Environmental Encyclopedia

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Environmental Encyclopedia 3

Septic tank

that affect the ability of the soil to absorb, treat, and dispose

of septic tank effluent without creating a public health hazard

or contamination of ground or surface waters. If a proposed

site is located on a gently sloping surface that is not suscepti-

ble to

flooding

, and has at least 6 ft (1.8 m) of well-drained,

permeable

soil, with a low content of coarse fragments, only

a minimum area is required for installation of the absorption

drainfield. However, area requirements increase as slope in-

creases and soil permeability, depth of suitable soil, and

depth to groundwater decrease. However, at some sites, the

soil type, depth, or site

topography

may not be suitable

for the use of the conventional soil absorption drainfield,

and modifications or additions to the conventional system

may be required.

Siting requirements usually also include that sufficient

area be reserved for installation of a repair system if the

original system fails. This additional area should meet all

requirements of the original soil absorption system and

should be kept free of development and traffic. The disposal

site should also be located at safe distances from ground

water supply sources,

wetlands

, lakes, streams, drain tile,

and escarpments where

seepage

may occur, as well as set

back from buildings and roads that may interfere with the

proper operation of the system.

A common problem encountered in drainfields is ex-

cessive development of a clogging mat at the interface be-

tween the gravel bed in the absorption trench and the under-

lying soil due to the accumulation of organic materials and

the growth of microorganisms. The development of a clog-

ging mat is a natural process and at some sites, such as those

with sandy soils, may be desirable to slow the movement of

the water through the sandy materials to allow for treatment

of the wastewater to occur. However, excessive development

of a clogging mat may result in formation of anaerobic soil

conditions, which are less conducive to degradation of the

organic waste

materials, as well as in surfacing of the

effluent or backing up of the wastewaters into the residence.

At sites with limiting features or where problems with

the excessive development of clogging mats occur, landown-

ers may modify or enhance the conventional soil absorption

drainfield to increase its performance. Examples of such

alterations include:

Alternating drainfields: The wastewater effluent from the

septic tank is directed to two or more separate drainfields;

a section of the drainfield receives effluent for six to 12

months and then is allowed to rest for a similar period of

time. The clogging mat that forms at the soil/trench inter-

face dries and is oxidized during this dormant period, thus

increasing the expected life span of the section and restoring

aerobic soil conditions.

Pressure distribution: A pressure head is created within

the distribution pipe system in the drainfield. This is usually

1277

achieved by using a dosing tank and a pump or a siphon

and yields uniform distribution of the wastewater through-

out the system. The pressure distribution system differs

from a conventional system because approximately the

same amount of effluent flows out of each hole in the

distribution pipes, rather than a concentrated amount of

effluent flowing by gravity into a few localized areas. The

effluent is discharged periodically to the drainfield so that

a dose/rest cycle is maintained, and in turn allows for the

wastewater to be absorbed into the underlying soil before

additional effluent is added to the drainfield. The dose/

rest cycle may also slow down the formation rate of the

clogging mat that naturally occurs over time. Most com-

monly, landowners use these types of pressure distribution

systems (which also employ vegetation to help evaporate

liquids): (a) low-pressure subsurface pipe distribution sys-

tem, which consists of a network of small-diameter perfora-

ted plastic pipes buried in narrow, shallow trenches; (b)

mound system, in which wastewater is pumped to perfora-

ted plastic pipe that is placed in a vegetated sand mound

constructed above the natural surface of the ground; and

(c)

evapotranspiration

bed, in which a vegetated sand

bed is lined with plastic or other waterproof material.

A wide variety of onsite septic systems exist from which

to select the most appropriate for a specific site. The primary

criterion for selection of an appropriate system is the ability

of the system to protect public health and to prevent

envi-

ronmental degradation

at the specific site.

Experimental septic treatment systems now run in

private solar-powered greenhouses that house complete eco-

systems of plants and fish to create a natural cleansing action

that can process wastewater into clean drinking water in as

little as 12 days. Systems were cropping up sparingly by the

end of the 1990s, often in milder climates where the solar

source is plentiful. One self-contained eco-system proved

capable of servicing an entire small town at a development

cost as low as $300,000. The potential for

third world

implementation is under consideration, and prototype sys-

tems developed in the early part of the decade were imple-

mented even in the harsh New England

climate

, where

water pollution

is particularly severe.

Serious ecological threats in the northeast led to a

series of comprehensive changes to the Massachusetts State

Environmental Code (Title V) beginning in 1995. The state

set restrictions on the siting and maintenance of septic tanks

and systems and imposed requirements for state-certified

testing of systems whenever a property title transfers. The

code changes were prompted by dangerous levels of water

pollution making it unsafe to swim and fish in many of the

state’s lakes and bays and contributing to

toxins

in the

drinking water. The legislation requires that detailed engi-

neering plans be included as part of construction permits.

Environmental Encyclopedia 3

Serengeti National Park

Initial inspection of existing systems is required combined

with regular inspections of certain private and public systems.

Follow-up inspections are mandated coincident with any

changes to building occupancy. Permissible septic system

additives are clearly defined.

Some developers hope to eliminate the septic tank

altogether with high-tech waste systems allowing an entire

sewer system to be housed inside a single-family dwelling,

including a 91-gal (344-l) wastewater tank that operates on

240 volts of electricity. The system, with an ability to pump

wastewater vertically or as far as 2 mi (3.2 km) horizontally,

can easily follow the contour of the landscape. The system

is easier and cheaper to build because it eliminates the deep

digging associated with septic tank system installation and

offers the advantages of a completely contained sewer system.

[Judith Sims]

ESOURCES

OOKS

Design Manual: Onsite Wastewater Treatment and Disposal Systems. Cincin-

nati: U.S. Environmental Protection Agency, Municipal Environmental

Research Laboratory, 1980.

National Small Flows Clearinghouse. So...Now You Own a Septic Tank.

Morgantown, WV: West Virginia University, 1990.

Northern Virginia Planning District Commission. A Reference Guide for

Homeowners: Your Septic System. Morgantown, WV: West Virginia Univer-

sity, National Small Flows Clearinghouse, 1990.

Small Wastewater Systems: Alternative Systems for Small Communities and

Rural Areas. Washington, DC: U.S. Environmental Protection Agency,

Office of Water Program Operations, 1980.

Serengeti National Park

Serengeti National Park lies in northern Tanzania between

Lake Victoria and the East African Rift Valley. It was estab-

lished in 1929 (and expanded in 1940) to protect 5,600

square miles (14,500 sq. km) of the Serengeti plains

ecosys-

tem

. This vast park spans an area twice the size of

Yel-

lowstone National Park

and supports over 94

species

mammals, 400 species of birds, and includes the spectacular

migration

routes of the largest herds of grazing animals to

be seen anywhere in the world.

Each year, migrating herds move clockwise around the

Park, constantly seeking better feeding grounds. Changing

water availability is the key factor in the annual migrations,

which correlate closely with the local cycles of rainfall. At

the right time of year, visitors to the Park can see hundreds

of thousands of migrating herds of wildebeest (Connochates

taurinus), running in winding lines several miles long. The

wildebeest are accompanied by herds of zebra (Equus bur-

chelli) and Thomson’s gazelle (Gazella thomsoni).

1278

During the peak dry season (August to November),

the grazers congregate in the Serengeti’s northern extension,

moving south east when the first storms appear in December.

The greatest concentration of animals occurs in the short

grass pastures of the eastern Serengeti from December to

May when millions of the Park’s migratory grazers assemble.

They are accompanied by packs of nomadic predators such

as lion (Panthera leo) and hyenas (Crocuta crocuta). As the

dry season progresses (June and July) and the grazing gets

worse, the massive herds move to the wooded savannas of

the western corridor of the Park. By mid-August, when this

food supply is exhausted, the herds move back into the

northern plains, crossing also into the adjacent Masai Mara

National Reserve in Kenya.

The non-migrant inhabitants of the Serengeti plains

include ostrich (Struthio camelus), impala (Aepyceros melani-

ous), topi (Damalicus korrigum), buffalo (Syncercus kaffer),

giraffe (Giraffa camelopardalis), Grant’s gazelle (Gazella

granti), leopard (Panthera pardus), cheetah (Acinonyx juba-

tus), hunting dogs (Lycaeon pictus), and jackals (Canis

adustus).

The three principle species of migratory grazers—ze-

bra, wildebeest, and Thomson’s gazelle—do not compete

directly for food, and it is common to find them grazing

together.

Zebras

eat the upper parts of the grass shoots,

exposing the softer leaf bases for the wildebeest. Grazing

wildebeest in turn expose the herb layer beneath the grass,

which is eaten by gazelles. Balanced populations of grazers

actively maintain the

stability

of grassland ecosystems: too

little grazing will allow woody vegetation to grow, while too

much grazing will turn grassland into

desert

Today, the Serengeti National Park is under pressure

from the rapidly growing human population outside the

Park. Domestic cattle herders and farmers operate inside

Park boundaries, competing with the

wildlife

for food,

water, and land, while well-armed poachers kill game for

meat, horns, and tusks. Human ancestors (Australopithecus

robustus and Homo habilis) once hunted game on the Ser-

engeti plains, as evidenced by the finds of the Louis and

Mary Leakey at Olduvai Gorge, which lies close to the Park’s

eastern entrance.

[Neil Cumberlidge Ph.D.]

ESOURCES

OOKS

A Field Guide to the National Parks of East Africa. London: J. G. Williams,

Collins, 1981.

Schaller, George B. Golden Shadows, Flying Hooves. Chicago: University

of Chicago Press, 1970.

Environmental Encyclopedia 3

Seveso, Italy

Zebras and wildebeasts at Ngorongoro Crater, Serengeti National Park, Tanzania. (Photograph by Carolina Biological

Supplies. Phototake. Reproduced by permission.)

Seveso, Italy

Accidents in which large quantities of dangerous

chemicals

are released into the

environment

are almost inevitable in

the modern world. Toxic chemicals are produced in such

large volumes today that it would be a surprise if such acci-

dents were never to occur. One of the most infamous acci-

dents of this kind occurred at Seveso, Italy, a town near

Milan, on July 10, 1976.

The Swiss manufacturing firm of Hoffman-LaRoche

operated a plant at Seveso for the production of hexachloro-

phene, a widely used disinfectant. One of the raw materials

used in this process is 2,4,5-trichlorophenol (2,4,5-TCP).

At one point in the operation, a vessel containing 2,4,5-

TCP exploded, releasing the chemical into the

atmosphere

A cloud 100–160 ft (30–50 m) high escaped from the plant

and then drifted downwind. It eventually covered an area

about 2,300 ft (700 m) wide and 1.2 m (2 km) long.

Although 2,4,5-TCP is a skin irritant, it was not this

chemical that caused concern. Instead, it was an impurity

in 2,4,5-TCP, a compound called 2,3,7,8-tetrachlorodi-

1279

benzo-p-dioxin, that caused alarm. This compound, one

of a family known as dioxins, is one the most toxic

chemicals known to science. It occurs as a by-product in

many manufacturing reactions in which 2,4,5-TCP is

involved. Experts estimated that 7–35 lb (3–16 kg) of

dioxin

were released into the atmosphere as a result of

the Seveso explosion.

People living closest to the Hoffman-LaRoche plant

were evacuated from their homes and the area was closed

off. About 5,000 nearby residents were allowed to stay, but

were prohibited from raising crops or farm animals.

Damage to plants and animals in the exposed area

was severe. Thousands of farm animals died or had to be

destroyed. More than 2.5 tons (225 kg) of

contaminated

soil

were removed before planting could begin again. Short-

and long-term effects on human health, however, were rela-

tively modest. In the months following the accident, 176

individuals were found to have chloracne, an inflammation

of the skin caused by chlorine-based chemicals. An addi-

tional 137 cases of the condition were found in a follow-up

survey six months after the accident.

Environmental Encyclopedia 3

Sewage treatment

Other health problems were also detected in the hu-

man population. About 8% of the exposed population had

enlarged livers and a few residents showed signs of minor

nerve damage. Some people claimed that exposed women

had higher rates of miscarriage and of deformed children,

but local authorities were unable to substantiate these claims.

No human lives were lost in the accident.

[David E. Newton]

ESOURCES

OOKS

Harrison, R. M., ed. Pollution: Causes, Effects, and Control. Cambridge,

Royal Society of Chemistry, 1990.

ERIODICALS

Walsh, J. “Seveso: The Questions Persist Where Dioxin Created a Waste-

land.” Science (September 9, 1977): 1064–1067.

———. “Reporter at Large: Dioxin Pollution of Seveso.” New Yorker (Sep-

tember 4, 1978): 34–36+.

Whiteside, T. “Reporter at Large: TCDD Explosion at Icmesa Chemical

Plant.” New Yorker (July 25, 1977): 41+.

Sewage treatment

Sewage is

wastewater

discharged from a home, business,

or industry. Sewage is treated to remove or alter contami-

nants in order to minimize the impact of discharging waste-

water into the

environment

. The operations and processes

used in sewage treatment consist of physicochemical and

biological systems.

The concerns of those involved in designing sewage

treatment systems have changed over the years. Originally,

the

biochemical oxygen demand

(BOD) and total sus-

pended solids (TSS) received most of the attention. This

was primarily because excessive BOD and TSS levels could

cause severe and readily apparent problems, such as oxygen

deficits that led to odors and

fish kills

, and

sludge

deposits

that suffocated benthic organisms. By removing BOD and

TSS, other contaminants were also removed and other bene-

fits were realized; so even today, some

discharge

permits

contain only limits for BOD and TSS. However, many

permits now contain limits on other contaminants as well,

and these limits, as well as other requirements, are constantly

changing.

Among the first contaminants to be added to the

requirements for discharge permits were nutrients. The most

commonly regulated nutrients are

phosphorus

and

nitro-

gen

. Originally removing phosphorus and nitrogen could

only be done through expensive, advanced methods. But

scientists have recently discovered ways to accomplish en-

hanced removals of nutrients in conventional biological

1280

treatment plants with relatively minor operational and struc-

tural adjustments.

The most recently regulated pollutants are toxicants.

There are regulations for specific toxic agents, and there are

the generic-type regulations, which specify that the toxicity

to certain test organisms should not exceed a certain level.

For example, the wastewater discharged from a particular

municipality may be restricted from killing more than 50% of

the Ceriodaphnia in an aquatic toxicity test. The municipality

would not need to determine what is causing the toxicity,

just how to minimize its effects. Efforts to understand the

causes of toxicity are referred to as toxicity reduction evalua-

tions. The generic limit can therefore sometimes turn into

a more specific standard, in the view of the municipality or

industry, when the identity of a toxicant is determined; the

general regulatory limit might remain, but treatment person-

nel are more cognizant of the role that a certain pollutant

plays in overall,

effluent

toxicity.

The systems used to treat sewage can be divided into

stages. The first stage is known as preliminary treatment.

Preliminary treatment includes such operations as flow

equalization, screening, comminution (or grinding), grease

removal, flow measurement, and grit removal. Screenings

and grit are taken to a

landfill

. Grease is directed to sludge

handling facilities at the plant.

The next stage is primary treatment, which consists

of gravity settling to remove suspended solids. Approxi-

mately 60% of the TSS in a domestic wastewater is removed

during primary settling. Grease that floats to the surface of

the

sedimentation

tank is skimmed off and handled along

with the sludge (known as primary sludge) collected from

the bottom of the tank.

The next stage is secondary treatment, which is de-

signed to remove soluble organics from the wastewater. Sec-

ondary treatment consists of a biological process and second-

ary settling. There are a number of biological processes.

The most common is

activated sludge

, a process in which

microbes

, also known as

biomass

, are allowed to feed on

organic matter in the wastewater. The make-up and dynam-

ics of the biomass population is a function of how the acti-

vated sludge system is operated. There are many types of

activated sludge systems that differ based on the time waste-

water remains in the biological reactor and the time microbes

remain there. They also differ depending on whether air or

oxygen is introduced, how gas is introduced, and where

wastewater enters the biological reactor, as well as the num-

ber of tanks and the mixing conditions.

There are also biological treatment systems in which

the biomass is attached. Trickling

filters

and biological

towers are examples of systems that contain biomass ad-

sorbed to rocks plastic. Wastewater is sprayed over the top

of the rocks or plastic and allowed to trickle down and over

Environmental Encyclopedia 3

Sewage treatment

Schematic representation of a sewage treatment system. (McGraw-Hill Inc. Reproduced by permission.)

the attached biomass, which removes materials from the

waste through

sorption

and biodegradation. A related type

of attached-growth system is the rotating biological con-

tactor, where biomass is attached to a series of thin, plastic

wheels that rotate the biomass in and out of the wastewater.

1281

It is important to note that each of the above biological

systems is

aerobic

, meaning that oxygen is present for the

microbes.

Anaerobic

biological systems are also available in

both attached and suspended growth configurations. Exam-

ples of the attached and suspended growth systems are,

Environmental Encyclopedia 3

Shade-grown coffee and cacao

respectively, anaerobic filters and upflow anaerobic sludge

blanket units.

The end-products of aerobic and anaerobic processes

are different. Under aerobic conditions, if completely oxi-

dized, organic matter is transformed into products that are

not hazardous. But an anaerobic process can produce

meth-

ane

(CH

), which is explosive, and ammonia (NH

) and

hydrogen

sulfide (H

S), which are toxic. There are thus

special design considerations associated with

anaerobic

systems

, though methane can be recovered and used as a

source of energy. Some materials are better degraded under

anaerobic conditions than under aerobic conditions. In some

cases, the combination of anaerobic and

aerobic systems

in a series provides better and more economical treatment

than either system could alone. Many substances are not

completely mineralized to the end-products mentioned

above, and other types of intermediate metabolites can be

considered in selecting a biological process.

Biomass generated during biological treatment is set-

tled in secondary clarifiers. This settled biomass or secondary

sludge is then piped to sludge-management systems or re-

turned to the biological reactor in amounts needed to main-

tain the appropriate biomass level. The hydraulic detention

time of secondary clarifiers is generally in the area of two

hours.

As mentioned above, biological systems are designed

on the basis of hydraulic

residence time

and sludge age. In

a conventional activated-sludge system, sewage is retained

in the reactor for about five to seven hours. Biomass, due

to the

recycling

of sludge from the secondary clarifier, re-

mains in the reactor, on average, for about ten days.

Disinfection follows secondary clarification in most

treatment plants. Disinfection is normally accomplished

with

chlorine

. Due to the potential environmental impact of

chlorine, most plants now dechlorinate wastewater effluents

before discharge.

Some facilities use another stage of treatment before

disinfection. This stage is referred to as tertiary treatment

or advanced treatment. Included among the more commonly

used advanced systems are

adsorption

to activated

carbon

filtration

through sand and other media,

ion exchange

various membrane processes, nitrification-denitrification,

coagulation-flocculation, and fine screening.

The treatment systems used for municipal sewage can

be different from the systems used by industry, for industrial

wastes can pose special problems which require innovative

applications of the technologies available. Additionally, in-

dustrial wastes are sometimes pretreated before being dis-

charged to a sewer, as opposed to being totally treated for

direct discharge to the environment. See also Aerobic sludge

digestion; Anaerobic digestion; Bioremediation; Industrial

1282

waste treatment; Sludge treatment and disposal; Waste man-

agement

[Gregory D. Boardman]

ESOURCES

OOKS

Metcalf and Eddy, Inc. Wastewater Engineering Treatment, Disposal, and

Reuse. Revised by G. Tchobanoglous and F. Burton. 3rd ed. New York:

McGraw-Hill, 1991.

Peavy, H. S., D. R. Rowe, and G. Tchobanoglous. Environmental Engi-

neering. New York: McGraw-Hill, 1985.

Viessman, W., and M. J. Hammer. Water Supply and Pollution Control.

4th ed. New York: Harper and Row, 1985.

Shade-grown coffee and cacao

Coffee (Coffea arabica) and cacao (Theobroma cacao) are im-

portant agricultural crops in the developing world that have

been traditionally grown under a light canopy of rainforest

trees created by thinning the original rainforest. In the 1970s,

growers in South America began changing their planting

practices, setting out sun-tolerant varieties of these plants

in uniform rows. Coffee and cacao grown in full sun require

more pesticides and

fertilizer

in order to thrive. In addition,

when rainforest is cleared in order to grow these crops in

sun, animals and native plants lose their

habitat

, and

biodiv-

ersity

(the number of different plant an animal

species

a habitat) decreases.

Coffee and cacao are grown in places that would nor-

mally support tropical rainforests with enormous biodiver-

sity. The original technique of thinning the forest and grow-

ing these crops in shade under a light canopy of trees reduced

biodiversity. Completely clearing the forest and growing a

single crop in full sun severely reduces biodiversity. When

coffee and cacao are grown in shade, far less of the original

habitat is destroyed.

Destruction of tropical rainforests due to

logging

subsistence cultivation (

slash and burn agriculture

), and

cash-crop cultivation, including the growing of coffee and

cacao, has become of increasing concern to ecologists world-

wide because of its far-reaching effects. In the late 1990s,

ecologists in the United States recognized that

deforesta-

tion

in the tropics was destroying the winter habitat of many

migrating songbirds as well as native birds. One solution,

among many, was to advocate for the return of traditional

agricultural methods for South American coffee and cacao.

Combined efforts of

conservation

groups, farmers, and

coffee buyers working across international borders led to a

growing market in shade-grown coffee in the early 2000s.

Advocating for shade-grown cacao has met with a more

limited success.

Environmental Encyclopedia 3

Shadow pricing

The coffee plant is a low shrub or tree originating in

Africa in the high forests of Ethiopia and the Sudan. Colo-

nists introduced the plant to Central and South America in

the 1700s. Coffee developed into an increasingly important

cash crop

in the nineteenth century. It grew well in the

higher elevations of Central and South America, where moist

conditions and the cloud and tree cover of the rainforests

allowed it to flourish. Coffee production grew two- to three-

fold in parts of Central America between 1870 and 1910,

as coffee became a valued commodity worldwide. By 2000,

over 40% of cropland in Central America was planted with

coffee, and coffee was second only to oil as Central America’s

most valuable export.

Until the 1970s, coffee was produced mostly by small

farmers who grew the crop under the forest canopy. Farmers

began planting coffee in rows in full sun in the 1970s. United

States Agency for International Development (USAID) and

local government groups encouraged farmers to apply

mono-

culture

plantation farming to their coffee farms, setting

the plants out in deforested fields and treating them with

chemical pesticides and fertilizers. Almost 70% of Colum-

bia’s coffee plantations were transformed to full-sun planta-

tions between the 1970s and early 1990s. In Mexico, Costa

Rica, and other parts of Central America, some 30–40% of

coffee production shifted to full-sun fields.

In many cases, sun-grown plants produced larger crops

than shade-grown plant. Yet this method had hidden costs,

because the plants soon depleted nutrients from the

soil

and required chemical fertilizer to continue to produce high

yields. Coffee plants grown in full sun also do not live as

long as plants grown in shade. While a shade-grown coffee

shrub can survive for 80–100 years, plants grown in full sun

live only about 15 years.

Clearing land for full-sun coffee production (and to

plant other agricultural crops and for logging) had devasta-

ting effects on all parts of the

ecosystem

. For example, full-

sun coffee plantations were found to support fewer than ten

percent of the species of birds found in the rainforest.

Conservationists in the United States began recording

a decline in the population of migratory songbirds such as

the northern oriole (Icterus galbula) in the 1980s. By the

1990s some scientists suspected the falling songbird popula-

tion in the United States was due in part to loss of habitat

in the birds’ winter homes in Central and South America.

This loss of habitat was wide-ranging, with full-sun planta-

tions making up only one small part of the problem.

Conservation groups began promoting shade-grown

coffee in the late 1990s as a way to conserve rainforest

habitat. One of the biggest coffee buyers in the United

States, Starbucks, began purchasing shade-grown coffee

from Mexico in 2000 to support the rainforest conservation

effort. A growing market for gourmet coffee in the United

1283

States, made it economically feasible for some farmers to

return to traditional shade-grown crops.

Cacao production has followed a similar path. Cacao

is native to South America, and grows in similar conditions

to coffee. The conversion to full-sun cacao plantations began

in the 1970s. In Ecuador, a prime producer of cacao, collapse

of the market led farmers to replant with quick-growing,

sun-tolerant hybrids. Like coffee, cacao grown on plantations

without forest shade depletes the soil, requiring the addition

of chemical fertilizers. Furthermore, monoculture fields di-

minish biodiversity and increase susceptibility to disease and

pests. Some growers’ cooperatives, in league with North

American conservation groups, began returning to shade-

grown cacao in the late 1990s. To date, shade-grown cacao

has lacked the substantial market shade-grown coffee has

found, yet by 2000, hundreds of small cacao growers in

Ecuador had converted to traditional shade cultivation.

[Angela Woodward]

ESOURCES

ERIODICALS

Chou, Sophie. “Coffee and Deforestation.” World Watch (March/April

1998): 9.

“Finally, the Message Is Clear: Less Pollution, More Profits.” In Business

23, no. 4 (September/October 2001): 30.

Goldberg, Carey. “Songbirds’ Plight Starts a Buzz in Coffee Circles.” New

York Times (July 27, 1997): 12.

Hull, Jennifer Bingham. “Can Coffee Drinkers Save the Rainforest?” Atlan-

tic Monthly (August 1999): 19–21.

LaFranchi, Howard. “Made in the Shade: Java that Saves Forests.” Christian

Science Monitor 92, no. 69 (March 2, 2000): 1.

Rice, Robert A. “A Place Unbecoming: The Coffee Farm of Northern

Latin America.” Geographical Review 89, no. 4 (October 99): 554–580.

“Shade-Grown Cocoa Returns to Ecuador.” Candy Industry 165, no. 6

(June 2000): 20.

RGANIZATIONS

Rainforest Alliance, 65 Bleecker Street, New York, NY USA 10012 (212)

677-1900, Email: canopy@ra.org, <http://www.rainforestalliance.com>

Shadow pricing

A practice employed by some economists that involves put-

ting a price on things that normally do not have a market

value. For example,

pollution

degrades common property

and the natural heritage of present and

future generations

but because it is considered a “free” good, no one “pays” for

it at the marketplace. Yet pollution has a cost even if the

market fails to explicitly take into account this cost and

assign it to responsible parties. Thus pollution is perceived

by most economists as a defect that undermines otherwise

efficient markets. To correct this defect, economists often

advocate the use of some type of shadow pricing for pollu-

Environmental Encyclopedia 3

Shanty towns

tion. Such prices are set by the “shadow” procedure of asking

people what they would be willing to pay for breathing clean

air, watching

whales

migrate, or preventing the

extinction

of a particular

species

of plant or animal. Hypothetical

or shadow prices for these “commodities” can thereby be

estimated. Some environmentalists and economists, how-

ever, criticize shadow pricing for falsely attempting to assign

a monetary value to things that are invaluable precisely be-

cause they (like beauty, love, and respect) are not and cannot

be bought, sold, or traded in markets. To assign a shadow

price, these critics claim, is to make the mistake of assuming

that nothing has

intrinsic value

and that the worth of every-

thing can be measured and reduced to its utilitarian or instru-

mental value.

Shanty towns

The United Nations estimates that at least one billion peo-

ple—20% of the world’s population—live in crowded, un-

sanitary slums of the central cities and in the vast shanty

towns and squatter settlements that ring the outskirts of

most

Third World

cities. Around 100 million people have

no home at all. In Bombay, India, for example, it is thought

that half a million people sleep on the streets, sidewalks,

and traffic circles because they can find no other place to

live. In Sa

o Paulo, Brazil, at least three million “street kids”

who have run away from home or have been abandoned by

their parents live however and wherever they can. This is

surely a symptom of a tragic failure of social systems.

Slums are generally legal but otherwise inadequate

multifamily tenements or rooming houses, either custom

built for rent to poor people or converted from some other

use. The chals of Bombay, for example, are high-rise tene-

ments built in the 1950s to house immigrant workers. Never

very safe or sturdy, these dingy, airless buildings are already

crumbling and often collapse without warning. Eighty-four

percent of the families in these tenements live in a single

room; half of those families consist of six or more people.

Typically they have less than 22 ft

(2 m

) of floor space

per person and only one or two beds for the whole family.

They may share kitchen and bathroom facilities down the

hall with 50–75 other people. Even more crowded are the

rooming houses for mill workers, where up to 25 men sleep

in a single room only 75 ft

(7 m

). Because of this over-

crowding, household accidents are a common cause of in-

juries and deaths in cities of developing countries, especially

to children. Charcoal braziers or kerosene stoves used in

crowded homes are a routine source of fires and injuries.

With no place to store dangerous materials beyond the reach

of children, accidental poisonings and other mishaps are a

constant hazard.

1284

Shanty towns are created when people move onto un-

developed lands and build their own houses. Shacks are built

of corrugated metal, discarded packing crates, brush, plastic

sheets, or whatever building materials people can scavenge.

Some shanty towns are simply illegal subdivisions where

the landowner rents land without city approval. Others are

spontaneous or popular settlements or squatter towns where

people occupy land without the owner’s permission. Some-

times this occupation involves thousands of people who move

onto unused land in a highly organized, overnight land inva-

sion, building huts and laying out streets, markets, and

schools before authorities can evict them. In other cases,

shanty towns gradually appear.

Called barriads, barrios, favelas,orturgios in Latin

America, bidonvillas in Africa, or bustees in India, shanty

towns surround every megacity of the developing world.

They are not an exclusive feature of poor countries, however.

Some 200,000 immigrants live in the colonias along the

southern Rio Grande in Texas. Only 2% have access to

adequate

sanitation

. Most live in conditions as poor as

those of any city of a developing nation. Smaller enclaves

of the poor and dispossessed can be found in most Ameri-

can cities.

The problem is magnified in

less developed coun-

tries

. Nouakchott, Mauritania, the fastest growing city in

the world, consists almost entirely of squatter settlements

and shanty towns. It has been called “the world’s largest

refugee camp.” About 80% of the people in Addis Ababa,

Ethiopia, and about 70% of those in Luanda, Angola, live

in these squalid refugee camps. Two-thirds of the population

of Calcutta live in shanty towns or squatter settlements and

nearly half of the 19.4 million people in

Mexico City, Mex-

ico

, live in uncontrolled, unauthorized shanty towns and

squatter settlements. Many governments try to clean out

illegal settlements by bulldozing the huts and sending riot

police to drive out the settlers, but the people either move

back or relocate to another shanty town elsewhere.

These popular but unauthorized settlements usually

lack sewers, clean water supplies, electricity, and roads. Often

the land on which they are built was not previously used

because it is unsafe or unsuitable for habitation. In

Bhopal,

India

, and Mexico City, for example, squatter settlements

were built next to deadly industrial sites. In such cities as

Rio de Janiero, Brazil; La Paz, Bolivia; Guatemala City,

Guatemala; and Caracas, Venezuela, they are perched on

landslide-prone hills. In Bangkok, Thailand, thousands of

people live in shacks built over a fetid tidal swamp. In Lima,

Peru; Khartoum, Sudan; and Nouakchott, shanty towns have

spread onto sandy deserts. In Manila in the Phillipines,

20,000 people live in huts built on towering mounds of

garbage

amidst burning industrial waste in city dumps.

Environmental Encyclopedia 3

Shanty towns

Living in tents on the streets of New Delhi, India.

(Visuals Unlimited. Reproduced by permission.)

Few developing countries can afford to build modern

waste treatment systems for their rapidly growing cities, and

the spontaneous settlements or shanty towns are the last to

be served. The

World Bank

estimates that only 35% of urban

residents in developing countries have satisfactory sanitation

services. The situation is especially desperate in Latin

America, where only 2% of urban sewage receives any treat-

ment. In Egypt, Cairo’s sewer system was built about 50

years ago to serve a population of two million people. It is

now being overwhelmed by more than 11 million inhabit-

ants. Only 217 of India’s 3,119 towns and cities have even

partial sewage systems and

water treatment

facilities.

These systems serve less than 16% of India’s 200 million

urban residents. In Colombia, the Bogota River, 125 mi

(200 km) downstream from Bogota’s five million residents,

still has an average fecal bacterial count of 7.3 million cells

per liter, more than 7,000 times the safe drinking level and

3,500 times higher than the limit for swimming.

Some 400 million people, or about one-third of the

population in developing world cities, do not have safe drink-

ing water, according to the World Bank. Where people must

buy water from merchants, it often costs 100 times as much

as piped city water and may not be safe to drink after all.

Many rivers and streams in Third World countries are little

more than open sewers, and yet, they are all that poor people

1285

have for washing clothes, bathing, cooking, and, in the

worstcases, for drinking. Diarrhea, dysentery, typhoid, and

cholera

are epidemic diseases in these countries, and infant

mortality

is tragically high.

A striking aspect of most shanty towns is the number

of people selling goods and services of all types on the streets

or from small stands in informal markets. Food vendors

push carts through crowded streets; children dart between

cars selling papers or cigarettes; curb-side mechanics make

repairs using primitive tools and ingenuity. Nearly everything

city residents need is available on the streets. These individ-

ual entrepreneurs are part of the informal economy: small-

scale family businesses in temporary locations outside the

control of normal regulatory agencies. In many developing

countries, this informal sector accounts for 60–80% of the

economy.

Governments often consider these independent busi-

nesses to be backward and embarrassing, a barrier to orderly

development. It is difficult to collect taxes or to control these

activities. In many cities, police drive food vendors, beggars,

peddlers, and private taxis off the streets at the same time

that they destroy shanties and squatter settlements.

Recent studies, however, have shown that this informal

economy is a vital, dynamic force that is more often positive

than negative. The sheer size and vigor of this sector means

that it can no longer be ignored or neglected. The informal

economy is often the only feasible source of new housing,

jobs, food distribution, trash removal,

transportation

,or

recycling

for the city. Small businesses and individual entre-

preneurs provide services that people can afford and that

cities cannot or will not provide.

The businesses common to the informal sector are

ideal in a rapidly changing world. They tend to be small,

flexible, and labor intensive. They are highly competitive

and dynamic, avoiding much of the corruption of developing

nations’ bureaucracies. Government leaders beginning to

recognize that the informal sector should be encouraged

rather than discouraged are making microloans and assisting

communities with self-help projects. When people own their

houses or businesses, they put more time, energy, and money

into improving and upgrading them.

[William P. Cunningham Ph.D.]

ESOURCES

OOKS

Hardoy, J. E., and D. E. Satterthwaite. “Third World Cities and the

Environment of Poverty.” In Global Possible, edited by R. Repetto. Washing-

ton, DC: World Resources Institute, 1985.

Livermash, R. “Human Settlements.” In World Resources 1990–1991. Wash-

ington, DC: World Resources Institute, 1990.

Environmental Encyclopedia 3

Sharks

ERIODICALS

“The World’s Urban Explosion.” Unesco Courier (March 1985): 24–30.

Sharks

Sharks are eight orders of cartilaginous fishes in the class

Elasmobranchii. Sharks first appear in the fossil record of

about 430 million years, during the Silurian Period. The

Silurian is sometimes known as “Age of Fishes,” because

this is when the first kinds of fish-like animals appeared and

then rapidly radiated into a great diversity of forms. Today,

there are about 400 living

species

of sharks, divided into

eight orders and 30 families. New species continue to be

discovered as marine biologists begin to explore the relatively

unknown abyssal waters of the oceans.

The living orders of sharks are:

Squatiniformes, including 13 species of angelsharks, with

a flat body, extremely wide and elongate pectoral fins, two

dorsal fins, no anal fin, and a body length up to 8 ft

(2.4 m); an example is the Pacific angelshark (Squatina

californica).

Pristiophoriformes, including five species of sawsharks,

with a narrow cylindical body, two dorsal fins, no anal fin,

a long blade-like snout edged with needle-like teeth, and

a body length up to 6 ft (1.8 m); an example is the longnose

sawshark (Pristiophorus cirratus).

Squaliformes, including more than 80 species of dogfish

sharks, with a cylindrical body, two dorsal fins, no anal

fin, a moderately long snout, and a body length up to 23

ft (7.0 m); examples are the Greenland shark (Somniosus

microcephalus) and spiny dogfish (Squalus acanthias).

Hexanchiformes, including five species of six-gill and

seven-gill sharks, with a cylindrical body, one dorsal fin,

an anal fin, and a body length up to 16.5 ft (5.0 m); an

example is the six-gill shark (Hexanchus griseus).

Carcharhiniformes, including almost 200 species of ground

sharks, with a cylindrical body, two dorsal fins, an anal fin,

a moderately long snout, a nictitating eye membrane, and

a body length up to 25 ft (7.6 m); examples are the tiger

shark (Galeocerdo cuvieri) and scalloped hammerhead

(Sphyrna lewini).

Lamniformes, including 16 species of mackerel sharks, with

a cylindrical body, two dorsal fins, an anal fin, a moderately

long snout, and a body length up to 45 ft (14 m); examples

are the megamouth shark (Megachasma pelagios), pelagic

thresher shark (Alopias pelagicus), and basking shark (Cetor-

hinus maximus).

Orectolobiformes, including 33 species of carpet sharks,

with a cylindrical body, two spineless dorsal fins, an anal

fin, a short snout, and a body length up to 45 ft (14 m);

examples are the nurse shark (Ginglymostoma cirratum),

1286

great white shark (Carcharodon carcharias), and whale shark

(Rhincodon typus; the world’s largest fish).

Heterodontiformes, including eight species of bullhead

sharks, with a cylindrical body, two spined dorsal fins, no

anal fin, a short snout, teeth adapted for either gripping

or crushing, and a body length up to 66 in (1.7 m); an

example is the horn shark (Heterodontus francisci).

Species of sharks vary greatly in body design. In gen-

eral, however, they have a relatively streamlined body shape,

which allows them to swim without using much energy. The

conservation

of energy is important to sharks because they

do not appear to sleep and most species must swim continu-

ously to maintain a flow of water over their gills, which is

necessary for the exchange of respiratory oxygen and

carbon

dioxide

. As sharks swim, water passes through their mouth,

over the gills, and then exits the body through lateral gill

slits located behind the head.

Sharks do not have true bones; rather, their skeleton

is made up of a softer material known as cartilage. The

center of their larger vertebrae, however, may contain a bone-

like deposit of calcium phosphate. Sharks do have hard teeth,

and to a lesser degree hard scales and spines, which preserve

well in the fossil record and are the main indicators of their

presence in ancient times. Sharks grow new teeth throughout

their life, replacing the ones that break or wear down with

use. Sharks also have rigid fins, and they do not have an air

bladder. Sharks have extremely acute senses, including those

of vision, hearing (or vibration), smell, taste, and electro-

perception.

Sharks appear to be highly resistant to infections, can-

cers, and circulatory diseases, and they can often recover

from severe injuries. Sharks are slow-growing animals that

can live for a long time, and most species appear to take

decades to reach sexual maturity. Almost all species are

ovoviviparous, meaning the eggs are retained inside the body

of the mother until they hatch, and so the young are born

“alive,” or as fully formed miniatures of the adult form. The

fecundity

of sharks is much less than that of most other

fish, and ranges from as few as two to as many as about 135

pups per reproductive event.

All species of sharks are predators or scavengers of

other sea creatures. However, the size range of the prey varies

enormously among species of sharks. The largest species are

the whale shark and the basking shark, which can attain a

length of up to 45 ft (14 m) and may weigh as much as one

ton (1 tonne). However, these enormous animals filter-feed

on such relatively tiny prey as

zooplankton

, small fish, and

fish eggs and larvae. The smallest species of shark is the

spined pygmy shark (Squaliolus laticaudus), which only grows

to a length of about 10 in (25 cm). Some sharks are fierce

predators of large fish, marine mammals, and other relatively

big animals. Almost any shark longer than about 6 ft (2 m)