Nanoplastic Degradation in the Wadden Sea: The Role of Microorganisms & Photodegradation.
Supervisor: Helge Niemann (Utrecht Univ)
Plastic debris has become a major kind of marine litter since it was produced on a large scale in the 1950s. The plastic pollution in the oceans has reached alarming levels due to its uncontrolled production and poor management practices. Although there are many sources of marine plastic debris, land-based and maritime activities account for the largest share. Even though the current accumulation level of marine plastic debris could be controlled, it would take decades for the already existent plastics to degrade. Most frequently, the kind or geometry of the marine debris is used for categorization rather than the size. Based on the size the marine plastic litter can be classified as: macroplastics (>5mm in size), microplastics (5 mm – 1μm in size), and nanoplastics (NP) (<1μm in size). Due to the lack of accurate detection techniques, there are very few studies investigating NP in the marine environment. Physical, chemical, and biological processes cause weathering and fragmentation of macroplastics, which triggers the formation of NP. The aerobic or anaerobic microbial degradation determines the fate of these NP. This study showed that UV induced plastic fragmentation into NP could induce microbial degradation. The study used 13C labelled polyethylene (PE) & polypropylene (PP). Several methods like Gas Chromatography (GC), Gas Chromatography – Mass Spectrometry (GC-MS), Isotope-Ratio Mass Spectrometry (IR-MS) were used for analyzing the kinetics of NP degradation. The main findings of this study show that 13C-CO2 was produced, indicating that the microorganisms were using the dissolved organic carbon (DOC) from the plastics to synthesize the degradation product CO2. The degradation rate of 13C labelled PP was higher than 13C labelled PE by the microbes thus suggesting that the type plastic polymer along with the age may be crucial factors for the degradation. Such a microbiological-biogeochemical approach could be particularly useful in marine NP pollution studies. On the other hand, even though these microbial degradation processes are very slow, they could represent a major contributor to plastics mineralization in the marine environment.