## 3 Results
### Total Hg in Biota
[PERSON] and [PERSON] [45] investigated the THg content within a population of 208 individuals caught in the Marano Lagoon and found the highest levels in females (0.74 mg kg\({}^{-1}\) ww) rather than males (0.48 mg kg\({}^{-1}\) ww), even though the captured males were bigger than females (18.5 and 16.0 TL cm on average). The authors hypothesised that THg bioconcentration for this species is affected not only by individual size and environmental characteristics of the sampling area but also by gender and reproductive season. The twaite shad, _Alosa fallax_, is an anadromous species that spends most of its life at sea and migrates to freshwater environments for breeding [121]. Only one specimen was successfully caught in this study (Marano basin; 28.5 cm in TL) and 0.76 mg kg\({}^{-1}\) ww of THg were measured in the muscle tissue, which is approximately three times higher than the median value recorded in adult specimens collected from the Gironde Estuary (South West France) [122]. This further confirms that the THg concentrations of fish in the Mediterranean Sea are higher compared to those caught in the adjacent Atlantic Ocean [123]. The anchovy, _Engranulis encrasicolus_, is a marine migrant and planktonic feeder that uses the lagoon habitat as a nursery ground. Only two specimens of 9 cm TL were analysed for Marano, with a THg concentration of 0.07 and 0.17 mg kg\({}^{-1}\) ww. These values fall within the range found in specimens (n = 45) from the eastern Adriatic (Croatia) (0.001-0.52 mg kg\({}^{-1}\); mean value 0.04 mg kg\({}^{-1}\) ww) [124], whereas the average value was 0.05 and 0.028 mg kg\({}^{-1}\) ww for the Mediterranean and Atlantic Oceans, respectively [123; 125]. The golden grey mullet C. _auratus_ was selected as the target species for priority pollutants monitoring in biota sensu WFD because it is one of the dominant species in the surveyed lagoon, being easy to identify and capture. It is a marine migrant species with a detritivore feeding strategy [52], and its life history makes it particularly appropriate to the current goals [126]. The TL content of FM1 specimens was slightly lower than that of the Marano and Grado basins, but the THg content was at least twice as high in FM1 and Grado as it was in Marano. The significant linear relationship (r = 0.7249; \(p\) < 0.001) occurring among these variables suggests the influence of THg content in sediment on bioaccumulation for this detritivore species and confirmed the observation reported in the Ria de Aveiro (Portugal), a lagoon adjacent to the Atlantic Ocean that received Hg-containing effluents from a CAP from the 1950s until 1994 [126]. Taking into consideration that this species lives in proximity (contact) to the sediment, it is suitable for the calculation of the biota sediment accumulation factor (BSAF) [53] according to the formula:  
\[\text{BSAF}=\text{C}_{\text{(beta)}}/\text{C}_{\text{(sediment)}}\]  
The calculated values ranged from 0.023 to 0.098 (TEU4 and FM4, respectively), which were always lower than 1 and suggest that the Hg bioavailable for the transfer from sediment to biota is small (Figure 5). [PERSON] et al. [127] reported significantly higher values (up to 0.2) calculated for European seabream (_Sparus aurata_) and seabass (_Dicentrarchus labrax_) collected in the Orbetello Lagoon (Tuscany). However, it should be noted that these species have different feeding habits with respect to grey mullet and are at an upper level along the trophic chain. Taking into consideration the results found for Hg speciation, no significant relationships were found between the calculated BSAFs and the fractions investigated. The consumption of fish accounts for about 17% of the total proteins provided to the population with the diet [128], and it is strongly recommended also for the assumption of minerals, vitamins, and omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) [129]. Therefore, the calculation of the potential exposure/risk to humans must be carefully considered.