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CHAPTER II
Environmental Quality
Through Chemistry
Every society tries to provide itself with adequate food and shelter and a
healthful environment. When these elemental needs are assured, attention turns to
comfort and convenience. The extent to which all of these wishes can be satisfied
determines the quality of life. Generally, however, choices are required because
one or another of these qualities is most easily attained at the expense of others.
Today we find our desires for more abundant consumer goods, energy, and
mobility in conflict with maintenance of a healthful environment. A major concern
of our times is the protection of our environment in the face of increasing world
population, continued concentration of population (urbanization), and rising stan-
dards of living.
Environmental degradation with accompanying threats to health and disruption
of ecosystems is not a new phenomenon. Human disturbance of the environment
has been noted from the earliest recorded history. The problem of sewage disposal
began with the birth of cities. Long before the twentieth century, London was
plagued with air pollution from fires used for heating and cooking. An early
example of an industrial hygiene problem was the shortened lifetime of chimney
sweeps due to cancer, which we can now attribute to prolonged exposure to soot
with its trace carcinogen content (polynuclear aromatic hydrocarbons).
There is small consolation, though, in the fact that environmental pollution is not
a new invention. The global population becomes ever larger, while cities grow even
faster. Per capita consumption and energy use continue to increase. Pollution
problems are becoming increasingly obvious, and we are recognizing subtle
interactions in the world around us and discovering secondary effects that went
unnoticed before. A number of environmental disturbances have begun to appear
on a global scale. Occasional industrial accidents, like those at Bhopal, India and
Seveso, Italy, remind us that large-scale production of needed consumer products
may require handling of large amounts of potentially dangerous feedstock sub-
stances. The tragic Bhopa] accident highlights the dilemma. This occurred in a
country plagued by starvation the toxic substances were being used to manufac-
ture products that annually saved many thousands of lives by increasing the food
supply.
On the positive side, there is high public awareness of the importance of maintaining
environmental quality. In the United States, a large majority of citizens from across the
5
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6
ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
political spectrum have indicated they are prepared to pay more for products (e.g.,
lead-free gasoline), and pay more taxes, to improve their environment. These attitudes
are spreading abroad, an essential aspect of environmental protection for the more
global problems.
Effective strategies for safeguarding our surroundings require adequate knowI-
edge and understanding. We must be able to answer the following questions:
· What potentially undesirable substances are present in our air, water, soil,
and food?
· Where did these substances come from?
· What options are there alternate products and processes to reduce or
remove known problems?
· How does the degree of hazard depend on the extent of exposure to a given
substance? How shall we choose among the available options that offer corrective
action?
Plainly, chemists play a central role in the first three crucial questions. To find
out what substances are present in the environment, we need analytical chemists to
develop more and more sensitive and selective analytical techniques. To track
pollutants back to their origin, again we look to analytical chemists acting as
detectives, usually in collaboration with meteorologists, oceanographers, voicanol-
ogists, climatologists, biologists, and hydrologists. Finding origins can require
detailed chemical understandings of reactions that take place between the source of
the pollution and the final noxious or toxic product. Thus, development of options
calls on the full range of chemistry. If the worId's mortality rate due to malaria is
not to be reduced with DDT because of its environmental persistence, what
substances can be synthesized that are equally effective in saving lives but are
spontaneously decomposed? If we must use lower-grade energy sources to satisfy
our energy needs, what catalysts and new processes can be developed to avoid
making worse the existing problems of acid rain and carcinogen release from
coal-fired power plants?
Thus, our society must assure the health of its chemistry enterprise if it wants
early warning of emerging environmental damage, understanding of the origins of
that degradation, and economically feasible options from which to choose solu-
tions. Other disciplines make their own particular contributions, but none plays a
more central and essential role than chemistry.
The fourth question, concerning how much exposure to a substance must be
considered hazardous, is the province of the medical profession, toxicologists, and
epidemiologists. These scientific disciplines face serious challenges now that
society has recognized the inverse relationship between how small a risk can be
made and the cost to society to attain it. The medical profession must refine its
knowledge of risks associated with substances such as lead in the atmosphere,
chloroform in Unnking water, radiostrontium in milk, benzene in the workplace,
and formaldehyde in the home. A qualitative statement that a certain class of
substances might be carcinogenic is no longer sufficient. We must be able to weigh
risks and costs against the benefits that would be lost if use of that class of
substances were restricted. We must be able to compare those risks with those
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ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
already present because of natural background levels. More importantly, society
cannot afford to pay the excessive cost to eliminate all risk, since, as the desired
degree of risk approaches zero, the cost escalates toward infinity.
Finally, the choice among options must move into the public arena. Chemists and
scientists in the other relevant disciplines carry a special and important informa-
tional responsibility here. Every political decision deserves the best and most
objective scientific input available. There is nothing more frustrating to our citizens
and our government than to be faced with making decisions without having all the
facts and a useful understanding of the science involved. Scientists, including
chemists, must carry responsibility for providing the public, the media, and the
government with a factual picture expressed in language free of technical jargon.
That picture must establish the scientific setting for a given decision and indicate
the options that lie before us.
TURNING DETECTION INTO PROTECTION
All of our environmental protection strategies should be based on realistic hazard
thresholds and on our ability to detect a particular offending substance well before
its presence reaches that threshold. Chemists must continue to sharpen their
analytical skills so that, even at tiny concentrations well below the hazard
threshold, a given substance can be monitored long before frantic corrective action
is necessary. When this is possible, we see that detection can be equated to
protection.
Unfortunately, the media, the public, and our governmental agencies have too
often equated detection with hazard. This is based on the common assumption that
a substance that is demonstrably toxic at some particular concentration will be
toxic at any concentration. There are innumerable examples to prove that this is not
generally true. Consider carbon monoxide. This ever-present atmospheric com-
pound becomes dangerously toxic at concentrations exceeding 1,000 parts per
million and is considered to have negative health effects for prolonged exposure to
concentrations exceeding 10 parts per million. We do not, however, leap to the
conclusion that CO must be completely removed from the atmosphere! This would
be foolish (and impossible) because we live and thrive in a natural atmosphere that
always contains easily detectable CO, about one part per million. Plainly, our task
is to decide where we should begin cleanup action between the known toxicity
threshold and the known safe range (as the Environmental Protection Agency has
attempted to do).
Selenium presents another interesting example. Certain plants growing in soils
with relatively high selenium content tend to concentrate the element to levels such
that grazing animals are poisoned. Astragalus is an example- it has the common
name "locoweed." Wheat can do the same, and while humans are not noticeably
affected, chickens fed high-selenium wheat produce deformed embryos. On the
other hand, it is now well established that selenium is nutritionally essential in the
diets of rats, chickens, and pigs. Furthermore, it has been found that selenium at
proper levels is a natural anticarcinogen; it is a component of glutathione peroxi-
dase, an enzyme that breaks down injurious hydroperoxides. Ire China, children in
7
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8
ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
populations with low blood levels of selenium suffer from multiple myocarditis
(Keshan disease), and the adults display high cancer death rates and a high
incidence of liver cancer. Plainly, selenium is an element that is essential to human
and animal health at appropriate levels and it becomes toxic at excessive levels.
The daily dietary intake of selenium for adults recommended by the National
Research Council is 50 to 100 micrograms per day. Presently, the permissible level
of selenium in drinking water, as fixed by the EPA, is 10 parts per billion. This
level, set to avoid possible toxicity, may be 10-fold below the level needed for
optimum health. The example shows vividly that trace-level detection in the
environment of a substance that might be toxic at high concentrations does not
imply that a hazard exists. Quite the opposite, such early detection allows time for
deliberate decisions concerning sources, trends, and levels at which corrective
action will be timely. Detection is protection.
Some people have forcefully called for a "zero-risk" approach to environmental
pollution. Zero risk means achieving absolute and complete freedom from any
conceivable hazard. In the carbon monoxide example above it would mean removal
of every single molecule of CO from the entire atmosphere. In recent trends, this
unattainable zero-nsk approach is gradually being replaced by a more sophisticated
risk assessment/risk management philosophy. In both assessment and manage-
ment, a major theme is the crucial importance of being able to analyze complex air,
water, soil, and biological systems that may contain hundreds of natural chemical
compounds. Conclusions regarding the sources, movements, and fates of pollut-
ants depend upon adequate environmental measurements, whether the issue is acid
rain, global climate change, ozone layer destruction, or toxic waste disposal.
Enormously costly decisions about how to protect the quality of our air, water, and
land resources are sometimes based on environmental information that is danger-
ously inadequate and inaccurate. Crash projects (like the "Superfund") to remedy
crises caused by ineffective strategies of the past have been expensive. The best
future investment would be in long-term fundamental environmental science and
monitoring techniques to avoid the need for costly patch-up programs.
Increased effectiveness of environmental measurements requires improved
tools. The challenge is to measure trace levels of a particular compound present
in a complex mixture containing many harmless compounds. The principal
objectives of research in environmental analysis and monitoring are improved
sensitivity, selectivity, separation, sampling, accuracy, speed, and data interpre-
tation. For example, an active research area is connected with separation
techniques to allow rapid and reliable analysis of complex mixtures of pollutants
and pesticides found in toxic wastes, polluted streams and lakes, and biological
samples. A success story in analytical selectivity can be seen in the development
of analytical methods to allow separation and quantitative measurement of each
of the individual 22 isomers of tetrachiorodioxin at the parts per trillion level (one
part in 10~2~!
Highly reactive species in the atmosphere cannot be camed to the laboratory for
analysis. These substances pose special challenges; they require research aimed at
remote sensing techniques that are capable of measuring them where they are
originally formed. Past successes include the measurement of formaldehyde and
~ - x~ ~
_
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ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
nitric acid in Los Angeles smog
by infrared spectroscopy in
which absorption due to these
pollutants was measured over
a one-kilometer distance. With
these experiments it was possi-
ble to determine the simulta-
neous concentrations of form-
aldehyde, formic acid, nitric
acid, peroxyacety} nitrate, and
ozone in the air at the parts per
billion level. Notice that one
part per billion (one part of a
pollutant in 109 parts of air) is a
tiny concentration, too small to
be an irntant. However, it can
be sufficient to be significant in
atmospheric reactions. Scan-
ning laser devices based on ra-
dar-like technology (called "lidar") have been used successfully to measure sulfur
dioxide at the part per million level in the smoke plumes found downwind of
coal-fired power plants. Tunable diode lasers are also capable of providing
immediate detection of pollutants from internal combustion engines right at the
exhaust pipe.
Several laser techniques, including absorption, fluorescence, coherent Raman,
and two-laser methods, need to be examined more extensively for possible use in
atmospheric analysis. One goal of such research should be better measurements in
the troposphere (the layer of the Earth's atmosphere closest to the surface) and in
the stratosphere above. Rapid, reliable, accurate, and less-expensive methods are
needed for measuring concentrations of trace species, such as OH radicals, that
play key roles in atmospheric chemistry.
Research directed at fixing the chemical state of environmental constituents is
gaining importance because we now recognize that both toxicity and ease of
movement from place to place vary markedly with the particular chemical for.
Chromium in the hexavalent oxidation state is toxic, while in the trivalent form it
is much less so, and for some living systems, it is probably a trace element essential
to life. Arsenic in some forms can move rapidly through natural underground water
supplies, while other forms are held tightly, adsorbed on rock or soil surfaces. Of
the 22 distinct structural arrangements of tetrachiorodioxin, one of them is a
thousand times more toxic to test animals than the second most toxic form. These
examples illustrate the importance of analytical methods that allow identification of
chemical form as well as quantity of potential pollutants. Electrochemistry,
chromatography, and mass spectrometry are among the powerful tools used for
such studies.
The complexity of environmental problems requires analysis of massive amounts
of data. Research is needed to assist in the interpretation and wise utilization of the
THERE ARE 22 DIFFERENT TETRACHl ORODIOXINS
Cl woo ~'Ct
Cl
Cl=O`~] 2,3.6,9
Ct
Ct
Ct~°˘ 1 237
etc.
HOW MU CH IS IN THE TORI C 2,3,7 .8 FORM?
AN ANALYTICAL CHALLENGE
9
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10
ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
accumulated information. Developments in the field of artificial intelligence that
use pattern recognition should provide a valuable interpretive aid. Recent advances
in microprocessors and small computers are coming into use as "intelligent"
measuring devices. Attention should be given to organizing, storing, and collecting
environmental data.
OZONE IN THE STRATOSPHERE
The possibility of polluting the stratosphere to the point of partially removing the
protective ozone layer was first raised only about a dozen years ago. This
seemingly improbable notion found much scientific support and has become one of
the best examples of a potentially serious environmental problem of global extent.
It is a problem, furthermore, that points up chemistry's central role in its
understanding, analysis, and solution.
Why do we need to worry about stratospheric chemistry? Ozone in the
stratosphere is the natural filter that absorbs and blocks the Sun's short wavelength
ultraviolet radiation that is harmful to life. The air in the stratosphere, a cloudless,
dry, cold region between about 10- and 50-km altitude, mixes very slowly in the
vertical direction, but rapidly in the horizontal. Consequently, harmful pollutants,
once introduced into the stratosphere, not only remain there for many years but are
also rapidly distributed around the Earth across borders and oceans, making the
problem truly global. A large reduction of our ozone shield would result in an
increase of dangerous ultraviolet radiation at the Earth's surface.
To understand how easily the ozone layer might be disturbed, it is useful to
recognize that ozone is actually only a trace constituent of the stratosphere; at its
maximum concentration ozone makes up only a few parts per million of the air
molecules. If the ozone layer were concentrated into a thin shell of pure ozone gas
surrounding the Earth at atmospheric pressure, it would measure only about 3
millimeters (1/8 inch) in thickness. Furthermore, ozone destruction mechanisms
are based on chain reactions in which one pollutant molecule can destroy many
thousands of ozone molecules before being transported to the lower atmosphere
and removed by rain.
Chemistry's crucial role in understanding this problem has emerged through the
identification of several ozone-destroYine chain processes. FiftY Years ados the
~ .. ~ . . .. .. . . . . . . .. . . .
formation of an ozone layer In the midstratosphere was crudely described In teens
of four chemical and photochemical reactions involving pure oxygen species (O.
O2, and Old. Today, we know that the rates of at least 150 chemical reactions must
be considered in order to approach an accurate model that will describe the present
stratosphere and predict accurately the changes that would result from the
introduction of various pollutants. The chemistry begins with absorption of
ultraviolet radiation from the Sun by O2 molecules in the stratosphere. Chemical
bond rupture occurs and ozone, O3, and oxygen atoms, O. are produced. Then, if
nitric oxide, NO, is somehow introduced into the stratosphere, an important
chemical chain reaction takes place. The NO reacts with ozone to produce NO2,
and this NO2 reacts with an oxygen atom to regenerate NO. These two reactions
together furnish a true catalytic cycle in which NO and NO2 are the catalysts.
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E - lRONMENTAL QUALITY THROUGH CHEMISTRY
US down
to l5Onm
J~ZONE
ABSORBS
UY
LIGHT
I
~—Vdown_C>~N2O
STRATA SPHERED
[-9 N-O + he ~ N + NO
Elf w ,~uu rat
50 Em
280'~
.
3 NO ANON ~ O2 ~ 0-7 Parr
o ~ NO2~NO ~ O2
net 0+O3 iO2.O2
~02+ OH
HNO3
TROPOSPHERE _i...:~:.:~.::.::T3 10- 15 km
~ ~.:::.:::.:::.:.:.~::~:..-:.:,::.::~ ~ g
~ ~ . . :.: .:~:...~::~. :~. f 70 torr
. ~ ~ ~ .
Tic_ I _
NITROGEN OXIDES REDUCE STRATOSPHERIC OZONE
Neither species is consumed since each is regenerated in a complete cycle. Each
cycle has the net effect of destroying one oxygen atom and one ozone molecule
(collectively called "odd oxygenic. This catalytic cycle is now believed to be the
major mechanism of ozone destruction in the stratosphere. In the natural atmo-
sphere the oxides of nitrogen are provided by natural biological release of nitrous
oxide, N2O, at the 'Earth's surface by soil and sea bacteria. This relatively inert
molecule slowly mixes into the stratosphere where it can absorb ultraviolet light
and then react to form NO and NO2.
Of course, oxides of nitrogen directly introduced into the stratosphere are
expected to destroy ozone as well, and this was the basis of the first perceived
threat to the ozone layer large fleets of supersonic aircraft flying in the strato-
sphere and depositing oxides of nitrogen through their engine exhausts. Nuclear
explosions also produce very large quantities of oxides of nitrogen, which are
carried into the stratosphere by the buoyancy of the hot fireballs; a significant
depletion of the ozone layer in the event of a major nuclear war was forecast in a
1975 study by the National Academy of Sciences, although this environmental
effect of nuclear war may be insignificant in comparison with the recently suggested
potential of a `'nuclear winter." Both effects underscore the delicacy of the
atmo'sphere and its sensitivity to chemical transformations.
Then, in 1974, just as the possible impact of stratospheric planes was reaching the
analysis stage, concern was raised about other man-made atmospheric pollutants.
Halocarbons such as CFCI3 and CF2CI2 (chiorofluoromethanes, or CFMs) had
become popular as spray-can propellants and refrigerant fluids, mainly because of
their chemical inertness. This absence of reactivity meant absence of toxicity or
other harmful effects on living things. Ironically, this meant that there was no place
for the CFMs to go but Cup into the stratosphere where ultraviolet photolysis
could occur. Chemists then recognized that if this occurred, the resultant chlorine
species, C! and ClO, could enter into their own catalytic cycle, destroying ozone in
a manner just like the destruction caused by the oxides of nitrogen. Once this
11
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12
ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
UV down
to I60 nm
OZONE
ABSORBS
UV
LIGlIT
STRATOSPHERES
~CF2c92+hv ~C9+CF2C9
1
'O3+C] ~cgb~o2
50 lam
2~0. ~
\0.7 torr
0 echo ~ c,+ 0 C9+ CH4
net O+O3 ~O2~02~ 1
OWE ~ ~ ^-
at .~ ~^ __ ~= ~
OF: release ~
HC9
TROPOSPHERE O :10-15km
_ it.. ~ a: :::: ___ ~
-: ~ ~ ;~5~.:.~ f 70 tort
...... I : : . : : ~ : : ~
CHLORINE ALSO CAN REDUCE STRATOSPHERIC OZONE
possibility was recognized, analysis of the whole stratospheric ozone chemistry
began in earnest. An international committee of scientific experts assembled by the
National Academy of Sciences examined in detail the state of our knowledge in
every aspect of the problem. It became clear that the additional chemistry
introduced into the stratosphere added not just these two catalytic chemical
reactions to the roster but a total of about 40 new reactions involving such species
as CI, ClO, HCI, HOCI, ClONO2, the halocarbons, and several others. Most of
these reactions had never before been studied in the laboratory.
Chemists have responded to this challenge by measuring in the laboratory
reliable reaction rate constants and by clarifying the photochemistry of the suspect
compounds, using the growing array of modern experimental methods. Recent
progress here has been remarkable. It has become possible to generate nearly any
desired reactive molecular species in the laboratory and to measure their rates of
reaction with other atmospheric constituents. Such direct measurements of these
extremely rapid reactions, only a distant goal a decade ago, are now becoming a
reality.
Finally, field measurements of minor atmospheric species have been revolution-
ized by some of the recent advances in analytical chemistry. Methods originally
developed for ultrasensitive detection of extremely reactive species in laboratory
studies have been modified and adapted to measure such constituents as 0, OH, CI,
and ClO at parts per trillion concentrations in the natural stratosphere. This has
been accomplished recently in experiments in which a helium-fi~led balloon cames
an elaborate instrument package to the top of the stratosphere, where the package
is dropped while suspended by a parachute. As the instrument travels through the
stratosphere, it measures concentrations of several important trace chemical
species and relays the information to a ground station. Very recently, the first
successful reel-down experiment was performed in which the instrument package
was lowered 10 to 15 km from a stationary balloon platform and reeled back up
OCR for page 13
ENVIRONMENTAL QUALllY THROUGH CHEMISTRY
again, as if it were on a giant yo-yo. This method results in a huge increase in the
amount of data that can be obtained in a single balloon flight. Also, it allows study
of the variability of the stratosphere, both in space and in time.
Much has been accomplished in the past 10 years. Many of the needed 100 to 150
photochemical and rate processes have been measured in the laboratory and many
of the trace species have been measured in the atmosphere. Yet, two of the
important chemical species containing chlorine, HOCl and ClONO2, have yet to be
measured anywhere in the stratosphere. Refinements in the reaction rates for many
of the important processes are still required and exact product distributions for
many of the reactions are still lacking. Nevertheless, the onginal NAS study, the
research programs that it gave birth to, and the subsequent follow-up studies
provided firm and timely bases for legislative decisions about regulation of CFM
use. Industrial chemists produced alternative, more readily degradable substances
to replace the CFMs in some applications such as aerosol use, in air-conditioning,
and in refrigeration systems. Monitoring programs are in place so that trends or
changes in the stratospheric composition can be watched. The stratospheric ozone
issue provides a showcase example of how science can examine, clarify, and point
to solutions for a potential environmental disturbance. Premature initiation of
regulation was avoided because the problem was recognized early enough to permit
deliberate, objective analysis and focused research to narrow the uncertainty
ranges. From first recognition on, chemists played a lead role.
REDUCING ACID RAIN
Acid rain is one of the more obvious air quality problems facing us today. Acidic
substances and the compounds that lead to them are formed when fossil fuels are
burned to generate power and provide transportation. These are principally acids
derived from oxides of sulfur and nitrogen. There are some natural sources of these
compounds such as lightning, voicanos, burning biomass, and microbial activity,
but, except for rare volcanic eruptions, these are relatively small compared with
emissions from automobiles, power plants, and smelters.
The effects of acidic rainfall are most evident and highly publicized in Europe and
the northeastern United States, but areas at risk include Canada and perhaps the
California Sierras, the Rocky Mountains, and China. In some places precipitation
as acidic as vinegar has occasionally been observed. The extent of the ejects of
acid rain is the subject of continuing controversy. Damage to aquatic life in lakes
and streams was the original focus of attention, but damage to buildings, bndges,
and equipment have been recognized as other costly consequences of acid rain.
The effect of polluted air on human health is the most Circuit to determine
quantitatively .
The greatest damage is done to lakes that are poorly buffered. When natural
alkaline buffers are present, the acidic compounds in acid rain, largely sulfunc acid,
nitric acid, and smaller amounts of organic acids, are neutralized. However, lakes
{yin" on granitic (acidic) strata are susceptible to immediate damage because acids
in rain can dissolve metal ions such as aluminum and manganese. This can cause a
reduction in plant and algae growth, and in some lakes, the decline or elimination
13
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14
ENVIRONMENTALQUALITY THROUGH CHEMISTRY
c'8i n9 W ads Hi ,r IN i: . _
~ . ', '' i: ' I've '
A...;.. ~
\
_
Natural Source.
Photochemistry ,~ ~ _~~-
~ , , ~ ~
\ ~ r ~~ Cloud Processes
hi, /,:s . ,. . 1)' ~ ~
'it
...., tar =~
Marsh— Industry—Transportation
Ocean
Man-made Sources
_~, ~ errestr~a' tacos i, ~ Aquatic Ecosystem
ACID RAIN—SOURCES HERE, IMPACT THERE
of fish populations. Damage to plants from this form of pollution ranges from
harmful effects on foliage to destruction of fine root systems.
In a region such as the northeastern United States, the principal candidates for
pollutant reduction are the power plants burning coal with high sulfur content.
Chemical scrubbers that prevent the emission of the pollutants offer one of the
possible remedies. A chemical scrubber is a device that processes gaseous effluents
to dissolve, precipitate, or consume the undesired pollutants. Catalysts that reduce
oxides of nitrogen emissions from both stationary and mobile sources offer yet
another example of the role that chemistry can play in improving air quality.
The various strategies for reducing acid rain involve possible investments of
billions of dollars annually. With the stakes so high, it is essential that the
atmospheric processes involving transport, chemical transformation, and the fate
of pollutants be very well understood.
Acid deposition consists of both "wet" precipitation (as in rain and snow) and
dry deposition (in which aerosols or gaseous acidic compounds are deposited on
surfaces such as soil particles, plant leaves, etc.~. What ends up being deposited has
usually entered the atmosphere in a quite different chemical form. For example,
sulfur in coal is oxidized to sulfur dioxide, the gaseous form in which it is emitted
from smokestacks. As it moves through the atmosphere it is slowly oxidized and
reacts with water to form sulfuric acid—the form in which it may be deposited
hundreds of miles downwind.
The pathways by which oxides of nitrogen are formed, react, and are eventually
removed from the atmosphere are also very complex. Nitrogen and oxygen, when
heated at high temperatures in power plants, home furnaces, and auto engines,
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ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
form nitric oxide, NO,
which reacts with oxidants
to form nitrogen dioxide,
NO2, and eventually nitric
acid, HNO3. Quantitative
estimates of the global bud-
get for the oxides of nitro-
gen where they come from
and where they go—are still
quite uncertain.
It can readily be seen that
until we have a thorough
knowledge of the bio~eo-
,
15
NH3 ~ OH ~ NO2:
Cal
By
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X
I,, ~ - 2 4 ~
O O
1-10 ~ ,
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MICROBIAL T
ACTIVITY DRY DEPOSITION 12-42
IN SKI LS I
t 12-22
4- 16
TROPOPAUSE
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o
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TERRESTR I A L ~
LARGE UNCERTAINTIES REMAIN IN THE GLOBAL NOx BUDGET
chemical cycles for the var-
ious chemical forms of nitrogen, sulfur, and carbon, and of the global origins and
fates of these species, it will be difficult to select air pollution control strategies
with confidence. Atmospheric and environmental chemistry are central to a
clearer and more healthful environment. Development of reliable methods of
measurement of trace species in air, kinetics of important atmospheric reactions,
and the discovery of new, more effective chemical processes for reducing
pollutant emissions are goals that must receive a national commitment for the
coming decade.
GUARDING AGAINST CLIMATE CHANGE: THE GREENHOUSE EFFECT
In the quest for food, consumer goods, heat for homes, and energy for our
industrial society, we have increased the concentrations of many trace gases in
the atmosphere. Some of these absorb solar energy and convert it into heat that
might eventually cause climate changes with catastrophic consequences. If the
release of these gases to the atmosphere from man's activities causes significant
global warming, then the results could be flooding due to melting polar ice, loss
of productive farmland to desert, and eventually famine. The most publicized of
the gases that trap solar energy is carbon dioxide, but the combined effect of
increases in nitrous oxide, methane, and other gases could equal that of carbon
dioxide.
Approaches used to reduce emission of other pollutants are not sufficient in the
case of carbon dioxide because of the enormous quantities generated in the burning
of fossil fuels and biomass. Here the biogeochemical cycling of carbon assumes
great importance. What impact will the "slash and burn" clearing of forests and
jungles in the Third World countries have? What role does methane play as it is
produced by termites and other species? Are atmospheric solid particles and liquid
droplets coming from human activities likely to block sunlight and offset the effects
of increases in carbon dioxide, methane, and nitrous oxide? Large concentrations
of soot and other aerosols have been observed in Arctic regions. The origin,
composition, radiative properties, fate, and effects of these aerosols constituting
"Arctic Haze" all need to be understood.
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16
ENVIRONMENTAL QUAINT THROUGH CHEMISTRY
The behavior of soot in the atmosphere takes on even greater significance in
light of the uncertainties about the possible atmospheric effects of nuclear
warfare. It was not until 1982 that the hypothesis of global cooling from soot
generated by nuclear war was advanced. This has since been termed "nuclear
winter," because even limited nuclear wars have been predicted to cause the
injection into the atmosphere of enough soot to black out the Sun so that crops
would freeze in summertime. Great uncertainties exist concerning the length of
time aerosols remain in the atmosphere and the effects of soot on radiation
balance.
Unlike local pollutants, the global pollutant problems are perplexing because
they require action on a global scale and the citizens of different countries view
their priorities differently. Whether individual countries have emphasized fossil
fuel versus nuclear fuel in the past has been based primarily on economic factors
such as whether that nation had abundant coal reserves. As global threats such
as carbon dioxide buildup (which is accelerated by coal burning) become more
clearly defined, we may be forced to reevaluate the costs and benefits of nuclear
power. It takes years to develop the knowledge to allow a wise choice. We must
accumulate that knowledge base so that we can weigh wisely the real threat
posed by carbon dioxide buildup in the light of the options before us, including
the environmental safety and waste disposal problems of nuclear energy.
CLEANER WATER AND SAW DISPOSAL OF WASTES
Our surface and subsurface waters are precious resources. Most of us take it for
granted that when we want a drink of water or to go swimming or fishing, our
streams, lakes, and aquifers will be safe to use. Yet our progress in protecting
bodies of water from contamination has not generally been as successful as efforts
in air pollution cleanup. Nonetheless, some important progress has been made.
Lake Erie, once thought doomed to die biologically from reduced oxygen content
(eutrophication) induced by phosphates and other nutrients, is making a comeback.
Improved water treatment, coupled with more rigorous attention to hazardous
waste treatment and disposal, holds the key to future advances. To recognize and
control the sources of pollution, we must understand the intricacies of pollutant
movement and conversion.
Nearly half of the citizens of the United States depend upon wells for their
drinking water. A recent NAS assessment of groundwater contamination estimated
that about ~ percent of the aquifers in the continental United States may be
contaminated to some extent. Evidence of subsurface migration of pollutants
makes it increasingly important to protect, with the best science and technology
available, the aquifers feeding those wells.
A number of ground-burial disposal practices and waste deposit sites (repos-
itories) have been used for many years with only minimal groundwater contam-
ination. Procedures have been predicated on the assumptions that the waste
material was unlikely to migrate and that, over time, the compounds would be
oxidized, hydrolyzed, or microbially decomposed to harmless products. Now,
however, some instances of serious groundwater contamination have appeared.
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ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
Some compounds have proven to be more stable and mobile than expected, while
some of them are bacterially converted into more toxic and mobile forms.
Proposals currently under consideration for recovering seriously contaminated
aquifers are soberingly expensive. For example, estimated costs for "con-
tainment" efforts at the Rocky Mountain Arsenal near Denver, Colorado, are about
$100 million and for "total decontamination" up to $] billion. Such enormous
prospective cleanup costs require thoughtful weighing of the costlbenefit trade-offs
to society in deciding what to do. More relevant here is the inescapable conclusion
that it would be wise to invest the much smaller amount of public funds into
research that will better define cleanup options and lessen the chances of other such
incidents.
If the subsurface of the planet is to be used as a place for depositing our wastes,
we must have much more thorough understandings of the physical/chemicaLbio-
logical system it presents. We must be able to predict the movement and fate of
Well
_ .
Deep-Well
>, Disposal Injection aSnpdlls
Leaks
. ~ ~
...... a ., ......... ..........................
Buried
Wastes
, .,.' . I\ ~ ,
.. . ~ , .,. ace - - ;; .... Act, ~
:-: - w' i, . ~ ... ~ .... . ~ - . .:i ~
· 0. ,· ~ Her A; ~ :; :' {~u ~ ~
$:~·2~. . :;~ rabid ~ River
-
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IT GOES IN HERE—BUT IT COMES OUT THERE
waste compounds with much greater confidence than is now possible. Laboratory
and field studies must examine migration of compounds and ions through subsur-
face strata, and we must develop new analytical techniques for detecting and
following the movement of polluted subsurface plumes (e.g., by measuring subsur-
face soil gases).
Groundwater quality can also be improved by developing improved methods for
treating wastewaters, including industrial wastewaters that contain especially
stable contaminants. Conventional wastewater treatment depends upon combina-
tions of chemical and biological processes. While this is effective for some types of
wastes, research is needed on advanced techniques such as exposure to ozone
17
OCR for page 18
18
ENVIRONMENTAL QUALITY THROUGH CHEMISTRY
(ozonization), "wet air oxidation" (aqueous oxidation under high temperature and
pressure), high- temperature incineration, and the use of adsorbants and resins for
pollutant removal.
Innovative methods for recapture and recycling of valuable substances such as
metals that would otherwise contribute to water pollution are also needed. Solvent
extraction, ion exchange, reverse osmosis, and other chemical separation processes
deserve study. Mines pose special problems. Acid mine drainage and movement of
radioactive mine tailings are subjects of continuing studies that should reduce
unwanted environmental effects.
Agriculture has depended increasingly on pesticides to control disease and insects
and to increase food production. An undesired result has been gradual contamination
of water supplies In some areas. Assessment of the chemical fate of pesticides and the
development of acceptable, degradable alternatives are important research objectives.
It is clear that chemists, geologists, and environmental engineers will need to
address these problems in water and waste treatment to safeguard our water
resources.
RADIOACTIVE WASTE MANAGEMENT
At present, it is thought that the best place to store radioactive waste is
underground rather than, for example, in the oceans, in space, or in accessible
surface sites. This choice means that an understanding of the fundamental
geochemistry of the underground storage areas is required. We must be able to
make reliable predictions concerning possible radionuclide movement through the
earth surrounding the storage site. However, mathematical modeling of such
movements to indicate the suitability of a given site requires knowledge in several
key areas. First, we must understand how much the radiation and heat release
associated with the stored radioactivity will affect the local geochemistry (the
groundwater chemistry and mineralogy, for example). Next, we have to understand
the manner in which radioactive elements are carried through the soil. Do they form
water-soluble complexes? Are they adsorbed onto the surfaces of colloidal parti-
cles that are then carried along in suspension? We must also look for chemical
behaviors that would cause the radioactivity to stay forever wherever we put it.
Chemical conversion of the radioactive elements to compounds of very low
solubility in water is an example. Adsorption onto stationary solid surfaces is
another.
Perhaps most difficult is the need to make predictions that will be reliable far into
the future. Here we may find guidance in observations from the geologic record,
including those observations connected with the natural reactor discovered at
Oklo, in West Africa (see Section IV-C). This need for long-range predictability
implies that we should be looking at other means of dealing with radioactive waste
besides underground storage, means that will permit easier access to and monitor-
ing of waste deposits. Perhaps this way the risks can be more clearly defined and
controlled. Most important, we must have the knowledge base needed to be sure
we aren't missing any options and that we understand the relative advantages and
risks of each.
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E - IRONMENTAL QUALITY THROUGH CHEMISTRY
SUPPLEMENTARY READING
Chemical & Engineering News
"Tending the Global Commons: Nations
Struggle for Ways to Check Global Warm-
ing and Depletion of Stratospheric Ozone"
by L. Ember (C.& E.N. staff), vol. 64, pp.
14-64, Nov. 24, 1986.
`'Chemistry in the Thermosphere and Iono-
sphere" by R.G. Roble, vol. 64, pp. 23-38,
June 16, 1986.
"Incineration of Hazardous Wastes at Sea"
by P. Zurer (C.& E.N. staff), vol. 63, pp.
24-35, Dec. 9, 1985.
"Dioxin, A Special C.& E.N. Issue," vol.
61, pp. 7-63, June 6, 1983.
"Federal Food Analysis Program Lowers De-
tection Limits" by W. Worthy (C.& E.N.
staff), vol. 61, pp. 23-24, Mar. 7, 1983.
"Chemistry in the Troposphere" by W.L.
Chamedies and D.D. Davis, vol. 60, pp.
39-52, Oct. 4, 1982.
Science
"Treatment of Hazardous Wastes" by P.H.
19
Abelson, vol. 233, p. 509, Aug. 1, 1986.
'`Inorganic and Organic Sulfur Cycling in Salt-
Marsh Pore Waters" by G.W. Luther III,
T.M. Church, J.R. Scudlark, and M. Cos-
man, vol. 232, pp. 74~749, May 9, 1986.
Scientific American
'~Dioxin" by F.H. Tschirley, vol. 254, pp.
29-35, February 1986.
ACS Information Pamphlets
"Acid Rain," 8 pages, December 1985.
"Chemical Risk: A Primer," 12 pages, De-
cember 1984.
"Hazardous Waste Management," 12 pages,
December 1984.
"Ground Water," 13 pages, December 1983.
Pamphlets available from:
American Chemical Society
Department of Government Relations & Sci-
ence Policy
1155 16th Street, NW
Washington, DC 20036
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Representative terms from entire chapter:
acid rain
