Living things produce waste materials, such as urine and faeces. Humans produce these, too, but they also produce other waste materials. These materials can pollute the environment. They include:

• household and industrial rubbish
• chemicals from industrial processes
• smoke from burning fuels
• harmful gases from burning fuels

Landfill sites

Rubbish does not vanish when it is thrown away. A lot of it is buried in landfill sites. These may be disused quarries or rough ground that cannot be used for farming or housing. When landfill sites are full of rubbish, they are covered in soil and planted with trees and bushes.

Recycling rubbish is important because fewer landfill sites are needed, and the materials in the rubbish are re-used.

Fertilizers

Fertilisers are chemicals used by farmers to help their crops grow well. Rain can wash fertilizers off the fields and into rivers. This causes water plants to overgrow and block out the light. Other plants die as a result. They use up oxygen as they rot away, and fish and other animals suffocate. This process is called eutrophication.

Smog

Smoke from burning fuels makes buildings turn black. With other waste chemicals in the air, it can form smog. This makes the air hazy, especially over large towns and cities. The polluted air can make it difficult to breathe.

Acid rain

Acidic gases such as sulfur dioxide are produced when fossil fuels like coal, oil and gas burn. Sulfur dioxide dissolves in the clouds and causes acid rain. This damages buildings, trees and harms life in rivers and lakes. It also causes chemical weathering of rocks to happen much faster than normal.