What you'll learn
Every product has an environmental cost, from digging up raw materials to throwing it away. A life cycle assessment (LCA) is the method chemists use to work out that total cost, and recycling is one of the main ways of reducing it. For AQA GCSE Chemistry you need to know the four stages of an LCA, understand which parts are difficult to judge objectively, explain the benefits of reducing, reusing and recycling, and be able to compare two products using LCA data. This guide covers each stage in turn, the problem of subjectivity in LCAs, and how recycling saves energy and resources. By the end you should be able to carry out a simple comparison and evaluate how reliable an LCA really is.
Key terms and definitions
Life cycle assessment (LCA) — An assessment of the environmental impact of a product across its whole life, from raw materials to disposal.
Raw material — A natural substance, such as ore, crude oil or timber, used to make a product.
Finite resource — A resource that is being used up faster than it is replaced, such as crude oil or metal ore.
Recycling — Processing a used product so its materials can be used again to make something new.
Reuse — Using a product again for the same or a different purpose without reprocessing it.
Biodegradable — Able to be broken down naturally by microorganisms.
Landfill — A site where waste is buried in the ground.
Subjective — Based on opinion or judgement rather than measurement alone.
Core concepts
The four stages of a life cycle assessment
An LCA considers the environmental impact of a product at four stages:
- Extracting and processing raw materials — mining ore or extracting crude oil damages habitats, uses large amounts of energy, and can cause pollution of air and water.
- Manufacturing and packaging — making the product uses energy and may produce waste and pollutants; packaging uses further materials.
- Use and operation during its lifetime — some products use energy or resources while being used, and some release pollutants; a product that lasts a long time spreads its impact over more use.
- Disposal at the end of life — the product may go to landfill, be incinerated, be reused, or be recycled; each option has a different impact, including the energy used to transport and process the waste.
Transport and distribution are considered throughout, because moving materials and products between each stage uses energy and produces pollution.
What an LCA measures
An LCA looks at the use of resources such as water, energy and raw materials, and at the production of waste and pollutants at each stage. Some of these figures can be measured quite accurately — the amount of water used or the mass of a material, for example, can be quantified reliably.
Why LCAs are not fully objective
The difficulty is that the effect of pollutants is much harder to measure than a mass or a volume. Deciding how damaging a particular pollutant is, or how to compare damage to a habitat against the use of energy, requires value judgements. Because different people weigh these factors differently, two LCAs of the same product can reach different conclusions. This makes an LCA partly subjective, and it means LCAs can be misused — for example, a selective LCA might be produced for advertising to make a product look more environmentally friendly than it really is. Being able to say that an LCA is not purely objective, and to explain why, is a common exam requirement.
Reduce, reuse, recycle
The environmental impact of using resources can be lowered in three ways. Reducing means using less material in the first place, for example by making thinner packaging. Reusing means using a product again without reprocessing it, such as refilling a glass bottle. Recycling means processing the material so it can be made into something new. Reducing and reusing generally save more energy than recycling, because recycling still requires collection, sorting and processing.
Recycling metals
Metals are obtained from ores, which are a finite resource. Extracting a metal from its ore requires a great deal of energy — for example, aluminium is extracted by electrolysis, which uses enormous amounts of electricity. Recycling a metal usually involves melting and recasting it, which uses far less energy than extracting it from ore. Recycling therefore conserves the limited supply of ore, uses less energy, reduces the waste sent to landfill, and cuts the environmental damage caused by mining.
Recycling glass and other materials
Glass bottles can often be reused after washing, or crushed and melted to make new glass products. Different materials require different processes, and some, such as certain plastics, are harder to recycle because they must be separated by type first. Sorting and transport are part of the environmental cost, which is why reducing and reusing are preferable where possible.
Finite resources and sustainability
Many of the raw materials used to make everyday products are finite resources — they are being used up much faster than natural processes can replace them. Crude oil, used to make plastics and fuels, and metal ores, used to make metals, are both finite. Once they are gone, they cannot easily be replaced, so using them carefully matters for future generations. Sustainable development means meeting the needs of people today without stopping future generations from meeting their own needs. Recycling supports sustainability by making the existing supply of a material last longer, so less new raw material has to be extracted. This is why governments and companies increasingly design products to be recycled and encourage people to recycle rather than send waste to landfill.
Worked examples
Example 1: Listing the stages
State the four stages considered in a life cycle assessment. Extracting and processing raw materials; manufacturing and packaging; use during the product's lifetime; and disposal at the end of its life. Transport is considered between each stage.
Example 2: Comparing two bags
A shop compares a plastic bag with a cotton bag. The plastic bag uses less energy to make, but the cotton bag can be reused many times. How should the comparison be made? The comparison must consider the whole life cycle, not just manufacture. The cotton bag has a higher impact to produce, but if it is reused many times, the impact per use may be lower than repeatedly making and disposing of plastic bags. The number of times each bag is used is therefore essential to a fair comparison.
Example 3: Explaining why recycling saves energy
Explain why recycling aluminium is better for the environment than extracting new aluminium. Extracting aluminium from its ore uses electrolysis, which requires very large amounts of electrical energy. Recycling involves melting the metal, which uses much less energy. Recycling also conserves the finite ore, reduces mining damage, and cuts landfill waste.
Example 4: Evaluating an LCA
A company publishes an LCA showing its product is environmentally friendly. Suggest why this should be treated with caution. Parts of an LCA involve value judgements about the effects of pollutants, so it is not entirely objective. A company may present a selective LCA for advertising, leaving out stages that show its product unfavourably, so the assessment should be checked independently.
Common mistakes and how to avoid them
A common error is listing only manufacture and disposal. An LCA covers four stages, including the extraction of raw materials and the use of the product during its lifetime. Missing stages loses easy marks.
Students often state that an LCA is completely objective because it uses data. In fact, allocating numerical values to the effects of pollutants requires judgement, so LCAs are partly subjective and can differ between assessors.
Another mistake is treating recycling as though it has no environmental cost. Recycling still uses energy for collection, transport, sorting and processing — it is better than extraction, but not free.
When comparing products, do not compare a single use of one with the whole lifetime of the other. A fair comparison must use the same basis, such as impact per use.
Finally, do not confuse reuse with recycling. Reuse means using the item again as it is; recycling means processing the material into something new.
Exam technique for "Life cycle assessment and recycling"
Questions frequently give you a table of LCA data for two products and ask which has the lower environmental impact. Work stage by stage, quote figures from the table to support your points, and give a clear conclusion. Referring to the data is essential — vague answers score poorly.
"Evaluate" questions expect a balanced answer: give advantages and disadvantages, then a judgement. When asked about the reliability of an LCA, mention that pollutant effects require value judgements and that LCAs can be selective when used in advertising.
For recycling questions, the standard marking points are conserving finite resources, using less energy than extraction, and reducing landfill and mining damage. Learn these as a set, and be ready to apply them to a named metal such as aluminium or copper.
Quick revision summary
- An LCA assesses environmental impact over four stages: raw materials, manufacture and packaging, use, and disposal — with transport throughout.
- LCAs measure resource use, waste and pollutants, but assessing pollutant effects requires value judgements, so they are not fully objective.
- Selective LCAs can be used misleadingly in advertising.
- Reduce, reuse, recycle all lower impact; reducing and reusing usually save more energy than recycling.
- Recycling metals conserves finite ores, uses far less energy than extraction, and cuts landfill and mining damage.
- Fair comparisons must be made on the same basis, such as impact per use.