Life Cycle Assessment (AQA GCSE Chemistry: Combined Science)

• A life cycle assessment (LCA) is an analysis of the overall environmental impact that a product may have throughout its lifetime
• The cycle is broken down into four main stages which are:
  • Raw Materials
  • Manufacture
  • Usage
  • Disposal

Lifecycle assessment

Diagram showing the four stages in a life-cycle assessment

Raw materials

• Obtaining the necessary raw materials has an impact on the environment which may include:
  • Using up limited resources such as ores and crude oil
  • Damaging habitats through deforestation or mining

Manufacturing

• Manufacturing processes also have an impact on the environment which may include:
  • Using up land for factories
  • The use of fossil fuelled machines for production and transport
  • Production of waste

Use

• Usage of a product may also affect the environment although it depends on the type of product
• For example, a wooden desk has very little impact whereas a car will have a significant impact (air pollution)

Disposal

• The disposal of outdated products has an impact on the environment which may include:
  • Using up space at landfill sites
  • Whether the product or its parts can be recycled

How is a lifecycle assessment carried out?

• A life cycle assessment is carried out using the data of a given product and the criteria of the assessment
• Some stages are easily quantifiable, e.g. the amount of water used during manufacturing of a product or quantity of waste materials produced
• However, other stages are more difficult to allocate a numerical value to, e.g. the polluting effect of a product 
• In these cases, people can make a value judgement about their effect but this is not an objective process and different people may allocate different values, or they may be biased
• Rarely is there a perfect product with zero environmental impact, so often a compromise is made between environmental impact and economical factors

Lifecycle assessment (LCA)

• An LCA can be carried out on plastic and paper shopping bags

A life cycle assessment of paper and plastic shopping bags

	Plastic	Paper
Raw materials	Crude oil is a finite source which requires a lot of energy to process	Recycled paper or tress. Making paper requires more energy than recycling paper but much less than making plastics
Manufacture	Fractional distillation cracking & polymerisation, not much waste as crude oil is completely used and cheap to manufacture	Pulping paper uses a lot of energy, sulfur dioxide and produces waste
Usage	Is reusable	Most are not reusable
Disposal	Can be recycled but is costly and produces pollution. Can be stored in landfill, takes up space and is not biodegradable	Biodegradable, non-toxic and can be recycled

Conclusion

• Considering both life-cycle assessments, the plastic bag may be the better option. Even though they aren’t biodegradable, they do have a much longer lifespan and thus are less harmful than paper bags
• Much depends on the usage of the item:
  • If the paper bag is recycled then it could be more favourable to use it
  • If the plastic bag is used only once, then then the argument for using plastic bags is less favourable