Environ. Sci. Technol. 1999, 33, 4416-4421
Present Century Record of Organolead Pollution in High Altitude Alpine Snow MONIKA HEISTERKAMP,† KATJA VAN DE VELDE,‡ C H R I S T O P H E F E R R A R I , ‡,§ C L A U D E F . B O U T R O N , ‡,| A N D F R E D D Y C . A D A M S * ,† Micro and Trace Analysis Centre, University of Antwerp (UIA), Universiteitsplein 1, 2610 Wilrijk, Belgium, Laboratoire de Glaciologie et Ge´ophysique de l’Environnement du CNRS, 54 rue Molie`re, B. P. 96, 38402 Saint Martin d’He`res, France, Institut des Sciences et Techniques de Grenoble, Universite´ Joseph Fourier de Grenoble, 28 Avenue Benoıˆt Frachon, B.P. 53, 38041 Grenoble, France, and Unite´s de Formation et de Recherche de Me´canique et de Physique, Universite´ Joseph Fourier de Grenoble (Institut Universitaire de France), B.P. 68, 38041 Grenoble, France
Organolead compounds are tracers of lead additives used as anti-knocking agents in leaded gasoline, and snow/ ice cores are useful archives of environmental pollution. Determination of these species in those archives provides information on their influence on the Pb pollution by monitoring the changes of organolead concentrations during the years. Organolead compounds have been analyzed by gas chromatography coupled to microwave-induced plasma atomic emission spectrometry (GC-MIP-AES) in a series of snow pit and snow/ice core samples deposited in a high altitude site in the Mont Blanc area between 1956 and 1994. Measured concentrations ranged from 0.1 to 3 pg/g for dimethyllead, from 0.08 to 3.4 pg/g for trimethyllead, from 0.01 to 0.57 pg/g for diethyllead, and from 0.01 to 0.13 pg/g for triethyllead. No organolead compounds were detected in ice deposited before 1962. Concentrations of total alkyllead increased from 1962 till the late 1980s but then declined significantly during the 1990s. Changes in consumption of these species in France were compared with the obtained data. A delay of several years was observed between the restricted consumption of these additives and the subsequent decrease in concentrations observed in the ice. Furthermore, the data were compared with two records for organolead pollution obtained for the Northern Hemisphere: one for Central Greenland snow and the other for vintages originating from the Rhoˆ ne Valley in southeast France.
Introduction Murozumi et al. (1) made the first successful determination of Pb concentrations in remote Greenland snow and ice. * Corresponding author tel: +32 3 820 20 10; fax: +32 3 820 23 76; e-mail:
[email protected]. † Micro and Trace Analysis Centre. ‡ Laboratoire de Glaciologie et Ge ´ ophysique de l’Environnement du CNRS. § Institut des Sciences et Techniques de Grenoble. | Unite ´ s de Formation et de Recherche de Me´canique et de Physique. 4416
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 24, 1999
This investigation showed a large scale atmospheric pollution and gave rise to a long argument about to what extent human activities have modified the Pb and other heavy metal levels in the entire terrestrial atmosphere (2-4). To evaluate the change in Pb concentrations, measurements were done for Greenland ice and snow dated from 8000 years BP to the present (5, 6). The results showed a ∼100-fold increase in Pb concentrations over the past three millennia. The prominent role of organolead compounds, which are used as antiknocking agents in leaded gasoline for motor vehicles, was unambiguously demonstrated in this large scale pollution by isotopic analysis and speciation analysis of the different Pb species in Greenland snow and ice (7, 8). Organolead analysis of Greenland snow revealed a straightforward illustration of the effect of anti-knocking agents on the overall global environmental geochemistry of Pb. Undetected in snow layers deposited prior to 1930, the organolead concentrations underwent a 5-fold increase from the early 1970s until their maximum in the early 1980s. Until now, no investigations were made on snow and ice archives of mid-latitude glaciers. Such data could provide valuable information on the history of the regional atmospheric pollution. To our knowledge, the only time series obtained for organolead species were obtained by analyses of old wine vintages (9). The analyses of 19 Chaˆteauneuf-du-Pape vintages covering 40 years of grape collection allowed tracing the local atmospheric pollution for these species. This paper presents a record from the late 1950s to 1994 of organolead species (including trimethyllead [TML, (CH3)3Pb+], dimethyllead [DML, (CH3)2Pb2+], triethyllead [TEL, (C2H5)3Pb+], and diethyllead [DEL, (C2H5)2Pb2+]) in high altitude alpine snow. Isotopic composition and total Pb concentrations of the samples previously were analyzed by Rosman et al. (10). Various sections of a snow/ice core drilled at a high altitude location in the Mont Blanc massif at the French-Italian border were analyzed. These analyses were performed using GC-MIP-AES after propylation of the different ionic organolead species using either an appropriate Grignard reagent or sodium tetrapropylborate.
Experimental Section Field Drilling and Sample Dating. Samples dated from before 1992 were taken from a 140-m snow/ice core in June 1994 at an altitude of 4250 m, about 1.5 km northwest of the summit of Mont Blanc, close to the French-Italian border (45°50′ N, 6°51′ E) (11). The samples dated from 1994 came from a 1.4 m deep snow pit made near the drilling site. The relevant parameters of the sampling site are as follows: mean annual temperature -11 °C, mean annual snow accumulation rate 3.5 m of water equivalent/year, close off depth at 60 m, and ice core diameter 10 cm. To minimize contamination during drilling and sampling procedures, a Teflon- (PTFE) coated drill was used, and operators handling the core sections wore cleanroom garb and shoulder-length polyethylene gloves. The different sections were individually sealed in acid-cleaned polyethylene bags and transported frozen to the laboratory (LGGE). The 43 analyzed samples could be correlated to a time period between 1956 and 1994. The depths of the different samples analyzed for organolead species ranged from the surface down to 100 m (year 1956). Thirty-two samples came from the ice core. Each ice core section was decontaminated at the LGGE using the ultra-clean procedures described by Candelone et al. (12). Successive veneers of ice or snow were mechanically removed from the outside to the central part of each section inside a laminar flow clean bench at -10 °C 10.1021/es990612n CCC: $18.00
1999 American Chemical Society Published on Web 11/10/1999
to get the innermost part of the core. This inner core was then divided into three parts. Each part of the inner core and veneer layer was melted separately inside a clean bench in the cleanroom at the LGGE to allow subaliquots of each original sample to be taken and distributed to the different laboratories using ultra-clean procedures (13). The other 11 samples came from the snow pit that was hand dug down to a depth of 1.4 m; the operator was wearing cleanroom garb and polyethylene gloves. A 20 cm thick snow layer was cut back from the vertical sampling wall with an acid-cleaned polyethylene shovel in order to prepare a fresh surface. Acid-cleaned 1-L wide-mouth polyethylene bottles were pushed horizontally through the sampling wall. Then the bottles were capped again and preserved in double-sealed acid bags. The part of the snow/ice core analyzed for organolead was dated by combining known reference levels from atmospheric nuclear weapon tests and the Chernobyl accident and a glaciological ice flow model (11). The precision of the ages so obtained is excellent for this part of the core (seasonal resolution). Dating of the snow pit samples was less certain, but from estimation of the annual deposition rates, it was a fairly good assessment to infer the bottom of the pit to snow deposited during March/April 1994 and the top to mid-June 1994. Sample Preparation and Analysis. Two different sample preparation procedures were applied for the speciation analysis of organolead compounds in the alpine snow. For these samples, the matrix is very simple, but the organolead concentrations are very low at a few femtogram per gram levels in some cases. Separation and detection of the organolead species was performed using GC coupled to MIPAES for all samples. The samples reflecting the year 1990 and earlier were analyzed according to a single-step procedure developed for polar snow (14). The Pb species were derivatized using sodium tetrapropylborate and simultaneously extracted into hexane. Inorganic Pb species were masked by adding a 0.1 M aqueous solution of the disodium salt of ethylenediaminetetraacetic acid dihydrate (EDTA) in order to avoid insufficient derivatization or memory effects caused by overloading of the detector. Based on 5 µL injection and 50 g sample, detection limits between 150 and 200 fg/g could be obtained for the different organolead species within a precision range between 4 and 15%. The fresh snow samples were analyzed according to the procedure described by Lobinski et al. (15). Using this method, detection limits between 10 and 20 fg/g can be calculated for the different species based on 25 µL injection and 50 g sample. Precision ranged between 7 and 16%. Analyses of these samples were done before the optimization of the faster and less contamination prone sample preparation procedure using sodium tetrapropylborate. Preparation of all the samples was performed in a laminar flow of a clean bench equipped with a HEPA filter in order to minimize contamination from organolead associated with the particulate material. Procedural blanks were checked each day before starting the analyses of the standards and samples. Total Pb was determined with graphite furnace atomic absorption spectrometry (GFAAS) at the LGGE in Grenoble using a Perkin-Elmer Analyst 100 spectrometer with a PE HGA 800 graphite furnace. A preconcentration step was necessary for part of the samples (16). All concentrations were corrected for procedural blanks (13). The precision ranged from 5 to 15%.
Results and Discussion Total Alkyllead Concentrations. The results of the analyses of the different samples from the snow/ice core and the fresh snow are summarized in Table 1. In the snow/ice core, only
TABLE 1. Results of Organolead Speciation Analysis in Fresh Snow (1994) and Snow/Ice Core from the Alps Reflecting the Years from 1991 to 1961a
year 1994
depth interval (m) 0.2-0.3 0.3-0.4 0.4-0.5 0.5-0.6 0.6-0.7 0.7-0.8 0.8-0.9 0.9-1.0 1.0-1.1 1.1-1.2 1.2-1.4
1991 21.9-22.2 1990 22.2-22.5 22.5-22.8 1989 38.6-38.9 1988 38.9-39.2 39.2-39.5 1981 54.1-54.3 1980 54.3-54.5 54.5-54.7 1978 62.7-63.0 1977 63.0-63.3 63.3-63.5 1975 69.2-69.5 1974 69.5-69.8 69.8-70.0 1971 78.9-79.0 1970 79.0-79.1 79.1-79.3 1968 81.4-81.6 81.6-81.8 81.8-82.3 1967 82.3-82.5 82.5-82.7 82.7-82.8 1966 82.8-83.1 83.1-83.4 83.4-83.6 1965 86.4-86.8 1964 86.8-87.2 87.2-87.5 1963 90.3-90.5 1962 90.5-90.6 90.6-90.8
total total TML DML TEL DEL alkyllead Pb (pg/g) (pg/g) (pg/g) (pg/g) (pg/g) (pg/g) 0.27 0.43 0.12 0.08 0.15 0.08 0.08 0.21 0.25 0.24 0.09
0.22 0.04 1.01 0.07 0.10 0.01 0.13 0.04 0.22
