Assessment of polycyclic aromatic hydrocarbon concentrations in the sediments of an estuary heavily affected by heavy industrial activities

Abstract

The Aviles estuary is one of the most anthropized in Spain due to the significant pressure exerted on it by industry. This study assesses the concentrations, origins, sources, and environmental implications of 16 polycyclic aromatic hydrocarbons (PAHs) as persistent contaminants of the estuary sediments. A total of 79 sediment samples were studied. Results indicate ⨊16PAH concentrations ranging from 0.086 to 305.771 μg g -1, with the highest values in the estuary's main channel. High-molecular-weight PAHs (4-6 rings) were predominant, suggesting a pyrogenic origin associated to industrial combustion processes. Lower molecular weight PAHs (2-3 rings) were mainly observed near the estuary mouth. Diagnostic ratio analysis confirmed that PAHs in the estuary predominantly originate from mixed combustion sources, including industrial processes, vehicle emissions, and maritime activities. Spatial distribution maps identified three contamination hotspots: (i) the Albares River, linked with steel industry emissions; (ii) a central estuary site near an aluminium smelter discharge point, connected to PAHs from industrial operations; and (iii) the estuary mouth, where PAHs from industrial wastewater discharges and shipping activities were detected. Cluster analysis further distinguished areas with similar contamination profiles, confirming the influence of industrial and maritime activities. Finally, the risk assessment comparisons with international pollution thresholds revealed that PAH levels in the Avilés Estuary are significantly higher than in other European and global estuarine environments. Over 90% of samples exceeded both low and median effect range limits, indicating substantial toxicity risks. Moreover, ecological risk quotient classified 92% of sediment samples as posing a high risk to aquatic life.