In a new study, scientists at the Spanish Institute of Environmental Assessment and Water Research and the Institute of Agrochemistry and Food Technology (IATA-CSIC) argue that compostable plastics, and to a lesser degree recycled plastics, contain extractable chemicals that are toxic to fish liver cells. European Bioplastics has disputed the methodology and conclusions of the study.
The article in question, “Comparative toxicity of conventional versus compostable plastic consumer products: An in-vitro assessment,” published in the Journal of Hazardous Materials, compared the “toxicity of [compostable plastics] and conventional plastics (virgin and recycled) to investigate whether photodegradation and composting of plastics can affect the toxic responses in PLHC-1 cells, a fish liver cell model successfully used in toxicological research.”
To that end, the researchers selected eight single-use plastic consumer products, including four compostable plastics (light bags for foodstuff and waste) and four conventional plastics (water bottles, carrier bag, garbage bags). Among the conventional plastics, they included two mechanically recycled plastic bags. The team then investigated “the in-vitro effects of methanolic extracts in terms of cytotoxicity, generation of reactive oxygen species (ROS), presence of CYP1A inducers and genotoxic compounds,” which are all indicators of how toxic a substance is to cells.
The scientists used methanol to extract substances from the different types of plastic to analyze their potential toxicity. The compounds were evaluated directly from the bag samples; after a simulation of aging with ultraviolet rays; through the tiny fragments of the bags that remained after being converted into compost, and through the fertilizer resulting from the composting process.
The team concluded that “methanolic extracts from compostable plastics were the most cytotoxic, while those from conventional plastics, particularly mechanically recycled plastics, had higher levels of CYP1A inducers and genotoxic compounds. Our results also show that plastic-induced toxicity can be enhanced by UV exposure, and that plastic residues remaining in final compost can be a significant source of pollutants to the environment.” They speculated that “this high toxicity is very likely due the addition of new plasticizers to biopolymers to improve their mechanical properties.”
European Bioplastics reacted by saying that “the method used in the study is a preliminary, not validated testing scheme, and the arguments made in the press release are misleading.” The news release has been picked up by tabloids like the Daily Mail in the United Kingdom, with accompanying sensationalist headlines.
The European bioplastics industry representative highlighted that compostable plastics and recycled or virgin conventional plastics are not classified as dangerous substances under EU Regulation (EC) No 1272/2008. They also noted that compostable plastics must pass ecotoxicity tests to be certified EN 13432 industrially compostable to ensure that there is no negative impact on soil.
In particular, experts from European Bioplastics argued that the choice of using methanol to extract substances from plastic was "questionable."
“The decision to use methanol is completely arbitrary on their end, and the paper provides no rationale for doing so,” the association said in a statement. “Further, methanol itself is classified as a toxic liquid. What is also lacking in the report is the proof that methanol extraction does not modify the chemical structure of the analyzed sample. The use of methanol therefore introduces a bias into the study, and the authors failed to provide enough information about the extraction procedure to rule out the possibility that it could have created artifacts.
"Extraction with methanol as a solvent does not have the same effect on all polymers meaning that results cannot be comparable for different types of polymers. Additionally, the results of toxicity tests on methanolic extracts from plastic cannot be directly applied to plastic itself. In fact, methanol extracts chemical substances from the product, and the highly concentrated extract is assessed. This is not at all comparable to a real-life chemical leakage in the environment or migration in food.”
The study’s authors briefly mention their choice of focusing on methanolic extracts, but do not elaborate on the reasons for that choice, nor do they address the objections above.
“We are aware that methanolic extracts represent the worst-case scenario, but even so, one of the most striking findings was that the chemicals extracted from compostable plastics (B1-B4) were cytotoxic to PLHC-1 cells, while those extracted from conventional plastics (P1-P4) were not.”
European Bioplastics said it was "extremely alarming" that the news release accompanying the study presented information in a sensationalist way. “We have seen this phenomenon reoccur more often recently, and not only is it harming the bioplastics industry, but all industries and the scientific community itself,” the industry body said in a statement. “One needs to remember that standards are ensuring at a legal and health level that the products are assessed and safe to use, according to their regulation requirements,” it concluded.