Article pubs.acs.org/est
Three Centuries of Eastern European and Altai Lead Emissions Recorded in a Belukha Ice Core Anja Eichler,†,‡,* Leonhard Tobler,†,‡ Stella Eyrikh,§ Gabriela Gramlich,†,‡,⊥ Natalia Malygina,§ Tatyana Papina,§ and Margit Schwikowski†,‡,⊥ †
Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland Oeschger Centre for Climate Change Research, University of Bern, CH-3012 Bern, Switzerland § Institute for Water and Environmental Problems, RU-656038 Barnaul, Russia ⊥ Department of Chemistry und Biochemistry, University of Bern, CH-3012 Bern, Switzerland ‡
ABSTRACT: Human activities have significantly altered atmospheric Pb concentrations and thus, its geochemical cycle, for thousands of years. Whereas historical Pb emissions from Western Europe, North America, and Asia are well documented, there is no equivalent data for Eastern Europe. Here, we present ice-core Pb concentrations for the period 1680−1995 from Belukha glacier in the Siberian Altai, assumed to be representative of emissions in Eastern Europe and the Altai. Pb concentrations and 207Pb/206Pb ratios were strongly enhanced during the period 1935−1995 due to the use of Pb additives in Russian gasoline mined in the Rudny Altai. Comparable to Western Europe and North America, Eastern European Pb emissions peaked in the 1970s. However, the subsequent downward trend in Eastern Europe was mainly caused by the economic crisis in the U.S.S.R. and not by a phase-out of leaded gasoline. Pb concentrations in the period 1680−1935, preceding the era of intensified industrialization in Russia, reflect the history of local emissions from Rudny Altai mining and related metallurgical processing primarily for the production of Russian coins. During this time, Altai ore Pb contributed about 40% of the regional atmospheric Pb. last 300 years.10,11 Anthropogenic Pb emissions from North America and Asia were detected in ice-core records from Devon Island12 and Mt. Logan,13 respectively. Ice cores from the Pamir (Muztagata ice core14) and the Himalayas (Dasuopu ice core,15 Mt. Everest ice core 16) documented a strong anthropogenic impact on Pb concentrations from Asian countries. However, there is no previous glaciochemical record available representing the Pb-emission history in Eastern Europe. In this study, we present Pb concentrations and Pb-isotopic ratios for the time period 1680−1995 AD, obtained from an ice core collected at the Belukha glacier in the Siberian Altai. The Altai region forming the border between Russia, Kazakhstan, Mongolia, and China is mainly affected by westerly air masses and thus by air pollution from Eastern Europe (Figure 1). The obtained Pb-concentration record is discussed in context with historical Pb-emission estimates for Eastern European countries and Kazakhstan and compared with Pb-concentration changes
1. INTRODUCTION Atmospheric Pb concentrations are strongly influenced by human activities including coal combustion, use of leaded gasoline, metal smelting, and mining. The oldest known Pb artifact was found at Catal Hüyük, a large Neolithic settlement in southern Anatolia (7500−5700 BC).1 Greenland ice cores and European peat bogs document the influence of human activities on atmospheric Pb concentrations and Pb-isotope ratios in the Northern Hemisphere during the last 3000 years.2,3 The earliest anthropogenic footprints in these archives are due to Greek and Roman Pb mining. Ice cores provide invaluable natural archives of past pollution levels. Greenland and Antarctic ice cores provide insight into the past changing levels of atmospheric Pb in remote areas of both hemispheres documenting strongly enhanced Pb emissions from North America and Australia, respectively, beginning at the end of the 19th century.4−9 Complementary, ice cores from high-elevated mountain glaciers preserve the history of natural and anthropogenic Pb emissions in low- and midlatitude regions. These regions are of particular interest because they are located close to the emission sources. Ice cores from the Swiss and French Alps were used to obtain a Pbemission history for Western Europe over approximately the © 2012 American Chemical Society
Received: Revised: Accepted: Published: 4323
November 9, 2011 March 13, 2012 March 15, 2012 March 15, 2012 dx.doi.org/10.1021/es2039954 | Environ. Sci. Technol. 2012, 46, 4323−4330
Environmental Science & Technology
Article
Figure 1. Left: Map showing the location of the Belukha glacier (red star), the Rudny Altai region (green) together with Northern Hemisphere icecore sites discussed in the text (1-Mt. Logan, 2-Devon Island, 3-Greenland ATC2, 4-Colle Gnifetti, 5-Muztagata, 6-Dasuopu); Right: Frequency plot of seven-day back trajectories for the period 1991−2000 using HYSPLIT and NCEP reanalysis. Back trajectories were run every 6 h.
Tambora, 1783-Laki, 1766-Hekla, 1739-Shikotsu, 1727-Oreafojokull) were detected;20 (iii) a nonlinear regression based on simple kinematic glacier flow modeling25 was fitted through the identified horizons to obtain a continuous age-depth relation; (iv) finally, a three-parameter annual layer-counting methodology was applied, using the high-resolution records of melt percent, δ18O, and ammonium concentration19 to refine the dating. The upper 113 m of the Belukha ice core were found to cover the time period 1680−2001. Dating uncertainty is ±3 years for the period 1815−2001 and ±5 years between 1680 and 1815. 2.3. Sample Preparation. Ice-core sections (0.7 m long, 7.8 cm diameter) were sealed in polyethylene tubes in the field and transported to the Paul Scherrer Institute (PSI), Switzerland in a frozen state. 484 samples with lengths varying from 10 to 70 cm were analyzed, covering the depth range from 8 to 113 m (period 1680−1995). Eight percent of this core interval could not be analyzed due to poor ice quality (small chips). Sampling resolution varied from up to 6 samples per year in the last 50 years to one sample per year in the deepest core sections. Because the outer portions of the core are potentially contaminated by the drilling operation, handling, and transportation, the inner pristine sections of the cores (∼2 × 2 cm) were cut out with a band saw in a cold room at −20 °C. Because of the potential contamination by the stainless steel saw blade and the handling, each ice-core section was further decontaminated in a second step. For firn samples, the outer layers (∼0.3 cm) were removed with a ceramic knife. Ice samples were rinsed with ultra pure water (18 MΩ cm quality, Milli-Q Element system, Millipore Inc.) in a class 100 clean bench to remove the outer ∼0.2 cm. This decontamination step was tested to be as efficient, but much less time-consuming26,27 than the method applied in other studies28 where the outer part of the ice cores was mechanically removed by chiseling with stainless steel scalpels to reveal the pristine inner part. The decontaminated ice-core sections were transferred into high-density polyethylene containers (HDPE, Nalgene), which were carefully cleaned three times with 0.1 mol/l nitric acid (HNO3, Ultrex II, Baker) prior to use. Subsequently, samples were acidified with hydrochloric acid (HCl, Ultrex II, Baker) to yield a final acid concentration of 0.4% and melted at room temperature. Acidification time was at least 24 h before analysis.
in Western Europe, North America, and Asia during the last 150 years. Furthermore, the Pb-isotopic composition is used to estimate the contribution of different Pb sources to the overall regional atmospheric Pb concentration.
2. EXPERIMENTAL SECTION 2.1. Sampling Site Characteristics and Ice-Core Archive. Samples analyzed in this study originate from a 139 m ice core drilled at the Belukha glacier (49°48′26″N, 86°34′43″E, 4062 m a.s.l.) in July 2001.17 The drilling site is located on the saddle between the two summits of Belukha, the highest mountain in the Altai. The Altai mountain region (47− 53°N, 84−92°E) comprises the common border regions of southwest Siberia, eastern Kazakhstan, northern China, and western Mongolia (Figure 1). The region is of particular interest due to the proximity to Eastern Europe. Low englacial temperatures of −17 °C (between 15 and 75 m depth)17 indicate that this part of the glacier is situated in the cold infiltration recrystallization zone,18 where meltwater formed under the influence of solar radiation and high air temperature subsequently refreezes some centimeters below the surface. Thus, the ice core contains well-preserved records of past airpollution levels and climate. The ice-core δ18O record was used to reconstruct the temperature history in the Siberian Altai19 revealing solar and anthropogenic forcing as major drivers for temperature changes during the period 1250−2001.20 Concentration records of major ions NH4+, NO3−, and SO42‑ were shown to represent anthropogenic NH3, NOx, and SO2 emissions from agricultural activities, traffic, and fossil fuel combustion in Eastern Europe in the industrial period 1940− 2001.21,22 Preindustrial NH4+ and HCOO− concentrations were used as proxies for the history of direct biogenic emissions from vast Siberian forests, whereas K+, NO3−, and charcoal records served to reconstruct the forest-fire history in the Altai during the past 750 years.21,23 2.2. Dating of the Ice Core. Ice-core dating was performed by a combination of several methods. (i) We applied radioactive dating using 210Pb;22 (ii) reference horizons related to the maximum of nuclear weapons testing (3H and 239Pu activity maxima in 1963)24 and to explosive volcanic eruptions (maxima in nondust sulfate (exSO42‑) and corresponding minima in temperature 1912-Katmai, 1854-Shiveluch, 18154324
dx.doi.org/10.1021/es2039954 | Environ. Sci. Technol. 2012, 46, 4323−4330
Environmental Science & Technology
Article
Figure 2. a) Concentration record of Pb in the 484 ice-core sections covering the period 1680−1995. Shown are single measurements (crosses) and 5-year means (red line). b) The same as in a) but for the period 1680−1935, with a magnified ordinate, to account for the lower Pb concentrations. c) Concentration record of Pb (red, 5-year means, period 1680−1995) together with historical Pb-emission estimates for the former U.S.S.R. countries (black, period 1955−1995, given in Table 1). d) 5-year mean Pb concentrations (red, period 1680−1935) and the number of smelters and metallurgical plants in the Altai region (black, period 1725−1935,34). Vertical black lines in a) and c) separate the period 1680−1935 from the period of intensified industry 1935−1995 in Russia.
aerosol related species and gases from the planetary boundary layer to high-altitude sites. In winter, mountain sites are within the free troposphere, decoupled from the boundary layer. For the interpretation of the long-term trend in the Pb data, individual data points were averaged over 5-year periods, thus removing the short-time fluctuations related to the transport and postdepositional processes (part a of Figure 2). The 5-year means are most likely determined by changes in the Pbemission source strength. Pb concentrations remained on a rather low level in the period 1680−1935 increased strongly after 1935 with maximum values between 1970 and 1975. Pb concentrations subsequently decreased and returned in the 1990s to the level of 1940−1950. Similar observations were made for other predominantly anthropogenic species including SO42− and NO3− (Figure 3),21,22 whereas components originating mainly from natural sources as mineral dust and sea salt did not show a trend during the period 1680−1995 (e.g., Ca2+, Figure 3). Further evidence that the enhanced Pb concentrations after 1935 are not due to natural variations in dust can be gained from the Pb crustal enrichment factors (EFs) (Figure 3). Conservative crustal elements as for example Fe, Al, and Ti could not be used for the EF calculation because they are affected by anthropogenic sources particularly from mining activities. We used Ca as a dust tracer for the EF calculation, following the conventional equation EF(Pb) = [Pb/ Ca]sample/[Pb/Ca]reference, with the composition of the upper continental crust as reference.32 The EFs post 1935 are elevated relative to 1680−1935 similar to the Pb concentration record. Air mass back trajectory analyses performed for the period 1991−2000 revealed that the major source area for air pollution observed at the Belukha site is Eastern Europe, with the closest source regions being West and Central Russia and Kazakhstan (Figure 1). Pb-emission estimates for Eastern European countries are to our knowledge only available for the period 1955−2010 (Table 1).33 Estimates for the period 1955−1990 include Pb emissions from the European part of the U.S.S.R. but are not exclusively given for Russia. The European part of
HCl was applied for acidification instead of the most commonly used HNO310 because the additional analyses of Hg in the same samples required HCl as solvent.29 2.4. Pb Concentration and Pb-Isotope Analyses. Concentrations of Pb were determined by inductively coupled plasma sector field mass spectrometry (ICP-SF-MS) using a Finnigan MAT Element1 (Thermo Finnigan Bremen, Germany).10,30 A 100 μl self-aspirating PFA-nebulizer (Elemental Scientific Inc., Omaha, NE, USA) with a cooled Scotttype glass spray chamber together with an autosampler (221 XL, Gilson Inc., Middleton, WI, USA) were used for sample introduction. The ICP-SF-MS inlet was placed in a laminar flow clean bench (class 100). External calibration with linear regression of the calibration curves was used for quantification. Standard solutions with concentrations from 1 ng/l to 5000 ng/l were prepared from 1000 mg/l stock solutions by dilution with 0.4% high-purity HCl. In addition, Pb-isotopic ratios 207Pb/206Pb and 208Pb/206Pb were determined. Isotope ratios were corrected for detector dead time and mass bias. Accuracy of the isotope ratios was assessed by analyzing solutions with different concentrations of the certified isotope standard NIST 981 (National Institute of Standards and Technology). Pb-isotope ratios agreed within
