Environ. Sci. Technol. 2000, 34, 1906-1913
The Historical Record of Atmospheric Pyrolytic Pollution over Europe Registered in the Sedimentary PAH from Remote Mountain Lakes P I L A R F E R N AÄ N D E Z , * , † ROSA M. VILANOVA,† C A R O L I N A M A R T IÄ N E Z , † PETER APPLEBY,‡ AND JOAN O. GRIMALT† Environmental Chemistry Department, Institute of Chemical and Environmental Research (C.S.I.C.), Jordi Girona, 18-26, 08034 Barcelona, Catalonia, Spain, and Department of Mathematical Sciences, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, United Kingdom
Historical records of the deposition fluxes of polycyclic aromatic hydrocarbons (PAH) in 10 remote high altitude lakes distributed throughout Europe have been studied. Cores from each site were dated radiometrically, and the results were used for the reconstruction of the pollutant changes between 1830 and present. In general, both PAH pyrolytic fluxes and concentrations (Σ ) 23 compounds) increased from uniform background levels (5-30 µg m-2 yr-1, 20-100 ng g-1 dw, respectively) at the turn of the century to maximum values in 1960-1980. After these peak values a slight decrease to present day levels has been observed in some lakes, though they are still 3-20 times greater than the preindustrial period. Distinctive features in the downcore PAH profiles and concentrations between sites allowed for differentiation between five regions in Europe: peripheral areas (Norway and the Iberian Peninsula), Pyrenees and western Alps, central Alps, Tatra Mountains, and the Arctic. Atmospheric PAH inventories were estimated from the vertical integration of sedimentary inventories using 210Pb to correct for postdepositional transport processes. This approach consistently reduces variability among lakes from the same region. The results obtained define the lakes in the Tatra mountains and that on Spitsbergen Island as those of highest and lowest atmospheric PAH input. The other lakes exhibit lower differences although their atmospheric inventory values group consistently with the above-mentioned regions.
Introduction Fossil fuel combustion and industrial/domestic processes are responsible for the general increase of polycyclic aromatic hydrocarbons (PAH) over the last 100 yr (1). These compounds, many of which are known carcinogens, may result from both organic matter diagenesis and anthropogenic * Corresponding author phone: 3434006122; fax: 3432045904; e-mail:
[email protected]. † Institute of Chemical and Environmental Research (C.S.I.C.). ‡ University of Liverpool. 1906
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 10, 2000
processes (2-5). However, the anthropogenic contribution usually outweighs the inputs from other sources. Pyrolytic PAH are transported through the atmosphere over long distances affecting many aquatic systems (6, 7), even when situated at remote sites. A fraction of these PAH inputs is incorporated into the underlying sediments. Thus, in the absence of historic deposition measurements, undisturbed dated sediment cores may provide information on the atmospheric loading of these pollutants through time. Lacustrine sediment cores have been used for the assessment of the historical inputs of trace metals (8, 9), pesticides (10, 11), PCBs (12, 13), and PAH (3, 5, 14-21). However, in most cases the interpretation is complicated by mixed, non atmospheric PAH sources and in-lake processes, such as remobilization from catchment, losses through outfall and sediment redistribution. These processes are influenced by the configuration of the lake basin and may change with time. To this end, high mountain lakes, defined as those situated above the local tree-line, far from any pollution source and lacking major water inputs from the catchment, are unique environments for the assessment of the atmospheric pollution load over continental areas. The hydrology of these lakes is only related to atmospheric precipitation. In these conditions, the atmospheric to sedimentary fluxes of pollutants associated to settling particles can be estimated by reference to the 210Pb fluxes. In the present study, nine high mountain lakes distributed over all Europe (Sierra Estrela, Sierra Gredos, Pyrenees, Alps, Tatra, Caledonian) and one situated on Spitsbergen Island have been selected for examination of the PAH sedimentary record. Sediment cores were collected in all them, and their PAH composition was analyzed at high time resolution. Dating was performed with 210Pb, 226Ra, 137Cs, and 241Am. These cores have allowed the reconstruction of the history of the atmospheric anthropogenic PAH load over Europe for the last 160 years.
Materials and Methods Site Description and Sampling. The physical and morphometric characteristics of the lakes selected for study are summarized in Table 1. All lakes, by reason of altitude or latitude, are situated above the local tree line. They are oligotrophic (median total phosphorus 4.1 µg/L) and remain ice-covered for long periods. Soils in the catchments are poorly developed, and vegetation is sparse, with more than 80% of the catchments consisting of bare rock. Lake catchment-to-area ratio is lower than 20 for most of them; only Lakes Dlugi and Noir have values of 40-50. Therefore, lake hydrology depends on atmospheric precipitation. Likewise, pollution inputs are related to atmospheric transport and deposition since the lakes are free from local pollution sources (e.g., land-use or wastewater pollution). Sediment cores were taken in the deepest point of each lake during 1993-1995, with the exception of Øvre Neadalsvatn and Gossenko¨llesee which were sampled in 1996 and 1998, respectively. Sediment cores were obtained using a gravity corer (Glew, 7.5 cm diameter, 30 cm length) and extruded vertically in the field. Cores were subsampled for measurement of radionuclide tracers (2.5 mm slices from 0 to 5 cm, and 5 mm slices from 5 cm to the base of the core) and organic compounds (5 mm sections between 0 and 8 cm, and 10 mm sections from 8 cm to bottom). Samples for organic pollutants were wrapped in prerinsed aluminum foil and stored frozen until analysis. 10.1021/es9912271 CCC: $19.00
2000 American Chemical Society Published on Web 04/08/2000
TABLE 1. Physical and Morphometric Characteristics of the Lakes Selected for Study lake Escura Cimera Redo´ Noir Schwarsee ob So¨ lden Gossenko¨ lle Dlugi Starolesnianske Øvre Neådalsvatn Arresjφen a
mountain range (country)
latitude
longitude
altitude (m asl)
lake area (ha)
catchment water max. area (km2) depth (m)
Serra Estrela (Portugal) Sierra Gredos (Spain) Pyrenees (Spain) Alps (France) Alps (Austria)
40°21′17′′N 7°38′06′′W
1680
0.22
0.051
40°16′N
2140
4.5
0.85
45°25′N 7°07′E 46°57′57′′N 10°56′46′′E
2750 2799
1.2 4.3
0.59 0.14
Alps (Austria) Tatra (Poland) Tatra (Slovakia) Caledonian (Norway) Danskoyad (Norway)
47°13′49′′N 49°13′36′′N 49°10′N 62°46′30′′N
11°00′51′′E 20°00′39′′E 20°10′E 9°00′E
2417 1783 2000 728
1.7 1.6 0.75 50
0.16 0.66 0.027 16
79°40′N
10°48′E
In brackets, mean depth.
b
4°36′50′′W
42°38′34′′N 0°46′13′′E
2240
20
24
35
See text for calculation. c Not available, na.
Radionuclide Analysis. Subsamples of dried sediment from each section were analyzed in the Environmental Radioactivity Research Centre (University of Liverpool) for 210Pb, 226Ra, 137Cs, and 241Am using Ortec HPGe GWL series well-type coaxial low background intrinsic germanium detectors (22). PAH Analysis. Detailed description of the methodology for PAH analysis is described elsewhere (23). Briefly, wet sediments were extracted by sonication with methanol and subsequently with dichloromethane:methanol (2:1). The extracts were spiked with perdeuterated PAH as analyte surrogate and hydrolyzed overnight with KOH in methanol. Neutral compounds were recovered with n-hexane and fractionated by adsorption chromatography with aluminum oxide. The PAH fraction was eluted with hexane/dichloromethane (1:2), concentrated to almost dryness, and redissolved in isooctane prior to instrumental analysis. Procedural blanks were performed with each set of eight samples. Total organic carbon was determined with a CHN analyzer after acidification for carbonate removal. Aromatic compounds were analyzed by gas chromatography-mass spectrometry (GC-MS) using a Carlo Erba GC8000 gas chromatograph coupled to a Fisons MD800 mass detector in the selected ion recording (SIR) mode. The molecular weight mass fragments of the individual PAH were used for identification and quantitation; m/z 219 (M+ - 15) was also recorded for retene. Quantitation was performed by the external standard method (EPA mix 16). The reported values are corrected for surrogate recovery.
Results and Discussion. Sediment Dating. The down-core decline in 210Pb activity in excess of that supported by in situ 226Ra decay was used to determine a chronology for the past 130-150 years. 210Pb is a naturally occurring radionuclide with a half-life of 22.26 years. The results were validated where possible from stratigraphic records of the artificial radionuclides 137Cs and 241 Am. These can be used to identify the depth of the 1963 level, the year of peak fallout from the atmospheric testing of nuclear weapons, and 1986, the year of the Chernobyl reactor fire. In Arresjøen and Øvre Neadalsvatn, unsupported 210Pb activity in the sediments declined more or less exponentially with depth indicating relatively constant sedimentation rates throughout the entire 130-150 year period. At the other sites, changes in sedimentation rates were observed, including accelerated sedimentation in the recent decades (e.g., Redo´ and Starolesnianske Pleso) and also brief episodes of rapid sedimentation possibly due to land-slips or sediment slumps
1.55
3 d
ice cover period
12.5(3.2)a nac 9.4(4.8)
sampling date July 93
total org matter transport (av, %) coeffb 11
0.33
Nov-May July 93
3.0
0.31
73(32)
Jan-May
July 93
4.3
0.70
11(5.2) 18(10)
nac Oct-June
Sept 93 June 95
3.8 4.3
0.59 0.96
9.9 10.6(5) 4.1(1.6) 18(4)
Nov-June Nov-June Nov-May Nov-May
July 98 Oct 93 Oct 93 Sept 96
15 9.4 12 7.4
2.30 3.04 1.47 0.74
32(11)
Oct-June
Aug 93
5.6
0.98
Spitsbergen Island.
(e.g., Noir, Schwarsee ob So ¨ lden, Dlugi). Two standard dating methods for calculating 210Pb dates (24), CRS (constant rate of 210Pb supply) and CIC (constant initial 210Pb concentration), were used as appropriate (25). In most cases, major uncertainties in the 210Pb dates were resolved using the 137Cs and 241Am records. Total Organic Carbon (TOC). TOC was determined in all core sections postdating the middle of the 19th century (only back to 1930 in Gossenko¨lle). In most lakes the accumulation of organic carbon has been fairly uniform with fluctuations mainly related to changes in sedimentation rate (Figure 1). No major changes in sources of organic matter and postdepositional conditions are therefore observed during the investigated time period. Only Gossenko¨lle deviates from this general pattern, with a TOC reduction from 20% d.w. in 1950 to 9% at the surficial sediment. These TOC variations could be related to changes in the trophic status of the lake and/or in the watershed. All lakes exhibit high TOC values which a priori contrasts with their oligotrophic character. These high TOC can be attributed to small water columns (short sinking times) and depleted postdepositional oxidation due to low bottom water temperatures (
