## 4 Bioindicators and Levels of PAEs in the Aquatic Environment
Understanding bioaccumulation processes is of considerable importance for several reasons: (i) bioaccumulation in the tissues of organisms may increase the persistence of chemicals in the environment; (ii) stored chemicals are not exposed to physical, chemical, or direct biochemical degradation; (iii) accumulated biologically active substances can directly affect the health of an individual; and (iv) predators of those contaminated organisms may be threatened by the effects of the toxic substances as they can, at their turn, accumulate such substances, even at higher concentrations (biomagnification) [66]. An ideal bioaccumulator is a bioindicator that, due to its characteristics, accumulates more pollutants than other species in the same environment. In this way, this sentinel organism will better reflect contamination levels even in areas where there is apparently nohuman impact. As reported in the literature [67], contamination levels of water posed varied ecological risks to organisms and environment composition. Generally, the concentration levels found in water are three orders of magnitude lower than that found in sediment and biota; however, the predominant PAEs' composition congeners are similar, for example, the greatest contribution of total phthalates is usually provided by DnBP and DEHP [68; 69] (see Table 3). Moreover, significant correlations were found between biota contamination levels and aqueous environment of biota origin [68]. In this context, some species bioaccumulate more than others, for example, due to their ecological behaviour (foraging/respiratory), which facilitates the assimilation of pollutants. Among these species, filter-feeding organisms are excellent models of biomonitoring (e.g., bivalves). Recently, for example, Mediterranean mussels (_Mytilus galloprovincialis_), organisms known to be bioindicators of environmental contamination, have been used as the sentinel species of pollution by plasticisers, including phthalates with excellent detection results [69]. Other eating habits, such as whales' 'bubble net feeding', lead to the accidental and massive ingestion of PAEs contained in plastic fragments and are one of the reasons why some organisms are more exposed to such dangerous substances [70]. For example, it has recently been observed that, among the blubber lipophilic constituents of the blue whale (_Balanoptera musculus_), four phthalates were significantly represented [71]. Phthalates can also highly contaminate organisms because they are contained in the plastic material exchanged for prey (e.g., plastic bags mistaken for jellyfish by sea turtles [72]). Emblematic cases of this frequent ingestion is associated with sea turtles, considered excellent descriptors of marine pollution [73; 74; 75; 76] and defined bioindicators for marine litter in the European Union Marine Strategy Framework Directive (MSFD) [77]. Recently, due to the high incidence of the discovery of plastic debris in the gastrointestinal tract of sea turtles, new evidences of major levels of phthalates in their tissues [78] and eggs [79]. Another frequent contamination process is related to the ingestion of prey that in turn had ingested plastic. This is now known for organisms at the top of the food chain (such as sharks) that therefore tend to accumulate pollutants due to biomagnification phenomena. In a case study in the Mediterranean Sea, the basking shark (_Cetorhinus maximus_) showed concentrations of mono-(2-ethylhexyl) phthalate (MEHP) (primary metabolite and DEHP exposure marker) in the muscles above the high values recorded in whale blubber (_Balanoptera physalus_) [70]. These organisms deserve particular interest and concern because they are often included in the lists of threatened species. In this context, the direct effects of exposure to PAEs could have negative effects on their health (including reproductive success) affecting their conservation status.