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Key findings of UK plastic bag report

By PRW Staff
Posted 2 March 2011
The amount of primary use required to take reusable bags below the global warming potential of HDPE bags with and without secondary reuse
Life Cycle Assessment of Supermarket Carrier Bags

Executive Summary

This study assesses the life cycle environmental impacts of the production, use and disposal of different carrier bags for the UK. In recent years, the relative environmental impacts of lightweight carrier bags and other options has been debated. By the Spring of 2009 leading supermarkets had halved the number of single use carrier bags used. However, questions still remain about the environmental significance of lightweight carrier bags, especially with regard to the wider debate on global warming.

The report considers only the types of carrier available from UK supermarkets. It does not examine personal bags nor carriers given out by other high street retailers. The report does not consider the introduction of a carrier bag tax, the effects of littering, the ability and willingness of consumers to change behaviour, any adverse impacts of degradable polymers in the recycling stream, nor the potential economic impacts on UK business.

The following types of carrier bag were studied:

• a conventional, lightweight carrier made from high-density polyethylene (HDPE);

• a lightweight HDPE carrier with a prodegradant additive designed to break the down the plastic into smaller pieces;

• a biodegradable carrier made from a starch-polyester (biopolymer) blend;

• a paper carrier;

• a “bag for life” made from low-density polyethylene (LDPE);

• a heavier more durable bag, often with stiffening inserts made from non woven polypropylene (PP); and

• a cotton bag.

These types of carrier bag are each designed for a different number of uses. Those intended to last longer need more resources in their production and are therefore likely to produce greater environmental impacts if compared on a bag for bag basis. To make the comparison fair, we considered the impacts from the number of bags required to carrying one month’s shopping in 2006/07.

We then calculated how many times each different type of carrier would have to be used to reduce its global warming potential to below that for conventional HDPE carrier bags where some 40 per cent were reused as bin liners. Finally the carriers were compared for other impacts: resource depletion, acidification, eutrophication, human toxicity, fresh water aquatic ecotoxicity, marine aquatic ecotoxicity, terrestrial ecotoxicity and photochemical oxidation (smog formation).

The study found that:

• The environmental impact of all types of carrier bag is dominated by resource use and production stages. Transport, secondary packaging and end-of-life management generally have a minimal influence on their performance.

• Whatever type of bag is used, the key to reducing the impacts is to reuse it as many times as possible and where reuse for shopping is not practicable, other reuse, e.g. to replace bin liners, is beneficial.

• The reuse of conventional HDPE and other lightweight carrier bags for shopping and/or as bin-liners is pivotal to their environmental performance and reuse as bin liners produces greater benefits than recycling bags.

• Starch-polyester blend bags have a higher global warming potential and abiotic depletion than conventional polymer bags, due both to the increased weight of material in a bag and higher material production impacts.

• The paper, LDPE, non-woven PP and cotton bags should be reused at least 3, 4, 11 and 131 times respectively to ensure that they have lower global warming potential than conventional HDPE carrier bags that are not reused. The number of times each would have to be reused when different proportions of conventional (HDPE) carrier bags are reused are shown in the table below.

• Recycling or composting generally produce only a small reduction in global warming potential and abiotic depletion.

For more information and to download the full report visit: www.environment-agency.gov.uk

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