Large quantities of plastics are released from terrestrial environments into the marine realm, creating significant environmental problems. The severity of this issue is increasing as the demand for plastic, and consequently the release of plastic debris into the ocean, continues to rise. Most plastics are petrochemical in origin, derived from the polymerization of monomers to create synthetic organic polymers. Their versatile properties have driven mass production to meet the growing demand for plastics in a wide range of applications. Nowadays, plastics are integral to almost all aspects of daily life, including transport, clothing, construction, and packaging materials. Due to waste mismanagement and littering, plastic debris accumulates widely in natural environments, including the ocean, heightening scientific concern and public awareness about plastic pollution.
Research has focused on microplastics (particle size: 1µm – 5mm) and, more recently, nanoplastics (particle size: <1µm), and their potential impact on the ocean environment. Micro- and nanoplastics can originate from primary industrial sources or from the degradation of macroplastics (particle size: >5mm). Various physical, chemical, and biological processes facilitate the fragmentation and degradation of plastics. Due to their small size, microplastics and nanoplastics become bioavailable and can bioaccumulate, although current evidence on biomagnification across marine food webs is ambiguous. Micro- and nanoplastics can negatively affect biota by causing inflammation, oxidative stress, and disruption of hormone signaling. Additionally, plastics often contain additives (e.g. softeners, flame retardants) that may be incorporated and lead to potentially harmful effects on host organisms. It is likely that organisms higher up in the food chain are also impacted by plastic pollution.
The longevity of plastic waste in the environment remains uncertain. Plastics are durable and degrade slowly, leading to the belief that they may persist in the environment for centuries or even millennia. However, floating plastics not only fragment in the marine environment but are also degraded through photooxidation, which, combined with microbial degradation, might significantly shorten their lifespan. Moreover, plastics are rich in chemical energy, making polymer oxidation reactions exergonic. Therefore, plastic degradation can be a viable strategy for microorganisms to obtain energy and/or carbon. Earlier studies have shown that a diversity of microbes colonize plastic marine debris (PMD), and some evidence suggests that these communities are not merely opportunistic, but that different polymers may select for specific, plastic-related communities. Other studies have found terrestrial microbes that seemingly degrade some plastic polymers directly. Nevertheless, it is currently debated whether such metabolic traits exist in the marine environment and to what extent they contribute to plastic removal from the ocean.
A significant challenge in ongoing research is to clearly link apparent plastic degradation to microbial action and to determine the rate of plastic degradation. The overarching goal of the ERC project VORTEX is to assess the marine degradation of important plastics by applying innovative stable isotope assays in tandem with lipidomics, NGS-based microbial diversity, and functional gene analyses. VORTEX comprises three major objectives and work packages with clear interconnections: (i) to estimate the potential for and kinetics of microbial degradation of the most relevant plastics in the ocean, (ii) to identify and quantify key microbes mediating degradation, and (iii) to determine the boundary conditions that promote or hinder degradation and to identify potential pathways of degradation.
