François De Vleeschouwer

Virginie Renson

Philippe Claeys

Karin Nys

Richard Bindler

Quantitative WD-XRF Calibration for Small Ceramic Samples and Their Source Material

A wavelength-dispersive X-ray fluorescence (WD-XRF) calibration is developed for small powdered samples (300 mg) with the purpose of analyzing ceramic artifacts that might be available only in limited quantity. This is compared to a conventional calibration using a larger sample mass (2 g). The comparison of elemental intensities obtained in both calibrations shows that the decrease in analyzed sample mass results in a linear decrease in measured intensity for the analyzed elements. This indicates that the small-and large-sample calibrations are comparable. Moreover, the elemental contents of four ceramic sherds and two potential clay sources fall well within the range of the certified reference materials that are the basis of the calibration curves. The advantage with the analytical method presented here is that it is rapid and requires only a small amount of sample that can easily be re-used for further analyses. This method has great potential in ceramic provenance studies.

INTRODUCTION

In archaeometry a wide range of chemical techniques has been used to assess the geochemical content of various archaeological objects (e.g., Adan-Bayewitz, [START_REF] Bindler | Determining pottery provenance: Application of a new high-precision X-ray fluorescence method and comparison with instrumental neutron activation analysis[END_REF]Szökefalvi-Nagi et al., 2004;[START_REF] Asaro | The history of the Lawrence Berkeley National Laboratory instrumental neutron activation analysis programme for archaeological and geological materials[END_REF][START_REF] Cultrone | Iberian ceramic production from Basti (Baza, Spain): First geochemical, mineralogical and textural characterization[END_REF][START_REF] Mazar | A cuneiform tablet from the Ophel in Jerusalem[END_REF][START_REF] Renson | Lead isotopic analysis for the identification of Late Bronze Age pottery from Hala Sultan Tekke (Cyprus)[END_REF]. Among these objects are ceramic sherds, which, if accurately quantified for their elemental content and analyzed in a multivariate statistical approach, can provide information on the source and trading of ceramics in ancient times. The main problem of analyzing archaeological objects is that, for conservation reasons, the availability of sample is often limited. In the case of ceramics, the sample often consists of small fragments found on archaeological sites or retrieved from collections. Archaeometrists are therefore in constant search for analytical techniques that allow elemental quantification on a minimum amount of material.

X-ray fluorescence (XRF) is an analytical technique that has been widely used in many industrial, environmental, geological, and archaeological investigations (see [START_REF] West | Atomic spectrometry update-X-ray fluorescence spectrometry[END_REF], for a recent review of XRF applications). Among the applications, XRF has been widely used in the earth sciences (e.g., Potts, 1987, and references therein;[START_REF] Gardner | Geochemical analysis of silicate rocks and soils by XRF using pressed powders and a two-stage calibration procedure[END_REF][START_REF] Cheburkin | An energy-dispersive miniprobe multielement analyser (EMMA) for direct analysis of trace and chemical age dating of single mineral grains[END_REF]Zambello & Enzweiller, 2002;West et al., 2010, and references therein) and has been developed to analyze vegetation samples (e.g., [START_REF] Cheburkin | An energy-dispersive miniprobe multielement analyser (EMMA) for direct analyses of Pb and other trace elements in peats[END_REF]Margui, Hidalgo, & Queralt, 2005) and liquid matrices (e.g., [START_REF] Cumming | The determination of iron in lubricating oils by X-ray fluorescence spectrometry[END_REF][START_REF] Varga | Gross alpha radioactivity and chemical trace element content of thermal waters measured by SSNTD and XRF methods[END_REF][START_REF] Oprea | IGAA and XRF methods used in oil contamination research[END_REF]. In archaeological studies, XRF has a wide range of applications, and samples can be potentially re-used for further analysis depending on the sample preparation (e.g., Adan-Bayewitz, [START_REF] Bindler | Determining pottery provenance: Application of a new high-precision X-ray fluorescence method and comparison with instrumental neutron activation analysis[END_REF][START_REF] Hein | Red clays from central and eastern Crete: Geochemical and mineralogical properties in view of provenance studies on ancient ceramics[END_REF][START_REF] Craig | Comparison of XRF and PXRF for analysis of archaeological obsidian from southern Peru[END_REF][START_REF] Tripathi | Geochemistry and origin of ferruginous nodules in weathered granodioritic gneisses, Mysore Plateau, southern India[END_REF][START_REF] Cultrone | Iberian ceramic production from Basti (Baza, Spain): First geochemical, mineralogical and textural characterization[END_REF]West et al., 2010, and references therein). The common drawbacks of XRF are the so-called matrix effects, which are principally caused by the composition, grain size, and mineralogy of the sample. A way to minimize these effects is to finely powder the samples and to apply subsequent pretreatments such as lithium borate fusion or pelletization using a wax binder [START_REF] Potts | A handbook of silicate rock analysis[END_REF]. However, these processes alter the properties of the samples, which then cannot be re-used for further analyses. Classical XRF on powder, pellets, or fused beads also requires several grams of sample to achieve an accurate elemental quantification (e.g., Zambello & Enzweiller, 2002;[START_REF] Cultrone | Iberian ceramic production from Basti (Baza, Spain): First geochemical, mineralogical and textural characterization[END_REF]. This limits its application to archaeological artifacts that are available only in sufficiently large quantity. For small samples, direct analysis of powdered material would therefore be generally preferred. Such an application needs to be carefully developed to provide accurate elemental quantification (Adan-Bayewitz, [START_REF] Bindler | Determining pottery provenance: Application of a new high-precision X-ray fluorescence method and comparison with instrumental neutron activation analysis[END_REF].

New generations of wavelength-dispersive XRF (WD-XRF) offer the potential to decrease the quantity of material by carefully developing calibrations on samples as small as a few hundred milligrams. A common WD-XRF setup allows the determination of major and selected trace elements without specific spectrometric design. In this short note we provide the details of a calibration that was purposely developed for quantifying selected elements in small ceramic fragments and their potential raw materials. We present some of the technical aspects of the selection and preparation of the certified reference materials (CRMs) as well as a specific calibration developed to optimize WD-XRF for ceramic matrices and their source materials. This specific calibration for small sample mass (300 mg) is validated by comparing the intensities obtained with a conventional calibration (i.e., using 2-g samples).

METHODOLOGY

Selection of Certified Reference Materials

Thirty-five commercially available CRMs were selected from our laboratory stock. All our CRMs are finely powdered and stored in desiccators. They consist of sedimentary and igneous rocks (NIST1d, NIST70a, NIST278, NIST2780, NIST688), river sediments (NIST8704, STSD3), lake sediments (LKSD1, LKSD4, BIL1, JLK1), estuarine sediments (NIST1646a), and marine sediments (NIST1944, NIST2702, NIST2703, MAG1, PACS2, MESS3) as well as sands (NIST81a, NIST1413), clays (NIST97b, NIST98b, NIST679), and soils (SO2, SO3, SO4, NIST2711, NIST2586, NCSDC73325, NCSDC73326, JSO1) from sedimentary outcrops, and coal fly ash (JCFA1, NIST1633a, NIST1633b, ZUK1), the latter type being added to extend the range of various trace elements. Rather than exclusively choosing fine sediments, we have included several sediment and rock types to represent mixed matrices (i.e., fine material and temper) that may be found in ceramics [START_REF] Rapp | Archaeomineralogy[END_REF].

Sample Preparation

All the analyses were carried out directly on CRM powders. Two calibrations were developed: one based on 2 g of each CRM, as commonly done in XRF analyses, and a second based on 300 mg of powder that was specifically developed here. For the first calibration, 2 g of dried and homogenized loose powder was transferred to 40-mm-opening plastic cups with a 2.5-mm transparent mylar film at its base. These samples were placed in 36-mm-opening metallic cup holders for analysis. The challenging part of this study was the development of the second calibration, using 300 mg of powder, which was transferred to a plastic cup with a 10-mm opening, also with a 2.5-mm mylar film at the base. In these small cups the powder was slightly compressed manually to reduce porosity effects. These plastic cups were subsequently loaded in a metallic cup holder with an opening (i.e., analytical) diameter of 8 mm.

XRF Optimization

All the analyses were conducted using a Bruker S8-Tiger WD-XRF analyzer equipped with a Rh anticathode X-ray tube, four analyzing crystals (XS-55, PET, LIF200, LIF220), a flow proportional counter (for light elements), and a scintillation counter (for heavy elements). Analyses were performed under helium atmosphere to avoid powder loss in the analytical chamber, which may occur under vacuum conditions. The main parameters, used for each calibration and each element, are reported in Table I. Such a WD-XRF setup allows the determination of a wide range of elements, generally from C to U. In this study, the following elements were selected: Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Ba, and Pb. This selection is based on the certified values available in each CRM, which are matched with the expected detectable concentrations of our WD-XRF spectrometer. The WD-XRF resolution and sensitivity have been optimized by combining the proper collimators, crystals, and counters for each element (Table I). The peak acquisition time was optimized using the built-in SpectraPlus ® software interface, which calculates the time necessary to achieve an average selected detection limit. The acquisition time varies, therefore, among elements as well as among concentrations of a given element (i.e., the lower the concentration, the greater the time). To avoid any excessively long acquisition times, a maximum time was set for each element, which varies from 30 to 100 s (Table I). The background measurement times have been fixed manually, generally at 10 s, except for a few trace elements

Table I.

Main parameters used to develop both large mass (2 g) and small mass (300 mg) calibrations. The minimum and maximum CRM concentrations are also reported. where intensities were expected to be low (see Table I). The overall measurement time is about 40 min per sample (i.e., 36 samples/24 h). The calibration procedure is achieved in two steps: (1) all the CRMs are scanned at standard conditions to allow for optimization of sensitivity, resolution, and detection limits (see preceding), and then (2) a full analysis of the CRMs selected to give the best fit (i.e., to minimize standard error) of the ultimate calibration line is conducted. This necessary selection depends on (a) the available certified values; (b) the behavior of each CRM matrix in both calibrations (2 g loose powder vs. 300 mg pressed powder); and (c) the targeted standard error, which can be decreased by carefully removing values slightly off the calibration line without changing its slope. This selection process explains why, for a given element, the number of CRMs may vary between both calibrations (Table I). A posteriori corrections are also applied. They are of two types: (1) a software-built matrix correction that takes into account the inter-elemental interferences in the sample (i.e., a fluorescence X-ray originating from an element that causes electronic transitions in elements with lower energies), and (2) overlay corrections that are applied individually for peak overlaps commonly encountered in XRF spectra (see Table I). Finally, a quantitative calibration curve has been developed for each element by using a linear regression between the corrected intensities and the CRM concentrations through the built-in software.

Acquisition

In addition, an in-house standard (STG) is measured daily to check the analytical performance of the XRF. Three additional internal standards (SQ1, SQ3, Ausmon) are used to monitor the long-term (yearly) drift of the device and to correct intensities if necessary. Lower limits of detections (LLD) are calculated as follows:

where S i is the analytical sensitivity (Cps/concentration), I b is the background intensity (in kilocounts per second, Cps), and T b is the background measurement time (s). It is also possible to recalculate a corrected concentration for each CRM by plotting its corrected intensity on the calibration line. This value was used to monitor the total analytical accuracy for each CRM and each element as follows:

where C CRM is the certified concentration and C cor is the corrected (i.e., recalculated) concentration. Finally, reproducibility has been assessed for both calibrations using an external CRM (which is not included in the calibration process) with a similar matrix (NCS-ZC73002, soil). Multiple (n ϭ 10) runs of this CRM provide a reproducibility expressed as follows: where Average and Stdeva represent the mean (n ϭ 10) CRM concentration and standard deviation, respectively. Results, as well as detection limits, accuracies, and reproducibilities are reported in Table I.

RESULTS AND DISCUSSION

Potassium (K), titanium (Ti), zinc (Zn), and phosphorus (P) were chosen to illustrate the comparison of the two calibrations and the reliability of the small-sample calibration. Potassium (major constituent) and Ti (minor constituent) were selected because they represent two important lithogenic elements commonly used in provenance studies. Zinc illustrates the behavior of heavy metals and phosphorus a calibration that displays greater uncertainty. Figure 1 presents biplots of the corrected intensities for both large-cup and small-cup calibrations. Because the number of CRMs for a given element differs between the large-cup and small-cup calibrations, only the intensities of the CRM common to each calibration are plotted together. For most of the studied elements, the CRM intensities plot nicely along a line (R 2 Ն 0.89 for elements in Figure 1), which indicates that decreasing the amount of material results in a linear decrease in the peak intensities. The intensities generally decrease by a factor 15 to 25 from the 2-g to the 300-mg samples. However, both elemental peak and background intensities decrease, allowing for a good peakbackground resolution. This is also supported by the low and comparable LLD found in both calibrations: a few tens of mg g Ϫ1 and a few mg g Ϫ1 for major and trace elements, respectively (Table I). These values are generally below or equal to previously reported data [START_REF] Cheburkin | An energy-dispersive miniprobe multielement analyser (EMMA) for direct analysis of trace and chemical age dating of single mineral grains[END_REF][START_REF] Boyle | Rapid elemental analysis of sediment samples by isotope source XRF[END_REF][START_REF] Hein | Standardisation of elemental analytical technique applied to provenance studies of archaeological ceramics: An interlaboratory calibration study[END_REF]Zambello & Enzweiller, 2002;[START_REF] Cultrone | Iberian ceramic production from Basti (Baza, Spain): First geochemical, mineralogical and textural characterization[END_REF]. Similarities between the two calibrations can also be observed for the accuracies, which remain within Յ10% for most elements except for S, P, and Br. These accuracy values are slightly below values encountered in the literature [START_REF] Cheburkin | An energy-dispersive miniprobe multielement analyser (EMMA) for direct analysis of trace and chemical age dating of single mineral grains[END_REF][START_REF] Boyle | Rapid elemental analysis of sediment samples by isotope source XRF[END_REF]Zambello & Enzweiller, 2002;[START_REF] Cultrone | Iberian ceramic production from Basti (Baza, Spain): First geochemical, mineralogical and textural characterization[END_REF]. Improvements in both LLD and accuracy can be explained by the continuous analytical development of commercially available XRF and the careful selection of appropriate CRMs and WD-XRF optimization. Lower detection limits and accuracies have been reported by Adan-Bayewitz, [START_REF] Bindler | Determining pottery provenance: Application of a new high-precision X-ray fluorescence method and comparison with instrumental neutron activation analysis[END_REF], who have used a specific Ag-cathode XRF setup. While such a configuration results in lower LLD and accuracies, it does not allow the determination of all major elements, which is crucial in provenance studies. Moreover, such a configuration is of limited availability compared to largely commercially available Rh-cathode WD-XRF.

Compared to the large-cup calibration, reproducibility values are generally 5-10% lower for the small-cup calibration (Table I). This can be explained by the smaller analytical surface (8-mm vs. 36-mm opening), which results in a lower signal integration. However, these reproducibilities are fully satisfactory, with values mostly above 90%, except for a very few elements (e.g., Cu: 78% and Ni: 82%). One notable exception is Br, which shows rather poor reproducibility (47%). This may be explained by (1) the low concentration encountered in the CRM analyzed for this test (2.8 mg g Ϫ1 ), (2) the relatively low amount of CRM with certified values for Br (n ϭ 8; see Table I), and (3) the low intensities (0-0.15 kilocounts per second) recovered for this element. Bromine concentrations should therefore not be taken as a fully quantified element using the small-cup calibration, but rather as indicative of large variations, which may be taken into account when using multivariate statistics, where covariance is considered rather than absolute values. The linear relationship between the two calibration intensities also implies that results are independent of the calibration. In other words, the results of samples quantified with one calibration can be compared directly with the results obtained using the other. In the specific context of a provenance study, it is therefore possible to compare source materials where a large amount of material is available, such as soils, rocks, and sediments, with small ceramic sherds (where the amount of material may be limited) using the two different calibrations based on the same CRM, but differing in the amount of material (2 g vs. 300 mg) and analytical surface (36 mm vs. 8 mm). Both major and trace elements display linear behaviors similar to K, Ti, and Zn, with low intercept offsets. Two elements display poor agreement: P and Ba. However, it should be noted that these two elements can be accurately quantified using the large-cup calibration. The comparison between the two calibrations is poor because P and Ba are inaccurately quantified using the small-cup calibration. This can be explained by a narrow CRM concentration range for P and bad peak-background ratios for P and Ba. Caution is therefore required when using these elements in ceramic provenance studies where their concentrations have been measured with the technique described here. However, in provenance studies where multivariate statistical approaches are often used to identify pottery groups and provenances, the loss of two minor elements out of a total suite of 20 elements will not influence significantly the results of multivariate statistical calculations.

The small-cup calibration curves for K, Ti, Zn, and P are reported in Figure 2. To briefly illustrate the applicability of the small-cup calibration to ceramic artifacts, the elemental concentrations of four Cypriot Late Bronze age ceramic sherds and two potential raw materials have been measured; complete analyses of those samples will be presented in a separate publication. The concentration ranges found in the sherds and sediments are well enclosed within the CRM concentration ranges (Figure 2). As shown by the Zn biplots, trace metal concentrations are found to be relatively low in these sherds and sediments. This is also the case for the Pb concentrations (Ͻ15mg g Ϫ1 , not shown here), which may potentially limit the applicability of XRF to trace metals in ceramic provenance studies. These considerations regarding elemental chemistry need, however, to be confirmed by the analysis of a wider range of ceramic artifacts in order to better explore the concentration range of each element using WD-XRF. One last but major advantage of WD-XRF, besides providing quantitative data on a large amount of elements (here 18 to 20 elements), is that these same powdered samples can be re-used for further analyses such as mineralogy determination by X-ray diffraction, or isotopic analyses. The calibration developed here renders this re-use possible even on very small samples. It should finally be emphasized that while 300 mg of sample powder is sufficient, one should make sure that such a small amount is sufficiently representative of the whole object.

CONCLUSIONS

This study presents a rapid, non-destructive (i.e., the powdered samples can be re-used) WD-XRF protocol developed for small sample masses, down to 300 mg of dry powder. This protocol allows the accurate determination of major (Na, Mg, Al, Si, K, Ca, Fe), minor (Ti, P, S, Mn), and trace (V, Ni, Cu, Zn, Br, Rb, Sr, Ba, Pb) elements. With the exception of three elements (P, Ba, Br), this specific calibration is fully comparable to conventional calibration using larger amounts of sample (2 g). Lower limits of detections and accuracies are comparable to, if not below, those found in the literature using similar XRF designs. Such a small sample calibration developed for pottery sherds may be widely applied in the field of ceramic provenance studies.

  ; mA: milli-amperes; XS-55: W/Si multilayer crystal; LIF200 and 220: lithium fluoride crystals; PET: pentaerythrite crystal; LLD: lower limit of detection. The accuracy (Acc.) is the median value obtained by comparing the CRMs and the corrected XRF concentrations for each element in each standard. The reproducibility (Repr.) is obtained by repeated measurements (n ϭ 10) of the same CRM (NCSZC73002). Units for CRM minimum and maximum as well as LLD are same as units of measurement.

Figure 1 .

 1 Figure 1. Biplot comparison of intensities (kilocounts per second-kCps) obtained using the large and the small calibrations for K, Ti, Zn, and P. Black dots represent the CRMs.

Figure 2 .

 2 Figure 2. Calibration lines (corrected intensities in kCps vs. CRM concentrations) obtained using the small cups for K, Ti, Zn, and P. Black dots represent the CRM. Open squares represent the pottery sherds. Black diamonds represent two potential raw materials from Cyprus.

*Corresponding author; E-mail: francois.devleeschouwer@ensat.fr.

The WD-XRF acquisition, setup, and optimization was made possible through a research grant from the Kempe Foundation to R.B., which also provided a post-doc fellowship to F.D.V. Additional support was provided by the Research Foundation Flanders (FWO grants KN137 to K.N. and G.0585.06 to P.C.), the Research Council of the Vrije Universiteit Brussel (grant HOA11 to K.N. and P.C.), and the Swedish Research Council (grant to R.B.). We also thank Dr. Flourentzos, Director of the Department of Antiquities, Cyprus, for granting export permission for the sherds from Hala Sultan Tekke-Vyzakia. The comments of M. Kylander, A. Martinez-Cortizas, as well as two anonymous reviewers and editor G. Huckleberry improved an earlier version of this manuscript.


François De Vleeschouwer
email: fdevleeschouwer@gmail.com

Nathalie Fagel

Andriy Cheburkin

Anna Pazdur

Jaroslaw Sikorski

Nadine Mattielli

Virginie Renson

Barbara Fialkiewicz

Natalia Piotrowska

Gaël Le Roux

François Fagel De Vleeschouwer

Nadine Renson

Virginie Fialkiewicz

Le Roux

Gaël

François De Vleeschouwer

Anthropogenic impacts in North Poland over the last 1300 years -A record of Pb, Zn, Cu, Ni and S in an ombrotrophic peat bog

Keywords:

published or not. The documents may come

Introduction

Numerous studies have demonstrated the potential of ombrotrophic bogs to record past anthropogenic activities (e.g., [START_REF] Roux | Identifying the sources and timing of ancient and medieval atmospheric lead pollution in England using a peat profile from Lindow bog, Manchester[END_REF][START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14 C "bomb pulse curve[END_REF][START_REF] Weiss | The geochemistry of major and selected trace elements in a forested peat bog, Kalimantan, SE Asia, and its implications for past atmospheric dust deposition[END_REF][START_REF] Mighall | Geochemical evidence of atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmystwyth, mid-Wales, UK[END_REF][START_REF] Brännvall | The Medieval metal industry was the cradle of modern large-scale atmospheric lead pollution in northern[END_REF]. However, studies dealing with peat inorganic geochemistry in Eastern European countries are scarce (e.g., [START_REF] Fialkiewicz | The minerotrophic peat bog "Bagno Bruch"as a potential archive of past changes in heavy metal concentrations[END_REF][START_REF] Syrovetnik | Accumulation of heavy metals in the Oostriku peat bog, Estonia: determination of binding processes by means of sequential leaching[END_REF][START_REF] Mihaljevič | Lead fluxes, isotopic and concentration profiles in a peat deposit near a lead smelter (Pribram, Czech Republic)[END_REF][START_REF] Novak | Origin of lead in eight Central European peat bogs determined from isotope ratios, strengths, and operation times of regional pollution sources[END_REF][START_REF] Vile | 200 years of Pb deposition throughout the Czech Republic: patterns and sources[END_REF]. Poland is one of the top polluting countries in Europe, especially in terms of lead pollution [START_REF] Van Den Hout | The impact of atmospheric deposition of non-acidifying substances on the quality of European forest soils and the North Sea[END_REF]. Millennial records of anthropogenic impacts are lacking, despite successful mid-resolution attempts by [START_REF] Ciszewski | The use of heavy metal concentrations and dendrochronology in the reconstruction of sediment accumulation, Mala Panew River Valley, southern Poland[END_REF], and Strzyszcz and Magiera (2001 and references therein). Within Poland, lake and peat bog deposits contain archive records, which are suitable for the reconstruction of historical pollution. Northern Poland is of particular interest because it possesses several peat deposits, some of which are ombrotrophic, i.e., exclusively fed by atmospheric deposition. This region is also interesting as it is located at a relatively far distance (several hundreds of km) from the main Polish pollution centres (Fig. 1), which could possibly mask any middle-to long-range signal by a high level of local pollution. Finally, the selection of an appropriate near-shore site may offer the opportunity to investigate pollution over the Baltic region, which has been of high interest during the last decade (e.g., Schneider et al., 2000 and reference therein). During the last couple of decades, the dominant contributors of lead emission (from coal, lead mines and gasoline) over the Baltic Sea are Poland (23%), Germany (20%) and Finland (16%) [START_REF] Von Storch | Four decades of gasoline lead emissions and control policies in Europe: a retrospective assessment[END_REF]. By coupling elemental geochemistry and lead isotopes together with 14 C and 210 Pb age-dating of a 1-m ombrotrophic peat core, we aim to:

(1) reconstruct the history of lead pollution during the last millennium over North Poland, (2) link the Pb record to historical events, (3) trace the source of this lead, (4) replace our record into a more regional history of lead pollution over Eastern Europe.

Site description

Słowińskie Błoto bog (54°21′52.53″N, 16°29′24.72″E, 30 m a.s.l.) is located in northern Poland, 8 km to the South-East of Darłowo City, and 10 km away from the Baltic Sea (Fig. 1). It is described as a Baltic bog (e.g., [START_REF] Kulczyński | Peat bogs of Polesie[END_REF]. The area covered by the bog is ca. 120 ha. A study by [START_REF] Herbichowa | Ekologiczne studium rozwoju torfowisk wysokich wlasciwych na przykladzie wybranchych obietkow z srodkowej czesci probrzeza baltyckiego[END_REF] on 59 cores revealed an average peat thickness of 2.8 m and a consistent peat stratigraphy over most of the bog. The base of the mire was dated at 3693-3965 BC [START_REF] Herbichowa | Ekologiczne studium rozwoju torfowisk wysokich wlasciwych na przykladzie wybranchych obietkow z srodkowej czesci probrzeza baltyckiego[END_REF]. Raised-bog vegetation began to develop around AD 50-356 (now at 2 m peat depth) with mainly Sphagnum and E. vaginatum. Sphagnum fuscum-peat started to develop between ca. AD 470 and AD 1400 [START_REF] Herbichowa | Ekologiczne studium rozwoju torfowisk wysokich wlasciwych na przykladzie wybranchych obietkow z srodkowej czesci probrzeza baltyckiego[END_REF]. The actual vegetation of the central part of the bog is composed of several species of Sphagnum (S. fallax and S. magellanicum) with Eriophorum vaginatum, Trichophorum cespitosum and rare dwarf P. sylvestris [START_REF] Herbichowa | Ekologiczne studium rozwoju torfowisk wysokich wlasciwych na przykladzie wybranchych obietkow z srodkowej czesci probrzeza baltyckiego[END_REF]. In the outer parts, Vaccinium uliginosum, Calluna vulgaris and Betula pubescens are also present (Fig. 1). Until the end of 18th century, Słowińskie Błoto bog has been an open bog (i.e., not covered by the forest). It has been drained twice: (1) in 1880 when surrounding ditches were dug and (2) in 1970 when two ditches were dug through the central part of the bog. These latter were renewed in 1985.

Methods

Coring and subsampling

In August 2005, a one-meter core was retrieved at a distance of 20 m from the central part of the bog (Fig. 1), but away from the drainage ditches, using a stainless steel 10 × 10 cm Wardenaar corer [START_REF] Wardenaar | A new hand tool for cutting peat profiles[END_REF]. The core was then wrapped in a plastic bag, stored in a fridge and sub-sampled soon after. The edges of the core were removed to avoid any metal contamination by the corer. The remaining core was then sliced in ca. 1 cm-thick samples using a titanium knife. All the sub-samples were stored in plastic bags.

Chronological control of the peat core

The chronological control of the core consists of 10 radiocarbon measurements performed by accelerator mass spectrometry on selected plant macrofossils (mainly Sphagnum spp. stems and opercula, Calluna vulgaris stems, Erica tetralix stems and inflorescences, and Andromeda polifolia leaves), following the protocols developed by [START_REF] Kilian | Dating raised bogs: new aspects of AMS 14 C wiggle matching, a reservoir effect and climatic change[END_REF] and [START_REF] Mauquoy | Changes in solar activity and Holocene climatic shifts derived from 14 C wiggle-match dated peat deposits[END_REF]. The samples were prepared at the GADAM Centre (Gliwice, Poland) using an acid-alkali-acid washing, drying and graphitisation following [START_REF] Goslar | Sample preparation in the Gliwice Radiocarbon Laboratory for AMS 14 C dating of sediments[END_REF]. The measurements took place at the Poznan radiocarbon Laboratory (Poznan, Poland) following the protocol from [START_REF] Goslar | Energy 14 C AMS in Poznan Radiocarbon Laboratory, Poland[END_REF]. Calibration of radiocarbon dates was undertaken using the IntCal04 calibration curve [START_REF] Reimer | IntCal04 terrestrial radiocarbon age calibration, 26-0 ka BP[END_REF] and OxCal 4.0 software (Bronk [START_REF] Ramsey | Radiocarbon calibration and analysis of stratigraphy: The OxCal program[END_REF][START_REF] Ramsey | Development of the radiocarbon calibration program OxCal[END_REF].

Lead 210 was also measured in recent layers (down to 35 cm depth) after 210 Po extraction from 2 g of dry peat powder spiked with 208 Po using a sequential H 2 O 2 -HNO 3 -HCl digestion. Measurements were performed using an α-spectrometer (Canberra model 7401) for two days for each sample in order to obtain sufficient accuracy. The results of the calculation were corrected for the radioactive decay of 208 Po since the moment of its calibration, and the decay of 210 Pb since the moment of polonium extraction from the sediment. More details about the 210 Pb measurements at the GADAM Centre (Gliwice, Poland) can be found in Sikorski (2008 and reference therein). The Constant Rate of Supply (CRS) model [START_REF] Appleby | Chronostratigraphic techniques in recent sediments. Tracking environmental change using lake sediments, volume 1: basin analysis, coring and chronological techniques[END_REF] was then applied in order to build the 210 Pb age-model.

X-ray fluorescence

Selected samples (n = 44) were freeze-dried and then powdered in an automatic agate mortar (400 rpm, 1 h). One gram of the resulting powder was analysed for selected elements at the Institute of Environmental Geochemistry (Heidelberg, Germany) using two different XRF instruments. Energy-dispersive Miniprobe Multielement analyzer EMMA [START_REF] Cheburkin | An energy-dispersive miniprobe multielement analyser (EMMA) for direct analyses of Pb and other trace elements in peats[END_REF] was used to analyse trace elements (Ni, Cu, Zn, Pb) while Energy dispersive XRF spectrometer TITAN [START_REF] Cheburkin | Energy-dispersive XRF spectrometer for Ti determination (TITAN)[END_REF] was used to analyse minor elements (S and Ti). The two analysers are calibrated with various organic international standards: coals (NIST1632b, NIST1635, SARM19 and SARM 20) and plant material (NIST1515, NIST1547, NIST1575, BCR 60 and BCR62). Accuracies are below or equal to 10% except for Ni, which displays an accuracy of 15%. Results are given in Table 1 along with accuracy and detection limits.

Isotopic analyses

Regarding the Pb concentration in peat, 10 to 500 mg of dry peat powder was taken, in order to obtain 2000 ng of Pb in the final solution. Galenas and one bulk coal from various locations were also digested and analysed in order to provide isotopic signature of the local mining background. About 1 mg of galena and 150 mg of coal were taken, respectively. For peat and coal samples, the powder was firstly calcined (550 °C, 4 h) and then digested in 6 ml HF 24 N suprapur (Merck) +1 ml HNO 3 14 N cc. sub. in Teflon beakers (120 °C, 48 h) in class 1000 laminar flow clean air cabinets (University of Brussels, Belgium). For galena samples, the powder was directly digested in 2 ml of HCl 6.8 N. After complete evaporation, HCl 6.8 N was added and the solutions were slowly evaporated. Dried residues were dissolved in HBr 0.8 N prior to chromatographic separation. Lead was separated using pre-conditioned anionic resin (AG1X8) exchange micro-columns by successive HBr and HCl additions [START_REF] Weis | High-precision Pb-Sr-Nd-Hf isotopic characterization of USGS, BHVO-1 and BHVO-2 reference materials[END_REF]. The eluted pure Pb solution was evaporated and stored. Before isotopic analysis, the Pb elution was redissolved in 100 μl of HNO3 14 N cc. sub., evaporated and finally dissolved in 1.5 ml of HNO3 0.05 N.

Lead isotopic ratios were measured on a Nu Instruments Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) at the Département des Sciences de la Terre et de l'Environnement (DSTE, University of Brussels) during a one-day analytical session. Details about MC-ICP-MS tuning and calibration for this type of sample are reported in De [START_REF] Vleeschouwer | Atmospheric lead and heavy metal pollution records from a Belgian peat bog spanning the last two millenia: human impact on a regional to global scale[END_REF]. As an internal isotopic standard, a Tl solution was added to each sample and standard to monitor and correct for mass dependent isotopic fractionation. The sample solutions were prepared to obtain a beam-intensity in the axial collector ( 204 Pb) of a minimum of 100 mV and a Pb/Tl ratio of 5, matching the Pb and Tl concentrations of the NIST-SRM 981 Pb standard (200 ppb in Pb, with 50 ppb in Tl). Repeated measurements of NIST-SRM 981 Pb standard were carried out before starting the analysis of samples, and between each sample. The reproducibility on each measured ratio is equal to 100% (n = 25 [START_REF] Galer | Practical applications of lead triple spiking correction of instrumental mass discrimination[END_REF][START_REF] Weis | High-precision Pb-Sr-Nd-Hf isotopic characterization of USGS, BHVO-1 and BHVO-2 reference materials[END_REF][START_REF] Weis | High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS[END_REF]. Although the NIST-SRM 981 Pb standard results were within the error of the triple-spike values after online correction for instrumental mass bias by Tl addition, the sample results were further corrected by the sample-standard bracketing method described by [START_REF] White | High-precision analysis of Pb isotope ratios by multicollector ICP-MS[END_REF] and [START_REF] Weis | High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS[END_REF] to circumvent any instrumental drift during the analytical session. Accuracies derived from standard deviations average from 14 to 49 • 10 -4 for 208 Pb/ 204 Pb, 5.8 to 10 • 10 -4 for 207 Pb/ 204 Pb, 6.1 to 14• 10 -4 for 206 Pb/ 204 Pb, 2.9 to 8 • 10 -5 for 208 Pb/ 206 Pb and from 0.9 to 2 • 10 -5 for 207 Pb/ 206 Pb (Table 2). One replicate (i.e., a re-run of the same sample solution) of the peat sample 9 and one duplicate (i.e., sample which is processed twice from weighting, acid digestion to analysis) of galena 2 have been analysed. Results fall within the measurement accuracies of their counterparts. Results are summarized in Table 2.

Results and discussion

Ombrotrophy

The vegetation characteristics (i.e., Sphagnum dominance, see Section 2) described in [START_REF] Herbichowa | Ekologiczne studium rozwoju torfowisk wysokich wlasciwych na przykladzie wybranchych obietkow z srodkowej czesci probrzeza baltyckiego[END_REF], and more recently in [START_REF] Lamentowicz | Climate and human induced hydrological change since AD 800 in an ombrotrophic mire in Pomerania (N Poland) tracked by testate amoebae, macro-fossils, pollen and tree rings of pine[END_REF] and [START_REF] Vleeschouwer | Multiproxy evidences of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland[END_REF] indicate the presence of acidic, nutrient-poor conditions and strongly support the ombrotrophic character of the bog. Moreover, [START_REF] Herbichowa | Ekologiczne studium rozwoju torfowisk wysokich wlasciwych na przykladzie wybranchych obietkow z srodkowej czesci probrzeza baltyckiego[END_REF] reported that the dome of the bog is elevated at ca. 1.2 m above its surroundings, which makes it a raised bog.

Chronology

Both 210 Pb and 14 C models were linked by the sample at 34.5 cm depth (dated by both techniques) and combined in a non-linear age-depth model approach (generalized additive model, GAM) described by [START_REF] Heegaard | Relationships between calibrated ages and depth in stratigraphical sequences: an estimation procedure by mixed-effect regression[END_REF]. Complete details of these measurements and the resulting age model are reported in [START_REF] Vleeschouwer | Multiproxy evidences of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland[END_REF]. The agreement between the oldest 210 Pb derived ages and the youngest radiocarbon ages are also discussed in Piotrowska et al. (in press).

De [START_REF] Vleeschouwer | Multiproxy evidences of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland[END_REF] provided a modelled-age for each sample (here reported in Table 1). Using multiple linear regressions, De [START_REF] Vleeschouwer | Multiproxy evidences of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland[END_REF] also demonstrated three main periods of different accumulation rates. From the base of the core up to 52.5 cm depth (5 dates), the peat accumulation rate averages ca. 1 mm yr -1 . Between 52.5 cm and 34.5 cm depth (4 dates), the mean peat accumulation rate decreases towards 0.3 mm yr -1 . Then it increases dramatically towards the surface ( 210 Pb-dated interval) with a mean accumulation rate of 5.7 mm yr -1 .

Mobility of heavy metals in peata short review

Heavy metals have been abundantly monitored in peat. Studies are dedicated to two main topics: (1) the history of past heavy metals pollution (e.g., [START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF] and (2) their mobility (mainly because of their potential toxicity) linked to various phenomena such adsorption on organic matter (e.g., [START_REF] Grybos | Is trace metal release in wetland soils controlled by organic matter mobility or Fe-oxyhydroxides reduction?[END_REF] and scavenging by oxi-hydroxides (e.g., [START_REF] Tessier | Metal sorption to diagenetic iron and manganese oxyhydroxides and associated organic matter: narrowing the gap between field and laboratory measurements[END_REF]. However, despite the numerous studies undertaken, their behaviour is not always well understood.

Numerous studies have concluded that ombrotrophic bogs are probably the best continental Pb archive since these ecosystems only receive Pb from the atmosphere (e.g., [START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF][START_REF] Weiss | The geochemistry of major and selected trace elements in a forested peat bog, Kalimantan, SE Asia, and its implications for past atmospheric dust deposition[END_REF][START_REF] Mighall | Geochemical evidence of atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmystwyth, mid-Wales, UK[END_REF]. Lead is by far the most intensively studied heavy metal in peat mainly because it is considered by most authors to be immobile in ombrotrophic peat. These peat deposits efficiently retain Pb despite a low pH, the abundance of organic acids and seasonal variation in redox conditions (e.g., [START_REF] Shotyk | Biogeochemistry and cycling of lead[END_REF][START_REF] Mighall | Geochemical evidence of atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmystwyth, mid-Wales, UK[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF]. Also, the isotopic composition of lead keeps a fingerprint of its source, making a powerful tool for distinguishing natural from anthropogenic sources (e.g., [START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF][START_REF] Mighall | Geochemical evidence of atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmystwyth, mid-Wales, UK[END_REF][START_REF] Shotyk | Biogeochemistry and cycling of lead[END_REF]. Moreover, using such isotopic fingerprints, [START_REF] Weiss | Sphagnum mosses as archives of recent and past atmospheric lead deposition in Switzerland[END_REF] demonstrated Pb immobility by comparing Pb isotopic composition in dated herbarium Sphagnum samples from Swiss and Southern Germany and in 210 Pb-dated peat samples from the same age and same location. The similarity of age dating made using the 210 Pb CRS model and 14 C Bomb Pulse Curve also supports the immobility of Pb [START_REF] Goodsite | High resolution AMS 14 C dating of post bomb peat archives of atmospheric pollutants[END_REF]. Over the last few years however, as some authors have continued to investigate the behaviour of lead in peat, the debate over Pb mobility reopened. For example, [START_REF] Sonke | A chemical and mineralogical reconstruction of Zn smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF] demonstrated that in organic sediment (including peat), Pb could be slightly leached. Recently, [START_REF] Novak | Mobility of trace metals in pore waters of two Central European peat bogs[END_REF] also showed that Pb can be mobile to some extent, but it is still considered as immobile by most authors.

The behaviour of Zn is somewhat different to that of lead and is still under debate. Zinc usually accompanies lead in geochemical studies of peat, mainly because these two metals are associated in ores, which are an important source of pollution. In ombrotrophic peat, Mighall et al. (2002 and reference therein) showed relatively similar concentration profiles for Pb and Zn, suggesting the immobility of Zn in raised peat bogs. However, in his synthesis of inorganic components found in peat, [START_REF] Shotyk | Review of the inorganic geochemistry of peats and peatland waters[END_REF] explained that Zn distribution is linked, among others, to bioaccumulation, water table fluctuations and pH conditions. [START_REF] Nieminen | Enrichments of Cu, Ni, Zn, Pb and As in an ombrothrophic peat bog near a Cu-Ni smelter in Southwest Finland[END_REF] showed that Zn was highly mobile in ombrotrophic peat as the Zn concentration profile showed low Zn concentrations compared to high Zn emission from nearby smelters, but showed no relation with other elemental profiles. [START_REF] Novak | Mobility of trace metals in pore waters of two Central European peat bogs[END_REF] showed that Zn was highly mobile by comparing its particulate and pore water content. It seems therefore that in an attempt to use Zn as a tracer, one should carefully interpret its elemental profile and compare it to the Pb profile.

Compared to lead and zinc, less studies exist for copper behaviour in peat. Cu has been demonstrated to be either immobile or mobile. [START_REF] Nieminen | Enrichments of Cu, Ni, Zn, Pb and As in an ombrothrophic peat bog near a Cu-Ni smelter in Southwest Finland[END_REF] showed possible preservation of Cu after atmospheric deposition, regarding the rapid evolution of the vertical Cu enrichment factor gradient. Using herbarium samples, [START_REF] Shotbolt | Reconstructing temporal trends in heavy metal deposition: assessing the value of herbarium moss samples[END_REF] showed the immobility of Cu. However, [START_REF] Shotyk | A peat bog record of natural, pre-anthropogenic enrichments of trace elements in atmospheric aerosols since 12,370 14 C yr BP, and their variation with Holocene climate change[END_REF] and [START_REF] Ukonmaanaho | Heavy metal and arsenic profiles in ombrogenous peat cores from four differently loaded areas in Finland[END_REF] argued that, in ombrotophic peat, Cu could be affected by plant uptake like Zn. [START_REF] Novak | Mobility of trace metals in pore waters of two Central European peat bogs[END_REF] also recently concluded that Cu was highly mobile. In a detailed study of three ombrotrophic bogs in Finland, [START_REF] Rausch | Comparison of atmospheric deposition of copper, nickel, cobalt, zinc, and cadmium recorded by Finnish peat cores with monitoring data and emission records[END_REF] demonstrated that Cu mobility was affected by pH and mineralogy. At one site with relatively high pH and where CuFeS 2 (chalcopyrite) was the dominant Cu bearing phase, [START_REF] Rausch | Comparison of atmospheric deposition of copper, nickel, cobalt, zinc, and cadmium recorded by Finnish peat cores with monitoring data and emission records[END_REF] found that Cu was immobile. In a second site presenting lower pH and dominance of Cu oxide, [START_REF] Rausch | Comparison of atmospheric deposition of copper, nickel, cobalt, zinc, and cadmium recorded by Finnish peat cores with monitoring data and emission records[END_REF] found Cu to be mobile.

Very few studies have been carried out to investigate the behaviour of Ni in ombrotrophic peat, and the conclusions of this research are contradictory. [START_REF] Krachler | Atmospheric deposition of V, Cr, and Ni since the late glacial: effects of climatic cycles, human impacts, and comparison with crustal abundances[END_REF] concluded that Ni is mainly immobile in ombrotrophic peat, although it may be affected by weathering in minerotrophic peat. In contrast, [START_REF] Nieminen | Enrichments of Cu, Ni, Zn, Pb and As in an ombrothrophic peat bog near a Cu-Ni smelter in Southwest Finland[END_REF] showed that Ni is mobile in ombrotrophic peat. [START_REF] Ukonmaanaho | Heavy metal and arsenic profiles in ombrogenous peat cores from four differently loaded areas in Finland[END_REF] demonstrated that Ni was very mobile and affected by leaching. [START_REF] Rausch | Comparison of atmospheric deposition of copper, nickel, cobalt, zinc, and cadmium recorded by Finnish peat cores with monitoring data and emission records[END_REF] also demonstrated the high mobility of Ni in three ombrotrophic peat cores from Finland, one of which is nearby a Cu-Ni mine and another one close to a Cu-Ni smelter. All the Ni records did not follow the exploitation history of the nearby mines and smelters. The mobility of Ni was recently confirmed using herbarium samples, by comparing Ni concentrations and Pb (assumed immobile) concentrations in specific peat vegetation samples of various ages [START_REF] Shotbolt | Reconstructing temporal trends in heavy metal deposition: assessing the value of herbarium moss samples[END_REF].

Natural vs. anthropogenic sources

Enrichment factors (E.F., Table 3) relative to the upper continental crust (U.C.C.) were calculated using Ti as a conservative element (e.g., [START_REF] Shotyk | A peat bog record of natural, pre-anthropogenic enrichments of trace elements in atmospheric aerosols since 12,370 14 C yr BP, and their variation with Holocene climate change[END_REF][START_REF] Kempter | Der Verlauf des anthropogenen elementeintrags in Regenwassermoore des westlichen Mitteleuropas während des jüngeren Holozäns[END_REF]. It was not possible to calculate a regional natural background from deep samples as only a 1-m core was retrieved. However, the mean Pb concentration in natural (i.e., non-polluted) soils from Poland is ca. 16 mg kg -1 [START_REF] Jarosinska | Environmental lead exposure in Polish children: blood lead levels, major sources and principles of the lead poisoning prevention[END_REF], which is in good agreement with the mean U.C.C. value (17 mg kg -1 ). The main particle sources to Słowińskie Błoto bog are rainwater, sea salt sprays, atmospheric dust and particles due to human activities (coal burning, metal smelting and gasoline use). The latter is the main source for Ni, Cu, Zn, Pb and S. However, EF is limited in deciphering between the various anthropogenic sources. Therefore, lead isotopes will be used in order to specify which anthropogenic source is dominant over a period of time.

Selected trace element depth profiles record similar trends, especially for Pb and S (Fig. 2). Low values are observed below 40 cm depth. Copper and nickel are below detection limits until ca. 40 cm depth, where they increase towards maximum values at ca. 25 cm depth (AD 1955). Two peaks in Pb concentration are recorded at 36.5 (AD 1719) and 26.5 cm depth (AD 1945), respectively, in addition to sulphur. Towards the surface, all the concentrations decrease progressively. The zinc profile is different from the other heavy metal profiles. It records only one peak between 23 cm and 15 cm depth. The discrepancies between the Zn and the other heavy metals have been linked to zinc mobility and zinc plant uptake (e.g., [START_REF] Nieminen | Enrichments of Cu, Ni, Zn, Pb and As in an ombrothrophic peat bog near a Cu-Ni smelter in Southwest Finland[END_REF][START_REF] Shotyk | Review of the inorganic geochemistry of peats and peatland waters[END_REF]. Zinc is therefore not the best reference element to detect historic metal pollution. Lead is generally preferred as it is considered to be immobile in ombrotrophic bogs [START_REF] Shotbolt | Reconstructing temporal trends in heavy metal deposition: assessing the value of herbarium moss samples[END_REF][START_REF] Weiss | Sphagnum mosses as archives of recent and past atmospheric lead deposition in Switzerland[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF]. Cu and Ni are considered by most authors to be mobile (e.g., [START_REF] Rausch | Comparison of atmospheric deposition of copper, nickel, cobalt, zinc, and cadmium recorded by Finnish peat cores with monitoring data and emission records[END_REF] because they can be affected by changing redox conditions and therefore be leached. Their profile must therefore be interpreted with care. We may only assume that they are evidence for pollution by these metals, even in this remote area of Poland.

Lead isotopic ratios ( [1970][1971][1972][1973][1974][1975][1976][1977][1978][1979][1980] and a recent increase were also observed in Sphagnum bogs from the Czech Republic [START_REF] Novak | Origin of lead in eight Central European peat bogs determined from isotope ratios, strengths, and operation times of regional pollution sources[END_REF].

The isotopic composition of selected peat samples from Słowińskie Błoto are compared to the isotopic signatures of (a) the U.C.C. (i.e., Upper Continental Crust as a natural source of dust particles), (b) galena and coal samples from south Poland, and (c) modern aerosols (1994)(1995)(1996)(1997)(1998)(1999) from Eastern European countries (Fig. 3) measured by [START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the Northern Hemisphere[END_REF]. Isotopic ratios for Słowińskie Błoto samples confirm the hypothesis given by Pb E.F. that the main source of lead supplied to the bog is anthropogenic. In the 206 Pb/ 207 Pb vs. 208 Pb/ 206 Pb biplot, all the peat samples are spread between the isotopic field of (1) Polish galena and coals, and (2) modern aerosols (Fig. 3). No sample is found close to the isotopic field of continental crust. Samples from ca. AD 800 to ca. AD 1700 fall close to the galena isotopic field. It is difficult to distinguish between Polish galena and coal using the lead isotopic signatures, as both fields overlap. However, historical studies on metal trade in Medieval Poland show that galena was mined and smelted throughout Medieval times in Poland, and the peak of mining and smelting occurred between ca. AD 1500 and AD 1650 [START_REF] Carter | Trade and urban development in Poland: an economic geography of Cracow, from its origins to 1795[END_REF]Molenda et al., 1965). It is therefore assumed that the main anthropogenic Pb source over Poland during the medieval period was Pb-Zn (and Pb-Ag) mining and smelting. During the 20th century, samples fall into the field of modern aerosols, recording a more mixed signature, due to various lead emissions from coal burning, lead smelting and gasoline combustion. Samples spanning the last two centuries display isotopic ratios similar to aerosols from Ukraine, Russia and Lithuania. However, [START_REF] Bykowszczenko | Determination of heavy metal concentration in mosses of Słowińsky National Park using atomic absorption spectrometry and neutron activation analysis methods[END_REF] noticed that, owing to wind directions, the main atmospheric pollutants reaching the Słowińskie Błoto area originated from Western and South Western Poland and East Germany. It is assumed that although the lead isotopic signature found in Słowińskie Błoto during the last two centuries is in good Table 3 Enrichment factors calculated in the five depth intervals of the core using values from the upper continental crust [START_REF] Mc Lennan | Relationships between the trace element composition of sedimentary rocks and upper continental crust[END_REF] and Ti as a conservative element.

Concentrations in UCC (mg kg -1 ) Values/Ti UCC 100 cm-50 cm E.F. (Ti) 50 cm-35 cm E.F. (Ti) 35 cm-25 cm E.F. (Ti) 20 cm-10 cm E.F. (Ti) 10 cm-0 cm E.F. ( Ti agreement with lead originating from Russia and Ukraine, its signature is roughly similar to all the east European countries, and significantly different from the western part of Europe. The trend of the 206 Pb/ 207 Pb ratio in northern Poland during the last two centuries follow the one recorded in the other locations (Fig. 5). It decreases from the early 19th century to the 1960s. From the 1960s, the 206 Pb/ 207 Pb ratio in Słowińskie Błoto starts to increase drastically. Although the other records also display such an increase, their values generally stay below 1.15. This can be explained by the predominance of leaded gasoline (with low 206 Pb/ 207 Pb values) among the pollution sources in western European countries. In Eastern European countries, coal burning (with higher 206 Pb/ 207 Pb values) remained more important. This fact was previously mentioned by [START_REF] Novak | Origin of lead in eight Central European peat bogs determined from isotope ratios, strengths, and operation times of regional pollution sources[END_REF], who noticed that the main difference between eastern and western Europe in terms of lead isotopic signature was that atmospheric 206 Pb/ 207 Pb ratios in Eastern Europe averaged 1.15 during the 1970s, and not 1.10, because Pb-ore treatment and coal burning remained important sources of Pb. In Słowińskie Błoto, 206 Pb/ 207 Pb ratio in 1970 is equal to 1.153, which is in good agreement with the importance of extractive industries relative to lead gasoline in Eastern European countries. In Poland, leaded gasoline was progressively withdrawn in favour of unleaded gasoline during the first years of the 21st century. This introduction is also clearly recorded by the lead isotopes in Słowińskie Błoto, displaying higher 206 Pb/ 207 Pb and lower 208 Pb/ 206 Pb values (sample at 2000 AD on Fig. 3).

History of pollution recorded in Słowińskie Błoto and a comparison with European pollution history

The calculated lead accumulation rate (Fig. 4) displays two peaks around AD 1600 and AD 1940, separated by a low-value period around AD 1800. This trend can be explained by the history of Poland and its extractive industry. By its commonwealth pact with the Duchy of Lithuania, Poland entered the apogee of its cultural and economic development between ca. AD 1500 and 1650 [START_REF] Lukowski | A concise history of Poland[END_REF]. This prosperity gradually decreased between ca. AD 1650 and 1800 when Poland entered a period of semi-permanent war, ending with its partition by the countries bordering it: the Russian Empire, Austria and Prussia [START_REF] Lukowski | A concise history of Poland[END_REF]. The production of lead is strongly affected by this cultural trend. Lead production in Silesia, detailed in [START_REF] Molenda | Gornictwo Kruszcowe Na Terenie Zloz Slasko-Krakowskish do Polowt XVII Wieku[END_REF] and in [START_REF] Keckowa | Zdobywanie surowcow mineralnych[END_REF], increased from 500 t yr -1 in ca. AD 1500 to 3000 t yr -1 in ca. AD 1650, to dramatically decrease afterwards. This apogee and phasing out of the Medieval and Renaissance Polish culture and economy is clearly recorded in the lead accumulation rate at Słowińskie Błoto (Fig. 4), suggesting that metal extraction and processing was relatively important during the Polish apogee and subsequently decreased during the 17th century. This peak of lead pollution during the Polish Renaissance was also recorded in a peatland from southern Poland, 30 km north of the Silesian region [START_REF] Chrost | Depozycja zanieczyszczen w glebach Podhala na przestrzeni ostatniego tysiaclecia" w Materialach na seminarium: "Program rozwoju ekoenergetyki I ratowania zasobow naturalnych Tatr, Podhala, Spisza, Orawy, Pienin I Gorcow[END_REF]. During the industrial revolution, the increasing mining activities and, more recently, the introduction of leaded gasoline explain why the lead accumulation rate increased so dramatically to reach a maximum between 1920 and 1940 and remains elevated until the eighties (Fig. 5). The calculated cumulative lead (assuming a negligible amount of lead deposited prior to AD 750) shows an almost perfect exponential increase from AD 750 towards the present, with a slowing down during the last 25 years (Fig. 4). It also shows that approximately one half of the lead was deposited prior to AD 1820, while the other half was deposited during the last two centuries. This trend emphasises the significant pollution during the industrial revolution. The decline of the communist regime in Poland caused a strong decrease in industrial activities in addition to new EU regulations introduced to reduce particle emissions from smelters. As a consequence, the Pb accumulation rate starts to decrease during the 1970s (Fig. 5). The amount of lead accumulated during the past 25 years is therefore less important, explaining the attenuation in the slope of the cumulative lead curve for this period.

The lead enrichment factor profile (Fig. 4) shows two periods of enrichment (AD 1000-AD 1200 and AD 1700-present) separated by lower values between AD 1200 and AD 1700. This last period in characterized by high Ti content from high atmospheric soil dust input [START_REF] Vleeschouwer | Multiproxy evidences of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland[END_REF], therefore decreasing the lead EF. The last Pb EF maximum (Pb E.F. = 250) is around between ca. AD 1965 and AD 1985 (Fig. 5). However, the maximum calculated Pb accumulation rate is found in the deeper adjacent layer 210 Pb dated between 1920 and 1940. This discrepancy between these two [START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14 C "bomb pulse curve[END_REF], Ocean and Rybarenska peat bogs, Czech Republic (Novak et al., 2008), and a lake record from Ziegelsee, North Germany [START_REF] Gäbler | Chronology of anthropogenic heavy-metal fluxes and P biotope ratios derived from radiometrically-dated lake sediments in Northern Germany[END_REF].

indicators of Pb atmospheric pollution can be explained by the largest Pb E.F. induced by leaded gasoline combustion which would not produce any particles containing Ti. Coal combustion on the other hand would produce particles enriched in Pb but also in Ti [START_REF] Eskenasy | Trace elements in the Goze Delchev coal deposit, Bulgaria[END_REF][START_REF] Xu | Status of trace element emission in a coal combustion process: a review[END_REF], which does not make Pb E.F. the best indicator to follow Pb pollution. The Pb E.F. maximum around ca. AD 1000 can be associated with medieval Pb smelting production in Germany and Poland (e.g., [START_REF] Brännvall | The Medieval metal industry was the cradle of modern large-scale atmospheric lead pollution in northern[END_REF], and the Pb accumulation rate peak around AD 1800 with coal combustion.

The lead accumulation for the last two centuries in Słowińskie Błoto is compared with peat records from Denmark [START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14 C "bomb pulse curve[END_REF], the Czech Republic (Novak et al., 2008) and with a lake record from North Germany [START_REF] Gäbler | Chronology of anthropogenic heavy-metal fluxes and P biotope ratios derived from radiometrically-dated lake sediments in Northern Germany[END_REF] in Fig. 5. The Pb accumulation rate found in Northern Poland (this study) is generally lower than the ones found in nearby Denmark and Northern Germany. Discrepancies also occur in the timing of the highest lead accumulation rate periods. This maximum occurs between 1920 and 1940 in Słowińskie Błoto, then later in Denmark (late 1950s) and later still in northern Germany (1970s). Historical data show that maximum lead emission over Europe generally took place between 1970and 1985(von Storch et al., 2003 and references therein) and references therein). Moreover, [START_REF] Pacyna | Atmospheric emissions of anthropogenic lead in Europe: improvements, updates, historical data and projections[END_REF] showed that the maximum lead emission over Poland occurred in AD 1975, when the mean annual Pb emission was 7000 metric t yr -1 . The former U.S.S.R. recorded maximum lead emission during the 1970s (annual mean = 54,100 metric t yr -1 ), in addition to Germany (annual mean= 16,500 metric t yr -1 ). [START_REF] Schneider | Atmospheric Pb and Cd input into the Baltic Sea: a new estimate based on measurements[END_REF] also demonstrated that the maximum lead emission to the nearby Baltic Sea occurred during the early 1970s. Using peat bog records from the Czech Republic, [START_REF] Vile | 200 years of Pb deposition throughout the Czech Republic: patterns and sources[END_REF] also demonstrated that a maximum of Pb emission took place between 1965 and 1990 and was due to coal burning and lead smelting. These authors also noted a decrease in Pb emission between AD 1975 and AD 1980. The strong decrease of pollution levels recorded in Słowińskie Błoto during the last 30 years is also in good agreement with results found by Bykowszczenko et al. (2006 and reference therein) who estimated a 38% decrease in anthropogenic particle emissions over Poland during the 1990s, due to better control of dust emission and better filter technologies introduced in Polish industries. Similarly, Grodzinska and Szrek-Lukaszewska (2001) noticed a decrease in Pb and other heavy metal concentrations in mosses between 1975 and 1998. However, the peak in Pb accumulation rate found in Słowińskie Błoto between AD 1920 and AD 1940 seems to be in good agreement with Ocean bog (Czech Republic), which also displays a peak in accumulation rate during the 1930s. The late 19th century-peak in this bog is due to local Ag-Pb ore mining and smelting and is therefore not to be taken into consideration for our site. The fact that like Ocean bog, Słowińskie Błoto displays a maximum Pb accumulation rate between 1920 and 1940 is contradictory with the general trend over Europe, where maximum lead pollution generally occurs during the seventies. Like Ocean bog and conversely to Rybarenska bog (Fig. 5), Słowińskie Błoto may record distal pollution, and therefore lack some recent historical pollution peaks. The Pb flux cannot be correlated with Pb emission in the environment if the sources and the factors of emissions are changing.

The calculated lead accumulation rate (Fig. 5) in the top-most sample (1 mg m -2 yr -1 ) is also in very good agreement with the lead deposition scenario (between 1.1 and 1.2 mg m -2 yr -1 ) provided by the Meteorological Synthesizing Centre-East (www.msceast.org) and with lead wet deposition (1.16 mg m -2 yr -1 ) in this region of Poland measured by EMEP (www.emep.int) in 2005 (the year when the core was collected).

Sulphur record

In Słowińskie Błoto, lead and sulphur variations with depth are generally similar. [START_REF] Novak | Sulfur mobility in peat[END_REF] show that S was mobile in the peat cores they studied. However, [START_REF] Jeker | Sulfur profiles of the twentieth century in peat bogs of the Swiss Midlands measured by ICP-OES and by IC[END_REF] published a reconstruction of S deposition over Switzerland using peat cores. In our case (Table 1), Pb and S are very well correlated with r 2 equal to 0.96. Different temporal phases can be distinguished: (1) from the bottom of the core to AD 1000 moderate values of S, (2) from AD 1300 to AD 1700 decrease in S values, (3) from AD 1700 to AD 1945 increase in S values and (4) from AD 1945 until present, decrease of values. These periods are in good agreement with the periods deduced from the Pb isotopes. Sulphur inventories over the 210 Pb-age-dated period (34.5 cm depth to top) show an average 6.2 mg cm -2 . This value is above the value calculated from the Finnish polluted bogs near smelters investigated by [START_REF] Rausch | Comparison of atmospheric deposition of copper, nickel, cobalt, zinc, and cadmium recorded by Finnish peat cores with monitoring data and emission records[END_REF], which is 2.4 mg cm -2 . It also above the values found in the Black forest (4.8 mg cm -2 , Le Roux and Shotyk, pers. com.). However, it is well below the value calculated from Novak et al. (2008), which averages 15 mg cm -2 . This comparison clearly shows the fact that, even if Słowińskie Błoto is located in a rural area, not as polluted as Polish Silesia (SW-Poland) or northern Czech Republic, remote areas in Poland are still more polluted compared to similar areas (e.g., Black Forest, Germany) elsewhere or even compared to some smelting localities (e.g., Finland). However more investigations on parameters such as pH, water-table fluctuation, S species, S content in pore-water should be undertaken before using it as a tracer of anthropogenic activities in Słowińskie Błoto.

Conclusions

This investigation of a 1-m peat core recovered from Słowińskie Błoto bog (Pomerania) records 1300 years of anthropogenic pollution over northern Poland. Lead is mainly supplied by anthropogenic sources, which are Pb-Zn ore mining and smelting (from the Middle Ages), coal industries and gasoline. Other metals (Zn, Ni and Cu) may also originate from anthropogenic sources, but their history is difficult to interpret because of their possible mobility. Lead accumulation rates are in good agreement with the history of Poland and its cultural changes. The Polish Renaissance (ca. AD 1450-AD 1600) is clearly recorded by the lead accumulation rate, which peaks around AD 1600. The lead accumulation rate then decreases as a consequence of a period of political instability in the territory of Poland. The isotopic trend in Słowińskie Błoto is in good agreement with other records from Denmark and Germany during the last 200 years, although the maximum lead accumulation rate (between AD 1920 andAD 1940) in Słowińskie Błoto is not in agreement with the general trend over Europe (maximum emission between AD 1960 andAD 1980). This kind of discrepancy was recorded in another site from the Czech Republic (Ocean bog, Novak et al. 2008) but is still not understood. Interestingly, half of the lead in northern Poland was emitted during the last 200 years. Finally the reconstructed lead accumulation rate in the most recent peat layer in Słowińskie Błoto are in good agreement with the modelled lead level for the Baltic Region.

Fig. 1 .

 1 Fig. 1. Above. Site location and surrounding Pb-Zn ore (light grey) and coal (dark grey) basins in Poland (after Bibler et al., 1998; Mukai et al., 2001). Below -State of preservation in 1983 on the basis of stereoscopic aerial photographs (after Herbichowa, 1998). 1 -open peatland complex of Sphagno-tenelli-Rhynchosporetum albae, Sphagnetum magellanici typicum i S. m. and b5% single dwarf pines of ca. 2 m high. 2 -open Sphagnetum magellanici pinetosum peatland with more densely (max. 10%) distributed pines of 2 to 5 m height . 3 -small patches of open Sphagnetum magellanici pinetosum peatland with initial state of Vaccinio uliginosi-Pinetum, small patches of Sphagnetum magellanici typicum and sparse pine of 4 to 8 m high. 4 (4+ 5) -Eight-meter to 20-m high Pine and birch-pine cover (50% to 80%) tree (Vaccinio uliginosi-Pinetum and Betuletum pubescentis). 5 -community with Calluna vulgaris on a dried peat, 6degenerated form of alder and young pine forest, 7 -meadow and pasture communities (class Molinio-Arrhenatheretea) on humified peat, 8 (9 + 10) -deciduous forest meadow communities from Molinio-Arrhenatheretea class on mineral soils. 9 -initial stage of development of peatland vegetation and young forest planted in remnants of peat exploitation, 10anthropogenic vegetation (i.e., recent), 11 -active ditches.

Fig. 2 .

 2 Fig. 2. [Pb], [Zn], [Cu], [Ni] and [S] vs depth. 14 C age intervals and some 210 Pb reference points are also reported.

Fig. 4 .

 4 Fig. 4. Lead accumulation rate (black line), accumulated lead (grey line) and lead enrichment factor (thin grey line) in Słowińskie Błoto peat bog. Horizontal segments represent the time interval of each sample. Note that ca. 50 % (1.18 g m -2 ) of the total lead has been deposited during the last two centuries.

Fig. 5 .

 5 Fig. 5. Comparison of 206 Pb/ 207 Pb and Pb accumulation profiles in Słowińskie Błoto since AD 1840 with peat records from Denmark[START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14 C "bomb pulse curve[END_REF], Ocean and Rybarenska peat bogs, Czech Republic(Novak et al., 2008), and a lake record from Ziegelsee, North Germany[START_REF] Gäbler | Chronology of anthropogenic heavy-metal fluxes and P biotope ratios derived from radiometrically-dated lake sediments in Northern Germany[END_REF].

Table 1

 1 Elemental geochemistry on bulk dry samples.

	Sample	Mean	Mean density	Mean acc. rate	Age	Unc.	Ti	S	Ni	Cu	Zn	Pb
	label	depth (cm)	g cm -³	cm yr -1	cal yr. AD	cal yr. AD	mg kg -1	mg kg -1	mg kg -1	mg kg -1	mg kg -1	mg kg -1
	04-05	4.5	0.023	0.830	2002	3	36	1442	5.64	11.77	89.2	5.38
	05-06	5.5	0.024	0.826	2001	2	32.36	1229	2.65	7.56	55.9	3.39
	06-07	6.5	0.024	0.973	2000	2	27.3	1176	5.54	6.92	51.4	4.25
	07-08	7.5	0.024	1.120	1999	2	34.9	1157	D.L.	6.07	54.4	3.65
	08-09	8.5	0.027	1.024	1998	2	35.1	1258	D.L.	8.98	61.2	4.7
	09-10	9.5	0.03	0.883	1997	2	38.7	1235	2.81	8.04	64	3.41
	10-11	10.5	0.032	0.590	1996	2	69	1400	D.L.	8.47	90.3	5.23
	13-14	13.5	0.057	0.369	1991	2	31.6	1284	3.95	9.72	123	9.48
	16-17	16.5	0.056	0.429	1983	3	62.8	1584	4.63	5.31	170	19.6
	18-19	18.5	0.05	0.358	1978	3	57.7	1494	5.47	5.49	160	33.3
	21-22	21.5	0.044	0.275	1970	3	81	2157	4.62	7.05	155	64.8
	23-24	23.5	0.047	0.176	1962	3	95.3	2716	7.63	8.79	152	99.1
	26-27	26.5	0.065	0.117	1945	3	244	3992	6.77	17.73	126	204
	29-30	29.5	0.066	0.095	1920	3	272	3654	7.1	18.58	80.3	156
	32-33	32.5	0.065	0.029	1888	5	138	3566	4.46	13.14	59.8	125
	34-35	34.5	0.058	0.020	1820	41	155	2372	2.74	9.16	52.7	101
	36-37	36.5	0.071	0.022	1719	31	376	3873	3.64	7.24	55.2	155
	38-39	38.5	0.116	0.026	1627	29	353	2863	3.66	5.64	44.5	109
	41-42	41.5	0.101	0.031	1512	31	206	2007	D.L.	D.L.	34.7	52.5
	43-44	43.5	0.141	0.033	1447	32	180	1688	3.2	2.6	28.5	37
	45-46	45.5	0.149	0.036	1387	35	148	1462	3.93	3.22	26	31.4
	47-48	47.5	0.126	0.036	1331	39	138	1516	3.2	3.11	23.7	29.2
	50-52	51.0	0.05	0.073	1234	46	56	1364	D.L.	D.L.	22.1	18.7
	52-53	52.5	0.048	0.054	1214	47	34.3	1348	D.L.	D.L.	21.5	14.4
	54-55	54.5	0.045	0.063	1177	47	42.5	1320	D.L.	3.37	18.4	13.3
	57-58	57.5	0.03	0.071	1129	45	23.6	994	D.L.	D.L.	15.4	12
	59-60	59.5	0.033	0.077	1101	42	60.1	1505	2.68	D.L.	15.7	18.1
	61-62	61.5	0.031	0.089	1075	39	38.5	1483	D.L.	D.L.	17.6	15.2
	66-67	66.5	0.035	0.103	1019	30	23.3	974	D.L.	D.L.	11.9	7.87
	68-69	68.5	0.031	0.114	1000	27	18.9	924	D.L.	D.L.	8	5.72
	71-72	71.5	0.032	0.122	974	32	20.2	1121	D.L.	D.L.	8	4.42
	73-74	73.5	0.035	0.126	957	36	32.5	1116	D.L.	D.L.	7.8	4.83
	77-78	77.5	0.028	0.122	925	43	22.4	999	D.L.	D.L.	3.97	4.83
	79-80	79.5	0.028	0.116	909	46	25.5	1225	D.L.	D.L.	4.68	1.48
	82-83	82.5	0.037	0.110	883	49	28.3	1142	D.L.	D.L.	12.9	2.84
	84-85	84.5	0.04	0.106	865	51	32.5	1249	D.L.	D.L.	6.59	2.72
	86-87	86.5	0.04	0.104	846	52	37.1	1361	D.L.	D.L.	6	1.2
	88-89	88.5	0.028	0.101	827	54	30.4	1302	3.07	D.L.	5.96	1.1
	91-92	91.5	0.024	0.099	797	56	34.5	1171	D.L.	D.L.	3.53	D.L.
	95-96	95.5	0.031	0.098	757	59	34.9	1245	D.L.	D.L.	5.44	0.91
	97-98	97.5	0.025	0.098	736	60	22.5	1246	D.L.	D.L.	4.17	D.L.
	LLD						0.9	70	2.5	2.5	2	0.6
	Error (%)						7	10	15	5	8	10

D.L. refers to measurements below detection limit. Model-derived ages reported from De

[START_REF] Vleeschouwer | Multiproxy evidences of Little Ice Age palaeoenvironmental changes in a peat bog from northern Poland[END_REF]

.

Table 2

 2 Isotopic measurements on selected peat samples from Słowińskie Błoto bog (above), galenas and coal from Poland (below).

	Sample no.	Mean depth (cm)	208 Pb/ 204 Pb	2se × 10 -4	207 Pb/ 204 Pb	2se × 10 -4	206 Pb/ 204 Pb	2se × 10 -4	208 Pb/ 206 Pb	2se × 10 -5	207 Pb/ 206 Pb	2se × 10 -5
	1	6.5	38.0758	49	15.6151	10	18.1974	14	2.09251	4.3	0.85803	1.1
	2	13.5	37.9713	20	15.6048	6.8	18.0843	7.4	2.09974	4.3	0.86284	1.0
	3	21.5	37.8992	25	15.5911	9.8	17.9892	10	2.10677	3.8	0.86665	0.9
	4	26.5	37.9656	21	15.5963	7.3	18.0324	7.9	2.10541	3.6	0.86485	1.0
	5	29.5	38.0678	19	15.6012	6.1	18.1164	7.0	2.10133	3.9	0.86112	1.1
	6	32.5	38.1612	18	15.6102	7.3	18.1871	9.2	2.09830	3.8	0.85828	1.0
	7	36.5	38.2696	17	15.6176	6.7	18.2759	7.0	2.09402	4.6	0.85447	1.2
	8	41.5	38.3550	22	15.6218	7.8	18.3564	7.7	2.08948	3.8	0.85099	1.0
	9	59.5	38.3176	20	15.6269	7.3	18.3346	8.2	2.08992	3.9	0.85228	1.1
	9*	59.5	38.3164	17	15.6265	6.3	18.3343	6.2	2.08986	4.0	0.85226	1.0
	10	68.5	38.3025	19	15.6238	7.6	18.3315	9.1	2.08946	2.9	0.85225	0.9
	11	77.5	38.3270	16	15.6262	5.8	18.3555	6.1	2.08809	4.4	0.85127	1.3
	Samples	Location	208 Pb/ 204 Pb	2se × 10 -4	207 Pb/ 204 Pb	2se × 10 -4	206 Pb/ 204 Pb	2se × 10 -4	208 Pb/ 206 Pb	2se × 10 -5	207 Pb/ 206 Pb	2se × 10 -5
	Galena 1	Chrzanow	38.4018	31	15.6144	10	18.4103	11	2.08589	8	0.84809	2
	Galena 1 a	Chrzanow	38.4089	24	15.6165	8	18.4148	8	2.08578	6	0.84801	2
	Galena 2	Chrzanow	38.4091	20	15.6160	7	18.4158	8	2.08567	5	0.84794	1
	Galena 2 b	Chrzanow	38.4052	24	15.6146	10	18.4136	9	2.08566	6	0.84793	2
	Galena 3	Olkusz	38.3760	28	15.6226	9	18.3942	9	2.08632	6	0.84928	1
	Galena 4	Olkusz	38.3795	23	15.6222	8	18.3992	8	2.08588	5	0.84904	1
	Galena 5	Pomorzany	38.3837	26	15.6245	9	18.3992	9	2.08615	7	0.84914	2
	Galena 6	Pomorzany	38.3737	30	15.6218	10	18.3931	10	2.08632	7	0.84928	1
	Galena 7	Pomorzany	38.3772	31	15.6210	10	18.3966	10	2.08609	8	0.84908	2
	Galena 8	Pomorzany	38.3812	25	15.6217	9	18.4016	10	2.08573	7	0.84889	1
	Galena 9	Chrzanow	38.4106	22	15.6162	8	18.4133	9	2.08594	7	0.84805	1
	Coal	Katowice	38.1621	20	15.6173	8	18.2320	8	2.09311	3	0.85654	1
	2se refers to accuracy calculated from 2 standard deviation.

a Replicate, i.e.,, a re-run of the same sample solution. b Duplicate, i.e.,, sample which is processed twice from weighing, acid digestion to analysis.

  Table 2) show relatively stable values from the base of the core up to 40 cm depth: 38.303 b 208 Pb/ 204 Pb b 38.355, 15.624b 207 Pb/ 204 Pbb 15.627, 18.332b 206 Pb/ 204 Pbb 18.356. This interval corresponds to the Middle Ages. Above 40 cm depth, Pb isotopic ratios decrease towards a minimum at 21.5 cm depth ( 208 Pb/ 204 Pb=37.900; 207 Pb/ 204 Pb=15.591; 206 Pb/ 204 Pb=17.990), which corresponds to AD 1970. Isotopic ratios finally increase towards the surface ( 208 Pb/ 204 Pb=38.076; 207 Pb/ 204 Pb=15.615; 206 Pb/ 204 Pb=18.197). Such stable trends mainly during the Middle Ages, less radiogenic values during

Fig. 3. 206 Pb/ 207 Pb vs 208 Pb/ 206 Pb three-isotope plot and comparison with pollution sources. Plain black circles: samples from Słowińskie Błoto peat bog. Open circle: replicate of sample 9. Black triangle: coal from Poland this study), cross: coal from Poland (Farmer et al., 1999), grey shaded area: galena from Poland (n = 11). White area: coal from Czech Republic taken from Mihaljevič et al. (2009). U.C.C.: Upper continental crust field from Millot et al. (2004),[START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF],[START_REF] Grousset | Transient Pb isotopic signatures in the western-European atmosphere[END_REF] and[START_REF] Asmeron | The Pb isotopic evolution of the Earth: inferences from river water suspended loads[END_REF]. Modern industrial aerosols from Eastern Europe taken from[START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the Northern Hemisphere[END_REF].

Acknowledgements

We are grateful to Helen Kurzel (Umweltgeochemie Institut, Heidelberg) for her help in XRF analysis of samples, Konrad Tudyka and Agnieszka Wiszniowska for their help in 14 C sample preparation, and Arkadiusz Bulak for his help in 210 Pb preparation and measurement. Claude Maerschalk is warmly thanked for his help in lead isotopic separation and measurements. The help of Leszek Chróst («EKOPOMIAR», Laboratory for Ecological Research Measurement and Expertise, Gliwice, Poland) with the Polish literature about mining and pollution was greatly appreciated. We also thank Dmitri Mauquoy (Univ. Aberdeen) for the English smoothing of the manuscript. The core was taken within a larger project about 'Climatic changes in Pomerania (N Poland) in the last millennium based on the multiproxy high-resolution studies' (coord. M. Lamentowicz) granted by the Ministry of Scientific Research and Information Technology of Poland (Contract No.: 2P04G03228). Geochemical analyses and 14 C dating were granted by an individual support from University of Liège ("classic credit" to N. Fagel) and a stay-grant to F. De Vleeschouwer (CGRI Poland-Wallonia cooperation). F.D. was supported by F.R.I.A. (F.N.R.S.) fellowship.

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.scitotenv.2009.07.020.