Assessment of the biodegradability of polylactic acid (PLA) in freshwater using EN ISO 14851:2019: Challenges and outcomes

The biodegradability of bioplastics in natural environments remains a highly debated topic within the scientific community. It is assessed primarily using the compostability standard EN 13432, although this, however, does not accurately reflect degradation processes occurring in aquatic environments. To verify the biodegradability of polylactic acid (PLA) in freshwater, two tests, differing only in the inoculum sampling location, were conducted according to EN ISO 14851:2019, measuring oxygen demand. However, to gain a comprehensive understanding, bioplastics biodegradation should be thoroughly investigated at multiple levels beyond oxygen consumption. Additional analyses, including morphological and thermal characterization of polymers and assessment of inoculum characteristics, are fundamental in providing valuable insights into degradation mechanisms. Biodegradability tests revealed low biodegradation rates (44.04 % and 23.38 %), with no evident weight change in PLA pellets during testing. Analytical techniques (FT-IR, DSC, SEM) indicated negligible visual or structural modifications between virgin and tested pellets. Therefore, under conditions specified by the standard PLA pellets did not undergo significant biodegradation in freshwater. Discrepancies between tests α and β suggested variability due to inoculum quality. A series of challenges persist when implementing this standard, including the lack of a threshold for use in clearly classifying a bioplastic as "biodegradable" and flexibility in selecting process parameters (e.g., test material shape and size, duration, temperature, inoculum percentage). Accordingly, to facilitate a reliable assessment of the biodegradability of bioplastics in freshwater, the EN ISO 14851:2019 standard should be amended and updated.