During the last decades, the production of bioplastics has emerged as a promising alternative to mitigate the environmental impact generated by the accumulation of unmanaged plastic waste on natural ecosystems. Biodegradable bioplastics are expected to be less persistent than conventional oil-based polymers; however, the conditions under which biodegradation tests are conducted may lead to discrepancies between laboratory results and the real environmental conditions. For freshwater ecosystems, previous studies have highlighted important gaps, such as the variability caused by the inoculum. To assess if the use of commercial lyophilized bacteria as inoculum reduces the test variability, the biodegradation of three microplastics (MPs) with distinct polymer origins, poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), polylactic acid (PLA), and polypropylene (PP), was studied in closed respirometers. Subsequently, following the reduction of the variability, the impact of the incubation temperature was evaluated at 10, 20 and 30 °C. Finally, the potential differences in the biodegradation process caused using different inocula were assessed with three different inoculum sources: the commercial freeze-dried bacteria, an activated sludge and digestate from biowaste. The results showed that freeze-dried bacteria could be used as an alternative inoculum to reduce inter-laboratory differences in the standardized test. Although no statistical differences were observed for PHB under identical incubation conditions with the freeze-dried inoculum, the results showed that the biodegradation of PHBV is highly influenced by temperature with higher values obtained at 35 °C than at 20 °C and 10 °C. Finally, the diversity and relative abundance of the inocula may significantly influence biodegradation outcomes, highlighting the inoculum source as a critical factor contributing to variability in this type of assay.
Gutiérrez et al. (2026) studied this question.