Historical Pollution and the Risk of Heavy Metal Remobilization in Coastal Sediments of Barcelona

Industrial activity in the Besòs River watershed has historically contributed to significant heavy metal pollution in coastal sediments near Barcelona. While mitigation measures implemented since the 1980s have effectively reduced contamination in surface sediments, deeper layers remain polluted. Increasing societal and economic pressures, along with episodic natural disturbances, could remobilize these stored pollutants, posing environmental and public health risks.

The GeoCr-BCN project investigates heavy metal pollution in sediments from the Besòs and Llobregat river prodeltas, with a focus on chromium (Cr). Sediment cores were analyzed using X-ray fluorescence core scanning (XRF-CS) to quantify heavy metal concentrations. Additionally, X-ray absorption spectroscopy (XAS) at the ALBA Synchrotron was employed to determine Cr speciation, providing insights into its geochemical behavior and potential toxicity under different environmental conditions.

Preliminary findings indicate significant heavy metal contamination in Besòs cores, with distinct stratification separating older, anthropogenic layers from more recent, less contaminated sediments. In contrast, Llobregat cores show minimal heavy metal presence, reflecting differences in industrial and hydrological inputs. XAS analysis reveals that Cr is primarily found in its reduced form, forming less toxic compounds. However, sediment disturbance and reoxygenation could mobilize Cr and shift it to more toxic, and bioavailable forms.

These results underscore the effectiveness of past environmental policies while highlighting ongoing risks associated with sediment destabilization. High-energy events, such as storms, can exceed treatment capacities, leading to temporary increases in metal deposition. Moreover, societal and economic developments that disrupt sediment layers could exacerbate pollution risks.

This study emphasizes the need for continuous monitoring of heavy metals in coastal sediments and for sustainable, evidence-based policy decisions to ensure the long-term ecological and environmental stability of the Barcelona coastal shelf.