Titolo della tesi: The trophic status of Mediterranean loggerhead turtles (Caretta caretta) determined by stable isotope analysis and assessment of chemical contamination by plastic ingestion
Phthalic acid esters (PAEs) are regarded as the most ubiquitous chemicals, used in several industrial sectors for enhancing the properties of polymers, such as flexibility, softness, and workability. The monitoring of exposure to PAEs is crucial for animal health in the marine environment since several studies have demonstrated their toxicological action as endocrine disruptors, even at low exposures. The loggerhead turtle (Caretta caretta) is the most common sea turtle species in the Mediterranean Sea, where it can experience severe anthropogenic impacts and bioaccumulate heavy metals, organic contaminants and marine toxins from food, sediment, and water. Loggerhead turtles (Caretta caretta) can be chronically exposed to PAEs by ingesting plastic debris, but no information is available about PAEs levels in blood, and how these concentrations are related to the trophic ecology of turtles as a consequence of plastic ingestion.
This study, for the first time, investigated PAEs concentrations in blood of wild-caught Mediterranean loggerhead turtles throughout solid-phase extraction coupled with gas chromatography-ion trap/mass spectrometry. Secondly, the trophic ecology and integration of diet of turtles were studied through stable isotope analyses of delta13C and delta15N in skin and blood samples. Finally, plastic debris and polymers composition were analysed in faecal samples by ATR-FTIR Spectroscopy.
This study confirms that the loggerhead turtle is a good indicator of plastic pollution in the Mediterranean Sea, as has been proposed by EU Marine Strategy Framework Directive through the standardized protocol for the collection of marine debris. There is devastating evidence that plastic pollution is a threat for the loggerhead turtles living in the Mediterranean Sea, already at risk from overfishing, climate change and other forms of anthropogenic disturbance. Most of polymers (PP and PE) found in faecal samples are used in a wide variety of consumer products, mainly single-use plastics (floating debris).
In this study, a specific analytical methodology was developed and applied for the detection of different PAEs in blood samples of free-leaving loggerhead sea turtles and blood seems to be a good matrix to evaluate acute exposure to PAEs, especially when these data are correlated with dietary habitats and trophic conditions. The high concentration of some PAEs (DEHP and DBP) may be related to their crucial leaching from marine plastic litter, suggesting a more direct ingestion of plastic than bioaccumulation from contaminated prey. It is not excluded that the different distribution of PAEs with turtle size may be associated with accumulation of these chemicals during turtles’ lives. However, a significant correlation was found between DBP and DiBP levels and delta13C values, suggesting that turtle diet and foraging habitats might have also contributed to exposure among turtles. Isotope stable analyses of blood and skin showed a different isotopic signature in delta13C, suggesting also dietary habitat shift in different seasons.
The results of this study suggest that all marine species at high-trophic level in the marine food web may be largely exposed to phthalates, despite their different diet, feeding habitat and levels of exposure among species. There is a need for more research, especially long-term study to analyse the amount of plastic ingested (and their polymer composition) by different target marine species in order to find the relationship with concentration of several pollutants, in addition to plastic additives, in different tissues.