Written by: Frankie McGirr
Recently there has been debate over the use of plastic bags and whether cotton alternatives are truly better. In some cases levies or bans have been put in place to limit single-use plastic bags 1,2,3,4. Although reusing a bag will ultimately reduce its own impact compared to using the same bag only once, it does raise the question: Is a cotton bag more sustainable than a plastic one and if not, what would be necessary for it to become as sustainable?
A fundamental factor determining the sustainability of a grocery bag is its lifecycle assessment. This is an assessment on the energy and resources put into producing, using, and disposing of a product4. For comparing grocery bags most studies consider high density polyethylene (HDPE) as a standard for most single-use plastic bags 5,6,7. These studies all found similar results. When looking at the lifecycle, HDPE bags had a low production rate so were more efficient than woven cotton bags in this regard5,6,7. Looking just at production this is not surprising as cotton bags take more resources to produce a durable bag compared to lightweight HDPE bags.
However production is not the only factor, how often a bag is reused is vital. Muthu uses “Eco-functional assessment” to define this relationship between lifecycle impacts and functionality5. Eco-functional assessment is important when comparing cotton and plastic bags as more reuses reduce lifecycle impacts. One finding was that a cotton bag would have to be reused over 300 times to obtain the same or lesser impact as an HDPE bag reused 1-3 times5,7,8. This is one of the main contentions in the debate between grocery bags as this much use is unlikely. If a person were to reuse a cotton bag twice a week it would take roughly 3 years of constant use to equal a HDPE bag used 2-4 times, including use as a rubbish bin liner.
However, an issue found with plastic bags is the effect of poor disposal leading to pollution. Some of the unfortunate results are plastic waste in oceans creating areas such as The Great Pacific Garbage Patch and the possibility that by 2050 there will be as much plastic in the ocean in weight as there is fish 9,10,11. This pollution is important when thinking about the effect of grocery bags as it shows how there is more than lifecycle costs when looking at environmental effect. Poor disposal of bags has impacts and plastic is likely to have more impact than cotton.
When it comes to plastic vs cotton grocery bags there are mixed results. HDPE bags cost the environment less to produce however there are issues when looking at disposal. Reusable cotton bags are promoted to be more sustainable so long as they are reused substantially to outweigh costs of production. Due to this mix it is hard to indisputably say which is better however a reusable cotton bag that was continuously used would in time prove more sustainable due to a lower lifecycle and disposal impact.
- Jakovcevic, A., L. Steg, N. Mazzeo, R. Caballero, P. Franco, N. Putrino, and J. Favara, Charges for plastic bags: Motivational and behavioral effects. Journal of Environmental Psychology, 2014. 40: p. 372-380.
- Convery, F., S. McDonnell, and S. Ferreira. The Most Popular Tax in Europe? Lessons from the Irish Plastic Bags Levy. Environmental and Resource Economics, 2007. 38(1): p. 1–11.
- Luís, I. P., and H. Spínola. The Influence of a Voluntary Fee in the Consumption of Plastic Bags on Supermarkets from Madeira Island (Portugal). Journal of Environmental Planning and Management, 2010. 53(7): p. 883-89.
- Xanthos, D., and T. R. Walker, International policies to reduce plastic marine pollution from single-use plastics (plastic bags and microbeads): A review. Marine Pollution Bulletin, 2017. 118(1-2): p. 17-26.
- Muthu, S. S., and Y. Li, Assessment of Environmental Impact by Grocery Shopping Bags An Eco-Functional Approach. Singapore: Springer Singapore. https://doi-org.helicon.vuw.ac.nz/10.1007/978-981-4560-20-7.
- Muthu, S.S., Y. Li, J.Y. Hu, and P.Y. Mok, Carbon footprint of shopping (grocery) bags in China, Hong Kong and India. Atmospheric Environment, 2011. 45(2): p. 469-475.
- Evans, J., Plastic bags: an unfair reputation? PE carryout shopping bags have been in the news a lot lately–with key points about their production and use often missing from the discussion. Plastics Engineering, 2013. 69(8): p. 22.
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- Cózar, A., F. Echevarría, J.I. González-Gordillo, X. Irigoien, B. Úbeda, S. Hernández-León, Á. T. Palma, et al, Plastic debris in the open ocean. Proceedings of the National Academy of Sciences of the United States of America, 2014. 111(28): p. 10239-44.
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- Harse, G.A., Plastic, the Great Pacific Garbage Patch, and international misfires at a cure. UCLA Journal of Environmental Law & Policy, 2011. 29(2): p. 331-364