Compostable plastics in marine environment

The bestselling compostable plastics are polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT). These plastics are biodegradable in industrial compost conditions but their degradation and colonization by the microbial community is poorly documented. To better understand their degradation in marine environment as well as the dynamics of bacterial colonization of these plastics after a long time of immersion (99 days, 160 days and 260 days), compostable (PBAT, semi-crystalline and amorphous PLA) and non-compostable plastic (polystyrene) were immerged in marine aquarium. 16S rRNA amplicon sequencing and chemical analysis were used to characterize these samples. Moreover, the influence of the temperature on plastic degradation was investigated in artificial water. PBAT had a significative weight lost reaching 3% after 260 days of immersion, unlike other polymers having stable weight. Chemical parameters varied for the three compostable plastics but the degradation was very slow. The temperature, an abiotic parameter, significantly influenced the plastic degradation, with a better degradation for higher temperature. Finally, microbial community structure varied according the immersion time with a high proportions of Archeae, while the plastisphere structure of PBAT was specific. However, a core of microbial microorganisms was observed on all the plastics and after the three immersion times. A better understanding of compostable plastic degradability in marine environment is crucial to evaluate their impact on the environment and to eco-design new recyclable plastics with optimal properties degradation.