Biodegradability and impact on microbial biodiversity of bioplastics in marine environment

The dispersion of plastic waste in the marine environment is one of the most pressing global environmental challenges. Each year, millions of tons of plastics enter the oceans due to human activities and inadequate waste management. The persistence and poor biodegradability of conventional polymers cause long-term impacts on biodiversity and biogeochemical cycles. In response, research has increasingly focused on bio-based and potentially biodegradable plastics as more sustainable alternatives. However, their actual degradation under real marine conditions remains poorly understood, since most biodegradability tests are conducted under controlled settings such as composting or anaerobic digestion, which do not reflect the complexity of natural ecosystems. In addition, global environmental change, particularly rising atmospheric CO₂ and ocean acidification, may further influence the fate of bioplastics. By the end of the century, surface ocean pH is expected to decrease by approximately 0.08 units, potentially affecting both polymer degradation processes and the structure and activity of microbial communities involved. This thesis investigated the biodegradation of major commercial biopolyesters, including PBS, PBSA, PLA 3100HP, PLA Luminy Lx175, PBAT, and PHBH, in marine environments. The study evaluated polymer degradability, microbial colonization of plastic surfaces, known as the plastisphere, and the interaction between biodegradation and ocean acidification. Laboratory microcosm experiments simulated anoxic marine sediments, considered the final sink of plastic debris. Complementary in situ experiments were conducted near Panarea Island, Sicily, a natural CO₂ vent system providing a pH gradient to assess acidification effects under realistic conditions. Additionally, the thesis examined the impact of contaminants of emerging concern, alone and combined with acidification, on marine nanoplankton communities. By integrating physicochemical, microbiological, and molecular analyses, this research provides a comprehensive assessment of bioplastics and CECs in marine ecosystems, supporting more sustainable management strategies under future ocean change scenarios. These findings contribute to environmental risk assessment frameworks and policy development.