EFFECTS OF POLLUTANTS ORIGINATING FROM PLASTICS ON ASCIDIANS:DEVELOPMENT AND SURVIVAL

Marine pollution was defined as “the introduction by man of substances or energy into the marine environment, which results or is likely to result in deleterious effects such as harm to marine life” (UNCLOS, 1982). To develop management protocols for pollutants present in marine environment it is important to fill the gap of knowledge about their effects on environmental and human health. This work centers on the effects of different kinds of pollutants that originate from plastics on marine invertebrates. The first part of this study focused on toxic and teratogenic effects of a chemical produced by plastic degradation, Bisphenol A (BPA), particularly considering the effects on nervous system and sensory organs of ascidians. The second part is centered on the impact of microplastics (MPs), on ascidians and sea urchin larvae. BPA is an organic compound used in the manufacturing of polycarbonate plastics and epoxy resins. After the degradation of food and beverage containers made of BPA, it can be released in food and water and be ingested, or reach the environment. Many different negative effects have been reported on human health and on wildlife. In this study, the effects of different concentrations of BPA have been analyzed on ontogenetic processes, embryogenesis, nervous system development and sensory organ differentiation in different ascidian species, namely Ciona robusta, Ciona intestinalis and Phallusia mammillata. The most sensitive developmental step was the first cell division both in C. robusta and P. mammillata. The teratogenic effect of BPA was confirmed in ascidians and the main alterations reported involved GABAergic and dopaminergic neural populations and pigment cells differentiation. Specific alterations of pigmented organs were reported, namely abnormal deposition of pigments, absence of one or both pigmented organs or presence of supernumerary ones. Since similar effects on nervous system and sensory organs were already reported in different vertebrate species, ascidian species confirmed their value as invertebrate animal model for preliminary screenings of effects of pollutants. In C. intestinalis, exposure to BPA altered genes expression of transcription factors involved in central nervous system and pigment cells specification, as Ci-Six3/6 and Ci-Pax6. Similar alteration were previously described as a consequence of perturbation of FGF and Wnt signaling pathways leading to hypothesize that BPA act at some point of the cascade activated by these pathways. At last, the co-exposure to BPA and an inverse agonist of estrogen related receptor (ERR), 4-hydroxytamoxifen (4-OHT), during embryogenesis produced a rescue of normal pigmented organs phenotype in P. mammillata. In zebrafish, it was previously demonstrated that BPA 3 exposure determines otolith malformations through its binding to ERRγ. Our results support the idea that also in ascidians the effects of BPA were mediated by ERR. Plastic debris that reach the marine environment can become a threat to wildlife not only because they release chemicals compound in the seawater, but also because the fragmentation and degradation of these products produce small particles named microplastics (MPs). In this study, the effects of polystyrene micro particles of 1 and 10 μm of diameter were analyzed on embryonic development of ascidians and sea urchins and on metamorphosis and survival rate of ascidian juveniles. Ascidian lecitotrophic larvae were not affected by the presence of microsphere in culture medium. Filter feeders ascidian juveniles and suspension feeders plutei were both able to ingest MPs. Exposure during the metamorphosis produced a delay of growth in ascidians, since the presence of MPs in the digestive system reduced the food intake. Moreover, the effects on metamorphosis were more strong in presence of 10 μm beads than of 1 μm ones, probably because smallest ones can be more easily expelled with feces. Body growth was altered also in sea urchin. When MPs are present at low concentrations (0.125 and 1.25 μg/ml) juveniles were able to expel them in 24 hours and plutei in 6 hours. However at higher concentrations (12.5 and 25 μg/ml), MPs persisted longer in the digestive system. Moreover, comparing the intake efficiency of the ascidian and plutei, the sessile filtering organisms appeared more vulnerable to MPs effects than pelagic suspension feeders. At last, 1 μm MPs were able to translocate from digestive system of ascidian juveniles. Histological analysis revealed that some particles crossed the stomach wall, and some were phagocytized by blood cells. These data highlight that MPs not only negatively impact the feeding ability of marine species, but probably further affect the physiology of organisms after translocation. The wide range of alterations and the possible subsequent negative effects of BPA and MPs make clear that a monitoring of concentrations and distributions of these pollutants in natural environment is required. Moreover, a reduction of the use of plastic products and new policies on plastic wastes are desirable to avoid the increase of distribution of these new pollutants that could negatively impact marine wildlife.