Reusing carrier bags is greenest, says agency LCA

A life-cycle analysis study of plastic carrier bags has highlighted the importance of reuse as a way of reducing environmental impacts. So called green cotton and biodegradable bags came out with a relatively poor performance.

A long-awaited life-cycle analysis (LCA) by the Environment Agency has been published, finding that the reuse of conventional, flimsy plastic carrier bags and more durable ‘bag for life’ plastic carriers take some beating as best environmental option.

The LCA, which began in 2004, was specifically aimed at considering the environmental impacts of designs of bags used in the UK (ENDS Report, June 2004). The agency set up an advisory board including representatives from the Industry Council for Packaging and the Environment (INCPEN), the British Retail Consortium (BRC), the Waste and Resources Action Programme (WRAP) and various government departments to ensure all of these bodies’ concerns were covered.

As well as the traditional lightweight high-density polyethylene (HDPE) bags widely given away in supermarkets, the study considered similar bags with additives designed to help them break down in the environment, more substantial ‘bags for life’ made of thicker, low density polyethylene (LDPE), non-woven polypropylene (PP) bags, paper bags, cotton bags and starch/polyester bags designed to be biodegradable.

The analysis covered environmental impacts from the manufacture of the bags, their transport to the supermarket and their disposal. No reuse was considered, and recycled content was not included to simplify the analysis. Nor was littering considered, even though this can be a significant downside of free plastic bags.

Parameters measured in the analysis included global warming potential, resource depletion, acidification, eutrophication, human toxicity, freshwater toxicity, marine toxicity, terrestrial eco-toxicity and photochemical oxidation contributing to air pollution.

The LCA found that the extraction and production of raw materials was the most important impact of the bags – in common with similar previous studies. The study assumed the bags would be made in China, with much of the power coming from the Chinese power grid – largely dependent upon coal-fired generation. This greatly increased acidification and ecotoxicity impacts.

End-of-life impacts accounted for 0.2% to 33% of overall global warming potential of the bags. The starch/polyester blend and paper bags were worst because of the methane contribution from landfill.

One of the most useful measures calculated was the ‘required reuse’ level, which is the number of times a bag would need to be reused before final disposal to bring its global warming potential to equal or below the level of a single conventional plastic carrier bag - 2.08 kilograms of carbon dioxide equivalent (see table).

Plastic bag reuse

Although this considers only one impact, it is remarkable that cotton bags would need to be reused 131 times to equal a conventional plastic bag, with no reuse.

But research shows that about 40% of such bags are reused by householders as bin liners. If that was factored in, a cotton bag would have to be reused 173 times before its climate change impact came down to the level of an ordinary carrier bag.

And if conventional bags are reused to carry shopping, the requirement grows again to improbable numbers.

It is hard to escape the conclusion that reusing ordinary or ‘bag for life’ products is the environmental optimum, at least in terms of global warming impact.

The results are bad news for companies such as Holland and Barrett which have adopted supposedly green no-plastic-bag policies, and charge their customers for cotton or jute alternatives.

But the results for starch/polyester degradable bags are also bad. Their degradation emissions in landfill and higher raw material and transport impacts means these have a poor environmental performance.

Responding to the analysis, British Retail Consortium (BRC) sustainability director Andrew Opie said: “We’re pleased to see the Environment Agency’s report acknowledges single-use carrier bags can have less impact than the alternatives. Yes, the plastic bag has become symbolic but this report confirms it is not the great environmental evil some would have us believe.”

BRC members signed up to a voluntary agreement to cut plastic bag use by 50% by spring 2009 following threats of a plastic bag tax (ENDS Report, December 2008). WRAP reported a 48% cut in summer 2009, but more recent progress has been mixed (ENDS Report, September 2010).

The consortium says efforts will continue, but Mr Opie added: “Agonising over bags misses the point. There are much bigger targets supermarkets are helping customers to work on, such as reducing food waste.

“To obsess over bags distracts consumers from making bigger changes to their habits which would do more to benefit the environment.”

The Welsh Assembly Government however is proceeding with a 5p carrier bag tax to start on 1 October.

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