Formation, characterization of secondary nanoplastics released from biodegradable microplastics of starch origin, and cellular response and hyperspectral imaging of Caenorhabditis elegans exposed to them tue

In the last 50 years, plastic production has increased significantly due to its widespread use in strategic sectors, leading to serious environmental problems in both aquatic and terrestrial ecosystems. In this context, biodegradable plastics have emerged as an ecological alternative to conventional plastics, due to their potential to degrade more easily in the environment. However, during their degradation, these materials may generate micro- and nanoplastics, whose environmental impacts are still not fully understood. Particularly, secondary nanoplastics-nanoplastic particles resulting from the natural degradation of micro- and macroplastics-have recently been recognized as emerging but concerning environmental contaminants. The free-living nematode Caenorhabditis elegans stands out as an excellent model organism in ecotoxicological studies. This thesis examines the use of C. elegans to assess the bioavailability and toxicity of secondary nanoplastics (PBAT/SNP) formed by the abiotic degradation of poly (butylene adipate-co-terephthalate) (PBAT) microplastics, a biodegradable starch-derived plastic. After detailed characterization of these produced PBAT/SNPs, they were tested for cellular response by exposure to different concentrations. The bioavailability and toxicity of degradated PBAT/SNPs in C. elegans were evaluated using lethality, behavioral and reproductive endpoints. Hyperspectral imaging of PBAT/SNPs was evaluated using different microscopy techniques. It was recorded that PBAT/SNPs formed at the end of the 7-day abiotic degradation period were spherical particles with an average diameter of 69.93 mm, negative surface charged particles with a zeta potential of-7.28 mV, and very stable particles with a fairly homogeneous distribution with a PDI value of 0.043. The functional groups of PBAT/SNPs were confirmed by FT-IR spectra. This analysis revealed that after degradation, PBAT peaks weakened and some peaks disappeared or shifted, supporting our conclusion that degradation had occurred. Lethal effects of PBAT/SNPs in the concentration range of 50-500 mg/ml on C. elegans and survival percentages were evaluated with thermotolerance experiments and it was recorded that 100 mg/ml was the most effective. As a result of these bioassays, it was understood that nanoplastics were more toxic at low concentrations and did not have a toxic effect at high concentrations. The main reason for this situation is attributed to the aggregation of nanoplastics at high concentrations. At high concentrations, nanoplastics form larger particles, preventing uptake by C. elegans. These results are also supported by hyperspectral imaging performed with phase contrast microscopy. The intestinal contents of C. elegans in the control group without nanoplastics and the experimental groups containing PBAT/SNPs at high concentrations of 250 and 500 mg/ml were turquoise, changing to green. This appearance is evidence that C. elegans were fed only the OP50 strain.