introduction principles that govern the reactions, transport, effects and fate of chemical species...
DESCRIPTION
What is Environmental Chemistry Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. The study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of scienceTRANSCRIPT
Introduction Principles that govern the Reactions, Transport,
Effects and Fate of chemical Species in air, water, soil, and
Living Environment. Atmospheric reactions eg. Ozone chemistry in
the Troposphere and Stratosphere. Organic chemicals . Pesticides,
non-pesticides. Chemistry of natural water pollution Reactions,
transport, effects and fates of chemical species in water
principles of water purification. Toxic heavy metals, hazardous and
municipal waste contamination. In the living environment we shall
talk about living organisms and chemical species. Radioactivity,
Radon and Nuclear relation to their environmental effects. What is
Environmental Chemistry
Environmental chemistry is the scientific study of the chemical and
biochemical phenomena that occur in natural places. The study of
the sources, reactions, transport, effects, and fates of chemical
species in the air, soil, and water environments; and the effect of
human activity on these. Environmental chemistry is an
interdisciplinary science that includes atmospheric, aquatic and
soil chemistry, as well as heavily relying on analytical chemistry
and being related to environmental and other areas of science What
is a contaminant Contamination is the presence of a minor and
unwanted constituent (contaminant) in material, physical body,
natural environment, at a workplace, etc." It goes on to discuss
specifics. In case of the environment, "the term is in some cases
virtually equivalent to pollution, where the main interest is the
harm done on a large scale to humans or to organisms or
environments that are important to humans. " Difference between
contaiminant and pollutant
Contamination of the water supply may not constitute an actual
health hazard, even though the quality of the water is impaired
with respect to taste, odor or usefulness. However, pollution of
the water supply does constitute an actual health hazard. The
consumer will be subjected to potentially lethal water borne
chemicals and/or biological agents. Difference between pollution
and contamination
In chemistry, the term usually describes a single constituent, but
in specialized fields the term can also mean chemical mixtures,
even up to the level of cellular materials. In environmental
chemistry the term is in some cases virtually equivalent to
pollution, where the main interest is the harm done on a large
scale to humans or to organisms or environments that are important
to humans. Difference between pollution and contamination
All chemicals contain some level of impurity. Contamination may be
recognized or not and may become an issue if the impure chemical is
mixed with other chemicals or mixtures and causes additional
chemical reactions. The additional chemical reactions can sometimes
be beneficial, in which case the label contaminant is replaced with
reactant or catalyst. If the additional reactions are detrimental,
other terms are often applied such as toxin, poison or pollutant
depending on the chemistry involved. A major fraction of chemistry
is involved with identifying, isolating, and studying contaminants.
Forms of pollution The major forms of pollution are listed below
along with the particular contaminant relevant to each of them: Air
pollution:- the release of chemicals and particulates into the
atmosphere. Common gaseous pollutants include carbon monoxide,
sulfur dioxide, chlorofluorocarbons (CFCs) and nitrogen oxides
produced by industry and motor vehicles. Photochemical ozone and
smog are created as nitrogen oxides and hydrocarbons react to
sunlight. Particulate matter, or fine dust is characterized by
their micrometre size PM10 to PM2.5. Light pollution:- includes
light trespass, over-illumination and astronomical interference.
Forms of pollution Thermal pollution, is a temperature change in
natural water bodies caused by human influence, such as use of
water as coolant in a power plant. Visual pollution, which can
refer to the presence of overhead power lines, motorway billboards,
scarred landforms (as from strip mining), open storage of trash,
municipal solid waste or space debris. Forms of pollution such as
nuclear power generation and nuclear weapons research, manufacture
and deployment. (See alpha emitters and actinides in the
environment.) Forms of pollution Littering:- the criminal throwing
of inappropriate man-made objects, unremoved, onto public and
private properties. Noise pollution:- which encompasses roadway
noise, aircraft noise, industrial noise as well as high-intensity
sonar. Soil contamination occurs when chemicals are released by
spill or underground leakage. Among the most significant soil
contaminants are hydrocarbons, heavy metals, MTBE,[10] herbicides,
pesticides and chlorinated hydrocarbons. Radioactive contamination,
resulting from 20th century activities in atomic physics, Forms of
pollution Water pollution, by the discharge of wastewater from
commercial and industrial waste (intentionally or through spills)
into surface waters; discharges of untreated domestic sewage, and
chemical contaminants, such as chlorine, from treated sewage;
release of waste and contaminants into surface runoff flowing to
surface waters (including urban runoff and agricultural runoff,
which may contain chemical fertilizers and pesticides); waste
disposal and leaching into groundwater; eutrophication and
littering. A receptor and a Sink The "medium" (e.g. soil) or
organism (e.g. fish) affected by the pollutant or contaminant is
called a receptor, whilst a sink is a chemical medium or species
that retains and interacts with the pollutant. Techniques used in
enviromental chemistry
Common analytical techniques used for quantitative determinations
in environmental chemistry include classical wet chemistry, such as
gravimetric, titrimetric and electrochemical methods. More
sophisticated approaches are used in the determination of trace
metals and organic compounds. Metals are commonly measured by
atomic spectroscopy and mass spectrometry: Atomic Absorption
Spectrophotometry (AA) and Inductively Coupled Plasma Atomic
Emission (ICP-AES) or Inductively Coupled Plasma Mass Spectrometric
(ICP-MS) techniques. Organic compounds are commonly measured also
using mass spectrometric methods, such as Gas chromatography-mass
spectrometry (GC/MS) and Liquid chromatography-mass spectrometry
(LC/MS). Non-MS methods using GCs and LCs having universal or
specific detectors are still staples in the arsenal of available
analytical tools. Other parameters often measured in environmental
chemistry are radiochemicals. These are pollutants which emit
radioactive materials, such as alpha and beta particles, posing
danger to human health and the environment. Particle counters and
Scintillation counters are most commonly used for these
measurements. Bioassays and immunoassays are utilized for toxicity
evaluations of chemical effects on various organisms. The
atmosphere The chemistry of the Strastosphere (the ozone
layer)
The Ozone layer (How the ozone is formed). In the stratospere,
ozone is formed by the action of ultrviolet light on O2 as shown in
the equations (1)- (5). 1.O2 + hv O. + O. 2.O. + O2 + M O3 + M 3.
O3 + hv O2 + O. There is a repeating of(2), (3), (2), (3) etc until
finally the radical terminating steps 5. O. + O. +M O2 + M* Or 7.
O.+ O3 O2 + O2 Reaction leading to Ozone depletion
There two main natural ways in which ozone could be depleted The
formation of O-H. This formation is derived from stratospheric
water vapour 6.O + H2O 2OH 7.OH + O3 HOO + O2 8.These reactions
results in the depletion of 11% stratospheric ozone. Reaction with
NO (nitrous oxide). NO may get into the air by the natural N fixing
mechanism of azobacter and could also be by the Haber process
offertilizer production or lightening. The NO in the atmosphere
catalyses the reaction shown below 9. O3 + O 2O2 10. NO + O3 NO2 +
O2 11. NO2 + O NO + O2 O3 + O 2O2 Since NO remains unchanged in the
final reaction, NO is a catalyst. How man deplets Ozone The CFCs
breaks the ozone-producing chain as shown below: 1. F3CCl + hv F3C.
+ Cl. 2. Cl.+ O3 ClO + O2 3. ClO +O. Cl. + O2 The reactions (2),
(3), (7), (3) etc could be repeated. Tropospheric ozone and
Photochemical smog
Low level ozone (or tropospheric ozone) is an atmospheric
pollutant. It is not emitted directly by car engines or by
industrial operations, but formed by the reaction of sunlight on
air containing hydrocarbons and nitrogen oxides that react to form
ozone directly at the source of the pollution or many kilometers
down wind. Ozone Tropospheric reaction
The chemical reactions involved in tropospheric ozone formation are
a series of complex cycles in which carbon monoxide and VOCs are
oxidised to water vapour and carbon dioxide. The reactions involved
in this process are illustratedwith CO but similar reactions occur
for VOC as well. Oxidation begins with the reaction of CO with the
hydroxyl radical. The hydrogen atom formed by this reacts rapidly
with oxygen to give a peroxy radical HO2 Equation of Ozone reaction
at the lower atmosphere
OH + CO H + CO2 H + O2 HO2 Peroxy radicals then go on to react with
NO to give NO2 which is photolysed to give atomic oxygen and
through reaction with oxygen a molecule of ozone: HO2 + NO OH + NO2
NO2 + h NO + O O + O2 O3 The net effect of these reactions is: CO +
2O2 CO2 + O3 Ozone reactions HOx and NOx is terminated by the
reaction of OH with NO2 to form nitric acid or by the reaction of
peroxy radicals with each other to form peroxides. The chemistry
involving VOCs is much more complex but the same reaction of peroxy
radicals oxidizing NO to NO2 is the critical step leading to ozone
formation Ozone reaction in the lower atmosphere
Ozone reacts directly with some hydrocarbons such as aldehydes and
thus begins their removal from the air, but the products are
themselves key components of smog. Ozone photolysis by UV light
leads to production of the hydroxyl radical OH and this plays a
part in the removal of hydrocarbons from the air, but is also the
first step in the creation of components of smog such as peroxyacyl
nitrates which can be powerful eye irritants. Chemical mechanism of
the bromine explosion OZONE REMOVAL EVENTS IN LOWER ATMOSPHERE
(Bromine explosion)
Chemical mechanism of the bromine explosion. The blue area at the
bottom of diagram above represents the condensed phase (liquid
brine or ice surface). During springtime in the polar regions,
unique photochemistry converts inert halide salt ions (e.g. Br-)
into reactive halogen species (e.g. Br atoms and BrO) that deplete
ozone in the boundary layer to near zero levels. OZONE REMOVAL
EVENTS IN LOWER ATMOSPHERE
Since their discovery in the late 1980s, research on these ozone
depletion events (ODEs) has shown the central role of bromine
photochemistry. Due to the autocatalytic nature of the reaction
mechanism, it has been called bromine explosion. It's still not
fully understood how salts are transported from the ocean and
oxidized to become reactive halogen species in the air. OZONE
REMOVAL EVENTS IN LOWER ATMOSPHERE
Other halogens (chlorine and iodine) are also activated through
mechanisms coupled to bromine chemistry. The main consequence of
halogen activation is chemical destruction of ozone, which removes
the primary precursor of atmospheric oxidation, and generation of
reactive halogen atoms/oxides that become the primary oxidizing
species. OZONE REMOVAL EVENTS IN LOWER ATMOSPHERE
The different reactivity of halogens as compared to OH and ozone
has broad impacts on atmospheric chemistry, including near complete
removal and deposition of mercury, alteration of oxidation fates
for organic gases, and export of bromine into the free troposphere.
Recent changes in the climate of the Arctic and state of the Arctic
sea ice cover are likely to have strong effects on halogen
activation and ODEs. It is present in all modern cities, but it is
more common in cities with sunny, warm, dry climates and a large
number of motor vehicles. Because it travels with the wind, it can
affect sparsely populated areas as wellPhotochemical smog
Photochemical smog was first described in the 1950s. It is the
chemical reaction of sunlight, nitrogen oxides and volatile organic
compounds in the atmosphere, which leaves airborne particles and
ground-level ozone. This noxious mixture of air pollutants can
include the following:
Aldehydes Nitrogen oxides, such as nitrogen dioxide Peroxyacyl
nitrates Tropospheric ozone Volatile organic compounds All of these
chemicals are usually highly reactive and oxidizing. Photochemical
smog is therefore considered to be a problem of modern
industrialization. It is present in all modern cities, but it is
more common in cities with sunny, warm, dry climates and a large
number of motor vehicles. Because it travels with the wind, it can
affect sparsely populated areas as well How smog occurs
Photochemical smog
Photochemical smog was first described in the 1950s. It is the
chemical reaction of sunlight, nitrogen oxides and volatile organic
compounds in the atmosphere, which leaves airborne particles and
ground-level ozone. This noxious mixture of air pollutants can
include the following: Aldehydes Nitrogen oxides, such as nitrogen
dioxide Peroxyacyl nitrates Tropospheric ozone Volatile organic
compounds All of these chemicals are usually highly reactive and
oxidizing. Photochemical smog is therefore considered to be a
problem of modern industrialization. Exercise for students What is
the is the significance of ozone to organisms on earth? Write a
short account of how photochemical smog is a health hazard How is
ozone found at ground level Discus the mechanism of the Bromine
plum and its effects on ground level ozone Outline both the natural
and artificial ways in which ozone is depletedin the Stratosphere
Hydrological cycle Bushfires and hydrological cycle
Fire is a natural disturbance that occurs in most terrestrial
ecosystems. It is also used by man to manage ecosystems worldwide.
As such it can produce a spectrum of effects on soil, water,
riparian biota, and wetland components of ecosystems. Effects of
bush fire on the hydrological cycle
The effects of fire on the hydrological cycle depends on the
severity of the fire. The hydrological cycle represents the
processes and pathways in which water is circulated from land and
water bodies to the atmosphere and back again. While the
hydrological cycle is complex in nature and dynamic in its
functioning, it can be simplified as a system water-storage
components and the solid, liquid or gaseous flows of water within
and between storage points. Effects of bush fire on the
hydrological cycle
Precipitation inputs (rain, snow, sleet and so forth) to a
watershed are affected little by burning. However interceptions,
infiltration, evapo-transpiration, soil moisture storage and the
overland flow of water can be significantly affected by fire. It is
difficult to isolate the impact of fire on one component of the
hydrological cycle since all the components are interrelated.
Effects of bush fire on the hydrological cycle
Fire destroys vegetation decreasing organic matter accumulation
consequently decreasing rain water interception and infiltration
into the soil. The release of carbon dioxide to the atmosphere
increases the green house effect and global warming. High
temperatures may course evaporation of water from the seas, rivers
and streams causing flood in some areas of the earth. Effects of
bush fire on the hydrological cycle
Dry conditions may persist in areas where the vegetation is
destroyed since evapo-transpiration will be limited. When there is
very little vegetation, soil erosion becomes excessive, washing
good soils into rivers and streams silting them. Student exercise
1. Discuss the effect of fire on the following ecosystems Damps and
rivers Grassland Forest Sea 2. Discuss the merits and demerits of
fire on soil The carbon cycle Carbon Cycle - Photosynthesis
Photosynthesis is a complex series of reactions carried out by
algae, phytoplankton, and the leaves in plants, which utilize the
energy from the sun. The simplified version of this chemical
reaction is to utilize carbon dioxide molecules from the air and
water molecules and the energy from the sun to produce a simple
sugar such as glucose and oxygen molecules as a by product. Click
for larger image Carbon Cycle - Photosynthesis
The simple sugars are then converted into other molecules such as
starch, fats, proteins, enzymes, and DNA/RNA i.e. all of the other
molecules in living plants. All of the "matter/stuff" of a plant
ultimately is produced as a result of this photosynthesis reaction.
An important summary statement is that during photosynthesis plants
use carbon dioxide and produce oxygen. Carbon Cycle -
Combustion/Metabolism Reaction:
Combustion occurs when any organic material is reacted (burned) in
the presence of oxygen to give off the products of carbon dioxide
and water and ENERGY. The organic material can be any fossil fuel
such as natural gas (methane), oil, or coal. Other organic
materials that combust are wood, paper, plastics, and cloth.
Organic materials contain at least carbon and hydrogen and may
include oxygen. If other elements are present they also ultimately
combine with oxygen to form a variety of pollutant molecules such
as sulfur oxides and nitrogen oxides. Metabolism occurs in animals
and humans after the ingestion of organic plant or animal foods. In
the cells a series of complex reactions occurs with oxygen to
convert for example glucose sugar into the products of carbon
dioxide and water and ENERGY. This reaction is also carried out by
bacteria in the decomposition/decay of waste materials on land and
in the water. An important summary statement is that during
combustion/metabolism oxygen is used and carbon dioxide is a
product. The whole purpose of both processes is to convert chemical
energy into other forms of energy such as heat. Carbon Cycle -
Sedimentation:
Carbon dioxide is slightly soluble and is absorbed into bodies of
water such as the ocean and lakes. It is not overly soluble as
evidenced by what happens when a can of carbonated soda such as
Coke is opened. Some of the dissolved carbon dioxide remains in the
water, the warmer the water the less carbon dioxide remains in the
water. Some carbon dioxide is used by algae and phytoplankton
through the process of photosynthesis. In other marine ecosystems,
some organisms such as coral and those with shells take up carbon
dioxide from the water and convert it into calcium carbonate. As
the shelled organisms die, bits and pieces of the shells fall to
the bottom of the oceans and accumulate as sediments. The carbonate
sediments are constantly being formed and redissolved in the depths
of the oceans. Over long periods of time, the sediments may be
raised up as dry land or into mountains. This type of sedimentary
rock is called limestone. The carbonates can redissolve releasing
carbon dioxide back to the air or water. Human Impacts on the
Carbon Cycle - Fossil Fuels:
In the natural carbon cycle, there are two main processes which
occur: photosynthesis and metabolism. During photosynthesis, plants
use carbon dioxide and produce oxygen. During metabolism oxygen is
used and carbon dioxide is a product. Humans impact the carbon
cycle during the combustion of any type of fossil fuel, which may
include oil, coal, or natural gas. Fossil Fuels were formed very
long ago from plant or animal remains that were buried, compressed,
and transformed into oil, coal, or natural gas. The carbon is said
to be "fixed" in place and is essentially locked out of the natural
carbon cycle. Humans intervene during by burning the fossil fuels.
During combustion in the presence of air (oxygen), carbon dioxide
and water molecules are released into the atmosphere. The question
becomes as to what happens to this extra carbon dioxide that is
released into the atmosphere. This is the subject of considerable
debate and about it possible effect in enhancing the greenhouse
effect which may than result in global warming. Human Impacts on
the Carbon Cycle - Fossil Fuels:
In the natural carbon cycle, there are two main processes which
occur: photosynthesis and metabolism. During photosynthesis, plants
use carbon dioxide and produce oxygen. During metabolism oxygen is
used and carbon dioxide is a product. Humans impact the carbon
cycle during the combustion of any type of fossil fuel, which may
include oil, coal, or natural gas. Fossil Fuels were formed very
long ago from plant or animal remains that were buried, compressed,
and transformed into oil, coal, or natural gas. The carbon is said
to be "fixed" in place and is essentially locked out of the natural
carbon cycle. Humans intervene during by burning the fossil fuels.
During combustion in the presence of air (oxygen), carbon dioxide
and water molecules are released into the atmosphere. The question
becomes as to what happens to this extra carbon dioxide that is
released into the atmosphere. This is the subject of considerable
debate and about it possible effect in enhancing the greenhouse
effect which may than result in global warming. Humans impact the
carbon cycle during the combustion of any type of fossil fuel,
which may include oil, coal, or natural gas. Fossil Fuels were
formed very long ago from plant or animal remains that were buried,
compressed, and transformed into oil, coal, or natural gas. The
carbon is said to be "fixed" in place and is essentially locked out
of the natural carbon cycle. Humans intervene during by burning the
fossil fuels. During combustion in the presence of air (oxygen),
carbon dioxide and water molecules are released into the
atmosphere. The question becomes as to what happens to this extra
carbon dioxide that is released into the atmosphere. This is the
subject of considerable debate and about it possible effect in
enhancing the greenhouse effect which may than result in global
warming. Nitrogen cycle The main component of the nitrogen cycle
starts with the element nitrogen in the air. Two nitrogen oxides
are found in the air as a result of interactions with oxygen.
Nitrogen will only react with oxygen in the presence of high
temperatures and pressures found near lightning bolts and in
combustion reactions in power plants or internal combustion
engines. Nitric oxide, NO, and nitrogen dioxide, NO2, are formed
under these conditions. Eventually nitrogen dioxide may react with
water in rain to form nitric acid, HNO3. The nitrates thus formed
may be utilized by plants as a nutrient Ammonia is also made
through a synthetic process called the Haber Process. Nitrogen and
hydrogen are reacted under great pressure and temperature in the
presence of a catalyst to make ammonia. Ammonia may be directly
applied to farm fields as fertilizer. Ammonia may be further
processed with oxygen to make nitric acid. The reaction of ammonia
and nitric acid produces ammonium nitrate which may then be used as
a fertilizer. Animal wastes when decomposed also return to the
earth as nitrates. To complete the cycle other bacteria in the soil
carry out a process known as denitrification which converts
nitrates back to nitrogen gas. A side product of this reaction is
the production of a gas known as nitrous oxide, N2O. Nitrous oxide,
also known as "laughing gas" - mild anesthetic, is also a
greenhouse gas which contributes to global warming. Biological
Fixation About 90% of nitrogen fixation is done by bacteria
Biological Fixation About 90% of nitrogen fixation is done by
bacteria. Cyanobacteria convert nitrogen into ammonia and
ammonium.N2 + 3 H2 2 NH3 Ammonia can be used by plants directly.
Ammonia and ammonium may be further reacted in the nitrification
process. NitrificationNitrification occurs by the following
reactions: 2 NH3 + 3 O2 2 NO2 + 2 H+ + 2 H2O 2 NO2- + O2 2
NO3-
Aerobic bacteria use oxygen to convert ammonia and ammonium.
Nitrosomonas bacteria convert nitrogen into nitrite (NO2-) and then
nitrobacter convert nitrite to nitrate (NO3-). Some bacteria exist
in a symbiotic relationship with plants (legumes and some
root-nodule species). Plants utilize the nitrate as a nutrient.
Animals obtain nitrogen by eating plants or plant-eating animals.
Ammonification When plants and animals die, bacteria convert
nitrogen nutrients back into ammonium salts and ammonia. This
conversion process is called ammonification. Anaerobic bacteria can
convert ammonia into nitrogen gas through the process of
denitrification: NO3- + CH2O + H+ N2O + CO2 + 1 H2O Denitrification
returns nitrogen to the atmosphere, completing the cycle The
sulpher cycle Sulfur cycle continued
Sulfur (S), the tenth most abundant element in the universe, is a
brittle, yellow, tasteless, and odorless non-metallic element. It
comprises many vitamins, proteins, and hormones that play critical
roles in both climate and in the health of various ecosystems. The
majority of the Earth's sulfur is stored underground in rocks and
minerals, including as sulfate salts buried deep within ocean
sendiments Sulfur cycle continued
The sulfur cycle contains both atmospheric and terrestrial
processes. Within the terrestrial portion, the cycle begins with
the weathering of rocks, releasing the stored sulfur. The sulfur
then comes into contact with air where it is converted into sulfate
(SO4). The sulfate is taken up by plants and microorganisms and is
converted into organic forms; animals then consume these organic
forms through foods they eat, thereby moving the sulfur through the
food chain. As organisms die and decompose, some of the sulfur is
again released as a sulfate and some enters the tissues of
microorganisms. There are also a variety of natural sources that
emit sulfur directly into the atmosphere, including volcanic
eruptions, the breakdown of organic matter in swamps and tidal
flats, and the evaporation of water. Sulfur cycle continued
Sulfur eventually settles back into the Earth or comes down within
rainfall. A continuous loss of sulfur from terrestrial ecosystem
runoff occurs through drainage into lakes and streams, and
eventually oceans. Sulfur also enters the ocean through fallout
from the Earth's atmosphere. Within the ocean, some sulfur cycles
through marine communities, moving through the food chain. A
portion of this sulfur is emitted back into the atmosphere from sea
spray. The remaining sulfur is lost to the ocean depths, combining
with iron to form ferrous sulfide which is responsible for the
black color of most marine sediments. Sulfur cycle continued
One-third of all sulfur that reaches the atmosphere including 90%
of sulfur dioxide stems from human activities. Emissions from these
activities, along with nitrogen emissions, react with other
chemicals in the atmosphere to produce tiny particles of sulfate
salts which fall as acid rain, causing a variety of damage to both
the natural environment as well as to man-made environments, such
as the chemical weathering of buildings. However, as particles and
tiny airborne droplets, sulfur also acts as a regulator of global
climate. Sulfur dioxide and sulfate aerosols absorb ultraviolet
radiation, creating cloud cover that cools cities and may offset
global warming caused by the greenhouse effect. The actual amount
of this offset is a question that researchers are attempting to
answer. The Phosphorus cycle Phosphorus cycle continued
Phosphorus is an essential nutrient for plants and animals in the
form of ions PO43- and HPO42-. It is a part of DNA-molecules, of
molecules that store energy (ATP and ADP) and of fats of cell
membranes. Phosphorus is also a building block of certain parts of
the human and animal body, such as the bones and teeth. Phosphorus
can be found on earth in water, soil and sediments. Unlike the
compounds of other matter cycles phosphorus cannot be found in air
in the gaseous state. This is because phosphorus is usually liquid
at normal temperatures and pressures. It is mainly cycling through
water, soil and sediments. In the atmosphere phosphorus can mainly
be found as very small dust particles. Phosphorus cycle
continued
Phosphorus moves slowly from deposits on land and in sediments, to
living organisms, and than much more slowly back into the soil and
water sediment. The phosphorus cycle is the slowest one of the
matter cycles that are described here. Phosphorus is most commonly
found in rock formations and ocean sediments as phosphate salts.
Phosphate salts that are released from rocks through weathering
usually dissolve in soil water and will be absorbed by plants.
Because the quantities of phosphorus in soil are generally small,
it is often the limiting factor for plant growth. That is why
humans often apply phosphate fertilizers on farmland. Phosphates
are also limiting factors for plant-growth in marine ecosystems,
because they are not very water-soluble. Animals absorb phosphates
by eating plants or plant-eating animals. Phosphorus cycle
continued
Phosphorus cycles through plants and animals much faster than it
does through rocks and sediments. When animals and plants die,
phosphates will return to the soils or oceans again during decay.
After that, phosphorus will end up in sediments or rock formations
again, remaining there for millions of years. Eventually,
phosphorus is released again through weathering and the cycle
starts over. Soil Chemistry Soil chemistry is the study of the
chemical characteristics of soil. Soil chemistry is affected by
mineral composition, organic matter and environmental factors. Soil
Chemistry A knowledge of environmental soil chemistry is paramount
to predicting the fate, mobility and potential toxicity of
contaminants in the environment. The vast majority of environmental
contaminants are initially released to the soil. Once a chemical is
exposed to the soil environment a myriad of chemical reactions can
occur that may increase or decrease contaminant toxicity. These
reactions include absorption/desorption, precipitation,
polymerization, dissolution, complexation and oxidation/reduction.
These reactions are often disregarded by scientists and engineers
involved with environmental remediation. Understanding these
processes enable us to better predict the fate and toxicity of
contaminants and provide the knowledge to develop scientifically
correct, and cost-effective remediation strategies. Soil profile
SOIL Soil is a natural body consisting of layers (soil horizons) of
mineral constituents of variable thicknesses, which differ from the
parent materials in their morphological, physical, chemical, and
mineralogical characteristics.[1] It is composed of particles of
broken rock that have been altered by chemical and environmental
processes that include weathering and erosion. Soil differs from
its parent rock due to interactions between the lithosphere,
hydrosphere, atmosphere, and the biosphere. It supports a complex
ecosystem, which supports the plants on the surface and creates new
soil by breaking down rocks and sand. This microscopic ecosystem
has co-evolved with the plants to collect and store water and
nutrients in a form usable by plants. Soil Soil particles pack
loosely, forming a soil structure filled with pore spaces. These
pores contain soil solution (liquid) and air (gas). Accordingly,
soils are often treated as a three state-system Most soils have a
density between 1 and 2g/cm3. Soil is also known as earth: it is
the substance from which our planet takes its name. Soil forming
factors Soil formation, or pedogenesis, is the combined effect of
physical, chemical, biological, and anthropogenic processes on soil
parent material. Soil genesis involves processes that develop
layers or horizons in the soil profile. These processes involve
additions, losses, transformations and translocations of material
that compose the soil. Minerals derived from weathered rocks
undergo changes that cause the formation of secondary minerals and
other compounds that are variably soluble in water, these
constituents are moved (translocated) from one area of the soil to
other areas by water and animal activity. The alteration and
movement of materials within soil causes the formation of
distinctive soil horizons Soil forming factors continued
The weathering of bedrock produces the parent material from which
soils form. An example of soil development from bare rock occurs on
recent lava flows in warm regions under heavy and very frequent
rainfall. In such climates, plants become established very quickly
on basaltic lava, even though there is very little organic
material. The plants are supported by the porous rock as it is
filled with nutrient-bearing water which carries, for example,
dissolved minerals and guano. The developing plant roots,
themselves or associated with mycorrhizal fungi, gradually break up
the porous lava and organic matter soon accumulates. Soil forming
factors continued
Parent material Climate Biological Time Soil Characteristics (Soil
textural triangle) Soil Characteristics (Texture)
Soil texture refers to sand, silt and clay composition. Soil
texture affects soil behavior, including the retention capacity for
nutrients and water Sand and silt are the products of physical
weathering, while clay is the product of chemical weathering. Clay
content has retention capacity for nutrients and water. Clay soils
resist wind and water erosion better than silty and sandy soils,
because the particles are more tightly joined to each other. In
medium-textured soils, clay is often translocated downward through
the soil profile and accumulates in the subsoil. Soil structure
Soil structure is the arrangement of soil particles into
aggregates. These may have various shapes, sizes and degrees of
development or expression. Soil structure affects aeration, water
movement, resistance to erosion and plant root growth. Structure
often gives clues to texture, organic matter content, biological
activity, past soil evolution, human use, and chemical and
mineralogical conditions under which the soil formed. Soil colour
Soil color is often the first impression one has when viewing soil.
Striking colors and contrasting patterns are especially memorable.
Rivers carry sediment eroded from extensively in Oklahoma The
Yellow River in China carries yellow sediment from eroding loessal
soils. Mollisols in the Great Plains are darkened and enriched by
organic matter. Podsols in boreal forests have highly contrasting
layers due to acidity and leaching. Soil color is primarily
influenced by soil mineralogy. Many soil colors are due to the
extensive and various iron minerals. Soil Colour The development
and distribution of color in a soil profile result from chemical
and biological weathering, especially redox reactions. As the
primary minerals in soil parent material weather, the elements
combine into new and colorful compounds. Iron forms secondary
minerals with a yellow or red color, organic matter decomposes into
black and brown compounds, and manganese, sulfur and nitrogen can
form black mineral deposits. These pigments produce various color
patterns due to effects by the environment during soil formation.
Aerobic conditions produce uniform or gradual color changes, while
reducing environments result in disrupted color flow with complex,
mottled patterns and points of color concentration Soil Pollution
The soil has become increasingly subjected to various chemical
stresses, not only because of our need for more food and fiber, but
also because of ever-increasing industrialization. Various
anthropogenic substances, either organic or inorganic in nature,
upon entering the soil, may not only adversely affect its
productivity potential, but may also compromise the quality of the
food chain and groundwater. This situation may require risk
assessment and evaluation of remedial techniques in order to
restore the quality of the soil so that safe food products and
clean groundwater and air may be obtained once again. Soil
Contamination A wide variety of naturally occurring toxic and
recalcitrant organic compounds exist on earth. In addition, various
man-made materials have been dumped on land adjacent to industrial
plants in landfills and on unregulated dumping grounds. As a
result, the soils at many of these sites contain a complex mixture
of contaminants, such as petroleum products, organic solvents,
metals, acids, bases, brine, and radionuclides. Soil could be
contaminated by domestic and industrial wastes discharges. Micro
organisms that may be pathogenic can be put into soil. Heavy metals
such Mercury, Copper, Zinc Chromium, Cadmium can be in both
domestic and industrial wastes dumpedinto land fills. Agricultural
contaminants such as herbicides pesticides can contaminate soil,
absorbed into clay and organic matter colloids forming complex
organic compounds and clay heavy metal complexes Petroleum products
or oil could contaminate soil Even too much organic matter in soil
could be a contaminant supplying too Nsoil leaching nitrates into
ground water. Plant growth could be too luxerious. How soil
contaminants be reduced
Over a very long period of time, natural degradation activities may
eventually destroy most of these organic contaminants. However,
affordable technologies are needed to speed up the natural
remediation processes. Furthermore, natural degradation activities
would not solve the problems of metal contaminants. Therefore, risk
management through remediation is essential to reducing health
risks and restoring natural balances. The treatments currently used
to remove or destroy contaminants include physical, chemical and
biological technologies. Water Pollution Water pollution is the
contamination of water bodies (e.g. lakes, rivers, oceans and
groundwat). Water pollution occurs when pollutants are discharged
directly or indirectly into water bodies without adequate treatment
to remove harmful compounds. Groundwater pollution
Interactions between groundwater and surface water are complex.
Consequently, groundwater pollution, sometimes referred to as
groundwater contamination, is not as easily classified as surface
water pollution. By its very nature, groundwater aquifers are
susceptible to contamination from sources that may not directly
affect surface water bodies, and the distinction of point vs.
non-point source may be irrelevant. A spill or ongoing releases of
chemical or radionuclide contaminants into soil (located away from
a surface water body) may not create point source or non-point
source pollution, but can contaminate the aquifer below, defined as
a toxin plume. The movement of the plume, called a plume front, may
be analyzed through a hydrological transport model or groundwater
model. Analysis of groundwater contamination may focus on the soil
characteristics and site geology, hydrogeology, hydrology, and the
nature of the contaminants. Causes The specific contaminants
leading to pollution in water include a wide spectrum of chemicals,
pathogens, and physical or sensory changes such as elevated
temperature and discoloration. While many of the chemicals and
substances that are regulated may be naturally occurring (calcium,
sodium, iron, manganese, etc.) the concentration is often the key
in determining what is a natural component of water, and what is a
contaminant. High concentrations of naturally-occurring substances
can have negative impacts on aquatic flora and fauna. Causes
Oxygen-depleting substances may be natural materials, such as plant
matter (e.g. leaves and grass) as well as man-made chemicals. Other
natural and anthropogenic substances may cause turbidity
(cloudiness) which blocks light and disrupts plant growth, and
clogs the gills of some fish species. Causes Many of the chemical
substances are toxic. Pathogens can produce waterborne diseases in
either human or animal hosts. Alteration of water's physical
chemistry includes acidity (change in pH), electrical conductivity,
temperature, and eutrophication. Eutrophication is an increase in
the concentration of chemical nutrients in an ecosystem to an
extent that increases in the primary productivity of the ecosystem.
Depending on the degree of eutrophication, subsequent negative
environmental effects such as anoxia (oxygen depletion) and severe
reductions in water quality may occur, affecting fish and other
animal populations. Pathogens Coliform bacteria are a commonly used
bacterial indicator of water pollution, although not an actual
cause of disease. Other microorganisms sometimes found in surface
waters which have caused human health problems include:
Burkholderia pseudomallei Cryptosporidium parvum Giardia lamblia
Salmonella Novovirus and other viruses Parasitic worms (helminths)
Pathogens High levels of pathogens may result from inadequately
treated sewage discharges. This can be caused by a sewage plant
designed with less than secondary treatment (more typical in
less-developed countries). In developed countries, older cities
with aging infrastructure may have leaky sewage collection systems
(pipes, pumps, valves), which can cause sanitary sewer overflows.
Some cities also have combined sewers, which may discharge
untreated sewage during rain storms. Pathogen discharges may also
be caused by poorly managed livestock operations. Effects The
effects of water pollution are increasingly drawing the environment
and human beings as well to feel the pinch of polluted water. Water
pollution affects our, rivers, lakes, oceans and drinking water.
With the increase in population and industrial development, demand
for water has increased. Water is getting polluted when chemicals,
harmful contaminants are detected Human beings have the most
crucial impact on our water resources. Moreover the need for water
is far more in the society today than the quantity of water
available. Effects Some water pollution effects show up immediately
where as others dont show up for months or years. The water
pollution has damaged the food chain and is very important for the
food preparation of plants through photosynthesis When Filth is
thrown in water the toxins travel from the water and when the
animals drink that water they get contaminated and when humans tend
to eat the meat of the animals is infected by toxins it causes
further damage to the humans Effects Infectious diseases such as
cholera and typhoid can be contracted from drinking contaminated
water. Our whole body system can have a lot of harm if polluted
water is consumed regularly. Other health problems associated with
polluted water are poor blood pressure, vomiting, skin lesions and
damage to the nervous system. In fact the evil effects of water
pollution are said to be the leading cause of death of humans
across the globe. Pollutants in the water alter the over all
chemistry of water, causing a lot of changes in temperature. These
factors overall have had an adverse effect on marine life and
pollutes and kills marine life. Marine life gets affected by the
ecological balance in bodies of water, especially the rivers and
the lakes. Water pollution effects have a huge impact on the health
of an individual and the environment as a whole. Effects The
balance between the nature and the humans can be protected and
should be maintained .But t it will take efforts on all fronts by
each and every individual from the society to prevent and eliminate
water pollution locally and globally. Contaminants may include
organic and inorganic substances.
Organic water pollutants include: Detergents Disinfection
by-products found in chemically disinfected drinking water, such as
chloroform Food processing waste, which can include
oxygen-demanding substances, fats and grease Insecticides and
herbicides, a huge range of organohalides and other chemical
compounds Petroleum hydrocarbons, including fuels (gasoline, diesel
fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel
combustion byproducts, from stormwater runoff Contaminants may
include organic and inorganic substances.
Tree and bush debris from logging operations Volatile organic
compounds (VOCs), such as industrial solvents, from improper
storage. Chlorinated solvents, which are dense non-aqueous phase
liquids (DNAPLs), may fall to the bottom of reservoirs, since they
don't mix well with water and are denser. Polychlorinated biphenyl
(PCBs) Trichloroethylene Perchlorate Various chemical compounds
found in personal hygiene and cosmetic products Inorganic water
pollutants include:
Acidity caused by industrial discharges (especially sulfur dioxide
from power plants) Ammonia from food processing waste Chemical
waste as industrial by-products Fertilizers containing
nutrients--nitrates and phosphates--which are found in stormwater
runoff from agriculture, as well as commercial and residential
use[16] Heavy metals from motor vehicles (via urban stormwater
runoff) and acid mine drainage Silt (sediment) in runoff from
construction sites, logging, slash and burn practices or land
clearing sites Macroscopic pollution
large visible items polluting the watermay be termed "floatables"
in an urban stormwater context, or marine debris when found on the
open seas, and can include such items as: Trash or garbage (e.g.
paper, plastic, or food waste) discarded by people on the ground,
along with accidental or intentional dumping of rubbish, that are
washed by rainfall into storm drains and eventually discharged into
surface waters Nurdles, small ubiquitous waterborne plastic pellets
Shipwrecks, large derelict ships Thermal pollution Thermal
pollution is the rise or fall in the temperature of a natural body
of water caused by human influence. Thermal pollution, unlike
chemical pollution, results in a change in the physical properties
of water. A common cause of thermal pollution is the use of water
as a coolant by power plants and industrial manufacturers. Elevated
water temperatures decreases oxygen levels (which can kill fish)
and affects ecosystem composition, such as invasion by new
thermophilic species. Urban runoff may also elevate temperature in
surface waters. Thermal pollution can also be caused by the release
of very cold water from the base of reservoirs into warmer rivers.
Transport and chemical reactions of water pollutants
Most water pollutants are eventually carried by rivers into the
oceans. In some areas of the world the influence can be traced
hundred miles from the mouth by studies using hydrology transport
models. Advanced computer models have been used in many locations
worldwide to examine the fate of pollutants in aquatic systems.
Indicator filter feeding species such as copepods have also been
used to study pollutant fates. Oxygen depletion, caused by
chemicals using up oxygen and by algae blooms, caused by excess
nutrients from algal cell death and decomposition. Fish and
shellfish kills have been reported, because toxins climb the food
chain after small fish consume copepods, then large fish eat
smaller fish, etc. Each successive step up the food chain causes a
stepwise concentration of pollutants such as heavy metals (e.g.
mercury) and persistent organic pollutants such as DDT. This is
known as biomagnification, which is occasionally used
interchangeably with bioaccumulation. Water pollution Large gyres
(vortexes) in the oceans trap floating plastic debris. The North
Pacific Gyre for example has collected the so-called "Great Pacific
Garbage Patch" that is now estimated at 100 times the size of
Texas. Many of these long-lasting pieces wind up in the stomachs of
marine birds and animals. This results in obstruction of digestive
pathways which leads to reduced appetite or even starvation. Water
pollution Many chemicals undergo reactive decay chemically change
especially over long periods of time in groundwater reservoirs. A
noteworthy class of such chemicals is the chlorinated hydrocarbons
such as trichloroethylene (used in industrial metal degreasing and
electronics manufacturing) and tetrachloroethylene used in the dry
cleaning industry (note latest advances in liquid carbon dioxide in
dry cleaning that avoids all use of chemicals). Both of these
chemicals, which are carcinogens themselves, undergo partial
decomposition reactions, leading to new hazardous chemicals
(including dichloroethylene and vinyl chloride). Water pollution
Groundwater pollution is much more difficult to abate than surface
pollution because groundwater can move great distances through
unseen aquifers. Non-porous aquifers such as clays partially purify
water of bacteria by simple filtration (adsorption and absorption),
dilution, and, in some cases, chemical reactions and biological
activity: however, in some cases, the pollutants merely transform
to soil contaminants. Groundwater that moves through cracks and
caverns is not filtered and can be transported as easily as surface
water. In fact, this can be aggravated by the human tendency to use
natural sinkholes as dumps in areas of Karst topography. There are
a variety of secondary effects stemming not from the original
pollutant, but a derivative condition. An example is silt-bearing
surface runoff, which can inhibit the penetration of sunlight
through the water column, hampering photosynthesis in aquatic
plants. Pollution sources Point pollution Point source Point source
water pollution refers to contaminants that enter a waterway from a
single, identifiable source, such as a pipe or ditch. Examples of
sources in this category include discharges from a sewage treatment
plant, a factory, or a city storm drain. Non-point sources Nonpoint
Nonpoint source pollution refers to diffuse contamination that does
not originate from a single discrete source. NPS pollution is often
the cumulative effect of small amounts of contaminants gathered
from a large area. A common example is the leaching out of nitrogen
compounds from fertilized agricultural lands. Nutrient runoff in
stormwater from "sheet flow" over an agricultural field or a forest
are also cited as examples of NPS pollution. Contaminated storm
water washed off of parking lots, roads and highways, called urban
runoff, is sometimes included under the category of NPS pollution.
However, this runoff is typically channeled into storm drain
systems and discharged through pipes to local surface waters, and
is a point source. Sources of pollution Domestic garbage Sources of
pollution Sewage Sources of water pollution
Agriculture Point source pollution
Large farms eg poultry and lifestock Sources of pollution
Industries SOURCES OF POLLUTION Abandoned mine Analyses of water
pollutants
Sampling. Chemical measures of water quality
Water quality is the physical, chemical and biological
characteristics of water. It is most frequently used by reference
to a set of standards against which compliance can be
assessed....include dissolved oxygen (DO) Oxygen saturation or
Dissolved oxygen is a relative measure of the amount of oxygen that
is dissolved or carried in a given medium. It can be measured with
a dissolved oxygen probe such as an oxygen sensor or an optode in
liquid media, usually water.... Chemical oxygen demand
In environmental chemistry, the chemical oxygen demand test is
commonly used to indirectly measure the amount of organic compounds
in water. Most applications of COD determine the amount of organic
compound pollutants found in surface water , making COD a useful
measure of water quality.... 2Cr2O C + 6H 4Cr3+ + 3CO2 + 8H2O The
equation shows how COD could be measured. Biochemical oxygen
demand
Biochemical Oxygen Demand or Biological Oxygen Demand (BOD) is a
chemical procedure for determining how fast biological organisms
use up oxygen in a body of water. Thus BOD gives an idea of the
extent of organic waste present in water BOD is the milligrams, of
dissolved oxygen needed to break down the organic matter present in
one litre of water for five days at 20 degrees Celsius . 0-3ppm (1
ppm = 1 mg/L) pure water A BOD of 5ppm or slightly more would
indicate that the water is somewhat contaminated. Water in the
vicinity of factories is found to have a BOD as high as 1000ppm.
This means that the water is highly contaminated. Total dissolved
solids
Total Dissolved Solids is an expression for the combined content of
all inorganic and organic compound substances contained in a liquid
which are present in a molecular, ionized or micro-granular
suspended form.... pH pH is a measure of the Acid or Base of a
solution. It is defined as the negative logarithm of the Activity
of dissolved hydrogen ions . Hydrogen ion activity coefficients
cannot be measured experimentally, so they are based on theoretical
calculations.... Phosphorus Phosphorus is the chemical element that
has the symbol P and atomic number 15.. A Valency nonmetal of the
nitrogen group, phosphorus is commonly found in inorganic phosphate
minerals.... Heavy metal A heavy metal is a member of an
ill-defined subset of elements that exhibit metallic properties,
which would mainly include the transition metals, some metalloids,
lanthanides, and actinides.... Examples Copper (Cu), Zinc (Zn),
Cadmium (Cd), Lead (Pb), Mercury (Hg) Heavy metals Copper is a
chemical element with the symbol Cu and atomic number 29.It is a
ductile metal with very high thermal and electrical
conductivity....Zinc is a metallic chemical element with the symbol
Zn and atomic number 30. It is a first-row transition metal of the
group 12 element of the periodic table....Cadmium is a chemical
element with the symbol Cd and atomic number 48. A relatively
abundant , soft, bluish-white, transition metal, cadmium is known
to cause cancer and occurs with zinc ores.... Heavy metals Lead is
a main-group Chemical element with symbol Pb and atomic number 82.
Lead is a soft, malleable poor metal, also considered to be one of
the heavy metal Mercury , also called quicksilver or hydrargyrum ,
is a chemical element with the symbol Hg and atomic number 80. A
heavy, silvery d-block metal, mercury is one of six elements that
are liquid at or near room temperature and pressure.... PESTICIDE
POLLUTION. Pesticides pollution can be both in soil or water which
may finally leached or wash into the water bodies of the
environment Definition of a pesticide
A pesticide is a substance or mixture of substances used to kill a
pest A pesticide may be a chemical substance, biological agent
(such as a virus or bacteria), antimicrobial, disinfectant or
device used against any pest. Pests include insects, plant
pathogens, weeds, mollusks, birds, mammals, fish, nematodes
(roundworms) and microbes that compete with humans for food,
destroy property, spread or are a vector for disease or cause a
nuisance. Although there are benefits to the use of pesticides,
there are also drawbacks, such as potential toxicity to humans and
other animals. Types of pesticides Algicides or Algaecides for the
control of algae
Avicides for the control of birds Bactericides for the control of
bacteria Fungicides for the control of fungi and oomycetes
Herbicides for the control of weeds Insecticides for the control of
insects - these can be Ovicides (substances that kill eggs),
Larvicides (substances that kill larvae) or Adulticides (substances
that kill adult insects) TYPES PESTICIDES Miticides or Acaricides
for the control of mites
Molluscicides for the control of slugs and snails Nematicides for
the control of nematodes Rodenticides for the control of rodents
Virucides for the control of viruses (e.g. H5N1) Pesticides can
also be classed as synthetic pesticides or biological pesticides
(biopesticides), although the distinction can sometimes blur. Types
of pesticides Broad-spectrum pesticides are those that kill an
array of species, while narrow-spectrum, or selective pesticides
only kill a small group of species. A systemic pesticide moves
inside a plant following absorption by the plant. With insecticides
and most fungicides, this movement is usually upward (through the
xylem) and outward. Increased efficiency may be a result. Systemic
insecticides which poison pollen and nectar in the flowers may kill
needed pollinators such as bees. Most pesticides work by poisoning
pests. Water purification Water purification is the process of
removing contaminants and other harmful microorganisms from a raw
water source. The goal is to produce water for a specific purpose
with a treatment profile designed to limit the inclusion of
specific materials; most water is purified for human consumption
(drinking water). Water purification may also be designed for a
variety of other purposes, including to meet the requirements of
medical, pharmacology, chemical and industrial applications.
Methods include, but are not limited to: ultraviolet light,
filtration, water softening, reverse osmosis, ultrafiltration,
deionization and powdered activated carbon treatment. Water
purification Water purification may remove: particulate sand;
suspended particles of organic material; parasites, Giardia;
Cryptosporidium; bacteria; algae; viruses; fungi; minerals such as
calcium , silica, and magnesium; and toxic metals like lead,
copper, and chromium. Some purification may be elective in the
purification process, including smell (hydrogen sulfide
remediation), taste (mineral extraction), and appearance (iron
incapsulation). Water purification Read on the various types of
water purification in your handouts RADIOACTIVITY AND ENVIRONMENTAL
POLLUTION
The most common types of radiation are called alpha,() beta,() and
gamma() radiation, but there are several other varieties of
radioactive decay. Radioactive decay rates are normally stated in
terms of their half-lives, and the half-life of a given nuclear
species is related to its radiation risk. The different types of
radioactivity lead to different decay paths which transmute the
nuclei into other chemical elements. Examining the amounts of the
decay products makes possible radioactive dating Nuclear structure
Nuclear structure An atom consists of an extremely small,
positively charged nucleus surrounded by a cloud of negatively
charged electrons. Although typically the nucleus is less than one
ten-thousandth the size of the atom, the nucleus contains more than
99.9% of the mass of the atom! Nuclei consist of positively charged
protons and electrically neutral neutrons held together by the
so-called strong or nuclear force. This force is much stronger than
the familiar electrostatic force that binds the electrons to the
nucleus, but its range is limited to distances on the order of a
few x10-15 meters. Nuclear structure The number of protons in the
nucleus, Z, is called the atomic number. This determines what
chemical element the atom is. The number of neutrons in the nucleus
is denoted by N. The atomic mass of the nucleus, A, is equal to Z +
N. A given element can have many different isotopes, which differ
from one another by the number of neutrons contained in the nuclei.
In a neutral atom, the number of electrons orbiting the nucleus
equals the number of protons in the nucleus. Since the electric
charges of the proton and the electron are +1 and -1 respectively
(in units of the proton charge), the net charge of the atom is
zero. At present, there are 112 known elements which range from the
lightest, hydrogen, to the recently discovered and yet to-be-named
element 112. All of the elements heavier than uranium are man made.
Among the elements are approximately 270 stable isotopes, and more
than 2000 unstable isotopes. decay The emission of an a particle,
or 4He nucleus, is a process called a decay. Since a particles
contain protons and neutrons, they must come from the nucleus of an
atom. The nucleus that results from a decay will have a mass and
charge different from those of the original nucleus. A change in
nuclear charge means that the element has been changed into a
different element. Only through such radioactive decays or nuclear
reactions can transmutation, the age-old dream of the alchemists,
actually occur. The mass number, A, of an alpha particle is four,
so the mass number, A, of the decaying nucleus is reduced by 2. The
atomic number, Z, of 4He is two, and therefore the atomic number of
the nucleus, the number of protons, is reduced by two. This can be
written as an equation analogous to a chemical reaction. AYZ
A-4YZ-2 + 4He2 Decay Beta particles are negatively charged
electrons emitted by the nucleus. Since the mass of an electron is
a tiny fraction of an atomic mass unit, the mass of a nucleus that
undergoes b decay is changed by only a tiny amount. The mass number
is unchanged. The nucleus contains no electrons. Rather, b decay
occurs when a neutron is changed into a proton within the nucleus.
An unseen neutrino, , accompanies each b decay. The number of
protons, and thus the atomic number, is increased by one. For
example, the isotope 14C is unstable and emits a particle, becoming
the stable isotope 14NIn a stable nucleus, the neutron does not
decay. A free neutron, or one bound in a nucleus that has an excess
of neutrons, can decay by emitting a b particle. Sharing the energy
with the b particle is a neutrino. The neutrino has little or no
mass and is uncharged, but, like the photon, it carries momentum
and energy. The source of the energy released in b decay is
explained by the fact that the mass of the parent isotope is larger
than the sum of the masses of the decay products. Mass is converted
into energy just as Einstein predicted. 14C6 + 0-1 14N7 Decay Gamma
rays are a type of electromagnetic radiation that results from a
redistribution of electric charge within a nucleus. A g ray is a
high energy photon. The only thing which distinguishes a g ray from
the visible photons emitted by a light bulb is its wavelength; the
g ray's wavelength is much shorter. For complex nuclei there are
many different possible ways in which the neutrons and protons can
be arranged within the nucleus. Gamma rays can be emitted when a
nucleus undergoes a transition from one such configuration to
another. For example, this can occur when the shape of the nucleus
undergoes a change. Neither the mass number nor the atomic number
is changed when a nucleus emits a g ray in the reaction 152Dy*
----> 152Dy + Half-life The time required for half of the atoms
in any given quantity of a radioactive isotope to decay is the
half-life of that isotope. Each particular isotope has its own
half-life. For example, the half-life of 238U is 4.5 billion years.
That is, in 4.5 billion years, half of the 238U on Earth will have
decayed into other elements. In another 4.5 billion years, half of
the remaining 238U will have decayed. One fourth of the original
material will remain on Earth after 9 billion years. The half-life
of 14C is 5730 years, thus it is useful for dating archaeological
material. Nuclear half-lives range from tiny fractions of a second
to many, many times the age of the universe. Cosmic Rays High
energy electrons, protons, and complex nuclei can be produced in a
number of astronomical environments. Such particles travel
throughout the universe and are called cosmic rays. Some of these
particles reach our Earth. As these objects hit our atmosphere,
other particles called pions and muons are produced. These
particles then slow down or crash into other atoms in the
atmosphere. Since the atmosphere slows down these particles, the
higher we travel, the more cosmic radiation we see. When you visit
the mountains or take an airplane ride, you will encounter more
cosmic radiation than if you stayed at sea level. Cosmic Rays Most
cosmic radiation is very energetic. It can easily pass through an
inch of lead. Since cosmic radiation can cause genetic changes,
some scientists believe that this radiation has been important in
driving the evolution of life on our planet. While cosmic radiation
can cause some damage to individuals, it also has played an
important role in creating humans. Our atmosphere is naturally
shielding us from harmful effects. However, if we were to leave the
earth and travel to some planet, we could be subjected to very high
levels of radiation. Future space travelers will have to find some
way to minimize exposure to cosmic rays. RANDON Radon (reidon) is
the chemical element that has the symbol Rn and atomic number 86.
Radon is a colorless, odorless, naturally occurring, radioactive
noble gas that is formed from the decay of radium. It is one of the
heaviest substances that are gases under normal conditions and is
considered to be a health hazard. The most stable isotope, 222Rn,
has a half-life of 3.8 days and is used in radiotherapy. While
having been less studied by chemists due to its radioactivity,
there are a few known compounds of this generally unreactive
element. Randon Radon is a significant contaminant that affects
indoor air quality worldwide. Radon gas from natural sources can
accumulate in buildings and reportedly causes 21,000 lung cancer
deaths per year in the United States alone. Radon is the second
most frequent cause of lung cancer, after cigarette smoking, and
radon-induced lung cancer is thought to be the 6th leading cause of
cancer death overall. Radon can be found in some spring waters and
hot springs. Natural occurring radon
The naturally occurring 226Ra is a product of the decay chain of
238U. This decay series (with half-lives) is 238U (4.5 x 109 yr)
234Th (24.1 days) 234Pa (1.18 min) 234U (250,000 yr) 230Th (75,000
yr) 226Ra (1,600 yr) 222Rn (3.82 days) 218Po (3.1 min) 218At (1.5
s) 218Rn (35 ms) 214Pb (26.8 min) 214Bi (19.7 min) 214Po (164 s)
210Pb (22.3 yr) 210Bi (5.01 days) 210Po (138 days) 206Pb (stable)
Radon There are three other isotopes that have a half life of over
an hour: 211Rn, 210Rn and 224Rn. The 220Rn isotope is a natural
decay product of the most stable thorium isotope (232Th), named
thoron. It has a half-life of 55.6 seconds and also emits alpha
radiation. Similarly, 219Rn is derived from the most stable isotope
of actinium (227Ac) named actinon and is an alpha emitter with a
half-life of 3.96 seconds Radon Natural radon concentrations in
Earth's atmosphere are so low that radon-rich water in contact with
the atmosphere will continually lose radon by volatilization.
Hence, ground water has a higher concentration of 222Rn than
surface water, because the radon is continuously produced by
radioactive decay of 226Ra present in rocks. Likewise, the
saturated zone of a soil frequently has a higher radon content than
the unsaturated zone because of diffusional losses to the
atmosphere. Health effects Radon is a health hazard as exposure can
cause lung cancer it is, in fact, the second major cause of lung
cancer after smoking. Radon as a terrestrial source of background
radiation is of particular concern because, although on average it
is very rare, this intensely radioactive element can be found in
high concentrations in many areas of the world, where it represents
a significant health hazard. Radon-222 has been classified by
International Agency for Research on Cancer as being carcinogenic
to humans. Radon for commercial use
Radon commercialization is regulated, but it is available in small
quantities, at a price of almost $6,000 per mililitre. Because it
is also radioactive and is a relatively unreactive chemical
element, radon has few uses and is seldom used in academic
research. Radon is found in some petroleum. Because radon has a
similar pressure and temperature curve as propane, and oil
refineries separate petrochemicals based on their boiling points,
the piping carrying freshly separated propane in oil refineries can
become partially radioactive due to radon decay particles. Residues
from the oil and gas industry often contain radium and its
daughters. The sulfate scale from an oil well can be radium rich,
while the water, oil, and gas from a well often contains radon. The
radon decays to form solid radioisotopes which form coatings on the
inside of pipework. An oil processing plant, the area of the plant
where propane is processed, is often one of the more contaminated
areas of the plant as radon has a similar boiling point as propane.
Radon Radon, along with the noble gases krypton and xenon, is also
produced during the operation of nuclear power plants. A small
fraction of it leaks out of the fuel, through the cladding, and
into the cooling water, from which it is scavenged. It is then
routed to a holding tank where it remains for a large number of
half-lives. It is finally purged to the open air through a tall
stack, which is carefully monitored for radiation level. Radon
210Pb is formed from the decay of 222Rn. Here is a typical
deposition rate of 210Pb as observed in Japan as a function of
time. Radon collects over samples of radium-226 at a rate of about
cm3/day per gram of radium. The radon (222Rn) released into the air
decays to 210Pb and other radioisotopes, the levels of 210Pb can be
measured. The rate of deposition of this radioisotope is dependent
on the weather. In the early part of the 20th century in the USA,
gold which was contaminated with lead-210 entered the jewelry
industry. This was from gold seeds which had held radon-222 that
had been melted down after the radon had decayed. The daughters of
the radon are still radioactive today. Radon in moon In 1971,
Apollo 15 passed 110kilometres (68mi) above the Aristarchus plateau
on the Moon, and detected a significant rise in alpha particles
thought to be caused by the decay of radon-222. The presence of
radon-222 (222Rn) has been inferred later from data obtained from
the Lunar Prospector alpha particle spectrometer. Radon and housing
Depending on how houses are built and ventilated, radon may
accumulate in basements and dwellings. The highest average radon
concentrations in the United States are found in Iowa and in the
Appalachian Mountain areas in southeastern Pennsylvania Some of the
highest readings ever have been recorded in the Irish town of
Mallow, County Cork, prompting local fears regarding lung cancer.
Iowa has the highest average radon concentrations in the nation due
to significant glaciation that ground the granitic rocks from the
Canadian Shield and deposited it as soils making up the rich Iowa
farmland. Many cities within the state, such as Iowa City, have
passed requirements for radon-resistant construction in new homes.
A study made in December 2004 noted that the counties surrounding
Three Mile Island have the highest radon concentrations in the
United States and that this may be the cause of the increased lung
cancer noted in the region. Level of Radon that require
environmental action
The European Union recommends that action should be taken starting
from concentrations of 400 Bq/m (11 pCi/L) for old houses and 200
Bq/m (5 pCi/L) for new ones. After publication of the North
American and European Pooling Studies, Health Canada proposed a new
guideline that lowers their action level from 800 to 200 Bq/m (22
to 5 pCi/L). The United States Environmental Protection Agency
(EPA) strongly recommends action for any house with a concentration
higher than 148 Bq/m (4 pCi/L),[ and encourages action starting at
74 Bq/m (2 pCi/L). EPA radon risk level tables including
comparisons to other risks encountered in life are available in
their citizen's guide. The EPA estimates that nationally, 8% to 12%
of all houses are above their maximum "safe levels" (four
picocuries per liter the equivalent to roughly 200 chest x-rays).
The United States Surgeon General and the EPA both recommend that
all homes be tested for radon. Medical application It has been said
that exposure to radon gas mitigates auto-immune diseases such as
arthritis. As a result, in the late 20th century and early 21st
century, some "health mines" were established in Basin, Montana
which attracted people seeking relief from health problems such as
arthritis through limited exposure to radioactive mine water and
radon. The practice is controversial because of the
"well-documented ill effects of high-dose radiation on the body."
Health application Radioactive water baths have been applied since
1906 in Jchymov, Czech Republic, but even before radon discovery
they were used in Bad Gastein, Austria. Radium-rich springs are
also used in traditional Japanese onsen in Misasa, Tottori
prefecture. Drinking therapy is applied in Bad Brambach, Germany.
Inhalation therapy is carried out in Gasteiner-Heilstollen,
Austria, in Kowary, Poland and in Boulder, Montana, United States.
In the United States and Europe there are several "radon spas,"
where people sit for minutes or hours in a high-radon atmosphere in
the belief that low doses of radiation will invigorate or energize
them. Health application The radon gas which is used as a cancer
treatment in medicine is obtained from the decay of a radium
chloride source. In the past, radium and radon have both been used
for X-ray medical radiography, but they have fallen out of use as
they are radiotoxic alpha radiation emitters which are expensive
and have been replaced with iridium-192 and cobalt-60 since they
are far better photon sources. Radon in scientific study
Radon emanation from the soil varies with soil type and with
surface uranium content, so outdoor radon concentrations can be
used to track air masses to a limited degree. This fact has been
put to use by some atmospheric scientists. Because of radon's rapid
loss to air and comparatively rapid decay, radon is used in
hydrologic research that studies the interaction between ground
water and streams. Any significant concentration of radon in a
stream is a good indicator that there are local inputs of ground
water. Radon is also used in the dating of oil-containing soils
because radon has a high affinity of oil-like substances. Radon
scientific usage
Radon soil-concentration has been used in an experimental way to
map buried close-subsurface geological faults because
concentrations are generally higher over the faults. Similarly, it
has found some limited use in geothermal prospecting. Some
researchers have also looked at elevated soil-gas radon
concentrations, or rapid changes in soil or groundwater radon
concentrations, as a predictor for earthquakes. Results have been
generally unconvincing but may ultimately prove to have some
limited use in specific locations. Minimizing Radon pollution
Radon is a known pollutant emitted from geothermal power stations,
though it disperses rapidly, and no radiological hazard has been
demonstrated in various investigations. The trend in geothermal
plants is to re-inject all emissions by pumping deep underground,
and this seems likely to ultimately decrease such radon hazards
further.