23 Juli 2020

Conclusions of a study on compostable plastics and microplastics unsupported by data

A new, heavenly cited study suggests that thin compostable plastic bags show very limited degradation and are a source of microplastics

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Francesco Degli lnnocenti of Novamont comments on the results of a study by Accinelli et al., recently published by Waste Management titled “Persistence in soil of microplastic films from ultra-thin compostable plastic bags and implications on soil Aspergillus flavus population“.

The abovementioned and heavily cited study (https://doi.org/10.1016/j.wasman.2020.06.011) suggests that thin compostable plastic bags show very limited degradation and are a source of microplastics. “Therefore, the application of industrially processed compost to agricultural fields is likely to contaminate the soil with these UT (Ultra Thin) film particles” state the authors and say “regulation should be seriously considered”.

This news is clearly of great concern and fuels the over-emotional discussion over biodegradable plastics. I have read the paper and some statements are totally unsupported by the data. In normal time, any criticism over the methodology and the conclusions of a scientific publication should be delivered by using the same media. For example with a “letter to the editor”. This will be done in due time. However, a novelty of modern times, which would deserve a doctoral thesis in sociology, is the union between academic research and web communication. Scientific articles become media tsunamis, often bearers of news of doom. Yes, “news of doom” because positive news does not make “audience”. Thus, I am forced to anticipate some preliminary technical remarks using less formal but faster media.

  1. Accinelli et al. makes claim about the risk that compostable bags produce microplastics during composting
  2. The best thing to do in order to verify whether a material produces fragments “during composting” is to make a composting test.
  3. However, Accinelli et al. did not perform any composting test. Thus, it is not particularly robust to draw conclusions on the formation of fragments during composting without performing any composting test
  4. They instead tested soil degradation by using a test method, which is neither standardised nor verified, based on soil burial of samples protected with a net in centrifuge tubes.
  5. The fragments increase toxin-producing Aspergillus flavus population. How Accinelli et al. can judge the environmental and safety relevance of the findings without any reference? What is the effect of other packaging or natural materials on these species? No data.

Above all. What was the purpose and scope of the research? Was it about the ecological risk in case of littering? This is a relevant subject and research on it is called for (https://doi.org/10.1021/acssuschemeng.0c01230). However, a proper methodological approach is then needed to reach any sensible conclusion. What is the expected transport route (bags do not bury themselves into centrifuge tubes); what are the conditions found in the different environmental compartments? What is the Predicted Environmental Concentration (PEC) of the bags in soil? What type of environmental conditions do the centrifuge tubes try to simulate?
We trust the researchers will complete the study by considering the fate and effects of littering. In the meantime, it would be relevant if conclusions and abstract could be limited to the findings and framed within the scope of the search, in order not to stir unfounded discussions and political speculations.

Source: Bioplastics MAGAZINE, 2020-06-26.

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