introduction and identification of environmental chemistry · chapter 1 introduction and...

Introduction and Identification of Environmental Chemistry Chapter 1

1

1. Introduction This course is about Environmental Chemistry and Pollution. To understand that

topic, it is important to know what is Environmental Science? What is the meaning of Environment?

Environmental Science in its broader sense is the science of complex interactions that occur among the atmospheric, aquatic, biotic, terrestrial and anthropological environments. Scientifically, Environmental Science may be defined as the study of earth, water, air and living environments and the effects of technology upon them. It includes all the disciplines, such as chemistry, biology, ecology, sociology, and government, that affect or describe these interactions. To a significant degree, environmental science has evolved from investigations of the ways by which, and places in which, living organisms carry out their life cycles. This is the discipline of natural history, which in recent times has evolved into ecology, the study of environmental factors that affect organisms and how organisms interact with these factors and with each other.

The term Environment refer to a definable place where an organism lives, including both the physical and biologic features of the place. It include all conditions and circumstances which influences surroundings and affecting the organism. Environment means to all those which are physical and chemical (organic and inorganic) of the atmosphere, lithosphere and hydrosphere. It is the aggregate of external conditions that influence the life of an individual or pollution, specifically the life of human being. It ultimately determines the quality and survival of life. Organisms and environment are in constant change. Some changes are very rapid other are slow and may take thousands of years. The interrelation between the physical environment (soil, water, air) and organismal environment (plant and animal life) constitute the study of ecology.

2. Environmental Chemistry Environmental Chemistry may be defined as the study of chemical phenomenon in

the environment. Also, it may be defined as the study of the sources, reactions, transport, effects and fates of chemical species in hydrosphere, lithosphere, atmosphere and biosphere.

It is a multi-disciplinary science which includes many vastly different fields such as chemistry, physics, life sciences, public health, engineering, agriculture etc. Only in recent years many chemists have become deeply involved with investigations of Environmental Pollution. Environmental Chemistry helps in identifying and determination of specific pollutant present in environment. The branch of Environmental Chemistry which concern with life itself can be referred as


2

environmental biochemistry. In other words, it deals with the effects of environmental chemicals species on life. Another closely related branch is toxicological chemistry . It is the chemistry of toxic substances interaction with living organisms.

2.1. Atmosphere The atmosphere is the thin layer of gases that cover Earth’s surface. The atmosphere

moderates Earth’s temperature, absorbs energy and damaging ultraviolet radiation from the sun, transports energy away from equatorial regions, and serves as a pathway for vapor-phase movement of water in the hydrologic cycle.

The atmosphere is mainly composed of nitrogen and oxygen gases, while the minor components include argon, carbon dioxide, and other noble gases. It is the source of most wanted O2, gas essential for life on earth and CO2, essential for plant photosynthesis. It is also a major source of nitrogen which is present in all form of life. Nitrogen fixing bacteria fixes atmospheric nitrogen to ammonia which is then transferred to different parts of biosphere, lithosphere and hydrosphere.

2.2. Hydrosphere The hydrosphere contains Earth’s water. Over 97 % of Earth’s water is in oceans, and

most of the remaining fresh water is in the form of ice. Therefore, only a relatively small percentage of the total water on Earth is actually involved with terrestrial, atmospheric, and biological processes. Exclusive of seawater, the water that circulates through environmental processes and cycles occurs in the atmosphere, underground as groundwater, and as surface water in streams, rivers, lakes, ponds, and reservoirs.

The major uses of water include irrigation, thermal power plants, domestic and industrial consumption. There are thousands of chemical species and millions of living organisms make hydrosphere as their shelter. Any change in hydrosphere, therefore, affect all including man.

2.3. Lithosphere The geosphere, or solid Earth is that part of the Earth upon which humans live and

from which they extract most of their food, minerals, and fuels. The earth is divided into layers, including the solid, iron-rich inner core, molten outer core, mantle, and crust. Environmental science is most concerned with the lithosphere, which consists of the outer mantle and the crust. The latter is the earth’s outer skin that is accessible to humans. It is extremely thin compared to the diameter of the earth, ranging from 5 to 40 km thick.


3

2.4. Biosphere It is otherwise known as the life layer, it refers to all organisms on the earth’s surface

and their interaction with water and air. It consists of plants, animals and micro-organisms, ranging from the tiniest microscopic organism to the largest whales in the sea. Biology is concerned with how millions of species of animals, plants and other organisms grow, feed, move, reproduce and evolve over long periods of time in different environments. Its subject matter is useful to other sciences and professions that deal with life, such as agriculture, forestry and medicine. The richness of biosphere depends upon a number of factors like rainfall, temperature, geographical reference etc. Apart from the physical environmental factors, the man made environment includes human groups, the material infrastructures built by man, the production relationships and institutional systems that he has devised. The social environment shows the way in which human societies have organized themselves and how they function in order to satisfy their needs.

There is a direct influence of biosphere and environment on each other. This means oxygen and carbon dioxide levels in the atmosphere are entirely based upon plant animal kingdom. This is because both of these consume and release these two gases.

3. Natural Cycles of the Environment Cycles of matter, often based on elemental cycles, are of utmost importance in the

environment. The transfer of a chemical element between atmosphere, hydrosphere and lithosphere call be explained by means of a geochemical cycle.

Global geochemical cycles can be regarded from the viewpoint of various reservoirs, such as oceans, sediments, and the atmosphere, connected by conduits through which matter moves continuously. Each geochemical cycle is a model which explains the movement of a chemical element or its compound in different segments of environment. The movement of a specific kind of matter between two particular reservoirs may be reversible or irreversible (Figure 1.1).

Sedimentation Uplift

Sea Spray

Rain Dust

Sea Spray

Rain Dust

Atmosphere

Sediments

Ocean Land Rivers by dissolving and weathering of

land

Figure 1.1: General Representation of Geochemical Cycle


4

The fluxes of movement for specific kinds of matter vary greatly as do the contents of such matter in a specified reservoir. Cycles of matter would occur even in the absence of life on Earth but are strongly influenced by life forms, particularly plants and microorganisms. Organisms participate in biogeochemical cycles, which describe the circulation of matter, particularly plant and animal nutrients, through ecosystems. As part of the carbon cycle, atmospheric carbon in CO2 is fixed as biomass; as part of the nitrogen cycle, atmospheric N2 is fixed in organic matter. The reverse of these kinds of processes is mineralization, in which biologically bound elements are returned to inorganic states. Biogeochemical cycles are ultimately powered by solar energy, which is fine-tuned and directed by energy expended by organisms. In a sense, the solar-energy-powered hydrologic cycle acts as an endless conveyer belt to move materials essential for life through ecosystems.

Geochemical cycles may be divided into two categories: Endogenic cycles, these predominantly involve subsurface rocks of various kinds and Exogenic cycles, these occur largely on earth's surface, and usually have an atmospheric component. In general, sediments and soils are being shared between two cycles and constitute the predominant interface between them. The examples of exogenic cycles include oxygen cycle, nitrogen cycle, carbon cycle etc. where element spends part of the cycle in atmosphere. Many other cycles such as phosphorus cycle, do not have a gaseous component and is therefore an example of endogenic cycle.

3.1. Hydrologic Cycle Water can occur in three physical phases: solid, liquid, and gas and is found in

nature in all these phases in large quantities. Depending upon the environment of the place of occurrence, water can quickly change its phase.

The hydrologic cycle can be subdivided into three major systems: The oceans being the major reservoir and source of water, the atmosphere functioning as the carrier and deliverer of water and the land as the user of water (Figure 1.2). The amount of water available at a particular place changes with time because of changes in the supply and delivery. On a global basis, the water movement is a closed system but on a local basis it is an open system.

The major components of the hydrologic cycle are precipitation, evaporation, transpiration, infiltration, condensation, and runoff.


5

Evaporation of water takes place from the oceans and the land surface mainly due to solar energy. The moisture moves in the atmosphere in the form of water vapor which precipitates on land surface or oceans in the form of rain, snow, hail, sleet, etc. A part of this precipitation is intercepted by vegetation or buildings. Of the amount reaching the land surface, a part infiltrates into the soil and the remaining water runs off the land surface to join streams. These streams finally discharge into the ocean. Some of the infiltrated water percolates deep to join groundwater and some comes back to the streams or appears on the surface as springs.

This immense movement of water is mainly driven by solar energy: the excess of incoming radiation over the outgoing radiation. Therefore, sun is the prime mover of the hydrologic cycle. The energy for evaporation of water from streams, lakes, ponds and oceans and other open water bodies comes from sun. A substantial quantity of moisture is added to the atmosphere by transpiration of water from vegetation. Living beings also supply water vapor to the atmosphere through perspiration. Gravity has an important role in the movement of water on the earth’s surface and anthropogenic activities also have an increasingly important influence on the water movement.

An interesting feature of the hydrologic cycle is that at some point in each phase, there usually occur: (a) transportation of water, (b) temporary storage, and (c) change of state. For example, in the atmospheric phase, there occurs vapor flow, vapor storage in the atmosphere and condensation or formation of precipitation created by a change from vapor

Figure 1.2: Hydrologic Cycle


6

to either the liquid or solid state. Moreover, in the atmosphere, water is present in the vapor form while it is mostly liquid in the oceans.

3.2. Oxygen Cycle Oxygen, one of the main components of the Earth’s atmosphere, can always be found

with other elements. Two oxygen atoms (O2) make up one oxygen molecule, and three oxygen atoms (O3) together make up the molecule called ozone. As a gas, oxygen is odorless, colorless, and highly reactive. Oxygen is essential for the survival of many organisms, and, in the ozone, provides protection to life by filtering out the sun’s ultraviolet rays.

The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere (air), the biosphere (living things), and the lithosphere (Earth's crust) (Figure 1.3). The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life.

The oxygen in atmosphere is chemically reactive. It is mainly present as O2. The reactivity of O2 influences the geochemical cycle of many other element such as C, H, N, S, P and Fe. The O2 is being produced mainly due to photosynthesis and to a lesser extent due to photo-dissociation: 2H2O 2H2 + O2

Some of O2 is also being converted into O3 in atmosphere which again produces O2.

O2 O + O O + O2 O3 O3 O2 + O

Figure 1.3: Oxygen Cycle

UV light

UV light


7

Respiration is used mostly all organisms as a means of producing energy. This reaction combined with the oxidation of dead organic matter (a chemically similar reaction)

reverse the photosynthetic process: (CH2O)n + nO2 nCO2 + nH2O

The burning of fossil fuels also produces carbon dioxide and water at the cost of O2 but this is just a delayed oxidation of dead organic matter. Hydrogen sulfide, H2S from volcanoes and organic decay is converted to sulfur dioxide, SO2 in the atmosphere. This sulfur dioxide, plus that produced by the combustion of fossil fuels and extraction of metals from sulfide, ores, is eventually converted to sulfate, SO4

2- and comes back to the Earth's surface often as acid rain. Likewise the various oxides of nitrogen, produced by micro-organisms or by human activities are eventually converted to nitrate, NO3

-, and can also produce acid rain. On land, and a smaller extent in the oceans, many metals are converted to insoluble oxides by atmospheric dioxygen, but some other reduced species generally compounds of non-metals are oxidized to more soluble forms:

4Fe2+ + 3O2 2Fe2O3 (insoluble) S2- + 2O2 SO4

2- (soluble)

Oxygen is also cycled between the biosphere and lithosphere. Marine organisms in the biosphere create calcium carbonate shell material (CaCO3) that is rich in oxygen. When the organism dies its shell is deposited on the shallow sea floor and buried over time to create the limestone sedimentary rock of the lithosphere. Weathering processes initiated by organisms can also free oxygen from the lithosphere. Plants and animals extract nutrient minerals from rocks and release oxygen in the process.

3.3. Nitrogen Cycle The atmosphere contains 78 % of nitrogen and this is easily the most abundant gas in

the atmosphere. Nitrogen, though constituting much less of biomass than carbon or oxygen, is an essential constituent of proteins. However, atmospheric nitrogen is, in fact, unavailable to plants or animals and only some specialized microorganisms are able to use this huge potential source. Plants usually obtain the nitrogen they need by absorbing nitrate ions or ammonium ions through their roots. However some plants obtain much of their nitrogen by forming a symbiotic relationship with nitrogen fixing bacteria.

Nitrogen cycle refers to the incorporation of N2 from the atmosphere into living matter and chemically bound nitrogen in soil, water and then back into the atmosphere again. Figure 1.4 shows some of the most important micro-organism mediated chemical reactions involving nitrogen components in aquatic and soil environments.


8

Nitrogenous compounds may be added to the soil through: - Artificial fertilizers - Weathering of rocks - Acid rain - Lightning.

Nitrogenous compounds in the soil may be volatilized back into the atmosphere, washed down through the soil (leached) into sub-surface supplies, taken up by plants, broken down by micro-organisms such as bacteria, or they may remain fixed in the soil beyond the rooting depth of most plants.

3.3.1. Nitrogen fixation Nitrogen Fixation is the conversion of atmospheric nitrogen (N2) into reactive

compounds such as ammonia (NH3) and nitrate (NO3-). The breaking of the bonds between

the nitrogen atoms requires a great deal of energy and occurs naturally in two primary ways:

Figure 1.4: Nitrogen Cycle


9

Abiotic Fixation: Nitrate is the result of high energy fixation in the atmosphere from lightning and cosmic radiation. In this process, N2 is combined with oxygen to form nitrogen oxides such as NO and NO2, which are carried to the earth’s surface in rainfall as nitric acid (HNO3). This high energy fixation accounts for approximately 10 % of the nitrate entering the nitrogen cycle.

Biological fixation: This is carried out by nitrogen fixing bacteria such as Rhizobium, Azotobacter and Frankia as well as some cyanobacteria such as Nostoc.

3.3.2. Nitrification Nitrification is the process by which ammonia is oxidized to nitrite ions (NO2

-) and then to nitrate ions (NO3

-), which is the form most usable by plants. The two groups of micro-organisms involved in the process are Nitrosomas and Nitrobacter. Nitrosomas oxidize ammonia to nitrite and Nitrobacter oxidize nitrite to nitrate.

3.3.3. Assimilation Nitrates are the form of nitrogen most commonly assimilated by plants through root

hairs. Since heterotrophic organisms cannot readily absorb nitrogen as plants do, they rely on acquiring nitrogen-based compounds through the food they eat. Since plants are the base of the food chain, the nitrogen-based compounds they have assimilated into their tissue will continue to pass from one organism to another (through consumption) as matter and energy transfers through the ecosystem’s food web.

3.3.4. Ammonification In ammonification, a host of decomposing microorganisms, such as bacteria and

fungi, break down nitrogenous wastes and organic matter found in animal waste and dead plants and animals and convert it to inorganic ammonia (NH3) for absorption by plants as ammonium ions. Therefore, decomposition rates affect the level of nutrients available to primary producers.

3.3.5. Denitrification Denitrification is the process by which nitrates are reduced to gaseous nitrogen (N2)

and lost to the atmosphere. This process occurs by facultative anaerobes in anaerobic environments.

3.4. Phosphorus Cycle The phosphorus cycle is the biogeochemical cycle that describes the movement of

phosphorus through the lithosphere, hydrosphere, and biosphere, see Figure 1.5. The


10

phosphorus cycle differs from the other major biogeochemical cycles in that it does not include a gas phase; although small amounts of phosphoric acid (H3PO4) may make their way into the atmosphere, contributing in some cases to acid rain. The water, carbon, nitrogen and sulfur cycles all include at least one phase in which the element is in its gaseous state. Very little phosphorus circulates in the atmosphere because at Earth's normal temperatures and pressures, phosphorus and its various compounds are not gases. The largest reservoir of phosphorus is in sedimentary rock.

It is in these rocks where the phosphorus cycle begins. When it rains, phosphates are removed from the rocks (via weathering) and are distributed throughout both soils and water. Plants take up the phosphate ions from the soil. The phosphates then moves from plants to animals when herbivores eat plants and carnivores eat plants or herbivores. The phosphates absorbed by animal tissue through consumption eventually returns to the soil through the excretion of urine and feces, as well as from the final decomposition of plants and animals after death.

The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA. The double helix of our DNA is only possible because of the phosphate

Figure 1.5: Phosphorus Cycle


11

ester bridge that binds the helix. Phosphorus is also found in bones, whose strength is derived from calcium phosphate in enamel of mammalian teeth; exoskeleton of insects and phospholipids (found in all biological membranes) and it also functions as buffering agent in maintaining acid base homeostasis in the human body.

3.5. Sulfur Cycle Sulfur is an essential element for the macromolecules of living things. As part of the

amino acid cysteine, it is involved in the formation of proteins. As shown in Figure 1.6, sulfur cycles between the oceans, land, and atmosphere. Atmospheric sulfur is found in the form of sulfur dioxide (SO2), which enters the atmosphere in three ways: first, from the decomposition of organic molecules; second, from volcanic activity and geothermal vents; and, third, from the burning of fossil fuels by humans.

On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents. Atmospheric sulfur is found in the form of sulfur dioxide (SO2), and as rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid (H2SO4). Sulfur can also fall directly from the atmosphere in a process called fallout. Also, as sulfur-containing rocks weather, sulfur is released into the soil. These rocks originate from ocean sediments that are moved to land by the geologic

Figure 1.6: Sulfur Cycle


12

uplifting of ocean sediments. Terrestrial ecosystems can then make use of these soil sulfates (SO4

2-), which enter the food web by being taken up by plant roots. When these plants decompose and die, sulfur is released back into the atmosphere as hydrogen sulfide (H2S) gas.

Sulfur enters the ocean in runoff from land, from atmospheric fallout, and from underwater geothermal vents. Some ecosystems rely on chemoautotrophs using sulfur as a biological energy source. This sulfur then supports marine ecosystems in the form of sulfates.

Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases larger amounts of hydrogen sulfide gas into the atmosphere. As rain falls through this gas, it creates the phenomenon known as acid rain, which damages the natural environment by lowering the pH of lakes, thus killing many of the resident plants and animals. Acid rain is corrosive rain caused by rainwater falling to the ground through sulfur dioxide gas, turning it into weak sulfuric acid, which causes damage to aquatic ecosystems. Acid rain also affects the man-made environment through the chemical degradation of buildings.

3.6. Carbon Cycle Carbon is the major chemical constituent of most living matter including human

beings. Yet by weight, carbon is not one of the most abundant elements on the Earth's crust. In fact, the lithosphere is only 0.032 % carbon by weight. In comparison, oxygen and silicon respectively make up around 45 % and 29 % of all rocks. Carbon is stored on the planet in the following major reservoirs: as organic compounds (e.g. sugar, starch) in living and dead organisms in the biosphere; as the gas carbon dioxide (CO2) and methane (CH4) in the atmosphere; as organic matter in soil; in the lithosphere as fossil fuel and sedimentary rocks such as limestone (including chalk) and dolomite; in the oceans as dissolved hydrocarbons and as calcium carbonate in the shells of marine creatures (e.g. coral).

The movement of carbon, in its many forms, between the atmosphere, hydrosphere, biosphere and lithosphere is described by the carbon cycle (see Figure 1.7).

The global carbon cycle, one of the major biogeochemical cycles, can be divided into a geological and a biological component. The geological carbon cycle operates on a time scale of millions of years, whereas the biological carbon cycle operates on a time scale of days to thousands of years.


13

3.6.1. Geological Carbon Cycle Since the formation of the Earth, geological forces have slowly produced carbonic

acid, a weak acid formed by the reactions between atmospheric CO2 and water:

CO2 + H2O H2CO3

Carbonic acid is important in controlling the acidity (pH) of the oceans by releasing of hydrogen ions and bicarbonate: H2CO3 H+ + HCO3

-

Certain forms of sea life biologically fix bicarbonate with calcium (Ca2+) to produce calcium carbonate (CaCO3). This substance is used to produce shells and other body parts by organisms such as coral, crustaceans, some protozoa, and some algae. When these organisms die, their shells and body parts sink to the ocean floor where they sediment as carbonate-rich deposits and form reefs.

3.6.2. Biological Carbon Cycle

Biology plays an important role in the movement of carbon between the land, ocean, and atmosphere through the processes of photosynthesis and respiration. Through

Figure 1.7: Carbon Cycle


14

photosynthesis, green plants use solar energy and water to turn atmospheric CO2 into carbohydrates (i.e. sugars, starch and cellulose):

energy (sunlight) + 6CO2 + 6H2O C6H12O6 + 6O2

Carbohydrates are the principle compounds that are necessary to build up biomass for plants or the bodies of animals. Most carbon leaves the biosphere through respiration, the decomposition of dead organic matter (e.g. litter fall), which is the opposite process of photosynthesis.

When oxygen is present, aerobic respiration occurs, which releases carbon dioxide into the surrounding air or water, following the reaction:

C6H12O6 (organic matter) + 6O2 6H2O + 6CO2 + energy

Respiration frees the energy contained in the sugars for use and transforms carbohydrate ‘fuel’ back into carbon dioxide, which in turn is released back to the atmosphere. The amount of carbon taken up by photosynthesis and released back to the atmosphere by respiration each year is about 1,000 times greater than the amount of carbon that moves through the geological cycle on an annual basis.

When oxygen is lacking, for example, in soil that is stagnant due to poor drainage (often showing the characteristic olive and blue colours of gleyic conditions), then the breakdown of carbon compounds is carried out by microbial communities that catalyze the breakdown of organic matter without oxygen (anaerobically) to produce methane and carbon dioxide following the equation below:

C6H12O6 3CH4 + 3CO2

Carbon dioxide and methane are important greenhouse gases that affect the Earth’s climate. Their production makes soil an important component in the study of climate change.

4. Environmental Pollution Present day environmental pollution problem is the most horrible ecological crisis

since the civilization on earth. Just before last century, environment was pure undisturbed and hospitable for man to live. Environmental pollution may be defined as the unfavorable alteration of surrounding environment, wholly or largely due to by-products of man's activity, through direct or indirect effects of changes in energy patterns, radiation levels, chemical and physical constitution or abundances of organisms. These changes may affect man directly or through water supplies, agricultural or biological products, physical objects or possessions or opportunities for recreation and appreciation of nature.


15

Developmental activities such as construction, transportation and manufacturing not only deplete the natural resources but also produce large amount of wastes that leads to pollution of air, water, soil, and oceans; global warming and acid rains. Untreated or improperly treated waste is a major cause of pollution of rivers and environmental degradation causing ill health and loss of crop productivity. In this course you will study about the major causes of pollution, their effects on our environment and the various measures that can be taken to control such pollutions.

4.1. Types of Pollution Pollution normally classified according to environment segments in which it is

occurring. Sometimes it is also classified according to type of pollutant by which pollution is caused. A general classification may be natural (originates from natural processes) and artificial (originates due to man's activities) pollution. Based upon these classifications different types of pollution those need immediate attention are: Air Pollution, Water Pollution, Soil Pollution, Radiation Pollution (Radioactivity), and Thermal Pollution.

4.2. Pollutants In common usage, pollutant is a term used for non-living, manmade substances or

other nuisances which are present in excess (beyond a certain limit) in a particular location. Oxides of nitrogen and sulphur, carbon monoxide, smog and particulates all are examples of air pollutants, however all are produced naturally. Generally, those made by nature get widely dispersed are at low concentration and therefore are not the major threats to life. The excesses produced due to human activities when crosses a certain limit becomes a threat and thus called pollutants.

Also, the pollutant has been defined as any solid, liquid or gaseous substances present in such concentration as may be or tend to be injurious to environment. In addition to this, the unserviceable or residues of things we manufacture, use and throw are also regarded as pollutants.

4.3. Types of Pollutants The pollutants can be classified according to their physical and chemical properties.

They are as follows:

Gaseous Pollutants: Oxides of nitrogen (NO, NO2 , etc.), SO2, H2S, CO, Cl2, Br2, etc.;

Fluoride Compounds: CCl2F2, CClF3, CF4, etc.;

Metals: Cr, As, Hg, Pb, Fe, Zn, Ni, Sn, Cd, etc.;


16

Complex Organic Pollutants: Benzene, benzpyrene, ether, etc.;

Photochemical oxidants: Ozone, PAN (peroxyacetylnitrate), PBN (peroxybenzoylnitrate), aldehyde, ethylene, NOx (oxides of nitrogen), etc.;

Deposited Matter: Soot, smoke, dust, tar, grit, etc.;

Solid waste: Plastics, metal alloys, etc.;

Economic Poisons: Herbicides, fungicides, pesticides, namatocides, insecticides, rodenticide, and other biocides;

Fertilizers;

Radioactive waste;

Heat.

From the ecosystem view point, the pollutants can be classified as non-degradable pollutants or biodegradable pollutants. Many materials such as aluminum cans, mercuric salts, long chain phenolic compounds, plastics, high molecular weight artificial polymers, etc., either they do not degrade (converting to smaller molecules or returning to nature) or degrade only very slowly in the natural environment, are termed as non-degradable pollutants. Such non-degradable pollutants are serious threats to environment as they not only accumulate but often biologically magnified as they move to biogeochemical cycles and along food chains. Many times they react with other compounds in environment to produce toxins. Many materials and waste products such as domestic sewage can be rapidly decomposed by natural processes or in engineered systems (like a municipal sewage treatment plant) they are termed as biodegradable pollutants. These pollutants or materials enhance nature's great capacity to decompose and recycle. Biodegradable pollutants possess a problem when their input into one environment part get exceeded the decomposition or dispersal capacity.

4.4. Contaminant A contaminant may be defined as something which causes a deviation from the

normal composition of an environment. A contaminant not necessarily be a pollutant as it may not be having any adverse effect on environment. Contaminants, which are not classified as pollutants unless they have some detrimental effect, cause deviations from the normal composition of an environment. In simple words contaminant does not occur naturally in the segment of environment rather it gets introduced by some human activity, affecting the composition.


17

4.5. Source, Receptor and Sink of Pollutant Source is the place from where pollutant originates. The identification of source is

important since it can help in elimination of pollution. After a pollutant gets released from a source, it may act upon a receptor. This means receptor is anything which is affected by the pollutant. Man is the receptor for gaseous pollutants such as smog. Plant or vegetation is the receptor for oxides of sulphur as they die on excess exposure. Man is also receptor of photochemical smog causing irritation of the eyes and respiratory tract.

Sink is the medium which is able to retain or interact with a long lived pollutant, though not necessarily indefinitely. Thus a limestone wall may be the sink for atmosphere sulphuric acid. The reaction can be written as:

H2SO4 + CaCO3 CaSO4 + H2O + CO2

The above reaction fixes sulphate as part of the wall composition. Similarly oceans can be regarded as sinks for atmosphere carbon dioxide which is converted into carbonates or bicarbonates.

4.6. Threshold limit value (TLV): This value indicates the permissible level of a toxic pollutant in atmosphere to which

a healthy industrial worker can be exposed during an eight-hour day without any adverse effect. TLV of a pollutant is found by experimentation on animals, medical knowledge and experience and environmental studies.

introduction and identification of environmental chemistry · chapter 1 introduction and...

Documents