Pollution is the introduction of harmful or poisonous substances into an environment.

With the growth of the human population, there has been an improvement in living standards in many areas. However, the demand for resources to support this larger population has also led to an increase in waste and pollution. Few environments remain unpolluted.

The three different types of pollution we will look at are:

  • Land pollution
  • Air pollution
  • Water pollution

Land Pollution

Waste that cannot be recycled is buried in landfill sites. These are large holes in the ground where we dump disposable waste. Toxic chemicals from the waste can get into the soil (e.g., pesticides or batteries).

If organisms eat the plants that are covered in these toxic chemicals, they can accumulate further up the food chain. This can poison predators in the process.

A landscape photograph showing a large landfill with mounds of waste and a yellow bulldozer working amidst the rubbish. In the background, rolling green hills stretch out towards distant misty mountains.

Air Pollution

Burning fossil fuels and other materials releases smoke into the air, which contains tiny solid particulates that can remain suspended in the atmosphere and contribute to smog. When inhaled, these particulates can cause damage to the lungs and respiratory system in humans and animals.

The combustion of fossil fuels releases carbon dioxide, a greenhouse gas that contributes to global warming. It also emits acidic gases, such as sulfur dioxide and nitrogen oxides. These gases dissolve in rainwater to form acid rain, which can have negative impacts on ecosystems and infrastructure.

An illustrated depiction of the acid rain cycle. The atmosphere shows 'Dry Deposition' of dust particles and gases, and 'Wet Deposition' of acid rain and snow. Factories emit smoke with pollutants, labelled 'NOx' and 'SOx', which are transformed into acid particles through 'Photo-oxidation'. The landscape below features dying plants from acid rain, surface flow into a lake, and the harmful effects on soil. A warning at the bottom indicates the harmful effects of acid rain on soil, forests, water bodies and the ocean.

Air pollution can be blown from one location to another by the wind. So, pollution in one area can produce acid rain in another area or even a different country.

Water Pollution

Farmers use pesticides and herbicides to protect their crops from pests and diseases. However, if runoff occurs, these toxic chemicals can wash into rivers and lakes and be absorbed by aquatic plants.

Over time, these chemicals can build up in the tissues of organisms through a process called bioaccumulation. As they cannot be broken down by these organisms, they can accumulate to potentially harmful levels. This poses a threat to the health of the affected organisms and the ecosystem as a whole.

An underwater illustration depicting bioaccumulation. On the far left, toxic chemicals are introduced into the water. Small aquatic organisms ingest these chemicals. As we move to the right, the concentration of toxins increases up the food chain: small translucent fish consume the organisms, and then larger pink fish feed on the smaller fish. At the bottom right, a large, spotted fish, which has consumed many of the smaller fish, shows the accumulated effect of the toxins. Green arrows indicate the flow of toxins through the food chain.

The amount of toxic chemicals will increase at each stage of the food chain. Therefore, the top predators will have very toxic levels, which can lead to death.

Nitrate fertilisers are soluble in water. So, when the rain washes it off fields, it can reach rivers and lakes, which can lead to eutrophication.

"Comparative illustration of eutrophication in aquatic habitats. On the left, a vibrant underwater scene titled 'Healthy water "living organisms"' showcases fresh water with a balanced ecosystem of fish, jellyfish, and various plants, indicating a natural harmony between organisms, oxygen, algae, and nutrients with sufficient sunlight for plant growth. On the right, a stark contrast depicts the 'Eutrophication "dead zone"', characterised by a thick green algal bloom layer, with limited aquatic life beneath and a label 'destruction of habitat'. This side explains the impact of excess nutrients, particularly nitrogen and phosphorus, leading to reduced oxygen, sunlight penetration, and the disruption of natural chemical cycles.

As there are a lot of nitrates and phosphates, the algae will grow rapidly and die. Microorganisms will break down the algae, using a lot of oxygen for respiration. This will reduce oxygen levels for the aquatic organisms nearby.

  • The algae also block off sunlight, so underwater plants die and rot.

Indicator Species

Certain plant or animal species, when present or absent, can indicate pollution levels in an ecosystem. For example, the absence of certain species that are sensitive to pollution may suggest that there are pollutants in the environment.

We can use indicator species to determine levels and types of pollution, including:

  • Water pollution
  • Air pollution

Water quality

Certain aquatic species, such as fish or amphibians, can be used as indicators of water pollution. The presence or absence of these species, or changes in their populations, can provide information about the health of a water body and the presence of pollutants. For example:

  • Polluted water is often seen in the presence of bloodworms or sludge worms.
  • Water that contains freshwater shrimp and stoneflies indicates that the water is clean and unpolluted.

Air quality

Air quality can be assessed using certain species of lichen as indicators. These organisms are sensitive to pollutants, such as sulfur dioxide.

In areas with clean air, a diverse range of lichen species can be found, whereas heavily polluted areas tend to have fewer species. By studying the presence or absence of lichen, we can estimate the overall air quality in a given location.

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