Environmental Encyclopedia

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Environmental Encyclopedia 3

Atomic Energy Commission

The deposition of acidified snow or rain can result

in the

acidification

of vulnerable surface waters. This is

particularly the case of streams, rivers, ponds, and lakes that

have low concentrations of alkalinity and consequently little

capacity for neutralizing inputs of acidity. Acidification may

also be caused by the dry deposition of certain gases, espe-

cially sulfur dioxide and oxides of nitrogen. After they are

dry-deposited, these gases become oxidized in soil or water

into the ions sulfate and nitrate, respectively, a process ac-

companied by the production of equivalent amounts of hy-

drogen ions. In some environments the gaseous concentra-

tions of sulfur dioxide and oxides of nitrogen are relatively

high, particularly in areas polluted by gaseous emissions

from large numbers of automobiles,

power plants

, or other

industries. In those circumstances the dry deposition of acid-

ifying substances will be a much more important cause of

environmental acidification than the wet deposition of acidic

precipitation.

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Freedman, B. Environmental Ecology. San Diego, CA: Academic Press,

1995.

Joskow, P.L., A.D. Ellerman, R. Schmalensee, M. Juan-Pablo, and E.M.

Bailey, editors. Markets for Clean Air: The U.S. Acid Rain Program. Cam-

bridge, UK: Cambridge University Press, 2000.

RGANIZATIONS

United States Environmental Protection Agency, Clean Air Markets

Division, 1200 Pennsylvania Avenue, NW, Washington, D.C. USA 20460

(202) 564-9150, Email: , http://www.epa.gov/airmarkets/acidrain/

Worldwatch Institute, 1776 Massachusetts Ave., N.W., Washington, D.C.

USA 20036-1904 (202) 452-1999, Fax: (202) 296-7365, Email:

worldwatch@worldwatch.org, http://www.worldwatch.org/

Atmospheric inversion

Atmospheric inversions are horizontal layers of air that in-

crease in temperature with height. Such warm, light air often

lies over air that is cooler and heavier. As a result the air

has a strong vertical

stability

, especially in the absence of

strong winds.

Atmospheric inversions play an important role in

air

quality

. They can trap air pollutants below or within them,

causing high concentrations in a volume of air that would

otherwise be able to dilute air pollutants throughout a large

portion of the

troposphere

Atmospheric inversions are quite common, and there

are several ways in which they are formed. Surface inversions

can form during the evening when the radiatively cooling

ground becomes a heat sink at the bottom of an air mass

immediately above it. As a result heat flows down through

the air which sets up a temperature gradient that coincides

with an inversion. Alternatively, relatively warm air may flow

over a cold surface with the same results.

Elevated atmospheric inversions can occur when verti-

cal differences in wind direction allow warm air to set up over

cold air. However, it is more common in near-subtropical

latitudes, especially on the western sides of continents, to get

subtropical

subsidence

inversions. Subtropical subsidence

inversions often team with mountainous

topography

trap air both horizontally and vertically. This is the situation

on the coast of southern and central California.

Atmospheric pollutants

see

Carbon monoxide; Nitrogen oxides;

Particulate; Smog; Sulfur dioxide; Volatile

organic compound

Atomic bomb

see

Nuclear weapons

Atomic bomb testing

see

Bikini atoll; Nevada Test Site

Atomic energy

see

Nuclear power

Atomic Energy Commission

The Atomic Energy Commission (AEC) was established

by act of the United States Congress in 1946. It originally

had a dual function: to promote the development of

nuclear

power

and to regulate the nuclear power industry. These

two functions were occasionally in conflict, however. Critics

of the AEC claimed that the Commission sometimes failed

to apply appropriate safety regulations, for example, because

doing so would have proved burdensome to the industry and

hindered its growth. In 1975, the AEC was dissolved. Its

regulatory role was assigned to the

Nuclear Regulatory

Commission

and its research and development role to the

Energy Research and Development Administration

Atomic fission

see

Nuclear fission

Atomic fusion

see

Nuclear fusion

Environmental Encyclopedia 3

Atrazine

Atrazine is used as a selective preemergent

herbicide

crops, including corn, sorghum, and sugar cane, and as a

nonselective herbicide along fence lines, right-of-ways, and

road sides. It is used in a variety of formulations, both alone

and in combination with other herbicides. In the United

States it is the single most widely used herbicide, accounting

for about 15% of total herbicide application by weight. Its

popularity stems from its effectiveness, its selectivity (it in-

hibits

photosynthesis

in plants lacking a

detoxification

mechanism), and its low mammalian toxicity (similar to that

of table salt). Concern over its use stems from the fact that

a small percentage of the amount applied can be carried by

rainfall into surface waters (stream and lakes), where it may

inhibit the growth of plants and algae or contaminate

drink-

ing-water supply

. Because atrazine is classified as a possible

human

carcinogen

, the United States

Environmental Pro-

tection Agency

(EPA) has limited its concentration in

drinking water to 3 ␮g/L.

Attainment area

An attainment area is a politically or geographically defined

region that is in compliance with the National Ambient Air

Quality Standards, as set by the

Environmental Protection

Agency

(EPA). A region is considered to be an attainment

area if it does not exceed the specified thresholds for air

pollutants that may be a threat to public health. The stan-

dards are set for a variety of ambient air pollutants, including

particulates,

ozone

carbon monoxide

, sulfur oxides, and

nitrogen oxides

. A region can be an attainment area for

one pollutant and a

nonattainment area

for another.

John James Audubon (1785 – 1851)

American naturalist, artist, and ornithologist

John James Audubon, the most renowned artist and natural-

ist in nineteenth century America, left a legacy of keenly

observant writings as well as a portfolio of exquisitely ren-

dered paintings of the birds of North America.

Born April 26, 1785, Audubon was the illegitimate

son of a French naval captain and a domestic servant girl

from Santo Domingo (now Haiti). Audubon spent his child-

hood on his father’s plantation in Santo Domingo and most

of his late teens on the family estate in Mill Grove, Pennsyl-

vania—a move intended to prevent him from being con-

scripted into the Napoleonic army.

Audubon’s early pursuits centered around natural his-

tory, and he was continuously collecting and drawing plants,

insects, and birds. His habit of keeping meticulous field notes

of his observations at a young age. It was at Mill Grove that

Audubon, in order to learn more of the movements and habits

of birds, tied bits of colored string onto the legs of several

Eastern Phoebes and so proved that these birds returned to

the same nesting sites the following year. Audubon was the

first to use banding to study the movement of birds.

While at Mill Grove, Audubon began courting their

neighbor’s eldest daughter, Lucy Bakewell, and they were

married in 1808. They made their first home in Louisville,

Kentucky, where Audubon tried being a storekeeper. He

could not stand staying inside, and so he spent most of his

time afield to “supply fowl for the table,” thus dooming the

store to failure.

In 1810, Audubon met by chance Alexander Wilson,

who is considered the father of American ornithology. Wil-

son had finished much of his nine volume American Ornithol-

ogy at this time, and it is believed that his work inspired

Audubon to embark on his monumental task of painting

the birds of North America.

The task that Audubon undertook was to become The

Birds of America. Because Audubon decided to depict each

species

of bird life-size, thus rendering each on a 36.5 in

x 26.5 in (93 cm x 67 cm) page, this was the largest book

ever published up until that time. He was able to draw

even larger birds such as the

whooping crane

life-size by

depicting them with their heads bent to the ground. Audu-

bon pioneered the use of fresh models instead of stuffed

museum skins for his paintings. He would shoot birds and

wire them into life-like poses to obtain the most accurate

drawings possible. Even though his name is affixed to a

modern

conservation

organization, the

National Audu-

bon Society

, it must be remembered that little thought was

given to the conservation of birds in the early nineteenth

century. It was not uncommon for Audubon to shoot a dozen

or more individuals of a species to get what he considered the

perfect one for painting.

Audubon solicited subscribers for his Birds of America

to finance the printing and hand-coloring of the plates.

The project took nearly twenty years to complete, but the

resulting double elephant folio, as it is known, was truly a

work of art, as well as the ornithological triumph of the

time. Later in his life, Audubon worked on a book of the

mammals of North America with his two sons, but failing

health forced him to let them complete the work. He died

in 1851, leaving behind a remarkable collection of artwork

that depicted the natural world he loved so much.

[Eugene C. Beckham]

ESOURCES

OOKS

Audubon, J. J. Audubon’s Western Journal: 1849–1850. Irvine: Reprint Ser-

vices, 1992.

Environmental Encyclopedia 3

Australia

John James Audubon. (Corbis-Bettmann. Repro-

duced by permission.)

———. Life of John James Audubon: The Naturalist. Irvine: Reprint Ser-

vices, 1993.

Running Press Staff, eds. Audubon Journal. Philadelphia: Running Press,

1993.

ERIODICALS

Gopnik, A. “Audubon’s Passion.” The New Yorker 67 (25 February 1991):

96–104.

Audubon Society

see

National Audubon Society

Australia

The Commonwealth of Australia, a country in the South

Pacific Ocean, occupies the smallest continent and covers an

area of 2,966,200 mi

(7,682,000 km

). Along the northeast

coast of Australia, for a distance of 1,200 mi (2,000 km) in

length and offshore as much as 100 mi (160 km) into the

Pacific Ocean, lies the

Great Barrier Reef

, the greatest

assemblage of coral reefs in the world. The island of Tasma-

nia, which is a part of Australia, lies off the southeast coast

of the mainland. Australia consists mainly of plains and

plateaus, most of which average 2,000 ft (600 m) above sea

level. There are several low mountain ranges in the country.

Only about 16 million people live in Australia, of whom

about 150,000 are native people, the Aborigines.

More than a third of Australia receives under 10 in

(25 cm) of annual rainfall, while less than a third receives

over 20 in (51 cm). Many areas experience prolonged

drought

and frequent heat waves. The Outback is one such

area. It is comprised of dry, barren land and vast interior

deserts. Soils generally are poor, with fertile land found only

in the lowlands and valleys near the east and southeast coast.

The largest river is the Murray River in southeastern Austra-

lia. In the inland area, few rivers have much water due to

the lack of rainfall. In areas with coastal highlands, rivers

flow only a short distance to the sea. Lakes frequently dry

up and become beds of salt. In contrast, there are lush rain

forests in the north and snowy mountains in the southeastern

Blue Range.

The most common tree is the eucalyptus, of which

there are at least 600 different kinds. Since Australia is the

driest of the inhabited continents, there are few forests. The

acacia, or wattle, is Australia’s national flower. Many of the

mammals of Australia (kangaroos, wallabies, and koala bears)

are marsupials, unlike those found anywhere else in the

world. The young of marsupials are born premature and

require continued development outside the womb in pouches

on the parent’s body. The egg-laying mammal, or mono-

treme, is also only found in Australia. There are two

species

of monotreme: the duck-billed platypus and the echidna,

or spiny anteater. The most famous Australian bird is the

kookaburra. There are no hoofed animals in Australia. Two

flightless birds, the emu and the cassowary, also are found

only in Australia. Snakes are common and include many

poisonous species. Two kinds of

crocodiles

are found in

the northern part of Australia. All of these unique

fauna

and

flora

species have evolved due to the long separation

of the Australian continent from southeast Asia and a general

lack of predators.

The goal of environmental protection and manage-

ment in Australia is integration of the principles of ecologi-

cally

sustainable development

into policies and programs

encompassing all aspects of environmental issues.

Australia’s land resources form the basis of its unique

natural heritage and its agricultural industry. However, prob-

lems of land degradation are widespread. Land degradation

due to dryland

salinity

is a national problem that threatens

both

biodiversity

and agricultural productivity. Dryland

salinity affects about 5,434,000 acres (2.2 million ha) of

once-productive agricultural land and costs an estimated

$243 million per year in lost agricultural production. Dryland

salinity originates from salt deposited in the landscape over

millions of years due to marine

sedimentation

. Land clear-

ing over the last two hundred years and the replacement of

deep-rooted perennial native vegetation with shallow-rooted

Environmental Encyclopedia 3

Australia

annuals have caused water tables to rise, bringing saline

water close to the surface into the root zones of plants.

Excessive

irrigation

has also led to increases in levels of

water tables. Strategies to address this problem include re-

search for the prediction, prevention, and reversal of dryland

salinity. An example of a research effort to ameliorate the

effects of salinity is a project that addresses the identification

of salt-tolerant plant species and development of appropriate

establishment and growth management techniques to ensure

their survival. Australia’s naturally fire-adapted

ecosystem

has frequent brushfires that now threaten many new develop-

ments and even major cities. Other land degradation prob-

lems being addressed include the

rehabilitation

of mining

sites and

remediation

of sites contaminated by railway oper-

ations.

Australia contains about 10% of the world’s biological

diversity. The Commonwealth is addressing the issues of

loss of biodiversity through a program referred to as the

National Vegetation Initiative (NVI). About 988 million

acres (40 million ha) of land is protected within a terrestrial

reserves system, but 1,235 million acres (500 million ha), or

more than two-thirds of Australia’s land area, are managed

by private landholders. Biodiversity outside the reserves has

been affected by vegetation clearance and modification. The

NVI will attempt to reverse the long-term decline in the

quality and extent of Australia’s native vegetation by devel-

oping programs and incentives to conserve, enhance, and

manage remnant native vegetation; to increase revegetation

activities; and to encourage the integration of native vegeta-

tion into conventional farming systems.

The state of Australia’s rivers and other aquatic systems

has been declining due to a range of factors. Unsustainable

water extractions for agricultural production have resulted

in reduced flows in rivers that result in blue-green algae

outbreaks, declines in native fish populations, increases in

salinity, loss of

wetlands

, and loss of the beneficial aspects

of small floods. Research is being conducted to define envi-

ronmental flow requirements so that water allocations or

entitlements will include environmental needs as a legitimate

use. Other factors affecting the decline in aquatic systems

include poor land and vegetation management, agricultural

and urban

pollution

, salinity, destruction of native

habitat

and spread of exotic pests such as the European carp and

the water weed Salvinia.

In a 1997 Australian Bureau of

Statistics

survey, the

Australian people identified

air pollution

as their greatest

environmental concern. The government’s primary

air qual-

ity

objective is to provide all Australians with equivalent

protection from air pollution, which will be achieved by the

development of national air quality strategies and standards

that minimize the adverse environmental impacts of air pol-

lution. Since over 60% of the Australian population lives in

100

cities, the Government’s first priority is to develop measures

to reduce the impact of air pollution on urban areas.

The government of Australia considers

climate

changes as another of its most important environmental

issues. A National Greenhouse Response Strategy was

adopted in 1992 to respond to the need for greenhouse gas

emission

mitigation. The major thrust of the program is to

develop cooperative agreements with industry to abate and

reduce greenhouse gas emissions. In addition, large scale

vegetation plantings for improvement of land resources will

reduce

carbon dioxide

, a major greenhouse gas, in the

atmosphere

Methane

emission from intensive agriculture

will be reduced through livestock waste treatment. The use

of alternative transport fuels such as liquefied

petroleum

gas, compressed

natural gas

ethanol

, and other alcohol

blends will be encouraged through the use of a fuel excise

exemption.

Although

ozone layer depletion

in the atmosphere

occurs over most of the Earth, the most dramatic changes

are seen when an

ozone

“hole” forms over

Antarctica

each

spring. The ozone layer protects life on Earth from harmful

ultraviolet radiation

from the sun, but it can be depleted

by the use of some widely used ozone-depleting

chemicals

The ozone hole sometimes drifts over Australia and exposes

residents to dangerous levels of UV radiation. Australia,

because of its proximity to Antarctica, has taken a leading

role in ozone protection and has been influential in the

development and implementation of cost-effective mecha-

nisms to ensure the phase-out of use of ozone-depleting

substances by all countries. The government also monitors

solar ultraviolet radiation levels and assesses the conse-

quences for public health.

Australia’s marine and coastal environments are rich

in natural and cultural resources, are adjacent to most of the

nation’s population (about 86%), and are a focus of much

of Australia’s economic, social, tourism, and recreational

activity. Australia’s

Exclusive Economic Zone

(EEZ) is one

of the largest in the world, comprising 4.25 million mi

(11

million km

) of marine waters. Uncoordinated and ad hoc

development has been identified as a major contributing

factor to the decline of coastal

water quality

and marine

and estuarine habitats. Programs that include cooperation

of the Commonwealth government with state and local gov-

ernments, industry groups, nongovernmental organizations,

and the community have been developed to protect and

rehabilitate these environments. These programs include ad-

dressing threats to coastal water quality and marine biodiver-

sity from land-based and

marine pollution

; developing inte-

grated management plans for the

conservation

and

sustainable use of coastal resources, including fisheries re-

sources; supporting capital works and improvement of tech-

nologies to reduce the impacts of sewage and stormwater;

Environmental Encyclopedia 3

Automobile

controlling the introduction and spread of exotic marine

pests in Australian waters; protecting and restoring fish habi-

tats; and supporting comprehensive and consistent coastal

monitoring.

The Great Barrier Reef is facing growing pressures

from the reef-based tourism industry, commercial and recre-

ational fishing (which is worth about $1.3 billion per year),

expanding coastal urban areas, and downstream effects of

land use

from agricultural activities. Several programs are

being developed and implemented to ensure that activities

can continue on an ecologically sustainable basis. For exam-

ple, tourist and recreational impacts are being reduced while

providing diverse tourist activities. Fishing catches and ef-

forts are being monitored, major or critical habitats are being

identified, and fishing by-catch is being reduced through

the development of new methods.

Sediment

nutrient

, and

other land-based

runoff

that impacts the health of adjacent

marine areas are being controlled in coastal developments.

Also, spill contingency planning and other responses to pre-

vent pollution from ships, navigational aids, and ship re-

porting systems are all being improved. In addition, the state

of water quality is being monitored in long-term programs

throughout the Reef and threats from pollution are being

assessed. Finally, all planning exercises include consultation

with Aboriginal and Torres Strait Islander (ATSI) commu-

nities to ensure that their interests are considered.

The Commonwealth, through its National and World

Heritage programs, is protecting elements of Australia’s nat-

ural and cultural heritage that are of value for this and

future generations

. The National Estate comprises natural,

historic, and indigenous places that have aesthetic, historic,

scientific or social significance or other special value. The

listed. The Register educates and alerts Australians to places

of heritage significance. World Heritage properties are areas

of outstanding universal cultural or national significance that

are included in the

UNESCO

World Heritage List. In 1997,

there were 11 Australian properties on the World Heritage

List, including the Great Barrier Reef.

[Judith L. Sims]

ESOURCES

OOKS

Hill, R. Investing in Our Natural Heritage. Canberra, Australia: Annual

Report on the Commonwealth’s Environment Expenditure, Minister for

the Environment, 1997.

Autecology

A branch of

ecology

emphasizing the interrelationships

among individual members of the same

species

and their

101

environment

. Autecology includes the study of the life his-

tory and/or behavior of a particular species in relation to the

environmental conditions that influence its activities and

distribution. Autecology also includes studies on the toler-

ance of a species to critical physical factors (e.g., temperature,

salinity

, oxygen level, light) and biological factors (e.g.,

predation,

symbiosis

) thought to limit its distribution. Such

data are gathered from field measurement or from controlled

experiments in the laboratory. Autecology contrasts with

synecology, the study of interacting groups (i.e., communities)

of species.

Automobile

The development of the automobile at the end of the nine-

teenth century fundamentally changed the structure of soci-

ety in the developed world and has had wide-ranging effects

on the

environment

, the most notable being the increase of

air pollution

in cities. The piston-type internal

combustion

engine is responsible for the peculiar mix of pollutants that

it generates. There are a range of other engines suitable for

automobiles, but they have yet to displace engines using

rather volatile

petroleum

derivatives.

The simplest and most successful way of improving gas-

eous emissions from automobiles is to find alternative fuels.

Diesel fuels have always been popular for larger vehicles, al-

though a few private vehicles in Europe are also diesel-pow-

ered. Compressed natural gases have been widely used as fuel

in some countries (e.g., New Zealand), while

ethanol

has had

a limited success in places such as Brazil, where it can be pro-

duced relatively cheaply from sugar cane. There is some en-

thusiasm for the use of

methanol

in the United States, but it

has yet to be seen if this will be widely adopted as a fuel.

Others have suggested that fundamental changes to

the engine itself can lower the impact of automobiles on

air

quality

. The Wankel rotary engine is a promising power

source that offers both low vibration and pollutant emissions

from a relatively lightweight engine. Although Wankel en-

gines are found on a number of exotic cars, there are still

doubts about long-term engine performance and durability

in the urban setting. Steam and gas turbines have many of

the advantages of the Wankel engine, but questions of their

expense and suitability for automobiles have restricted their

use. Electric vehicles have had some impact for special sectors

of the market. They have proved ideal for small vehicles

within cities where frequent stop-start operation is required

(e.g., delivery vans). A few small, one-seat vehicles have

been available at times, but they have failed to achieve any

enduring popularity. The electric vehicle suffers from low

range, low speed and acceleration, and needs heavy batteries.

However these vehicles produce none of the conventional

Environmental Encyclopedia 3

Automobile emissions

combustion-derived pollutants during operation, although

the electricity to recharge the batteries requires the use of

an electricity generating station. Still, electricity generation

can be sited away from the urban center and employ air

pollution

controls.

Fuel cells

are an alternate source of elec-

tricity for electric automobiles. It is also possible to power

automobiles through the use of flywheels. These are driven

up to high speeds by a fixed, probably electric, motor, then

the vehicle can be detached and powered using the stored

momentum, although range is often limited.

Although

automobile emissions

are of great con-

cern, the automobile has a far wider range of environmental

impacts. Large amounts of material are used in their con-

struction, and discarded automobiles can litter the country-

side and fill waste dumps. Through much of the twentieth

century the vehicles have been made of steel. Increasingly,

other materials, such as

plastics

and fiberglass, are used as

construction materials. A number of projects, most fre-

quently on the European continent, have tried

recycling

automobile components. Responsible automobile manufac-

turers are aiming to build vehicles with longer road lives,

further aiding

waste reduction

The high speeds now possible for automobiles lead to

sometimes horrendous accidents, which can involve many

vehicles on crowded highways. The number of accidents have

been reduced through anti-lock braking systems, thoughtful

road design, and imposing harsh penalties for drunk driving.

In the future, on-board radar may give warning of impending

collisions. Safety features such as seat belts, padding, and

collapsible steering columns have helped lower injury during

accidents.

The structure of cities has changed with widespread

automobile ownership. It has meant that people can live

further away from where they work or shop. The need for

parking has led to the development of huge parking lots

within the inner city. Reaction to crowding in city centers

are seen in the construction of huge shopping centers out-

of-town, where parking is more convenient (or strip develop-

ment of large stores along highways). These effects have

often caused damage to inner city life and disenfranchised

non-car owners, particularly because a high proportion of

car ownership often works against the operation of an effec-

tive

mass transit

system. For people who live near busy

roads,

noise pollution

can be a great nuisance. The country-

side has also been transformed by the need for super high-

ways that cope with a large and rapid traffic flow. Such

highways have often been built on valuable agricultural land

or natural habitats, and once constructed, create both practi-

cal and aesthetic nuisances.

[Peter Brimblecombe]

102

ESOURCES

OOKS

Environmental Effects of Automotive Emissions. Paris: OECD Compass

Project, 1986.

Automobile emissions

The

automobile

, powered by piston-type internal

combus-

tion

engine, is so widely used that it has become the domi-

nant source of air pollutants, particularly of

photochemical

smog

, in large, urban cities.

Modern internal combustion engines operate through

the Otto cycle, which involves rapid batch-burning of

petro-

leum

vapors. The combustion inside the cylinder is initiated

by a spark and proceeds outward through the gas volume

until it reaches the cylinder walls where it is cooled. Close

to the cylinder wall, where combustion is quenched, a frac-

tion of the fuel remains unburnt. In the next cycle of the

engine the hot combusted gases and unburnt fuel vapor are

forced out through the exhaust system of the automobile.

Automotive engines generally operate on “fuel rich”

mixtures, which means that there is not quite enough oxygen

to completely burn the fuel. As a result there is an excess

of unburnt

hydrocarbons

, particularly along the cylinder

walls, and substantial amounts of

carbon monoxide

. This

efficient production of

carbon

monoxide has made automo-

biles the most important source of this poisonous gas in the

urban

atmosphere

The high

emission

levels of hydrocarbons and carbon

monoxide have caused some engineers to become interested

in “lean burn” engines that make more oxygen available

during combustion. While such an approach is possible, the

process also produces high concentrations of nitric oxide in

the exhaust gases.

When the fuel enters the cylinder of an automobile

engine in the gaseous form, it generally does not produce

smoke

. However in diesel engines where the fuel is sprayed

into the combustion chamber, it will become dispersed as

tiny droplets. Sometimes, especially under load, these drop-

lets will not burn completely and are reduced to fine carbon

particles, or soot, that are easily visible from diesel exhausts.

In many cities this diesel smoke can represent the principle

soiling agent in the air. In addition, soot, particularly those

from diesel engines, contain small amounts of carcinogenic

material.

Many of the carcinogens found in the exhaust from

diesel engines are

polycyclic aromatic hydrocarbons

(PAH) and are archetypical carcinogens. Best known of

these is benzo-a-pyrene, which was tentatively recognized

as a

carcinogen

in the eighteenth century from observations

of chimney sweepers who had high incidence of

cancer

Environmental Encyclopedia 3

Autotroph

Some of the PAH can become nitrated during combustion

and these may be even more carcinogenic than the un-

nitrated PAH. Diesel emissions may pose a greater cancer

risk than the exhaust gases from

gasoline

engines. There

are a number of emissions from gasoline engines that are

potentially carcinogenic.

Benzene

represents a large part of

the total volatile organic emissions from automobiles. Yet

the compound is also recognized by many as imposing a

substantial carcinogenic risk to modern society.

Toluene

although by no means as carcinogenic as benzene, is also

emitted in large quantities. Toluene proves a very effective

compound at initiating photochemical

smog

and also reacts

to form the eye irritant peroxybenzoyl nitrate. The highly

dangerous compound

dioxin

can be produced in auto ex-

hausts where

chlorine

is present (anti-knock agents often

contain chlorine). Formaldehyde, a suspected carcinogen, is

produced in photochemical smog but may also be an en-

hanced risk from engines burning the otherwise less polluting

methanol

as a fuel.

Many exotic elements that are added to improve the

performance of automotive fuels produce their own emis-

sions. The best known is the anti-knock agent

tetraethyl

lead

, which was added in such large quantities that it became

the dominant source of

lead

particles in the air. A wide

range of long-term health effects, such as lowering IQ, have

been associated with exposure to lead. Although lead in

urban populations are still rather high, the use of unleaded

gasoline have decreased the problem somewhat.

Most attention usually focuses on the engine as a

source of automobile emissions, but there are other sources.

Evaporative loss of volatile materials from the crank case,

carburetion system, and fuel tank represent important

sources of hydrocarbons for the urban atmosphere. The wear

of tires, brake linings, and metal parts contribute to particles

being suspended in the air of the near roadside

environ-

ment

. The presence of

asbestos

fibers from brake linings

in the urban air has often been discussed, although health

threats from this source is less serious than from other

sources.

There have been relatively few studies of the pollutants

inside automobiles, but there has been some concern about

the potential hazard of the build-up of automobile emissions

from malfunctioning units and from “leaks.” These can be

from the evaporation of fuel, especially leaded fuels where

the volatile tetraethyl lead is present. Carbon monoxide,

from the exhaust system, can cause drowsiness and impair

judgment. However in many cases the interior of a properly

functioning automobile, without additional sources such as

smoking, can have somewhat better

air quality

than the air

outside. In general, pedestrians, cyclists, and those who work

at road sites are likely to experience the worst of automotive

103

pollutants such as carbon monoxide and potentially carcino-

genic hydrocarbons.

Although huge quantities of

fossil fuels

are burnt

in power generation and a range of industrial processes,

automobiles make a significant and growing contribution to

carbon dioxide

emissions which enhance the

greenhouse

effect

Ethanol

, made from sugar cane, is a renewable source

and has the advantage of not making as large a contribution

to the

greenhouse gases

as gasoline. Automobiles are not

large emitters of

sulfur dioxide

and thus do not contribute

greatly to the regional

acid rain

problem. Nevertheless,

the

nitrogen oxides

emitted by automobiles are ultimately

converted to nitric

acid

and these are making an increasing

contribution to rainfall acidity. Diesel-powered vehicles use

fuel of a higher sulfur content and can contribute to the

sulfur compounds in urban air.

Despite the enormous problems created by the auto-

mobile, few propose its abolition. The ownership of a car

carries with it powerful statements about personal freedom

and power. Beyond this, the structure of many modern cities

requires the use of a car. Thus while

air pollution

problems

might well be cured by a wide range of sociological changes,

a technological fix has been favored, such as the use of

catalytic converters. Despite this and other devices, cities

still face daunting air quality problems. In some areas, most

notably the

Los Angeles Basin

, it is clear that there will

have to be a wide range of changes if air quality is to improve.

Although much attention is being given to lowering emis-

sions of volatile organic compounds, it is likely that non-

polluting vehicles will have to be manufactured and a better

mass transit

system created.

[Peter Brimblecombe]

ESOURCES

OOKS

Environmental Effects of Automotive Emissions. Paris: OECD Compass

Project, 1986.

Kennedy, D., and R. R. Bates, eds. Air Pollution, the Automobile, and Public

Health. Washington, DC: National Academy Press, 1988.

ERIODICALS

Renner, M. G. “Car Sick.” World Watch (November-December 1988):

36–43.

Autotroph

An organism that derives its

carbon

for building body tissues

from

carbon dioxide

(CO

or carbonates and obtains its

energy for bodily functions from radiant sources, such as

sunlight, or from the oxidation of certain inorganic sub-

stances. The leaves of green plants and the bacteria that

oxidize sulfur, iron, ammonium, and nitrite are examples of

Environmental Encyclopedia 3

Avalanche

autotrophs. The oxidation of ammonium to nitrite, and of

nitrite to nitrate, a process called

nitrification

, is a critical

part of the

nitrogen cycle

. Moreover, the creation of food by

photosynthetic organisms is largely an autotrophic process.

Avalanche

A sudden slide of snow and ice, usually in mountainous

areas where there is heavy snow accumulation on moderate

to steep slopes. Snow avalanches flow at an average speed

of 80 mph (130 km/hr), and their length can range from

less than 300 ft (100 m) to 2 mi (3.2 km) or more. Generally

the term “avalanche” refers to sudden slides of snow and ice,

but it can also be used to describe catastrophic debris slides

consisting of mud and loose rock. Debris avalanches are

especially associated with volcanic activity in which melted

snow, earthquakes, and clouds of flowing ash can trigger

movement of rock and mud. Snow avalanches generally con-

sist either of loose, fresh snow or of slabs of accumulated

snow and ice that move in large blocks. Snow avalanches

occur most often where the snow surface has melted under

the sun and then refreezes, forming a smooth surface of

snow. Later snow falling on this smooth surface tends to

adhere poorly, and it may slide off the slick plane of recrystal-

lized snow when it is shaken by any form of vibration—

including sound waves, earthquakes, or the movement of

skiers.

Several factors contribute to snow avalanches, includ-

ing snow accumulation, hill slope angle, slope shape (profile),

and weather. Avalanches are most common where there is

heavy snow accumulation on slopes of 25–65°, and they

occur most often on slopes between 30° and 45°. On slopes

steeper than 65° snow tends to sluff off rather than accumu-

late. On shallow slopes avalanches are likely to occur only

in wet (melting) conditions, when accumulated snow may

be heavy, and when snow melt collecting along a hardened

old snow surface within the snowpack can loosen upper

layers, allowing them to release easily. Slab avalanches may

be more likely to start on convex slopes, where snow masses

can be fractured into loose blocks, but they rarely begin on

tree-covered slopes. However, loose snow avalanches often

start among trees, gathering speed and snow as they cross

open slopes. Weather can influence avalanche

probability

by changing the

stability

and cohesiveness of the snow pack.

Many avalanches occur during storms when snow accumu-

lates rapidly, or during sustained periods of cold weather

when new snow remains loose. Like snow melt, rainfall, can

increase chances of avalanche by lubricating the surface of

hardened layers within the snow pack. Sustained winds in-

crease snow accumulation on the leeward side of slopes,

producing snow masses susceptible to slab movement. When

conditions are favorable, an avalanche can be triggered by

104

the weight of a person or by loud noises, earthquakes, or

other sources of vibration. Avalanches tend to be most com-

mon in mid-winter, when snow accumulation is high, and in

late spring, when melting causes instability in the snow pack.

Avalanches play an ecological role by keeping slopes

clear of trees, thus maintaining openings vegetated by

grasses, forbs, and low brush. They are also a geomorphologic

force, since they maintain bare rock surfaces, which are

susceptible to

erosion

Most research into the dynamics and causes of ava-

lanches has occurred in populous mountain regions such as

the Alps, the Cascades, and the Rocky Mountains, where

avalanches cause damage and fatalities by crushing buildings

and vehicles. Avalanches are very powerful: they can crush

buildings, remove full-grown trees from hillsides, and even

sweep railroad trains from their tracks. One of the greatest

avalanche disasters on record occurred in 1910 in the Cas-

cades near Seattle, Washington, when a passenger train,

trapped in a narrow valley in a snow storm for several days,

was caught in an avalanche and swept to the bottom of the

valley. Ninety-six passengers died as the cars were crushed

with snow. Although avalanches are among the more dan-

gerous natural hazards, they have caused fewer than 200

recorded mortalities in North America, and most avalanche

victims in North America are caught in slides they triggered

themselves by walking or skiing across open slopes with

accumulated snow.

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Brugnot, G., ed. Snow and Avalanches. Conference proceedings, Chamonix,

Switzerland, 1992. Zurich: Cemagret, 1995.

Salm, B., and H. Gubler. Avalanche Formation, Movement, and Effects.

Wallingford, Oxfordshire, UK: IAHS Press, 1987.

United States Forest Service. “Snow Avalanche: General rules for Avoiding

and Surviving Snow Avalanches.” Portland, OR: USDA Forest Service,

1982.

Bacillus thuringiensis

Bacillus thuringiensis,orB.t., is a family of bacterial-based,

biological insecticides. Specific strains of B.t. are used against

a wide variety of leaf-eating lepidopteran pests such as Euro-

pean corn borer, tomato hornworms, and

tobacco

moths,

and some other susceptible insects such as blackflies and

mosquitoes. The active agent in B.t. is toxic organic crystals

that bind to the gut of an insect and poke holes in cell

membranes, literally draining the life from the insect. B.t.

can be applied using technology similar to that used for

chemical insecticides, such as high-potency, low-volume

sprays of B.t. spores applied by aircraft. The efficacy of B.t. is

usually more variable and less effective than that of chemical

insecticides, but the environmental effects of B.t. are consid-

ered to be more acceptable because there is little non-target

toxicity.

Background radiation

Ionizing radiation

has the potential to kill cells or cause

somatic or germinal mutations. It has this ability by virtue

of its power to penetrate living cells and produce highly

reactive charged ions. It is the charged ions which cause cell

damage. Radiation accidents and the potential for radiation

from nuclear (atomic) bombs create a fear of radiation release

due to human activity. Many people are subjected to diagnos-

tic and therapeutic radiation, and older Americans were

exposed to

radioactive fallout

from atmospheric testing of

nuclear weapons

. There is some environmental contami-

nation from nuclear fuel used in

power plants

. Accordingly,

there is considerable interest in radiation effects on biological

systems and the sources of radiation in the

environment

Concern for radiation safety is certainly justified and

most individuals seek to minimize their exposure to human-

generated radiation. However, for most people, exposure

levels to radiation from natural sources far exceed exposure to

radiation produced by humans. Current estimates of human

105

exposure levels of ionizing radiation suggest that only about

18% is of human origin. The remaining radiation (82%)

is from natural sources and is referred to as “background

radiation.” While radiation doses vary tremendously from

person to person, the average human has an annual exposure

to ionizing radiation of about 360 millirem. (Millirem or

mrem is a measure of radiation absorbed by tissue multiplied

by a factor that takes into account the biological effectiveness

of a particular type of radiation and other factors such as

the competence of radiation repair. One mrem is equal to

10 ␮Sv; ␮Sv is an abbreviation for microSievert, a unit that

is used internationally.)

Some radiation has little biological effect. Visible light

and infrared radiation do not cause ionization, are not muta-

genic and are not carcinogenic. Consequently, background

radiation refers to ionizing radiation which is derived from

cosmic radiation, terrestrial radiation, and radiation from

sources internal to the body. (Background radiation has the

potential for producing inaccurate counts from devices such

as a Geiger counter. For example, cosmic rays will be rec-

orded when measuring the

radioactive decay

of a sample.

This background “noise” must be subtracted from the indi-

cated count level to give a true indication of activity of the

sample.)

Cosmic rays are of galactic origin, entering the earth’s

atmosphere

from outer space. Solar activity in the form of

sunflares and sunspots affects the intensity of cosmic rays.

The atmosphere of the earth serves as a protective layer for

humans and anything that damages that protective layer will

increase the

radiation exposure

of those who live under

it. The dose of cosmic rays doubles at 4,920 ft (1,500 m)

above sea level. Because of this, citizens of Denver, near

the Rocky Mountains, receive more than twice the dose of

radiation from cosmic rays as do citizens of coastal cities

such as New Orleans. The

aluminum

shell of a jet airplane

provides little protection from cosmic rays, and for this rea-

son passengers and crews of high flying jet airplanes receive

more radiation than their earth traveling compatriots. Even

greater is the cosmic radiation encountered at 60,000 ft

Environmental Encyclopedia 3

Background radiation

(18,300 m) where supersonic jets fly. The level of cosmic

radiation there is 1,000 times that at sea level. While the

cosmic ray dose for occasional flyers is minimal, flight and

cabin crews of ordinary jet airliners receive an additional

exposure of 160 mrem per year, an added radiation burden

to professional flyers of more than 40%. Cosmic sources for

non-flying citizens at sea level are responsible for about 8%

(29–30 mrem) of background radiation exposure per annum.

Another source of background radiation is terrestrial

radioactivity

from naturally occurring minerals, such as

uranium

, thorium, and cesium, in

soil

and rocks. The abun-

dance of these minerals differs greatly from one geographic

area to another. Residents of the Colorado plateau receive

approximately double the dose of terrestrial radiation as those

who live in Iowa or Minnesota. The geographic variations

are attributed to the local composition of the earth’s crust

and the kinds of rock, soil and minerals present. Houses

made of stone are more radioactive than houses made of

wood. Limestones and sandstones are low in radioactivity

when compared with granites and some shales. Naturally

occurring

radionuclides

in soil may become incorporated

into grains and vegetables and thus gain access to the human

body.

Radon

is a radioactive gas produced by the disintegra-

tion of radium (which is produced from uranium). Radon

escapes from the earth’s crust and becomes incorporated into

all living matter including humans. It is the largest source

of inhaled radioactivity and comprises about 55% of total

human radiation exposure (both background and human

generated). Energy efficient homes, which do not leak air,

may have a higher concentration of radon inside than is

found in outside air. This is especially true of basement air.

The radon in the home decays into radioactive “daughters”

that become attached to

aerosol

particles which, when in-

haled, lodge on lung and tracheal surfaces. Obviously, the

level of radon in household air varies with construction mate-

rial and with geographic location. Is radon in household air

a hazard? Many people believe it is, since radon exposure

(at a much higher level than occurs breathing household

air) is responsible for lung

cancer

in non-smoking uranium

miners.

Naturally occurring radioactive

carbon

(carbon-14)

similarly becomes incorporated into all living material. Thus,

external radiation from terrestrial sources often becomes in-

ternalized via food, water, and air. Radioactive atoms (radio-

nuclides) of carbon, uranium, thorium, and actinium and

radon gas provide much of the terrestrial background radia-

tion. The combined annual exposure to terrestrial sources,

including internal radiation and radon, is about 266 mrem

and far exceeds other, more feared sources of radiation.

Life on earth evolved in the presence of ionizing radia-

tion. It seems reasonable to assume that mutations can be

attributed to this chronic, low level of radiation. Mutations

106

are usually considered to be detrimental, but over the long

course of human and other organic

evolution

, many useful

mutations occurred, and it is these mutations that have con-

tributed to the evolution of higher forms.

Nevertheless, it is to an organism’s advantage to resist

the deleterious effects associated with most mutations. The

forms of life that inhabit the earth today are descendants of

organisms that existed for millions of years on earth. Inas-

much as background ionizing radiation has been on earth

longer than life, humans and all other organisms obviously

cope with chronic low levels of radiation. Survival of a partic-

ular

species

is not due to a lack of genetic damage by

background radiation. Rather, organisms survive because of

a high degree of redundancy of cells in the body, which

enables organ function even after the death of many cells

(e.g., kidney and liver function, essential for life, does not

fail with the loss of many cells; this statement is true for

essentially all organs of the human body). Further, stem cells

in many organs replace dead and discarded cells. Naturally

occurring antioxidants are thought to protect against free

radicals produced by ionizing radiation. Finally, repair mech-

anisms exist which can, in some cases, identify damage to

the double helix and effect DNA repair. Hence, while organ-

isms are vulnerable to background radiation, mechanisms

are present which assure survival.

[Robert G. McKinnell]

ESOURCES

OOKS

Benarde, M. A. Our Precarious Habitat: 15 Years Later. New York: Wi-

ley, 1989.

Hall, E. J. “Principles of Carcinogenesis: Physical.” In Cancer: Principles

and Practice of Oncology, edited by V. T. DeVita, et al. 4th ed. Philadelphia:

Lippincott, 1993.

Knoche, H. W. Radioisotopic Methods for Biological and Medical Research.

New York: Oxford University Press, 1991.

Sir Francis Bacon (1561 – 1626)

English statesman, author, and philosopher

Sir Francis Bacon, philosopher and Lord Chancellor of En-

gland, was one of the key thinkers involved in the develop-

ment of the procedures and epistemological standards of

modern science. Bacon thus has also played a vital role in

shaping modern attitudes towards

nature

, human progress,

and the

environment

. He inspired many of the great think-

ers of the Enlightenment, especially in England and France.

Moreover, Bacon laid the intellectual groundwork for the

mechanistic view of the universe characteristic of eighteenth

and nineteenth century thought and for the explosion of

technology in the same period.