The Science of the Total Environment 292 (2002) 33–44 0048-9697/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0048-9697 Ž 02 . 00031-1 Atmospheric Pb deposition in Spain during the last 4600 years recorded by two ombrotrophic peat bogs and implications for the use of peat as archive A. Martınez Cortizas *, E. Garcıa-Rodeja , X. Pontevedra Pombal , J.C. Novoa Munoz , a, a a a ´ ´ ´ ˜ D. Weiss , A. Cheburkin b c Departamento de Edafologıa y Quımica Agrıcola, Faculdad de Biologıa, Universidad de Santiago, Campus Sur E-15706, a ´ ´ ´ ´ Santiago de Compostela, Spain T.H. Huxley School, Imperial College, Prince Consort Road, London SW7 2BP, UK b EMMA Analytical Inc Canada, Elmvale, ON, Canada c Received 10 November 2000; accepted 20 December 2001 Abstract Two ombrotrophic peat bogs in Northwestern Spain provided a history of 4600 years of Pb accumulation. Highest Pb concentrations (84–87 mgg ) were found near the bogs’ surface, but there were also other significant peaks y1 (6–14 mgg ), indicating pre-industrial atmospheric pollution. The enrichment factors (EFs) in both cores show a y1 remarkably similar record. Atmospheric Pb pollution dates back to at least approximately 2500 years ago, reaching a first maximum during the Roman period. For the last 300 years, Pb EFs significantly increased due to industrial development, but the uppermost samples of the bogs show decreasing Pb EFs, probably due to the phasing out of leaded gasoline. These results are also supported by Pby Pb isotope ratios, as they continuously decrease from 206 207 ca. 3000 BP until 2000 BP (from 1.275 at 4070 C years BP to 1.182), indicating the growing importance of non- 14 radiogenic Pb released from Iberian ores by ancient mining. Peat samples at a 3–5-cm depth are even less radiogenic ( Pby Pbs1.157), indicating the strong influence of leaded gasoline. Despite the common history shared by the 206 107 two bogs, striking differences were found for Pb enrichment, whether this was calculated by normalising to the Pby Ti ratio of the upper continental crust or to the PbyTi ratios of peats from pre-anthropogenic times. This effect seems to be related to differences in Ti accumulation in both bogs, possibly due to physical fractionation of the airborne dust during wind transport. Enrichment has to be carefully considered when comparing the results obtained for different bogs, since our results suggest that normalising to crustal proportions is meaningless when the bulk of the deposition in an area is strongly influenced by short- and medium-range dust transport.  2002 Elsevier Science B.V. All rights reserved. Keywords: Pb pollution; Ombrotrophic peat bogs; Enrichment factors; Pb isotope ratios; Fractionation of lithogenic elements; Airborne dust transport; Spain *Corresponding author. E-mail address: edantxon@usc.es (A. Martınez Cortizas). ´