An Introduction of Environmental Chemistry

An Introduction of
Environmental Chemistry
Lecture notes

Chemistry has played a major role in the advancement of society and in
making our lives longer, healthier, more comfortable, and more enjoyable. The
effects 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 produced
and dispersed into the environment. Historically, chemists as a group have not
always paid enough attention to the environmental consequences of their
activities.

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 directly or indirectly;
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 production
activities; (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.

Environmental chemistry
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 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.
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.

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
noise, heat, or light. Pollutants, the elements of pollution, can be
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.

1. Pollutant:
A pollutant may be defined as anything, living or not living, or any physical agent
(e.g. heat, sound) that in it’s 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 photochemical
smog 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:
H 2 SO 4 + CaCO 3 CaSO 4 + H 2 O + CO 2

6. Pathway of the pollutant:
It refers to the mechanism by which the pollutant gets distributed from it’s source into
the environmental segments.
Pb (C 2 H 5 ) 4
PbCl 2 + PbBr 2 (released into the air)
To food crops and food chain.
PbCl 2 + PbBr 2
7. Speciation:
The term is used for different chemical forms or species of inorganic or organometallic
compounds which are present in the environment. For example , the
species such as (CH 3 Hg) + and (CH 3 ) 2 Hg 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/m 3
respectively.

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
as synergism. Some times the combined effects of two pollutants are less rather than more
severe, and this situation is referred to as 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.

COMPONENTS OF THE EARTH/ ENVIRONMENTAL SEGMENTS
1. Lithosphere
The earth’s crust, made of the mantle of rocks, is the lithosphere. It includes the soil
which covers the rock’s crust in many places. Rocks are subjected to continuous
weathering forces—rain, wind, chemical and biological. The resulting primitive soil is
suitable for the growth of plants—after death and decay, plant debris returns to soil.
Soil has a loose structure consisting of solid mineral and organic matter, air spaces. It
shows broadly three zones as its depth increases. The top layer, up to several inches
thick, is known as the top soil which is an index of the soil quality. This is the layer 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-soil which receives organic matter, salts and clay particles leached
from the top soil. The third layer (zone) consists of weathered parent rocks from
which the soil was formed. Plants draw water and nutrients from soil—they 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.

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
earth’s 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.

3. Atmosphere
The major components of the atmosphere are nitrogen and oxygen while the minor
components are argon, carbon dioxide and some trace gases.
4. Biosphere
The biosphere consists of the earth’s crust, hydrosphere, atmosphere and various
The biosphere consists of the earth’s crust, hydrosphere, atmosphere and various
living species (microorganisms to man) which exist in the zone 600 meters above
earth’s 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 responsible
for 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.

Types of pollution
1. 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:
Category Examples Important pollutants
1. Chemical plants
Petroleum refineries, fertilizers,
cements, papermills, ceramic clay
products, glass manufacture
2. Crop spraying Pesticides and weedicides
3. Fuel burning
4. Metallurgy plants
Domestic burning, thermal power
plants
Aluminium refineries and steel
plant
5. Nuclear device testing Bomb explosions
6. Ore preparations Crushing, grinding and screening
7. Spray painting, ink, solvent
cleansing
8. Transportation
Printing and chemical
separations, furniture, dyeing
Cars, trucks, aeroplanes and
railways
H 2 S, sulphur oxide, fluorides,
organic vapours and dust
Organophosphates, chlorinated
hydrocarbons, lead, arsenic
Sulphur and nitrogen oxides
Metal flumes (Pb and Zn)
fluorides and particulates
Radioactive fall out, Sr-90, Cs-137,
C-14 etc.
Uranium and beryllium dust,
other particulates
Hydrocarbons and other organic
vapours
CO, NO, NO2, Pb, smoke, soot,
smoke organic vapours etc.