Biodegradable plastics are designed for microbial conversion into CO2, methane, biomass, and mineral salts and include compostable plastics meant to decompose in industrial composting facilities (see the FPF factsheet on “bioplastics”). Since biodegradability strongly depends on the prevailing conditions (FPF reported) different stakeholders, such as the European Commission, concluded that biodegradable plastics are not a silver bullet for inappropriate waste management or plastic littering (FPF reported). Instead, they are considered suitable for specific applications (FPF reported).
Another factor to be considered is that biodegradable plastics just like conventional ones can contain a wide variety of chemicals, including hazardous substances (FPF reported). In an article published on July 21, 2023, in the Journal of Hazardous Materials, Tiantian Wang from the Environmental Chemistry Department of IDAEA –CSIC, Barcelona, Spain, and co-authors compared the toxicity of four compostable with four conventional (non-biodegradable) plastic consumer products (e.g., bags for foodstuff) by also investigating the impacts of photodegradation and composting on toxicity.
The researchers cut the samples and extracted them for an hour ultrasound at room temperature. Subsequently, they used Poeciliopsis lucida hepatocellular carcinoma cells (PLHC-1) to test the extracts’ impacts on cell viability, reactive oxygen species (ROS) generation, the induction of 7-ethoxyresorufin-O-deethy lase (EROD) activity as an indicator for the presences of CYP1A inducers, and the presence of genotoxic compounds by the frequency of micronuclei formation. To study the impact of sunlight exposure and composting on toxicity, they irradiated all the samples for six hours with UVA and UVB light, and performed disintegration tests in two types of composts with one sample.
The experiments showed that extracts of compostable plastics decreased cell viability already after 24h of exposure which was not the case for extracts of conventional plastics. Two biodegradable extracts led to a slight increase in ROS generation, and all but one sample significantly induced EROD activities. Wang and co-authors further reported that “toxicity was enhanced by either photodegradation or composting of biodegradable plastics.” Concerning conventional plastics, they compared two virgin with two recycled products and found particularly the latter to contain CYP1A inducers and genotoxic compounds that further increased with photodegradation.
The authors concluded that “plastic residues remaining in final compost can be a significant source of pollutants to the environment”. It would be “crucial to investigate the composition of newly developed formulations for biodegradable plastics, as they may be more harmful than conventional ones” as well as to consider impacts of degradation mechanisms on toxicity.
In an article published on June 15, 2023, in the journal Current Analytical Chemistry, Giulia Simonetti from the University of Rome, Italy, and co-authors performed extraction and migration testing on seven types of food packaging labeled biodegradable or compostable. Their goal was to analyze for the presence of brominated flame retardants (BFRs) and their migration in food simulants (in 3% acetic acid and 96% ethanol) using gas chromatography and liquid chromatography spectrometry (GC/LC-MS/MS).
The scientists classified the compounds into “new BFRs”, i.e., not yet regulated and used as substitutes “to classical BFRs”, and bromophenols (BPhs). They reported that the concentrations of BPhs in extracts were two to three times higher than those of new-BFRs and in almost all samples “above the chosen precautionary limit (0.01 mg/kg).” The highest levels were found in baking papers. Given the low concentrations of new-BFRs in the extracts they only evaluated the migration of BPhs. Here, “only one of the baking papers (sample 6) exceeded the limit of 0.01 mg/kg, whereas all the other samples were below.”
The authors emphasized that their results were preliminary calling for further research including other food simulants and contaminants to characterize biodegradable packaging. BFRs have especially been connected with products made of recycled plastics (FPF reported) since they may contain electronic waste (FPF reported).
Another challenge that comes with biodegradable plastics is that consumers are confused about how to dispose them correctly calling for labeling and behavior interventions (FPF reported and here).
References
Wang, T. et al. (2023). “Comparative toxicity of conventional versus compostable plastic consumer products: An in-vitro assessment.” Journal of Hazardous Materials. DOI: 10.1016/j.jhazmat.2023.132123
Simonetti, G. et al. (2023). “A Survey on Bio-based Food Packaging Material About the Presence and Migration of Flame Retardants.” Current Analytical Chemistry. DOI: 10.2174/1573411019666230531140818
