A comparative cradle-to-grave life cycle assessment of single-use plastic shopping bags and various alternatives available in South Africa.

Purpose: The pervasive use of plastics, coupled with inadequate waste management systems in many countries, has led to widespread leakage of plastics into the environment. In South Africa, the predominant type of shopping bags are single-use plastic bags; but paper, biodegradable plastic and re-usable bags have emerged as alternatives. To compare these alternatives in terms of environmental impacts across the whole product life cycle, we carried out a cradle-to-grave life cycle assessment (LCA) of 16 shopping bag types available in South Africa. Methods: The comparison includes single-use plastic, bioplastic and paper bags, as well as re-usable bags (typically made from plastic in South Africa). The functional unit was based on the estimated annual volume of groceries purchased per capita. An attributional LCA was carried out using the ReCiPe 2016 Midpoint(H) method, with 18 mid-point impact categories. In addition, given the lack of an impact category for plastic pollution in existing methods, we developed a mid-point indicator based on the persistence of plastics (and other materials) leaked to the environment (Persistence of leaked material, Persistence_LM). Specific attention was placed on modelling end-of-life and waste management in the South African context. Economic-based allocation at the point of substitution was used to apportion environmental impacts to virgin and recyclate material, and the production of recyclate was modelled using system expansion. Results and discussion: Re-usable bag types, specifically the 70 µm High Density Polyethylene (HDPE) and non-woven Polyester bags, had the lowest environmental impacts for all indicators, except Persistence_LM. Paper and biodegradable plastic bags had a lower Persistence_LM impact as compared to the petro-based plastic bags, and therefore may be preferable in terms of avoiding plastics accumulating in the environment. The re-usable bags need to be used at least 3 to 10 times to offer lower environmental impacts than single-use ones. Among the single-use bags, biodegradable bags made from imported Polybutylene Adipate Terepthalate (PBAT) plus starch showed the lowest environmental impacts across all impact categories, including Persistence_LM, followed by the Paper bag. The single-use 24 µm HDPE bag (HDPE_24) with no recycled content had the highest overall environmental impacts, while increasing the recycled content reduced overall environmental impacts by up to 52%. Compared to other countries, the high environmental impacts of plastic bags in South Africa can largely be attributed to the coal-to-liquids process used for polymer production, which is intensive in terms of both energy and raw materials. [ABSTRACT FROM AUTHOR]