Isotopic identification of natural vs. anthropogenic lead sources in marine sediments from the inner Ría de Vigo (NW Spain)

San Simón Bay, the inner part of the Ría de Vigo (NW Spain), an area previously identified as highly polluted by Pb, was selected for the application of Pb stable isotope ratios as a fingerprinting tool in subtidal and intertidal sediment cores. Lead isotopic ratios were determined by inductively coupled plasma mass spectrometry on extracts from bulk samples after total acid digestion. Depth-wise profiles of 206Pb/207Pb, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb and 208Pb/207Pb ratios showed, in general, an upward decrease for both intertidal and subtidal sediments as a consequence of the anthropogenic activities over the last century, or centuries. Waste channel samples from a nearby ceramic factory showed characteristic Pb stable isotope ratios different from those typical of coal and petrol. Natural isotope ratios from non-polluted samples were established for the study area, differentiating sediments from granitic or schist–gneiss sources. A binary mixing model employed on the polluted samples allowed estimating the anthropogenic inputs to the bay. These inputs represented between 25 and 98% of Pb inputs in intertidal samples, and 9–84% in subtidal samples, their contributions varying with time. Anthropogenic sources were apportioned according to a three-source model. Coal combustion-related emissions were the main anthropogenic source Pb to the bay (60–70%) before the establishment of the ceramic factory in the area (in the 1970s) which has since constituted the main source (95–100%), followed by petrol-related emissions. The Pb inputs history for the intertidal area was determined for the 20th century, and, for the subtidal area, the 19th and 20th centuries. ► Pb stable isotope ratios were applied to study Pb sources in coastal sediments. ► Pb isotopic ratios were determined for pre-pollution and for industrial samples. ► A binary mixing model was applied in polluted samples to study anthropogenic inputs. ► A three-source model was applied to apportion anthropogenic sources. ► Pb input history was established for the last one/two centuries in the study area.