Effects of bioplastics and their leachates on marine bacterial communities.

Biobased biodegradable plastics (bioplastics) are promising alternatives fuel-based plastics. However, higher additive content is generally used to perform similarly to fuel-based materials. Moreover, plastic additives are not covalently bound to carbon chains and can leach into aquatic environments such as seawater, potentially impacting marine biota, though the extent of these effects is not yet fully understood. To evaluate the leaching behaviour in seawater of plastic additives from bioplastics materials and its impact on coastal surface marine bacterial communities, microcosm experiments were conducted using seawater amended with non-aged pellets of polylactic acid (PLA), poly-hydroxybutyrate (PHB), and commercial materials, a knife of PLA and a bag of PLA&PHB, under biotic and abiotic conditions for two months. Samples were taken weekly to study the bacterial abundance, bi-weekly to evaluate the leaching process and potential biodegradation products and, finally, at the end of the experiment to study the microbial communities. Chemical analysis was performed using suspect screening by means of Liquid Chromatography coupled to High-Resolution Mass Spectrometry (LCHRMS) equipped with Electrospray Ionization source working in positive and negative conditions. The experiment showed that 177 compounds were tentatively identified at confidence level 2, including plasticizers, UV filters, flame retardants, and PLA- and PHB-related degradation products, which were detected in similar proportions under abiotic and biotic processes. Bacterial communities exposed to PLA showed higher production and significant differences in the community composition, with PLA degraders being identified in the different plastispheres studied. Leachates impacted differently microbial communities in the free-living fraction, particle-attached fraction and in the plastisphere, indicating taxa-specific responses. To the best of our knowledge, this is the first study providing further insights into the influence of bioplastics and their leachates on marine microbial communities, contributing to our understanding of bioplastics' effects on the global oceans.