Environmental Encyclopedia

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Environmental Encyclopedia 3

Sludge treatment and disposal

several sludge treatment options available. These operations

and processes are principally intended for size reduction, grit

removal, moisture removal, and stabilization of the organic

matter in the sludge. Examples of these sludge processing

methods are sludge grinding and

cyclone

degritter for the

preliminary operations, chemical conditioning and heat

treatment, centrifugation and vacuum

filtration

for dewater-

ing operations,

aerobic

anaerobic digestion

compost-

ing

, and

incineration

for sludge stabilization.

Other than its organic content, sewage sludge is known

to contain some essential

soil

nutrients, such as

phosphorus

and

nitrogen

, that make it suitable for use as

fertilizer

soil conditioner after further processing. Sludge may also be

disposed of in landfills. Landfilling and incineration, how-

ever, are strictly disposal methods and, unlike land applica-

tion, do not recycle sludge.

Raw sludge contains potentially harmful pathogens,

heavy metals

and toxic organics; it is regulated by the

Environmental Protection Agency

(EPA). The EPA has

recently proposed new regulations establishing management

practices and other requirements for the disposal of sewage

sludge. See also Aerobic sludge digestion; Contaminated soil;

Industrial waste treatment; Sewage treatment; Waste man-

agement

[James W. Patterson]

ESOURCES

OOKS

Sundstrom, D. W., and H. E. Klei. Wastewater Treatment. Englewood

Cliffs, NJ: Prentice-Hall, 1979.

Weber Jr., W. Physicochemical Processes for Water Quality Control. New York:

Wiley-Interscience, 1972.

ERIODICALS

Hasbach, A. C., ed. “Putting Sludge to Work.” Pollution Engineering (De-

cember 1991).

THER

Process Design Manual for Sludge Treatment and Disposal. Washington, DC:

U.S. Environmental Protection Agency, 1979.

Sludge digestion

see

Aerobic sludge digestion

Sludge treatment and disposal

The proper treatment and disposal of

sludge

require knowl-

edge of the origin of the solids to be handled, as well as

their characteristics and quantities. The type of treatment

employed and the method of operation determine the origin

of sludge. In

sewage treatment

plants, sludge is produced

1297

by primary settling, which is used to remove readily settleable

solids from raw

wastewater

. Biological sludges are pro-

duced by treatment processes such as

activated sludge

trickling filter, and rotating biological contractors. Chemical

sludges result from the use of

chemicals

to remove constit-

uents through precipitation; examples of precipitates that

are produced by this process include phosphate precipitates,

carbonate precipitates, hydroxide precipitates, and polymer

solids.

Sludge is characterized by the presence or absence

of organic matter, nutrients, pathogens, metals and toxic

organics. These characteristics are an important consider-

ation for determining both the type of treatment to be used

and the method of disposal after processing. According to

the

Environmental Protection Agency

(EPA), the typical

chemical compositions of untreated and digested primary

sludge include solids, grease and fats, protein,

nitrogen

phosphorus

, potash, iron, silica, and

Municipal sludge is a high-volume waste. Typical vol-

umes for raw primary sludge range from 2,950 to 3,530

gallons per million gallons of wastewater treated. Volumes

for trickling filter

humus

range from 530 to 750 gallons per

million, while the volumes for activated sludge are much

higher, from 14,600 to 19,400 gallons per million. It is

possible to calculate the quantities of sludge theoretically,

but the EPA recommends that treatment operations use

pilot plant equipment to make these calculations whenever

possible. In developing a treatment and disposal system,

the EPA also recommends that large wastewater treatment

plants adopt a methodical approach “to prevent cursory dis-

missal of options.” For small plants, with a capacity of less

than a million gallons a day, the task of determining an

operating procedure is often shorter and less complex.

Sludge treatment and disposal generally include several

unit processes and operations, which fall under the following

classifications: thickening, stabilization, disinfection, condi-

tioning, dewatering, drying, thermal reduction, miscellane-

ous processes, ultimate disposal, or

reuse

Thickening is a volume-reducing process in which the

sludge solids are concentrated to increase the efficiency of

further treatment. It has recently been reported that sludge

with 0.8% solids thickened to a content of 4% solids yields

a five-fold decrease in sludge volume. Thickening methods

commonly employed are gravity thickening,

flotation

thick-

ening, and centrifuge.

Sludges are stabilized to eliminate offensive odors and

reduce toxicity. A stable sludge has been defined as “one

that can be disposed of without damage to the

environment

and without creating nuisance conditions.” In sludges, toxic-

ity is characterized by high concentrations of metals and

toxic organics, as well as by high oxygen demand, abnormally

high or low pH levels, and unsafe levels of pathogenic

micro-

Environmental Encyclopedia 3

Slurry

organisms

. There are a variety of technologies available for

stabilizing toxic sludge; these include lime stabilization, heat

treatment, and biological stabilization, which consists of

aer-

obic

anaerobic digestion

and

composting

Sludge that has been stabilized may also be disinfected

in order to further reduce the level of pathogens. There are

several methods of sludge disinfection: thermal treatment

such as pasteurization, chemical treatment, and irradiation.

This process is important for the reuse and application of

sludge on land.

Dewatering is used to achieve further reductions in

moisture content. It is a process designed to reduce moisture

to the point where the sludge behaves like a solid; at the

end of this process, the concentration of solids in sludge is

often greater than 15%. Dewatering can include a number

of unit operations: Sludge can be dried in drying beds or

lagoons, filtered through a vacuum filter, a filter press, or a

strainer, and separated in machines such as a solid-bowl

centrifuge. It can be determined whether a sludge will settle

in a centrifuge by testing it in a test-tube centrifuge, where

the concentration of cake solids are determined as a function

of centrifugal acceleration. The Capillary Suction Time

(CST) and the specific

resistance

filtration

are important

parameters for the filterability of sludge.

Sludge is conditioned to prepare it for other treatment

processes; the purpose of sludge conditioning is to improve

the effectiveness of dewater and thickening. The methods

most commonly employed are the addition of organic mate-

rials such as polymers, or the addition of inorganic materials

such as

aluminum

compounds. Heat treatment is also used;

in this treatment, temperatures range from 356–392°F (180–

200°C) for a period of 20–30 minutes.

After thickening and dewatering, further reduction of

moisture is necessary if the sludge is going to be incinerated

or processed into, starved air

combustion

, co-disposal, and

wet oxidation. These processes have a number of advantages.

They can achieve maximum volume reduction; they can

destroy toxic organic compounds, and they also produce heat

energy which can be utilized. But sludge combustion cannot

be considered an ultimate or long-term disposal option be-

cause of the residuals it produces, such ash and air emissions,

which may have detrimental effects on the environment.

Landfills are another disposal option, but limitations on

space as well as regulatory constraints restrict their long-

term feasibility. Reuse is probably the best solution for the

long-term management of sludge; the most feasible benefi-

cial use option will probably be either land application, land

reclamation

, or raw material recovery. Examples include

the conversion of sludge into commercial

fertilizer

, fuel,

and building products.

Whatever the selected array of sludge treatment and

disposal measures are, the main factors that influence the

1298

choice will always be cost-effectiveness, public health, and

environmental protection. See also Activated sludge; Munici-

pal solid waste composting; Solid waste; Waste management

[James W. Patterson]

ESOURCES

OOKS

Vesilind, P. A. Treatment and Disposal of Wastewater Sludges. Ann Arbor,

MI: Ann Arbor Science Publishers, 1979.

ERIODICALS

Hasbach, A. C. “Putting Sludge to Work.” Pollution Engineering (Decem-

ber 1991).

THER

Process Design Manual for Sludge Treatment and Disposal. Washington, DC:

U.S. Environmental Protection Agency, 1979.

Slurry

A thin mixture of water and fine, insoluble materials suitable

for pumping as a liquid. Pipelines are the cheapest and

most efficient means of moving materials long distances. In

Arizona, the Black Mesa slurry pipeline carries eight tons

of powdered

coal

per minute to the electrical power plant

near Page on Powell

Reservoir

. A much longer pipeline

has been proposed for shipping subbituminous coal in Wyo-

ming to Midwestern cities. Water supply is a crucial factor

in these

arid

regions lying in the Rocky Mountain

rain

shadow

zone.

Small quantity generator

Small quantity generators (SQGs) are facilities that do

not generate more than 2,205 lb (1,000 kg) of regulated

hazardous waste

or more than 2.2 lb (1 kg) of acute

hazardous waste in a calendar month, or do not store more

than 13,228 lb (6,000 kg) of hazardous waste in any 180

day period. If the facility has to transport the waste for more

than 200 mi (322 km) to dispose of it, then the period that

waste can be stored may be increased to 270 days, without

the operator of the site losing the small quantity generator

designation. If a site generates 220 lb (100 kg) or less of

hazardous waste in a calendar year, then the site is designated

Environmental Encyclopedia 3

Smart growth

as a conditionally exempt small quantity generator or

(CESQG).

[Marie H. Bundy]

Smart growth

Smart growth is a relatively new movement in the United

States, at least by name, a movement promoted since the

early 1990s as a new way to direct growth and development,

especially in urban areas, away from sprawl and toward urban

centers of various kinds. There seems to be no universally

accepted definition of smart growth, and that alone indicates

problems in agreement about what it is, what its goals are,

the nature and extent of its benefits and impacts, and to

what degree it can be implemented.

Disagreements seem to be more at the level of specific

issues rather than broad goals, however, and a fairly simple

if still broad and somewhat vague definition can be readily

distilled from a rapidly increasing literature. A composite

definition suggests that smart growth is growth management

rather than “control of growth,” and probably no one would

disagree with that; it is inward development rather than

outward development, i.e., it is intended to limit sprawl and

to fill in or reclaim already developed areas rather than

expand into new ones; and it is high density rather than

low density. According to the

Environmental Protection

Agency

(EPA), “smart growth is development that serves

the economy, community, and the environment.”

Its advocates see it as a replacement for the “failed”

environmental movement of the 1960’s, but others describe

it as an attempt to gloss over growth, to hide continued

dominance by the marketplace in uncoordinated decisions

on human settlement patterns, or to avoid facing the eco-

nomic and political difficulties of the often better environ-

mental alternative of no growth. Still others claim that too

many smart growth advocates are just the opposite, ignorant

of and naive about those same market factors. Though

backed by individuals and groups that represent all spectrums

of political thought, smart growth is criticized by skeptics

from an equally broad range of viewpoints. Smart growth

as concept, as philosophy, and as policy, smart growth when

implemented, rejected or delayed, all remain controversial.

The advocates of smart growth do seem to agree on ten

principles, listed here essentially as they are stated in a 2002

EPA document titled Getting to Smart Growth. The benefits

foreseen by its proponents are evident in the principles as

stated. 1) Mix land uses rather than the separation mandated

by zoning codes in many communities in the United States.

Mix commercial with residential, high density with low,

pedestrian and bike access with other means of transport.

2) Take advantage of compact building design to create

1299

smaller footprints, to increase density, and to reduce the

amount of space required to accommodate increases in popu-

lation. 3) Create a range of housing opportunities and choices

to increase neighborhood diversity in multiple ways and

better accommodate the housing needs of a diverse popula-

tion. 4) Create walkable neighborhoods by making them

pedestrian-friendly and scaled to people on foot rather than

to people in cars. 5) Foster distinctive, attractive communi-

ties with a strong

sense of place

by introducing more dis-

tinctiveness and uniqueness to residential and retail areas,

for example, through less reliance on large malls that are

indistinguishable from one city to the next in every region of

the country. Create structures that reflect local and regional

differences in

climate

, vegetation, and landforms. 6) Pre-

serve open space, farmland, natural beauty, and critical envi-

ronmental areas to enhance quality of life and increase local

recreational opportunities. 7) Strengthen and direct develop-

ment towards existing communities through less reliance

on new, low-density dispersed developments outside urban

cores and close-in suburbs. 8) Provide a variety of

transpor-

tation

choices, especially by creating transit and non-motor-

ized alternatives to the

automobile

, in the process reducing

traffic congestion. 9) Make development decisions predict-

able, fair, and cost effective. 10) Encourage community and

stakeholder collaboration in development decisions.

Given the

visibility

of arguments in recent years

against sprawl, these principles seem like apple pie and moth-

erhood; who could be against them? But smart growth has

many critics. Numerous individuals and groups can and do

take issue, especially with specific principles when local im-

plementation is actually attempted on the ground. Some of

the statements are viewed more critically than others, and the

movement in general also has its skeptics. Critics, especially

those without a NIMBY interest, are as quick as proponents

to point out good elements in the smart growth movement,

most of them embodied in the ten stated principles. Such

elements as in-fill, high density, neighborhood development

and identity, and brownfield redevelopment, are widely sup-

ported, though not universally.

A problem pointed out over and over again by critics

of smart growth is that the

reclamation

and filling in of

already developed areas increases their attractiveness, raises

their value and the cost of living there, i.e., the areas are

gentrified and the people who did live in the reclaimed areas

are displaced. Minorities and the poor are squeezed out and

their difficulties in finding acceptable accommodations is

traced to declining stocks of affordable housing. Much of

the debate over smart growth centers on whether or not it

is the cause of increases in the price of housing. Critics say

yes, land prices do increase, affordable housing is torn down

and replaced by more expensive dwellings, and yes, these

Environmental Encyclopedia 3

Smelter

changes are directly attributable to reclamation efforts imple-

mented in the name of smart growth or growth management.

Proponents argue that growth management is not the

cause of declines in the availability of affordable houses,

but that increases are the result of conventional marketing

dynamics and growth in population, employment, and in-

come, especially during the boom of the 1990s. They further

argue that smart growth initiatives are much less expensive,

for individuals and families as well as for local governments,

because they decrease investments in infrastructure, espe-

cially that related to automobile use, and that such savings

can then be passed on to decrease housing costs.

Among the problems of implementing smart growth

is the tight hold many Americans have on the American

Dream: detached houses that “return people to nature” are

not located in the central parts of cities and certainly not in

brownfields

. And critics are quick to see the irony in the

coincidence of interest in a smart growth movement with

reports in the daily papers like the following two illustrations:

first, increases in “Supersize Suburbs,” “big-house communi-

ties” in which smaller families live in hypertrophy homes:

“in the country’s long pursuit of ever more elbow room...the

American house has been swelling for decades.” In some

suburban counties, “more than two-thirds of the houses have

nine rooms or more...” The mega-mansions are literally built

on green “fields” because many owners don’t want trees

and vegetation blocking the “full effect” the houses have on

passers-by. Surveys show that many of these monster homes

are occupied by an average of slightly more than three people.

A typical response when this trend is questioned: “We can

afford it, so why not?”

A second illustration is the realization by a big timber

company in Florida that its extensive timber holding in the

state are “too valuable for trees alone.” The company’s plans

for one stretch of 40 mi (64 km) of beaches on the panhandle

“are so sweeping that it hopes to reduce the “redneck riviera”

image of the area by calling it “Florida’s Great Northwest.”

Some 20 developments are in various stages of planning,

with more than 10,000 large, high-end homes permitted so

far, aimed at affluent buyers from Atlanta and Birmingham.

The chairman of the company calls the expected transforma-

tion “regional place making.” Locals shrug with “we’ve got to

take the hand we’re dealt” statements and environmentalists

concede that a company so powerful will prevail, so they try

to work with it to minimize the impacts, recognizing that

“it’s absolutely clear that the Florida Panhandle will change”

fundamentally, hopefully “in a way that creates livable com-

munities and protects the natural system, and with [this

company] we have at least a shot at doing that.”

These two illustrations are drawn from high-growth

areas, with little indication that such principles as compact

building or neighborhood diversity or people-scale neighbor-

1300

hoods not dependent on cars or less reliance on new low-

density developments outside urban areas or widely based

stake-hold collaboration are driving many land-use decisions

in the United States, at least on private land. The question

isn’t one of smart growth being or not being a policy in

these areas, but that the attitudes and actions in such illustra-

tions make smart growth as a solution to settlement problems

in the nation as a whole problematic at best.

One especially severe criticism is that nowhere in the

10 principles is there even a hint at any real attempt to

actually limit growth, or even delay it, that smart growth

just accommodates growth rather than addressing it as a

problem. Critics point out that the capability of local or

regional environmental systems—notably water supplies—

to support growth is not mentioned in any of the principles,

or anywhere in the smart growth philosophy. Growth is

still growth and calling it “smart” does not help answer the

question of ultimate limits, of how to plan for no growth.

Even its critics admit, however, that smart growth creates

better management and planning alternatives than totally

unregulated sprawl.

[Gerald L. Young Ph.D.]

ESOURCES

ERIODICALS

Chen, Donald D. T. “The Science of Smart Growth.” Scientific American

283, no. 6 (December 2000): 84–91.

Daniels, Tom. “Smart Growth: A New American Approach to Regional

Planning.” Planning Practice & Research 16, no. 3–4 (2001): 271–179.

Downs, Anthony. “What Does ‘Smart Growth’ Really Mean?” Planning

67, no. 4 (April 2001): 20–25.

Pelley, Janet. “Building Smart-Growth Communities.” Environmental Sci-

ence & Technology 33, no. 1 (January 1999): 28–32.

Staley, Samuel R., and Leonard C. Gilroy. “Why ‘Smart Growth’ Isn’t

Smart.” Consumers’ Research 85, no. 1 (January 2002): 10–13.

THER

Environmental Protection Agency. Getting to Smart Growth: 100 Policies

for Implementation. [cited July 2002]. <http://www.smartgrowth.org/pdf/

gettosg.pdf.>.

Smelter

Smelters are industrial facilities that are used to treat metal

ores or concentrates with heat,

carbon

, and oxygen in order

to produce a crude-metal product, which is then sent to a

refinery to manufacture pure metals.

In many cases, smelters process sulfide minerals, which

yield gaseous

sulfur dioxide

, a significant waste product.

Other smelters, including some that process iron ores, do

not treat sulfide minerals. Similarly, secondary smelters used

for

recycling

metal products, such as used

automobile

bat-

teries, do not emit sulfur dioxide. However, all smelters emit

Environmental Encyclopedia 3

Smelter

metal particulates to the

environment

, and unless this is

prevented by

pollution control

devices, these emissions can

cause substantial environmental damages.

The earliest large industrial smelting technique in-

volved the oxidation of sulfide ores using roast beds, which

were heaps of ore piled upon wood. The heaps were ignited

in order to oxidize the sulfide-sulfur to sulfur dioxide,

thereby increasing the concentration of desired metals in the

residual product. The roast beds were allowed to smoulder

for several months, after which the crude-metal product was

collected for further processing at a refinery. The use of roast

beds produced intense, ground-level plumes filled with sulfur

dioxide, acidic mists, and metals, which could devastate local

ecosystems through direct toxicity and by causing

acidifi-

cation

More modern smelters emit pollutants to the

atmo-

sphere

through tall smokestacks. These can effectively dis-

perse emissions, so that local

air quality

is enhanced, and

damages are greatly reduced. However, the actual acreage

of land affected by the contamination is enlarged because

the tall smokestacks broadcast emissions over a greater dis-

tance and

acid rain

may be spread over a larger area as well.

Emissions of toxic

chemicals

can be reduced at the

source. Metal-containing particulates can be controlled

through the use of electrostatic precipitators or baghouses.

These devices can remove particulates from flue-gas streams,

so that they can be recovered and refined into pure metals,

instead of being emitted into the atmosphere. Electrostatic

precipitators and baghouses can often achieve particle-re-

moval efficiencies of 99% or better.

It is more difficult and expensive to reduce emissions

of gases such as sulfur dioxide. Existing technologies usually

rely on the reaction of sulfur dioxide with lime or limestone

to produce a

slurry

of gypsum (calcium sulfate) that can

be disposed into landfills or sometimes manufactured into

products such as wallboard. It is also possible to produce

sulfuric

acid

by some flue-gas desulfurization processes. At

best, removal efficiencies for sulfur dioxide are about 95%,

and often considerably less.

The types of smelters that do not treat sulfide metals,

such as iron ore smelters, logically do not emit sulfur dioxide.

They do, however, spew metal particulates into the atmo-

sphere. For example, a facility that has been operating for

centuries at Gusum, Sweden, has caused a significant local

pollution

with

copper

and

lead

, the toxic effects of which

have damaged vegetation. The surface organic matter of sites

close to the Gusum facility has been polluted with as much

as 2% each of zinc and copper. Secondary smelters also do

not generally emit toxic gases, but they can be important

sources of metal particulates. This has been especially well

documented for secondary lead smelters, many of which are

present in urban or suburban environments. The danger

1301

from these is that people can be affected by lead in their

environment, in addition to long-lasting ecological effects.

For example, lead concentrations in

soil

as large as less than

5% dry weight were found in the immediate vicinity of a

battery smelter in Toronto, Ontario. In this case, people

were living beside the smelter. Garden soils and vegetables,

house dust, and human tissues were all significantly contami-

nated with lead in the vicinity of that smelter. Similar obser-

vations have been made around other lead-battery smelters,

including many that are situated dangerously close to human

habitation.

One of the best-known case studies of environmental

damage caused by smelters concerns the effects of emissions

from the metal processing plants around

Sudbury, Ontario

This area has a long history as a mining community. For

many years, roast beds were the primary metal-processing

technology used at Sudbury. In fact, in its heyday, up to 30

roast beds were operating in Sudbury. Unforturnately, this

process saturated the air and soil with sulfur dioxide,

nickel

and copper. Local ecosystems were devastated by the direct

toxicity of sulfur dioxide and, to a lesser extent, the metals.

In addition,

dry deposition

of sulfur dioxide caused a severe

acidification of lakes and soil. This caused much of the plant

life to die, which in turn started soil

erosion

. Naked bedrock

was exposed, and then blackened and pitted by reaction with

the sulfurous plumes and acidic mists.

When the devastating consequences of the roast bed

method became clear, the government prohibited their use.

The processors turned to new technology in 1928 when they

began construction of three smelters with

tall stacks

. Since

these emitted pollutants high into the atmosphere, they

showed substantial improvements in local air quality. How-

ever, the damage to vegetation continued; lakes and soils

were still being acidified, and toxic contaminants were spread

over an increasingly large area.

Over time, well-defined patterns of ecological damage

developed around the Sudbury smelters. The problems that

had occurred in the roast beds were being repeated on a

large scale. The most devastated sites were close to the

smelters, and had concentrations of nickel and copper in

soil in the thousands of

parts per million

; they were very

acidic with resulting

aluminum

toxicity, and frequently fu-

migated by sulfur dioxide. Such toxic sites were barren, or

at most had very little plant cover. The few plants that were

present were usually specific ecotypes of a few widespread

species

that had evolved a tolerance to the toxic effects of

nickel, copper, and acidity. Aquatic lake habitats close to

the smelters were similarly affected. These waterbodies were

acidified by the dry deposition of sulfur dioxide, and had

large concentrations of soluble nickel, copper, aluminum,

and other toxic metals. Of course, the plant and animal life

of these lakes was highly impoverished and dominated by

Environmental Encyclopedia 3

Smelter

life forms that were specifically adapted to the toxic stresses

associated with the metals and acidification.

It is well recognized that increased linear distance from

the

point source

of toxic chemicals reduces deposition rates

and toxic stress. Correspondingly, the pattern of environ-

mental pollution and ecological damage around the Sudbury

areas decreases more-or-less exponentially with increasing

distance from the smelters. In general, it is difficult to dem-

onstrate damages to terrestrial communities beyond 9–12

miles (15–20 km), although contamination with nickel and

copper can be found at least 62 miles (100 km) away. In

comparison, lakes that are deficient in plant life have little

acid-neutralizing capacity and can be shown to have been

damaged by the dry deposition of sulfur dioxide at least 25–

30 miles (40–48 km) from Sudbury.

To improve regional air quality, the world’s tallest

smokestack, at 1,247 feet (380 m), was constructed at the

largest of the Sudbury smelters. This “superstack” allowed

for an even wider dispersion of smelter emissions. At the

same time, a smelter was closed down, and steps were taken

to reduce sulfur dioxide emissions by installing desulferiza-

tion, or

flue-gas scrubbing

, equipment and by processing

lower-sulfur ores. In aggregate, these actions resulted in a

great improvement of air quality in the vicinity of Sudbury.

The improvement of air quality allowed vegetation

to regenerate over large areas, with many existing species

increasing in abundance and new species appearing in the

progressively detoxifying habitats. The revegetation has been

actively encouraged by re-seeding and liming activities along

roadways and other amenity areas where soil had not been

eroded. Aquatic habitats have also considerably detoxified

since 1972. Lakes near the superstack and the closed smelter

have become less acidic, metal concentrations have de-

creased, and the plants and animals have increased

biomass

However, there is important controversy about contri-

butions that the still-large emissions of sulfur dioxide from

Sudbury may be making towards the regional acid rain prob-

lem. The superstack may actually exacerbate regional diffi-

culties because of the wide dispersal of its emissions of sulfur

dioxide. It is possible that height of the superstack may be

decreased in order to increase the local dry deposition of

emitted sulfur dioxide and reduce the long range dispersion

of this acid-precursor gas.

The Sudbury scenario is by no means an unusual one.

Many other smelters have substantially degraded their sur-

rounding environment. The specifics of environmental pol-

lution and ecological damage around particular smelters de-

pend on the intensity of toxic stress and the types of

ecological communities that are being affected. Nevertheless,

broadly similar patterns of ecological change are observed

around all point sources of toxic emissions, such as smelters.

1302

In most modern smelters, a reduction of emissions at

the source can eliminate the most significant of the ecological

damages that have plagued older smelters. The latter were

commissioned and operated under social and political cli-

mates that were much more tolerant of environmental dam-

ages than are generally considered to be acceptable today.

See also Air pollutant transport; Electrostatic precipitation;

Water pollution

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Freedman, B. Environmental Ecology. San Diego: Academic Press, 1989.

———, and T. C. Hutchinson. “Sources of Metal and Elemental Contami-

nation of Terrestrial Ecosystems.” In Metals in the Environment. Vol. 2.

Edited by N. W. Lepp. London: Applied Science Publishers, 1981.

Nriagu, J., ed. Environmental Impacts of Smelters. New York: Wiley, 1984.

Robert Angus Smith (1817 – 1884)

Scottish chemist

Smith has two claims to fame. Through his studies of

air

pollution

he was, in 1852, the discoverer of

acid rain

, and

his appointment as Queen Victoria’s first inspector under

the Alkali Acts Administration of 1863 made him the proto-

type of the scientific civil servant. He was one of the earlier

scientists to study the chemistry of air and

water pollution

and among the first to see that such study was important

in identifying and controlling environmental problems

caused by industrial growth in urban centers. He was also

interested in public health, disinfection, peat formation, and

antiquarian subjects. Although his work has sometimes been

dismissed as pedestrian, Smith’s pioneering studies of the

chemistry of atmospheric precipitation, published in 1872

in the book Air and Rain, were far ahead of their time

and a major contribution to a new discipline that he called

“chemical climatology.”

[Eville Gorham Ph.D.]

ESOURCES

ERIODICALS

Gorham, E. “Robert Angus Smith, F.R.S., and ‘Chemical Climatology.’”

Notes and Records of the Royal Society of London 36 (1982): 267–72.

MacLeod, R. M. “The Alkali Acts Administration, 1863–84: The Emer-

gence of the Civil Scientist.” Victorian Studies 9 (1965): 85–112.

Environmental Encyclopedia 3

Smog

Smog over New York City. (Photograph by Yoav Levy. Phototake. Reproduced by permission.)

Smog

A term chosen by the Glasgow public health official Des

Voeux at the beginning of the twentieth century to describe

the smoky fogs that characterized coal-burning cities of the

time. The word is formed by adding the words

smoke

and

fog together and has persisted as a description of this type

of urban

atmosphere

. It has more and more been used to

describe

photochemical smog

, the

haze

that became a

characteristic of the

Los Angeles Basin

from the 1940s.

“Smog” is sometimes even used to describe

air pollution

general, even where there is no reduction in

visibility

at all.

However, the term is most properly used to describe the

two distinctive types of

pollution

that dominated the atmo-

spheres of late nineteenth century London, England, known

as winter smog, and twentieth century Los Angeles, called

summer smog.

The city of London burned almost 20 million tons of

coal

annually by the end of the nineteenth century. Although

industrialized, much coal was burned in domestic hearths,

and the smoke and

sulfur dioxide

produced barely rose

from the chimneys above the housetops. Only a few rather

1303

inaccurate measurements of the pollutant concentrations in

the air were made in the last century, although they hint at

concentrations much higher than what we might expect in

London today.

The smogs of nineteenth-century London took the

form of dense, vividly colored fogs. The smog was frequently

so dense that people became lost and had to be lead home

by linksmen. It is said that visibility became so restricted

that fingers on an outstretched arm were invisible. The fog

that rolled over window sills and into rooms became such

an integral part of what we know as Victorian London that

almost any Sherlock Holmes story mentions it.

With London’s high humidity and incipient fog,

smoke particles from coal-burning formed a nucleus for the

condensation of vapor into large fog droplets. This water

also serves as a site for chemical reactions, in particular the

formation of sulfuric

acid

. Sulfur dioxide dissolved in fog

droplets, perhaps aided by the presence of alkaline material

such as ammonia or coal ash. Once in solution the sulfur

was oxidized, a process often catalyzed by the presence of

dissolved metallic ions such as iron and manganese. Dissolu-

Environmental Encyclopedia 3

Smog

tion and oxidation of sulfur dioxide gave rise to sulfuric acid

droplets, and it was sulfuric acid that made the smog so

damaging to the health of Londoners.

London’s severe smogs occurred throughout the last

decades of the nineteenth century. Detective writer Robert

Barr even published The Doom of London at the turn of

the century, which saw the entire population of London

eliminated by an apocalyptic fog. Many residents of Victo-

rian London recognized that the fogs increased death rates,

but the most infamous incident occurred in 1952, when a

slow-moving anti-cyclone stalled the air over the city. On

the first morning the fog was thicker than many people

could ever remember. By the afternoon people noticed the

choking smell in the air and started experiencing discomfort.

Those who walked about in the fog found their skin and

clothing filthy after just a short time. At night the treatment

of respiratory cases was running at twice its normal level.

The situation continued for four days.

It was difficult to describe exactly what had happened,

because primitive air pollution monitoring equipment could

not cope with high and rapidly changing concentrations of

pollutants, but it has been argued that for short periods the

smoke and sulfur dioxide concentrations may have ap-

proached ten thousand micrograms per 1.3 yd

(1 m

). To-

day, in a relatively healthy city, the desired maximum is about

a hundred micrograms per 1.3 yd

in short-term exposures.

Normal death rates were exceeded by many thousands

through the four-day period of the fog. Public feelings ran

high, and the United Kingdom government, barraged with

questions, set up an investigative committee. The Beaver

Committee report eventually served as the basis for the UK

Clean Air Act

of 1956. This law was gradually adopted

through many towns and cities of the UK and has been seen

by many as a model piece of legislation. Although it is true

that the classic London smog has gone, it is far from clear the

extent to which this change came about through legislation

rather than through broader social developments, such as

the use of electricity in homes (although the act did encour-

age this).

Photochemical smog is sometimes called summer

smog, because unlike the classical London type smog, it is

more typical in summer at many localities, often because it

requires long hours of sunshine to build up. When photo-

chemical smogs were first noticed in Los Angeles, people

believed them to be much the same as the smogs of London

and Pittsburgh. Early attempts at control looked largely at

local industry emissions. The

automobile

was eliminated

as a likely cause because of low concentrations of sulfur in

the fuel and the fact that only minute amounts of smoke

were generated.

It was some time before the biochemist

Arie Jan

Haagen-Smit

recognized that damage to crops in the Los

1304

Angeles area arose not from familiar pollutants, but from a

reaction that took place in the presence of

petroleum

vapors

and sunlight. His observations focused unwelcome attention

on the automobile as an important factor in the generation

of summer smog.

The Los Angeles area proved an almost perfect place

for generating smogs of this type. It had a large number

of cars, long hours of sunshine, gentle sea breezes to back

the pollutants up against the mountains, and high level

inversions preventing the pollutants from dispersing verti-

cally.

Studies through the 1950s revealed that the smog was

generated through a photolytic cycle. Sunlight split

nitrogen

dioxide into nitric oxide and atomic oxygen that could subse-

quently react and form

ozone

. This was the key pollutant

that clearly distinguished the Los Angeles smogs from those

found in London. Although the highly reactive ozone reacts

rapidly with nitric oxide, converting it back into nitrogen

dioxide, organic radicals produced from petroleum vapor

react with nitric oxide very quickly. The nitrogen dioxide is

again split by the sunlight, leading to the formation of more

ozone. The cycle continues to build ozone concentrations

to higher levels throughout the day.

The nitrogen oxide-ozone cycle is just one of many

processes initiated in a smog of this kind. The photochemi-

cally active atmosphere contains a great number of reactive

molecular fragments that lead to a range of complex organic

compounds. Some of the hydrocarbon molecules of petro-

leum vapor are oxidized to aldehydes or

ketones

, such as

acrolein or formaldehyde, which are irritants and suspected

carcinogens. Some oxygenated fragments of organic mole-

cules react with the

nitrogen oxides

present in the atmo-

sphere. The best-known product of these reactions is

perox-

yacetyl nitrate

, often called PAN, one of a class of nitrated

compounds causing eye irritation experienced in summer

smogs.

The reactions that were recognized in the Los Angeles

smog are now known to occur over wide areas of the industri-

alized world. The production of smog of this kind is not

limited to urban or suburban areas, but may occur for many

hundreds of miles to the lee of cities using large quantities

of liquid fuel. The importance of

hydrocarbons

in sus-

taining the processes that generate photochemical smog has

given rise to control policies that recognize the need to lower

the

emission

of hydrocarbons into the atmosphere, and

hence the emphasis of the use of catalytic converters and

low volatility fuels as part of

air pollution control

strategies.

See also Alternative fuels; Environmental policy; Fossil fuels;

Respiratory diseases

[Peter Brimblecombe]

Environmental Encyclopedia 3

Snail darter

ESOURCES

OOKS

Findlayson-Pitts, B. J., and J. N. Pitts. Atmospheric Chemistry. New York:

Wiley, 1986.

THER

Exhausting Our Future: An Eighty-Two City Study of Smog in the 80s.

Washington, DC: U.S. Public Interest Research Group, 1989.

Smoke

Air pollutant, usually white, grey, or black in appearance,

that arises from

combustion

processes. Benjamin Franklin

recognized that smoke was the product of inefficient com-

bustion and argued that one should “burn one’s own smoke.”

Smoke generally forms when there is insufficient oxygen to

oxidize all the vaporized fuel to

carbon dioxide

, so much

remains as

carbon

or soot. Smoke is largely soot, although

it also contains small amounts of

fly ash

. Although domestic

smoke and poorly constructed chimneys had long been

annoying to city dwellers, it was the development of the

steam engine that drew particular attention to the need to

get rid of unwanted smoke. The first half of the nineteenth

century witnessed an awakening interest on the part of local

administrators in Europe and North America to combat the

smoke problem.

Smoke has long been recognized as more than just an

aesthetic nuisance. It has been proven to have a broad range

of effects on human health and well-being. Early laws were

preoccupied with reducing black smoke, and various tests

and “smoke shades” were created to test the color of smoke

in the

atmosphere

. For example, the Ringelmann Chart

showed a set of shades on a card, which was compared to

the color of smoke in the atmosphere. Today it has been

shown that the color of suspended smoke particles in cities

have gradually changed as

coal

is used less frequently as an

energy source. In many cities the principal soiling agent in

the air is now diesel smoke. Diesel smoke blackens buildings

and even gets inside houses, and studies show that diesel

smoke contains a range of carcinogens.

While in many of the major cities smoke production

has been reduced, coal, peat, and wood continue to be burnt

in large quantities. In these locations, often in developing

countries, smoke control represents considerable challenge

as environmental agencies remain underfunded. See also Cig-

arette smoke; Smog; Tobacco

[Peter Brimblecombe]

ESOURCES

OOKS

Brimblecombe, P. The Big Smoke. London: Methuen, 1987.

1305

Smoking

see

Cigarette smoke; Respiratory

diseases; Tobacco

Snail darter

Most new

species

are discovered, then described in the

scientific literature with little fanfare, and most are then

known only to a relatively small group of specialists. This

was not the case with the snail darter (Percina tanasi), a

small member of the freshwater fish family of perches, Perci-

dae. The snail darter’s discovery cast it in the limelight of a

highly controversial, environmental battle over the im-

poundment of the Little Tennessee River by the

Tellico

Dam

. Because its discovery coincided with the enactment

of the

Endangered Species Act

, its only known

habitat

was the free-flowing channel of the Little Tennessee River,

and it was perceived as a means of successfully challenging

the completion of this

Tennessee Valley Authority

project.

Two ichthyologists at the University of Tennessee,

Drs. David Etnier and Robert Stiles, discovered the snail

darter in the Little Tennessee River in August of 1973. After

catching several specimens of these three-inch creatures, they

returned to Knoxville to examine their find. By that fall,

after careful comparison with other members of the genus,

it was clear that they had found a new species of fish.

Because this darter was not known from any other

location, Dr. Etnier submitted a status report on the species

to the U.S.

Fish and Wildlife Service

the following year.

The darter’s existence was being threatened by the comple-

tion of the Tellico Dam, which would ultimately eliminate

the free-flowing, clear, riverine habitat needed for its sur-

vival. The darter was recommended for listing as an

endan-

gered species

in 1975, and in January 1976 its official

scientific description was published. It was now the snail

darter.

The notoriety this fish was beginning to receive did not

go unnoticed by the TVA. They began transplanting snail

darters to the Hiwassee River in 1975 and, by early 1976, had

moved over 700 to the new location. All of this was done in

secrecy, neither the Fish and Wildlife Service nor the appro-

priate Tennessee state agencies were notified. When the snail

darter was designated an endangered species, the court battles

began.Injunctions to haltcompletion of theTellico Dam were

granted and overturned all the way to the Supreme Court,

where the justices ruled in favor of the snail darter. However,

the High Court left an opening for the U.S. Congress to step

inand exempt Tellico Dam fromthe Endangered Species Act.

That is just what Congress did, and in January 1980 the gates

closed and the

reservoir

behind Tellico Dam began to fill,

Environmental Encyclopedia 3

Snow leopard

Snail darter. (Photograph by J. R. Shute. Visuals Unlim-

ited. Reproduced by permission.)

thus sealing the fate of the Little Tennessee River and its

darter population.

An additional population of snail darters was discov-

ered in the Hiwassee River, and this population seems to be

thriving. The snail darter, so named because of the principle

component of its diet, continues its existence and is thought

to number upwards of 100,000. It was moved from the

endangered listing to one of threatened by the Department

of the Interior (DOI) in 1984. Dr. Etnier believes that now

the snail darter should be removed from the list of threatened

species. The species’ scientific name, Percina tanasi,isin

reference to the ancient Cherokee Village and Native Ameri-

can burial ground of Tanasi, from which the state got its

name, and which, now, lies at the bottom of Tellico’s res-

ervoir.

Snail darters live for an average of two years, with a

maximum recorded longevity of four years. These darters

reach sexual maturity at one year and migrate from their

downstream, slackwater habitat to the sand and gravel shoals

upstream, where they will eventually spawn. These clear,

shallow shoal areas represent the habitat needed by the snail

darters and their mollusk prey for survival.

[Eugene C. Beckham]

ESOURCES

OOKS

Ono, R., J. Williams, and A. Wagner. Vanishing Fishes of North America.

Washington, DC: Stone Wall Press, 1983.

Page, L. Handbook of Darters. Neptune City, NJ: TFH Publications, 1983.

ERIODICALS

Etnier, D. “Percina (Imostoma) tanasi, A New Percid Fish From the Little

Tennessee River, Tennessee.” Proceedings of the Biological Society of Washing-

ton 88 (1976): 469–488.

1306

THER

Mansfield, Duncan. “Snail Darter is No Longer in Danger of Extinction.”

Appalachian Focus Environmental News December 11, 2000 [cited May

2002]. <http://www.appalachianfocus.org/_enviro1/00000011.htm>.

Snow leopard

The snow leopard (Uncia uncia), also known as the ounce,

or irbis, is a large cat that ranges over highland habitats

in Central Asia. It occurs from Turkistan and northern

Afghanistan in the western part of its range, through the

Kashmir region of Pakistan and India, to southern Mongolia,

extreme southwestern China, and Tibet. The snow leopard

is sometimes referred to as Panthera uncia, which indicates

affinity with other large cats, such as the tiger, African

lion, and mountain lion, which are also named in the genus

Panthera.

The snow leopard has an adult body length of 29–51

in (75–130 cm) and a tail of 27–39 in (70–100 cm). It stands

20–25 in (50–65 cm) at the shoulder, and has a body weight

of 77–155 lb (35–70 kg). Its pelage is characterized by dense,

long hair and a woolly underfur. The underbelly is whitish,

while the upper parts of the animal are a creamy yellowish

color, patterned by darker rings. Following a gestation period

of about 93–103 days, snow leopards give birth in a rocky

lair. Usually two cubs are born, but there can be as many as

five. Cubs reach sexual maturity at an age of two years in

captivity, but probably later in the wild. They have lived as

long as 17–19 years in captivity, but the life span would be

considerably less in the wild.

During the summer the snow leopard generally occurs

in alpine

tundra

habitats, including meadows and rocky

places above the forested tree line but below the snow line.

During the summer snow leopards venture to 19,685 ft

(6,000 m). During winter they occur as low as 5,000 ft (1,500

m), and in harsh winters they may occur in montane (or

sub-alpine) forests. Because of the sparse populations of their

natural prey, snow leopards have large home ranges, typically

amounting to several square miles. The ranges of adjacent

animals can overlap to a substantial degree.

Snow leopards are solitary predators. They typically

rest during the day and feed during the early morning or

late afternoon on wild prey, such as ibex, sheep, musk deer,

boar, hare, rabbit, pika, marmot, ptarmigan, and pheasant.

Because of expanding human populations and agriculture

within the range of snow leopards, they are increasingly

feeding on domestic animals, such as goats, sheep, dogs,

and chickens.

The global population of wild snow leopards is only

about 3,500–7,000 individuals. Another 600–700 animals

occur in zoos. Because of its small and decreasing populations

the snow leopard is an

endangered species

. Although the