La Pietra, Alessandra (2026) Microplastics in the aquatic environment: toxicity and combined effects with bisphenol A in zebrafish. [Tesi di dottorato]

Documento PDF TesiLaPietra38ciclo.pdf Visibile a [TBR] Amministratori dell'archivio Download (10MB) | Richiedi una copia

Abstract

Microplastics (MPs), generally defined as plastic particles in the range of 5 mm and 1 µm, are currently one of the most widespread and persistent contaminants in aquatic ecosystems. MPs derive from the fragmentation of larger plastic debris (secondary microplastics) or from primary sources such as microbeads and synthetic fibers (primary microplastics). These particles accumulate in the environment, and their persistence facilitates ingestion by a broad range of organisms, promoting bioaccumulation and trophic transfer within the food chain. One MPs characteristic is the hydrophobic surface that allows them to absorb environmental pollutants thus acting as carriers, a phenomenon known as the Trojan horse effect. Given the exponential increase in microplastic pollution, which is a cause for concern, and the still limited understanding of their biological effects, the scientific community is focalized to analyze their effects, accumulation and persistence in organisms. For this reason, the present study investigates the toxicity of microplastics and their role as carriers through multidisciplinary approach combining histological, biochemical, and molecular analyses and using zebrafish (Danio rerio), model organism widely used also in ecotoxicological research. In the first experimental phase, zebrafish embryos were used to compare two different sizes of polystyrene microplastics (PS-MPs) at 0.01, 0.1, 1.0, and 10.0 mgL-1. In the second phase the embryos were first exposed to bisphenol A (BPA), a known endocrine disruptor, at 6.25, 12.5, 25.0 and 50.0 µM for 72 h. Then, to assess the ability of PS-MPs to modulate the effects of BPA, embryos were co-exposed to 1 µm PS-MPs at 1.0 mgL-1 and BPA both at 12.5 µM and 25.0 µM. In the third experimental part, terephthalate microplastics (PET-MPs), ranging in size from 30 to 100 µm, were tested on adult zebrafish at concentration of 500 µgL-1, mixed into the food, for 10 and 20 days. The results show that both sizes of PS-MPs accumulate in the larvae, alter heart rate, and cause malformations in the zebrafish larvae at higher concentrations (1.0 and 10.0 mgL-1). Furthermore, smaller PS-MPs induce oxidative stress and apoptosis at 10.0 mgL-1. Regarding BPA, it reduces the survival at 50.0 µM and the hatching rate at higher concentrations tested (25.0 µM and 50.0 µM). In addition, it causes bradycardia at 12.5 and 25.0 µM in zebrafish larvae. During co-exposure with PS-MPs and BPA at 12.5 μM only a trend towards improvement is observed in the heart rate confirmed by molecular analysis of the genes involved in cardiac development. Instead, in co-exposure with higher concentration of BPA (25.0 µM), PS-MPs improve the hatching process, the heart rate and neurotoxicity impaired by BPA, findings confirmed by analyses of genes involved in the development. Furthermore, the same mitigating trend is observed in the analysis of poly(ADPribosyl)ation system, involved in DNA damage, in glial fibrillary acidic protein expression, essential for neurodevelopment, and in acetylcholinesterase activity. On the other hand, analysis of redox homeostasis reveals an exacerbation of BPA effects, suggesting an endpoint-specific role of PS-MPs. Studies conducted on adult zebrafish reveal that PET-MPs damage ovarian tissue. Prolonged exposure led to an increase in immature follicles and a decrease in mature ones, a finding consistent with the analysis of the gonadosomatic index, which decreases after 20 days of exposure. These results are confirmed by molecular analysis of the genes involved in the development and maintenance of ovarian tissue. In addition, an increase of poly(ADPribosyl)ation polymerase expression and activity emerged in both times of exposure suggesting DNA damage. Currently, further studies are underway to investigate tissue alterations in the intestine, brain, and gills, as well as changes in redox status, gene expression of key markers, and the potential accumulation of microplastics.

Downloads

Actions (login required)

Modifica documento