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Study of the ecotoxicity and biodegradation of bioplastics

Karakoula Konstantina

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Year 2022
Type of Item Diploma Work
Bibliographic Citation Konstantina Karakoula, "Study of the ecotoxicity and biodegradation of bioplastics", Diploma Work, School of Chemical and Environmental Engineering, Technical University of Crete, Chania, Greece, 2022
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A large part of the plastic waste produced worldwide ends up in terrestrial and aquatic ecosystems, resulting in chemical pollution of the planet and threatening the integrity of global ecosystems, on which the survival of the natural environment and, by extension, humanity depends. Plastics are a serious factor in environmental pollution as, with the progress of science and technology, the ever-increasing human activities have led to their excessive use, and thus their production. The use of bioplastics can solve the pollution caused by conventional plastics in the future. However, microplastics and nanoplastics produced during the aging process of biodegradable plastics are a global concern due to their wide distribution and large quantities. In the context of this thesis, the ecotoxicity of PLA and PBAT bioplastics, which are two of the most widely used bioplastics, was studied in combination with Coffee Silverskin and MMT Clays on biomarkers such as the bacterium Vibrio fischeri and the fungus Penicillium rubrum. The ecotoxicity test was carried out in aqueous solutions as well as two different types of soil sample. Isolation and quantification of the bacterial genetic material in the soil samples was also carried out, to investigate any effect of bioplastics on soil bacterial microorganisms. Regarding the results from the toxicity test of the bioplastics against the bacterium V. fischeri and the fungus P. rubrum, after 30 d and 14 d respectively, no reduction of the bacterial or fungal population was observed as the values compared to control remained almost constant or showed small differences which, however, did not indicate any toxicity against microorganisms. This bacterium is not a sufficiently sensitive model for examining plastic toxicity and organic pollution, so the results of the present study agree with the literature. Likewise, toxicity was not manifested against the fungus either, but instead a small population increase was indicated during the measurement interval, which is because fungi are more resistant to toxicity tests than bacteria and to the biodegradation of the samples by the microorganism. P. rubrum can use the sample as a carbon source thus contributing to its faster growth. In the results concerning the soil microbial population for the two soil samples, at the interval of 60 d, none of the bioplastic samples shows toxicity against soil bacteria and fungi. The concentration of bacteria remains constant in relation to the control, while the concentration of the fungal population appears to be increasing and the values range approximately in the same orders of magnitude for both soils. Bioplastics are inherently complex materials in their composition but non-toxic in specific amounts in the soil. Fungi are good decomposers of the soil and as a result show excellent abilities to degrade materials.Molecular quantification for the bacteria presents in the two soil samples showed small differences between the two soil types, with a population decrease for the second sample. More specifically, for the cases of the presence of the bioplastics PLA+PBAT+30%CS+8%MMT Clays and PBAT, a small degree of toxicity was noted, at least in terms of the specific amount of bioplastic added and the specific period of two months that the samplings were carried out. This may be due to a lack of nutrients in the soil resulting in the inhibition of bacterial growth, but also to the soil differences between the two samples. In summary, PLA and PBAT are not bioplastics that become toxic to the microorganisms studied. The fungi both in the case of laboratory growth and in soil samples showed excellent resistance with simultaneous growth since they can biodegrade bioplastics, in a terrestrial environment where they use plastic microspheres as a carbon source.

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