOURCES

OOKS

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

New York: Wiley, 1984.

Smith, R. L. Ecology and Field Biology. New York: Harper and Row, 1980.

Tropical rain forest

The richest and most productive biological communities in

the world are in the tropical forests. These forests have been

reduced to less than half of their former extent by human

activities and now cover only about 7% of Earth’s land area.

In this limited area, however, is about two-thirds of the

vegetation mass and about half of all living

species

in the

world.

The largest, lushest, and most biologically diverse of

the remaining tropical moist forests are in the

Amazon

Basin

of South America, the Congo River basin of central

Africa, and the large islands of southeast Asia (Sumatra,

Borneo, and Papua, New Guinea). Whereas the forests of

mainland southeast Asia, western Africa, and Central

America are strongly seasonal, with wet and dry seasons,

the South American and central African forests are true rain

forests. Rainfall is generally over 160 in (406 cm) per year

and falls at a relatively even rate throughout the year. It is

1428

said that such rainforests “make their own rain,” because

about half the rain that falls in the forests comes from con-

densation of water vapor released by

transpiration

from

the trees themselves. Rain forests at lower elevations are

hot and humid year-round. At higher elevations, tropical

mountains intercept moisture-laden clouds, so the forests

that blanket their slopes are cool, wet, and fog-shrouded.

They are aptly and poetically called “cloud forests.” Tropical

forests are generally very old. Unlike temperate rain forests,

they have not been disturbed by

glaciation

or mountain-

building for hundreds of millions of years. This long period

evolution

under conditions of ample moisture and stable

temperatures has created an incredible diversity of organisms

of amazing shapes, colors, sizes, habits, and specialized adap-

tations.

Habitats in a tropical

rain forest

are stratified into

three to five distinct layers from ground level to the tops of

the tallest trees. Hundreds of tree species grow together in

lush profusion, their crowns interlocking to form a dense,

dappled canopy about 120 ft (37 m) above the forest floor.

These unusually tall trees are supported by relatively thin

trunks reinforced by wedge-shaped buttresses that attach to

a thick mat of roots just under the

soil

surface. A few

emergent trees rise above the seemingly solid canopy into a

world of sunlight, wind, and open space. Numerous species

of birds, insects, reptiles, and small mammals live exclusively

in the forest canopy, never descending below the crowns of

the trees.

The forest understory is composed of small trees and

shrubs growing between the trunks of the major trees, as

well as climbing woody vines (lianas) and many epiphytes—

mainly orchids, bromeliads, and arboreal ferns—that attach

themselves to the trees. Some of the larger trees may support

50–100 different species of epiphytes and an even larger

population of animals that are specialized to live in the many

habitats they create. These understory layers are a world of

bright but filtered light abuzz with animal activity.

By contrast, the forest floor is generally dark, humid,

quiet, and rather open. Few herbaceous plants can survive

in the deep shade created by the layered canopy of the forest

trees and their epiphytes. The most numerous animals are

ants and termites that scavenge on the

detritus

raining down

from above. A few rodent species gather fallen fruits and

nuts. Rare predators such as leopards, jaguars, smaller cats,

and large snakes hunt both on the ground and in the un-

derstory.

A tropical rain forest may produce as much as 90 tons

(81.6 metric tons) of

biomass

per acre (0.4 ha) per year,

and one might think that the soil that supports this incredible

growth is rich and fertile. However, the soil is old, acidic,

and nutrient-poor. Ages of incessant tropical rains and high

temperatures have depleted minerals, leaving an iron- and

Environmental Encyclopedia 3

Troposphere

The layered communities of a tropical rain for-

est are directly related to the gradual lessening

of light, from the brightness of the canopy to

the dense shade of the forest floor. (Illustration by

Hans & Cassidy.)

aluminum-rich podzol. Tropical forests have only about 10%

of their organic material and nutrients in the soil, compared

to boreal forests, which may have 90% of their organic mate-

rial in litter and sediments.

The interactions of

decomposers

and living plant

roots in the soil are, literally, the critical base that maintains

the rain forest

ecosystem

. Tropical rain forests are able to

maintain high productivity only through rapid

recycling

nutrients. The constant rain of detritus and litter that falls

to the ground is quickly decomposed by populations of

fungi

and bacteria that flourish in the warm, moist

environment

Some of these decomposers have symbiotic relationships

with the roots of specific trees. Trees have broad, shallow

root systems to capitalize on this surface

nutrient

source;

an individual tree might create a dense mat of superficial

roots 328 ft (100 m) in diameter and 3 ft (0.9 m) thick. In

this way, nutrients are absorbed quickly and almost entirely

and are reused almost immediately to build fresh plant

growth, the necessary base to the trophic pyramid of this

incredible ecosystem. See also Biodiversity

[William P. Cunningham Ph.D.]

1429

ESOURCES

OOKS

Caufield, C. In the Rainforest. New York: Knopf, 1985.

Hecht, S., and A. Cockburn. Fate of the Forest. New York: Harper Col-

lins, 1991.

Myers, N. The Primary Source: Tropical Forests and Our Future. New York:

Norton, 1992.

Revkin, A. The Burning Season: The Murder of Chico Mendes and the Fight

for the Amazon Rain Forest. New York: Houghton Mifflin, 1991.

ERIODICALS

Repetto, R. “Deforestation in the Tropics.” Scientific American 262 (April

1990): 36–42.

Tropopause

The tropopause is the upper boundary of the

troposphere

a layer of the earth’s

atmosphere

near the ground. In the

troposphere, the temperature generally decreases with in-

creasing altitude, with restricted exceptions called inversions.

However, at a height of about 6 mi (10 km) at the poles 9

mi (15 km) at the equator, the temperature abruptly becomes

constant with increasing altitude. This isothermal region is

called the

stratosphere

, and the interface between it and

the troposphere is called the tropopause. Mixing of air across

the tropopause is slow, occurring on a time scale of weeks

on the average, while tropospheric mixing is more rapid.

The existence of the stratosphere is largely caused by

the

absorption

solar energy

, mostly ultraviolet light,

by oxygen to form

ozone

. The balance of the heating is

caused by absorption of other parts of the solar spectrum by

other trace gases. See also Ultraviolet radiation

Troposphere

From the Greek word tropos, meaning turning, troposphere

is the zone of moisture-laden storms between the surface

and the

stratosphere

above. Because ice crystals must form

before precipitation can begin, the troposphere rises to 10–

12 mi (16–19 km) over the equator but grades downward

to 5–6 mi (8–9 km) over the poles. It is marked by a sharp

drop in temperature vertically, averaging 3.5 degrees per

1,000 ft (305 m) because of exponentially decreasing density

of air molecules. Actual “lapse” rates vary enormously, rang-

ing from inversions, where temperatures rise and trap pollut-

ants, to steep lapse rates with warm surface air topped by

very cold polar air; the latter produces dangerous storms.

Environmental Encyclopedia 3

Tsunamis

Tsunamis are large seismic sea waves that can cause major

destruction in coastal regions. A tsunami (Japanese for “wave

in bay") is caused by underwater seismic activity, such as an

earthquake

While tsunamis are commonly called “tidal waves,”

this is an erroneous term; these potentially catastrophic waves

have nothing to do with the tides. Tides are the up and

down movements of the sea surface at the shore, caused by

the gravitational attraction of the moon and sun on our

marine waters. Tsunamis are caused by the movements of

Earth’s crustal plates. Tides rarely cause major damage unless

they are associated with a storm, while tsunamis can cause

major loss of life and property.

It has been known for several hundred years that tsuna-

mis are caused by seismic movements of the ocean floor.

This occurs most commonly during submarine earthquakes,

underwater landslides, and perhaps volcanoes, all of which

release large amounts of energy. The sudden movement of

the earth’s crust caused by an underwater earthquake, for

example, displaces or moves the water above it. This causes

a high-energy wave to form, which is passed rapidly through

the water.

Tsunamis are very long waves, with a period (the time

for one complete wave to pass a fixed point) ranging from

six to 60 minutes. These waves typically travel 450 mi/h

(200 m/s or 720 km/h). Therefore, an earthquake in the

Gulf of Alaska could result in a tsunami hitting Hawaii less

than five hours later.

It is almost impossible to feel a tsunami out at sea in

deep water, however, the form of the wave changes when

it reaches shallow water. Since the water is shallower, the

bottom of the wave begins to “feel” the ocean bottom. The

friction that results causes the wave to slow down from about

450 mi/h (200 m/s) in very deep ocean water to 49 mi/h

(22 m/s) in water 164 ft (50 m) deep. While the front part

of the wave has been reduced in speed, the part at sea is

still moving in quickly. As a result, the energy of the wave

is compressed. As the wave enters shallow water, like that

in a bay, the crest rises. It quickly builds up vertically as the

wave moves onto the shore. This wall of water can be more

than 100 ft (30.5 m) high, in extreme cases. Since gravity

is acting on this huge wall of water, it cannot support itself

and crashes or breaks onto the land, similar to a normal

breaker in the surf zone of a beach. However, the huge

amounts of energy released by a breaking tsunami are many

times greater and more destructive than an ordinary breaker

at the beach, and the tsunami can literally destroy anything

in its path.

In Japan, where some of the most destructive tsunamis

have occurred, there have been cases in which whole fishing

1430

villages were devastated. However, the fishermen, who were

at sea plying their trade, did not feel the wave, which passed

right under them. They did not discover the disaster until

they returned home and found their homes and villages

destroyed. Because these villages were often located within

shallow bays, and the fishermen, being at sea, did not experi-

ence the wave, they assumed that the tsunami arose within

the bay. Therefore, these waves were called tsunamis or

“wave in bay.”

While scientists are not yet able to predict submarine

seismic activity with much

accuracy

, they can easily measure

such events when they occur. Scientists use this information

about the causes of tsunamis to predict when these destruc-

tive sea waves will occur. This is extremely important in

reducing loss of life and property. After the destructive 1946

tsunami that hit Hawaii, a group of tsunami early warning

stations was set up to monitor seismic activity throughout the

Pacific Ocean. The geographical and administrative center of

this monitoring system is in Honolulu, Hawaii. When an

earthquake, underwater

volcano

,or

landslide

is sensed, its

location is pinpointed. If a wave is generated and a change

in the water height is measured at a nearby tide-measuring

station, scientists can then accurately calculate the speed of

the wave to determine when the wave will make landfall.

The appropriate agencies can be alerted, and if necessary,

evacuations and other preparations can be made. This early

warning system has been very successful in reducing damage

caused by tsunamis. For example, there were no deaths from

a tsunami in Hawaii in 1957 because of an early warning,

even though the tsunami was over 26 ft (8 m) tall.

Before the warning systems existed, the first indication

of an approaching tsunami was the rapid movement of water

in a bay out to sea. This exposed areas of the bay bottom

that were rarely or never exposed. The water that rushed

offshore rose to build the huge crest of the wave that would

crash down a few minutes later.

Despite the success of the early warning systems, there

are some problems. For example, not all seismic activity

generates tsunamis; they more commonly result from shallow

focus earthquakes, where the actual point of crustal move-

ment is closer to the surface. It is during these earthquakes

that major crustal movement is most likely. Deep focus

earthquakes, which can be very strong but often result in

less crustal movement, are less likely to trigger tsunamis. It

has been estimated that only one out of ten large underwater

earthquakes causes damage. In addition, the chances of a

tsunami hitting any one spot directly and causing major

damage are relatively small because the energy in the form

of the tsunami is not passed along equally in all directions.

Finally, there may be other factors that reduce or enhance

chances of a tsunami striking. For example, major tsunamis

are rare in regions with wide continental shelves, such as

Environmental Encyclopedia 3

Turnover time

the Atlantic coast of the United States. A wide continental

shelf is thought to both reflect the wave (with the energy

being sent back out to sea) and absorb some of the energy

of the wave through friction as it drags along the bottom.

Thus, the early warning system, while essential, often gives

false alarms.

Tsunamis are more common in the Pacific Ocean than

other oceans of the world, primarily because there is so much

seismic activity at the perimeter of the Pacific Ocean, where

crustal plates meet. Thus, this region is where some of the

world’s most damaging tsunamis have occurred. For exam-

ple, one of the most dramatic and destructive tsunamis oc-

curred on August 27, 1883, when the volcanic island of

Krakatoa

, located in the Pacific Ocean, between Sumatra

and Java, exploded and disappeared. The wall of water

reached over 98 ft (30 m) in height and left catastrophic

damage to coastal areas in the Sundra Strait in its wake.

Over 36,000 people lost their lives. The energy from the

tsunami was still measurable after it crossed the Indian

Ocean, moved around the southern part of Africa, and

headed north through the Atlantic Ocean into the English

Channel. In addition to the tsunami, the sound of the explo-

sion was heard 3,000 mi (4,827 km) away, and the dust that

entered the

atmosphere

caused unusual sunsets for almost

a year.

In 1896 there was a major tsunami in Japan that killed

27,000 people along the coast. In 1964, there was an earth-

quake in Alaska and the resulting tsunami caused major

damage in some ports such as Kodiak and Seward. In addi-

tion, the tsunami traveled to the south, where four and a

half hours later, despite warnings, it killed additional people

and did major damage in Crescent City, California. A total

of 119 people died and damage to property amounted to

over $100 million.

Tsunamis also occur along the chain of Caribbean

islands and in the Mediterranean. Both of these places, like

the Pacific, are at the edges of Earth’s crustal plates where

earthquakes and other seismic activity are common.

[Max Strieb]

ESOURCES

OOKS

Knauss, J. A. Introduction to Physical Oceanography. Englewood Cliffs, New

Jersey: Prentice-Hall, Inc., 1978.

Neshyba, S. Oceanography: Perspectives on a Fluid Earth. New York: John

Wiley and Sons, 1987.

Tumors

see

Cancer; Neoplasm

1431

Tundra

Tundra is a generic term for a type of low-growing

ecosys-

tem

found in climatically stressed environments. Latitudinal

tundra occurs in the Arctic and Antarctic, environments

with cool and short growing seasons. Altitudinal tundra

occurs at the top of mountains, where the growing season

is cool, although it can be long. A major environmental

factor affecting tundra communities is the availability of

moisture. Wet meadows are dominated by hydric sedges

and grasses, while mesic sites are dominated by dwarf shrubs

and herbaceous

species

and dry sites by cushion plants and

lichens

Turbidity

Turbidity is a characteristic of water that describes the

amount of suspended solids in the water. Suspended solids

can be

phytoplankton

sediment

,or

detritus

Anthropo-

genic

causes of turbidity include

dredging

activities,

runoff

from agricultural and urban areas, and shoreline

erosion

Highly turbid water can prevent light from reaching plants

on the bottom or phytoplankton in the water column, and

can therefore reduce the amount of

primary productivity

in an aquatic system. High concentrations of suspended

solids can settle onto

submerged aquatic vegetation

(SAV) and can smother shellfish beds and fish spawning

grounds. Turbidity is measured as total suspended solids as

milligrams of solids per liter, or with an instrument called

a nephelometer, which measures the amount and angle of

light scattering that is caused by particles suspended in the

water.

[Marie H. Bundy]

Turnover time

Turnover time refers to the period of time during which

certain materials remain within a particular system. For ex-

ample, the protein that we get from food is broken down

by enzymes in our bodies and then resynthesized in a differ-

ent form. The time during which any one protein molecule

survives unchanged in the body is called the turnover time

for that molecule. Each component of an environmental

system also has a turnover time. On an average, for example,

a molecule of water remains in the

atmosphere

for a period

of 11.4 days before it falls to the earth as precipitation. See

also Chemicals

Environmental Encyclopedia 3

Turtle excluder device

Sea turtles

of several

species

are often accidentally caught

in a variety of fishing gear in many areas of the world,

including the southwest Atlantic and the shallow waters of

the Gulf of Mexico. Up to 12,500 turtles died annually as

a result of entanglement in shrimp trawl fishery alone. It

became a concern for the

commercial fishing

industry and

environmentalists alike since almost all sea turtles are endan-

gered, and the turtle excluder device (TED) was developed

in the mid-1980s in an effort to prevent turtles from entering

nets designed to catch other marine animals.

Turtle excluder device (TED) designs began as barrier

nets preventing turtles from being caught in the main net,

then modified to gate-like attachments. Three main within-

net designs are currently used. The model designed by the

National Marine Fisheries Service (NMFS) consists of an

addition in the throat of the trawl net, where the diameter

narrows toward the end where the catch is held. The addition

includes a diagonal deflator grid, that, once encountered by

a turtle, forces the animal upwards and out through a door

in the top of the net. The trap door is called a by-catch

reduction device or BRD. A second grid deflects other fish

out another BRD in the side of the net. Several other TEDs

are approved that are lighter and less expensive than the

NMFS design, all designed to eject turtles and other by-

catch through either the top or bottom of the net. Few

shrimp are lost in this process, while the capture of turtles

and other by-catch is reduced significantly.

Although TEDs are required by law on Mexican

shrimp fleets in the Pacific and the Gulf of Mexico, convinc-

ing United States fishing boats to adopt their use has been

a struggle. A law mandating the use of TEDs on shrimp

trawlers operating between March 1 and November 30 was

to have gone into effect in 1988, but the State of Louisiana

obtained an injunction against the order. Continued chal-

lenges brought by Louisiana and Florida, as well as political

lobbying and civil disobedience in the fishing community,

delayed implementation even further. In March 1993 the

final United States regulations were announced, making

TEDs mandatory in inshore waters, and in all waters by

December 1994. TEDS became mandatory for Australian

prawn trawlers in 2000, and tests conducted in 2001 show

that

bycatch

is reduced by more than 90%. An unforeseen

financial advantage was obtained by the use of TEDs in the

Australian prawn industry because the devices are believed

to reduce physical damage to the prawns from larger, heavier

animals that crush the catch during capture and sorting.

Even with the required TEDs, some 50,000 turtles are

caught annually during shrimp trawling.

[David A. Duffus and Marie H. Bundy]

1432

ESOURCES

OOKS

Hillestad, H. O., et al. “Worldwide Incidental Capture of Sea Turtles.” In

Biology and Conservation of Sea Turtles, edited by K. A. Bjorndal. Washing-

ton, DC: Smithsonian Institution Press, 1981.

Seidel, W. O. and C. McVea. “Development of a Sea Turtle Excluder

Shrimp Trawl in the Southeast U.S. Penaeid Shrimp Trawl.” In Biology

and Conservation of Sea Turtles, edited by K. A. Bjorndal. Washington,

DC: Smithsonian Institution Press, 1981.

ERIODICALS

Hinman, K. “The Real Cost of Shrimp on Your Plate.” Sea Frontiers 38

(February 1992): 14–19.

Williams, T. “The Exclusion of Sea Turtles.” Audubon 92 (January 1990):

24–30.

2,4-D

One of the nation’s most popular weed killers, the

herbicide

2,4-D (also known as 2,4-dichlorophenoxyacetic

acid

) has

been widely used by homeowners, timber companies, gov-

ernment agencies, farmers, and power companies to elimi-

nate unwanted vegetation from lawns,

golf courses

, forests,

rangelands

, rights-of-way, pastures, highways, and even

farmlands. Scientists and environmentalists have warned for

years of the chemical’s toxic effects, and Rachel Carson’s

classic book Silent Spring described its dangers to human

health and the

environment

. Subsequent studies have

linked 2,4-D to cancers, miscarriages, and

birth defects

animals and humans who have been exposed to it.

Agent

Orange

, a defoliant used during the Vietnam War, was a

50/50 mixture of 2,4-D and a similar herbicide,

2,4,5-T

For years environmentalists have urged that 2,4-D be banned

or strictly controlled, but the U.S.

Environmental Protec-

tion Agency

(EPA) has so far not acted to do so.

2,4,5-T

A broad-leaf

herbicide

, now banned for use in the United

States. Its full name is 2,4,5-trichlorophenoxyacetic

acid

After postemergence treatment it is readily absorbed by fo-

liage and roots and translocated throughout the plant. This

herbicide gained much notoriety during and after the Viet-

nam War because it was a component in the defoliant

Agent

Orange

, which has been implicated in

cancer

occurrence

in some war veterans. The

carcinogen

2,3,7,8-TCDD is

formed as a byproduct in the manufacture of 2,4,5-T. The

Environmental Protection Agency

(EPA) restricted the

use of 2,4,5-T in 1971, and suspended usage in 1979 follow-

ing concerns that it caused miscarriages in women living in

areas where application of 2,4,5-T had occurred.

Ublic health risk assessment

see

Risk assessment

Ultraviolet radiation

Radiation of the sun including ultraviolet A (UV-A, 320-400

nanometers) and ultraviolet B (UV-B, 280-320 nanometers).

Exposure to UV-A radiation, which is utilized in tanning

booths, damages dermal elastic tissue and the lens of the

eye, and causes

cancer

in hairless mice. Exposure to UV-B

induces breaks and other mutations in DNA and is associated

with basal and squamous cell carcinoma as well as melanoma.

The

ozone

layer of the earth’s

atmosphere

provides protec-

tion from ultraviolet radiation, but this protective layer is

becoming depleted due to the release of

chlorofluorocar-

bons

and other causes. See also Ozone layer depletion; Radia-

tion exposure

Uncertainty in science, statistics

Uncertainty in

statistics

is measured by the amount of error

in an estimate of the mean or average value of a population.

The sample mean is the average of a group of measurements

or parameters taken from the population, and the standard

deviation of the mean provides an estimate of the uncertainty

that any one measurement will represent the true mean of

the population. In

environmental science

, it is often very

difficult to make enough measurements of interacting pro-

cesses so that uncertainty in the estimate of the mean values

of important parameters is low enough to prove whether

hypotheses are correct or not. Baysian statistical analysis is

a statistical method that estimates the

probability

that a

hypothesis is true, then modifies and updates the probability

1433

as more studies are conducted and more information be-

comes available.

[Marie H. Bundy]

Underground storage tank

see

Leaking underground storage tank

Union of Concerned Scientists

Founded in 1969 by faculty and students at the Massachu-

setts Institute of Technology, the Union of Concerned Sci-

entists (UCS) promotes four core objectives: nuclear arms

reduction, a rational national security policy, safe

nuclear

power

, and energy reform. UCS utilizes research, public

education, and lobbying and litigation to achieve these goals.

UCS also operates a speakers’ bureau and publishes various

informational materials, including a quarterly magazine ad-

dressing various energy and nuclear power issues.

UCS has engaged in a variety of programs targeting

a wide range of people. One of the organization’s first large-

scale programs was the 1971

Atomic Energy Commission

hearings, in which UCS revealed major weaknesses in nu-

clear plant system designs. Throughout the 1980s, UCS

sponsored an annual Week of Education focusing on the

nuclear arms race. The program was targeted at college

students throughout the United States. In 1984 the group

conducted a study that revealed technical mistakes, high

costs, and other flaws in the United States Strategic Defense

Initiative (SDI). In 1989 the organization operated a Voter

Education Project which resulted in a television special fo-

cusing on what Americans expected from their next presi-

dent. The show was broadcast in both the United States

and the Soviet Union. That same year, UCS participated in

the International Scientific Symposium on a Nuclear Test

Ban. The organization also conducts research for the U.S.

Nuclear Regulatory Commission

Environmental Encyclopedia 3

United Nations Commission on Sustainable Development

UCS has also been involved in projects of a more

political nature. Most notable are its lobbying and litigation

programs which lobby Congress on various issues. The orga-

nization also provides expert testimony to congressional

committees and participates in legislative coalitions. In 1991

legal action brought by UCS resulted in the closing of the

Yankee Rowe Nuclear Power Plant in western Massachu-

setts, the oldest commercial nuclear power plant in the

United States. While the plant closed voluntarily, UCS was

instrumental in pressuring the plant to shut down. UCS

litigators have also targeted the Kozloduy nuclear reactors

in Bulgaria, citing safety concerns. Legislative programs have

focused on the United States’ B-2 Stealth bomber and SDI.

The organization claimed a victory at the end of 1991 when

the United States Congress voted to cut back on both the

B-2 and SDI projects.

While the core of UCS consists of field experts, the

group also maintains a strong volunteer base. UCS is made

up of three core groups: the Scientists’ Action Network, the

Legislative Alert Network, and the Professionals’ Coalition

for Nuclear Arms Control. The Scientists’ Network focuses

on public education and lobbying, the Legislative Network

informs UCS members of upcoming elections and laws, and

the Professionals’ Coalition promotes arms control education

and legislation. The Scientists’ Action Network relies on

volunteers to carry out its programs on the local level. Like-

wise the Legislative Alert Network utilizes volunteer support

in letter-writing and phone-call campaigns to members of

Congress. The Professionals’ Coalition for Nuclear Arms

Control, too, works with physicians, lawyers, and design

professionals throughout the United States to promote arms

control education and legislation.

[Kristin Palm]

ESOURCES

RGANIZATIONS

Union of Concerned Scientists, 2 Brattle Square, Cambridge, MA USA

02238-9105 (617) 547-5552, Fax: (617) 864-9405, Email: ucs@ucsusa.org,

<http://www.ucsusa.org>

United Nations Commission on

Sustainable Development

A committee of 53 nations created by the United Nations

General Assembly for the purpose of implementing recom-

mendations made during the 1992

United Nations Earth

Summit

in Rio de Janeiro. Its overriding goal is to develop

economies around the world while preserving the

environ-

ment

and existing

natural resources

. Major issues of inter-

est include

water quality

desertification

, forest and

spe-

1434

cies

protection, toxic

chemicals

, and atmospheric and

oceanic

pollution

Chaired by Malaysian representative Razalie Ismail,

the commission endeavors to put into action the specific

policies of Agenda 21, a United Nations plan aimed at stop-

ping—or at least slowing down—global

environmental

degradation

. The United States has taken a strong leader-

ship role in supporting the commission’s objectives. Under

President Bill Clinton and Vice President Albert Gore, the

President’s Council on Sustainable Development

was

created to balance environmental policies with sound eco-

nomic development within this country.

With the formation of the commission, several devel-

oping countries have raised concerns that the group will

withhold financial aid to them based on their environmental

practices. Likewise, the more developed countries (MDC)

worry that money and technology allotted to the

less devel-

oped countries

(LDC) will go toward other needs rather

than towards protecting the environment. The commission

has no legal authority to enforce any of its policies but relies

on publicity and international pressure to achieve its goals.

ESOURCES

RGANIZATIONS

Secretariat of the United Nations Commission on Sustainable

Development, United Nations Plaza, Room DC2-2220, New York, NY

USA 10017 (212) 963-3170, Fax: (212) 963-4260, Email: dsd@un.org,

<http://www.un.org/esa/sustdev/csd.htm>

United Nations Conference on

Environment and Development

see

United Nations Earth Summit (1992)

United Nations Conference on the

Human Environment (1972)

Held in Stockholm in 1972, the United Nations Conference

on the Human Environment was the first global environ-

mental conference and the precursor to the 1992

United

Nations Earth Summit

in Rio de Janeiro, Brazil.

The purpose of the conference was not to discuss

scientific or technological approaches to environmental

problems but to coordinate international policy. A 27-nation

committee held four meetings in the two years preceding

the conference, and in the months leading up to it they

issued a report calling for “a major reorientation of man’s

values and redeployment of his energies and resources.” In

their preliminary report, the committee emphasized their

political priorities: “The very nature of environmental prob-

Environmental Encyclopedia 3

United Nations Division for Sustainable Development

lems—that is to say, their intricate interdependence—is such

as to require political choices.”

There was a remarkable lack of divisiveness, once the

conference began, on most issues under consideration. The

Soviet Union and the Eastern bloc did not attend because

East Germany, which was not a member of the United

Nations, had been denied full representation. But 114 of

the 132 member countries of the United Nations were there,

and the sessions were distinguished by what the New York

Times called a “groundswell of unanimity.” A number of

resolutions passed without a dissenting vote.

Many believe the most important result of the

conference was the precedent it set for international cooper-

ation in addressing

environmental degradation

. The

nations attending agreed that they shared responsibility

for the quality of the environment, particularly the oceans

and the

atmosphere

, and they signed a declaration of

principles, after extensive negotiations, concerning their

obligations. The conference also approved an environmental

fund and an “action program,” which involved 200 specific

recommendations for addressing such problems as global

climatic change,

marine pollution

population growth

the dumping of toxic wastes, and the preservation of

biodiversity

. A permanent environmental unit was estab-

lished for coordinating these and other international efforts

on behalf of the environment; the organization that became

the United Nations Environmental Programme was for-

mally approved by the General Assembly later that same

year and its base established in Nairobi, Kenya. This

organization has not only coordinated action but monitored

research, collecting and disseminating information, and it

has played an ongoing role in international negotiations

about environmental issues.

The conference in Stockholm accomplished almost

everything the preparatory committee had planned. It was

widely considered successful, and many observers were al-

most euphoric about the extent of agreement. In a speech

to the nations gathered in Stockholm, the anthropologist

Margaret Mead called the event “a revolution in thought

fully comparable to the Copernican revolution by which,

four centuries ago, men and women were compelled to revise

their whole sense of the earth’s place in the cosmos. Today

we are challenged to recognize as great a change in our

concept of man’s place in the biosphere.”

There were, however, some dissenting voices. Shirley

Temple Black and others formally protested the fact that

women were not fully represented at the gathering; only 11

delegations of the 114 nations represented included even one

woman. A large “counterconference” was held in Stockholm,

consisting of a number of scientific and political organiza-

tions, and environmentalists such as

Barry Commoner

ar-

gued that the official conference, though valuable, had failed

1435

to address the subjects that were most important to solving

the current environmental crisis, particularly poverty and

what he called “ecologically sound ways of producing goods.”

[Douglas Smith]

United Nations Division for

Sustainable Development

This United Nations division serves as the secretariat, or

the research staff, of the UN Commission on

Sustainable

Development

, whose representatives meet periodically to

develop policies for sustainable development in 40 coun-

tries. The division comprises 30 program officers working

in specific sectors: health, human settlements, freshwater

resources, toxic

chemicals

, hazardous wastes, solid wastes,

and radioactive wastes. According to Andre

Vasilyev, First

Officer, it prepares studies and analytical reports and

conducts research to support the work of the Commission.

It also measures the progress of and makes recommenda-

tions for development programs. The division’s stated

mission is to contribute to sustainable development world-

wide by working to implement Agenda 21, the Rio

Declaration on Environment and Development, the Forest

Principles (a United Nations statement of principles for

a global consensus on the management,

conservation

and sustainable development of all types of forests), and

the Global Programme of Action for Sustainable Develop-

ment of Small Island Developing States (SIDS). The

division carries out multi-year work programs on sustain-

able development indicators, changing consumption and

production patterns, and the transfer of environmentally

sustainable technology.

The Commission was established in 1992 as an adjunct

to Agenda 21, the plan of action for environmental sus-

tainability adopted at the United Nations Conference on

Environment and Development (UNCED) in Rio de Ja-

neiro. Its charge is to ensure that decisions made at UNCED

are carried out at national, regional and international levels,

and to further international cooperation and decision-mak-

ing on these issues.

The full Commission meets once a year. Ad hoc work-

ing groups meet periodically to address specific issues, in-

cluding trade and environmental development, consumption

patterns, financial resources, and technology transfer. Open-

ended working groups address such issues as integrated man-

agement of land resources, forests, combating

desertifica-

tion

, sustainable mountain development,

sustainable agri-

culture

, rural development, and biological diversity.

In recent years, the Commission has examined numer-

ous strategies to promote sustainable development: trading

debt for sustainable development, creating environmental

Environmental Encyclopedia 3

United Nations Earth Summit (1992)

user charges for air transport, implementing the Convention

on Biological Diversity and the Convention to Combat De-

sertification, and developing tools for integrated land man-

agement. In the spring of 1997, the full commission met to

conduct a five-year review of the results of UNCED.

[Carol Steinfeld]

ESOURCES

RGANIZATIONS

Division for Sustainable Development/DESA, United Nations Plaza,

Room DC2-2220, New York , NY USA 10017 (212) 963-3170, Fax:

(212) 963-4260, Email: dsd@un.org, <http://www.un.org/esa/sustdev/

dsdgen.htm>

United Nations Earth Summit (1992)

For 12 days in June 1992, more than 35,000 environmental

activists, politicians, and business representatives, along with

9,000 journalists, 25,000 troops, and uncounted vendors,

taxi drivers, and assorted others converged on Rio de Janeiro,

Brazil for the United Nations Conference on

Environment

and Development. Known as the Earth Summit, this was

the largest environmental conference in history; in fact, it

was probably the largest non-religious meeting ever held.

Like a three-ring environmental circus, this conference

brought together everyone from pin-striped diplomats to

activists in bluejeans and indigenous Amazonian people in

full ceremonial regalia. One cannot say yet whether the

conventions and treaties discussed at this summit meeting

will be effective, but they have the potential to make this

the most important environmental meeting ever held.

The first

United Nations Conference on the Human

Environment

met in Stockholm in 1972, exactly 20 years

before the Rio de Janeiro meeting. Called by the industrial-

ized nations of Western Europe primarily to discuss their

worries about transboundary

air pollution

, the Stockholm

conference had little input from

less developed countries

and almost no representation from non-governmental orga-

nizations (NGOs). Some major accomplishments came out

of this conference, however, including the

United Nations

Environment Programme

, the Global

Environmental

Monitoring

System, the Convention on International Trade

Endangered Species

(CITES), and the World Heritage

Biosphere Reserve Program, which identifies particularly

valuable areas of biological diversity. A companion book to

the Stockholm Conference entitled Only One Earth was

written by Rene

Dubos and Barbara Ward.

In 1983 the United Nations established an indepen-

dent commission to address the issues raised at the Stock-

holm conference and to propose new strategies for global

environmental protection. Chaired by Norwegian Prime

1436

Minister

Gro Harlem Brundtland

, the commission spent

four years in hearings and deliberations. A significantly

greater voice for the developing world was heard as it became

apparent that environmental problems affected the poor

more than the rich. The commission’s final report, published

in 1987 as

Our Common Future

, is notable for coining the

term “

sustainable development

” and for linking environ-

mental problems to social and economic systems.

In 1990 preparations for the Earth Summit began.

Maurice Strong, the Canadian environmentalist who chaired

the Stockholm conference, was chosen to lead once again.

A series of four working meetings called PrepComs were

scheduled to work out detailed agendas and agreements to

be ratified in Rio de Janeiro. The first PrepCom met in

Nairobi, Kenya, in August 1990. The second and third meet-

ings were in Geneva, Switzerland, in March and August

1991. The fourth and final PrepCom convened in New York

City, in March 1992. Twenty-one issues were negotiated at

these conferences including

biodiversity

climate

change,

deforestation

environmental health

, marine resources,

ozone

, poverty, toxic wastes, and urban environments. No-

tably, population crisis was barely mentioned in the docu-

ments because of opposition by religious groups.

Intense lobbying and jockeying for power marked the

two-year PrepCom process. As the date for the Rio de

Janeiro conference neared, it appeared that several significant

treaties would be ratified in time for presentation to the

world community. Among these were treaties on climate

change, biological diversity, forests, and a general

Earth

Charter

, which would be an environmental bill of rights

for all people. A comprehensive 400-page document called

Agenda 21 presented a practical action plan spelling out

policies, laws, institutional arrangements, and financing to

carry out the provisions of these and other treaties and con-

ventions. Chairman Strong estimated that it would take

$125 billion per year in aid to help the poorer nations of

the world protect their environment.

In the end, however, the United States refused to

accept much of the PrepCom work. During PrepCom IV

in New York City, for instance, 139 nations voted for manda-

tory stabilization of

greenhouse gases

at 1990 levels by

the year 2000, laying the groundwork for what promised to

be the showcase treaty of the Earth Summit. Only the United

States delegation opposed it, but after behind-the-scenes

arm twisting and deal-making, the targets and compulsory

aspects of the treaty were stripped away, leaving only a weak

shell to take to Rio de Janeiro. Many environmentalists

felt betrayed. Similarly, the United States, alone among the

industrialized world, refused to sign the biodiversity treaty,

the forest protection convention, or the promise to donate

0.7% of Gross Domestic Product to less developed countries

for environmental protection. The nation’s excuse was that