## 4 Results and Discussion
### Evaluation of the Contamination and Ecotoxicological Risks
#### 4.2.1 Contamination Assessment
Its distribution describes an almost regular increase seaward (Figure 7c). Pb. The average values of Pb in the whole area (12.1 ppm, Table 3), with a maximum of 24 ppm, match well with the background data (18 ppm, Table 2) and the average marine shale. Some samples, however, show a C\({}_{f}\) slightly over 1 (Table 4). The ER and I\({}_{geo}\) indexes are permanently less than the minimum threshold values (Table 4). Both the present average Pb contents and the background values are strongly lower than the L1 threshold level of 30 ppm (Table 2) suggesting limited anthropogenic Pb inputs. Sr. Strontium has an average concentration of 353 ppm (maximum of 436 ppm, Table 3) that are comparable to the local background and slightly higher than average marine shale (Table 2). This element has a strong affinity for carbonates and its concentrations show higher values in correspondence of the residual facies BSF3. Among the sedimentary quality index, the I\({}_{geo}\) is constantly lower than minimum threshold value, but the EF index is higher than 2 (low enrichment, Table 4) in many samples, likely due for the way the index is calculated on a normalized base. Zn. Zinc concentration records an average of 49 ppm and a maximum of 95 ppm (Table 3) that are, in general, slightly lower than local background and average marine shale values (Table 2). The sediment quality index displays few observations of the C\({}_{f}\) value of 1, whereas the EF and I\({}_{geo}\) indexes are constantly lower than minimum threshold values (Table 4). All the observations are below the L1 threshold levels (100 ppm, Table 2) pointing therefore to a limited anthropogenic contribution for this element. As regard the cumulative impact of the elements it is important to recall that the mC\({}_{d}\) and the PLI were calculated considering only metals or trace elements that show almost one value of C\({}_{f}\) > 1 (As, Ba, Ga, Pb, Sr, and Zn). Despite the cumulative impact of more anthropogenic substances, the values of mC\({}_{d}\) are always below the threshold of 1.5, so all sample sites fall in the very low polluted class (Table 4). On the other hand, the PLI shows values slightly higher than 1 in front of the Civitanova Marche, at the higher depths towards the offshore, particularly on the south-eastern part of the study area, and in front of the Tronto River. While the high values of PLI present in the offshore are attributed to the fine grain size sediments coming from the north and belonging to the BSF1 Facies (Table 3, Figure 9), those occurring in the area between Chienti and Ete Vivo Rivers could be the results of local pollution inputs, in particular the pollution in this area could have been higher if it were related to finer grain-size. In this coastal area, the pollution is due to high values of As, followed by Pb and Zn. The high concentrations of heavy metals, mainly As, could be caused by the discharge of processing residues of fertilizer production industries that were operative along the southern Marche coast in the last century. The following elements exhibit a Cf lower than one. Co. The concentrations of Co in the whole area display an average value of 7.8 ppm and reach a maximum of 13 ppm (Table 3), in general below the local background and the average marine shale (Table 2), that suggest a regional depletion compared to global references. Its distribution displays an almost regular increase seaward (Figure 8a), common to all the elements included in the BSF1. The C\({}_{f}\) values are constantly less than 1. Cr. Chromium average concentration is 61.5 ppm with a maximum of 101 ppm (Table 3). The average marine shale (90 ppm Cr, Table 2) and the local background (128 ppm Cr, Table 2) values are comparable or higher indicating that there is no enrichment respect to the pre-industrial period. In some stations close to the coast, mainly sandy, some higher values are recorded and could be either related to possible anthropic inputs or to selective enrichment in heavy minerals, given the high values of other elements such as Zr and Ti.