Types of LCA studies

The inner ring of the figure below shows the distribution of studies per LCA type (Figure 2). The results show that the number of carbon footprints conducted within the review period is 10 (Supplementary Table S1), traditional LCAs is 57 (Supplementary Table S2), and six studies that combined the traditional structure of an LCA with an additional environmental indicator estimating the impact of plastic pollution (Supplementary Table S3). The balance of the studies (defined as ‘other’ studies in the chart) consisted of assessments which included aspects that differed from the traditional scope of an LCA (Supplementary Table S4). Examples of these are studies that compared various end-of-life scenarios and waste management options (Hou et al. Reference Hou, Xu, Taiebat, Lastoskie, Miller and Xu2018; Martin et al., Reference Martin, Oliveira, Oliveira and Bezerra2021).

Figure 2. Distribution of life cycle-based studies per type and location.

One study incorporated life cycle costing into the analysis (Foolmaun and Ramjeeawon, Reference Foolmaun and Ramjeeawon2012a) while another study used a hybrid approach to evaluate the environmental benefits of a re-designed plastic milk bottle (Pomponi et al., Reference Pomponi, Li, Saint, Lenzen and D’Amico2022). An additional example of a study that used LCA as part of a two-step process is Cottafava et al. (Reference Cottafava, Costamagna, Baricco, Corazza, Miceli and Riccardo2021) where an environmental break-even point was established by comparing several end-of-life and use phase strategies for single-use versus reusable cups.

Only one study considered circularity by taking a material circularity indicator into account (Lonca et al., Reference Lonca, Lesage, Majeau-bettez, Bernard and Margni2020). Additionally, two studies used a combination of material flow analysis (MFA) and LCA to link mass-based indicators to indicators of environmental damage (Kang et al., Reference Kang, Auras and Singh2017; Lonca et al., Reference Lonca, Lesage, Majeau-bettez, Bernard and Margni2020). MFA and LCA are complementary tools enabling further analysis of complex systems (Laner and Rechberger, Reference Laner, Rechberger and Finkbeiner2016).

Carbon footprint and water footprint are also considered special types of LCAs (Finkbeiner, Reference Finkbeiner2016). The analysis indicated that studies that considered the estimation of GHG emissions (namely a carbon footprint) also include a calculation of energy consumption/cumulative energy demand within the scope of the assessment (Pasqualino et al., Reference Pasqualino, Meneses and Castells2011; Nikolic et al., Reference Nikolic, Kiss, Miladenovic, Bukurov and Stankovic2015). Furthermore, Fetner and Miller (Reference Fetner and Miller2021) examined water consumption as an additional indicator to determine environmental payback periods. The overall number of studies found also indicated that although increasing attention has been paid to global warming and climate change, the majority of studies included multiple environmental indicators.

In recent years, the concern surrounding marine plastic pollution has become reflected in LCA studies. The Medellin declaration on marine litter in LCA (Sonnemann and Valdivia, Reference Sonnemann and Valdivia2017) acknowledged that impacts related to marine debris including plastics are not suitably addressed in the current LCA methodology. Life cycle studies to date are yet to characterise the impacts of leakage of plastic fractions to the surrounding environment. Thus, no major life cycle database has included these emission flows into their datasets nor developed specific characterisation factors that convert leakage flows into indicators of environmental impact. It is noted that there are ongoing projects such as marine impacts in LCA (MarILCA) aimed at integrating marine litter impacts in LCA (Marine Impacts in LCA n.d.). This may provide useful information regarding impact assessment methods and indicators to quantitatively address potential impacts arising from plastic leakage in the marine environment.

Although plastic litter impact models are the subject of recent research, its application to case studies illustrating the use of these models is limited. Some studies have investigated the development of effect factors and characterisation of plastic pollution impacts. In 2019, Woods et al. developed a preliminary effect factor for the impacts associated with entanglement. However, the authors acknowledged that the lack of data on the effects on populations for species as well as the associated impacts of litter densities along the water column (Woods et al., Reference Woods, Rødder and Verones2019). Saling et al. (Reference Saling, Gyuzeleva, Wittstock, Wessolowski and Griesshammer2020) developed a characterisation model for the impacts of microplastics on species which took into consideration fragmentation and degradation rates. More recently, in 2022, Corella-Puertas et al. (Reference Corella-Puertas, Guieu, Aufoujal, Bulle and Boulay2022) proposed simplified fate and characterisation factors for microplastics resulting from expanded polystyrene and tyre wear. The work took into consideration different degradation, fate and sedimentation rates. However, the development of robust models is still hampered by the poor understanding of the impacts of plastic on species as a population and ecosystems at large (Woods et al. Reference Woods, Veltman, Huijbregts, Verones and Hertwich2016, Reference Woods, Rødder and Verones2019).

In the absence of these marine litter impact assessment methods, rudimentary indicators have been applied in lieu of it. The proposed marine litter indicators are based on a number of factors including weight (Civancik-Uslu et al., Reference Civancik-Uslu, Puig, Hauschild and Fullana-i-Palmer2019; Herberz et al., Reference Herberz, Barlow and Finkbeiner2020; Stefanini et al., Reference Stefanini, Borghesi, Ronzano and Vignali2021), leakage rates (Chitaka et al., Reference Chitaka, Russo and von Blottnitz2020; Zanghelini et al., Reference Zanghelini, Cherubini, Dias, Kabe and Delgado2020; Gao and Wan, Reference Gao and Wan2022) and degradation (Civancik-Uslu et al., Reference Civancik-Uslu, Puig, Hauschild and Fullana-i-Palmer2019; Chitaka et al., Reference Chitaka, Russo and von Blottnitz2020; Stefanini et al., Reference Stefanini, Borghesi, Ronzano and Vignali2021; Gao and Wan, Reference Gao and Wan2022). For the six studies that were located, three were conducted for European countries with the remainder of research conducted for South Africa, Brazil, and the United States of America respectively.

Geographical spread

The outer ring of the doughnut chart (Figure 2) describes the location of studies where the geographical context is divided per continental region. Across the various types of studies and in total, 44% of the studies have been conducted for European countries. Just over 35% of the total studies were conducted for countries within the European Union (EU). This includes studies conducted for the region. Within Europe, the predominant countries where studies occurred are Italy and Spain with eight studies apiece. Of the eight studies conducted for the African continent, half of the assessments were for Mauritius while the remainder were carried out in the southern parts of Africa namely South Africa and Zimbabwe. For Asia, the countries that featured the highest number of studies were Thailand and China with four and five studies respectively. The United States of America had the greatest number of studies within North and South America.

In some cases, the study covers a region rather than a specific country (Brock and Williams, Reference Brock and Williams2020) while, for other assessments, studies were located across multiple countries (Muthu et al., Reference Muthu, Li, Hu and Mok2011; Schmidt et al., Reference Schmidt, Laner, Eygen and Stanisavljevic2020).

For several studies, the location of the research was unspecified which potentially hinders the value of the publication; it limits the interpretation of the results and its potential comparability. From the online search conducted, there were no studies reviewed that were conducted for Australasia. This is not due to an absence of LCA studies but a reflection of our eligibility criteria.

Scope of studies

The scope of the LCA is dependent on the system boundaries selected by the researcher/practitioner. Traditionally an LCA should be conducted from cradle-to-grave, however, one may choose to focus on one section of the production process (eg, gate-to-gate) (Figure 3). With the rising popularity of circularity and recovery and recycling of waste products, one may also conduct an LCA from cradle-to-cradle (Figure 3) as previously discussed.

Figure 3. Scopes of reviewed LCA studies.

The majority (62%) of studies had a scope of cradle-to-grave. However, there was a growing focus on end-of-life impacts, including in some cases where a cradle-to-grave assessment was conducted (Romero-Hernández et al., Reference Romero-Hernández, Romero-Hernández, Munoz, Detta-Silveira, Palacios-Brun and Laguna2009; Foolmaun and Ramjeeawon, Reference Foolmaun and Ramjeeawon2012a; Simon et al., Reference Simon, Amor and Foldenyi2016). For example, for beverage bottles, there was a notable interest in the potential benefits of product waste recycling (Romero-Hernández et al., Reference Romero-Hernández, Romero-Hernández, Munoz, Detta-Silveira, Palacios-Brun and Laguna2009; Foolmaun and Ramjeeawon, Reference Foolmaun and Ramjeeawon2012a, Reference Foolmaun and Ramjeeawon2012b; Simon et al., Reference Simon, Amor and Foldenyi2016; Martin et al., Reference Martin, Oliveira, Oliveira and Bezerra2021). One study integrated two different scopes, that is, cradle-to-gate and cradle-to-grave (Muthu et al., Reference Muthu, Li, Hu and Mok2011).

Product foci

The largest product groups of focus were aligned with items identified as major contributors to plastic pollution. Beverage packaging has been a focus area of LCA for many years, representing the largest category of LCA studies reviewed (Figure 4). They started rising in popularity in 2011 with 5 publications in 2012, 6 in 2016 and 10 in 2021. The majority of beverages under investigation were milk (Bertolini et al., Reference Bertolini, Bottani, Vignali and Volpi2016; Stefanini et al., Reference Stefanini, Borghesi, Ronzano and Vignali2021; Cappiello et al., Reference Cappiello, Aversa, Genovesi and Barletta2022; Pomponi et al., Reference Pomponi, Li, Saint, Lenzen and D’Amico2022), and mineral water (Gironi and Piemonte, Reference Gironi and Piemonte2011; Garfí et al., Reference Garfí, Cadena, Sanchez-ramos and Ferrer2016; Ferrara et al., Reference Ferrara, Feo and Picone2021; Grisales et al., Reference Grisales, Tua and Rigamonti2022). However, not all LCA studies specified the beverage type.

Figure 4. Product composition of reviewed LCAs.

A total of 70% of the beverage packaging LCAs included PET bottles. They started gaining popularity from 2011 with 1–4 studies published yearly, excluding 2019, culminating in seven studies being published in 2021. PET bottles are either studied in isolation or compared to glass bottles or aluminium cans. Generally, PET was found to outperform both glass and aluminium however, this was subject to a number of factors including the number of glass reuses and the respective disposal scenarios (Amienyo et al., Reference Amienyo, Gujba, Stichnothe and Azapagic2013; Saleh, Reference Saleh2016; Boutros et al., Reference Boutros, Saba and Manneh2021; Ferrara et al., Reference Ferrara, Feo and Picone2021).

Plastic bags and disposable cups each contributed 15% of the LCAs reviewed respectively. Plastic bags have seen periods of high interest with nine studies conducted from 2009 to 2012, none from 2013 to 2016 and a renewed interest from 2017. This may be linked with public concern surrounding pollution associated with plastic bags. The ‘other’ category consisted of a variety of products including jars, cutlery, meat trays and clamshell containers.

Product focus can be influenced by public discourse. This is clearly represented in the case of straw LCA studies. In recent years, straws have been in the spotlight as a major contributor to marine plastic pollution. This may have contributed to the products being studied, with straw LCA studies only first being published in 2020. Results varied, being impacted by factors such as the location and the number of reuses for reusable straws. Most of the studies incorporated a marine litter indicator further linking the studies to marine plastic pollution (Chitaka et al., Reference Chitaka, Russo and von Blottnitz2020; Herberz et al., Reference Herberz, Barlow and Finkbeiner2020; Zanghelini et al., Reference Zanghelini, Cherubini, Dias, Kabe and Delgado2020; Gao and Wan, Reference Gao and Wan2022). This further supports the notion that LCA product foci is influenced by the global concern surrounding plastic pollution.