Historical signature of Roman mining activities in the Bidasoa estuary (Basque Country,northern Spain): an integrated micropalaeontological,geochemical and archaeological approach

This work presents an integrated micropalaeontological (foraminiferal content), geochemical (Pb, Zn, Cu, Ni, Cr, and Al, Pb isotope ratios, radiocarbon dating) and archaeological approach to the environmental impact caused by Roman mining in the Bidasoa estuary (northern Spain). Sediments collected in the ancient Roman port of Irun represent a typical infilling sequence, reflecting a progressive isolation from the estuarine environment. They exhibit elevated contents of Pb, clearly higher than those recommended nowadays for acceptable sediment quality. Isotope composition confirms exploitation of local galenas as the main source for this metal. Results from a borehole (25 m long) reveal that Pb pollution extended also to the adjacent estuarine area. The beginning of Roman mining activities is recorded by a marked increase in Pb concentrations. However, the maximum value appears later in time (after 660 cal AD). Although this enrichment could be related to the reworking upstreams of previously polluted materials, recently obtained archaeological data suggest that episodes of historically non-documented mining activities could have taken place in the surrounding area after Roman times.