Carbon Footprint of Grocery Bags Considering Drivers of Variability in Mexico City

Abstract

AbstractPublic awareness of the environmental problems associated with single-use plastic bags is growing and different management alternatives are being implemented, including regulatory interventions. At least 35 countries around the world have taken steps to tax or ban single-use bags. Evaluating the carbon footprint of different bags is not a trivial or intuitive matter; it requires consideration of material and energy inputs throughout the life cycle of each bag and each material has its own characteristics and environmental impacts. To calculate the carbon footprint of grocery carrying bags, it is necessary to consider the efficiency in the use of the bag, the distribution process, the possibility of reusing or recycling and the final disposal. This chapter presents the evaluation of the carbon footprint of four types of carrying bags through the Life Cycle Assessment methodology, using data published in scientific literature, so as to identify the variability of the results. In this work, the “cradle to grave” approach is adopted, which considers the environmental impacts of the grocery bags, considering the extraction of raw materials, the processing of raw materials, the manufacture of the bags, their commercialization, use and final disposal (landfill/recycling). The bags analyzed are made of the following materials: High Density Polyethylene (HDPE), Low Density Polyethylene bags (LDPE), Polypropylene (PP) bags and Polycaprolactone (PCL) bags. PCL bags are adopted as a reference for biodegradable bags because they are the most common polymer for which information was available in bibliographic sources. This material is from fossil origin but has the characteristic of being biodegradable. The calculation of the carbon footprint is based on bibliographic data that come from published scientific articles, considering 8 articles on HDPE bags, 8 articles on LDPE, 5 on PP (non woven) and 7 articles of PCL. It was decided to use only the information on nonwoven PP and PCL, since the information found on the other variants would not present sufficiently representative data. The Functional Unit (UF) was defined as “the number of grocery bags needed per year for an average family in Mexico City to carry their groceries”. The analysis is performed at two levels: (1) Generation of a Base Bag (or generic), whose inventory represents the quantities of inputs and average emissions of all the items analyzed and, (2) Minimum and maximum levels. It refers to the modeling of life cycle impacts considering the specific inventory data of each item but adjusting them according to the weight of the bags, the quantity of the bags, the distances considered in this study and using electricity from Mexico. The results show that PP bags have the lowest carbon footprint, between 1.28 and 1.54 kg of CO2 eq/family-year. On the other hand, the range of impact of HDPE bags goes from 1.26 to 2.08 kg of CO2 eq/family-year, with an average impact (base bag) of 1.9 kg of CO2 eq/family-year. The LDPE bag is the bag with the highest carbon footprint, followed by the PCL bags. The use of PP bags generated a lower carbon footprint per family-year, mainly due to the number of reuses (11 in this study). According to the results obtained in this study, it can be concluded that the use of LDPE bags shows the worst environmental performance followed by the PCL bags, while HDPE bags are in third place in terms of CFP, which is due to the fact that they are very light and present a secondary reuse as garbage bags, however, their ease of becoming waste (risk of abandonment) and their difficult collection to introduce recycling processes, are important disadvantages that reduce their attractiveness, at least from an environmental point of view. The use of PP bags generates the lowest CFP per family-year in Mexico City, however, it is very important to highlight that the fewer uses this bag has given, the greater impacts it will generate, and it may be the worst alternative in environmental terms if it does not present primary reuses and at the moment there is no objective information on the number of actual reuses given to this type of bags.KeywordsGrocery bagsHigh density polyethylene bagsLow density polyethylene bagsPolypropylene bagsPolycaprolactone bagsCarbon footprintLife cycle assessmentMexico City