## 4 Results and Discussion
### Metal(Oids) in Surface Sediments  
As shown in Table 1, where the statistical summary of the metal(oid) concentrations is presented, the global concentrations in the sediments of the study area ranged from 6.00  
Figure 2: Spatial distribution of the sand fraction, mud (silt + clay) fraction and TOC concentrations in the surface sediments of the study area. to 56.40 (average 20.87 ug g\({}^{-1}\)) for As, 0.04 to 32.80 (average 6.39 ug g\({}^{-1}\)) for Cd, 3.00 to 248.00 (average 29.90 ug g\({}^{-1}\)) for Cr, 2.10 to 152.00 (average 34.71 ug g\({}^{-1}\)) for Cu, 0.05 to 18.35 (average 2.55 ug g\({}^{-1}\)) for Hg, 3.30 to 83.40 (average 11.14 ug g\({}^{-1}\)) for Ni, 8.90 to 806.00 (average 187.45 ug g\({}^{-1}\)) for Pb, and 49.00 to 6360.00 (average 1042.12 ug g\({}^{-1}\)) for Zn. In the case of the elements analyzed, their general average concentrations were, in decreasing order, Zn \(>\) Pb \(>\) Cu \(>\) Cr \(>\) As \(>\) Ni \(>\) Cd \(>\) Hg. Comparing between the port area and the adjacent coastal area, all the elements analyzed, except for As, showed higher concentrations within the port area. On the other hand, Figure 3 shows the spatial distribution maps of metal(oid) concentrations in the sediments of the studied area. In general, the highest concentrations of metal(oids) in the sediments correspond to the middle-inner part of the estuary, while in the coastal area, only As, as shown in Table 1, was present at remarkable concentrations. In the cases of Cr and Ni, their presence in the coastal area has been attributed to a very local anomaly due to the lack of spatial continuity. In addition to the spatial distribution maps, Figure S1 of the Supplementary Material shows the Pearson correlation matrix of the different metal(oids) analyzed, together with the granulometric sizes and the TOC. According to this, all the metal(oids) presented significant correlations (\(p<0.05\)) with the sizes of the sediments and the concentrations of TOC in them. This is because both finer sediments and organic matter are widely recognized as important metal(oid) sinks due to their electronegativity, which allows them to trap metal(oid) cations mainly by adsorption mechanisms [42; 44], and due to the high correlation detected, they play a very important role in trapping metal(oids) in the study area. Among the different correlations identified, both Ni and Cr showed the lowest correlation coefficients, below 0.65 (\(p<0.05\)). This fact, contrasted with the spatial distribution maps, shows that both have different behaviors from the rest of the analyzed elements. Excluding the coastal anomalies of both elements, their highest concentrations are very localized in the innermost part of the estuary, where their concentrations decrease rapidly towards the coastal area, which indicates that the highest concentrations are derived from a source located in the tail of the estuary. The locations of anomalies inside the estuary are consistent with the locations of different authorized industrial wastewater points in surrounding industries, such as a steel complex, an industry that produces primary aluminum and an urban solid waste dump. All these facilities report significant quantities of Ni and Cr in their treated effluents, and we thus consider these effluents as the main source of both elements in the sediments.