Organic and inorganic pollutants
Dr. Kiran Hina
( B )
and inorganic pollutants
Organic pollution occurs when large
quantities of organic compounds, which act as substrates for microorganisms,
are released into watercources. During the decomposition process the dissolved
oxygen in the receiving water may be used up at a greater rate than it can be
replenished, causing oxygen depletion and having severe consequences for the
stream biota. Organic effluents also frequently contain large quantities of
suspendid solids which reduce the light available to photosynthetic organisms
and, on settling out, alter the characteristics of the river bed, rendering it
an unsuitable habitat for many invertebrates. Toxic ammonia is often present.Organic
pollutants consist of proteins, carbohydrates, fats and nucleic acids in a
multiplicity of combinations. Raw sewage is 99,9 per cent water, and of the 0,1
per cent solids, 70 per cent is organic (65 per cent proteins, 25 per cent
carbohydrates, 10 per cent fats). Organic wastes from people and their animals
may also be rich in disease-causing (pathogenic) organisms.
What are the origins of organic pollutants?
Organic pollutants originate from
domestic sewage (raw or treated), urban run-off, industrial (trade) effluents
and farm wastes. Sewage effluents is the greatest source of organic materials
discharged to freshwaters. In England and Wales there are almost 9000
discharges releasing treated sewage effluent to rivers and canals and several
hundred more discharges of crude sewage, the great majority of them tot the
lower, tidal reaches of rivers or, via long outfalls, to the open sea. It has
been assumed, certainly incorrectly, that the sea has an almost unlimited
capacity for purifying biodegradable matter.
Origin and Occurrence in Discharges
A broad range of organic substances are
produced by human society and appear in discharges such as sewage, stormwater
and industrial discharges. These discharges can represent major sources of the
pollutant substance. For example the concentration of organic pollutants in
sewage is low but the volume is large making it a major source of many
pollutants. A similar situation applies with stormwater where these substances
often originate from discharges from motor vehicles on to road surfaces and are
subsequently swept into waterways by storm run-off. Motor vehicles are major
sources of petroleum hydrocarbons, polycyclic aromatic hydrocarbons and dioxins
which are often discharged to the atmosphere in particulate form. These
particulates are deposited close to busy roadways leading to contamination of
urban soils and potential human exposure. Urban and industrial wastes are
often, either currently or in the past, disposed directly into pits dug into
the ground which leads to contamination of the soil and in some cases the
adjacent ground water. Outside urban areas agricultural activities are the
major sources of pollutants. The growing of crops often involves the release of
pesticides into the environment, which can result in the contamination of
waterways and soils, as well as the urban environment. Perhaps the most
spectacular example of contamination of the environment is due to the
accidental spillage of petroleum. Over the years many disasters of this kind
have occurred releasing tens of thousands of tonnes of petroleum into the
Classes and Properties of Organic
The various types of organic pollutant can be
placed into three general classes:
v Nitrogen and phosphorus compounds or
v Organometallic compounds.
Probably the major category is the
hydrocarbons and related compounds, which contains such compounds as DDT, the
dioxins and the polycyclic aromatic hydrocarbons (PAHs). These compounds
contain the elements of carbon and hydrogen, with some containing chlorine and
oxygen as well. There are a limited number of types of chemical bonds present,
which are principally C-H, C-C, C-Cl, C=Cand C=C (aromatic). All of these bonds
are relatively stable and have limited polarity and this property is then
conferred onto the related compounds. Some typical structures are shown in
As a result of the low polarity, these
compounds are, in general, soluble in fat (i.e. lipophilic), poorly soluble in
water and persistent in the environment. Thus, they will be sorbed by sediment
and bioaccumulated by organisms (in fatty tissues) and have low concentrations
in water and air. The lipophilicity of compounds can be measured in the
laboratory as the octanol-water partition coefficient ( ow K ). The higher the
ow K value the higher the lipophilicity. This class includes the most toxic
organic compound of abiotic origin, 2,3,7,8-tetrachlorodibenzo(1,4)dioxin, also
known as 2,3,7,8-TCDD or TCDD.
The group containing oxygen, nitrogen and
phosphorus compounds is very diverse but as a general rule it contains
compounds with relatively high solubility in water, low fat solubility and
relatively low persistence in the environment. This is due to the presence of
bonds with relatively high levels of polarity due to carbon and other atoms
being attached to oxygen, nitrogen or phosphorus conferring a high level of
polarity onto the related compounds. As a general rule the ow K values are
relatively low, much lower than those of the hydrocarbons. In addition, such
bonds are relatively easily dissolved by environmental processes and consequently
such compounds are less persistent.
The substances in this group only rarely form
residues in the environment due to their low persistence, low accumulation in
sediments and low bioaccumulation capacity in organisms. The organometallic
group is probably the least important from an environmental perspective and
includes compounds that are combinations of metal, such as lead and tin, with
organic components based on carbon.
Figure 1: Chemical structures of some well
known organic pollutants
Persistent Organic Pollutants and Endocrine Disruptors:
There are a group of chemicals which have
posed particular environmental problems due to their fat solubility,
bioaccumulation potential and environmental persistence as well as usage
patterns. These are referred to as Persistent Organic Pollutants (POPs) and
these substances are often distributed over long distances up to a global
scale. POPs are commonly members of the hydrocarbon and related compounds group
(see Figure 2) and include such compounds as DDT, PCBs and the dioxins (see
Persistent Organic Wastes, Pathways of Organic Chemical Contamination in
Ecosystems). The POPs have been associated with adverse biological effects
often related to disruption of the endocrine system in organisms. The endocrine
system is a complex array of glands and other organs that control hormone
levels within organisms. When POPs are taken up by an organism, even in very
low concentrations, they can disrupt the endocrine system causing hormonal
changes that can result in reproductive problems. In addition these compounds
are often carcinogens. There are several examples of the adverse effects of
POPs on reproductive success in the natural environment. Perhaps the best known
is the effects of DDE on the reproductive success of birds. In recent times the
number of endocrine disrupters has increased dramatically and now includes most
organic pollutants as well as the range of other substances. In addition there
have been reports of adverse effects, usually associated with reproduction, in
relationship to humans as well.
The effects of organic effluents on receiving waters:
When an organic polluting load id
discharged into a river it is gradually eliminated by the activities of micro
organisms in a way very similar to the processes in the sewage treatment works.
This self-purification requires sufficient concentrations of oxygen, and
involves the breakdown of complex organic molecules into simple in organic
molecules. Dilution, sedimentation and sunlight also play a part in the
process. attached micro organisms in streams play a greater role than suspended
organisms in self-purification. Their importance increases as the quality of
the effluent increases since attached microorganisms are already present in the
stream, whereas suspended ones are mainly supplied with the discharge.
Effects on the biota
Organic pollution affects the organisms
living in a stream by lowering the available oxygen in the water. This causes
reduced fitness, or, when severe, asphyxiation. The increased turbidity of the
water reduces the light available to photosynthetic organisms. Organic wastes
also settle out on the bottom of the stream, altering the characteristics of
What is Inorganic Pollution?
Inorganic Pollution are things found
naturally but because of human production of goods have been altered to
drastically increase the amount of them in the environment (some examples
include arsenic, lead, as well as many different air pollutants).
Examples of Inorganic Pollution:
Our first experiment was aimed at
figuring out exactly how Organic and Inorganic pollution effect soil acidity
(Ph level) which can have a drastic affect on the environment; an example is
that in acidic ponds algae grows much more easily which can literally suffocate
fish, killing them. For our second experiment we are trying to see how plant life
actually grows in the soil that has an pollutant in it that will make its Ph
level lower than neutral, with a normal plant planted in regular soil as the
Classification of Inorganic chemical
Fig-2Classification of Inorganic chemical pollutants
Lists some of the pure-inorganic chemical pollutants and their
Table-1 Pure inorganic chemical
Pure-inorganic chemical pollutants
is a contributor to Alzheimer’s
is highly toxic to humans and is
chronic, or cumulative in human and animal organs
affects the gastrointestinal tract
and the central nervous system
is toxic to fish and aquatic life and
various plants and inhibits photosynthesis in terrestrial plants
at approximately 1 to 4 mg/l, can be
toxic to plants and at approximately 30 mg/l, can have physiological effects
on animals and humans.
affects metabolism and is quite toxic
to animals and humans; it is cumulative in the kidney and liver organs and
can cause death.
at levels above 100 mg/l is highly
toxic to animals and humans and can cause vomiting and liver damage.
can be fatal at 8 mg/l. At low pH, CN
forms hydrogen cyanide (HCN), which is a highly toxic, almond smelling
it is cumulative in animal and human
organs; with concentration greater than 0,5 mg/l causes lead poisoning.
Plumbism is a disease caused by lead that affects the central nervous system
of animals and humans.
Certain tests have been developed to
indicate water quality based on chemical characteristics that can be simpler,
less expensive or more indicative of water quality than a chemical compounds
tests. CaCO3 is used as a standard for many of the indicator
tests since its molecular weight is 100 and calculations are simplified.
Table-2 lists description of some of the Chemical Indicator Tests.
Chemical Indicator Tests
Table- 2Chemical Indicator Tests (Water
Quality control Handbook)
Chemical Indicator Tests
is an indicator of capacity of water
to react with a strong base to a designated pH. Titration with a standard
alkali solution to an end point of 3.8 pH is used for most wastewaters.
Acidity is reported in mg/l of CaCO3.
is primarily a function of the
carbonate(CO3), bicarbonate (HCO3) and hydroxide (OH)
content of wastewater. Titration with a standard acid to an end point of 8.3
pH is reported as phenolphthalein alkalinity and titration to an end point of
approximately 4.5 is reported as total alkalinity. Alkalinity is measured in
mg/l as CaCO3.
is a quantification of the ability of
water to carry an electric current. Most conductivity tests are accomplished
with an instrument.
is generally a measure of the
capacity of water to precipitate soap. Hardness is either calculated from the
results of separate calcium and magnesium tests or is determined from a
colour change when titrating a sample with ethylenediaminetetracetic acid
Oil and Grease
quantify substances that are soluble
in trichlorotrifluoroethane. These tests will include the presence of certain
sulfur compounds, organic dyes and chlorophyll that is not volatilised.
is used to indicate the intensity of
the acidic or basic character of a solution.
is a measure of the dissolved salts
in solution. mg/l
Various pollutant limitations are shown
in Table -3.
Chemical inorganic Pollutant Limitations:
Table-3Chemical Pollutant Limitations
(Water Quality control Handbook)
Drinking water protection
Fish & Widlife protection
11?g/l in soft water
1100 ?g/l in hard water
4 ?g/l in soft water
12 ?g/l in hard water
0,1x 96 hr LC50
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