6. Exploring circular economy through plastic recycling
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We are living in the Plasticene era or the age of plastics where they are an integral part of everyday life (Haram et al., 2020). Plastics are made up of an array of synthetic or semi-synthetic polymers, with varying chemical compositions, derived primarily from fossil fuels (Wiesinger, Wang and Hellweg, 2021). It is estimated that over 8.3 billion metric tonnes of plastic have been produced since the 1950s (Geyer, Jambeck and Law, 2017), which marks the beginning of the time frame of compilation of global manufacturing data on plastics. Plastics continue to be one of the fastest growing sectors. Due to properties that make them versatile, lightweight, durable and cheap to produce, they can be found in a number of applications – building and construction, electrical and electronics, automotive industry as well as agriculture and healthcare sectors (Yates et al., 2021).
However, plastics are among the most ubiquitous and persistent pollutants on Earth (Dris, Agarwal and Laforsch, 2020). Some of the very properties that make them useful for certain applications also make them resistant to degradation when they reach the end of their intended purpose allowing them to accumulate in our environment for decades or longer. Plastics that are littered or dumped in landfills can be found in soils (FAO, 2021a) or find their way into rivers by rain or wind, and eventually end up in the ocean (Drummond et al., 2022). An estimated 8 million metric tonnes of plastic waste enter the ocean each year (National Academies of Sciences, Engineering, and Medicine, 2021). However, the endurance of plastics is dependent on their environment, with various environmental conditions contributing to the breakdown or fragmentation of plastics into macro-, micro- and nano-sized particles (Box 12). Apart from being pervasive, plastic pollution is also a cross-boundary issue (Borrelle et al., 2017),21 with extreme weather events, such as hurricanes and flooding, linked to climate change potentially exacerbating the distribution of plastic pollution in the terrestrial and aquatic ecosystems. Moreover, manufacturing and refining of plastics in addition to extraction and transport of fossil fuels for plastic production make it one of the more greenhouse gas intensive industries, contributing to climate change (CIEL, 2019).
Box 12. The issue of microplastics
Microplastics (>5 mm), a term coined in 2004 (Thompson et al., 2004), are created when plastics, from a variety of sources, get weathered and broken down into smaller pieces (1µm to 5 mm) in the environment through processes such as photodegradation, physical abrasion, hydrolysis and biodegradation (Evangeliou et al., 2020). They can also be produced industrially and find application in various products, such as cosmetics and abrasive cleaners (SAPEA, 2019).
Microplastics are so ubiquitous in our environment that Brahney et al. (2021) suggested that they now circulate around the Earth, almost like global biogeological cycles, with distinct “resident” times in the atmosphere, oceans, cryosphere and terrestrial systems (Evangeliou et al., 2020; Hou et al., 2021). While methods to detect and track their distribution in the environment are improving (Evans and Ruf, 2021), there is no reliable data on the quantitative global estimates of their presence in our environment. Inhalation and ingestion from various sources are the two major known routes that humans are exposed to microplastics (Rahman et al., 2021), with aquatic products being one of the more well-studied sources of dietary exposure (Garrido Gamarro et al., 2020). New sources of microplastics – fishmeal, infant feeding bottles, organic fertilizers and table salt – that can find their way into our diets are also being routinely identified (Lee et al., 2019; Li et al., 2020; Thiele et al., 2021; Weithmann et al., 2018).
Microplastics represent a diverse class of contaminants as they are of different orders of magnitude in size, come in diverse shapes (e.g. fragments, fibres) and are composed of various polymeric materials and chemical mixtures. This diversity imparts distinct transport and fate characteristics as well as determines how they impact both biota and humans. However, the mechanisms of action by which microplastics pose a risk to human health is still not well understood (Lim, 2021; Rahman et al., 2021), and one of the major challenges in risk assessment and exposure characterization is the lack of standardization of analytical methods for effective sampling, identification and quantification of microplastics, which leads to data incomparability.
Various microorganisms, including opportunistic human pathogens, are known to colonize microplastics and form biofilms (Amaral-Zettler, Zettler and Mincer, 2020). Microplastics can also facilitate distribution of potentially harmful pathogens, such as Vibrio spp., pathogenic serotypes of Escherichia coli, invasive algal species, and pathogenic fungi, into new areas, as well as facilitate the spread of antimicrobial resistance (Amaral-Zettler, Zettler and Mincer, 2020; Gkoutselis et al., 2021; Pham, Clark and Li, 2021).
Various chemicals, either originating from the polymeric raw materials of the plastics themselves or through adsorption from the environment, have been identified in microplastics that may potentially pose a health risk to humans (Diepens and Koelmans, 2018; Arp et al., 2021). These include persistent organic pollutants, endocrine disruptors, heavy metals, flame retardants, and pthalates that can leach into the environment and therefore the food chain (Campanale et al., 2020; Chen et al., 2019; Lim, 2021; Rahman et al., 2021). Whether ingesting microplastics directly significantly raises our exposure to these chemicals is a question that still needs to be determined (FAO, 2017; FAO, 2019; Lim, 2021). Nanoparticles (<1 µm) that are small enough to penetrate and accumulate in tissues and cells can be a cause for concern (Fournier et al., 2020) and more studies are needed to understand the scope of this impact
According to United Nations Environment Programme, the natural capital cost of plastic use in the consumer goods sector, from environmental degradation, greenhouse gas emissions, and health impacts, was estimated to be USD 75 billion annually, but the figure is likely to be a significant underestimate (UNEP, 2014). Over 30 percent of the figure is estimated from greenhouse gas emissions from raw material extraction and processing, with marine pollution amounting to the most significant downstream cost.
Plastics in agrifood systems and circular economy
Modern agricultural practices include the use of plastics in a wide variety of applications, such as mulch films, bags/sacks, silage films, driplines, plant protectors among others. A new report by FAO provides an overview of the extent of plastic use in agriculture, the benefits and trade-offs, followed by recommendations on how to reduce their potential for harm to human health and the environment (FAO, 2021a).
Plastic packaging of food acts as barriers for contamination thereby prolonging the shelf-life, preserving the quality and maintaining the safety of food products. Since food supply chains often involve moving food products across long distances, packaging also plays an important role in facilitating the transit of food (Han et al., 2018). While it is estimated that approximately 42 percent of plastics produced globally since the 1950s have been used for packaging, it is difficult to obtain data on the exact amount of plastic packaging used exclusively for food (Geyer, Jambeck and Law, 2017; Schweitzer et al., 2018).
Most plastic packaging are engineered for function and tend to be used only once with generally no appropriate end-of-life management processes in place. Prevention and management of food waste often provided as the justification for single-use plastics. However, according to Schweitzer et al. (2018) per capita food waste and plastic waste rates in Europe remain one of the highest globally, demonstrating that food packaging that is not fit-for-purpose to the food needs may not sufficiently contribute to preventing food loss and waste (Verghese et al., 2015).
On the other hand, recycling of plastic packaging remains a challenge as plastics tend to be made of different types of polymers, mixed with various processing additives (flame-retardants, colourants, plasticizers, UV-stabilizers and so on). In addition, packaging in general can be comprised of multi-materials – plastics, glass, metal and so on – which makes it difficult to separate before recycling (Hopewell, Dvorak and Kosior, 2009). It is estimated that as of 2015 only 9 percent of the approximately 6 300 metric tons of plastic waste generated globally has been recycled (Geyer, Jambeck and Law, 2017). Plastics that do get recycled cannot often be turned into products of the same quality and can get relegated to lower value applications that may not be recyclable again after use (Ellen MacArthur Report, 2016).
To help overcome some shortcomings commonly associated with mechanical recycling (Schnys and Shaver, 2020), various biorecycling and chemical recycling methods are under development – the former uses microbes or insects to break down plastics (Espinosa et al., 2020; Yang et al., 2015), while the latter can recover the petrochemical components of the polymers which can then be used to remanufacture plastics (Lantham, 2021; Meys et al., 2020; Zhao and You, 2021). Most of these recycling methods are still in their infancy and come with their own technical challenges (Rollinson and Oladejo, 2020).
Scientific advancements in recycling approaches, development and introduction of new materials, improvements in sorting and reprocessing technologies, are offering opportunities to move from a linear to a circular economy when it comes to plastic packaging. In addition, as awareness of plastic pollution grows together with efforts to reduce demand for fossil fuels and recognition of the short term impacts of clean-up activities, many are advocating for a change in how we manufacture and use plastics in agrifood systems (Yates et al., 2021). Circular economy is a model which aims to close material loops by keeping resources in use for as long as possible to extract the maximum value out of them while minimizing the negative impacts associated with disposing them (Stahel, 2016). This concept has been gaining a lot of attention globally as a way to overcome our linear way of consumption of resources (Ghisellini, Cialani and Ulgiati, 2016). Redesign-reduce-reuse-recycle are the main options under circular economy approach with respect to plastic food packaging, whereby the usage of single-use (and virgin) plastics is reduced while encouraging the effective reuse and recycle of plastics already in circulation through better coordinated strategies, and redesigning our current systems to be more sustainable by integrating greater environmental and social responsibility throughout the supply chain (FAO, 2021b).
In addition to reusing and recycling of plastics, biobased plastics are gaining attention as environmentally friendly alternatives with similar functionality to conventional petroleum-based non-biodegradable plastics (van der Oever et al., 2017). Although still ill-defined at this point, the term “bioplastics” tend to be used interchangeably with either biobased plastics or biodegradable plastic, or both. Biobased plastics are made from renewable natural resources (such as corn, sugar cane, potatoes, seaweeds, and others) and can be engineered to be either biodegradable or non-biodegradable. Plastics made from materials that can degrade naturally by microorganisms are biodegradable plastics. Compostable plastics are a subset under this category (Davis and Song, 2006; FAO, 2021a; Lambert and Wagner, 2017).
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While such alternative plastics are available, they do not yet represent viable substitutes for the conventional plastics, for most applications. Plastics containing variable amounts of both petrochemical and biobased components can also be found labelled as “bioplastics”, but they are not easily biodegradable (FAO, 2017). In addition, a number of plastics marketed as “biodegradable” do not degrade, as quickly or effectively, in the natural, open environment if they are littered or found in landfills (Napper and Thompson, 2019; Nazareth et al., 2019), leading to concerns about introducing additional sources of microplastics (and nanoplastics) (Box 12) in the environment (FAO, 2017; Weinstein et al., 2020). Bioplastics may require industrial composting conditions to break down properly and therefore, such plastic waste will have to be properly managed and routed to specialized recycling facilities, which may not be compatible with the existing waste management options (Ferreira-Filipe et al., 2021; Silva, 2021). In addition, with a number of bioplastics derived from carbohydrate-rich plants (corn, sugarcane, etc.), there are a number of concerns raised, for instance, potential for exacerbating deforestation, pesticide usage, and societal impacts linked to competition from food production.
What are the the food safety implications to be considered?
While the concept of circular economy for food packaging seems feasible in theory, recycling and reuse of food packaging require careful considerations. Apart from requiring post-consumer collection and sorting of packages of mixed materials, as well as giving consideration to the extent of contamination originating from their initial use, economic viability of the recycling process, and constraints from lack of appropriate legislative frameworks, there are also food safety concerns that arise from the plastic recycling processes that need to be acknowledged for food-contact applications.
Using recycled or virgin plastics or a mixture of both, if not adequately assessed and controlled, have the potential for introducing chemical hazards into foods and beverages. Food contact materials are not inert and contain many different chemicals from known components that can migrate from packaging into food (Groh et al., 2019).22 Some of these chemicals are not added intentionally (also called the Non-Intentionally Added Substances or NIAS) – known or unknown impurities, reaction products and breakdown products of the ingredients used to make the food contact materials or can be derived from possible contaminants from the manufacturing processes, or through indirect sources such as printing inks, coatings, adhesives and secondary packaging. Substances of concern may also arise if non-food grade polymers enter the recycling process for food-grade materials, for instance, the presence of brominated flame retardants originating from electric and electronic equipment in black food contact articles (Samsonek and Puype, 2012).
Chemicals that can migrate from food contact materials (from both recycled and virgin plastics) and are of particular food safety concern include poly-fluoroalkyl substances (PFAS), phthalates, 4-nonlyphenol, mineral oils, among others (Edwards et al., 2021; Kitamura et al., 2003; Lyche et al., 2009; Rubin, 2011; Yuan et al., 2013). These chemical hazards can pose various health risks like carcinogenicity, mutagenicity, reproductive toxicity, and others through various modes of action, such as persistence and bioaccumulation, endocrine disruption, among many. Therefore, risk assessments are required to take into account the extent of actual exposure to such chemicals. But not all regions have validated methods to measure the migration of chemicals and therefore, assess the potential health impacts. This migration or leaching depends on a number of factors, including temperature and time of contact between food and packaging; food matrix properties and composition; presence of functional barriers; and physicochemical properties of packaged food or beverage, such as pH. (Fang and Vitrac, 2017).
As awareness about these chemical hazards grow, functional alternatives for them are being sought out, sometimes with potential adverse health consequences either not fully characterized or no different than the original option. For instance, because of potential health concerns arising from migration of bisphenol A (EFSA, 2015; FAO and WHO, 2010; Ma et al., 2019; Vilarinho et al., 2019), it was replaced by other bisphenols (bisphenol S and bisphenol F). However, the alternatives were also found to have migration issues of their own, with potential human health impacts that are not yet fully understood (Kovačič et al., 2020; Rochester and Bolden, 2015).
Nanomaterials – nanoclay (Montmorillonite clay), nano metal oxides (silver, zinc, copper, titanium, among others), nanocellulose and so on – can be added to polymers to produce nanocomposites in order to confer certain properties, such as increased mechanical strength, provide better barriers against water, antimicrobial properties, among others (Bumbudsanpharoke and Ko, 2015; Garcia, Shin and Kim, 2018). Adverse health impacts from the ingestion of some nanoparticles, as described in literature, include potential to interfere with the normal functioning of the gastrointestinal tract and cause dysbiosis of the gut microbiota, impacts on the immune system, genotoxicity and carcinogenicity, depend on the different compositions, structures and properties of nanoparticles (McClements and Xiao, 2017). However, the release, migration and measurement of nanoparticles from food contact materials is still not well understood, which complicates the assessment of nanomaterial safety (Bandyopadhyaya and Sinha Ray, 2018; Froggett et al., 2014; Störmer, Bott and Franz, 2017; Szakal et al., 2014).
Plastic alternatives like bioplastics, including those that have food contact applications, contain a broad set of chemicals, similar to conventional petroleum-based plastics, that can potentially migrate and induce toxicity (Yu et al., 2016; Zimmerman et al., 2020). Biobased food contact materials that are produced from a diverse biomass derived from agricultural products raise additional food safety issues, such as presence of heavy metals, persistent organic contaminants, residues (e.g. pesticides), mycotoxins, among others. These hazards also have the potential to migrate upon contact with food (FERA, 2019).
Apart from food packaging, the food we consume also comes in contact with various other materials – utensils, cutting boards, cups and so on – which may be potential sources of food safety risks, especially as new materials are being explored from a circular economy perspective (Bilo et al., 2018). For instance, stalks left over after wheat grains are harvested are traditionally treated as waste, but they can instead be turned into wheat-based straws as a substitute for single-use plastic straws. A number of different mycotoxins produced by the Fusarium spp. are known to be associated with wheat under poor storage conditions. In addition, depending on their composition allergenicity may be another issue with wheat-based straws (FERA, 2019). However, only limited information about such food safety risks and their potential for migration in biobased food contact materials is available in the published literature. It is also not known if processing and manufacturing processes involved in the production of such biobased food contact materials breaks down or modifies any of the chemical hazards mentioned earlier.
What is the way forward?
The circular economy can decouple plastics from fossil fuel feedstocks and find ways to sustainably produce plastics, repurpose plastic waste as well as manage plastic pollution. Such policies are likely to have consequences across multiple sectors, including the food sector, with overlapping implications for health and food safety, the environment, food security and economic outcomes. While there are many innovations and improvement efforts to implement a circular economy approach for plastics that show potential, they are still too fragmented to make any lasting impact at larger scales and remain largely disconnected from the development and deployment of appropriate after-use systems. The implementation of circular economy is also characterized by various barriers – financial, logistical, lack of technical knowledge and skills, and technological gap.
It can be difficult to recycle certain types of plastics without perpetuating the harmful chemicals they contain unless adequate regulatory frameworks are put in place to control it and risk assessments underpinning these frameworks are carried out with wide support. How some of these chemical hazards, arising from recycled plastics as food contact materials, pose a risk to human health remains to be fully determined. Risk assessments currently focus on monomers and plastic additives used in the manufacture of food contact products, but it does not cover plastic polymers and complex chemical mixtures formed during the production processes. There is a need for improved international harmonization of the methods used to assess the fates and physiological effects of chemicals arising from plastic packaging in contact with food. The lack of crucial data on exposure, also in terms of migration of chemical mixtures, presents a knowledge gap that needs to be addressed moving forward (Groh et al., 2021; Muncke et al., 2017). Advances in analytical or quality control measures may provide a feasible way to assure that the supply of recycled plastics is safe for the intended end-use (Geueke, Groh & Muncke, 2018; Muncke et al., 2017; Muncke et al., 2020). In addition, as the debate for plastic alternatives continue (van der A & Sijm, 2021), migration of substances and their potential for chemical toxicity will need to be an area that is given due consideration. Solutions for improving the safety of food contact materials, especially within the context of circular economy, will need to include all relevant experts and stakeholders of the supply chain (Muncke et al., 2020)
- 21 Plastic in a bottle, 2021: https://pame.is/projects/arctic-marine-pollution/plastic-in-a-bottle-live-map, Wageningen University and Research.
- 22 Migration can be defined as the “mass transfer from an external source into food, in physical contact with it, by sub-microscopic processes” (Katan, 1996).