## 4 Bioindicators and Levels of PAEs in the Aquatic Environment
Moreover, these species, which best represent the environmental contamination of phthalates, allow us to deduce the incidence of these ubiquitous substances along the food chain, with consequent risks associated with the health of ecosystems and humans. In aquatic environments, the concentration levels of PAEs recorded are variable, as the pollution associated with different sampling areas. In this context, within the same sampling site, a further variability is given by the type of bioindicator analysed based on physiological characteristics, trophic level, feeding behaviour, etc. Table 3 shows data on the concentration of the main phthalates industrially used and analysed for environmental biomonitoring in different classes of organisms. In this table, the different concentration values of 16 phthalates appear to be related to the type of organism, the geographical area, and the type of tissue analysed. \begin{table}
\begin{tabular}{l l l l l l l l l l l l l l l l l} \hline \hline  
Considering two tissue types from three fish species, the DiNP showed greater values in the gills than the muscles, with a higher average value recorded in the gills of _M. barbatus_ (1491 ng/g d.w.). Similarly, the same sample shows a higher mean concentration value of DMP (649 ng/g d.w.) than the corresponding muscle sample, the other samples of the same work, and all samples of other organisms analysed in Table 3 (thirty-three fish, four bivalves, two crustaceans, one gastropod, one mammal, seven sea turtles, and three different zooplankton samples). High DEP values were found in fat samples of _L. albirostris_ (13,800 ng/g d.w.) and _T. truncatus_ (4800 ng/g d.w.) [90]. However, in the latter, the concentration is expressed in dry weight, despite the low water content in the fat samples (about 10%) [93] and the levels would be comparable to those found in the gonads (5718 ng/g w.w.) and liver (3937 ng/g w.w.) of sea turtles _D. coriacea_ stranded in the coast of Sicily (Mediterranean Sea) [78]. High DEP values, although a smaller order of magnitude than those discovered in _D. coriacea_, were also observed in the soft tissues of the bivalve _A. noae_ (540.0 ng/g w.w.) and in some holduurian species (490 ng/gw.w.) in the marine-protected area of Cabrera (Balearic Sea) [69], indicating that these animals may be considered good bioliotators of that substance. Regarding the DiBP, the highest levels were found by [PERSON] et al. (2021) in China in the muscles of fish _C. striata_ (1938 ng/g d.w.), _S. ocellatus_ (1822 ng/g d.w.), and _T. ovatus_ (1791 ng/g d.w.). For the DnBP, the highest levels were detected in sea turtles _D. coriacea_ and _C. caretta_ and, considering the different analysed tissues, the gonads showed greater contamination (12,166.7 ng/g w.w. in _D. coriaceous_ and 4520.8 in _C. caretta_) [78]. DMEP, DBEP, DCHP, and DPHP are analysed in one work reported in Table 3 [81] and the concentration values are relatively lower than the other investigated phthalates in the same work and, in general, in the table. The highest concentrations of BBzP are related to _D. coriacea_ (16,014.5 ng/g w.w. in the liver and 12,532.6 ng/g w.w. in the gonads) [78]. Except for the work of [PERSON] et al. (2020), which investigates only the DEP as phthalate, in all the research illustrated in Table 3, the DEHP has been studied. Significant levels of DEHP were observed in asciadians _H. momus_ (9095.0 and 5556.0 ng/g d.w.) and _M. exasperatus_ (4988.0 and 4851.0 ng/g d.w.) [84] in mussels (8355.6 ng/g d.w.) [86] and in zooplankton (size class: 150-500 \(\upmu\)m and size \(>\) 1000 \(\upmu\)m, 6659.2 and 5586.7 ng/g d.w., respectively) [92]. However, considering the high water content of the latter organisms (for example, zooplankton consists of 90% water [94]), the concentration values in wet weight would be lower. In this context, the highest average subsequent values are for the gonads of _D. coriacea_ (5572.9 ng/g w.w.) and the fat of _C. caretta_ (4295.6 ng/g w.w.) [78], or the soft tissues of bivalve _A. noae_ (2580.0 ng/g w.w.) [69].