Andriy K. Cheburkin

Geochemistry of the peat bog at Etang de la Gruère, Jura Mountains, Switzerland, and its record of atmospheric Pb and lithogenic trace metals (Sc, Ti, Y, Zr, and REE) since 12,370 14C yr BP

A 650 cm core from a Swiss bog represents 12,370 14C years of peat accumulation and provides the first complete record of atmospheric Pb deposition for the entire Holocene. Excess, non-atmospheric Sr in the peat was calculated by normalizing Sr/Sc to crustal abundance; this was used to differentiate between the ombrogenic section of the bog in which inorganic solids are supplied exclusively by atmospheric deposition and the minerogenic zone where mineral-water interactions contribute metals to the peat. While sediment dissolution contributes significantly to the Sr inventory of the minerogenic section of the peat profile, there is no measurable effect of this process on the Pb burden. Isotopic analyses (204Pb, 206Pb, 207Pb, 208Pb) show that effectively all of the Pb in the peat profile was supplied exclusively from the atmosphere. To separate natural and anthropogenic Pb, Sc was selected over Ti, Y, Zr, Hf and REE as a conservative, reference element which is supplied by soil dust aerosols derived from rock weathering. Enrichment factors (EF) were calculated using the Pb/Sc ratio in the peat samples, normalized to the “natural, background” Pb/Sc which is found in peats dating from 8030 to 5320 14C yr BP. The results show that anthropogenic source have dominated the supply of atmospheric Pb to the peat core continuously since 3000 14C yr BP. The aerosols supplied to the bog can be divided into 3 classes: a) Pre-Anthropogenic (older than 3000 14C yr BP with Pb EF 1.194); b) Pre-Industrial (dating from 3000–240 14C yr BP, with Pb EF ≥ 2 but 20 and 206Pb/207Pb < 1.179). Elevated soil dust fluxes are observed at 5320, 8230 and 10,590 14C yr BP; the latter corresponds to the Younger Dryas. Aluminum, Zr, Hf, and REE/Sc ratios also are elevated at the same depths, suggesting differences in particle size, wind strength, or source regions. Pre-Anthropogenic aerosols deposited since 8230 14C yr BP reveal Pb/Sc which is significantly higher, and 206Pb/207Pb which is less radiogenic, than during the early Holocene. While the trend toward increasing Pb/Sc could be due to chemical weathering and soil development, this could not explain the shift in Pb isotopic composition. The changes which took place at 8230 14C BP, therefore, may be related to a large scale climatic reorganization which, at present, is poorly understood.

A peat bog record of natural, pre-anthropogenic enrichments of trace elements in atmospheric aerosols since 12 370 14C yr BP, and their variation with Holocene climate change

Abstract A peat bog in the Jura Mountains, Switzerland, provides a continuous record of peat accumulation since 12 370 14 C yr BP. Periods of enhanced soil dust deposition (10 590 14 C yr BP, 8230 14 C yr BP, and after 5320 14 C yr BP) are characterized by strongly elevated Ti/Sc and Zr/Sc ratios which imply an increase in the abundance (both relative and absolute) of heavy minerals such as ilmenite and zircon. With respect to trace elements such as Cu, Zn, As, Cd, Sb and Au, the M/Sc ratios are at their lowest, and often approach crustal values, during periods of enhanced soil dust deposition. The lowest rates of atmospheric deposition of soil dust date from 8030 to 5320 14 C yr BP, corresponding to the Holocene climate optimum, but here many trace elements exhibit their greatest natural enrichments: the average enrichment factor (calculated using Sc as the reference element, and normalizing to crustal abundance) was Zn 4.1±1.4, Sb 4.8±1.4, Cu 8.8±3.3, As 14.9±3.2, Au 53.9±25.1, and Cd 357.4±53.8. These enrichments cannot be explained by chemical diagenesis within the deeper sections of the peat profile during or subsequent to peat formation, but rather reflect the chemical composition of airborne material supplied to the surface layers of the bog at the time of deposition. The enrichments of trace metals in ancient peats, relative to crustal abundance, most likely reflects the natural enrichment of these elements in the fine fraction of soils during rock weathering. Periods of enhanced soil dust deposition such as the Younger Dryas cold climate phase (10 590 14 C yr BP) are characterized by reduced vegetation cover, greater exposed soil surface, and higher wind strengths; these conditions promote the transport of locally derived soil materials of greater particle size, lower concentration of trace metals, and M/Sc ratios approaching crustal values. During the Holocene climate optimum, vegetation cover was extensive, and with lower wind strengths and a reduction in erodible soil materials, long range transport of soil dust became relatively more important to the soil dust inventory of the bog; soil dust particles in this size class are characterized by strong enrichments of a wide range of trace elements. At the end of the Holocene optimum, dust fluxes increased once again, due mainly to soil erosion resulting from the combined effects of human activities (tillage) and the climatic deterioration at the beginning of the Neoglaciation Period; this promoted the supply of local, more coarse soil particles with M/Sc ratios approaching those of crustal rocks. While biological cycling and volcanic emissions probably also contributed to the atmospheric supply of many of these elements in the pre-anthropogenic past, these contributions appear to be less important than the chemical weathering, physical fractionation, and atmospheric transport of soil dust particles.

Comparative study of the temporal evolution of atmospheric lead deposition in Scotland and eastern Canada using blanket peat bogs

The temporal evolution of atmospheric lead deposition and its possible sources were assessed in eastern Canada and in western Scotland, using blanket peat bogs as geochemical archives. Short cores were taken from two remote sites located close to the sea. Significant lead enrichments in the upper layers at both sites reflect the increasing emission of lead into the atmosphere due to anthropogenic activities during the last century. At the Scottish site, a region under aeolian influence from Europe, anthropogenic derived lead could be recognized by the distinctive unradiogenic composition (206Pb/207Pb ratios down to approximately 1.115), being clearly different from the pre-industrial values (206Pb/207Pb approximately 1.166). In contrast, the lead pollution in eastern Canada (influenced by North American sources) is identified by a more radiogenic lead isotope composition (206Pb/207Pb ratios up to approximately 1.199) compared to preindustrial values (206Pb/207Pb approximately 1.161). Emission inventories and isotope characteristics suggest that industrial (coal burning, mining) and traffic (leaded gasoline) outputs are the most likely sources during the first and the second half of the 20th century, respectively, in both, western Scotland and eastern Canada alike. The Scottish record is in line with previous studies of past atmospheric lead deposition. However, the Canadian deposit suggests that the wind derived, pre-industrial lead, is less radiogenic as previously implied using sediment archives. These results are thus the first to report pre-industrial lead isotope ratios and concentrations of atmospheric derived aerosols in North America.

Anthropogenic impacts in North Poland over the last 1300 years - a record of Pb, Zn, Cu, Ni and S in an ombrotrophic peat bog.

Lead pollution history over Northern Poland was reconstructed for the last ca. 1300 years using the elemental and Pb isotope geochemistry of a dated Polish peat bog. The data show that Polish Pb-Zn ores and coal were the main sources of Pb, other heavy metals and S over Northern Poland up until the industrial revolution. After review of the potential mobility of each element, most of the historical interpretation was based on Pb and Pb isotopes, the other chemical elements (Zn, Cu, Ni, S) being considered secondary indicators of pollution. During the last century, leaded gasoline also contributed to anthropogenic Pb pollution over Poland. Coal and Pb-Zn ores, however, remained important sources of pollution in Eastern European countries during the last 50 years, as demonstrated by a high (206)Pb/(207)Pb ratio (1.153) relative to that of Western Europe (ca. 1.10). The Pb data for the last century were also in good agreement with modelled Pb inventories over Poland and the Baltic region.

Influence of extractant on quality and trace elements content of peat humic acids

Among several extractants used to isolate humic acids (HA) from terrestrial environments, sodium hydroxide (NaOH) and sodium pyrophosphate (Na(4)P(2)O(7)) are the most utilized. In order to evaluate the influence of these different extractant solutions on the HA quality and on their trace elements content, HA were isolated from five Sphagnum-peat samples using three different solutions: (a) 0.5M NaOH; (b) 0.1M Na(4)P(2)O(7); (c) 0.5M NaOH+0.1M Na(4)P(2)O(7). The obtained HA have been analyzed with respect to ash content, elemental composition, main atomic ratios and characterized by FT-IR and total luminescence (TL) spectroscopies. In addition, both raw peat and HA have been analyzed using X-ray fluorescence in order to determine the Br, Cu, Fe, Ni, Pb and Zn contents. Results showed that HA extracted with NaOH and NaOH+Na(4)P(2)O(7) are quite similar with respect to ash, elemental contents and spectroscopic characteristics, while Na(4)P(2)O(7) solution, which in general reduces the extraction yield, seems to affect the nature of HA, featuring a more complex and aromatic character. With respect to the contents in the corresponding raw peat samples, the HA fractions were richer in Br, Cu and Ni, regardless of the extractant used, and poorer in Fe, Pb and Zn. Further, Br, Cu, Ni and Zn were more concentrated in HA extracted with Na(4)P(2)O(7) than in those extracted with NaOH and NaOH+Na(4)P(2)O(7), probably because of the greater affinity of these elements for these more aromatic humic molecules.

Six millennia of atmospheric dust deposition in southern south America (Isla Navarino, Chile)

To characterize dust deposition in southern South America for the Holocene, a 542 cm long core from a peat bog in southern Chile (Oreste bog, Isla Navarino) was studied. Peat formation started ~11 160 14C yr before present (BP). The titanium (Ti) concentration in bulk peat, combined with dry bulk density, and peat accumulation rate, were used to calculate the mineral accumulation rate (MAR) in the Oreste bog. The distribution of calcium (Ca), manganese (Mn) and titanium (Ti) showed that mineral accumulation for the last c. 6000 yr was predominantly atmospheric with a record of effectively constant deposition (0.43 ± 0.12 g/m2 per yr). Similarly, Ti and zirconium (Zr) concentrations in the acid insoluble ash (AIA) were also effectively constant and agreed well with the MAR for the last six millennia, except at c. 4200 cal. yr BP, where Zr was enriched relative to Ti. Here, Scanning Electron Microscope (SEM) micrographs showed that the AIA was dominated by volcanic particles (>20—40 μm), with the Mt Burney eruption identified as the most likely source. In contrast with this anomalous zone, SEM studies showed that the mineral particles found in the majority of the sample were predominantly fine grained (<20 μm) and rounded. Derived from surficial sediment and supplied by long-range atmospheric transport, they reflect the climate stability for the past 6000 yr.

Suggested protocol for collecting, handling and preparing peat cores and peat samples for physical, chemical, mineralogical and isotopic analysesPresented as part of the Archives of Environmental Contamination at the 6th International Symposium on Environmental Geochemistry, Edinburgh, Scotland, 7?11 September 2003.

For detailed reconstructions of atmospheric metal deposition using peat cores from bogs, a comprehensive protocol for working with peat cores is proposed. The first step is to locate and determine suitable sampling sites in accordance with the principal goal of the study, the period of time of interest and the precision required. Using the state of the art procedures and field equipment, peat cores are collected in such a way as to provide high quality records for paleoenvironmental study. Pertinent field observations gathered during the fieldwork are recorded in a field report. Cores are kept frozen at -18 degree C until they can be prepared in the laboratory. Frozen peat cores are precisely cut into 1 cm slices using a stainless steel band saw with stainless steel blades. The outside edges of each slice are removed using a titanium knife to avoid any possible contamination which might have occurred during the sampling and handling stage. Each slice is split, with one-half kept frozen for future studies (archived), and the other half further subdivided for physical, chemical, and mineralogical analyses. Physical parameters such as ash and water contents, the bulk density and the degree of decomposition of the peat are determined using established methods. A subsample is dried overnight at 105 degree C in a drying oven and milled in a centrifugal mill with titanium sieve. Prior to any expensive and time consuming chemical procedures and analyses, the resulting powdered samples, after manual homogenisation, are measured for more than twenty-two major and trace elements using non-destructive X-Ray fluorescence (XRF) methods. This approach provides lots of valuable geochemical data which documents the natural geochemical processes which occur in the peat profiles and their possible effect on the trace metal profiles. The development, evaluation and use of peat cores from bogs as archives of high-resolution records of atmospheric deposition of mineral dust and trace elements have led to the development of many analytical procedures which now permit the measurement of a wide range of elements in peat samples such as lead and lead isotope ratios, mercury, arsenic, antimony, silver, molybdenum, thorium, uranium, rare earth elements. Radiometric methods (the carbon bomb pulse of (14)C, (210)Pb and conventional (14)C dating) are combined to allow reliable age-depth models to be reconstructed for each peat profile.

Identifying the sources and timing of ancient and medieval atmospheric lead pollution in England using a peat profile from Lindow bog, ManchesterElectronic supplementary information (ESI) available: Two tables and two figures showing modelling of the age?depth relationship in sediments and Pb isotope results. See http://www.rsc.org/suppdata/em/b4/b401500b/

A peat core from Lindow bog near Manchester, England, was precisely cut into 2 cm slices to provide a high-resolution reconstruction of atmospheric Pb deposition. Radiocarbon and (210)Pb age dates show that the peat core represents the period ca. 2000 BC to AD 1800. Eleven radiocarbon age dates of bulk peat samples reveal a linear age-depth relationship with an average temporal resolution of 18.5 years per cm, or 37 years per sample. Using the Pb/Ti ratio to calculate the rates of anthropogenic, atmospheric Pb deposition, the profile reveals Pb contamination first appearing in peat samples dating from ca. 900 BC which clearly pre-date Roman mining activities. Using TIMS, MC-ICP-MS, and SF-ICP-MS to measure the isotopic composition of Pb, the (208)Pb/(206)Pb and (206)Pb/(207)Pb data indicate that English ores were the predominant sources during the pre-Roman, Roman, and Medieval Periods. The study shows that detailed studies of peat profiles from ombrotrophic bogs, using appropriate preparatory and analytical methods, can provide new insight into the timing, intensity, and predominant sources of atmospheric Pb contamination, even in samples dating from ancient times.

Closed-vessel microwave digestion technique for lichens and leaves prior to determination of trace elements (Pb, Zn, Cu) and stable Pb isotope ratios

A reliable and robust procedure using closed-vessel microwave digestion of lichens and leaves for precise and accurate determination of trace elements (Pb, Zn and Cu) and stable Pb isotope ratios is presented. The method was developed using certified reference material CRM 482 Pseudovernia furfurea (Lichens), NIST 1515 (Apple Leaves) and NIST 1547 (Peach Leaves) and tested on lichens from a mining site in Russia. A mixture of 3 mL of HNO3, 3 mL of H2O2, 2 mL of H2O and 0.8 mL of HF ensured complete sample dissolution with 100 ± 5% recovery for Pb, Zn and Cu at a maximum temperature of 210°C and pressure of 350 psi. The amount of HF and microwave pressure significantly influenced Pb, Zn and Cu recovery. Comparison between EMMA-XRF and ICP-AES showed a good correlation between Pb, Zn and Cu concentrations. Using the newly developed digestion method, Pb isotopes in lichens from the mining site were determined with an internal precision better than 0.02%.

Nondestructive chemical dating of young monazite using XRF 2. Context sensitive microanalysis and comparison with Th-Pb laser-ablation mass spectrometric data

A newly developed XRF-microprobe at the Institute of Mineralogy and Petrology, University of Bern, Switzerland has been applied for precise chemical Th–U–Pb dating of individual monazite grains separated from Pb-free polished petrographic thin sections. The nondestructive nature of the XRF-measurement permitted a comparative study of dating methods by sequentially applying chemical dating by electron microprobe analysis (EMPA), chemical dating by XRF-microprobe analysis, and isotopic 208Pb/232Th dating by Laser Ablation Plasma Ionisation Multi-collector Mass Spectrometry (LA-PIMMS) analysis. As an example, the 2σ precision achieved with the XRF-microprobe for well characterised reference material, monazite FC-1 (TIMS age 54.3±1 Ma; μ-XRF age 55.3±2.6 Ma), doubly polished to 30 μm in thickness, is below 5% after 90 min integration time (50 kV; 30 mA) at a spatial resolution of 90 μm. At 38-μm spatial resolution, the uncertainty is 35% for the same integration time. The sample characteristics are 200–300 ppm of Pb (μ-XRF), 3.8–5.1 wt.% of Th (EMPA), and 0.4–1.4 wt.% U (EMPA). Combined with an electron microprobe and conventional optical microscopy, the XRF-microprobe is thus a competitive low-cost and nondestructive alternative to more costly isotopic methods. The XRF-microprobe is easy to use and maintain.