## 1 Introduction  
One of the major issues in aquatic ecosystems is the metal(oids) and organic chemicals load present in sediments, which may lead to serious environmental problems [1; 2]. Regarding marine environments, it is necessary to highlight estuaries due to the huge biological diversity that settles on them [3]. Moreover, estuaries are areas where fluvial waters and seawaters converge, which contributes to enabling the physical and chemical processes in aquatic compartments [4]. This has a notable impact on the water column, which conditions the spatial distribution, transformation, transfer to sediments and bioaccumulation processes of the potential contaminants present in the ecosystem [5]. Metal(oids) could enter into estuaries from both natural and anthropic sources, and many of them may be toxic even at very low concentrations [6; 7; 8]. In unpolluted areas, the metal(oid) concentrations detected in estuarine sediments are mostly derived from the lithology of the bedrocks that compose the river catchment [9; 10]. Nevertheless, the strategic location of estuaries in relation to economical and industrial activities turns these areas into target zones for human settlement [11]. Even though new environmental policies have reduced anthropogenic impacts in the recent years, estuaries are still impacted by several human activities, such as agricultural and chemical fertilizers, industrial uses, and recreational occupation [12; 13; 14]. These human activities can be potential sources of contamination, since they may introduce metal(oids) into estuarine environments. After being introduced into the aquatic environment, metal(oids) from the aqueous phase can be accumulated into the sediment through physical, chemical or biological mechanisms [15; 16]. Due to these mechanisms, sediments are considered as \"reservoirs\" of metal(oids) in estuaries, since they can act as sinks and sources of these elements depending on the natural or anthropological events that occur in the area [17]. This long persistence and bioaccumulation in sediments raises a serious threat to the biota, and also to human health [18; 19]. One of the most important estuaries on the Cantabrian coast is the Aviles estuary, known not only for its environmental importance but also for the industrial and port activities developed in its surroundings. The Aviles estuary has supported direct discharges from the main Asturian metallurgical plants, and other pollutants such as fertilizers and chemicals, along with a multitude of small activities located in this important industrial area. These facilities cause not only morphological alterations, such as the construction and expansion of the docks, which has altered the marshes and dunes that surround the river, but also exponentially increased the atmospheric emissions, turning Aviles into one of the world's most polluted cities in the 1980s [20], which has affected soil and sediment quality [21; 22]. These activities have developed since the 19 th century with a variable intensity, leading to a significant deterioration in the environment of the area over the course of decades [23]. Fortunately, over the last few years, the main industries in the area have made significant improvements in their processes, making them more efficient from an environmental point of view. Moreover, the passage of large ships, as well as river avenues and infrastructure operations, in Aviles' harbor maintain navigation channels and docks, but entail the moving of marine sediments to the bottom of the navigable waters. These processes and operations involve the resuspension of sediments containing potential contaminants, which may give rise to several environmental risks. Although urban infrastructure and industrial developments have almost entirely altered the estuary, it still holds a very important diversity of both animal and plant species, which has earned it the designation as a Special Protection Area for birds (ZEPA) and a Place of Cultural Interest (SCI).