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An Introduction ofEnvironmental Chemistry

Lecture notes

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Chemistry has played a major role in the advancement of society and in

making our lives longer, healthier, more comfortable, and more enjoyable. Theeffects of human-made chemicals are ubiquitous and in many instances quite

positive. Without chemistry there would be no pharmaceutical drugs, no

computers, no automobiles, no TVs, no DVDs, no lights, no synthetic fibers.

However, along with all the positive advances that result from chemistry,

copious amounts of toxic and corrosive chemicals have also been producedand dis ersed into the environment. Historicall chemists as a rou have not

always paid enough attention to the environmental consequences of their

activities.

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Environment is the sum total of all conditions and influences that affect the

development and life of all organisms on earth. The living organisms vary

from the lowest micro-organisms such as bacteria, virus, fungus, etc. to the

highest, including man. Each organism has its own environment.

The functions of the environment in relation to man have been analyzed:

1. recreation;

2. source of natural resources agricultural, mineral and forestry which man

consumes rect y or n rect y;

3. sink for receiving wastes produced by man and his activities. The capacity

of the environment to carry out these functions is damaged by human

activities which imposes four stresses on the environment: (i) eutrophic, i.e.

the task of decomposing wastes produced by consumption and productionactivities; (ii) exploitative, i.e. cropping of plants, extraction of minerals and

hunting of animals; (iii) disruptive brought about by activities like

deforestation, construction of highways and towns; and (iv) chemical and

industrial stress which results from industrial development.

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It can be defined as the study of the sources, reactions, transport, effects,

and fates of chemical species in the air, soil and water environments; and theeffect 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.

Environmental chemistry

Environmental chemistry deals with the reactions, fates, movements, and

sources of chemicals in the air, water, and soil In the absence of humans, the

discussion would be limited to naturally occurring chemicals. Today, with the

burgeoning population of the Earth, coupled with continually advancing

technology, human activities have an ever-increasing influence on the

chemistry of the environment. To the earliest humans, and even until less than

a century ago, humans must have thought of the Earth as so vast that human

activity could scarcely have any more than local effects on the soil, water, and

air. Today we realize that our activities can have not only local and regional

but also global consequences.

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Pollution

is the introduction of contaminants into an environment that causes

instability, disorder, harm or discomfort to the ecosystem i.e. physical

systems or living organisms.

Pollution can take the form of chemical substances or energy, such as, , . , ,

foreign substances or energies, or naturally occurring; when naturally

occurring, they are considered contaminants when they exceed natural

levels. Pollution is often classed as point source or nonpoint source

pollution.

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1. Pollutant:

A pollutant may be defined as anything, living or not living, or any physical agent

(e.g. heat, sound) that in its excess makes any part of the environment

undesirable.

A pollutant has been defined as any solid, liquid or gaseous, substance present in

such concentration as may be or tend to be injurious to environment.

2. Contaminant:

A contaminant may be defined as something which causes deviation from the

normal composition of an environment. A contaminant does not occur in nature

but gets introduced by human activity into the environment, affecting its

composition.

3. Source:

It is generally the logic place from which the pollutant originates. The identity of

source is important to eliminate pollution.

4. Receptor

It is anything which is affected by the pollutant. Man is the receptor of photochemicalsmog causing irritation of the eyes and respiratory tract.

5. Sink:

It is the medium which is able to retain and interact with a long-lived pollutant.

Limestone wall may be the sink for the atmospheric sulfuric acid, through the

reaction:

H2SO4+ CaCO3 CaSO4+ H2O + CO2

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6. Pathway of the pollutant:

It refers to the mechanism by which the pollutant gets distributed from its source into

the environmental segments.

Pb (C2H5)4 PbCl2+ PbBr2 (released into the air)

PbCl2+ PbBr2To food crops and food chain.

7. Speciation:

The term is used for different chemical forms or species of inorganic or organo-

metallic compounds which are present in the environment. For example , the

species such as (CH3Hg)+ and (CH3)2Hg have been found to be deadly poisonous as

compared to the other species of mercury.

8. Threshold Limit Value (TLV):

It refers to the permissible level of a toxic pollutant in atmosphere to which a healthy

industrial worker gets exposed during an eight hour day without getting any

adverse effect. TLV values for Be and Zn have been 0.002 and 1.000 mg/m3

respectively.

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9. Synergism and Antagonism:

In many cases the combined effects of two or more pollutants are more severe or even

qualitatively different from the individual effects of separate pollutants- a phenomenon known

assynergism. Some times the combined effects of two pollutants are less rather than moresevere, and this situation is referred toas Antagonism.

Cyanide in industrial wastes are quite poisonous to aquatic life, and in the presence of zinc or

cadmium they are extremely poisonous (synergistic effect), apparently due to the formation of

complexes; in the presence of nickel, however, a nickel-cyanide complex that is not very toxic is

formed.

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COMPONENTS OF THE EARTH/ ENVIRONMENTAL SEGMENTS

1. Lithosphere

The earths crust, made of the mantle of rocks, is the lithosphere. It includes the soilwhich covers the rocks crust in many places. Rocks are subjected to continuous

weathering forcesrain, wind, chemical and biological. The resulting primitive soil is

suitable for the growth of plantsafter death and decay, plant debris returns to soil.

Soil has a loose structure consisting ofsolid mineralandorganic mat ter,air spaces. It

showsbroadly three zones as its depth increases.The top layer, up to several inchesthick is known as theto soilwhich i an inde of the soil ualit.This is the la er of

maximum biological productivity and it contains bulk of the organic matter. Hence it

is very important for vegetation cover and agricultural crops. Reckless deforestation

causes loss of top soil which also means loss of agricultural production.The underlying

layer is the sub-soilwhich receives organic matter, salts and clay particles leached

from the top soil. The third layer (zone) consists ofweathered parent rocksfromwhich the soil was formed. Plants draw water and nutrients from soilthey transport

water into the plant body (roots and leaves) and then excess water into the

atmosphere through leaves by the process of transpiration. Soils have an important

function, i.e. exchange of cations whereby essential trace metals are made available to

plants as nutrients.

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2. Hydrosphere

The hydrosphere consists of all types of water resources oceans, seas, rivers, lakes,

streams, reservoirs, glaciers, polar ice caps and ground water (i.e. water below the

earths surface). Surface water gets polluted by domestic sewage, industrial waste

and agricultural run-off including pesticides and fertilizers. Water-borne diseases

from sewage alone kill millions of people in developing countries.

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3. Atmosphere

The major components of the atmosphere are nitrogen and oxygen while the minorcomponents are argon, carbon dioxide and some trace gases.

4. Biosphere

The biosphere consists of the earths crust, hydrosphere, atmosphere and various

living species (microorganisms to man) which exist in the zone 600 meters above

earths surface and 10,000 meters below sea level. Both biosphere and environment

have close interactions with each other. Thus oxygen and carbon dioxide levels of the

atmosphere depend entirely on the plant world. Green plants alone are responsiblefor the accumulations of oxygen in the atmosphere through photosynthesis and decay.

In the early stages atmosphere was devoid of oxygen and there was no life

form on earth.

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Category Examples Important pollutants

1. Chemical plants

Petroleum refineries, fertilizers,

cements, papermills, ceramic clay

products, glass manufacture

H2S, sulphur oxide, fluorides,

organic vapours and dust

2. Crop spraying Pesticides and weedicidesOrganophosphates, chlorinated

hydrocarbons, lead, arsenic

Domestic burning, thermal power

Types of pollution1. Air Pollution

Air pollution is the presence of materials in air in such concentration which are harmful to

man and his environment. Various causes of air pollution are:

.plants

4. Metallurgy plantsAluminium refineries and steel

plant

Metal flumes (Pb and Zn)

fluorides and particulates

5. Nuclear device testing Bomb explosionsRadioactive fall out, Sr-90, Cs-137,

C-14 etc.

6. Ore preparations Crushing, grinding and screening Uranium and beryllium dust,other particulates

7. Spray painting, ink, solvent

cleansing

Printing and chemical

separations, furniture, dyeing

Hydrocarbons and other organic

vapours

8. TransportationCars, trucks, aeroplanes and

railways

CO, NO, NO2, Pb, smoke, soot,

smoke organic vapours etc.