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Study Session 7 Pollution: Types,Sources and Characteristics

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ContentsIntroduction 3Learning Outcomes for Study Session 7 37.1 What is pollution? 37.2 Physical nature of the pollutant 57.3 Sources of pollution 7

7.3.1 Domestic sources 87.3.2 Industry 97.3.3 Agriculture 97.3.4 Transport 10

7.4 Pathways of pollution 117.5 Sector of the environment affected by pollution 12

7.5.1 Water pollution 127.5.2 Air pollution 147.5.3 Soil and land pollution 14

Summary of Session 7 15Self-Assessment Questions (SAQs) for Study Session 7 16

2 of 18 Tuesday 22 March 2016

IntroductionYou were introduced to wastes and pollutants in Study Session 1, where we discussed theinteractions between humans and our environment. Pollution was defined as theintroduction into the environment of substances liable to cause harm to humans and otherliving organisms. Many human activities pollute our environment, adversely affecting thewater we drink, the air we breathe, and the soil in which we grow food.In this and the next study session we will look more closely at pollution. In this session youwill learn about the different types and sources of pollution and the various humanactivities that can cause pollution. We will also describe the ways pollution can affectdifferent sectors of the environment: water, air and soil. Study Session 8 describes someof the significant effects of pollution on the environment and on human health. It alsodiscusses options for preventing and controlling pollution.

Learning Outcomes for Study Session 7When you have studied this session, you should be able to:7.1 Define and use correctly all of the key words printed in bold. (SAQs 7.1, 7.2, 7.3and 7.4)7.2 Describe the main types of pollution. (SAQ 7.3)7.3 Describe the sources of pollution and the way pollutants reach the environment.(SAQ 7.4)7.4 Describe the main characteristics of water, air and soil pollution. (SAQ 7.5)

7.1 What is pollution?If you hold up a glass of water in front of you, how can you tell if it’s polluted? You wouldexpect drinking water to be colourless, odourless and transparent (not turbid withsuspended particulates). If it was not all of these things, then it could be polluted. If youwere looking at water in a river, it is unlikely to be as clear as drinking water in a glass, butyou could deduce it was probably not polluted if you observed that the water did not lookdirty or smell bad. You might also observe that animals were drinking the water without illeffects and fish were swimming in it. However, if the water was discoloured or had anunpleasant odour, or you could see dead fish floating on the surface you could concludethat pollution was the problem.Let us consider the human activity that could have caused the pollution. Imagine a riverthat flows through an area of land on the edges of a town. The water is used by thecommunity for drinking and other domestic uses and also for vegetable farming. Severalresidents use this water to irrigate small areas of land where they cultivate vegetables andmany of the farmers use fertiliser and pesticide to improve productivity (Figure 7.1).Fertilisers are made of chemicals such as nitrogen, potassium and phosphorus, which areessential plant nutrients. Pesticides are chemicals that destroy pests but can be harmfulto other forms of life – including humans.

Introduction


Figure 7.1 Farmers use fertilisers and pesticides on their vegetable crops to improveproductivity.

Imagine that one farmer has finished spreading the chemicals on his crop and decides towash the empty pesticide sack he has been using in the river. Later that day, it rainsheavily and rainwater is seen running off the field into the river. What do you thinkhappens? The river is receiving run-off containing fertiliser and pesticide chemicals thathad been applied to the crops, which is made worse by the farmer washing his sack thathad contained the pesticide. This could harm fish and other organisms living in the water –possibly killing them. The river is also used by the community so the chemicals could getinto drinking water that is consumed by humans. The river has been polluted by thecareless action of the farmer washing his sack and by the action of rainwater washing thechemicals into the river.Pollution always has a source and a recipient. The source is where the pollution comesfrom, that is, where the pollution is released into the environment. The recipient is wherethe pollution ends up, which may be a part of the environment or people or animals thatbecome contaminated or damaged.

� In the above example about the farmer washing the pesticide sack in the river, whatis the source and what is the recipient of the pollution?

� The pollution source is the activity of urban farming with pesticides and fertilisers andwashing sacks so that pollutants get into the river. In this example, the primaryrecipient is the water body that receives the pollutants. Other recipients are the

7.1 What is pollution?


people who drink the contaminated water and animals such as fish that also areaffected.

There are a number of ways of identifying pollution. These include finding symptoms ofdamage to aquatic plants and animals (such as dead fish), finding chemicals in the water,comparing the previous history of the quality of water with the present quality, and gettingcomplaints from water users. Even when a problem has been found, investigations toidentify the source may take time. For example, water samples from several differentpoints upstream and downstream will need to be analysed to locate precisely where theproblem originated.There are several different ways of classifying pollutants. They can be categorised bytheir physical nature, by their source, by the recipient or by the sector of the environmentaffected. In the following sections we will look at each of these classification groups

7.2 Physical nature of the pollutantPollutants may be in the form of gas, liquid, solid or energy.

� What polluting gases can you think of?� Greenhouse gases are pollutants that contribute to human-induced climate change

(mentioned in Study Session 1). The main greenhouse gases are carbon dioxide,methane and nitrogen oxides.

Liquid pollutants usually come from liquid waste. Liquid waste includes human excreta(both faeces and urine), industrial wastewaters and other forms of waste from water-usingactivities (Figure 7.2). Factories generate liquid waste from activities related to washing inthe manufacturing process, cleaning objects and chemical mixing. Sewage is a mixture ofhuman excreta from water-flushed toilets and other wastewater from houses andbusinesses. Sewage and human waste from overflowing septic tanks and latrines arefrequent sources of pollution.

7.2 Physical nature of the pollutant


Figure 7.2 Car washing produces contaminated water containing engine oil and fuel,which may flow into rivers and lakes.

Urban run-off is another type of liquid waste that can cause pollution. Rainwater washesmany different types of waste from the land surface into lakes and rivers. Urban run-offcan contain a lot of organic matter. This may come from open defecation or inappropriatehandling of organic wastes produced from households and businesses. Organic matterincludes anything that is derived from living organisms, such as human and animalwastes, decaying plants and food wastes.Pollutants also come in solid form. Plastic bags are one of the most common solid wastes.Solid waste is any solid material that is assumed not to be useful and is therefore thrownaway. Factories, businesses and households produce different kinds of solid waste suchas paper, plastics, metals, chemicals in solid form, pieces of cloth or food and animalremains (Figure 7.3). Sometimes you may have observed faecal matter discarded withsolid waste, which adds to the problems.

Figure 7.3 Solid waste is an unsightly problem in many towns.

There is a fourth type of pollution that is common in urban communities. This is energy inthe form of noise pollution. Noise pollution means unacceptable levels of noise in work,residential and recreational places. Noise makes it difficult to have a conversation andalso irritates and disturbs us and in the long term can damage our hearing. Loud musicfrom music shops and clubs in an urban community is a known source of noisedisturbance. Such noise may please some, but it disturbs many other people because itinterferes with communication in the daytime and sleeping at night.

7.2 Physical nature of the pollutant


7.3 Sources of pollutionAnother way of classifying pollution is by the sector of human activity that produces it.Before we look at the various sectors, there is an important distinction to be made aboutpollution sources. Sources of pollution can be categorised as point or non-point sources.Point sources are identifiable points or places that you can easily locate. An example is adiesel truck that produces visible black exhaust fumes from its tailpipe. Liquid wastereleased from a pipe into a river is another example (Figure 7.4). A non-point source(also known as ‘diffuse pollution’) is one where it is difficult to identify the exact origin ofthe pollution. A good example is floodwater that washes all types of waste from the land(possibly including faecal matter) into a river. In this situation you cannot identify theindividual or household or establishment that has caused the water pollution (Figure 7.5).

Figure 7.4 Point source: liquid waste entering a small stream.

7.3 Sources of pollution


Figure 7.5 Non-point source: solid waste and faecal matter are distributed all along thebanks of the river so no single source can be identified.

� Can you think of examples of point and non-point source pollution from earlier in thisstudy session?

� The farmer washing his sack is an example of a point source because you couldidentify where he washed his sack. However, the pesticide washing from the field isan example of a non-point source. The pollutant would wash into the river at severalplaces, and could possibly also have come from other fields. This is an example ofhow difficult it can sometimes be to accurately identify the source.

7.3.1 Domestic sourcesDomestic sources of pollution include toilets, latrines and wastewater from kitchens andbathrooms. If these wastes are properly contained and prevented from getting into theenvironment, they will not cause pollution. However, frequently this is not the case. Opendefecation obviously releases human waste into the environment, which can then bewashed into rivers and other surface waters.

� What types of organic waste are produced by a typical household?� The organic wastes from domestic sources include human excreta and also food

waste and other kitchen waste such as cooking oil residues.

Solid wastes from households and also from shops, markets and businesses include foodwaste, packaging materials and other forms of rubbish. Domestic sources are alsoresponsible for gaseous pollutants in the form of smoke and carbon dioxide from domesticfires.



7.3.2 IndustryPollution from the industrial sector in Ethiopia has been on the rise, posing a seriousproblem to the environment. Many industrial processes produce polluting wastesubstances that are discharged to the environment, frequently through chimneys (to theair) or through pipes (to surface water) (Figure 7.6). Among the most polluting industriesare food processing, tanneries and textiles with processing plants and factories thatproduce liquid effluents which are discharged into rivers, often without treatment (Ademeand Alemayehu, 2014; Wosnie and Wondie, 2014). In practice, rivers frequently receivepolluting discharges from many different sources all at the same time. The Little AkakiRiver in Addis Ababa, for example, is polluted by several different industrial sources aswell as by domestic wastes (Tegegn, 2012).

Figure 7.6 Air pollution from an industrial source.

7.3.3 AgricultureLike industry, agricultural activities are also increasing in Ethiopia, and changing too.Nowadays, agricultural activities in Ethiopia use more pesticides and fertilisers. Ethiopiaimports over 3000 tons of various types of pesticides annually (Federal EnvironmentProtection Authority, 2004). Fertiliser use in Ethiopia has increased from 140,000 metrictons in the early 1990s to around 650,000 metric tons in 2012 (Rashid et al., 2013).Fertiliser contains phosphate and nitrate and if these reach water bodies they can causeexcessive plant growth (Figure 7.7).



Figure 7.7 Plant fertilisers can encourage excessive growth of vegetation if they arewashed into lakes and other water bodies.

Agriculture is also responsible for gaseous pollutants in the form of methane produced bylivestock and solid pollutants from crop residues, packaging materials and other wastessimilar to those produced domestically. Animals also contribute to waste products andpotential pollutants with their excrement.

7.3.4 TransportDo you live in a city or have you visited a city close to where you live? If so you will nodoubt be familiar with the variety of vehicles on our roads (Figure 7.8). Some are smallcars, others are heavy motor trucks. These vehicles differ not only in their size, but also byusing different types of fuel such as petrol, diesel, and blended fuel (10% ethanol andpetrol). If you observe the tailpipe of diesel engine vehicles, you will have seen the blackexhaust gas produced. The intensity of the black colour is greater for poorly maintainedvehicles, to the extent sometimes that it makes the air hazy or smoky and causes coughsand eye irritation. The lack of a policy to remove old vehicles from the roads adds to theproblem. Tiwari (2012) found that nearly a third of vehicles in Addis Ababa were over 30years old, resulting in high levels of tailpipe emissions. Traffic jams, common in all bigcities, make the problems worse.



Figure 7.8 Pollution from exhaust is worse if vehicles are poorly maintained.

7.4 Pathways of pollutionWe said earlier that pollution always has a source and a recipient. The pathway ofpollution is the way the pollutant moves from the source, enters into the environment, andfinally how it reaches the human body or other recipient. The pathway between sourceand recipient can take several different forms depending on the type of pollutant. Primaryrecipients for pollution are water, air, and soil. Pollutants usually reach humans throughthe consumption of contaminated and polluted water and food, and breathing polluted air.Once released into the environment, the worst effects of many pollutants are reduced byone or more of the following processes:

l Dispersion – smoke disperses into the air and is no longer noticeable away from thesource.

l Dilution – soluble pollutants are diluted in the water of a river or lake.l Deposition – some suspended solids carried in a river settle (are deposited) on the

river bed.l Degradation – some substances break down (degrade) by natural processes into

different, simpler substances that are not polluting.

7.4 Pathways of pollution


In each case the effect is to reduce the concentration of the pollutant. Concentration is ameasure of the amount of the substance in a known volume of water or air. The units usedfor water pollutants are usually milligrams per litre (mg/l, also written as mg l-1), althoughsometimes you may see ppm which stands for ‘parts per million’.These processes do not apply to all pollutants. There are some persistent pollutantswhich remain intact when released into the environment because they do not break downby natural processes. These are described in Study Session 8.

7.5 Sector of the environment affected bypollutionClassifying pollution by the sector of the environment affected – water, air, soil and land –is probably the most commonly used method.

7.5.1 Water pollutionWater pollution can affect surface water such as rivers and lakes, soil moisture andgroundwater in aquifers, and the oceans. As you know from Study Session 4, the actionsof the water cycle connect all these different reservoirs of water. For example, a pollutedriver will discharge into the ocean and could damage the marine environment. However,the volume of water in the ocean can disperse and dilute the pollutant so that its worsteffects are only felt near the mouth of the river.Water pollution is characterised by the presence of excess physical, chemical orbiological substances that change the qualities of the water and are capable of causingharm to living organisms. We mentioned earlier that natural or unpolluted water iscolourless, odourless and transparent. Water that tastes or smells bad or is cloudy can besaid to have the symptoms of water pollution. However, some water pollutants cannot beseen or tasted, for example some chemicals, such as pesticides, and most of the micro-organisms that cause waterborne diseases. So, water pollution involves more than justthe appearance of the water. Polluted water should not be used for drinking, washing,bathing or agriculture. If polluted water is used by humans, then it can adversely affect thebody in different ways, depending on the type and concentration of pollutant.You also read in Study Session 4 that most rivers and streams in Ethiopia containsignificant quantities of suspended solids that are carried along in the flow and make thewater look brown in colour, especially in the rainy season (Figure 7.9). Most of the solidsare fine particles of soil that have been washed into the river from surrounding land byrain, often following cultivation or construction work. Large quantities of solids in the watercan reduce light penetration into the water which can affect the growth of plants.

7.5 Sector of the environment affected by pollution


Figure 7.9 Akaki River: suspended solids carried in the flow make the water look brown.

Biological water pollutants are micro-organisms that are harmful to humans and otherforms of life. They are responsible for many different waterborne diseases. The originalsource of these pollutants is people or animals already infected with the micro-organismsconcerned. If faeces from infected people are not correctly contained and treated, thepollutants can get into surface and groundwater. The main groups of biological pollutantsare bacteria, viruses, protozoa and helminths (worms).Chemical water pollutants take many different forms depending on their source. Theyinclude plant nutrients (compounds of phosphorus and nitrogen) used as fertilisers which,as you read earlier, can be washed from fields into rivers. These nutrients are alsoproduced by the breakdown of human and animal wastes and are common pollutants ofsurface waters.



Chemical pollutants also include heavy metals, pesticides and other persistentpollutants. Heavy metals are a group of toxic chemical pollutants that contain compoundsof persistent metals such as mercury, cadmium, lead and chromium. The presence ofheavy metals in water in excess of acceptable levels can cause illness and death amonganimals and humans if consumed through drinking and food (Zinabu and Pearce, 2003).Persistent organic pollutants (POPs) are also toxic to humans and wildlife. Theyinclude many different synthetic organic chemicals manufactured for use as pesticidesand in industrial processes, e.g. DDT, aldrin and PCBs (polychlorinated biphenyls). Manyof these persistent chemicals have been banned in some countries. Their persistence inthe environment creates specific problems that are described in Study Session 8.

7.5.2 Air pollutionAir pollution can exist at all scales, from local to global, and can include gases and solidparticles. It can affect you in your own home, or in your town or city, and can contribute toglobal atmospheric changes. The most common sources of air pollution in the urbancentres of Ethiopia include the burning of wood, charcoal and other biomass fuel byhouseholds, small businesses such as bakeries, manufacturing industries, and vehicles.Air pollution is defined as the presence in the air of abnormal amounts of chemicalconstituents capable of causing harm to living organisms. Clean air consists of nitrogen(78% by volume), oxygen (21%) and trace gases (< 1%). Polluted air may containparticulate matter (such as black soot) and many different gaseous chemicals such ascarbon monoxide, carbon dioxide, nitrogen oxides, sulphur oxides, ozone, nitrates,sulphates, organic hydrocarbons and many others. Many of these are also found in cleanair as trace gases but they become pollutants if present in abnormal quantities.The emission of black smoke is an indication of intense pollution. However, not all airpollution is visible or can be smelled. Gases such as carbon monoxide and carbon dioxideare invisible and odourless. Carbon monoxide is very dangerous to humans. It can beproduced by inefficient burning of fuel (for example a charcoal stove in a home withinadequate air supply) and if breathed in large quantities it can be deadly. Carbon dioxideis an important pollutant that is involved in climate change. (You will learn about in climatechange in Study Sessions 9, 10 and 11.)

7.5.3 Soil and land pollutionSoil pollution, also called land pollution, is linked to water pollution. Liquid wastescontaining toxic chemicals or pathogenic micro-organisms on the surface of the land canseep slowly into the soil and may percolate down to contaminate groundwater, which canaffect people using springs or wells in the area. Possible sources include open defecation,pit latrines or leaking storage containers for industrial chemicals and wastes.Solid waste can cause soil pollution. A collection of solid wastes in one place or scatteredaround is unsightly and might smell bad to you as you pass by (Figure 7.10). Householdwaste typically consists mostly of food waste that will gradually decompose. Thisproduces a bad odour and attracts insects and rats, both of which contribute to thetransmission of disease. As the waste decomposes it produces a liquid called leachatewhich trickles down into the soil. Leachate is a highly concentrated liquid pollutant thatmay contain toxic chemicals and pathogenic micro-organisms as well as high levels of



organic compounds. Rainwater falling on, and washing through, solid waste adds to theproblem.

Figure 7.10 Urban solid waste contains a mixture of many different types of waste andcan pollute soil and water if it is not contained and managed correctly.

Summary of Session 7In Study Session 7, you have learned that:

1 Environmental pollution is the result of human activity and development that occurswhen physical, biological and chemical agents are released to the environment insuch quantities that the pollution adversely affects human health and damages theenvironment.

2 Pollution can be classified by its physical nature, by its source, by its recipient, by thesector affected or by its effects.

3 Pollution may be in the form of a gas, liquid, solid or energy.4 Sources of pollution may be point sources, which are easily identified, or non-point

sources, where the pollution comes from diffuse sources that are not easy topinpoint.

Summary of Session 7


5 There are different types of pollution: water pollution, air pollution, solid wastepollution and noise pollution. All of these can be found in urban areas.

6 The main sources of pollution are household activities, factories, agriculture andtransport.

7 Once they have been released into the environment, the concentration of somepollutants is reduced by dispersion, dilution, deposition or degradation.

8 Water can be contaminated by physical pollutants (solid material), biologicalpollutants (such as bacteria that cause waterborne diseases), and many differentchemical pollutants.

9 Air pollution can be caused by gases or solid particulates.10 Soil pollution is linked to groundwater pollution. Solid waste can produce highly

polluting leachate which contaminates soil groundwater.

Self-Assessment Questions (SAQs) forStudy Session 7Now that you have completed this study session, you can assess how well you haveachieved its Learning Outcomes by answering these questions.

SAQ 7.1 (tests Learning Outcome 7.1)Why is a point source of pollution easier to identify than a non-point source ofpollution?

AnswerPoint sources of pollution are easier to identify because they come from points orplaces that you can easily locate, such as a pipe discharging waste into a river. A non-point source is more difficult to identify because it does not come from just one place,but can come from a wide area, for example fertiliser washing off a number of fields orfloodwater that washes waste from latrines.

SAQ 7.2 (tests Learning Outcome 7.1)Rewrite the sentences below using terms from the list provided to fill the gaps:concentration, heavy metals, organic matter, persistent pollutant, sewage.……………… consists of human excreta and wastewater. It has a high ………………of ………………Some pollutants, called ………………, do not break down naturally in the environment.Examples are mercury, cadmium and other ………………

AnswerSewage consists of human excreta and wastewater. It has a high concentration oforganic matter.Some pollutants, called persistent pollutants, do not break down naturally in theenvironment. Examples are mercury, cadmium and other heavy metals.

Self-Assessment Questions (SAQs) for Study Session 7


SAQ 7.3 (tests Learning Outcomes 7.1 and 7.2)Describe what is meant by the terms liquid waste and solid waste, using examplesfrom your own experience to illustrate your answer.

AnswerLiquid waste is liquid material that is thrown away, or discharged into the environment.From the household you might include human excreta (both faeces and urine) andother wastewaters. In your area you might also see urban run-off when rain washeswaste from the land surface. You might also see liquid waste discharged from factoriesthrough a pipe into a river.Solid waste is any solid material that is assumed not to be useful and is thereforethrown away; examples that you might use include food waste, cloth, paper and plasticthat are thrown out from your own household or that you see in the area where youlive.

SAQ 7.4 (tests Learning Outcomes 7.1 and 7.3)For the scenarios (a) to (d), fill in the table below to show the pollutant, the source ofpollution, the possible pathways and the recipients:

(a) A farmer washes an empty pesticide sack in a river; the river flows into a lakewhich is used for drinking water by people from a local town.

(b) Rain falls on a waste dump used to collect household waste; the waste dump isn’tproperly sealed and liquid percolates down into the soil and into groundwater thatis extracted from a nearby well for domestic use.

(c) A tannery based in a town produces liquid waste that contains organic matter andchemicals used in the tanning process; this effluent is discharged into the localriver which flows out of the town and through a nature park.

(d) A bus driving through a busy town emits black smoke from its tailpipe.

Pollutant Source Pathway Recipient

(a)

(b)

(c)

(d)

Answer

Pollutant Source Pathway Recipient

(a) pesticide agriculture through the river lake, humans

(b) leachate domestic /household

through soil andgroundwater

soil,groundwater,humans

(c) liquid effluent (organic matterand tannery chemicals)

industry through the river river, humans,wildlife



(d) black smoke transport through the air humans

SAQ 7.5 (tests Learning Outcome 7.4)Describe how water pollution can change the characteristics of water.

AnswerNatural or unpolluted water is colourless, odourless and transparent. Water pollutionchanges the characteristics of water by the presence of excess physical, chemical orbiological substances that change the qualities of the water and are capable of causingharm to living organisms.Polluted water can taste or smell bad or be cloudy. Polluted water can containsuspended solids that make the water look brown in colour; most of the solids are fineparticles of soil that have been washed into the river by rain from surrounding land.Large quantities of solids in the water can reduce light penetration into the water whichcan affect the growth of plants.Water pollution changes more than just the appearance of the water. Polluted watercan also contain chemicals, such as pesticides, fertilisers and heavy metals that aretoxic. Polluted water also can contain biological substances such as organic matterand micro-organisms that cause waterborne diseases.



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