Environmental Segments and Natural/Biogeochemical cycles

CHM-406: ENVIRONMENTAL CHEMISTRY
Pranshu K. Gupta
M.Sc. Chemistry, 4th Semester,
Roll No.: 29, Enroll. No.: 373379
E-mail: pranshuvns01@gmail.com
Department of Chemistry,
Institute of Science (I.Sc.),
Banaras Hindu University (BHU),
Varanasi-221005, UP, India
ENVIRONMENTAL SEGMENTS
AND NATURAL CYCLES

Definition of environment
The circumstances, objects, or conditions by which one is surrounded
OR
The complex of physical, chemical, and biotic factors (such as climate, soil,
and living things) that act upon an organism or an ecological community
and ultimately determine its form and survival
OR
2b: the aggregate of social and cultural conditions that influence the life of an individual or
community.
- Merriam Webster
Definition of Environmental Chemistry
It is a multidisciplinary science of chemical phenomena in the environment
which studies sources, reaction, transport and effect and fate of chemical
species in the air, water, soil, and the impacts of human activities on these.
- Environmental Chemistry, A.K. De
TO BEGIN WITH ………

 Definition: The atmosphere is a protective and life sustaining
blanket of gases surrounding the Earth that saves it from
hostility of outer space, by absorbing most of the cosmic rays,
and a major portion of harmful electromagnetic radiations
from sun, and transmitting ultravoilet, visible, infrared
radiations (300-2500 nm) and radio waves (0.14-40 m).
 It plays a key role in maintaining Earth’s temperature/heat
balance by absorbing the infrared radiation and re-emitting it
back from the Earth. Major component of Earth’s atmosphere
are N2(71%), O2(21%), while minor components are Ar,
CO2(0.03%), and some trace gases.
 Oxygen and carbon dioxide, are the two most dynamic and
most necessary gases that sustain life on Earth and their levels
are ideally maintained by photosynthetic plants. Nitrogen
fixing bacteria utilizes nitrogen fixation to gain their energy
currency.
 However, with the progress of science and technology, man
has been dumping waste materials into atmosphere that are
posing serious threat to survival of mankind itself on Earth.
SEGMENT 1 : ATMOSPHERE
Scheme: Major regions of atmosphere, temperature
profile. (Adapted from: Environmental Chemistry, Edn. 7,
pp. 19, by A.K. De and A.K. De, New Age International
(P) Limited, Publishers, New Delhi-11002, India

 Definition: Hydrosphere includes all types of water
resources like seas, oceans, rivers, lakes, streams,
reservoirs, glaciers, polar icecaps and ground water
(i.e., water below Earth’s surface).
 About 97% of the Earth’s water supply in in oceans
where high salt concentration makes it unfit for
consumption. About 2% of water resources are
locked in the polar icecaps and glaciers, while only
about 1% is available as fresh water (surface water-
rivers, lakes, streams, and ground water) for human
consumption and other uses.
 History of ancient civilization-growth and decline-is
intimately linked with the quantum of water supply.
The major uses of water are for irrigation (30%) and
thermal power plants (50%), while other uses are
domestic(7%) and other consumption(12%).
 Surface water gets contaminated by pesticides and
fertilizers and agricultural runoff water, human and
animal wasters in sewage and industrial wastes.
Water borne from sewage alone have killed million
of people in developing countries.
 Aquatic environment chemistry is based on proper
understand of the sources, transport, characteristics
and chemical species of water.
SEGMENT 2: HYDROSPHERE
97%
2%
1%
Saline water
(Oceans)
Water fit for
consumption
Portable water
locked as polar
ice
70%
8%
2%
12%
8% Evaporation
Irrigation
Domestic Use
Electrical use
Others
Earth’s water
supply
Mass balance of
annual Rainfall

 Definition: Lithosphere is the outer mantle of the solid Earth, consisting up of
the solid minerals in the Earth crust and the soil.
 Soil is a complex mixture of minerals, organic matter, air and water. The soil
hence is the most important part of the lithosphere.
 Soil of land decides its fertility and its agricultural and thus commercial
importance. Fertility of the soil however, depends on the topmost layer of the
soil, rich in dead organic matter, minerals and micronutrients. This layer is
termed as Humus.
 The layers found below the humus is shows a decrement in its fertility as one
descends down. However, lower layers have been helpful in as a natural semi-
efficient water purifying system that percolates rainwater to the ground water
at water table.
SEGMENT 3: LITHOSPHERE

 Definition: This denotes the realm of living organism and their interaction with
living environment, and its other segments like hydrosphere, lithosphere and
atmosphere.
 Both Environment and biosphere are influenced considerably by each other.
Example: O2 and CO2 level in atmosphere entirely depends on the plant kingdom.
 As a matter of fact, photosynthetic plants are sole responsible for accumulation of
O2 in atmosphere, the original atmosphere has been devoid of oxygen. Biosphere in
its widest context consists of Earth’s crust, atmosphere, various species of life,
which exist in the zone 600 meters above, and 10,000 meters below the sea level.
 Being highly complex, biosphere has been divided in smaller units called
ecosystems, that refer to a definite zone where plants, animals and microbes live,
by exhibiting a dynamic interrelationship amongst themselves as well with their
physical environment.
 Biogeochemical cycles or Natural cycles represents these dynamic
interrelationships between living forms and their physical environment by
providing a balanced and continuous circulation of life-sustaining constituents,
hence stabilizing biosphere by sustaining life processes.
SEGMENT 4: BIOSPHERE

 Definition: Anthrosphere may be defined as an man-made part
of the environment, that is part of the environment made or
modified by human activities.
 Prehistoric humans made little impact on environment but
industrialization, particularly after Industrial Revolution
(1780), this impact became more and more pronounced as a
separate area in terms of effects on environment s a whole.
 UNIT OF ANTHROSPHERE:
1. Structures/houses used for living
2. Structures used for commerce, manufacturing, education and
other activities.
3. Infrastructures including water, fuel and other electricity
distribution systems, waster disposal systems such as sewers.
4. Infrastructure transport: roads, railways, airports and
waterways.
 Natural process have led to finely tuned balance among the
systems composing Earth’s natural environment. Life forms on
Earth have influenced Earth’s climate which determine
suitability of life.
SEGMENT 5: ANTHROSPHERE
GAIA HYPOTHESIS
(James Lovelock, British Chemist)
Atmospheric O2/CO2 balance is established
and sustained by organisms which determine
and maintain Earth’s climate and other
environmental conditions. It is essential that
ultimate balance (Man-Environment) is not
upset but is sustained by Man for his own
survival.

CLASSIFICATION OF NATURAL CYCLES
 On the basis of its place of occurrence:
1. Endogenic Cycles: Largely occur on sub-surface
rocks. E.g.: Phosphorous cycle
2. Exogenic Cycles: Largely occur on Earth surface.
E.g.: Oxygen, Carbon or Nitrogen cycle
NOTE:
1. Sediments and soil predominant components that connect
endogenic and exogenic cycle.
2. Rocks irrespective of their type weathers to give
soil/sediments, melts to give magma, and revert back to
rocks under pressure-temperature catastrophe.
3. Nutrient from soil or sediments exchange between
lithosphere and hydrosphere, or to atmosphere, or to
biosphere either directly or indirectly from lithosphere to
hydrosphere to atmosphere and then to biosphere by
changing their physical/chemical state. They return back to
soil/sediments either of the forms. This explains the
inherent connectivity between endogenic and exogenic
cycles.
Scheme: The carbon cycle. (Adapted from: Environmental
Chemistry, Edn. 7, pp. 9, by A.K. De and A.K. De, New Age
International (P) Limited, Publishers, New Delhi-11002, India

CLASSIFICATION OF NATURAL CYCLES
 On the basis of its reservoir:
1. Gaseous Cycles: Cycles in which elements spends
most of the cycle in atmosphere.
2. Sedimentary Cycles: Cycles in which elements exists
as dissolved minerals in soil/sediment solution.
NOTE:
1. Sediments and soil predominant components that connect
endogenic and exogenic cycle.
2. Rocks irrespective of their type weathers to give
soil/sediments, melts to give magma, and revert back to
rocks under pressure-temperature catastrophe.
3. Nutrient from soil or sediments exchange between
lithosphere and hydrosphere, or to atmosphere, or to
biosphere either directly or indirectly from lithosphere to
hydrosphere to atmosphere and then to biosphere by
changing their physical/chemical state. They return back to
soil/sediments either of the forms. This explains the
inherent connectivity between endogenic and exogenic
cycles.
Scheme: The carbon cycle. (Adapted from: Environmental

 Definition: The Hydrological Cycle is a continuous natural
process, which helps in exchange of water between
atmosphere, the land the sea, living plants and animals.
 About 1/3rd of the solar flux is acts as an endless conveyer
belt driving the hydrological cycle via sequential steps like,
evaporation, cloud formation, precipitation, runoff,
percolation, etc, providing us with our supply and reserve of
freshwater.
 Normal evaporation from ocean exceeds precipitation by
rain into the seas by about 10% and this excess amount
ultimately moves as water vapour over land surface. This
balances the hydrological cycle, and fulfils our requirement
of additional water.
 Each year about 50 Tm3 water evaporates, and then
precipitates over earth surface. From land, about 44.5 Tm3
water flows to sea per year, and this is available as man’s
natural water supply. (NOTE: 1 Terra m3 (Tm3)= 1012 m3)
HYDROLOGICAL CYCLE
Scheme: Concept map for hydrological cycle

HYDROLOGICAL CYCLE
About
1/3rd of
solar
flux
Water reservoir
evaporates by
sunlight
Light condenses the clouds giving
rise to rainfall
Fall of
water on
condensa
tion
Movement
of water
with some
speed Infiltration
to ground
50 Tm3/year
50 Tm3/year
44.5 Tm3/year
Scheme: The hydrological cycle. (Adapted from: Environmental Chemistry, 3 Edn., by
S.E. Manhan, pp. 8, 1979, Willard Grant Press, Brooks/Cole Publishing Company,
Sartler office building, Boston, Massachusetts, Monterery, California-93940, USA.

HISTORICAL AND ITS PRESENT SCENNARIO:
 History of human civilization reveals that water
supply and civilization are almost synonymous,
and several civilizations and cities have
disappeared due to water shortages originating
from climatic changes.
 A very small percentage of fresh water is available
for human consumption. (statistics shown in the
pie chart). Most of the this water is polluted though
agricultural runoff. World Health Organization
(WHO) has estimated that water supply has to be
cut by 50% by 2025 if nation fails to address
imbalance in global water supply and demand.
 Nordic company (Norway) is engaged in the
business of towing 35,000 tonnes of
freshwater/day from Turkey to Greek islands using
giant polyester bags of length 200 meters. Future
plans are to transport 1,00,000 tonnes of
freshwater/day from Iran to Saudi Arab via
Caribbean and Red sea using supertankers of
length 300 meters.
HYDROLOGICAL CYCLE
97%
2%
1%
Saline water
(Oceans)
Water fit for
consumption
Portable water
locked as polar
ice
70%
8%
2%
12%
8% Evaporation
Irrigation
Domestic Use
Electrical use
Others
Earth’s water
supply
Mass balance of
annual Rainfall

 Definition: Carbon cycle operates the circulation of
carbon over various segments of environment in different
physical/chemical states.
 An important form of carbon is present as CO2(0.03%) in
atmosphere. Part of it is dissolved in surface water as
HCO3
- ions, that is finally fixed as CO3
-2 minerals at the
bottom of the sea/ocean as limestone.
 A part of Carbon is fixed as CH2O (biological carbon) by
photosynthesis, that serve as an important constituent of
biomolecules. Another form of carbon is fixed as lignite,
coal, petroleum and natural gas.
 Significance of this cycle is its ability to transfer C from
biological systems to geosphere via geochemical process
as fossil fuels.
 Photosynthetic microbes are important carbon fixing
compounds in water bodies that take up CO2 causing
precipitation of CaCO3 and CaCO3.MgCO3, or fossil
fuels.
 The scavenging action of microbes maintain carbon
balance by degrading organic biomass, oil spills and
carbon-containing hazardous wastes as CO2, that finally
return to atmosphere.
CARBON CYCLE
Geosphere: Solid Earth upon which humans and other
life beings live and form which they extract their food,
minerals and fuels, and therefore are able to fulfil all
requirements to sustain their livelihood.
Scheme: The carbon cycle. (Adapted from:
Environmental Chemistry, Edn. 7, pp. 9, by A.K. De and
A.K. De, New Age International (P) Limited, Publishers,
New Delhi-11002, India

 Definition: Oxygen cycle is based on the exchange of
oxygen among various environmental segments, and has
a key role in atmospheric chemistry, geochemical
transformation and life processes.
 Atmospheric O2 (21%) is a life sustaining gas for
aerobic respiration, and enzymatic oxidation of organic
food in aerobes, hence sustaining their general
metabolism.
 Photosynthetic living beings, are the ultimate source of
O2 sets up the oxygen cycle, by maintaining original O2
stock and its continuous flow. Apart form this, there is a
continuous exchange of O2 between atmosphere and all
water surface on Earth. However, its total amount
remains relatively constant to stabilize O2 cycle.
 Oxygen participates in combustion processes,
degradation of organic materials and some weathering
processes. However, the total oxygen stock gets affected
by its consumption, for the combustion of fossil fuels and
reducing gases (CO), released from volcanoes.
OXYGEN CYCLE
Scheme: The oxygen cycle. (Adapted from: Environmental

Oxygen contributes to various processes on Earth surface:
1. Combustion:
C + O2  CO2
CH4 (in natural gas) + 2O2  CO2 + 2H2O
2CO + O2  2CO2 (Consumption of Oxygen stock)
2. Oxidative Weathering of minerals:
4FeO + O2  2Fe2O3
3. Fe2O3 deposits in primitive Earth: Obtained from soluble Fe(II)
4Fe2+ + O2 + 4H2O  2Fe2O3 + 8H+
4. Photosynthesis by green plants:
CO2 + H2O + hv  [CH2O] + O2 (Original Oxygen stock)
OXYGEN CYCLE

“Today nitrogen atom may be throbbing in the cells of the meadow
grass; tomorrow it may be pulsating through the tissue of living animal.
The nitrogen atom afterwards may rise from decaying animal refuse and
stream to the upper regions of the atmosphere where it may be yoked
with oxygen in a flash of lightning and return as plant food to the soil in
a torrent of rain or it may be directly absorbed from atmosphere by the
soil and are rendered available for plant food by the action of symbiotic
bacteria. Thus each nitrogen atom has doubtless undergone a never
ceasing cycle of changes through countless aeons of time”
-- Mellor
NITROGEN CYCLE

 Definition: Nitrogen cycle maintains essential cycling
of nitrogen over various environmental segments, in
soluble or insoluble form in an ecosystem.
 Plants and animals continuously produce proteins, that
are N-containing organic compounds. Death and decay
of plants and animals as well animal excreta comprise a
major load of organic N-containing organic residues.
 Some soils microbes like Denitrosomonas,
Denitrobacter, denitrify NO3
- to N2, while other
microbes like Nostoc, Nitrobacter, Nitrosomonas, etc,
perform biologically fix atmospheric N2 to NH3 through
various NO2
-s, and NO3
-s (Addition rate: 4-7 ton/ha/yr;
Fixation rate: 1 ton/ha/yr)
 Although freshwater NO3
- leaching may cause some
loss, N cycle is balanced and [N2] remains same.
However, it is misbalanced by dumping of agricultural
wastes at a rate of 40 million tonnes/year. Fresh water
resources get polluted by agricultural runoff i.e.,
leaching of excessive NO3
- from agricultural lands.
NITROGEN CYCLE
Scheme: The nitrogen cycle. (Adapted from: Environmental

 Definition: A type of endogenous
sedimentary cycle that balances phosphorous
on lithosphere as well as in hydrosphere, by
circulating through these segments in soluble
or insoluble form.
 PO4
-3s is necessary for growth and
maintenance of animal bones and teeth, while
organophosphates (POR4
-3) helps in cell
division and DNA/RNA synthesis.
 The ultimate energy currency of plants and
animals that facilitate nutrient derivation via
metabolic pathways is adenosine triphosphate
(ATP).
 This cycle is badly affected by pollution,
mainly from agricultural run-off containing
super PO4
-3s and triple-super PO4
-3s and also
from domestic sewage containing PO4
-3s
derived from excreta and detergents. This
cause algal bloom and accelerated
eutrophication that reduces dO2 in water
disrupting the natural food chain.
PHOSPHOROUS CYCLE
Scheme: The phosphorous cycle on land. (Adapted from:
Environmental Chemistry, Edn. 7, pp. 12, by A.K. De and A.K. De, New
Age International (P) Limited, Publishers, New Delhi-11002, India
On land soluble and insoluble PO4
-3s, stored in rocks/soil are
absorbed as inorganic PO4
-3 via plants, which convert them to
POR4
-3s. Animals consume plants to obtain their share in this
cycle. When dead, these decay, and release these PO4
-3s to
the soil that convert to humus by microbes. Bulk PO4
-3
absorbed on soil particles leach out in to water sources.

PHOSPHOROUS CYCLE
Scheme: The phosphorous cycle in water. (Adapted from:
Environmental Chemistry, Edn. 7, pp. 13, by A.K. De and A.K. De, New
Age International (P) Limited, Publishers, New Delhi-11002, India
In water, inorganic PO4
-3s, are absorbed by freshwater phyto-
planktons, which convert them to POR4
-3s. Zoo-planktons
consume phyto-planktons to obtain their share in this cycle.
When dead, both settle at the bottom of oceans, where they
decay, and release these PO4
-3s that recycle again.
 Definition: A type of endogenous
sedimentary cycle that balances phosphorous
on lithosphere as well as in hydrosphere, by
circulating through these segments in soluble
or insoluble form.
 PO4
-3s is necessary for growth and
maintenance of animal bones and teeth, while
organophosphates (POR4
-3) helps in cell
division and DNA/RNA synthesis.
 The ultimate energy currency of plants and
animals that facilitate nutrient derivation via
metabolic pathways is adenosine triphosphate
(ATP).
 This cycle is badly affected by pollution,
mainly from agricultural run-off containing
super PO4
-3s and triple-super PO4
-3s and also
from domestic sewage containing PO4
-3s
derived from excreta and detergents. This
cause algal bloom and accelerated
eutrophication that reduces dO2 in water
disrupting the natural food chain.

 Definition: An exogenic cycle that circulates sulpher
from atmosphere to biosphere by oxidizing and
reducing it in inorganic form and assimilating it in
organic form.
 Sulpher is an important constituent of S-containing
amino acids like cysteine and its dimers. These lead S-
proteins.
 Sulpher as S-2s oxidizes to SO4
-2s, via aerial oxidation
in atmosphere. These SO4
-2s are assimilated as cellular
proteins. These plants are consumed by animals and
they get their share of S. On their death, they are
decomposed by S-assimilating microbes releasing S-2s.
 In polluted water under anaerobic conditions H2S is
produced by bacteria giving deposits of FeS.
 In unpolluted water under aerobic conditions sulpher
bacteria transforms S-2s to SO4
-2s, for production of
proteins.
SULPHER CYCLE
Scheme: The sulpher cycle. (Adapted from:
Environmental Chemistry, Edn. 7, pp. 13, by A.K. De and
A.K. De, New Age International (P) Limited, Publishers,
New Delhi-11002, India

 Environment is a complex of physical, chemical, and biotic factors (such as climate, soil, and living
things) that act upon an organism or an ecological community and ultimately determine its form and
survival. Environmental Chemistry is the It is a multidisciplinary science of chemical phenomena in
the environment which studies sources reaction, transport and effect and fate of chemical species in
the air, water and soil, and the impacts of human activities on these.
 The atmosphere is a protective and life sustaining blanket of gases surrounding the Earth that saves
it from hostility of outer space, by absorbing most of the cosmic rays, and a major portion of
harmful electromagnetic radiations from sun, and transmitting ultravoilet, visible, infrared
radiations (300-2500 nm) and radio waves (0.14-40 m).
 Hydrosphere includes all types of water resources like seas, oceans, rivers, lakes, streams, reservoirs,
glaciers, polar icecaps and ground water (i.e., water below Earth’s surface).
 Lithosphere is the outer mantle of the solid Earth, consisting up of the solid minerals in the Earth
crust and the soil. Soil is a complex mixture of minerals, organic matter, air and water. The soil
hence is the most important part of the atmosphere. The topmost layer of the soil is rich in dead
organic matter, minerals and micronutrients. This layer is termed as Humus.
 Biosphere denotes the realm of living organism and their interaction with living environment, and its
other segments like hydrosphere, lithosphere and atmosphere. Biosphere has been divided in smaller
units called ecosystems, that refer to a definite zone where plants, animals and microbes live, by
exhibiting a dynamic interrelationship amongst themselves as well with their physical environment.
 Anthrosphere may be defined as an man-made part of the environment, that is part of the
environment made or modified by human activities. As per Gaia Hypothesis (James Lovelock,
British Chemist) Atmospheric O2/CO2 balance is established and sustained by organisms which
determine and maintain Earth’s climate and other environmental conditions. It is essential that
ultimate balance (Man-Environment) is not upset but is sustained by Man for his own survival.
SUMMARY

 Biogeochemical cycles or Natural cycles represents dynamic interrelationship between living forms
and their physical environment by providing a balanced and continuous circulation of life-
sustaining constituents, hence stabilizing biosphere by sustaining life processes.
 On the basis of its place of occurrence, natural cycles can be endogenic that largely occur on sub-
surface rocks (E.g.: Phosphorous cycle) and exogenic that largely occur on Earth surface (E.g.:
Oxygen, Carbon or Nitrogen cycle). They are also classified on the basis of reservoir as gaseous and
sedimentary.
 Nutrient from soil or sediments exchange between lithosphere and hydrosphere, or to atmosphere,
or to biosphere either directly or indirectly from lithosphere to hydrosphere to atmosphere and
then to biosphere by changing their physical/chemical state. They return back to soil/sediments
either of the forms. This explains the inherent connectivity between endogenic and exogenic cycles.
 Normal evaporation from ocean exceeds precipitation by rain into the seas by about 10% and this
excess amount ultimately moves as water vapour over land surface. This balances the hydrological
cycle, and fulfils our requirement of additional water. Each year about 50 Tm3 water evaporates,
and then precipitates over earth surface. From land, about 44.5 Tm3 water flows to sea per year,
and this is available as man’s natural water supply.
 Carbon cycle transfer C from biological systems to geosphere (Solid Earth upon which humans and
other life beings live and form which they extract their food) via geochemical process as fossil fuels.
Photosynthetic microbes are important carbon fixing compounds in water bodies that take up CO2
causing precipitation of CaCO3 and CaCO3.MgCO3, or fossil fuels. The scavenging action of
microbes maintain carbon balance by degrading organic biomass, oil spills and carbon-containing
hazardous wastes as CO2, that finally return to atmosphere.
SUMMARY

 Photosynthetic living beings, are the ultimate source of O2 sets up the oxygen cycle, by maintaining
original O2 stock and its continuous flow. Apart form this, there is a continuous exchange of O2
between atmosphere and all water surface on Earth. However, its total amount remains relatively
constant to stabilize O2 cycle.
 Some soils microbes like Denitrosomonas, Denitrobacter, denitrify NO3
- to N2, while other microbes
like Nostoc, Nitrobacter, Nitrosomonas, etc, perform biologically fix atmospheric N2 to NH3 through
various NO2
-s, and NO3
-s (Addition rate: 4-7 ton/ha/yr; Fixation rate: 1 ton/ha/yr). It is
misbalanced by dumping of agricultural wastes at a rate of 40 million tonnes/year. Fresh water
resources get polluted by agricultural runoff i.e., leaching of excessive NO3
- from agricultural
lands.
 Soluble and insoluble PO4
-3s, are absorbed as inorganic PO4
-3 via phytological entities like
plants(on land) and phyto-planktons(in water body) which convert them to POR4
-3s. Zoological
entitites like Animals(on land) and zooplanktons(on water body) consume phytological origin to
obtain their share in this cycle. When dead, these decay, and release these PO4
-3s to the soil that
convert to humus, or settle at bottom. Bulk PO4
-3 absorbed on soil particles leach out in to water
sources.
 Sulpher as S-2s oxidizes to SO4
-2s, via aerial oxidation in atmosphere. These SO4
-2s are assimilated
as cellular proteins. These plants are consumed by animals and they get their share of S. On their
death, they are decomposed by S-assimilating microbes releasing S-2s. In polluted water under
anaerobic conditions H2S is produced by bacteria giving deposits of FeS. In unpolluted water
under aerobic conditions sulpher bacteria transforms S-2s to SO4
-2s, for production of proteins.
SUMMARY

1. A.K. De, A.K. De, Environmental Chemistry, New Age International (P),
Limited, 7th Edn., 2015 (International Edition).
2. S.E. Manahan, Environmental Chemistry, CRC Press, Boca Raton, Fl., 8th
Edn., 2005.
3. A.M. Dix, Environmental Pollution, John Wiley, New York, 1980.
4. A. Kashlinsky et al., Nature, 2005, Cited in Independent, London (Nov.
2005).
REFERENCES

Environmental Segments and Natural/Biogeochemical cycles

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