Mediterranean marine biodiversity is under threat by pollution. For this reason, the main objective of this thesis was to analyse the presence of pollutants of concern in Mediterranean marine species. These studies are located in the Valencian Community (Spain), where we find loggerhead turtles, striped dolphins, and jewel lanternfish. Hence, we: 1. Analysed pesticides, heavy metals and phthalates in tissues of loggerhead turtles. 2. Studied microdebris present in beaches that are sporadically used as nesting grounds by loggerhead turtles. 3. Analysed striped dolphins# exposure to microplastics. 4. Quantified jewel lanternfish exposure to microplastics and tested their role as bioindicators of microplastic pollution in the bathypelagic environment. Results indicate the ubiquity of all the analysed pollutants. Pesticide analyses showed that all the analysed loggerheads (N=25) were exposed to 39 pesticides, of which 38.5% are forbidden in the EU. Results indicated low heavy metal burden. Mean concentrations of Cd, Pb and Hg were 0.04 μg/g., 0.09 μg/g. and 0.03 μg/g w.w. in fat and 0.05 μg/g, 0.08 μg/g and 0.04 μg/g w.w. in muscle. The juvenile size could account for these low concentrations. Seven phthalate metabolites in turtles were detected in more than 85% of the samples (DR>85%). The sum of the median concentration of the phthalate metabolites that had DR>85%, showed a negative correlation with size and also a significant increase in concentration from 2020 onwards; possibly explained by an increase in single-use plastic, or by uncontrolled wastewater discharges. Microdebris in beaches was ubiquitous although concentrations were not of concern for the success of loggerhead turtle clutches. In July, total mean±SD was 5.66 ± 3.66 MPs/kg at surface and 12.15 ± 7.76 MPs/kg at depth; while in November values were 6.45 ± 4.42 MPs/kg at surface and 5.51 ± 3.14 MPs/kg at depth. There were no significant differences among beaches, months, depths nor protection regime. Polymers found were commonly used in consumer goods and tires.MPs were present in 90.5% of the striped dolphins (N=43), although amount per dolphin was low and variable (median = 5, range = 0 - 82). Polyacrylamide, PET and HDPE were the most common polymers. MPs concentration from different periods of time (1989 # 2007/2010#2017) or locations were not different. Finally, the jewel lanternfish, (N=97), showed high frequency of occurrence of MPs, although a low body burden. Size and body condition were not correlated with the number of MPs. To sum up, an overview of the pollutants in the westernmost part of the Mediterranean Sea is provided, focusing on the aforementioned species and highlighting their potential as bioindicators.