Sources and chronology of atmospheric lead deposition to a Canadian Shield lake: Inferences from Pb isotopes and PAH profiles

The depth-distribution of lead and its stable isotope ratios were determined in a dated sediment core from a Canadian Shield lake receiving anthropogenic Pb inputs exclusively from atmospheric deposition. The results demonstrate that anthropogenic Pb deposited to the sediments of this lake since the preindustrial period can be modeled successfully using as little as two isotopically distinct Pb types. The first, whose flux was not detectable before 1850, reached a maximum value around 1950, and then decreased significantly thereafter; it was characterized by ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁸Pb ratios of 1.222 and 0.495, respectively, and was derived mainly from coal combustion. The second, whose flux was not detectable before 1880, increased sharply to exceed that of the Pb type derived from coal combustion around 1930, and reached a maximum in the mid 1970s; it is characterized by ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁸Pb ratios of 1.179 and 0.482, respectively, and was derived mainly from leaded gasoline combustion and industrial sources. The chronology of deposition of these two anthropogenic lead types agrees well with the historical records of fossil fuel uses in Canada and the USA, and also with the history of sediment-deposited polycyclic aromatic hydrocarbons (PAHs) originating from coal combustion. The inventory of Pb derived from coal combustion (0.09 μmol cm⁻²) is ∼30% of that derived mainly, but not exclusively, from leaded gasoline (0.31 μmol cm⁻²). Apportionment among source regions of lead deposited to the sediments during the period when leaded gasoline dominated Pb atmospheric emissions indicates that ∼50% of this lead originated in the USA.     

Isotopic lead investigations on the Allende carbonaceous chondrite

Uranium and lead concentrations and the isotopic compositions of lead were determined on samples of total rock, matrix, white inclusion, pink inclusion, white aggregate and four chondrules from the Allende carbonaceous chondrite. Observed ²⁰⁶Pb/²⁰⁴Pb ratios varied from 10.004 to 107.29; ²⁰⁷Pb/²⁰⁴Pb ratios from 10.695 to 69.07; ²⁰⁶Pb/²⁰⁴Pb ratios from 30.062 to 207.96. In a ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagram a regression line fitted to all of data has a slope of 0.6240 ± 0.0015, corresponding to a single stage model age of 4.565 ± 0.004 AE. The regression line also includes the ratios for primordial lead as determined in previous investigations from Canyon Diablo troilite and the Mezö-Madaras chondrite.Although the lead in the matrix is not very radiogenic, the ²⁰⁷Pb/²⁰⁶Pb ages of four samples average 4.505 AE, a value 0.06 AE younger than that of the chondrules and inclusions. The matrix age agrees closely with a total rock Pb/Pb model age previously reported for Allende by Tatsumoto, Knight and Allegre. The matrix Pb/Pb model age is also 0.06 AE younger than the Pb/Pb isochron ages determined by previous investigators on total samples of H and L chondrites. The H and L chondrite and Allende chondrule and inclusion Pb/Pb ages are indistinguishable. The lead isotope systematics require either that the matrix is ca. 0.06 younger than the silicate inclusions and chondrules (or that radiogenic lead was inherited from a younger external source) or that the initial lead in the matrix differed from primordial lead. The lead data cannot be reconciled to a model in which the bulk material of Allende first crystallized 4.57 AE ago, followed by transfer of radiogenic lead between phases since that time.In a concordia diagram four chondrules and three inclusions plot along a chord intersecting concordia at 4.57 and 0.28 ± 0.07 AE. This indicates disturbance of the U-Pb systems relatively recently, perhaps around 0.3 AE ago. The time of disturbance is not readily understood and needs further confirmation. It correlates most closely with a possible cut-off in K-Ar and U, Th-He ages of chondrites.Although the Th/U ratios of the bulk samples and matrix are around the normal value of 3.8, much higher values are observed in some of the inclusions, the highest being 9.0.     

Application of lead stable isotopes to the Guadiamar Aquifer study after the mine tailings spill in Aznalcóllar (SW Spain)

On 25 April 1998 the tailings dam of the Aznalcóllar mine burst, a great quantity of pyrite waste sludge and acid water was spilled reaching the vicinity of the Doñana National Park. In surface and ground water samples taken a week after dam breaking, metals, trace elements and Pb isotopic ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) were analysed. In September 1998 a second sampling survey was carried out. The surface waters have a similar isotopic composition as the lead contained in the pyrite from the Aznalcóllar mine. The polluted groundwater of the Guadiamar aquifer also shows the influence of the mining origin of the lead. Lead isotope ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) in the groundwater of the Almonte-Marismas are very low and they differ clearly from the rest of groundwater samples. A further group of wells has a lead isotope composition intermediate between the Aznalcóllar mine and the atmospheric aerosols of the Iberian Peninsula.     

Differences in lead isotope composition in the stratiform McArthur zinc-lead-silver deposit

Lead isotopic composition and uranium and lead concentrations have been determined for galena, sphalerite, pyrite and acetic acid soluble material from the McArthur area in order to test the hypothesis of a dual sulphur source suggested by the sulphur isotope data of Smith and Croxford (Sulphur isotope ratios in the McArthur lead-zinc-silver deposit, Nature Phys. Sci. 245, 10–12 (1973)). Galena, sphalerite and the acetic acid washes from the McArthur deposit have uniform isotopic ratios (²⁰⁶Pb/²⁰⁴Pb, 16.07–16.15; ²⁰⁷Pb/²⁰⁴Pb, 15.37–15.47; ²⁰⁸Pb/²⁰⁴Pb, 35.57–35.89) consistent with other conformable ore deposits, whereas the ratios for pyrite are variable and quite radiogenic (²⁰⁶Pb/²⁰⁴Pb, 16.24–16.49; ²⁰⁷Pb/²⁰⁴Pb, 15.42–15.58; ²⁰⁸Pb/²⁰⁴Pb, 35.82–36.98). Acid washes where dolomite is a major dissolved phase are also radiogenic. The lead in the pyrite appears to have been derived from at least two sources: the less radiogenic lead coming from an exhalative source as for galena and sphalerite and the more radiogenic lead probably being leached from the country rocks. It is proposed that analysis of pyrite for isotopic composition and concentration of lead could be used as an indicator for similar types of deposits in this area.     

Determination of the extent of anthropogenic Pb migration through fractured sandstone using Pb isotope tracing

The extent of vertical migration of anthropogenic Pb beneath a medieval smelting site in Derbyshire, U.K. has been estimated using the determination of total Pb concentrations and ²⁰⁶Pb/²⁰⁷Pb isotope ratio from samples taken down 6 m of drill core. Preliminary studies of total Pb concentrations established that the surface slag derived from the smelting contained up to 16% Pb and that the normal background levels in uncontaminated sandstone were 10±2 ppm. Sample analyses beneath the site revealed elevated Pb concentrations in fracture infill clays (270 ppm Pb) and sandstone (76–83 ppm Pb). Both are well above the background Pb concentration.Lead isotope analysis of the slag wastes, the underlying contaminated sandstone and fracture infill has shown that all 3 contain very similar isotope ratios for ²⁰⁶Pb/²⁰⁷Pb (1.1802–1.1820). However, matched control sandstone samples show that the background ²⁰⁶Pb/²⁰⁷Pb isotope ratio (1.1670 ± 0.003) is distinctly different. This would indicate that both the sandstone and fracture infill underlying the historical smelting site contain a substantial proportion of Pb that has been derived from the overlying contamination.The application of total Pb concentrations along the core and isotope analysis suggest that anthropogenically derived Pb from the smelting site (that was operated between 665 and 445 a BP) has migrated to a depth of 4.50 m. Assuming a uniform migration rate and a mean time of migration of 555 a, then the mean migration rate is estimated to be 8 ± 2 mm/a.The proportion of natural versus anthropogenic Pb in the samples has been estimated from small variations in the ²⁰⁶Pb/²⁰⁷Pb isotope ratio. If the slag is considered to contain 100% anthropogenic Pb and the uncontaminated sandstone considered to contain 100% natural Pb, the linear interpolation can be applied between the 2 end members of the isotope ratio. The use of this approach to the ²⁰⁶Pb/²⁰⁷Pb ratio measurements has shown that 88% of the Pb in the contaminated sandstone (i.e. 69 ppm from a mean total Pb concentration of 78.5 ppm) has been derived from the anthropogenic Pb at the surface. For the fracture infill sample taken at a depth of 4.50 m, and with a total Pb concentration of 270 ppm, the % of Pb that has been derived from the slag wastes is approximately 98% (equivalent to 265 ppm Pb). The remaining Pb in both these samples (9.4 and 5 ppm, respectively) is deduced to have originated from the natural background concentration of Pb in the sandstone.The closeness of these estimates to the measured background concentration, suggests that a simple two-source model of Pb contamination is valid for this site.     

Isotopic evidence for the source of lead in the North Pacific abyssal water

The absence of accurate measurements of lead (Pb) isotopic composition in the North Pacific abyssal water has made it difficult to assess the relative importance of what are believed to be the two major Pb sources: the natural Pb introduced during preindustrial time and recent anthropogenic Pb resulting from leaded gasoline combustion and high temperature industrial activities. Here we report a vertical profile of seawater ²⁰⁶Pb/²⁰⁷Pb ratio and a meridional section of Pb concentration in the North Pacific Ocean. We observe 2-3-fold increases in Pb concentration along the deep-water flow path and a deep-water ²⁰⁶Pb/²⁰⁷Pb ratio (∼1.188) substantially lower than the pre-industrial value (∼1.210). These data suggest that anthropogenic Pb has invaded the North Pacific abyssal water and become the predominant Pb source there. A simple model calculation based on these data indicates that the anthropogenic Pb is transported to the deep ocean by sinking particles and that this Pb vertical flux has a ²⁰⁶Pb/²⁰⁷Pb ratio that decreased during the past two centuries.     

U-Pb age and lead isotopic characterization of Au-bearing skarn related to the Andorra granite (central Pyrenees,Spain)

Auriferous skarns are associated with post- and late-kinematic Hercynian granites that intruded into Cambro-Ordovician to Devonian sediments of the central Pyrenees. We determined the age of the Andorra granite and the associated skarn at 305 ± 3 Ma by U-Pb dating titanite from the endo-skarn. The sulfur isotopic composition from sulfides in the skarn (Cardellach et al. 1992) shows a significant variation with isotopically light sulfur (³⁴S +3) in the barren skarns and heavy sulfur (³⁴S +11) in the gold-bearing skarns. Outwards, it increasingly resembles sulfur from arsenopyrite disseminations in the Cambro-Ordovician sediments. The lead isotopic composition from sulfides of the skarns is very homogeneous (²⁰⁶Pb/²⁰⁴Pb = 18.410, ²⁰⁷Pb/²⁰⁴Pb = 15.699, ²⁰⁸Pb/²⁰⁴Pb = 38.574) in contrast to the one in gold-bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments (e.g. ²⁰⁶Pb/²⁰⁴Pb varies from 18.54 to 30.36). Combined, sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite, whereas the sulfur is derived at variable portions from both the granite and the sediments.     

Origin of lead in the Gulf of California Ecoregion using stable isotope analysis

The magnitude and sources of lead (Pb) pollution in the Gulf of California Ecoregion (GCE) in northwest Mexico were evaluated using various samples collected from urban and rural areas around two typical subtropical coastal ecosystems. Lead concentrations and isotopic compositions (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb, ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb) were measured using high resolution inductively-coupled plasma mass spectrometry (HR-ICP-MS) and thermal ionization mass spectrometry (TIMS). Urban street dust (157 ± 10.1 μg g^− 1) was heavily enriched with Pb, compared to the Pb enrichment of agricultural soils (29.0 ± 16.0 μg g^− 1) and surface estuary sediments (35.6 ± 15.4 μg g^− 1), all of which contained higher Pb concentrations than found in the natural bedrock (16.0 ± 5.0 μg g^− 1). Pb concentrations in SPM (> 95% of total Pb) were significantly higher in sewage effluent (132 ± 49.9 μg g^− 1) than in agricultural effluents (29.3 ± 5.9 μg g^− 1), and river runoff (7.3 ± 4.2 μg g^− 1). SPM in estuary water column averaged 68.3 ± 48.0 μg g⁻¹. The isotopic composition of Pb (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁷Pb) in rural samples of aerosols (1.181 ± 0.001, 2.444 ± 0.003) and soil runoff (1.181 ± 0.003, 2.441 ± 0.004) was comparable to that of natural Pb-bearing bedrock (1.188 ± 0.005, 2.455 ± 0.008); while urban samples of aerosols, street dust, and sewage (1.190–1.207, 2.452–2.467) showed a significant contribution from automotive emissions from past leaded gasoline combustion (1.201 ± 0.006, 2.475 ± 0.005). The absence of lead from fertilizer (1.387 ± 0.008, 2.892 ± 0.005) suggests that this mixture is not representative of the GCE. A mixing model revealed that the Pb content in the environmental samples is predominantly derived from natural weathering and the past leaded gasoline combustion with the later influence of inputs from a more radiogenic source related with anthropogenic lead of North American origin (1.21 ± 0.02; 2.455 ± 0.02).     

Lead isotope study of Zn-Pb ore deposits associated with the Basque-Cantabrian basin and Paleozoic basement, Northern Spain

A total of forty-three galena samples from syngenetic and epigenetic Pb-Zn mineralizations emplaced in the Lower Cretaceous Basque-Cantabrian basin and Paleozoic basement of the Cinco Villas massif in the western Pyrenees, have been analyzed for Pb-isotopic composition. Galena from sedex mineralizations hosted in Carboniferous clastic rocks in the Cinco Villas massif display an homogeneous lead isotopic signature (²⁰⁶Pb/²⁰⁴4Pb 18.43, ²⁰⁷Pb/²⁰⁴Pb 15.66, ²⁰⁸Pb/ ²⁰⁴Pb 38.69) suggesting a single lead reservoir. These values are slightly more radiogenic than lead from other European Hercynian deposits, possibly reflecting the influence of a more evolved upper crustal source. Underlying Paleozoic sediments are proposed as lead source for the Cinco Villas massif ores. Analyses from twenty-six galena samples from the four strata-bound ore districts hosted in Mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition. Galena from the western Santander districts (e.g., Reocin) is characterized by more radiogenic isotope values (²⁰⁶Pb/²⁰⁴Pb 18.74, ²⁰⁷Pb/²⁰⁴Pb 15.67, ²⁰⁸Pb/ ²⁰⁴Pb 38.73) than those from the central and eastern districts (Troya-Legorreta, Central and Western Vizcaya, ²⁰⁶Pb/²⁰⁴Pb 18.59, ²⁰⁷Pb/²⁰⁴Pb 15.66, ²⁰⁸Pb/ ²⁰⁴Pb 38.73). In all districts, the most likely source for these mineralizations was the thick sequence of Lower Cretaceous clastic sediments. The existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories. In both sub-basins, isotopic ratios indicate an increase in crustal influence as the age of the ores decreases.     

A lead isotope study of mineralization in the Saudi Arabian Shield

New lead isotope data are presented for some late Precambrian and early Paleozoic vein and massive sulfide deposits in the Arabian Shield. Using the Stacey Kramers (1975) model for lead isotope evolution, isochron model ages range between 720 m.y. and 420 m.y. Most of the massive sulfide deposits in the region formed before 680 m.y. ago, during evolution of the shield. Vein type mineralization of higher lead content occurred during the Pan African event about 550 m.y. ago and continued through the Najd period of extensive faulting in the shield that ended about 530 m.y. ago. Late post-tectonic metamorphism may have been responsible for vein deposits that have model ages less than 500 m.y. Alternatively some of these younger model ages may be too low due to the mineralizing fluids acquiring radiogenic lead from appreciably older local crustal rocks at the time of ore formation.The low²⁰⁷Pb/²⁰⁴Pb ratios found for the deposits in the main part of the shield and for those in north-eastern Egypt, indicate that the Arabian craton was formed in an oceanic crustal environment during the late Precambrian. Involvement of older, upper-crustal material in the formation of the ore deposits in this part of the shield is precluded by their low²⁰⁷Pb/²⁰⁴Pb and²⁰⁸Pb/²⁰⁴Pb characteristics.In the eastern part of the shield, east of longitude 44°20E towards the Al Amar-Idsas fault region, lead data are quite different. They exhibit a linear²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb relationship together with distinctly higher²⁰⁸Pb/²⁰⁴Pb characteristics. These data imply the existence of lower crustal rocks of early Proterozoic age that apparently have underthrust the shield rocks from the east. If most of the samples we have analyzed from this easterly region were mineralized 530 m.y. ago, then the age of the older continental rocks is 2,100±300 m.y. (2).The presence of upper crustal rocks, possibly also of early Proterozoic age, is indicated by galena data from Hailan in South Yemen and also from near Muscat in Oman. These data are the first to indicate such old continental material in these regions.     

Lead isotopic compositions in fault gouges and their parent rocks: implications for ancient fault activities

This is the first study on Pb stable isotopes in fault gouges and their parent rocks. We analyzed the composition of Pb isotopes and contents of U and Pb in 10 pairs of fault gouges and their parent rocks collected along several active faults in central Japan. Thorium-232-²⁰⁸Pb ages of two fault systems were determined as pre-Tertiary, which are consistent with the data from KAr ages and geological considerations.Naturally, the²³⁵U²⁰⁷Pb system is of little use for dating because the magnitude of difference in²⁰⁷Pb/²⁰⁴Pb between gouges and parent rocks is too small. It is found that the²⁰⁶Pb/²⁰⁴Pb can indicate the contribution of²⁰⁶Pb resulting from excess supplies of²²⁶Ra and²²²Rn along the fault. The excess²⁰⁶Pb accumulation rate corresponds to the average²²²Rn concentration in soil gas or groundwater through geological time since the gouge formation. A comparison of Quaternary fault activity and estimated Tertiary activity reveals the characteristics of each fault system.     

Lead isotopes as tracers of anthropogenic pollution in urban topsoils of Mexico City

A survey was performed to trace the main source of anthropogenic Pb pollution in Mexico City through Pb isotopic signatures (²⁰⁸Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁷Pb, and ²⁰⁸Pb/²⁰⁷Pb) from 103 urban topsoil (0–5 cm) samples. Those were collected in the metropolitan area of Mexico City and compared with isotopic compositions of leaded gasoline (LG), domestic Pb ores (DLO) and parent rock (PR). The isotope ratios (IRs) of Pb were determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and total Pb concentration analyzed by wavelength dispersive X-ray fluorescence (WDXRF). The range of Pb concentrations levels in urban topsoil samples was 15–473 mg/kg. The IR values obtained for these samples were 37.965–39.718 (²⁰⁸Pb/²⁰⁴Pb), 18.375–19.204 (²⁰⁶Pb/²⁰⁴Pb), 1.177–1.218 (²⁰⁶Pb/²⁰⁷Pb) and 2.443–2.496 (²⁰⁸Pb/²⁰⁷Pb). Analyzed topsoil samples with low Pb content (<50 mg/kg) displayed high dispersion in ²⁰⁸Pb/²⁰⁴Pb values, which are determined by different natural sources. Samples with 51–200 mg/kg Pb content, shown low dispersion that revealed the mixing between the natural Pb and anthropogenic Pb. The assessment of the IR values shown that, as Pb concentration increases, a trend toward gasoline IR data has been observed. The results obtained by this research suggest that although the use of leaded petrol had been banned in Mexico since 1997, the Pb pollution in the urban topsoils due to the historical use of Pb in petrol is still significant.     

Evaluation of drilling priorities using lead isotopes at the Lady Loretta lead-zinc-silver deposit, Australia

The weathered surface expression of the Lady Loretta lead-zinc-silver deposit outcrops almost continuously over a distance of about 4 km. Lead isotope ratios have been determined for samples, some of which contain > 4000 ppm Pb, from geochemically anomalous areas in order to assign drilling priorities to the anomalies.Twelve of the 43 samples analyzed contain isotopically homogeneous lead with ratios (²⁰⁷Pb/²⁰⁶Pb 0.9532–0.9549) similar to the expected targets for major ore deposits in the Mount Isa-McArthur River metallogenic province (²⁰⁷Pb/²⁰⁶Pb 0.955–0.962). Three main zones of interest can be outlined on the basis of lead isotopic data. The top priority is assigned to a 100-m-long section of the ironstone which coincides with the known outcrop of the ore. Lower priority for drilling is given to the two other zones which outcrop over smaller areas and have more radiogenic lead in their immediate surroundings. Several samples with anomalously high lead contents (> 1000 ppm) contain more radiogenic lead (²⁰⁷Pb/²⁰⁶Pb < 0.950) which was most likely derived from the weathering country rocks by supergene leaching and redeposition. Of the 22 samples containing ≥ 380 ppm Pb, lead isotopic analyses would have reduced the number deserving further attention to 10. Lead isotopic analyses in the early stages of exploration could have assisted in minimizing exploration expenditure at Lady Loretta.     

Contemporary lead concentration and stable lead isotope ratio distribution in forest moss across the Czech Republic

Lead concentrations and stable lead isotopes (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb) were measured in forest moss samples (Pleurozium schreberi or Scleropodium purum) collected at 273 sites across the Czech Republic during 2010. Continuously decreasing median Pb concentrations in moss were documented over the last two decades: 1995: 11 mg/kg, 2000: 5.66 mg/kg, 2005: 4.94 mg/kg and 2010: 2.85 mg/kg. Several local anomalies have decreased in scale, the overall regional distribution patterns remained, however, the same. The regional Pb isotope ratio distributions show that the ratios show little variation for a large central part of the country and provide the large-scale background isotope ratios for the Czech Republic of about ²⁰⁴Pb/²⁰⁶Pb = 0.0550, ²⁰⁶Pb/²⁰⁷Pb = 1.167, ²⁰⁶Pb/²⁰⁸Pb = 0.478 and ²⁰⁷Pb/²⁰⁸Pb = 0.409 for 2010. This background Pb isotope ratio signal in moss has been locally (900–7500 km²) modified by specific Pb isotopic ratio signals caused by deposition of Pb emissions from known local anthropogenic Pb emission sources, such as industrial combustion of local coal, and a variety of industrial enterprises (metallurgical, engineering and glass works). At some sites where mining of uranium and polymetallic ores took place the moss samples show also a locally specific Pb isotope signal. The in terms of area affected largest deviations in the Pb-isotope ratios, e.g., in the Bohemian Massif, may be due to the input of geogenic dust.     

The Teutonic Bore deposit,Western Australia: a lead isotope study of an ore and its gossan

The Teutonic Bore deposit occurs in an Archaean greenstone belt within the Eastern Goldfields Province of the Yilgarn Block in Western Australia. The ore is hosted by basaltic rocks and consists of a conformable massive sulfide lens underlain by a thick zone of pyritic stringer ore. The zone of oxidation reaches a depth of 90–100 m with the development of secondary copper sulfides. The lead isotopic compositions of six samples of massive sulfide, three mineral separates from the ore and eight gossan samples collected from the open cut were determined by standard mass-spectrometric techniques. Four of the massive sulfide samples, all three mineral separates and seven of the eight gossan samples have lead isotopic compositions identical to each other, within experimental error. These results confirm the findings of earlier studies that the lead isotopic signature of a massive sulfide ore is transferred to its gossan, and provide additional data suggesting the usefulness of lead isotopic determinations in ore prospect evaluation. The Teutonic Bore leads plot below the average global lead evolution curves for the uranogenic isotopes ²⁰⁶Pb and ²⁰⁷Pb, suggesting that the lead in the ore contains a significant mantle component. This feature of the isotopic data is consistent with the idea of a mantle plume origin of the Eastern Goldfields greenstone belts.     

Isotopic composition of lead in moss and soil of the European Arctic

Moss, O and C horizons of podzols, mainly forming complementary sample triplets, as well as filter residues of molten snow from northern Norway, northern Finland and NW Russia have been analyzed by TIMS for their Pb isotopic composition in order to study the impacts of local geogenic/anthropogenic sources and long range atmospheric transport on the Pb balance in the European Arctic. Samples were taken along two N-S transects covering an area of ∼188.000 km², including both pristine environments in the W and certain regions towards the E severely contaminated by heavy metal emissions originating from large nickel smelters and processing plants in NW Russia.The lead in moss and O horizon samples clearly reflects atmospheric deposition, as it displays overall uniform isotope ratios and is decoupled from the geogenic background, i.e. the underlying mineral soils in the C horizon. Moss and O horizon samples from the eastern N-S transect are isotopically indistinguishable from those taken along the western transect but their Pb concentrations tend to be ∼2 times higher. This points to considerable contamination originating from the nearby Russian industrial and urban centers. However, isotopic signals of emissions from individual industrial point sources cannot be unambiguously identified because they lack characteristic isotope signatures. Pb derived from gasoline additives is swamped by Pb from other sources and can also be excluded as a major contributor to the environmental Pb in the European Arctic.Overall, the Pb isotopic signatures of moss and O horizon overlap values recorded in atmospheric lead all over central and southern Europe, more than 2000 km south of the study area. This may be taken as indicating continent-wide mixing of Pb derived from similar sources in the atmosphere or as reflecting economic globalization, or both. O horizon samples, which accumulate lead over 20-30 yr, conform to a distinct Pb isotope reference line in ²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb space (“European Standard Pollution,” ESP) defined by atmospheric Pb considered to be representative for the technical civilization in Europe. Conversely, the Arctic moss samples with a lifetime of <3 yr display a deviating linear trend reflecting a recent change of atmospheric input towards significantly more radiogenic Pb derived from Mississippi Valley-type ores in the U.S., fully compatible with signatures found in epiphytic lichens from Canada, but also in Pb from urban waste incinerators in central Europe. Considering the elevated Pb concentrations in moss collected along the eastern N-S transect, this congruence indicates that the Pb in moss of the European Arctic most probably originates from the nearby Russian centers of urbanization and not from transatlantic transport. We therefore suspect imported industrial goods and their subsequent attrition to be a more plausible explanation for the appearance of MVT lead in Europe.     

The isotopic evolution of atmospheric Pb in central Ontario since AD 1800, and its impacts on the soils, waters, and sediments of a forested watershed, Kawagama Lake

A peat core from an ombrotrophic bog documents the isotopic evolution of atmospheric Pb in central Ontario since AD 1804 ± 53 (²¹⁰Pb dating). Despite the introduction of unleaded gasoline in the mid-1970’s, the ratio ²⁰⁶Pb/²⁰⁷Pb in atmospheric deposition has not increased as expected, but rather continues to decline. In fact, snowpack sampling (2005 and 2009) and rainwater samples (2008) show that the isotopic composition of atmospheric Pb today is often far less radiogenic than the gasoline lead that had been used in Canada in the past. The peat, snow, and rainwater data presented here are consistent with the Pb isotope data for aerosols collected in Dorset in 1984 and 1986 which were traced by Sturges and Barrie (1989) to emissions from the Noranda smelter in northern Quèbec, Canada’s largest single source of atmospheric Pb. Understanding atmospheric Pb deposition in central Ontario, therefore, requires not only consideration of natural sources and past contributions from leaded gasoline, but also emissions from metal smelting and refining.Lead in the streams which enter Kawagama Lake today (²⁰⁶Pb/²⁰⁷Pb = 1.16 − 1.19) represents a mixture between the natural values (1.191 − 1.201 estimated using pre-industrial lake sediments) and the values found in the humus layer of the surrounding forest soils (²⁰⁶Pb/²⁰⁷Pb = 1.15 − 1.19). In the lake itself, however, Pb is much less radiogenic (²⁰⁶Pb/²⁰⁷Pb as low as 1.09) than in the streams, with the dissolved fraction less radiogenic than particulate material. The evolution of Pb isotope ratios within the watershed apparently reflects preferential removal by sedimentation of comparatively dense, radiogenic, terrestrial particles (derived from the mineral fraction of soils) from the humus particles with lower ratios of ²⁰⁶Pb/²⁰⁷Pb (because of atmospheric Pb contamination). Despite the contemporary enrichments of Pb in rain and snow, concentrations of dissolved Pb in the lake are extremely low (sometimes below 10 ng/l), with Pb concentrations and Pb/Sc ratios approaching “natural” values because of efficient binding to particles, and their subsequent removal in the watershed.     

High-resolution210Pb dating of Lake Constance sediments: Stable lead in Lake Constance

Two sediment cores (BO90/13b and BO90/17b) from Lake Constance were investigated by-spectrometry for²¹⁰Pb,¹³⁴Cs,¹³⁷Cs,²⁴¹Am,²³⁴Th, and other members of the²³⁸U decay chain. The sediments were dated using the constant-flux model for²¹⁰Pb, and accumulation rates were determined. These range from 0.04 to 0.65g/cm ²/yr (BO90/13b) and 0.04 to 0.8g/cm ²/yr (BO90/17b), respectively. The mean accumulation rate amounts to 0.16g/cm ²/yr for both cores. The cores had already been dated by lamination counting and reconstruction of high-water events at the Limnological Institute at Constance, so that a very precise time scale was available. Both ages derived are in agreement within statistical error up to 1900, which means dating with the constant-flux model for²¹⁰Pb was confirmed up to that age. The position of the maxima of bomb cesium and americium confirm the stratigraphic and²¹⁰Pb datings. With²⁴¹Am a further radioactive isotope is available, which can, due to the half-life of²⁴¹Pu (t _1/2=14.4yr) be detected now by-spectrometry and can serve as an additional time indicator, the maximum being dated at 1963. By applying the various time scales, the depth profiles of stable lead and zinc of core BO90/13b were dated. Both heavy metals show a very significant maximum located beneath the layer of the maxima of bomb cesium and americium, showing that these maxima are older than those of the bomb isotopes. It is remarkable in this context that the maximum of zinc concentration occurs a little later than that of stable lead. Similar concentration profiles are observable in core BO90/17b and other, older sediment cores (CS6-CS10) on a transect across the lake. In contrast to a former assumption, the depth profile of stable lead in Lake Constance sediments does not reflect the anthropogenic gasoline lead emissions into the atmosphere for Germany, their maximum being dated at 1971.     

Lead isotope studies of strata-bound,vein-type,and unconformity-related Pb,Sb, and Bi ore mineralizations from the western edge of the Bohemian Massif (F.R. Germany)

Specimens from strata-bound/stratiform Kieslager, lineament-bound, and unconformity-related Pb occurrences from the NE Bavarian Saxothuringian and Moldanubian belts and samples from stibnite and polymetallic Sb-Au quartz veins were analyzed for their lead isotope composition.The strata-bound Pb at Bodenmais yielded an Upper Proterozoic ²⁰⁷Pb/²⁰⁶Pb model age which correlates with the assumed stratigraphic age of the host rock. Late Precambrian rift activity may have triggered the formation of this ore mineralization. This type of Pb was also found in the Kieslager at Waldsassen hosted by Early Paleozoic country rocks and in the fluorite veins at Kittenrain.The vein-type lineament-bound, and unconformity-related Pb occurrences show a similar isotopic pattern which suggests that this type of Pb originated from the same source. The ²⁰⁷Pb/²⁰⁶Pb model ages which are too old compared to the assumed age of formation and the accelerated ²⁰⁸Pb evolution indicate that the detritus of the source rock underwent a high-grade metamorphism in the Precambrian.The formation of the unconformity-related Pb concentrated in galena of fluorite-barite veins is correlated with late Variscan magmatic intrusions. The older model ages of about 100–150 Ma from the lineament-bound lead, located along deep-seated lineamentary fault zones, suggest an earlier separation of this type of Pb possibly triggered by the Caledonian A-subduction-related metamorphism.     

Uptake and recycling of lead by boreal forest plants: Quantitative estimates from a site in northern Sweden

As a consequence of deposition of atmospheric pollution, the lead concentration in the mor layer (the organic horizon) of remote boreal forest soils in Sweden is raised far above natural levels. How the mor will respond to decreased atmospheric pollution is not well known and is dependent on future deposition rates, downward migration losses and upward fluxes in the soil profile. Plants may contribute to the upward flux of lead by ‘pumping’ lead back to the mor surface through root uptake and subsequent litter fall. We use lead concentration and stable isotope (²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb) measurements of forest vegetation to quantify plant uptake rates from the soil and direct from the atmosphere at two sites in northern Sweden; an undisturbed mature forest and a disturbed site with Scots pine (Pinus sylvestris) growing on a recently exposed mineral soil (C-horizon) containing a minimum of atmospherically derived pollution lead. Analyses of forest mosses from a herbarium collection (spanning the last ∼100 yr) and soil matrix samples suggest that the atmospheric lead deposited on plants and soil has an average ²⁰⁶Pb/²⁰⁷Pb ratio of 1.15, while lead derived from local soil minerals has an average ratio of ∼1.47. Since the biomass of trees and field layer shrubs has an average ²⁰⁶Pb/²⁰⁷Pb ratio of ∼1.25, this indicates that 70% ± 10% of the inventory of 1 ± 0.8 mg Pb m⁻² stored in plants in the mature forest originates from pollution. Needles, bark and apical stemwood of the pine growing on the disturbed soil, show lower ²⁰⁶Pb/²⁰⁷Pb ratios (as low as 1.21) than the roots and basal stemwood (having ratios > 1.36), which indicate that plants are able to incorporate lead directly from the atmosphere (∼50% of the total tree uptake). By partitioning the total uptake of lead into uptake from the atmosphere and different soil layers using an isotopic mixing model, we estimate that ∼0.03 ± 0.01, 0.02 ± 0.01 and 0.05 ± 0.01 mg Pb m⁻² yr⁻¹ (mean ± SD), is taken up from the mor layer, the mineral soil and the atmosphere, respectively, by plants in the undisturbed mature forest. These small fluxes, which are at least a magnitude lower than reported downward migration losses, suggest that plant uptake will not strongly prolong the self-cleaning rate of the mor layer.