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Table S1—Surface samples of FF borrow area: Concentrations of As, Cd, Cr, Cu, Ni, Pb, Zn and Hg (mg kg-1) and PCBs, PAHs e HCB (ng g-1). Classification according to the Portuguese legislation (Ordinance 1450/2007).

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The Cascais Canyon delivers contaminated sediments from the shelf to the deep marine environment. Multi-core PE252-32, located at 2100 m water depth in the canyon, records the latest 300 years of sedimentation. It was dated by 210Pb and analyzed texturally and geochemically for major elements and selected trace metals (Cu, Cr, Hg, Li, Ni, Pb and Zn). Cluster analysis performed on the down-core geochemical data identified four groups of variables related by grain-size, geochemical source and composition. Mercury, Pb and Zn were grouped in a cluster representing the anthropogenic component. Cluster analysis was applied again particularly to the latter cluster relatively to depth, in order to constrain the onset and temporal evolution of anthropogenic contamination. A second clustering, made on the basis of Hg, Pb and Zn, grouped samples by age and degree of anthropogenic contamination. One cluster contained relatively uncontaminated samples older than 1900 AD, and another cluster samples younger than 1900 AD with distinct metal enrichment. Maximum enrichments occurred during the early 1980s, followed by a slight recovery from the mid-1980s to the present. Mercury was the element with the highest enrichment factor (EFHg=5). Despite relatively low accumulation rates at this core location, our results show the importance of the Cascais Canyon as a transport route for contaminated sediments from the Tagus prodelta into the deep regions of the Portuguese Margin., El Cañón submarino de Cascais distribuye sedimentos contaminados de la plataforma continental al medio marino profundo. El testigo PE252-32, situado a 2100 metros de profundidad dentro del cañón, registra los últimos 300 años de su sedimentación. Se ha datado con 210Pb y ha sido analizada su granulometría, elementos mayoritarios y traza (cobre, cromo, mercurio, litio, níquel, plomo y zinc). Se ha llevado a cabo un análisis estadístico clúster, inicialmente aplicado a las series de datos geoquímicos en función de la profundidad, identificándose 4 grupos de variables, relacionados por la granulometría, procedencia y composición geoquímica. Los metales mercurio, plomo y zinc aparecen agrupados en un clúster que representa la componente antropogénica. A continuación el mismo análisis estadístico se aplicó específicamente a este grupo, en función de la profundidad, organizando las muestras según la edad de contaminación antropogénica. Como resultado las muestras quedan agrupadas en dos clústers principales, el de las muestras no contaminadas y más antiguas de 1900 AC, y el de las muestras más recientes de 1900 AC, marcando esta fecha el inicio de la contaminación por impacto de la actividad humana. Los máximos enriquecimientos ocurren durante el inicio de la década de los años ochenta, seguidos de un ligero descenso a partir de mediados de la misma década hasta la actualidad. De entre los demás, el mercurio es el elemento con el mayor grado de enriquecimiento (EFHg=5). Aunque la tasa de acumulación de sedimentos en este lugar es relativamente baja, los resultados obtenidos ponen en evidencia la importancia del Cañón submarino de Cascais como vía de transporte de sedimentos contaminados depositados en el pro-delta del Tajo a las regiones profundas del margen de Portugal.

Temporal variations in lead concentrations and stable lead isotopic ratios in two sediment cores from the Cascais Canyon shows changes in sources of Pb during the last two centuries. The increase of total Pb contents wIth the evolution of Pb ratio recorded in both cores reveals the Increase of Pb from industrial sources. Nevertheless, this increase is lower in deeper core location (252-32) due to dilution and mixing with uncontaminated marine materials. An isotopic shift towards lower Pb/Pb in the shallower core (252-35) during the 1970s may reflect the increasing number of vehicles in the Lisboa area during that time.