In an opinion article published on December 26, 2022, in the journal Waste Management, Ika Paul-Pont from the University Brest, Plouzané, France, and ten other scientists located in France, discuss the potential and limitations of biodegradable plastics as a solution to plastic pollution, focusing on potentially suitable applications, waste collection and treatment, biodegradability tests, and toxicity. Biodegradable plastics are designed for microbial conversion into CO2, methane, biomass, and mineral salts (see the FPF factsheet on “bioplastics”).
The scientists consider biodegradable plastics suitable for specific applications (FPF reported), for instance, if end-of-life collection is not possible or it is difficult (e.g., mulch films or fishing gear lost at sea). However, they highlighted that reduction strategies should always be favored over the shift to alternative materials. They think compostable plastics could be promising for food packaging if collected together with food waste. But, the author emphasized that existing organic waste collection and treatment facilities would need to be adapted. Only then the contamination of compostable waste with non-compostable waste (here also the education of consumers is key, FPF reported) would be prevented and the complete mineralization of biodegradable material guaranteed. The European Commission (EC) has also reported on biodegradable plastics in the open environment and concluded that these materials are no silver bullet for inappropriate waste management or plastic littering (FPF reported).
The scientists further discussed that, currently, tools are missing “to properly evaluate either the fate of biodegradable material or its rate of biodegradation in the natural environment.” For instance, biodegradation tests performed in the laboratory would not reflect natural environments, e.g., microbial composition, or available carbon sources. Moreover, Paul-Pont and co-authors pointed out that “universal biodegradability in any ecosystem on earth does not exist” since the parameters determining biodegradation rates (water, nutrients, temperature, etc.) vary greatly.
Most of the statements made by Paul-Pont correspond with those made in the EU policy framework on bio-based, biodegradable, and compostable plastics which the EC published on November 30, 2022 (FPF reported). Biodegradable plastics are also mentioned in a proposal for the revision of the EU legislation on packaging and packaging waste which the EC published also on November 30, 2022 (FPF reported). The EC is collecting feedback on the proposed changes to the packaging and packaging waste regulation until March 22, 2023.
Paul-Pont et al. additionally highlighted that it is currently not assured that biodegradable materials are safe. “There is still no regulation making them [compliance certifications] compulsory.” This would mean that if harmful compounds are released during biodegradation it would not necessarily be detected.
A study published in 2020 analyzed extracts of 43 bio-based and biodegradable materials for their chemical composition and mixture toxicity. It found that these “bioplastics” can contain thousands of chemicals and that their in vitro toxicity is comparable with conventional plastics (FPF reported).
In a more recent article published on December 26, 2022, in the journal Environmental Pollution, Marco Capolupo from the Italian Institute for Environmental Protection and Research (ISPRA), Rome, Italy, and co-authors assessed the chemical composition of bioplastic leachates as well as the biological effects of the leachates on the mussel Mytilus galloprovincialis.
Among the commercially available bioplastic products examined by the authors, the research focused on two made of biodegradable materials, a cup made of polylactic acid (PLA) and a compostable bag made of a mixture of PLA and polybutylene adipate terephthalate (PBAT). The researchers cut the products into pieces < 5 mm and leached them in artificial seawater for 14 days at room temperature. The chemical composition of the leachates was analyzed by gas chromatography-mass spectrometry (GC-MS) while that of the untreated plastic products was assessed by analytical pyrolysis (Py-GC-MS). To further investigate impacts on M. galloprovincialis embryo-larval development, motility, and survival as well as on nine biomarkers, Capolupo and co-authors exposed sperm and adult mussels to different leachate concentrations.
The scientists detected trace metals and bisphenol A (BPA, CAS 80-05-7) in all leachates. The concentrations of BPA ranged from 0.3 to 4.8 µg/L. Furthermore, they pointed out that the predominant chemical type in the compostable bag was non-intentionally added substances (NIAS). Concerning biological effects, the authors reported that the leachates induced embryotoxicity, and reduced egg fertilization and larvae motility in a concentration and material type-dependent manner. The assessment of biomarkers showed that leachates affected all lysosomal parameters as well as inhibited lysozyme activity. The differences in effects between the analyzed samples are “possibly reflecting the different chemical composition and/or concentration of the compounds in the leachate mixtures. However, the effects of some bioplastic leachates were comparable to (or even greater than) previously tested conventional polymers.”
References
Capolupo, M. et al. (2022). “Bioplastic leachates characterization and impacts on early larval stages and adult mussel cellular, biochemical and physiological responses.” Environmental Pollution. DOI: 10.1016/j.envpol.2022.120951
Paul-Pont, I. et al. (2022). “Discussion about suitable applications for biodegradable plastics regarding their sources, uses and end of life.” Waste Management. DOI: 10.1016/j.wasman.2022.12.022
