Thesis Title: Biodegradation of microplastics (pellets) polystyrene (PS) and polypropylene (PP) after exposure to UV radiation in marine environment microcosms.

Friday 23 November 2018, at: 12:00, Venue: Hall Κ2.A7

Examination Committee

• Professor Nicolas Kalogerakis (advisor)
• Associate Professor Danae Venieri
• Dr. Evdokia Syranidou

Abstract

Much of the world's plastic waste ends up in the aquatic and terrestrial ecosystems, endangering organisms and human life, while degrading the aesthetic value of the area and human well-being. Plastic pellets are one of the most common plastic waste found in seas and coasts throughout the world. They consist the raw material of the Plastic Industry and their transfer and behavior at sea is an interesting research field for the scientific community. Microspheres, while being in the marine environment, are exposed to solar radiation, resulting in a decrease of their structural integrity and fragmentation. The weathering which is taking place has been found to help in the process of biodegradation by microorganisms.

The purpose of this dissertation is to study the effect of the microbial communities of the Agios Onoufrios pelagic zone on polystyrene and polypropylene pellets in a simulated marine environment, where microplastics are the only source of carbon. The microspheres were initially kept in a UV-A irradiation chamber for a period of 4 months to achieve aging of the plastic (weathering). Subsequently the weathered plastics were placed in sterile conical flasks with sterile seawater and inoculated with the marine microbial communities. They were placed in a stirring bench for 4 months. Weight estimations of microplastics, microbial growth, extracellular polymer growth, sinking velocity, and microplastic size distribution were performed each month, in order to assess the effect of marine microorganisms on microspheres.

Overall, marine micro-organisms have succeeded in developing and successfully flourishing in the simulated marine microcosm. During the 2nd and 3rd month, there was a decrease in extracellular polymeric substances, namely proteins and carbohydrates, as well as in microbial growth, however during the 4th month they showed an increasing tendency. For polypropylene a weight reduction of 6.37% was observed, while for polystyrene the weight reduction was calculated at 1.30%. Yet a large percentage of nanoparticles were observed in polypropylene samples of the 4th month due to its biodegradation by marine microorganisms.