Environ. Sci. Technol. 2010, 44, 3260–3266
Post 17th-Century Changes of European PAH Emissions Recorded in High-Altitude Alpine Snow and Ice J A C O P O G A B R I E L I , †,‡,§ P A U L V A L L E L O N G A , §,| G I U L I O C O Z Z I , †,§ P A O L O G A B R I E L L I , §,⊥ A N D R E A G A M B A R O , †,§ M I C H A E L S I G L , #,∇,O F A B I O D E C E T , ‡ M A R G I T S C H W I K O W S K I , #,∇,O ¨ G G E L E R , #,∇,O HEINZ GA C L A U D E B O U T R O N , [ P A O L O C E S C O N , †,§ A N D C A R L O B A R B A N T E * ,†,§ Department of Environmental Sciences, University Ca’ Foscari of Venice, Dorsoduro 2137, 30123 Venice, Italy, Environmental Protection Agency of Veneto (ARPAV), Belluno Department, via Tomea 5, 32100 Belluno, Italy, Institute for the Dynamics of Environmental Processes - CNR, University of Venice, Dorsoduro 2137, 30123 Venice, Italy, Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland, Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland, Oeschger Centre for Climate Change Research, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland, and Laboratoire de Glaciologie et Geophysique de l’Environnement, BP 96, 38402 Saint Martin D’Herez Cedex, France
Received November 16, 2009. Revised manuscript received March 24, 2010. Accepted March 26, 2010.
The occurrence of organic pollutants in European Alpine snow/ ice has been reconstructed over the past three centuries using a new online extraction method for polycyclic aromatic hydrocarbons (PAH) followed by liquid chromatographic determination. The meltwater flow from a continuous ice core melting system was split into two aliquots, with one aliquot directed to an inductively coupled plasma quadrupole mass spectrometer for continuous trace elements determinations and the second introduced into a solid phase C18 (SPE) cartridge for semicontinuous PAH extraction. The depth resolution for PAH extractions ranged from 40 to 70 cm, and corresponds to 0.7-5 years per sample. The concentrations of 11 PAH were determined in dated snow/ice samples to reconstruct the atmospheric concentration of these compounds in Europe for the last 300 years. The PAH pattern is dominated by * Corresponding author phone: +39 041 2348942; fax: +39 041 2348549; e-mail:
[email protected]. † Department of Environmental Sciences, University Ca’ Foscari of Venice. ‡ Environmental Protection Agency of Veneto (ARPAV). § Institute for the Dynamics of Environmental Processes - CNR, University of Venice. | Present address: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark. ⊥ Present address: School of Earth Sciences and Byrd Polar Research Center, Ohio State University, 43210 Columbus, OH. # Paul Scherrer Institut (PSI). ∇ Department of Chemistry and Biochemistry, University of Bern. O Oeschger Centre for Climate Change Research, University of Bern. [ Laboratoire de Glaciologie et Geophysique de l’Environnement. 3260
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phenanthrene (Phe), fluoranthene (Fla), and pyrene (Pyr), which represent 60-80% of the total PAH mass. Before 1875 the sum of PAH concentration (ΣPAH) was very low with total mean concentrations less than 2 ng/kg and 0.08 ng/kg for the heavier compounds (ΣPAH*, more than four aromatic rings). During the first phase of the industrial revolution (1770-1830) the PAH deposition showed a weak increase which became much greater from the start of the second phase of the industrial revolution at the end of 19th Century. In the 1920s, economic recession in Europe decreased PAH emissions until the 1930s when they increased again and reached a maximum concentration of 32 ng/kg from 1945 to 1955. From 1955 to 1975 the PAH concentrations decreased significantly, reflecting improvements in emission controls especially from major point sources, while from 1975 to 2003 they rose to levels equivalent to those in 1910. The Fla/(Fla+Pyr) ratio is often used for source assignment and here indicates an increase in the relativecontributionofgasolineanddieselcombustionwithrespect to coal and wood burning from 1860 to the 1980s. This trend was reversed during the last two decades.
Introduction Polycyclic aromatic hydrocarbons (PAH) are ubiquitous pollutants which are considered “priority pollutants” by the U.S. Environmental Protection Agency (EPA) (1) and can be detected in various environmental matrices in both populated and remote areas. Some PAH have several sources but others can be related to particular combustion processes. They primarily originate from incomplete combustion of organic matter and fossil fuels (e.g., diesel engines, domestic heating, industrial combustion) and for this reason they can be used as tracers of combustion activities (2-5). Approximately 90% of recent PAH emissions are estimated to be anthropogenic in origin (6). Several PAH and their degradation products, including partially oxygenated and nitrated PAH, are known to have a high carcinogenic and mutagenic potential and therefore pose a threat to human health (7), in addition to being of major interest with respect to emissions control. The historical environmental burden of PAH in remote areas as a consequence of human activities have essentially been obtained by analyzing lake sediments from high altitude sites (8-10). The European Alps are a valuable observation area for anthropogenic emissions as they are located in one of the most industrialized regions of the world. They are heavily influenced by the presence of international and national highways, industries, refuse incineration plants and the greatest density of winter sport infrastructure of any mountain area. Alpine glaciers may act as possible condensation sites for volatile and semivolatile compounds after long-range transport (11). Snow deposited on the Alps documents the effects of anthropogenic emissions in Europe (12) and mountain glaciers have been used as natural archives for studying historical trends of pollutants such as heavy metals (13, 14), and organic compounds (15, 16). Previous studies regarding PAH in glaciological records are limited to Greenland (17-19) and, only recently, to the Himalaya region (20, 21). There are many reasons for monitoring organic pollutants in glaciers: (i) they provide a tool to better assess the effectiveness of emission control measures and the need for a more stringent worldwide control; (ii) they may lead to a better understanding of local and global transport patterns; (iii) they allow the risk assessment of organic compounds on 10.1021/es903365s
2010 American Chemical Society
Published on Web 04/14/2010
highly vulnerable biological communities in cold environments including polar and high mountain ecosystems (22); (iv) they allow high-resolution reconstruction of the contamination history of these substances through time. The extraction of glacio-chemical information from ice cores is a challenge exacerbated by the very low concentrations of some impurities, thereby demanding rigorous control of external contamination sources and very sensitive analytical techniques. High resolution chemical sampling profiles are normally required, especially for glaciers with low annual snow accumulation of fresh snow. The development of continuous ice-core melting systems over the past few years has considerably increased the temporal resolution with respect to the extremely labor-intensive and time-consuming traditional chiseling procedure (23). Melting systems allow possible simultaneous online determinations of a large number of compounds such as major ions, dust (24-26), stable isotopes (27, 28), total organic carbon (29), and trace elements (30-32). However, high resolution melting system techniques have never been applied to determinations of organic pollutants such as PAH. Traditionally, PAH in aqueous environmental matrixes are extracted by liquid-liquid extraction, both with or without microfiltration (33). In the past decade, solid-phase extraction (SPE) techniques have improved and good recoveries using both C8 and C18 cartridges (34, 35) and disks (36) are possible. Recently, researchers have used solid-phase micro extraction (SPME) for trace organic compounds extraction in discrete samples of Himalayan snow and firn (20). We describe here the novel coupling of an ice-core melting device with an online solid phase extraction (SPE) for HPLC-FR determination of PAH in ice and firn sections from a high altitude site in the Western European Alps (Colle Gnifetti, 4455 m above sea level (a.s.l.)) with a resolution ranging from 1 to 5 years (40-70 cm per sample). This new method not only allows PAH extraction but also allows continuous highresolution determination of 24 trace elements by ICP-QMS, continuous conductivity measurements and discrete sampling. This multiparametric approach, with the high resolution extraction of PAH, represents a new advance in the icecore studies.
Materials and Methods Sampling Site. In September 2003, two ice/firn-cores were drilled to bedrock on Colle Gnifetti, Monte Rosa massif, in the Swiss/Italian Alps (Supporting Information (SI) 1) (45°55′50′′ N, 07°52′33′′ E; 4,450 m a.s.l.) by a Swiss/Italian team. The two parallel cores were drilled approximately 2 m from each other. Bedrock was reached at 81.9 (core A) and 81.1 m (core B), respectively. The dating of this part of the firn/ice core was established by combining several methods (37), as described in SI 1. In this work we discuss the upper 58 m of core (core A) which corresponds to the last three centuries. Sample Preparation. The ice cores were transported frozen to the laboratory at the University of Venice and then cut to fit the ice core melting system used for the decontamination. The core sections were cut to obtain ice with a cross-section of 32 × 32 mm and a length of 30-70 cm, depending on the core conditions. Samples were cut with a modified commercial band saw, with a stainless steel blade and a polyethylene tabletop and guides. The table, guides and the blade were carefully cleaned with acetone and methanol to remove contamination before every use. All exposed ice surfaces were rapidly scraped with a stainless steel knife cleaned with 0.1% ultrapure HNO3 (Romil, Cambridge, UK), rinsed several times and carefully dried after each use. This knife was used to remove the thin contaminated ice layer and more mass was scraped from the two base surfaces which directly contact the melting head.
These ends were then scraped deeper using a second clean knife which removed several mm of ice from each end. Each sample was then inserted in a polyethylene holder and placed on the melting head. Two 50 mm long pieces of frozen ultrapure water (Purelab Ultra-Analytic, Elga LabWater, High Wycombe, UK) were employed to monitor the blank level and provide a baseline before and after each melting procedure. Continuous Ice Core Melting System and PAH Extraction. The melting head consists of two concentric sections. The meltwater from the innermost part of the ice-core was drawn to an inner channel, whereas that from the outer section of the core was pumped out by a high stability peristaltic pump (Ismatec IP12A, Glattbrugg, Switzerland) via four outer drain channels using PTFE tubes. The inner meltwater channel was used for continuous trace elements determinations and collection of discrete samples, while the four external fluxes were joined together and introduced into a C18 solid phase extraction (SPE) cartridge (1 g, C18 Supelco Discovery, St Louis, MO). The melting system is extensively described in SI 2. The SPE cartridge was prewashed with 8 mL of dichloromethane (GC grade; Merck, Darmstadt, Germany) and conditioned with methanol (HPLC grade; Merck, Darmstadt, Germany) and ultrapure water. The analyzed ice core sections varied in length between 50 and 70 cm and correspond to a total meltwater amount of 250-500 g per core section. As such, the temporal resolution ranged from 0.7 years in the uppermost part of the core to 4-5 years at 50-58 m depth. After extraction the C18 cartridges were dried by fluxing anhydrous nitrogen under vacuum for at least 30 min, then wrapped in aluminum foil and kept frozen at -20 °C until elution. Determination of PAH Concentrations. The elution was performed in three steps using 6 mL of dichloromethane, 6 mL of cyclohexane (HPLC grade; Merck, Darmstadt, Germany) and another cycle of 6 mL of dichloromethane. Before each elution cycle, the cartridge was soaked in the solvent for at least for 5 min. The total amount of solvent was concentrated to 50 µL by a gentle stream of nitrogen (TurboVap-LP; Zymark, Allschwil, Switzerland). Acetonitrile (HPLC grade; Merck, Darmstadt, Germany) was then added to attain a final volume of 500 µL. The concentrations of phenantrene (Phe), anthracene (Ant), fluoranthene (Fla), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (dBA), benzo[ghi]perylene (BghiP), and indeno[1,2,3-cd]pyrene (InP) were determined by reversed phase high-performance liquid chromatography (RP-HPLC) on a C18 column (Supelcosil LC-PAHs 250 × 4.6 mm, 5.0 µm; Supelco, St Louis, MO). The mobile phase was an acetonitrile/ water gradient comprising of 50% CH3CN for 5 min, then 50-100% CH3CN for 25 min and finally 100% CH3CN for 8 min. The eluent flux was fixed at 1.50 mL/min. A HPLC chromatograph system (Waters 2695; Milford, U.S.) was coupled to a fluorimetric detector (Waters FD-2475, Milford, U.S.) programmed to change the excitation/emission wavelengths as a function of time (38). The injection volume was set to 50 µL. The system was calibrated by external calibration using a certified multistandard solution containing the 16 PAH specified by EPA as priority pollutants (Supelco, St Louis, MO). Concentrations in the standard solutions ranged from 0.25 to 25 ng/g.
Results and Discussion PAH Blanks, Decontamination Efficiency and Detection Limits. The blank values were obtained by extracting 1 kg of ultrapure water using the same procedure described above. The eluted cartridge residue was analyzed using the same VOL. 44, NO. 9, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Blank Values Were Obtained by Extracting and Analysing 1 kg of Ultra-Pure Water with Relative Standard Deviations (n = 5) and Detection Limits (d.l.) Calculated As Three Times the Standard Deviation of the Blank. Blank Core Values (Procedural Blank, n = 3) Have Been Obtained by Analysing Artificial Ice Sections Prepared by Freezing Ultra-Pure Water under Strict Contamination Control (Class 100 Clean Bench at -20 °C). Recovery Tests and Relative Precision Values (As Standard Deviation) Were Obtained by Analysing Spiked Melted Snow Samples (n = 5). The PAH Concentrations in the Samples Were Not Corrected for the Recovery recovery test compound
blank (pg/kg)
d.l. (pg/kg)
blank core (pg/kg)
expected (ng/kg)
this work (ng/kg)
recovery (%)
Phe Ant Fla Pyr BaA Chr BbF BkF BaP dBA BghiP InP
508 ( 155 48 ( 3 201 ( 47 282 ( 65 756 ( 84 65 ( 14 19 ( 6 20 ( 2 41 ( 8
