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Pollutants are everywhere. If I asked you to think about what a pollutant is, what would come to mind? Maybe the fumes spewed out from the cars we drive, the bleaches we use, or the litter present in the bins we pile up every day. The fact is, all of those are right. Pollution takes many different forms. Polluting chemicals…

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Pollutants are everywhere. If I asked you to think about what a pollutant is, what would come to mind? Maybe the fumes spewed out from the cars we drive, the bleaches we use, or the litter present in the bins we pile up every day. The fact is, all of those are right. Pollution takes many different forms. Polluting chemicals endanger the environment, ecosystems, and human health so knowing what they are and where they come from is essential. There are a variety of dangerous pollutants stemming from human activity that cause serious damage to our planet. Today we shall be covering the various types of pollutants and their sources.

Pollutant Definition

Parts of the environment that can be polluted are the atmosphere, water, and soil.

A pollutant is any particle, molecule, compound, or energy that disturbs the natural composition of the environment.

Humans, plants, and animals require very specific environmental conditions to survive so pollution can lead to negative impacts on human health and the breakdown of ecosystems.

Pollution is the presence of chemicals or forms of energy that alter the composition of the environment away from the norm.

Primary pollutants are substances released from initial pollution, whereas secondary pollutants are released as a consequence of the effects of primary pollutants.

List of pollutants

There are many types of pollutants you need to come to terms with in environmental science. Here is a list of the most important and dangerous ones:

Examples of pollutants

Let's have a look at these pollutants in more detail:

Smoke (PM10)

Smoke is a form of particulate matter shrouded in gas and normally contains carbon, condensed tar, or ash. Smoke is produced as a by-product of the incomplete combustion of fossil fuels and biofuel. The release of smoke is prominent in highly industrial areas and from old, energy-inefficient cars. Smoke can cause respiratory problems, high blood pressure, and cancer if inhaled by humans and animals. Areas shrouded in smog will be displeasing to look at too, and will block out sunlight.

PM10 simply means particulate matter which has a diameter of less than 10 microns (1 micron is 0.0001cm).

Smoke in the atmosphere will increase the Earth's albedo effect (amount of infrared radiation reflected back into space) and cool the planet.

China experiences a 'Winter smog' each year which stems from an increase in small-scale coal burning. This smog is so intense that cities are forced to shut down roads, schools, and airports.

China Winter smog

Figure 1: 'Winter smog' in China, via Wikimedia Commons.

Acid Precipitation

Acid precipitation (acid rain) is rainfall that has a pH of less than 5.2 meaning it is acidic enough to corrode material and cause damage. Acid rain forms from the reaction between nitrous oxide/sulphur dioxide emissions and water in clouds. Nitrous oxides and sulphur dioxide are released as:

  • By-products from the burning of fossil fuels
  • Smelting of sulphide ores
  • Industrial methods using high temperatures (such as the Haber-Bosch process).
  • Waters high in nitrogen and sulphur content can evaporate and form acid rain as well.

Acid rain can damage habitats, corrode rocks and buildings, and pollute waterways.

Smelting involves the heating of metal ore to extract the metal on its own.

Sulphur dioxide is extremely dangerous in the stratosphere too. They will initiate the formation of free radicals that break down ozone and reduce the atmosphere's ability to absorb ultraviolet radiation.

Nitrous Oxides

Nitrous oxides are any molecules with the formula NOx. These molecules are formed from the incomplete combustion of fossil fuels, high temperature and pressure reactions involving nitrogen, and are released from the breakdown of agricultural fertilisers. As covered previously, nitrous oxides can react with atmospheric water vapour to form acid rain. Nitrous oxides are also greenhouse gases and contribute to the formation of photochemical smog and ozone (which acts as a greenhouse gas in the lower atmosphere).

First, peroxy-radicals react with nitrous oxides to form nitrous oxide
HO2 + NO → OH + NO2

Then, nitrous oxide is split up by ultraviolet radiation to form ground-level oxygen atoms.

NO2 + hν → NO + O, λ<400 nm (wavelength)

These oxygen atoms react with oxygen molecules to produce ground-level ozone.

O(3P) + O2 → O3


Hydrocarbons are organic molecules released from the incomplete combustion of fossil fuels. They can also be released from solvents and aerosol propellants. Volatile organic compounds (VOCs) come under the group of hydrocarbons. Some VOCs like benzene and butadiene have been shown to cause cancer. Some groups of hydrocarbons contribute to the greenhouse effect, while others cause the formation of ground-level ozone (photochemical smog).

1,3 butadiene is primarily from vehicle exhausts, whereas benzene comes from evaporation or the incomplete combustion of petrol.

Crude oil is the same as liquid petroleum and is extracted from porous rocks beneath the Earth's surface.

Vehicle exhaust

Figure 2: butadiene is released from vehicle exhausts, via Wikimedia Commons.

Carbon Monoxide

Carbon monoxide (CO) is a colourless, odourless gas that is released from the incomplete combustion of fossil fuels. Older, petrol and diesel using vehicles release lots of carbon monoxide, but stoves and chimneys can release CO too. Carbon monoxide can be seriously dangerous if inhaled. This is because it will bind to haemoglobin proteins (the ones that normally carry your blood around) and form carboxyhaemoglobin. This will reduce the amount of oxygen in your blood and can cause heart attacks and unconsciousness.

Carbon monoxide detectors are often installed in people's homes and work much like a smoke detector. When they sense carbon monoxide particles in the air, they will sound a siren.

Heat pollution

Heat pollution involves the temperature of a water source increasing above the norm because of an external source. Anthropogenic global warming from greenhouse gas emissions is causing global warming and this heat is being absorbed by the oceans. Industrial factories and power plants can release 'cooling water' into nearby waterways. This water is much warmer than rivers and lakes so causes heat pollution. Water cannot hold as much oxygen in warmer temperatures so oxygen availability will decrease. Species' metabolic rates and decomposition rates will increase in warmer temperatures further reducing oxygen levels.

Water does not hold as much oxygen at warmer temperatures because the particles have more kinetic energy so are moving around lots and have bigger spaces between them, allowing oxygen molecules to escape.

Oil Pollution

Oil pollution can stem from a variety of sources such as:

  • Oil tanker leaks
  • Pipeline leaks
  • Waste lubricating oil
  • Oil tanker accidents
  • Leaks from drilling sites.

Basically, any accidents or mistakes in the use or transport of oil will cause oil pollution. This can be extremely dangerous for aquatic ecosystems, oil will trap and drown species, poison them, and disturb feeding grounds. When wildlife come into contact with the oil they may experience hypothermia.

Oil released into the sea will be at much lower temperatures than the seawater, so will induce hypothermia in marine organisms.

Hypothermia is the condition of having a much lower body temperature than normal, and causes shivering, confusion, dizziness, and in extreme cases death.


Pesticides are manufactured in order to exterminate and deter species, so are very dangerous for wildlife in agroecosystems. Artificial pesticides may be specific to certain species, but you cannot ensure they do not affect any other species. Some pesticides target a wide range of pests and so can severely reduce biodiversity. When leached into nearby watercourses, pesticides will harm aquatic organisms. The reduction of biodiversity in agroecosystems from the use of pesticides will increase susceptibility to disease as the gene pool shrinks. Even if the pesticide targets a specific organism, you cannot account for all the interspecific relationships the organism may have with other species in the ecosystem and food web.

Biological control involves introducing the natural enemy to the pest in order to reduce damage to crops. This method can still have consequences for the dynamics of the ecosystem though so a measured approach must be taken.

Biomagnification is the presence of toxins in increasingly larger amounts as you go up the food chain. This is a result of a pesticide that has become a part of the ecosystem. This is called persistence.


Nutrient pollution is prominent in agricultural areas but can also occur in urban cities and towns. In agriculture, the overuse of nitrogen and phosphorus-containing fertilisers causes soils to become overloaded with nutrients.

  • High nutrient concentrations can impair the growth of some crop species, but cause the most damage when they run off as leachate.
  • Leaching will cause nearby waters to become over-concentrated with nutrients and algal blooms to form.
  • When aerobic decomposing bacteria break down these algal blooms they will suffocate the ecosystem of its oxygen, in a process called eutrophication.

Nitrogenous and phosphate compounds can be released into waters as sewage effluent as well. This sewage will contain huge numbers of microorganisms that break down the compounds (sucking up oxygen) and release nutrients into the water.

Leachate is water which has infiltrated and percolated through a permeable solid (such as soil) and taken some of the nutrients available in this solid.

Effluent is sewage or any form of liquid waste that is discharged into water.

Heavy Metals

There are a few heavy metals that can cause soil and water pollution that you should know:


Lead can get into waters by corrosion of lead pipes. The longer the water flows through pipes, the more likely it is to become polluted with lead (this is exacerbated in old and rusty pipes). Lead compounds are found in paint and some cosmetics, that can make their way into soils and waters after improper disposal. Lead is also a vital component of petrol, so incomplete combustion can release lead into the atmosphere as suspended particulates. If lead gets in the body, either through drinking water or inhalation, it can cause:

  • Kidney problems
  • Brain damage
  • Reduce haemoglobin production.

Lead can undergo biomagnification in ecosystems and bioaccumulation in human populations!

In the UK there are now regulations to prevent lead from being used in things like paint.


Mercury is naturally released from volcanic activity, rocks, and soils, but this only accounts for 10% of mercury emissions. Human activities such as incomplete coal combustion, cement production, and oil refining release lots of atmospheric mercury. Humans can come into contact with mercury by eating contaminated fish or inhaling mercury particulates. The compound methyl mercury can pollute waterways and cause biomagnification of aquatic ecosystems. Mercury ingestion can lead to neurological problems such as seizures, strokes, and memory loss.


Noise pollution involves a change in the relative volume of sound emitted from a certain area. Sources of noise pollution include:

  • Vehicle noise (aeroplanes and trains make huge amounts of noise)
  • Industrial noise (drills, heavy machinery)
  • Public noise (loudspeakers, concerts, festivals).

Noise pollution can cause hearing defects and stress in humans as well as disrupt migration and reproduction in ecosystems.

Pollutants - Key takeaways

  • Pollutants are any chemical, substance, or energy that causes a change to the environment.
  • The incomplete combustion of fossil fuels is the largest source of pollutants and releases smoke, carbon monoxide, hydrocarbons, nitrous oxides, lead, and sulphur dioxide.
  • Agriculture is another major source of pollution as intensive practices involve fossil fuels being burnt, as well as pesticides and fertilisers to damage soil and leach into nearby water.
  • Influxes of heat from climate change and power plants, oil spills, and noise are other types of pollution.
  • Some of the most damaging consequences of pollution to ecosystems are eutrophication of waters, biomagnification of poisonous chemicals in food webs, and corrosive acid precipitation.

Frequently Asked Questions about Pollutants

Smoke, sulphur dioxide, hydrocarbons (VOCs), carbon monoxide, greenhouse gases.

Sulphur dioxide and nitrous oxide.

Pollutants that are released because of the initial pollution (e.g., ground-level ozone from nitrous oxide emissions).

Primary pollutants are those released initially, and secondary ones are those released because of the primary pollutants.

Carbon monoxide and smoke are the greatest direct threats to human health.

Final Pollutants Quiz

Pollutants Quiz - Teste dein Wissen


What is a pollutant?

Show answer


A molecule, substance, or form of energy that causes a change to the environment.

Show question


Which gases react with water to form acid rain?

Show answer


Nitrous oxides and sulphur dioxide.

Show question


What chemicals form photochemical smog in sunlight?

Show answer


Volatile organic compounds (VOCs) and nitrous oxides.

Show question


What does PM10 mean?

Show answer


The particulate matter has a diameter of less than 10 microns.

Show question


How is carbon monoxide dangerous to humans?

Show answer


Carbon monoxide binds to haemoglobin and restricts the transportation of blood around the body.

Show question


Why are increasing water temperatures dangerous?

Show answer


Water cannot hold as much oxygen in higher temperatures so aquatic ecosystems will be affected.

Show question


What are some causes of oil pollution?

Show answer


Oil tanker leaks, oil tanker accidents, drilling site leaks, and waste lubricating oil.

Show question


What is bioaccumulation?

Show answer


The process by which a poisonous chemical becomes prevalent within living organisms.

Show question


What is biomagnification?

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When organisms contain an increasing amount of a poisonous chemical at higher trophic levels.

Show question


How does leachate cause eutrophication?

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Leached waters that are rich in nutrients will cause algal blooms. When these algal blooms are broken down by aerobic decomposing bacteria, the ecosystem's oxygen will be used up (eutrophication). 

Show question


How does lead make its way into drinking water?

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By the corrosion of lead pipes.

Show question


What are some examples of human activity that release mercury into the atmosphere?

Show answer


The incomplete combustion of coal, cement production, and oil refinery.

Show question


What are the potential effects of mercury poisoning?

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Neurological damage such as memory loss, seizures, and strokes.

Show question


What is effluent?

Show answer


Sewage or any liquid waste that is discharged into water.

Show question


What is biological control?

Show answer


The introduction of the natural enemy to the pest in order to reduce pest populations.

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