Thesis Title: Βiodegradation of microplastics of polystyrene (PS) and polyethylene (LDPE) in seawater mesocosms

Monday 23 September 2019, at: 11:00, Venue: Hall Κ2.A7

Examination Committee

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

Abstract

Τhe advantages of plastics, mainly due to their durability, low cost and resistance, coupled with low production costs, have contributed to the worldwide development of a large industry. As a result, an increased production of plastic waste has been noticed. Plastics' characteristics, as well as their resistance to degradation, have created one of the bigger ecological problems of modern era, which requires increased efforts in order to deal with it. Biodegradation of plastics has been offering realistic answers to the problem of dealing with plastic waste in the last few years.

The current thesis aims to monitor the activity of microbial communities collected from the Souda pelagic zone in Chania and the effect of solar radiation on polystyrene and low density polyethylene films. The experiment simulated the marine environment, using four different aquariums, where the plastic was the only source of carbon. Virgin plastics of the two polymer types, were cut into square pieces (2 cm x 2 cm), were hanged on strings and were placed in the aquariums using appropriate stainless steel construction and remained there for four months. In two of the four aquariums, the maritime communities were inoculated. Sampling occurred every month in order to estimate the weight reduction, microbial growth, extracellular polymeric substances, sinking velocity and microplastic size distribution. Finally, Fourier transform infrared spectroscopy (FTIR) was performed to determine the effect of marine micro-organisms and solar radiation on the surface of the films. It was found that microorganisms managed to grow successfully in the marine mesocosm. During the second and third month both carbohydrates and proteins concentration, as well as microbial growth in all aquariums, decreased compared to the first month, but they again increased during the fourth month of sampling. For polystyrene, a weight reduction of 0,33% for Aquarium A, 3,02% for Aquarium B, 1.02% for Aquarium C, and 0,21% for Aquarium D was calculated. For the polyethylene, the weight reduction during the fourth month estimated as 0,46% for the Aquarium A, 2,85% for the Aquarium B, 1,36% for the Aquarium C, and 1,78% for the Aquarium D . In addition, nanoplastics were observed in some of the aquariums due to the combination of sunlight and of the microorganisms' action. Finally, the FTIR profiles of the LDPE films revealed the effect of UV radiation on the surface of the films in the first months and the microbial activity after biofilm development.