Historical Record of European Emissions of Heavy Metals to the

Environ. Sci. Technol. 2004, 38, 4085-4090

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Historical Record of European Emissions of Heavy Metals to the Atmosphere Since the 1650s from Alpine Snow/Ice Cores Drilled near Monte Rosa C A R L O B A R B A N T E , * ,†,‡ MARGIT SCHWIKOWSKI,§ THOMAS DO ¨ R I N G , §,| H E I N Z W . G A¨ G G E L E R , § , | ULRICH SCHOTTERER,| LEO TOBLER,§ KATJA VAN DE VELDE,⊥ C H R I S T O P H E F E R R A R I , ⊥,# GIULIO COZZI,† ANDREA TURETTA,† KEVIN ROSMAN,3 MICHAEL BOLSHOV,f G A B R I E L E C A P O D A G L I O , †,‡ P A O L O C E S C O N , †,‡ A N D C L A U D E B O U T R O N ⊥,O,* Department of Environmental Sciences, University of Venice, Ca’ Foscari, 30123 Venice, Italy, Institute for the Dynamics of Environmental Processes CNR, University of Venice, Ca’ Foscari, 30123 Venice, Italy, Paul Scherrer Institut, CH-5232 Villigen-PSI, Switzerland, Departement fu ¨ r Chemie und Biochemie, Universita¨t Bern, Freiestrasse 3, CH-3000 Bern, Switzerland, Laboratoire de Glaciologie et Ge´ophysique de l’Environnement, UMR CNRS/UJF 5183, 54 rue Molie`re, Boıˆte Postale 96, 38402 Saint Martin d'He`res, France, Polytech Grenoble, Universite´ Joseph Fourier de Grenoble (Institut Universitaire de France), 28 avenue Benoıˆt Frachon, Boıˆte Postale 53, 38041 Grenoble, France, Department of Applied Physics, Curtin University of Technology, Western Australia 6845 Perth, Australia, Institute of Spectroscopy, Russia Academy of Sciences, 142092 Troitzk, Moscow Region, Russia, and Unite´ de Formation et de Recherche de Physique et Observatoire des Sciences de l’Univers, Universite´ Joseph Fourier de Grenoble (Institut Universitaire de France), Boıˆte Postale 68, 38041 Grenoble, France

Cr, Cu, Zn, Co, Ni, Mo, Rh, Pd, Ag, Cd, Sb, Pt, Au, and U have been determined in clean room conditions by inductively coupled plasma sector field mass spectrometry and other analytical techniques, in various sections of two dated snow/ice cores from the high-altitude (4450 m asl) glacier saddle Colle Gnifetti, Monte Rosa massif, located in the Swiss-Italian Alps. These cores cover a 350-year time period, from 1650 to 1994. The results show highly enhanced concentrations for most metals in snow/ice dated * Corresponding author phone: +39 041 234 8942; fax: +39 041 234 8549; e-mail: [email protected]. † Department of Environmental Sciences, University of Venice. ‡ Institute for the Dynamics of Environmental Processes CNR, University of Venice. § Paul Scherrer Institut. | Universita ¨ t Bern. ⊥ Laboratoire de Glaciologie et Ge ´ ophysique de l’Environnement. # Polytech Grenoble, Universite ´ Joseph Fourier de Grenoble (Institut Universitaire de France). 3 Curtin University of Technology. f Russia Academy of Sciences. O Unite ´ de Formation et de Recherche de Physique et Observatoire des Sciences de l’Univers, Universite´ Joseph Fourier de Grenoble (Institut Universitaire de France). 10.1021/es049759r CCC: $27.50 Published on Web 07/02/2004

 2004 American Chemical Society

from the second half of the 20th century, compared with concentrations in ancient ice dated from the 17th and 18th centuries. The highest increase factors from the pre1700 period to the post-1970 period are observed for Cd (36), Zn (19), Bi (15), Cu (11), and Ni (9), confirming the importance of atmospheric pollution by heavy metals in Europe. Metal concentrations observed in Colle Gnifetti snow around 1980 appear to be quantitatively related to metal emissions from Italy, Switzerland, Germany, France, Belgium, and Austria at that time, making it possible to reconstruct past changes in metal emission in these countries during the last centuries.

1. Introduction Atmospheric pollution by heavy metals is an important problem in Europe. Considerable efforts have been made to assess it, especially through extensive monitoring programs (see for instance (1, 2) and emission inventories (3-5)). A major difficulty with such approaches is that they provide information only for recent decades and do not allow us to go back in time to the pre-industrial period, which is necessary to put recent changes in proper perspective. Information on past changes in European atmospheric pollution for heavy metals can be obtained only from atmospheric archives such as peat bogs (6, 7), lake sediments (8, 9), or high-altitude Alpine snow/ice cores (10, 11). The only published data for heavy metals in Alpine snow/ ice cores are those which were recently obtained from the analysis of a 140-m snow/ice core, drilled in 1994 on the Eastern slope of Dome du Gou ˆ ter (45°50′N; 6°51′E, 4250 m asl) in the Mont Blanc massif. Although the ice at the bottom of the core was at least 200 years old, only the upper 110 m were dated with a good precision. They correspond to a ∼60year period from the early 1940s to the early 1990s. Various metals were determined in this core (10-17). A very interesting opportunity to get a longer time series with good quality dating arose from the availability of snow/ ice cores drilled at Colle Gnifetti (45°53′33′′N; 7°51′5′′E, 4450 m asl), a glacier saddle between two summits of Monte Rosa at the Italian-Swiss border. Systematic investigations of possible drilling sites in the Alps have shown that Colle Gnifetti is probably the place where the longest Alpine time series could be obtained (18). Here we present time series for various metals (Cr, Mn, Cu, Zn, Co, Ni, Mo, Rh, Pd, Ag, Cd, Sb, Bi, Pt, Au, and U), obtained from the analysis of two well-dated snow/ice cores from Colle Gnifetti, which cover a ∼350-year period from the 1650s to the mid 1990s. These elements were chosen because they are emitted by human activities to the atmosphere and might pose a threat to the environment, especially in populated areas such as Europe (3-5).

2. Experimental Section 2.1 Field Sampling. The snow and ice samples analyzed in this work are sections of two cores drilled at Colle Gnifetti. The Colle Gnifetti is a high-altitude (4450 m) glacier saddle located between two summits of the Monte Rosa, the secondhighest mountain (4634 m) in Western Europe (Figure 1). Measured ice temperatures never exceed the range between -9 and -14 °C (19). As mentioned above, the snow accumulation rate is rather low, which is due to wind erosion preferentially removing parts of the winter snow (18). This is a distinct advantage in obtaining a long time series; a VOL. 38, NO. 15, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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2.3 Analytical Procedures. All operations took place in clean room conditions. The core sections were first mechanically decontaminated in cold rooms to remove contamination from the core exterior from the drilling operations (23). The inner cores so obtained were then analyzed using a variety of techniques. Inductively coupled plasma sector field mass spectrometry (ICP-SFMS) (17, 24, 25) was used to determine Cu and Zn in all the sections and Cr, Co, Ni, Mo, Rh, Pd, Ag, Sb, Pt, Au, and U in some of them. Graphite furnace atomic absorption spectrometry (GFAAS) was used to determine Cu, Cd, and Zn in some of the samples. Laserexcited atomic fluorescence spectrometry (LEAFS) (26) was used for the determination of Bi in some of the samples. Typical uncertainties ranged from 5 to 20% (RSD). Finally, Pb and Pb isotopes were determined either by ICP-SFMS or thermal ionization mass spectrometry (TIMS), but the results are presented and discussed in a companion paper (20).

FIGURE 1. Schematic map of Europe showing the position of Monte Rosa at the Swiss-Italian border.

3. Results and Discussion

drawback, however, is that the accumulation is dominated by summer snow. Two cores were recovered using electromechanical drills. The longest core (diam ∼7.6 cm) was drilled in 1982 and reached a depth of 109 m (about 15 m above the bedrock); the second core (diam ∼10 cm) was drilled in 1995 and reached a depth of 25 m. In this work only the upper 83 m of the 109 m core and the upper 13 m of the 25 m core were analyzed. All core sections were packed inside sealed polyethylene bags and kept frozen until brought back to the laboratory (20). 2.2 Age Assignment. Age dating of the cores was performed by combining several methods: counting of annual layers from continuous concentration profiles of seasonally varying species, such as ammonium (21), calcium, and sulfate; use of stratigraphic markers, such as large Saharan dust events, atmospheric nuclear tests (identified from tritium profiles), and major volcanic eruptions; 210Pb measurements for the post-1900 period; and a three-dimensional ice flow model (21). The results show that the upper 83 m of the 109-m snow/ice core analyzed in this work covers a period of ∼330 years from the 1650s to 1982, while the upper 13 m of the 25-m snow core analyzed in this work covers a period of 22 years, from 1972 to 1994. The dating uncertainty is estimated to be (2 years for the period 1883-1994, (5 years for the period 1760-1882 (22), and (10 years for the preceding period (20).

3.1 Character of the Data. Altogether, decontaminated samples were obtained from 476 depth intervals. Cu and Zn were determined in all of them, whereas the other elements were analyzed only in part of the samples. Summary statistics are given in Table 1, showing a pronounced variability in concentrations for the different metals. Possible explanations for this variability are discussed in section 3.2. The only other data to which our data can be compared are those obtained from Dome du Gouˆter, Mont Blanc massif (10-12, 14, 16, 17). The two locations are ∼80 km apart (Figure 1) and they are at nearly the same altitude. It should, however, be kept in mind that the snow accumulation rate is much higher at Dome du Gou ˆ ter than at Colle Gnifetti. It can be seen in Table 1 that the concentrations are rather similar at the two locations, which is reasonable when remembering that the two locations are such a short distance from each other. 3.2 Short-Term Variability. A striking feature of the data set is that there is a pronounced variability in concentrations. As an illustration, Figure 2 shows the whole data set for Zn and Cu, which are the only metals that were measured in all 476 depth intervals. Concentration differences of up to 2-3 orders of magnitude are observed between nearby core sections. This confirms that there are pronounced short term (inter-annual and intra-annual) variations in heavy metal inputs to Colle Gnifetti as was previously observed for other

TABLE 1. Summary Statistics for Concentrations (in pg g-1) of Trace Metals in Dated Snow and Ice from Colle Gnifetti (Monte Rosa, Swiss-Italian Alps), This Work Dome du Gouˆ tera

Colle Gnifetti 20th century

pre-20th century

20th century

pre-20th century

element

min-max

mean

min-max

mean

min-max

mean

min-max

Cr Cu Zn Co Ni Mo Rh Pd Ag Cd Sb Pt Au Bi U

83-920 1-14500 15-38200 1.0-1080 1-1530 3.1-66 0.01-0.43 0.7-17 0.01-35 0.1-270 2-690 0.08-2.7 0.06-0.3 2.1-8.4 0.2-28

320 460 2280 156 127 17 0.12 3.7 2.4 52 48 0.35 0.13 4 5.0

54-195 1.0-1960 1-4780 7-126 1-420 1.8-20 0.02-0.07 0.5-10 0.11-1.4 0.1-81 1.0-62 0.12-0.23 0.12-0.18 0.17-1.6 0.8-7.2

110 75 270 43 33 4 0.04 2.3 0.5 7.3 8.5 0.15 0.15 0.9 2.8

7.7-830 2.0-900 35-11700 16-1040 6.5-710 0.44-50 0.01-0.4 0.5-10 0.15-12 1.1-130 0.2-110 0.08-0.6 0.07-0.4 0.18-24 0.2-37

142 142 1790 155 136 9.3 0.10 2.5 1.6 25 22 0.27 0.22 3.5 4.6

37-102 6.0-48 96-2200 26-140 0.21-3.5 0.02-0.1 0.5-2.4 0.17-0.5 0.6-14 2.4-26 0.1-0.4 0.07-0.24 0.46-1.7 1.0-4.4

mean 57 19 360 71 1.1 0.05 1.7 0.3 2.6 7.2 0.31 0.18 0.83 2.0

a Also shown are summary statistics of data obtained for dated snow and ice from Dome du Gou ˆ ter (Mont Blanc, French-Italian Alps) from refs 10-12, 14, 16, and 17.

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TABLE 2. Colle Gnifetti: Average Concentrations (in pg g-1) in Ice Dated from Before 1700 and Snow Dated from After 1970; Increase Factors between These Two Periods Are Also Reported

FIGURE 2. Changes in Cu (black triangles) and Zn (open circles) concentrations in dated snow/ice from a high-altitude Alpine site (Colle Gnifetti, Monte Rosa massif, Swiss-Italian Alps). species such as ammonium, sulfate, and nitrates (18, 21, 22) as well as for aerosol concentrations in ambient air (27). This fact was explained by seasonal changes in the efficiency of vertical transport of boundary layer air to high-alpine sites (27, 28). Previous investigations on seasonal variations of heavy metals in the Dome du Gou ˆ ter snow/ice core (10, 12, 14, 16, 17) have confirmed that such short-term variations are largely linked with seasonal changes in the vertical structure of the regional troposphere. Winter is indeed characterized by frequent low-altitude thermal inversions limiting the transportation of pollutants from low-altitude source areas to highaltitude locations. The pollutant content of high-altitude winter snow is then largely derived from distant sources. Conversely, there are stronger vertical exchanges in the troposphere during summer, which allow locally and regionally emitted pollutants to reach the high-altitude areas (20). 3.3 Changes in Concentrations Since the Mid-17th Century. Figure 3 shows long-term changes in the concentration of Cr, Co, Zn, Co, Ni, Mo, Rh, Pd, Ag, Cd, Sb, Pt, Au, and U from the 1650s onward. To isolate the long-term time trends, we have averaged individual data points over periods of several years to compensate for the pronounced shortterm variations discussed in the previous section. Five-year averages were used for the period 1900-1995; averaging times of 10 years were applied for the pre-1990 period, because less data were available for that period. Bi was not included because available data are very few. Cu and Zn are the only metals that were determined in all sections (Figure 2), giving rather complete concentration profiles over the 350-year period (Figure 3a). Although the profiles show elevated concentrations for both metals during the 20th century, they do, however, differ markedly for several time periods. For instance, the Cu profile shows elevated concentrations around 1800, which are not seen in the Zn profile. Conversely, the Zn profile shows elevated concentrations around 1870, which are not observed for Cu. Ni was determined in 404 sections, giving quite a detailed concentration profile, except for the most recent years (Figure 3b). The Ni profile looks very similar to the Cu profile, with elevated concentrations around 1800 and a pronounced increase in concentrations during the 20th century. The profiles for the other metals are less detailed because only part of the samples were analyzed for them. Especially, we have very few data points for the period from the mid18th century to the early 20th century. Very interesting features can nevertheless be observed. The most interesting one is that for most metals, concentrations remained fairly low until the beginning of the 20th century, but then show highly enhanced values especially during the second half of

Cr Cu Zn Co Ni Mo Rh Pd Ag Cd Sb Bi Pt Au U

average concn before 1700

average concn after 1970

increase factor

144 39 171 70 24 3.4 0.030 0.86 0.34 1.6 21 0.25a 0.15 0.16 2.9

350 412 3176 144 218 18.0 0.10 3.7 1.16 58 53 3.9b 0.40 0.13 4.7

2.4 10.6 18.6 2.1 9.1 5.4 3.3 4.2 3.4 36.3 2.5 15.6 2.7 0.8 1.6

a No data are available before 1700; the value quoted here is for the 1780s. b No data are available after 1970; the value quoted here is for the 1950s.

the last century, Figure 3. Au is a clear exception, with fairly constant concentrations during the whole period. The only other ice/snow time series to which the Colle Gnifetti data can be compared are those obtained at Dome du Gou ˆter (10, 11, 14, 16). It should be remembered, however, that the Dome du Gou ˆ ter core was dated with good precision only for the post 1940s period, although the ice at the bottom was at least 200 years old. There are many common features between the Colle Gnifetti and Dome du Gou ˆter concentration profiles. Notably, both data sets show enhanced concentrations for many metals during the second half of the 20th century. In addition, both show no time trends for Au. For some metals however, there are some differences: for Pt, enhanced concentrations after ∼1980s are observed in the Colle Gnifetti profile, which were not seen in the Dome du Gou ˆ ter profile. Table 2 gives the mean factors of increase of concentrations for the various metals from the pre-1700 period to post1970. The post-1970 period was chosen because it corresponds to the period with the highest concentrations for many metals; conversely, the pre-1700 period was selected because it corresponds to low anthropogenic inputs, before the Industrial Revolution. The highest factor of increase is observed for Cd (∼36), followed by Zn (∼19), Bi (∼16), and Cu and Ni (∼10), Table 2. The opposite is observed for Au, with a factor that is close to one. These pronounced increases of concentration for most metals reflect the increasing pollution of the atmosphere by emissions of heavy metals in Europe. 3.4 Comparison of the Colle Gnifetti Data with Emission Data for Nearby Countries from the Late 1970s to Early 1980s. Inventories of emission of metals from anthropogenic sources in Europe during recent decades were published by several authors, especially Pacyna and co-workers (see, e.g., 4, 5, 29-31). They give estimates of total European emissions and in some cases also of emissions for individual countries and/or different source categories for various metals considered in our work (especially Cr, Cu, Zn, Co, Mo, Cd, and Sb). The main sources considered were conventional thermal power plants; industrial, commercial, and residential combustion of fuel; nonferrous metal production; and iron and steel ferro-alloys manufacturing (29). The most detailed published inventory of European emissions we could find is for the year 1979, i.e., during the VOL. 38, NO. 15, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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time period when enhanced concentrations were observed for many metals at Colle Gnifetti. At that time, Co, Mo, Ni, and Sb were mostly emitted by coal and oil combustion in power plants and industrial, commercial, and residential boilers, while nonferrous metal production was the major emission source for Cd, Cu, and Zn. Cr was mainly emitted from iron and steel ferro-alloy manufacturing. To determine if changes observed in the Colle Gnifetti snow/ice atmospheric archives does faithfully reflect changes in emissions from the nearby European countries, we have compared our snow/ice data with emissions data as follows. The most favorable time period for such a comparison appears to be around 1980. We have indeed the detailed emission data for 1979 from Pacyna (29). For the snow we have data for all metals considered in this work for the years 1981-1985, which is reasonably close to 1979 (we did analyze snow dated from 1979 obtained from the upper part of the 109-m core, but for only a few metals). To make the comparison clearer, we decided to use the Zn data for normalization as follows: for a given metal M we have calculated the M/Zn ratio, both for snow concentrations and for emissions. For convenience, these ratios were then 4088

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multiplied by 1000. As an example, the ratio R for Cr for Colle Gnifetti snow is as follows:

R)

[Cr]snow [Zn]snow

× 1000

where [Cr]snow represents the mean concentration of Cr in snow at Colle Gnifetti for the period 1981-1985, and [Zn]snow is the mean concentration of Zn in the snow for the same period. For emissions, we selected data from the following countries: Italy, Switzerland, Germany, France, Belgium, and Austria. These countries are likely to be important contributors for heavy metal inputs to Colle Gnifetti (20). As an example the ratio R for Cr for emissions was calculated as follows:

R)

Cremission × 1000 Znemission

where Cremission represents the total estimated emissions of Cr from Italy, Switzerland, Germany, France, Belgium, and

FIGURE 3. Changes in heavy metals concentrations in dated snow/ice from a high-altitude Alpine site (Colle Gnifetti, Monte Rosa massif, Swiss-Italian Alps). The individual data obtained for 476 different depth intervals have been averaged over periods of 5-10 years, giving the bars shown in the figures, allowing us to compensate for short-term variations and reveal the long-term time trend more clearly: (a) Cr, Co, Zn, and Cu; (b) Ni, Mo, Rh, and Pd; (c) Ag, Cd, Sb, and Pt; and (d) Au and U.

TABLE 3. Comparison of Metal over Zinc Ratios for Colle Gnifetti Snow Dated from the Early 1980s and Emissions to the Atmosphere in the Late 1970s from Italy, Switzerland, Germany, Belgium, France, and Austria ratio (M/Zn) × 1000

Colle Gnifetti snow emissions in 1979b

1981-1985a

Cr

Cu

Co

Mo

Rh

Pd

Ag

Cd

Sb

Bi

Pt

Au

U

138 177

124 110

43 18

6 7

0.04

2

0.2

23 30

9 4

42

0.04

0.04

2

a From mean concentration values for snow dated from 1981 to 1985. and Austria; from ref 30.

Austria in 1979 and Znemission represents the corresponding emissions of Zn for the same year. Zn was selected as a normalizing metal for the calculations because it is the metal with the highest emissions in Europe in 1979 (29) and it is studied in detail in our work. It is one of the metals measured in all depth intervals, and, moreover, it was measured in part of the samples using two independent

b

From emissions data for Italy, Switzerland, Germany, Belgium, France,

analytical techniques, ICP-SFMS and GFAAS, giving us a high confidence in the results. The results are shown in Table 3. It can be seen that for the metals for which both snow and emission data are available (Cr, Cu, Co, Mo, Cd, and Sb), the R values observed in Colle Gnifetti snow are in reasonably good agreement with the R values for total emissions in Italy, Switzerland, VOL. 38, NO. 15, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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Germany, France, Belgium, and Austria, despite the fact that the emission data have rather large uncertainties. As an example, Pacyna and Pacyna (4) suggest that their emission estimates for Cd might not be better than 50% accurate. For other metals they suggest that the accuracy of the emission values are only within a factor of 2. Keeping that in mind, the results shown in Table 3 indicate that Colle Gnifetti snow is a good surrogate for emissions from a large portion of Western Europe. 3.5 Estimation of Metal Emissions from the Colle Gnifetti Data. It looks reasonable to assume that the above relationship is valid for the other metals which we measured in the snow and for which no emission data are available. It allows us to obtain tentative values for emissions of these metals in Italy, Switzerland, Germany, France, Belgium, and Austria around 1980 from Zn emission in these countries in 1979 (∼30 000 t/year) (29). It gives the following values (in t/year): 1.3 for Rh and Pt; 6 for Ag; 60 for U and Pd; and 1300 for Bi. Au was not included in the calculation because the contribution from natural sources for this metal may be dominant as suggested by the lack of increase in Au concentration from the 17th Century to present (Table 2). If we now assume that the relationship between the concentration of metals in the snow and emissions to the atmosphere remains valid for previous time periods, then changes in concentrations in Colle Gnifetti snow and ice since 1650 (Figure 3) can be considered as good proxies of past changes in the emissions of metals to the atmosphere in a large portion of Western Europe. Tentatively, it then opens the way to a quantitative reconstruction of past changes in emissions during periods before emission inventories became available. Using this approach we have estimated a mean yearly Cu emission for the portion of Western Europe quoted above, for the period between 1650 and 1750, of ∼340 t/year. Let us now check if this value fits correctly with available data on Cu production in Europe, and Cu emission factors at that time. Cu production in Europe in 1750 was estimated at ∼3000 t/year by Hong et al. (32). Cu emission factors for mining and smelting activities at that time were estimated at ∼15% (32, 33). When combining these figures, it comes to an emission of Cu in Europe of ∼450 t/year in 1750. This value is in remarkable agreement with the value of ∼ 340 t/year obtained from Colle Gnifetti data, which validates the approach of using the Colle Gnifetti time series to reconstruct past changes in emissions.

Acknowledgments We thank Hansueli Bu ¨ rki for ice sample and data management. The generous support of the MIGROS Verteilzentrale Neuendorf, Switzerland, for storing firn and ice cores at stable deep freeze conditions is gratefully acknowledged. We thank the Swiss Army for helicopter transportation. Part of this study was performed in the framework of Projects on “Environmental Contamination” and “Glaciology and Paleoclimatology” of the Italian Programma Nazionale di Ricerche in Antartide and was financially supported by ENEA through cooperation agreements with the Universities of Venice and Milan, respectively. This work was also supported by the Institut Universitaire de France, the French Ministere de l’Amenagement du Territoire et de l’Environnement, the Agence de l’Environnement et de la Maitrise de l’Energie, the Institut National des Sciences de l’Univers, and the University Joseph Fourier of Grenoble. We also acknowledge the kind financial support from the Istituto Nazionale per la Ricerca Scientifica e Tecnologica sulla Montagna (INRM) and from Alliance for Global Sustainability (project title: Platinum Group Elements from Automobile Emission to Global Distribution). 4090

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Received for review February 16, 2004. Revised manuscript received May 5, 2004. Accepted May 14, 2004. ES049759R