William Shotyk

Two thousand years of atmospheric arsenic, antimony, and lead deposition recorded in an ombrotrophic peat bog profile, Jura Mountains, Switzerland

A peat core from a Swiss bog reveals significant enrichments of As, Sb and Pb extending back to Roman times, indicating that the anthropogenic fluxes of these metals have exceeded the natural fluxes for more than 2000 years. The isotopic composition of Pb provides no evidence of vertical downward Pb migration, suggesting that the bog has faithfully preserved the historical record of atmospheric Pb deposition. Age dating using210Pb (verified independently using pollen markers) provides the chronology of changing metal concentrations during the past 150 years. Present day enrichment factors (relative to the metal/Sc ratios of typical crustal rocks) are of the order of 20 times (As), 70 (Sb), and 130 (Pb). Given the potential toxicity of As and Sb, these new findings suggest that the environmental significance of these, and perhaps other less common trace elements, deserve more attention.

9000 years of geochemical evolution of lithogenic major and trace elements in the sediment of an alpine lake - the role of climate, vegetation, and land-use history.

A 9000cal. year record of geochemistry was analysed in a sediment core obtained from a Swiss alpine hard-water lake (1937 ma.s.l.) that is located at the present-day tree-line. Geochemical stratigraphies are compared to changes in mineralogy, grain-size, pollen, and macrofossil records. This allows the reconstruction of the effects of changes in vegetation and of 3500 years of land-use in the catchment area on sediment geochemistry. Using principal component analysis, two major geochemical groups are distinguished: (i) Changes in concentrations of Rb, Ti, Zr, Fe, As, and Pb are closely related to corresponding changes in the concentrations of quartz and clay. They are thus considered to represent the silicate fraction which shows an increase from the oldest to the youngest core section. (ii) In contrast, Ca and Sr concentrations are positively correlated with changes in silt, sand, and calcite. They are therefore considered to represent the carbonate fraction which gradually decreased. Based on constrained cluster analysis, the core is divided into two major zones. The oldest zone (A; 9000–6400 cal.BP) is characterised by high concentrations of detrital carbonates. The more open catchment vegetation at that time promoted the physical weathering of these carbonates. The second major zone (B, 6400 cal.BP–1996 AD) is divided into four subsections with boundaries at ca. 3500, 2400, and 160cal. BP. The lower part of this zone, B1, is characterized by a gradual decrease in the carbonate-silt fraction and a pronounced increase in the silicate-clay fraction. This is concurrent with the expansion of Picea in the catchment area, which probably stabilized the soil. The middle part, B2 and B3 (3500–160cal. BP), comprises pronounced fluctuations in all elements, especially Ca, Sr, Mn, and Rb, but also in clay and silt. These changes are related to varying intensities of alpine farming. In the same section, Mn/Fe ratios are highly variable, suggesting changes in the mixing regime of the lake with phases of anoxic bottom water. The uppermost section, B4 (since 160cal. BP), is characterized by a steep decline in the silicate fraction and an increase in Ca and Sr. Despite the decrease in the silicate fraction, Pb increases, due to elevated atmospheric input resulting from early metal pollution, are masked by the high natural variability. Generally, changes in vegetation, which correspond to climate changes in the early Holocene and to human activities since ca. 3700cal. BP, are the controlling factor for variations in the geochemical composition of the sediment of Sägistalsee.

Geochemistry, mineralogy, and geochemical mass balance on major elements in two peat bog profiles (Jura Mountains, Switzerland)

Abstract The mineralogical and chemical composition of peats from two Sphagnum bogs in the Franches Montagnes region (Jura Mountains, Switzerland) were compared. The peats in the top 102 cm at Etang de la Gruere (EGr) represent 2110 years of peat formation compared with 1730 years for the first 84 cm at Tourbiere de Genevez (TGe). Scandium was used as a conservative tracer to distinguish between the primary sources of major elements to the bogs: atmospheric deposition of soil-derived aerosols (EGr and TGe); physical incorporation of elements along with mineral matter from the underlying sediments (TGe); and adsorption or complexation by the peat following diffusion from groundwater (TGe). These results support previous findings which showed that the EGr core (102 cm) is exclusively ombrogenic compared with TGe where the peats below approx. 30 cm become predominantly minerogenic. The modern rates of Sc accumulation (past 100 years) are similar in the two cores: 39 μg m −2 a −1 at EGr versus 52 μg m −2 a −1 at TGe. However, comparison with deeper sections of the EGr core reveals that the present-day rates of atmospheric Sc deposition are nearly 3 times greater than the long-term average rate, reflecting the higher concentrations of soil-derived atmospheric aerosols today. The rates of Sc accumulation in the TGe core are slightly higher than at EGr; this reflects the incorporation of mineral matter from the underlying sediments In the deeper, minerogenic peats at TGe, the long term rates of Fe and Ca accumulation are 5 and 7 times higher, respectively, than in the EGr core. These fluxes greatly exceed the difference in Sc flux, and cannot be explained by the differences in amount of mineral matter in the peats. These enrichments require an independent explanation, and are most likely the result of adsorption and/or complexation of cationic Ca and Fe species diffusing from deeper layers in the profile. The mineralogical composition of the ash is mainly quartz (60–90%), with feldspar (5–15%) and muscovite (5–15%), although various other minerals (5–10%) are commonly present. Biogenic Si represents another important fraction of ash and is abundant (30–70%) at discrete depths. The vertical profiles showed no significant changes in mineralogy with depth: assuming a constant composition of source materials, the lack of progressive mineralogical change suggests that the fine-grained silicates supplied by soil dust have not been measurably weathered during the past two millennia. A number of peaks in Fe/Sc are found in both cores above peaks in ash content and density. These appear to correspond with temporal fluctuations in wet/dry conditions: accumulation of Fe-oxides during dry periods and leaching during wetter conditions.

A 14 500 year record of the accumulation of atmospheric mercury in peat: volcanic signals, anthropogenic influences and a correlation to bromine accumulation

A 14 500 calendar year record of mercury accumulation rates has been obtained from an ombrotrophic peat bog in the Swiss Jura mountains. The range of natural (pre-industrial) mercury accumulation rates varied from 0.3 to 8.0 W gm 32 yr 31 . During the Late Glacial and Holocene, climatic and volcanic signals were evident in the mercury record. Mercury accumulation rates increased by a factor of ca 5 during the Younger Dryas cold period. Short-term spikes in mercury accumulation rates, which correspond in time to known volcanic eruptions, occur during the late Boreal and Older Atlantic periods, when volcanic influences on mercury deposition appear to have been intensified due to increased atmospheric humidity. A correlation of mercury to bromine accumulation is observed throughout the preanthropogenic period. During the Holocene, mercury accumulation only exceeded the range of this correlation for a few short periods of elevated mercury deposition which correspond to known volcanic eruptions during the Older Atlantic. During historical times, mercury accumulation rates have exceeded the range of the correlation of mercury to bromine continuously since ca 1330 AD. This excess in mercury accumulation is interpreted as an indication of pollution. During the industrial period, mercury accumulation rates reached 107.6 W gm 32 yr 31 , of which 84% was mercury that exceeded the correlation range. Mercury accumulation rates peaked again during the 1970s, with 78.8 Wg m 32 yr 31 . Early 20th century pollution appears to have been dominated by non-Swiss emissions from coal burning, whereas Swiss mercury emissions appear to have been the dominant pollution source during the mid and late 20th century. Current mercury accumulation rates at the site are similar to those ca 10 years ago, with modern deposition rates being ca 15 times their prehistorical average. Anthropogenic emissions of reactive brominated compounds could be contributing to increased atmospheric deposition rates of mercury. A 2002 Elsevier Science B.V. All rights reserved.

Sphagnum mosses as archives of recent and past atmospheric lead deposition in Switzerland

Sphagnum mosses received from a herbarium and collected recently from a peat bog surface, were used to assess the isotopic character of past and recent atmospheric Pb deposition in Switzerland and to constrain possible Pb sources. Lead removed from the moss surface was isotopically similar to that measured in the corresponding solid plant, suggesting that neither preservative actions for the herbarium samples nor dust had affected the isotopic composition of the samples. The addition of HCl to aqueous extracts to remove surface particles from the plants released more Pb compared to H2O alone. The changes in isotope ratios between Sphagnum collected during the past c. 130 yr were significantly greater than the small fluctuations between and among species collected at any one time. Three isotope ratio plots and emission inventories indicated that the most likely source of atmospheric Pb was coal-burning at the turn of the century, fly ash from waste incineration until approximately 1950, and gasoline combustion after that. The pollution record derived from the Sphagnum plants is in good agreement with other archives from Switzerland (peat, sediment, ice) and with other herbarium records in Europe.

Archives of Atmospheric Lead Pollution

Environmental archives such as peat bogs, sediments, corals, trees, polar ice, plant material from herbarium collections, and human tissue material have greatly helped to assess both ancient and recent atmospheric lead deposition and its sources on a regional and global scale. In Europe detectable atmospheric lead pollution began as early as 6000 years ago due to enhanced soil dust and agricultural activities, as studies of peat bogs reveal. Increased lead emissions during ancient Greek and Roman times have been recorded and identified in many longterm archives such as lake sediments in Sweden, ice cores in Greenland, and peat bogs in Spain, Switzerland, the United Kingdom, and the Netherlands. For the period since the Industrial Revolution, other archives such as corals, trees, and herbarium collections provide similar chronologies of atmospheric lead pollution, with periods of enhanced lead deposition occurring at the turn of the century and since 1950. The main sources have been industry, including coal burning, ferrous and nonferrous smelting, and open waste incineration until c .1950 and leaded gasoline use since 1950. The greatest lead emissions to the atmosphere all over Europe occurred between 1950 and 1980 due to traffic exhaust. A marked drop in atmospheric lead fluxes found in most archives since the 1980s has been attributed to the phasing out of leaded gasoline. The isotope ratios of lead in the various archives show qualitatively similar temporal changes, for example, the immediate response to the introduction and phasing out of leaded gasoline. Isotope studies largely confirm source assessments based on lead emission inventories and allow the contributions of various anthropogenic sources to be calculated.

Changing Concentrations of Cu, Zn, Cd and Pb in a High Altitude Peat Bog from Bolivia during the Past Three Centuries

A core consisting of minerogenic peat and organic-rich mineral sediments was collected at an altitude of 4275 m in the Ovejuyo valley, 100 km NE of La Paz in Bolivia. Age dating with 210Pb showed that the core represents approximately three centuries of sediment accumulation. None of the peats are ombrotrophic. Despite this, the Cd/Al, Cu/Al, Zn/Al, and Pb/Al ratios are all significantly higher in the surface layers, particularly in the top 6 cm: natural, abiological geochemical processes, therefore, cannot account for these elevated heavy metal/Al ratios. There are two possible explanations for the metal enrichments, relative to Al, in the surface layers: bioaccumulation by living plants, and anthropogenic atmospheric metal deposition. While the living plant layer may be responsible for the Cd, Cu, and Zn enrichments, this is an unlikely explanation for the Pb profile. In contrast to the other metals, the concentration of Pb in the first sample (dating from 1985-1994) is less than that of the second sample (dating from 1970-1985). The Pb/Al profile is consistent with the well documented, rapid increase in atmospheric Pb emissions during the present century (which accelerated following the introduction of leaded gasoline), and the decline in Pb pollution during the past 20 years (as a result of the introduction of unleaded gasoline). Thus, the Ovejuyo Valley mire has provided one of the first records of atmospheric Pb pollution in South America.

Ion chromatography of organic-rich natural waters from peatlands: I. Cl−, NO2−, Br−, NO3−, HPO42−, SO42− and oxalate

Abstract Organic-rich natural waters from peat bogs in continental (Switzerland) and maritime (Shetland Islands, Scotland) areas were analysed for Cl−, NO2−, Br−, NO3−, HPO42−, SO42− and oxalate using ion chromatography. These anions can be determined simultaneously in the surface and pore water samples from the continental bogs using a 250-μl injection loop. Using this loop, the detection limits were ca. 5 ng/g for the monovalent anions and SO42− and 10 ng/g for HPO42− and oxalate. An organics-removal cartridge (Dionex OnGuard P) was used to remove humic materials. These cartridges did not significantly affect the measured concentrations of anions in blind standards. Analyses of deionized water treated with these cartridges are not significantly different from those for untreated deionized water. For the maritime bogs, the relatively high concentrations of Cl− (more than 100μ/g in many samples) and SO42− (up to 50 μg/g) require two separate determinations for complete analyses. A 10-μl injection loop was used to determine Cl−, Br− and SO42−. A 250-μl injection loop was used to measure NO2−, NO3−, HPO 42− and oxalate. In each instance a Dionex OnGuard P cartridge was used to remove humic materials. In addition, a chloride-removal cartridge (Dionex OnGuard AG) was used to remove Cl− when the larger injection loop was used. This cartridge has no significant effect on the measurement of HPO4-2− at concentrations of 20 ng/g. In each of the bog water chromatograms there were usually a number of unknown peaks. These are probably due mainly to organic anions.

Incongruent and congruent dissolution of plagioclase feldspar: effect of feldspar composition and ligand complexation

Abstract Secondary ion mass spectrometry (SIMS) was used to characterize the surfaces of plagioclase feldspar (two labradorite compositions and one anorthite) leached in water (pH 5.8), and in 10−4M HCl, HF, and oxalic acid, all at the same pH (4.0–4.1). Labradorite (An54 and An60) leached at pH 4 for 72 days dissolved incongruently in HCl, oxalic acid, and HF, yielding altered layers strongly depleted in Al, Ca, and Sr and residually enriched in Si. The leached layers formed on the more calcic composition (An60) were approximately 3 times thicker than those formed on the more sodic (An54) composition. The thinnest leached layers were produced by HCl (up to 1000 A on An54 and up to 3000 A on An60), and the thickest leached layers by HF (up to 1700 A on An54 and up to 5000 A on An60). Because the H+ concentration was the same in each solution, it was possible to clearly separate the relative importance of proton-promoted dissolution (in HCl) and ligand-promoted dissolution (in oxalic acid and in HF) for a given feldspar composition. To do this, the SIMS depth profiles obtained from An60 labradorite leached in oxalic acid and in HF were normalized to those produced in response to HCl. This comparison clearly shows that the ligands oxalate and fluoride significantly increased the formation of leached layers, compared to the effect of H+ alone. In contrast, anorthite (An100) leached in the same solutions essentially dissolved congruently. In response to HCl only very thin leached layers formed in which Al and Ca were only weakly depleted relative to Si. Chemical analyses of the output solutions showed that the molar ratio of Si to Al in solution (1.1 to 1) is equal to the molar ratio of Si to Al in the fresh solid, confirming that the anorthite dissolved congruently. While the leached layers found on anorthite leached in oxalic acid and HF were thinner and less intensively depleted compared to the leached layers formed in response to HCl, the concentrations of Si and Al in the output solutions were significantly greater than those in the HCl solutions. While oxalate and fluoride again promoted the dissolution of the feldspar, Si and Al were still released to solution in the same molar proportion as they are found in the solid (congruent dissolution). The early stages of feldspar dissolution, therefore, may be either incongruent or congruent, depending upon the chemical composition of the feldspar.

Determination of Cd, Co, Cu, Fe, Mn, Ni and Zn in coral skeletons by chelation ion chromatography

Cadmium, Co, Cu, Fe, Mn, Ni and Zn incorporated in the aragonitic skeletons of corals (Porites) were analyzed by chelation ion chromatography (CIC). A 500-mg amount of bleached, oven-dried coral powder was dissolved in 1 ml of 14.4 M HNO 3 and buffered at pH 5.4 ± 0.1 using 50 ml of 2 M ammonium acetate. A 30-g amount of sample was concentrated on-line by pumping the solution through a Dionex MetPac CC-1 chelating concentrator column at a rate of 3 ml/min, and the MetPac was rinsed with 2 M ammonium acetate to elute alkaline earth metals to waste. The transition metals were eluted on a second concentrator column (Dionex TMC-1) using 2 M HNO 3 , and the TMC-1 was then converted to a salt form using 0.1 M NH 4 NO 3 and switched on-line with the analytical column, the Dionex IonPac CS-5. The metals were then eluted from the separator column using 6 mM pyridine-2,6-dicarboxylic acid-0.4 M NaOH ; the pH of this eluent was 4.4. The separated metals were, after they had left the column, complexed by 0.5 mM 4-(2-pyridylazo)resorcinol, and the absorbance was measured in a Dionex ultraviolet-visible detector at 520 nm. The use of two separator columns in series improved the metal separation. This is especially important for Ni and Co because coral samples typically contained an order of magnitude more Zn than Ni or Co. With two columns in series, Ni, Co and Zn were baseline-separated even when a 30-g sample containing 5 ppb Ni, 5 ppb Co and 100 ppb Zn was concentrated. The absolute sensitivity of the instrument was approximately 10 ng Cd. Although Cd was successfully determined in several corals using CIC, most coral samples contain on the order 1 ng/g Cd or less and, thus, the quantitative measurement of Cd in most corals by CIC would require tens of grams of coral powder. Unfortunately, it is not possible to obtain such large quantities of coral material from annual bands. The chelation system may be useful, however, to pre-concentrate coral digests for Cd analyses using more sensitive methods of detection (e.g. graphite furnace atomic absorption spectrometry or inductively coupled plasma mass spectrometry).