## 4 Results and Discussion
### Multivariate Analysis  
To study the relevance of the data to factorial analyses, the Kaiser-Meyer-Olkin (KMO) test was used, which measures the adequacy of the sampling performed for each variable in the model, as well as the whole model itself, evaluating the proportion of variance between variables, which could be caused by several factors. The results of this analysis show a general KMO of 0.892, indicative of good fitness. The multivariate analysis was performed using the main components with autoscaled values, followed by varimax rotation using Euclidean distance and [PERSON]'s clustering method, which obtaining only two factors that explained 87.9% of the variance. The first factor explained 78.4% of the variance, and grouped all the parameters analyzed except for Ni and Cr. In this case, the only variable with a negative factorial weight is the sand size, while the rest present positive factorial weights. This allows us to link this variable with metal(oids) with a greater rate of dispersion in the studied area, the higher concentrations of which are associated with the finer size of the sediment. It should be noted that all the variables analyzed have comparable relative weights, so there is no dominant pollutant in the area. The second factor explained 9.5% of the total variance, and in this case, the factorial weights of the Ni and Cr variables were both negative. Between both, Ni, which is the element with the lowest variability, is the one with the greatest discrimination. This allows us to link this factor with natural geochemical factors, except in the innermost zone of the estuary, where it seems to be linked to the anthropic contribution of these metal(oids), especially Cr. With the matrix of factorial weights of the previous PCA (Table 2), a cluster hierarchy analysis was carried out, which resulted in two main geochemical groups of samples (Figure S2, Supplementary Material) that can be divided into three subgroups each, the geographical distributions of which are shown in Figure 4.  
In detail, cluster \(1\) shows areas where the predominance of sand sizes produces a lower metal(oids) load, therefore indicating a low impact of anthropogenic contributions, as is shown in Figure 4. In general, this group includes the entire coastal area and the inland area of Zelu\(\check{\text{a}}\)n. Within this group, subgroup 1.1 (Figure S2, Supplementary Material) constitutes the sandy samples of the general group that present the highest metal(oid) loads, \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & **As** & **Cd** & **Cr** & **Cu** & **Hg** & **Ni** & **Pb** & **Zn** & **Sand** & **Mud** & **TOC** \\ \hline
**PC1** & 0.311 & 0.326 & 0.249 & 0.329 & 0.309 & 0.187 & 0.331 & 0.317 & \(-0.318\) & 0.318 & 0.284 \\ \hline
**PC2** & \(-0.139\) & 0.176 & \(-0.494\) & 0.081 & 0.259 & \(-0.749\) & 0.122 & 0.131 & \(-0.126\) & 0.126 & \(-0.070\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Factor matrix obtained by principal components analysis (PCA). Figure 4: Geographical representation of the cluster hierarchy analysis results. and that are related to the confluence zones of the main rivers containing flushed fresh materials, giving rise to the metallic load in the sediments (Figure 4). Subgroup 1.2 (Figure S2, Supplementary Material) samples were taken in front of Salinas beach (Figure 4) and present significant amounts of metal(oids) despite being sandy, possibly because of aerial depositions of contaminated particles from the city of Aviles [22], as E-W is the prevailing direction of winds in this area. Finally, subgroup 1.3 (Figure S2, Supplementary Material) is formed of sandy samples with the lowest metal(oids) load, and most of the samples are grouped in front of the Xago beach and in the Zeluan area (Figure 4). The second main cluster (Figure S2, Supplementary Material) fits perfectly with the samples from the port area, located in the navigation channel, characterized by a predominance of fine sizes and a significant metal(oids) load.