Environmental Encyclopedia

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Environmental Encyclopedia 3

Heat (stress) index

tion to the surface or to vegetation. Still other hazes are of

mixed origin, as noted above, and an event such as a dust

storm can be enhanced by human-caused devegetation of

soil

Though it may contain particles injurious to health,

haze is not of itself a health hazard. It can have a significant

economic impact, however, when tourists cannot see scenic

views, or if it becomes sufficiently dense to inhibit aircraft

operations. See also Air pollution; Air quality; Air quality

criteria; Los Angeles Basin; Mexico City, Mexico

[James P. Lodge Jr.]

ESOURCES

OOKS

Husar, R. B. Trends in Seasonal Haziness and Sulfur Emissions Over the

Eastern United States. Research Triangle Park, NC: U. S. Environmental

Protection Agency, 1989.

ERIODICALS

Husar, R. B., and W. E. Wilson. “Haze and Sulfur Emission Trends in

the Eastern United States.” Environmental Science and Technology 27 (Janu-

ary 1993): 12–16.

Malm, W. C. “Characteristics and Origins of Haze in the Continental

United States.” Earth-Science Reviews 33 (August 1992): 1–36.

Raloff, J. “Haze May Confound Effects of Ozone Loss.” Science News 141

(4 January 1992): 5.

Heat (stress) index

The heat index (HI) or heat stress index—sometimes called

the apparent temperature or comfort index—is a temperature

measure that takes into account the relative humidity. Based

on human physiology and on clothing science, it measures

how a given air temperature feels to the average person at

a given relative humidity. The HI temperature is measured

in the shade and assumes a wind speed of 5.6 mph (9 kph)

and normal barometric pressure.

At low relative humidity, the HI is less than or equal

to the air temperature. At higher relative humidity, the HI

exceeds the air temperature. For example, according to the

National Weather Service’s (NWS) HI chart, if the air tem-

perature is 70°F (21°C), the HI is 64°F (18°C) at 0% relative

humidity and 72°F (22°C) at 100% relative humidity. At

95°F (35°C) and 55% relative humidity, the HI is 110°F

(43°C). In very hot weather, humidity can raise the HI to

extreme levels: at 115°F (46°C) and 40% relative humidity,

the HI is 151°F (66°C). This is because humidity affects

the body’s ability to regulate internal heat through perspira-

tion. The body feels warmer when it is humid because perspi-

ration evaporates more slowly; thus the HI is higher.

The HI is used to predict the risk of physiological

heat stress for an average individual. Caution is advised

707

at an HI of 80–90°F (27–32°C): fatigue may result with

prolonged exposure and physical activity. An HI of 90–

105°F (32–41°C) calls for extreme caution, since sunstroke,

muscle cramps, and heat exhaustion are possible. Danger

warnings are issued at HIs of 105–130°F (41–54°C), when

sunstroke and heat exhaustion are likely and there is a poten-

tial for heat stroke. Category IV, extreme danger, occurs at

HIs above 130°F (54°C), when heatstroke and sunstroke are

imminent.

Individual physiology influences how people are af-

fected by high HIs. Children and older people are more

vulnerable. Acclimatization (being used to the

climate

) can

alleviate some of the danger. However sunburn can increase

the effective HI by slowing the skin’s ability to shed excess

heat from blood vessels and through perspiration. Exposure

to full sunlight can increase HI values by as much as 15°F

(8°C). Winds, especially hot dry winds, also can increase

the HI. In general, the NWS issues excessive heat alerts

when the daytime HI reaches 105°F (41°C) and the night-

time HI stays above 80°F (27°C) for two consecutive days;

however these values depend somewhat on the region or

metropolitan area. In cities, high HIs often mean increased

air pollution

. The concentration of

ozone

, the major com-

ponent of

smog

, tends to rise at ground level as the HI

increases, causing respiratory problems for many people.

The National Center for Health

Statistics

estimates

that heat exposure results in an average of 371 deaths annu-

ally in the United States. About 1,700 Americans died in

the heat waves of 1980. In Chicago in 1995, more than 700

people died during a five-day heat wave when the nighttime

HI stayed above 89°F (32°C).

At higher temperatures, the air can hold more water

vapor; thus humidity and HI values increase as the

atmo-

sphere

warms. Since the late nineteenth century, the mean

annual surface temperature of the earth has risen between

0.5 and 1.0°F (0.3 and 0.6°C). According to the National

Aeronautics and Space Administration, the five-year-mean

temperature increased about 0.9°F (0.5°C) between 1975

and 1999, the fastest rate of recorded increase. In 1998 global

surface temperatures were the warmest since the advent of

reliable measurements and the 1990s accounted for seven of

the 10 warmest years on record. Nighttime temperatures

have been increasing twice as fast as daytime temperatures.

Greenhouse gases

, including

carbon dioxide

methane

nitrous oxide

, and

chlorofluorocarbons

, in-

crease the heat-trapping capabilities of the atmosphere.

Evaporation from the ocean surfaces increased during the

twentieth century, resulting in higher humidity that en-

hanced the

greenhouse effect

. It is projected that during

the twenty-first century greenhouse gas concentrations will

double or even quadruple from pre-industrial levels. In-

creased urbanization also contributes to global warming, as

Environmental Encyclopedia 3

Heavy metals and heavy metal poisoning

buildings and roads hold in the heat. Climate simulations

predict an average surface air temperature increase of 4.5–

7°F (2.5–4°C) by 2100. This will increase the number of

extremely hot days and, in temperate climates, double the

number of very hot days, for an average increase in summer

temperatures of 4–5°F (2–3°C). More heat-related illnesses

and deaths will result.

The

National Oceanic and Atmospheric Adminis-

tration

projects that the HI could rise substantially in humid

regions of the tropics and sub-tropics. Warm, humid regions

of the southeastern United States are expected to experience

substantial increases in the summer HI due to increased

humidity, even though temperature increases may be smaller

than in the continental interior. Predictions for the increase

in the summer HI for the Southeast United States over the

next century range from 8–20°F (4–11°C).

[Margaret Alic Ph.D.]

ESOURCES

OOKS

Wigley, T. M. L. The Science of Climate Change: Global and U.S. Perspectives.

Arlington, VA: Pew Center on Global Climate Change, 1999.

ERIODICALS

Delworth, T. L., J. D. Mahlman, and T. R. Knutson. “Changes in Heat

Index Associated with CO

-Induced Global Warming.” Climatic Change

43 (1999): 369–86.

THER

Darling, Allan. “Heat Wave.” Internet Weather Source. June 27, 2000 [cited

May 2002]. <http://weather.noaa.gov/weather/hwave.html>.

Davies, Kert. “Heat Waves and Hot Nights.” Ozone Action and Physicians for

Social Responsibility. July 26, 2000 [cited May 2002]. <http://www.psr.org/

heatreport.pdf>.

National Assessment Synthesis Team. Climate Change Impacts on the United

States: The Potential Consequences of Climate Variability and Change. Over-

view: Southeast. U. S. Global Change Research Program. March 5, 2002

[May 2002]. <http://www.usgcrp.gov/usgcrp/Library/nationalassessment/

overviewsoutheast.htm>.

Union of Concerned Scientists. Early Warning Signs of Global Warming:

Heat Waves and Periods of Unusually Warm Weather. 2000 [cited May 2002].

<http://www.ucsusa.org/balance/gw_heat.html>.

Trenberth, Kevin E. “The IPCC Assessment of Global Warming 2001.”

FailSafe. Spring 2001 [cited May 2002]. <http://www.felsef.org/

spring01.htm#3>.

RGANIZATIONS

National Weather Service, National Oceanic and Atmospheric

Administration, U. S. Department of Commerce, 1325 East West

Highway, Silver Spring, USA 20910 , <http://www.nws.noaa.gov>

Physicians for Social Responsibility, 1875 Connecticut Avenue, NW, Suite

1012, Washington , DC USA 20009 (202) 667-4260, Fax: (202) 667-

4201, Email: psrnatl@psr.org, <http://www.psr.org>

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

02238 (617) 547-5552, Email: ucs@ucsusa.org, <http://www.ucsusa.org>

708

Heavy metals and heavy metal

poisoning

Heavy metals are generally defined as environmentally stable

elements of high specific gravity and atomic weight. They

have such characteristics as luster, ductility, malleability, and

high electric and thermal conductivity. Whether based on

their physical or chemical properties, the distinction between

heavy metals and non-metals is not sharp. For example,

arsenic

, germanium, selenium, tellurium, and antimony

possess chemical properties of both metals and non-metals.

Defined as metalloids, they are often loosely classified as

heavy metals. The category “heavy metal” is, therefore, some-

what arbitrary and highly non-specific because it can refer

to approximately 80 of the 103 elements in the periodic

table. The term “trace element” is commonly used to describe

substances which cannot be precisely defined but most fre-

quently occur in the

environment

in concentrations of a

few

parts per million

(ppm) or less. Only a relatively small

number of heavy metals such as

cadmium

copper

, iron,

cobalt, zinc,

mercury

, vanadium,

lead

nickel

, chromium,

manganese, molybdenum, silver, and tin as well as the met-

alloids arsenic and selenium are associated with environmen-

tal, plant, animal, or human health problems.

While the chemical forms of heavy metals can be

changed, they are not subject to chemical/biological destruc-

tion. Therefore, after release into the environment they are

persistent contaminants. Natural processes such as bedrock

and

soil weathering

, wind and water

erosion

, volcanic

activity, sea salt spray, and forest fires release heavy metals

into the environment. While the origins of

anthropogenic

releases of heavy metals are lost in antiquity, they probably

began as our prehistoric ancestors learned to recover metals

such as gold, silver, copper, and tin from their ores and to

produce bronze. The modern age of heavy metal

pollution

has its beginning with the Industrial Revolution. The rapid

development of industry, intensive agriculture,

transporta-

tion

, and urbanization over the past 150 years, however, has

been the precursor of today’s environmental contamination

problems. Anthropogenic utilization has also increased heavy

metal distribution by removing the substances from localized

ore deposits and transporting them to other parts of the

environment. Heavy metal by-products result from many

activities including: ore extraction and smelting, fossil fuel

combustion

, dumping and landfilling of industrial wastes,

exhausts from leaded gasolines, steel, iron, cement and

fertil-

izer

production, refuse and wood combustion. Heavy metal

cycling has also increased through activities such as farming,

deforestation

, construction,

dredging

of harbors, and the

disposal of municipal sludges and industrial wastes on land.

Thus, anthropogenic processes, especially combustion,

have substantially supplemented the natural atmospheric

Environmental Encyclopedia 3

Heavy metals and heavy metal poisoning

emissions of selected heavy metals/metalloids such as sele-

nium, mercury, arsenic, and antimony. They can be trans-

ported as gases or adsorbed on particles. Other metals such

as cadmium, lead, and zinc are transported atmospherically

only as particles. In either state heavy metals may travel long

distances before being deposited on land or water.

The heavy metal contamination of soils is a far more

serious problem than either air or

water pollution

because

heavy metals are usually tightly bound by the organic compo-

nents in the surface layers of the soil and may, depending

on conditions, persist for centuries or millennia. Conse-

quently, the soil is an important geochemical sink which

accumulates heavy metals rapidly and usually depletes them

very slowly by

leaching

into

groundwater

aquifers or bi-

oaccumulating into plants. However, heavy metals can also

be very rapidly translocated through the environment by

erosion of the soil particles to which they are adsorbed or

bound and redeposited elsewhere on the land or washed into

rivers, lakes or oceans to the

sediment

The cycling, bioavailability, toxicity, transport, and

fate of heavy metals are markedly influenced by their phys-

ico-chemical forms in water, sediments, and soils. Whenever

a heavy metal containing

ion

or compound is introduced

into an aquatic environment, it is subjected to a wide variety

of physical, chemical, and biological processes. These in-

clude: hydrolysis, chelation, complexation, redox, biomethy-

lation, precipitation and

adsorption

reactions. Often heavy

metals experience a change in the chemical form or specia-

tion as a result of these processes and so their distribution,

bioavailability, and other interactions in the environment

are also affected.

The interactions of heavy metals in aquatic systems

are complicated because of the possible changes due to many

dissolved and

particulate

components and non-equilibrium

conditions. For example, the speciation of heavy metals is

controlled not only by their chemical properties but also by

environmental variables such as: 1)

; 2) redox potential;

dissolved oxygen

; 4) ionic strength; 5) temperature; 6)

salinity

; 7) alkalinity; 8) hardness; 9) concentration and

nature

of inorganic ligands such as carbonate, bicarbonate,

sulfate, sulfides, chlorides; 10) concentration and nature of

dissolved organic chelating agents such as organic acids,

humic materials,

peptides

, and polyamino-carboxylates; 11)

the concentration and nature of particulate matter with sur-

face sites available for heavy metal binding; and 12) biological

activity.

In addition, various

species

of bacteria can oxidize

arsenate or reduce arsenate to arsenite, or oxidize ferrous

iron to ferric iron, or convert mercuric ion to elemental

mercury or the reverse. Various

enzyme

systems in living

organisms can biomethylate a number of heavy metals.

While it had been known for at least 60 years that arsenic

709

and selenium could be biomethylated,

microorganisms

ca-

pable of converting inorganic mercury into monomethyl and

dimethylmercury in lake sediments were not discovered until

1967. Since then, numerous heavy metals such as lead, tin,

cobalt, antimony, platinum, gold, tellurium, thallium, and

palladium have been shown to be biomethylated by bacteria

and

fungi

in the environment.

As environmental factors change the chemical reactivi-

ties and speciation of heavy metals, they influence not only

the mobilization, transport, and bioavailability, but also the

toxicity of heavy metal ions toward biota in both freshwater

and marine ecosystems. The factors affecting the toxicity

and

bioaccumulation

of heavy metals by aquatic organisms

include: 1) the chemical characteristics of the ion; 2) solution

conditions which affect the chemical form (speciation) of

the ion; 3) the nature of the response such as acute toxicity,

bioaccumulation, various types of

chronic effects

, etc.; 4)

the nature and condition of the aquatic animal such as age

or life stage, species, or

trophic level

in the food chain.

The extent to which most of the methylated metals are

bioaccumulated and/or biomagnified is limited by the chem-

ical and biological conditions and how readily the methylated

metal is metabolized by an organism. At present, only meth-

ylmercury seems to be sufficiently stable to bioaccumulate

to levels that can cause adverse effects in aquatic organisms.

All other methylated metal ions are produced in very small

concentrations and are degraded naturally faster than they

are bioaccumulated. Therefore, they do not biomagnify in

the food chain.

The largest proportion of heavy metals in water is

associated with suspended particles, which are ultimately

deposited in the bottom sediments where concentrations are

orders of magnitude higher than those in the overlying or

interstitial waters. The heavy metals associated with sus-

pended particulates or bottom sediments are complex mix-

tures of: 1) weathering and erosion residues such as iron and

aluminum

oxyhydroxides, clays and other aluminosilicates;

2) methylated and non-methylated forms in organic matter

such as living organisms, bacteria and algae,

detritus

and

humus

; 3) inorganic hydrous oxides and hydroxides,

phos-

phates

and silicates; and 4) diagenetically produced iron

and manganese oxyhydroxides in the upper layer of sedi-

ments and sulfides in the deeper, anoxic layers.

In anoxic waters the precipitation of sulfides may con-

trol the heavy metal concentrations in sediments while in

oxic waters adsorption,

absorption

, surface precipitation

and

coprecipitation

are usually the mechanisms by which

heavy metals are removed from the water column. Moreover,

physical, chemical and microbiological processes in the sedi-

ments often increase the concentrations of heavy metals in

the pore waters which are released to overlying waters by

diffusion or as the result of consolidation and bioturbation.

Environmental Encyclopedia 3

Heavy metals precipitation

Transport by living organisms does not represent a signifi-

cant mechanism for local movement of heavy metals. How-

ever, accumulation by aquatic plants and animals can lead

to important biological responses. Even low environmental

levels of some heavy metals may produce subtle and chronic

effects in animal populations.

Despite these adverse effects, at very low levels, some

metals have essential physiological roles as micronutrients.

Heavy metals such as chromium, manganese, iron, cobalt,

molybdenum, nickel, vanadium, copper, and selenium are

required in small amounts to perform important biochemical

functions in plant and animal systems. In higher concentra-

tions they can be toxic, but usually some biological regulatory

mechanism is available by means of which animals can speed

up their excretion or retard their uptake of excessive quan-

tities.

In contrast, non-essential heavy metals are primarily

of concern in terrestrial and aquatic systems because they

are toxic and persist in living systems. Metal ions commonly

bond with sulfhydryl and carboxylic

acid

groups in amino

acids, which are components of proteins (enzymes) or poly-

peptides. This increases their bioaccumulation and inhibits

excretion. For example, heavy metals such as lead, cadmium,

and mercury bind strongly with -SH and -SCH

groups in

cysteine and methionine and so inhibit the

metabolism

the bound enzymes. In addition, other heavy metals may

replace an essential element, decreasing its availability and

causing symptoms of deficiency.

Uptake, translocation, and accumulation of potentially

toxic heavy metals in plants differ widely depending on soil

type, pH, redox potential, moisture, and organic content.

Public health officials closely regulate the quantities and

effects of heavy metals that move through the agricultural

food chain to be consumed by human beings. While heavy

metals such as zinc, copper, nickel, lead, arsenic, and cad-

mium are translocated from the soil to plants and then

into the animal food chain, the concentrations in plants

are usually very low and generally not considered to be an

environmental problem. However, plants grown on soils

either naturally enriched or highly contaminated with some

heavy metals can bioaccumulate levels high enough to cause

toxic effects in the animals or human beings that consume

them.

Contamination of soils due to land disposal of sewage

and industrial effluents and sludges may pose the most signif-

icant long term problem. While cadmium and lead are the

greatest hazard, other elements such as copper, molybdenum,

nickel, and zinc can also accumulate in plants grown on

sludge-treated land. High concentrations can, under certain

conditions, cause adverse effects in animals and human be-

ings that consume the plants. For example, when soil con-

tains high concentrations of molybdenum and selenium,

710

they can be translocated into edible plant tissue in sufficient

quantities to produce toxic effects in ruminant animals. Con-

sequently, the U. S.

Environmental Protection Agency

has

issued regulations which prohibit and/or tightly regulate the

disposal of contaminated municipal and industrial sludges

on land to prevent heavy metals, especially cadmium, from

entering the food supply in toxic amounts. However, pres-

ently, the most serious known human toxicity is not through

bioaccumulation from crops but from mercury in fish, lead

gasoline

, paints and water pipes, and other metals derived

from occupational or accidental exposure. See also Aquatic

chemistry; Ashio, Japan; Atmospheric pollutants; Biomagni-

fication; Biological methylation; Contaminated soil; Duck-

town, Tennessee; Hazardous material; Heavy metals precipi-

tation; Itai-Itai disease; Methylmercury seed dressings;

Minamata disease; Smelters; Sudbury, Ontario; Xenobiotic

[Frank M. D’Itri]

ESOURCES

OOKS

Craig, P. J. “Metal Cycles and Biological Methylation.” The Handbook of

Environmental Chemistry. Vol. 1, Part A, edited by O. H. Hutzinger. Berlin:

Springer Verlag, 1980.

rstner, U., and G. T. W. Wittmann. Metal Pollution in the Aquatic

Environment. 2nd ed. Berlin: Springer Verlag, 1981.

Kramer, J. R., and H. E. Allen, eds. Metal Speciation: Theory, Analysis and

Application. Chelsea, MI: Lewis, 1988.

Heavy metals precipitation

The principle technology to remove metals pollutants from

wastewater

is by chemical precipitation. Chemical precipi-

tation includes two secondary removal mechanisms,

copreci-

pitation

and

adsorption

. Precipitation processes are char-

acterized by the solubility of the metal to be removed. They

are generally designed to precipitate trace metals to their

solubility limits and obtain additional removal by coprecipi-

tation and adsorption during the precipitation reaction.

There are many different treatment variables that af-

fect these processes. They include the optimum

, the type

of chemical treatments used, and the number of treatment

stages, as well as the temperature and volume of wastewater,

and the chemical specifications of the pollutants to be re-

moved. Each of these variables directly influences treatment

objectives and costs. Treatability studies must be performed

to optimize the relevant variables, so that goals are met and

costs minimized.

In theory, the precipitation process has two steps, nu-

cleation followed by particle growth. Nucleation is repre-

sented by the appearance of very small particle seeds which

are generally composed of 10–100 molecules. Particle growth

Environmental Encyclopedia 3

Robert Louis Heilbroner

involves the addition of more atoms or molecules into this

particle structure. The rate and extent of this process is

dependent upon the temperature and chemical characteris-

tics of the wastewater, such as the concentration of metal

initially present and other ionic

species

present, which can

compete with or form soluble complexes with the target

metal species.

Heavy metals

are present in many industrial waste-

waters. Examples of such metals are

cadmium

copper

lead

mercury

nickel

, and zinc. In general, these metals

can be complexed to insoluble species by adding sulfide,

hydroxide, and carbonate ions to a solution. For example,

the precipitation of copper (Cu) hydroxide is accomplished

by adjusting the pH of the water to above 8, using precipitant

chemicals

such as lime (Ca(OH)

) or sodium hydroxide

OH). Precipitation of metallic carbonate and sulfide spe-

cies can be accomplished by the addition of calcium carbon-

ate or sodium sulfide. The removal of coprecipitive metals

during precipitation of the soluble metals is aided by the

presence of solid ferric oxide, which acts as an adsorbent

during the precipitation reaction. For example, hydroxide

precipitation of ferric chloride can be used as the source

of ferric oxide for coprecipitation and adsorption reactions.

Precipitation, coprecipitation, and adsorption reactions gen-

erate suspended solids which must be separated from the

wastewater. Flocculation and clarification are again em-

ployed to assist in solids separation. The treatment is an

important variable which must be optimized to effect the

maximum metal removal possible.

Determining the optimal pH range to facilitate the

maximum precipitation of metal is a difficult task. It is

typically accomplished by laboratory studies, such as by-jar

tests rather than theoretical calculations. Often the actual

wastestream behaves differently, and the theoretical metal

solubilities and corresponding optimal pH ranges can vary

considerably from theoretical values. See also Heavy metals

and heavy metal poisoning; Industrial waste treatment; Itai-

itai disease; Minamata disease; Sludge; Waste management

[James W. Patterson]

ESOURCES

OOKS

Nemerow, N. L., and A. Dasgupta. Industrial and Hazardous Waste Treat-

ment. New York: Van Nostrand Reinhold, 1991.

Robert Louis Heilbroner (1919 – )

American economist and author

An economist by profession, Robert Heilbroner is the author

of a number of books and articles that put economic theories

711

and developments into historical perspective and relate them

to contemporary social and political problems. He is espe-

cially noteworthy for his gloomy speculations on the future of

a world confronted by the environmental limits to economic

growth.

Born in New York City in 1919, Heilbroner received

a bachelor’s degree from Harvard University in 1940 and a

Bronze Star for his service in World War II. In 1963 he

earned a Ph.D. in economics from the New School for Social

Research in New York, and in 1972, became the Norman

Thomas Professor of Economics there. His books include

The Worldly Philosophers (1955), The Making of Economic

Society (1962), Marxism: For and Against (1980), and The

Nature and Logic of Capitalism (1985). He has also served

on the editorial board of the socialist journal Dissent.

In 1974, Heilbroner published An Inquiry into the

Human Prospect, in which he argues that three “external

challenges” confront humanity: the population explosion,

the threat of war, and “the danger...of encroaching on the

environment

beyond its ability to support the demands

made on it.” Each of these problems, he maintains, arises

from the development of scientific technology, which has

increased human life span, multiplied weapons of destruc-

tion, and encouraged industrial production that consumes

natural resources

and pollutes the environment. Heil-

broner believes that these challenges confront all economies,

and that meeting them will require more than adjustments

in economic systems. Societies will have to muster the will

to make sacrifices.

Heilbroner goes on to argue that persuading people to

make these sacrifices may not be possible. Those living in one

part of the world are not likely to give up what they have for

the sake of those in another part, and people living now are not

likelyto make sacrifices for

futuregenerations

.His reluctant

conclusion is that coercion is likely to take the place of persua-

sion. Authoritarian governments may well supplant democra-

cies because “the passage through the gantlet ahead may be

possible only under governments capable of rallying obedi-

ence far more effectively than would be possible in a demo-

cratic setting. If the issue for mankind is survival, such govern-

ments may be unavoidable, even necessary.”

Heilbroner wrote An Inquiry into the Human Prospect

in 1972 and 1973, but his position had not changed by the

end of the decade. In a revised edition written in 1979, he

continued to insist upon the environmental limits to eco-

nomic growth: “the industrialized capitalist and socialist

worlds can probably continue along their present growth

paths” for about 25 years, at which point “we must expect...a

general recognition that the possibilities for expansion are

limited, and that social and economic life must be maintained

within fixed...material boundaries.” Heilbroner has pub-

lished a number of books, including 21st Century Capitalism

Environmental Encyclopedia 3

Hells Canyon

Robert L. Heilbroner. (Photograph by Jose Pelaez. W.

W. Norton. Reproduced by permission.)

and Visions of the Future. He also received the New York

Council for the Humanities Scholar of the Year award in

1994. Heilbroner currerently holds the position of Norman

Thomas Professor of Economics, Emeritus, at the New

School for Social Research, in New York City.

[Richard K. Dagger]

ESOURCES

OOKS

Heilbroner, Robert L. An Inquiry into the Human Prospect. Rev. ed. New

York: Norton, 1980.

———. The Making of an Economic Society. 6th ed. Englewood Cliffs, NJ:

Prentice-Hall, 1980.

———. The Nature and Logic of Capitalism. New York: Norton, 1985.

———. Twenty-First Century Capitalism. Don Mills, Ont.: Anansi, 1992.

———. The Worldly Philosophers: The Lives, Times and Ideas of the Great

Economic Thinkers. 6th ed. New York: Simon & Schuster, 1986.

Straub, D., ed. Contemporary Authors: New Revision Series. Vol. 21. Detroit,

MI: Gale Research, 1987.

Hells Canyon

Hells Canyon is a stretch of canyon on the Snake River be-

tweenIdaho and Oregon.This canyon, deeperthan the Grand

Canyon and formed in ancient basalt flows, contains some of

712

the United States’ wildest rapids and has provided extensive

recreational and scenic boating since the 1920s. The narrow

canyonhas also provided outstandingdam sites. Hells Canyon

became the subject of nationwide controversy between 1967

and 1975, when environmentalists challenged hydroelectric

developers over the last stretch of free-flowing water in the

Snake River from the border of Wyoming to the Pacific.

Historically Hells Canyon, over 100 mi (161 km) long,

filled with rapids, and averaging 6,500 ft (1,983 m) deep,

presented a major obstacle to travelers and explorers crossing

the mountains and deserts of southern Idaho and eastern

Oregon. Nez Perce

, Paiute, Cayuse, and other Native Amer-

ican groups of the region had long used the area as a mild

wintering ground with good grazing land for their horses.

European settlers came for the modest timber and with cattle

and sheep to graze. As early as the 1920s travelers were

arriving in this scenic area for recreational purposes, with

the first river runners navigating the canyon’s rapids in 1928.

By the end of the Depression the

Federal Power Commis-

sion

was urging regional utility companies to tap the river’s

hydroelectric potential, and in 1958 the first dam was built

in the canyon.

Falling from the mountains in southern

Yellowstone

National Park

through Idaho, and into the Columbia River,

the Snake River drops over 7,000 vertical ft (2,135 m) in

1,000 mi (1,609 km) of river. This drop and the narrow

gorges the river has carved presented excellent dam opportu-

nities, and by the end of the 1960s there were 18 major

dams

along the river’s course. By that time the river was

also attracting great numbers of whitewater rafters and kay-

akers, as well as hikers and campers in the adjacent national

forests. When a proposal was developed to dam the last free-

running section of the canyon, protesters brought a suit to

the United States Supreme Court. In 1967, Justice William

O. Douglas led the majority in a decision directing the

utilities to consider alternatives to the proposed dam.

Hells Canyon became a national environmental issue.

Several members of Congress flew to Oregon to raft the

river. The

Sierra Club

and other groups lobbied vigorously.

Finally, in 1975 President Gerald Ford signed a bill declaring

the remaining stretch of the canyon a National Scenic Wa-

terway, creating a 650,000-acre (260,000-ha) Hells Canyon

National

Recreation

Area, and adding 193,000 acres

(77,200 ha) of the area to the National

Wilderness

Preserva-

tion System. See also Wild and Scenic Rivers Act; Wild river

[Mary Ann Cunningham Ph.D.]

ESOURCES

OOKS

Collins, R. O., and R. Nash. The Big Drops. San Francisco: Sierra Club

Books, 1978.

Environmental Encyclopedia 3

Herbicide

THER

Hells Canyon Recreation Area. “Hells Canyon.” Washington, DC: U.S.

Government Printing Office, 1988.

Hazel Henderson (1933 – )

English/American environmental activist and writer

Hazel Henderson is an environmental activist and futurist

who has called for an end to current “unsustainable industrial

modes” and urges redress for the “unequal access to resources

which is now so dangerous, both ecologically and socially.”

Born in Clevedon, England, Henderson immigrated

to the United States after finishing high school; she became

a naturalized citizen in 1962. After working for several years

as a free-lance journalist, she married Carter F. Henderson,

former London bureau chief of the Wall Street Journal in

1957. Her activism began when she became concerned about

air quality

in New York City, where she was living. To

raise public awareness, she convinced the FCC and television

networks to broadcast the

air pollution index

with the

weather report. She persuaded an advertising agency to do-

nate their services to her cause and teamed up with a New

York City councilman to co-found Citizens for Clean Air.

Her endeavors were rewarded in 1967, when she was com-

mended as Citizen of the Year by the New York Medical

Society.

Henderson’s career as an advocate for social and envi-

ronmental reform took flight from there. She argued pas-

sionately against the spread of industrialism, which she called

“pathological” and decried the use of an economic yardstick

to measure quality of life. Indeed, she termed economics

“merely politics in disguise” and even “a form of brain dam-

age.” Henderson believed that society should be measured by

less tangible means, such as political participation, literacy,

education, and health. “Per-capita income,” she felt, is “a

very weak indicator of human well-being.”

She became convinced that traditional industrial de-

velopment wrought little but “ecological devastation, social

unrest, and downright hunger...I think of development, in-

stead,...as investing in ecosystems, their restoration and man-

agement.”

Even the fundamental idea of labor should, Henderson

argued, “be replaced by the concept of ’Good Work’—which

challenges individuals to grow and develop their faculties;

to overcome their ego-centeredness by joining with others

in common tasks; to bring forth those goods and services

needed for a becoming existence; and to do all this with an

ethical concern for the interdependence of all life forms...”

To advance her theories, Henderson has published

several books, Creative Alternative Futures: The End of Eco-

nomics (1978), The Politics of the Solar Age: Alternatives to

713

Economics (1981), Building a Win-Win World (1996), Toward

Sustainable Communities: Resources for Citizens and Their

Governments (1998), and Beyond Globalization: Shaping a

Sustainable Global Economy (1999). She has also contributed

to several periodicals, and lectured at colleges and universi-

ties. In 1972 she co-founded the Princeton Center for Alter-

native Futures, of which she is still a director. She is a

member of the board of directors for

Worldwatch Institute

and the Council for Economic Priorities, among other orga-

nizations. In 1982 she was appointed a Horace Allbright

Professor at the University of California at Berkeley. In

1996, Henderson was awarded the Global Citizen Award.

[Amy Strumolo]

ESOURCES

OOKS

Henderson, H. Beyond Globalization: Shaping a Sustainable Global Econ-

omy. 1999.

———. Building a Win-Win World. 1996.

———. Creative Alternative Futures: The End of Economics. 1978.

———. The Politics of the Solar Age: Alternatives to Economics. 1981.

———. Toward Sustainable Communities: Resources for Citizens and Their

Governments. 1998.

Telephone Interview with Hazel Henderson. Whole Earth Review (Winter

1988): 58–59.

ERIODICALS

Henderson, H. “The Legacy of E. F. Schumacher.” Environment 20 (May

1978): 30–36.

Holden, C. “Hazel Henderson: Nudging Society Off Its Macho Trip.”

Science 190 (November 28, 1975): 863–64.

Herbicide

Herbicides are chemical pesticides that are used to manage

vegetation. Usually, herbicides are used to reduce the abun-

dance of weedy plants, so as to release desired crop plants

from

competition

. This is the context of most herbicide

use in agriculture, forestry, and for lawn management. Some-

times herbicides are not used to protect crops, but to reduce

the quantity or height of vegetation, for example along high-

ways and transmission corridors. The reliance on herbicides

to achieve these ends has increased greatly in recent decades,

and the practice of chemical weed control appears to have

become an entrenched component of the modern technolog-

ical culture of humans, especially in agroecosystems.

The total use of pesticides in the United States in the

mid-1980s was 957 million lb per year (434 million kg/

year), used over 592,000 mi

(1.5 million km

). Herbicides

were most widely used, accounting for 68% of the total

quantity [646 million lb per year [293 million kg/year]), and

applied to 82% of the treated land [484,000 square miles

Environmental Encyclopedia 3

Herbicide

per year (121 million hectares/year)]. Note that especially

in agriculture, the same land area can be treated numerous

times each year with various pesticides.

A wide range of

chemicals

is used as herbicides, in-

cluding:

chlorophenoxy acids, especially

2,4-D

and

2,4,5-T

, which

have an auxin-like growth-regulating property and are se-

lective against broadleaved angiosperm plants;

triazines such as

atrazine

, simazine, and hexazinone;

chloroaliphatics such as dalapon and trichloroacetate;

the phosphonoalkyl chemical, glyphosate, and

inorganics such as various arsenicals, cyanates, and chlo-

rates.

A “weed” is usually considered to be any plant that

interferes with the productivity of a desired crop plant or

some other human purpose, even though in other contexts

weed

species

may have positive ecological and economic

values. Weeds exert this effect by competing with the crop

for light, water, and nutrients. Studies in Illinois demon-

strated an average reduction of yield of corn or maize (Zea

mays) of 81% in unweeded plots, while a 51% reduction was

reported in Minnesota. Weeds also reduce the yield of small

grains, such as wheat (Triticum aestivum) and barley

(Hordeum vulgare), by 25–50%.

Because there are several herbicides that are toxic to

dicotyledonous weeds but not grasses, herbicides are used

most intensively used in grain crops of the Gramineae. For

example, in North America almost all of the area of maize

cultivation is treated with herbicides. In part this is due to

the widespread use of no-tillage cultivation, a system that

reduces

erosion

and saves fuel. Since an important purpose

of plowing is to reduce the abundance of weeds, the no-

tillage system would be impracticable if not accompanied

by herbicide use. The most important herbicides used in

maize cultivation are atrazine, propachlor, alachlor, 2,4-D,

and butylate. Most of the area planted to other agricultural

grasses such as wheat, rice (Oryza sativa), and barley is also

treated with herbicide, mostly with the phenoxy herbicides

2,4-D or MCPA.

The intended ecological effect of any

pesticide

appli-

cation is to control a

pest

species, usually by reducing its

abundance to below some economically acceptable threshold.

In a few situations, this objective can be attained without

important nontarget damage. For example, a judicious spot-

application of a herbicide can allow a selective kill of large

lawn weeds in a way that minimizes exposure to nontarget

plants and animals.

Of course, most situations where herbicides are used

are more complex and less well-controlled than this. When-

ever a herbicide is broadcast-sprayed over a field or forest,

a wide variety of on-site, nontarget organisms is affected,

714

and sprayed herbicide also drifts from the target area. These

cause ecotoxicological effects directly, through toxicity to

nontarget organisms and ecosystems, and indirectly, by

changing

habitat

or the abundance of food species of

wild-

life

. These effects can be illustrated by the use of herbicides

in forestry, with glyphosate used as an example.

The most frequent use of herbicides in forestry is for

the release of small coniferous plants from the effects of

competition with economically undesirable weeds. Usually

the silvicultural use of herbicides occurs within the context

of an intensive harvesting-and-management system, which

may include

clear-cutting

, scarification, planting seedlings

of a single desired species, spacing, and other practices.

Glyphosate is a commonly used herbicide in forestry

and agriculture. The typical spray rate in silviculture is about

2.2–4.9 mi (1–2.2 kg) active ingredient/ha, and the typical

projection is for one to two treatments per forest rotation

of 40–100 years.

Immediately after an aerial application in forestry,

glyphosate residues are about six times higher than litter on

the forest floor, which is physically shielded from spray by

overtopping foliage. The persistence of glyphosate residues

is relatively short, with typical half-lives of two to four weeks

in foliage and the forest floor, and up to eight weeks in

soil

The disappearance of residues from foliage is mostly due to

translocation and wash-off, but in the forest floor and soil

glyphosate is immobile (and unavailable for root uptake or

leaching

) because of binding to organic matter and clay,

and residue disappearance is due to microbial oxidation.

Residues in oversprayed waterbodies tend to be small and

short-lived. For example, two hours after a deliberate

overspray on Vancouver Island, Canada, residues of glypho-

sate in stream water rose to high levels, then rapidly dissi-

pated through flushing to only trace amounts 94 hours later.

Because glyphosate is soluble in water, there is no

propensity for

bioaccumulation

in organisms in preference

to the inorganic

environment

, or to occur in larger concen-

trations at higher levels of the

food chain/web

. This is in

marked contrast to some other pesticides such as DDT,

which is soluble in organic solvents but not in water, so it

has a strong tendency to bioaccumulate into the fatty tissues

of organisms.

As a plant poison, glyphosate acts by inhibiting the

pathway by which four essential amino acids are synthesized.

Only plants and some

microorganisms

have this metabolic

pathway; animals obtain these amino acids from food. Con-

sequently, glyphosate has a relatively small acute toxicity to

animals, and there are large margins of toxicological safety

in comparison with environmental exposures that are realisti-

cally expected during operational silvicultural sprays.

Acute toxicity of chemicals to mammals is often in-

dexed by the oral dose required to kill 50% of a test popula-

Environmental Encyclopedia 3

Herbicide

tion, usually of rats (i.e., rat LD

). The LD

value for pure

glyphosate is 5,600 mg/kg, and its silvicultural formulation

has a value of 5,400 mg/kg. Compare these to LD

s for

some chemicals which many humans ingest voluntarily: nic-

otine 50 mg/kg, caffeine 366, acetylsalicylic

acid

(ASA)

1,700, sodium chloride 3,750, and

ethanol

13,000. The

documented risks of longer-term, chronic exposures of mam-

mals to glyphosate are also small, especially considering the

doses that might be received during an operational treatment

in forestry.

Considering the relatively small acute and chronic tox-

icities of glyphosate to animals, it is unlikely that wildlife

inhabiting sprayed clearcuts would be directly affected by a

silvicultural application. However, glyphosate causes large

habitat changes through species-specific effects on plant pro-

ductivity, and by changing habitat structure. Therefore, wild-

life such as birds and mammals could be secondarily affected

through changes in vegetation and the abundance of their

arthropod foods. These indirect effects of herbicide spraying

are within the context of

ecotoxicology

. Indirect effects

can affect the abundance and reproductive success of terres-

trial and aquatic wild life on a sprayed site, irrespective of

a lack of direct, toxic effects.

Studies of the effects of habitat changes caused by

glyphosate spraying have found relatively small effects on

the abundance and species composition of wildlife. Much

larger effects on wildlife are associated with other forestry

practices, such as clear-cutting and the broadcast spraying

of insecticides. For example, in a study of clearcuts sprayed

with glyphosate in Nova Scotia, Canada, only small changes

in avian abundance and species composition could be attrib-

uted to the herbicide treatment. However, such studies of

bird abundance are conducted by enumerating territories,

and the results cannot be interpreted in terms of reproductive

success. Regrettably, there are not yet any studies of the

reproductive success of birds breeding on clearcuts recently

treated with a herbicide. This is an important deficiency in

terms of understanding the ecological effects of herbicide

spraying in forestry.

An important controversy related to herbicides focused

on the military use of herbicides during the Viet Nam war.

During this conflict, the United States Air Force broadcast-

sprayed herbicides to deprive their enemy of food production

and forest cover. More than 5,600 mi

(14,503 km

) were

sprayed at least once, about 1/7 the area of South Viet Nam.

More than 55 million lb (25 million kg) of 2,4-D, 43 million

lb (21 million kg) of 2,4,5-T, and 3.3 million lb (1.5 million

kg) of picloram were used in this military program. The

most frequently used herbicide was a 50:50 formulation of

2,4,5-T and 2,4-D known as

Agent Orange

. The rate of

application was relatively large, averaging about 10 times

the application rate for silvicultural purposes. About 86% of

715

spray missions were targeted against forests, and the remain-

der against cropland.

As was the military intention, these spray missions

caused great ecological damage. Opponents of the practice

labelled it “ecocide,” i.e., the intentional use of anti-environ-

mental actions as a military tactic. The broader ecological

effects included severe damage to mangrove and tropical

forests, and a great loss of wildlife habitat.

In addition, the Agent Orange used in Viet Nam was

contaminated by the

dioxin

isomer known as TCDD, an

incidental by-product of the manufacturing process of 2,4,5-

T. Using post-Vietnam manufacturing technology, the con-

tamination by TCDD in 2,4,5-T solutions can be kept to

a concentration well below the maximum of 0.1

parts per

million

(ppm) set by the United States

Environmental Pro-

tection Agency

(EPA). However, the 2,4,5-T used in Viet

Nam was grossly contaminated with TCDD, with a concen-

tration as large as 45 ppm occurring in Agent Orange, and

an average of about 2.0 ppm. Perhaps 243–375 lb (110–170

kg) of TCDD was sprayed with herbicides onto Vietnam.

TCDD is well known as being extremely toxic, and it can

cause

birth defects

and miscarriage in laboratory mammals,

although as is often the case, toxicity to humans is less well

understood. There has been great controversy about the

effects on soldiers and civilians exposed to TCDD in Viet-

nam, but epidemiological studies have been equivocal about

the damages. It seems likely that the effects of TCDD added

little to human

mortality

or to the direct ecological effects

of the herbicides that were sprayed in Vietnam.

A preferable approach to pesticide use is

integrated

pest management

(IPM). In the context of IPM, pest

control is achieved by employing an array of complementary

approaches, including:

use of natural predators,

parasites

, and other biological

controls;

use of pest-resistant varieties of crops;

environmental modifications to reduce optimality of pest

habitat;

careful monitoring of pest abundance; and

a judicious use of pesticides, when necessary as a component

of the IPM strategy.

A successful IPM program can greatly reduce, but not neces-

sarily eliminate, the reliance on pesticides.

With specific relevance to herbicides, more research

into organic systems and into procedures that are pest-spe-

cific are required for the development of IPM systems. Ex-

amples of pest-specific practices are the biological control

of certain introduced weeds, for example:

St. John’s wort (Hypericum perforatum) is a serious weed

of pastures of the United States Southwest because it is

Environmental Encyclopedia 3

Heritage Conservation and Recreation Service

toxic to cattle, but it was controlled by the introduction in

1943 of two herbivorous leaf beetles;

the prickly pear cactus (Opuntia spp.) became a serious

weed of Australian

rangelands

after it was introduced as

an ornamental plant, but it has been controlled by release

of the moth Cactoblastis cactorum, whose larvae feed on the

cactus.

Unfortunately, effective IPM systems have not yet

been developed for most weed problems for which herbicides

are now used. Until there are alternative, pest-specific meth-

ods to achieve an economically acceptable degree of control

of weeds in agriculture and forestry, herbicides will continue

to be used for that purpose. See also Agricultural chemicals

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Freedman, B. Environmental Ecology. 2nd Edition. San Diego, CA: Aca-

demic Press, 1995.

McEwen, F. L., and G. R. Stephenson. The Use and Significance of Pesticides

in the Environment. New York: Wiley, 1979.

ERIODICALS

Pimentel, D., et al. “Environmental and Economic Effects of Reducing

Pesticide Use.” Bioscience 41 (1991): 402–409.

———. “Controversy Over the Use of Herbicides in Forestry, With Particu-

lar Reference to Glyphosate Usage.” Environmental Carcinogenesis Reviews

C8 (1991): 277–286.

Heritage Conservation and Recreation

Service

The Heritage Conservation and

Recreation

Service

(HCRS) was created in 1978 as an agency of the U. S.

Department of the Interior (Secretarial Executive Order

3017) to administer the National Heritage Program initiative

of President Carter. The new agency was an outgrowth of

and successor to the former Bureau of Outdoor Recreation.

The HCRS resulted from the consolidation of some 30 laws,

executive orders and interagency agreements that provided

federal funds to states, cities and local community organiza-

tions to acquire, maintain, and develop historic, natural and

recreation sites. HCRS focused on the identification and

protection of the nation’s significant natural, cultural and

recreational resources. It classified and established registers

for heritage resources, formulated policies and programs for

their preservation, and coordinated federal, state and local

resource and recreation policies and actions. In February

716

1981 HCRS was abolished as an agency and its responsibili-

ties were transferred to the

National Park Service

Hetch Hetchy Reservoir

The Hetch Hetchy Reservoir, located on the Tuolumne

River in

Yosemite National Park

, was built to provide

water and hydroelectric power to San Francisco. Its creation

in the early 1900s led to one of the first conflicts between

preservationists and those favoring utilitarian use of

natural

resources

. The controversy spanned the presidencies of

Roosevelt, Taft, and Wilson.

A prolonged conflict between San Francisco and its

only water utility, Spring Valley Water Company, drove

the city to search for an independent water supply. After

surveying several possibilities, the city decided to build a

dam and reservoir in the Hetch Hetchy Valley because the

river there could supply the most abundant and purest water.

This option was also the least expensive, since the city

planned to use the dam to generate hydroelectric power. It

would also provide an abundant supply of

irrigation

water

for area farmers and the

recreation

potential of a new lake.

The city applied to the U. S. Department of the Inte-

rior in 1901 for permission to construct the dam, but the

request was not approved until 1908. The department then

turned the issue over to Congress to work out an exchange

of land between the federal government and the city. Con-

gressional debate spanned several years and produced a num-

ber of bills. Part of the controversy involved the Right of

Way Act of 1901, which gave Congress power to grant

rights of way through government lands; some claimed this

was designed specifically for the Hetch Hetchy project.

Opponents of the project likened the valley to Yosem-

ite on a smaller scale. They wanted to preserve its high cliff

walls, waterfalls, and diverse plant

species

. One of the most

well-known opponents,

John Muir

, described the Hetch

Hetchy Valley as “a grand landscape garden, one of Nature’s

rarest and most precious mountain temples.” Campers and

mountain climbers fought to save the campgrounds and trails

that would be flooded.

As the argument ensued, often played out in newspa-

pers and other public forums, overwhelming national opin-

ion appeared to favor the preservation of the valley. Despite

this public support, a close vote in Congress led to the

passage of the Raker Act, allowing the O’Shaughnessy Dam

and Hetch Hetchy Reservoir to be constructed. President

Woodrow Wilson signed the bill into law on December

19, 1913.

The Hetch Hetchy Reservoir was completed in 1923

and still supplies water and electric power to San Francisco.

In 1987, Secretary of the Interior Donald Hodel created a