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Published on March 26th, 2018 | by Ricky Dunbar

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How Do We Carry Our Shopping Home Now?

March 26th, 2018 by  


Part I: Doing without lightweight plastic shopping bags

The environmental damage caused by lightweight, single-use plastic shopping bags is well known. Largely used as a disposable item despite the known negative environmental impacts, this simple carrying-aid is an excellent symbol of the harmful throw-away culture of modern industrialized society. Therefore, the success of the global national phase-out of these bags, which is already underway, is symbolically important for the environmental movement. Policymakers have the opportunity to approach the phaseout as a flagship measure for a broader elimination of waste. Unfortunately, after more than 25 countries have implemented policies to ban or disincentivize these bags, consumers in many jurisdictions are often left to choose between alternatives, not all of which are sustainable. In part I of this article, we’ll discuss the environmental credentials of the common alternatives, and in part 2, we’ll look at which emerging cleantech products might be the strongest candidates for the ideal shopping bag.

The not-so-innocent lightweight plastic bag

The incumbent bag causing the trouble is the generic lightweight plastic bag, which we’ll refer to here as the LP bag. Having become an entrenched part of consumerism in so many parts of the world, it is almost certain to be known to the reader. In fact, The Guinness Book of World Records has reportedly named these bags as “the most ubiquitous consumer item in the world.” LP bags are usually constructed from low- or high-density polyethylene (LDPE, HDPE) plastic and are typically characterized by the following properties:

Fossil-fuel derived: Predominantly from petroleum.

High durability: As stated in a 2009 paper in Phil. Trans. R. Soc. B, ‘the longevity of plastics is a matter for some debate, and estimates range from hundreds to thousands of years. It is considered that (with the exception of materials that have been incinerated) all of the conventional plastic that has ever been introduced into the environment still remains to date unmineralized either as whole items or as fragments’. Polyethylene (regardless of physical fragmentation) is not biodegradable, and so it may never fully degrade in the natural world.

Low value: They cost on the order of a couple of cents to produce and, in many parts of the world, have been given to shoppers for free.

Lightweight: Usually weigh less than 10 g.

Poorly regulated production and recyclability: Information on recyclability and additives is usually absent.

It is perhaps the combination of these properties, together with the fact that adequate disposal services are often lacking or poorly utilized, that enables the LP bag to inflict the environmental harm that it does (schematically shown in Figure 1). The lightweight nature of plastic bags means that even if they are disposed of correctly, wind can displace them from waste facilities and disperse them throughout the natural environment. One of the well-known negative impacts is ingestion by marine animals. The high durability of most plastics means that once ingested by an animal, for instance, due to being mistaken for food, the plastic won’t break down and can steadily accumulate in their stomachs. As stated in a press release  for a 2016 study published in Global Change Biology, “plastic ingestion can kill turtles by blocking the gut or piercing the gut wall, and can cause other problems through the release of toxic chemicals into the animals’ tissues.” This study estimated that around 52% of all sea turtles have ingested plastic debris. A similar study for seabirds estimated that 59% of investigated species and 29% of investigated individuals had ingested plastic. Note that the numbers of the above two studies pertain to plastic debris in general, not just debris from plastic bags.

While LP bags are recyclable in principle, metropolitan recycling rates are generally poor. Accurate national recycling rates are typically difficult to infer, but where values are reported, they are typically lower than 5%. Reasons for this low recycling rate can include low profitability for recyclers (which is, among other things, dependent on oil prices), rejection by recyclers due to food contamination, and technical challenges of dealing with such thin, lightweight materials in co-mingled recycling streams. As a consequence, collection services can often be lacking, even in regions that offer high-quality collection services for other recyclables. Therefore, the fate of most plastic bags is landfill, incineration or litter, which constitutes a large waste of (fossil-fuel) resources, in particular given the disposable fashion in which LP bags are typically used.

The production of LP bags is also typically poorly regulated, which means that labels indicating their recyclability are usually absent. Moreover, most plastics contain more than just the constituent polymer (which for LP bags is usually high-density polyethylene, HDPE); during processing, various chemicals, known as additives, are often added. Due to the typical lack of labeling in LP bags, it is generally unclear which additives have been added during production and what dangers they pose to humans and the environment if (or when) they leach out of the product. Those that have seen the label “BPA-free lining” on tins or plasticware have encountered the consequences of public concern over plastic additives. Plastic fragments are also known to act as marine transport vessels for harmful chemicals. In correspondence with CleanTechnica, Edward Kosior, Managing Director of Nextek, a resource management consultancy firm, summarized the current practice of plastic bag use as: “We are creating CO2 and dispersing materials into the environment in an uncontrolled way.”

Figure 1: Flowchart indicating the relationship between the properties of single-use plastic bags (ovals) and their negative environmental impacts (rectangles). Black circles indicate situations where two properties or practices combine to create a consequence, e.g. top-right circle: the lack of recycling for a product derived from fossil-fuels constitutes a depletion of finite resources. The link to the source for the plastic bag photo is included at end of the article.

There is another negative impact which could upset even those who aren’t the least bit concerned about dead turtles. In addition to finding their way into the natural environment, bags are also often scattered by the wind about man-made landscapes, the consequence of which is a reduction in the visual aesthetics of roads, towns, and cities. In other words, these bags, strewn gracelessly across parks and roadsides, can also be … eyesores.

Phasing out the lightweight plastic bag

Jurisdictions evidently have plenty of reasons to implement measures to phase-out LP bags. The most common approaches include banning them outright — such as has occurred in Bangladesh, China, California, and most recently Kenya — or gently nudging shoppers towards alternatives by prohibiting retailers from simply giving them to shoppers for free, which has happened in Ireland and England.

The outcomes have mostly been positive. China reportedly reduced LP bag consumption at supermarkets by 66% within the first year of its 2008 ban. In Ireland, the annual consumption of bags dropped rapidly from 328 to 21 per person (a reduction of around 95%) after the introduction of a levy. England’s bag use reportedly dropped by 85% within the first 6 months of the introduction of their levy.

In addition to reducing the circulation of LP bags, one would hope that these policies also increase the use of the “no bag.” According to data from at least two cities that have reported data on this, this does seem to have happened. For instance, in Palo Alto, USA, where legislation was introduced in 2009 to ban LP bags, the number of shopping trips which were performed without a bag of any kind increased from 8.7 to 41%. Similar results were observed in nearby San Jose. This increase in the “no bag” is important, as a reduction in consumption is generally the most effective waste reduction method (recall the Three Rs: Reduce, Re-use, Recycle — a list of approaches for minimizing environmental impact, arranged in order of decreasing preference). Such a significant increase in the “no bag” option, along with the reduction in LP bag use, is a compelling indicator of the importance of bans/levies.

However, after LP bags are eliminated from consideration, shoppers can be faced with multiple options with which to transport their purchases. The question arises: which of these has the lowest environmental impact?

The alternatives

Amongst the alternatives, it appears that one bag can be eliminated immediately: the oxo-degradable bag, which is a plastic bag with additives to promote degradation. A recent position paper from the Fraunhofer-Gesellschaft, a German research organization, states: “Plastic bags made of polyethylene (PE) with catalytic additives which enhance oxidative fragmentation (so-called oxo-degradables) are to be strictly rejected. They purposefully produce microplastics which can have severe consequences in the low trophic levels (plankton, bivalves, worms etc.) of the food chain.”

Given that oxo-degradable bags seem to be a bad choice, what options remain? Some of the common alternatives are (thicker) low-density polyethylene (LDPE) plastic bags, paper bags, non-woven polypropylene (NWPP) plastic bags, and cotton bags (Figure 2).

Figure 2: Commonly encountered shopping bags. Images used via Creative Commons 2.0 license — links are included at the end of this article.

But which bag is the right bag? A type of study called a life cycle assessment (LCA) is commonly used to attempt to answer this question. This approach attempts to quantify the impacts – such as global warming, acidification and eutrophication of water systems and ozone creation –  for each stage of the product’s life cycle, including production (“cradle”), transport, usage and end-of-life (“grave”). An advantage of an LCA is that the methodology is clearly defined (international standards exist) which promotes consistent implementation. However, results must be interpreted with caution, as they depend heavily on assumptions made, and combining multiple environmental impacts to assess overall sustainability can be difficult. For instance, if bag A is more benign than B in the categories of global warming and marine toxicity, but is more damaging in resource depletion and eutrophication, which bag is better?

Reviews of LP bag policies performed on behalf of governments often to tend to cite, and form their conclusions based on, LCA studies. The conclusions of one of the most recent reports (released in 2014) generally reached the same conclusions as earlier studies. All studies indicated that reusable bags are preferable to disposable bags. Paper bags, perhaps counter-intuitively, were considered more environmentally damaging than reusable plastic counterparts. Cotton bags are also typically found to be more environmentally damaging than other reusable options, due to reasons of toxicology and eutrophication commonly associated with cotton production. Almost all of these major studies identified one bag in particular as being among the most sustainable options: the non-woven polypropylene (NWPP) bag (pictured in Figure 2).

Can we now, safe in this knowledge that the majority of LCA studies identify NWPP bags as one of the best alternatives to LP bags, use them to carry our shopping home without a care? NWPP bags certainly have many good properties, such as good strength-to-weight ratios and durability, but they have major shortcomings too. Let’s take a closer look.

The current solution

Although these LCA studies supporting NWPP bags may have been carried out with the greatest of care, they all share one major flaw: they are all a reflection of what could be done with existing materials, processes, disposal facilities, and energy mixes at the time the study was performed. In other words, they identified the best option that is immediately available, but did not attempt to speculate on the best options that will become available in the future. This particular danger of interpreting LCAs was pointed out in the 2016 report The New Plastics Economy: Rethinking the future of plastics, released by the Ellen Macarthur Foundation.

In other words, the studies – and the policies that were implemented on the weight of them – may have successfully identified the least unsustainable solution immediately available, but this doesn’t mean the solution is actually sustainable.

One of the key factors in determining sustainability is the end-of-life disposal. Recycling is generally considered to be a desirable solution. However, the effectiveness of recycling varies markedly between materials. This is particularly true for plastics. A major distinction is drawn between closed-loop recycling, where products are recycled into the same product of the same quality, and down-cycling (or cascaded recycling), where the recycled materials are considered to be of a lower quality. Closed-loop recycling is generally considered superior, as the recycled materials retain more of the original value. In practice however, virtually none of the currently available plastics (one exception being Nylon 6) are infinitely closed-loop recyclable, and eventually other options, such as down-cycling must be used.

Few would disagree that one criterion for a truly sustainable solution must be that the bag needs to be highly amenable to recycling, ideally in a closed loop. Unfortunately, NWPP bags do not appear to meet it. In a 2009 review paper on plastics recycling, it was listed that the closed-loop recyclability of PP was possible, in theory. [Polystyrene was also classified in that way, whereas for HDPE, polyvinyl chloride (PVC) and LDPE, some closed-loop recycling occurs whereas polyethylene terephthalate (PET) can be readily closed-loop recycled]. It also stated that “the only parts of the post-consumer plastic waste stream that have routinely been recycled in a strictly closed-loop fashion are clear PET bottles and recently in the UK, HDPE milk bottles.” According to Edward Kosior, one of the authors of the article, the situation today isn’t greatly different: “The situation has not changed. PET and HDPE are still the main (only) polymers recycled in a closed loop.” In a correspondence with CleanTechnica, Tracy McGrath, the USA Sales Director of Mettler Packaging LLC (a company that manufactures carrier bags) confirms this: “… the commonly used reusable bags in the US market are produced with several types of material such as: woven and non-woven polypropylene (WPP or NWPP) and recycled PET (rPET). The false assumption is that these bags are produced with natural fibers or cotton, when they are indeed plastic and more importantly not recyclable in the US recycle stream.”

Given this current infeasibility of large-scale closed-recycling of PP bags, the end-of-life fate of these bags is, at worst, landfill/incineration as a bag or, at best, landfill/incineration as a recycled PP product, which is considered to be of a lower quality than virgin PP. Recycled PP is not currently used to make new bags — rather, it is currently used to make things like watering cans, storage bins, shovels, and battery cases. But even if PP bags are re-used hundreds of times each (as intended), they would still be manufactured on a truly massive scale if they were to completely displace the one million LP bags used every minute globally. How much sub–virgin quality recycled polypropylene will that produce? And what are we going to do with all of those watering cans?

The point isn’t that NWPP bags aren’t an improvement on LP bags (they are) or that it won’t eventually be possible to effectively closed-cycle recycle NWPP bags (early-stage pilot studies that will likely be of relevance are now underway, links here and here). The point is that simply introducing a ban on LP bags without instilling a sustainable alternative and accompanying recycling facilities allows the continuation of environmental damage and occupation of landfills, and robs governments of the opportunity to get it right the first time and implement a truly effective, sustainable solution.

In part 2 of this short series, we’ll discuss products and infrastructure that could help to contribute to a truly sustainable alternative to lightweight plastic bags.


Links to images made available with Creative Commons 2.0 license:

Fig 1: Plastic bag photo modified from Mike Licht

Fig 2:

  1. londonista_londonist
  2. IndiaMart
  3. Jeffrey Beall
  4. foldablebags.com
  5. Milada

References:

25 countries with restrictions on plastic bags: World Economic Forum, Ellen MacArthur Foundation and McKinsey & Company, The New Plastics Economy — Rethinking the future of plastics, Executive Summary, 2016, https://www.ellenmacarthurfoundation.org/assets/downloads/EllenMacArthurFoundation_TheNewPlasticsEconomy_Pages.pdf

The not-so-innocent lightweight plastic bag

World’s most ubiquitous consumer item: As reported in: A small look at a big problem, Benazir Wehelie, CNN, http://edition.cnn.com/2015/07/26/world/cnnphotos-plastic-bags-bolivia-trees/index.html, accessed 2018-01; The Plastic Bag Wars, Kitt Doucette, Rolling Stone, 2011, https://www.rollingstone.com/politics/news/the-plastic-bag-wars-20110725, accessed 2018-01.

High durability: Accumulation and fragmentation of plastic debris in global environments, David K. A. Barnes et al., Phil. Trans. R. Soc. B 2009 364 1985-1998; DOI: 10.1098/rstb.2008.0205, 2009; ‘Biochemically inert’: Transport and release of chemicals from plastics to the environment and to wildlife, Emma L. Teuten et al., Phil. Trans. R. Soc. B 2009 364 2027-204, 2009.

Low-value: ‘one to two cents each’, page 4, Plastic Shopping Bags – Analysis of Levies and Environmental Impacts, Nolan ITU Pty. Ltd. for the Department of Environment and Heritage, Australia, 2002. ‘2-5 cents each’, page 16, An Overview of Carryout Bags in Los Angeles County, A Staff Report to the Los Angeles County Board of Supervisors, 2007.

Sea turtles: World’s turtles face plastic deluge danger, University of Queensland, 2015, https://www.eurekalert.org/pub_releases/2015-09/uoq-wtf091315.php, accessed 2018-01. Study: Schuyler, Q. A., Wilcox, C., Townsend, K. A., Wedemeyer-Strombel, K. R., Balazs, G., van Sebille, E. and Hardesty, B. D. (2016), Risk analysis reveals global hotspots for marine debris ingestion by sea turtles. Glob Change Biol, 22: 567–576. doi:10.1111/gcb.13078

Seabirds: Threat of plastic pollution to seabirds is global, pervasive, and increasing, Wilcox et al., Proceedings of the National Academy of Sciences of the United States of America, vol. 112 no. 38, 11899-11904, 2015.

Recycling rates:

  • 3% in Australia,  Plastic Shopping Bags – Analysis of Levies and Environmental Impacts, Nolan ITU Pty. Ltd. for the Department of Environment and Heritage, Australia, 2002.
  • 1.5% in Illinois, USA, 3% in California, USA: Travis P. Wagner, Reducing single-use plastic shopping bags in the USA, In Waste Management, Volume 70, 2017, Pages 3-12, ISSN 0956-053X, https://doi.org/10.1016/j.wasman.2017.09.003.

Transport vessels: Transport and release of chemicals from plastics to the environment and to wildlife, Emma L. Teuten et al., Phil. Trans. R. Soc. B 2009 364 2027-204, 2009.

Phasing out the lightweight plastic bags

Bans:

Fees:

Palo Alto Study: Palo Alto Disposable Checkout Bag Ordinance, Store Exit Surveys of Customer Bag Types 2008-2014, https://www.cityofpaloalto.org/civicax/filebank/blobdload.aspx?BlobID=48074 Accessed 2018-01.

The alternatives

Most recent LCA study: Life Cycle Assessment of Grocery Bags in Common Use in the United States, Robert M. Kimmel, Clemson University Digital Press, 2014, http://tigerprints.clemson.edu/cudp_environment/6/.

The current solution

Closed-loop recycling retains more value: World Economic Forum, Ellen MacArthur Foundation and McKinsey & Company, The New Plastics Economy — Rethinking the future of plastics, 2016, http://www.ellenmacarthurfoundation.org/publications, Box 3.

Nylon 6: World Economic Forum, Ellen MacArthur Foundation and McKinsey & Company, The New Plastics Economy — Rethinking the future of plastics, 2016, http://www.ellenmacarthurfoundation.org/publications, Box 6.

Closed-loop recycling of PP: Plastics recycling: challenges and opportunities, Jefferson Hopewell, Robert Dvorak, Edward Kosior, Phil. Trans. R. Soc. B 2009 364 2115-2126; DOI: 10.1098/rstb.2008.0311. Published 14 June 2009.

Applications of recycled polypropylene: What plastics are recycled? And what happens to recycled plastics like polypropylene? American Chemistry Council. Published on May 16, 2016.  https://www.plasticsmakeitpossible.com/plastics-recycling/plastics-recycled-happens-recycled-plastics/. Accessed 2018-01.

One million LP bags used every minute: The Plastic Bag Wars, Kitt Doucette, Rolling Stone, 2011, https://www.rollingstone.com/politics/news/the-plastic-bag-wars-20110725, accessed 2018-01 
 
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About the Author

has worked in solar energy (the vast majority with solar PV, but also with concentrated solar thermal) since 2008. During his career, he has worked in Germany, Austria, Australia and the USA. He has published 11 peer-reviewed scientific papers on solar energy and established an independent solar cell test facility in Australia, one of only a handful of such labs in the world who are relied upon to certify new breakthroughs in PV technology. Aside from renewable energy, his other interests include sustainable living, the outdoors and classic literature.



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