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A life-cycle assessment or LCA analyses the impact of a manufactured product.

The main stages analysed as part of a life-cycle assessment are:

1. making materials for the product from the raw materials needed
2. manufacturing the product
3. transport of the product (and raw materials)
4. using the product
5. disposing of the product at the end of its useful life

The life-cycle assessment is a complex process and judgements are not exact. For example, people do not always follow the disposal advice from the manufacturer.

Disposal methods may have both drawbacks and benefits. For example, incineration may emit harmful gases into the environment, but the energy released can be used to generate electricity.

At each stage a life-cycle assessment considers:

• use of raw materials (including water)
• use of energy
• release of waste substances into the environment

1. Raw materials

All the raw materials we need come from the Earth's crust, atmosphere or oceans, or are due to living organisms. Obtaining these materials has an impact on the environment, including:

• using up limited resources, such as ores and crude oil
• damaging habitats through quarrying, mining or felling trees

2. Manufacture

The manufacture of products has an impact on the environment, including:

• using up land for factories
• production of polluting waste (emitted into rivers or the atmosphere)

3. Transport

The transport of both the final product, and the raw materials used to make it, requires energy. The amount of pollutants released into the atmosphere varies according to the type of transport use and the length of the journeys that have to be made.

4. Use

The impact of a product on the environment during its use depends on the type product. For example, a wooden chair has very little impact unless it needs cleaning or repair. On the other hand, a car will have a significant impact.

5. Disposal

Most of the rubbish we throw away ends up in landfill sites but there are other methods of disposal.

Incinerators can burn polymer waste and use the energy to generate electricity that can then power people's homes.

Some materials can be recycled. During recycling, products are broken down into the materials used to make them. These materials can then be used to make something else.

Many items can be reused meaning they do not need to be disposed of at all (for example, glass milk bottles). This uses less energy than recycling them.

The method of disposal of old products has an impact on the environment, including:

• using up land for landfill sites
• release of waste gases during incineration
• use of energy and production of waste substances if the product is recycled
• reduction in impact if the product is reused