Impact statement

Unsustainable plastic production, overconsumption and mismanagement have resulted in increased global plastic pollution in the environment, threatening sustainability. Most plastics (99%) are produced from fossil-based sources (i.e., conventional fossil-based plastics) and only 1% are derived from bioplastics. For an effective development and implementation of a legally binding agreement (the Global Plastics Treaty) by the United Nations Environment Assembly to curb plastic pollution by 2024, careful consideration should be given to switching to alternatives to conventional fossil-based plastics to avoid unintended consequences. For example, alternatives to conventional fossil-based plastics include plastics that are composed of renewable or fossil-based carbon sources or combinations of both, which can undergo biodegradation and are marketed as “biodegradable plastics”. However, biodegradable plastics undergo biodegradation only under specific conditions. Other alternatives to conventional fossil-based plastics include those that are derived from renewable resources (“biobased plastics”). These alternatives to conventional fossil-based plastics are often described as being sustainable compared to conventional plastics; however, they cause widespread consumer confusion, are unregulated, and have unintended environmental consequences. Simply substituting these alternatives with conventional fossil-based plastics may not be a realistic solution to combat global plastic pollution as they pose hazards to organisms and human health. Increased consumer use of biobased and of biodegradable plastics must not distract from calls to reduce global plastic production to curb plastic pollution. The Global Plastics Treaty must carefully consider the potential advantages and disadvantages of biobased and biodegradable plastics compared to conventional fossil-based plastics.

Bioplastics are not silver bullets to curb plastic pollution

Bioplastics are chemically diverse. Bioplastics are derived from plant-based materials like cellulose (e.g., ‘biobased’) and can occur in different blends with other plastic materials. In other words, ‘biobased’ only indicates that the carbon atoms used in the molecule chains are derived from nature (i.e. they are of “bio” origin) (SAPEA, 2020). The most popular ‘biobased’ materials which consist of ~60% of bioplastic production, include polylactic acid (PLA), which is a thermoplastic monomer derived from renewable, organic sources such as corn starch or sugar cane and poly-3-hydroxybutyrate (P3HB), which is a polymer belonging to the polyester class of bioplastics (Balla et al., Reference Balla, Daniilidis, Karlioti, Kalamas, Stefanidou, Bikiaris, Vlachopoulos, Koumentakou and Bikiaris2021). PLA bioplastics are both biobased and biodegradable (but only under industrial composting conditions, usually at a high temperature) (Naser et al., Reference Naser, Deiab and Darras2021). Unlike PLAs, P3HBs are compostable and biodegradable in natural environments and toted as being nontoxic (Naser et al., Reference Naser, Deiab and Darras2021). Another example of a widely marketed ‘biobased’ bioplastic that is not biodegradable is biopolyethylene (BioPE). While BioPEs can be obtained from sugar cane and possess similar characteristics to conventional petroleum-based polyethylene, they are not biodegradable which means that they do not mineralize into natural substances such as water, carbon dioxide or compost, making their end-of-life claims and disposal in natural environments highly problematic.

Despite the widely used name, blended ‘bioplastic’ products often include petroleum-based plastics such as polypropylene in various proportions (Mateos–Cárdenas, Reference Mateos–Cárdenas2022). ‘Biodegradable’ and ‘oxo-biodegradable’ labeled plastic products include additives that catalyze the degradation of larger polymers. However, these plastics are not truly biodegradable or compostable because they produce plastic fragments that generate microplastics and leach harmful chemicals, presenting hazards to organisms and human health (Zimmermann et al., Reference Zimmermann, Dombrowski, Völker and Wagner2020; Venâncio et al., Reference Venâncio, Lopes and Oliveira2022; SCEPT, 2023). ‘Compostable’ plastics need to chemically breakdown by 90% in 180 days, but this process often requires industrial processing with high heat conditions, which is often lacking in most municipal waste management facilities, which means these ‘compostable’ plastics either contaminate the waste stream or must be diverted to landfill (Purkiss et al., Reference Purkiss, Allison, Lorencatto, Michie and Miodownik2022). Thus, the lack of standardization of these labels is problematic because it assumes that waste management facilities and infrastructure are geographically uniform and can process this specialized waste under ideal conditions.

Lack of consistency in labeling causes confusion

Currently, there are no international harmonized standards for the labeling of ‘compostable’ or ‘biodegradable’ plastics (Purkiss et al., Reference Purkiss, Allison, Lorencatto, Michie and Miodownik2022). However, these labels can be used based on regional and national standards (where they exist) where these products are commercially available (Napper and Thompson, Reference Napper and Thompson2019). Examples of regional and national standards have been established by the International Organization for Standardization (ISO), European Norm (EN) and the American Society for Testing and Materials (ASTM) (Napper and Thompson, Reference Napper and Thompson2019). For instance, products that are labeled ‘compostable’ in Europe must adhere to the EN13432 standard, which indicates the ability to be processed in the industrial composting system in Europe (European Bioplastics, 2015). However, few municipal waste management facilities are capable of processing these ‘compostable’ or ‘biodegradable’ plastics making these misleading labels confusing for consumers and problematic at the end-of-life. To use these labels claiming ‘compostable’ or ‘biodegradable’ on products, producers must adopt independent certification systems that adhere to ISO, EN or ASTM standards until international regulations are developed.

Experimental studies testing the validity of the end-of-life claims by these labels are rare, yet a recent study revealed the complicated legacy of bioplastics (Mateos–Cárdenas, Reference Mateos–Cárdenas2022). Mateos–Cárdenas (Reference Mateos–Cárdenas2022) demonstrated that popular consumer products using bioplastics are not always accurate to their definitions of being compostable or biodegradable. Eight different commercially popular biodegradable teabags sold in Ireland were tested and shown to not fully degrade in soil (Mateos–Cárdenas, Reference Mateos–Cárdenas2022). While products containing non-synthetic plastic cellulose degraded into smaller fragments in a matter of weeks, the products made of bioplastic PLA remained intact in the soil for one full year. Bioplastics that were blended with synthetic plastics were not able to fully biodegrade. Despite the so-called positive branding of environmentally sustainable options for such plastics, this study shows the current flaws in the branding and messaging behind these labels (Mateos–Cárdenas, Reference Mateos–Cárdenas2022). Results from the Mateos–Cárdenas (Reference Mateos–Cárdenas2022) study help reinforce inconsistencies widely used in greenwashing labels in other consumer products.

Similarly, plastic disposable carrier bags have been shown to behave inconsistently when placed in the natural environment (Napper and Thompson, Reference Napper and Thompson2019). Different products labeled as biodegradable, oxo-biodegradable and compostable did not deteriorate uniformly over a 3-year timeline while submersed in seawater, buried in soil or left exposed in open-air conditions (Napper and Thompson, Reference Napper and Thompson2019). The functionality of these products after exposure to the elements under realistic environmental conditions demonstrates that bags still maintained their functionality and could carry groceries up to 6.8 kg (Napper and Thompson, Reference Napper and Thompson2019). Inconsistent labeling of other popular consumer products has been documented by Walker (Reference Walker2023). For example, littering of pet waste bags may be occurring due to confusion by pet owners, who believe that these so-called ‘biodegradable’ bags are compostable in the natural environment, which in the absence of industrial composting facilities, is untrue (Walker, Reference Walker2023).

These studies have been critical to help demonstrate the consistent inconsistencies of bioplastics use, marketing and “greenwashing” labeling. As a result of these inconsistencies, there is an urgent need for international regulations under the Global Plastics Treaty to carefully consider the potential advantages and disadvantages of biobased plastics and biodegradable plastics compared to conventional fossil-based plastics. Following detailed assessment, international standards must be applied to ensure that bioplastics are properly labeled to avoid unintended consequences due to end-of-life mismanagement. The mislabeling of plastics has long been oversimplified and confuses the public with inaccurate information about the end-of-life potential of plastic waste. It is a widely used form of “greenwashing”. While bioplastics are often described as being sustainable alternatives to conventional plastics, it is only under restricted applications that may bring some advantages over conventional petroleum-based plastics (SAPEA, 2020; SCEPT, 2023).