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1.
The use of stable Pb isotopes for tracing Pb contamination within the environment has strongly increased our understanding of the fate of airborne Pb contaminants within the boreal forest. This paper presents new stable Pb isotope (206Pb/207Pb ratio) measurements of solid soil samples, stream water (from a mire outlet and a stream draining a forest dominated catchment) and components of Picea abies (roots, needles and stemwood), and synthesizes some of the authors’ recent findings regarding the biogeochemistry of Pb within the boreal forest. The data clearly indicate that the biogeochemical cycling of Pb in the present-day boreal forest ecosystem is dominated by pollution Pb from atmospheric deposition. The 206Pb/207Pb ratios of the mor layer (O-horizon), forest plants and stream water (mainly between 1.14 and 1.20) are similar to atmospheric Pb pollution (1.14–1.19), while the local geogenic Pb of the mineral soil (C-horizon) has high ratios (>1.30). Roots and basal stemwood of the analyzed forest trees have higher 206Pb/207Pb ratios (1.15–1.30) than needles and apical stemwood (1.14–1.18), which indicate that the latter components are more dominated by pollution derived Pb. The low 206Pb/207Pb ratios of the mor layer suggest that the upward transport of Pb as a result of plant uptake is small (<0.04 mg m−2 a−1) in comparison to atmospheric inputs (∼0.5 mg m−2 a−1) and annual losses with percolating soil-water (∼2 mg m−2 a−1); consequently, the Pb levels in the mor layer are now decreasing while the pool of Pb in the mineral soil is increasing. Streams draining mires appear more strongly affected by pollution Pb than streams from forested catchments, as indicated by Pb concentrations about three times higher and lower 206Pb/207Pb ratios (1.16 ± 0.01 in comparison to 1.18 ± 0.02). To what extent stream water Pb levels will respond to the build-up of Pb in deeper mineral soil layers remains uncertain.  相似文献   

2.
The organic horizon (the mor layer) of podzolized boreal forest soils has accumulated atmospheric fallout of mercury and lead over centuries, resulting in current concentrations close to levels where negative effects on soil biota are thought to occur. To what extent the pollution history is preserved in the stratigraphy of this horizon is not well known. In this study we asses whether the chronology of a large historic pulse of atmospheric pollution emitted from the Rönnskär smelter in northern Sweden, particularly between 1950 and 1980, is preserved within the stratigraphy of the mor layer, which is typically 5-cm thick. Vertical sub-sampling (?5 mm) of five mor profiles sampled along a 100-km pollution gradient away from the smelter are analyzed for mercury and lead concentrations, spheroidal carbonaceous particles from fossil fuel combustion (SCPs) and stable lead isotopes (206Pb/207Pb and 208Pb/207Pb). Their vertical distribution is compared with the temporal variations in atmospheric inputs reconstructed for the last ∼100 years from analyses of an ombrotrophic peat core and a varved lake sediment core sampled within a distance of 50 km of the smelter. The mor profiles situated ?12 km from the smelter record the pollution history of the smelter. There is a 20 to 40-times enrichment of Hg, Pb and SCP at the transition in the O-horizon from the F- to H-layer compared to the basal part and a distinct peak in the 206Pb/207Pb ratio (∼1.22) in the F-layer. The mor profiles situated outside the historical contamination range of the smelter (80 and 100 km away) record no obvious influence from the Rönnskär smelter, instead their vertical 206Pb/207Pb profiles follow the general regional pollution history in northern Sweden. We conclude that the mor layer preserves a record of atmospheric Hg, Pb and SCP inputs and due to low leaching rates this organic horizon serves as a semi-archive of atmospheric Hg and Pb pollution. We stress the need of including this property in the existing ‘black-box’ models predicting the fate of Hg and Pb within contaminated boreal forest soils.  相似文献   

3.
This paper assesses the role of airborne pollution and natural geological sources for lead enrichment in lake sediments and in surface soils of boreal forests. This assessment is based on analyses of stable lead isotopes (206Pb and 207Pb) and lead concentrations in sediment cores (>30 lakes), ombrotrophic peat and soil samples in Sweden. The 206Pb/207Pb ratio and concentration profiles in the sediment cores change synchronously over the last 3,000 years in different lakes, temporal concentration changes in sediments and peat deposits are very consistent, and these temporal concentration changes coincide well with the history of lead production in Europe. The 206Pb/207Pb ratio is almost the same in all soil mor samples (1.152ǂ.009; n=94), and similar to values recorded in aerosols, despite very high and different 206Pb/207Pb ratio of the mineral soil in the C-horizon (1.3-1.7). This study provides evidence that lead enrichment in recent sediments and peat, and in the mor layer are caused by deposition of pollution lead and not natural processes.  相似文献   

4.
Anthropogenic Pb affects the environment worldwide. To understand its effect on forest ecosystem, Pb isotope ratios were determined in precipitation, various components of vegetation, the forest floor, soil and parent material in a Japanese cedar (Cryptomeria japonica D. Don) forest stand. The average 206Pb/207Pb ratio in bulk precipitation was 1.14 ± 0.01 (mean ± SD), whereas that in the subsoil (20–130 cm) was 1.18 ± 0.01. Intermediate ratios ranging from 1.15 to 1.16 were observed in the vegetation, the forest floor, and the surface soil (0–10 cm). Using the 206Pb/207Pb ratios, the contribution of anthropogenic sources to Pb accumulated in the forest were estimated by the simple binary mixing model. Sixty-two percent of the Pb in the forest floor, 71% in the vegetation, and 55% in the surface soil (0–10 cm) originated from anthropogenic sources, but only 16% in the sub-surface soil (10–20 cm) was anthropogenic. These results suggest that internal Pb cycling occurs mainly between surface soil and vegetation in a Japanese cedar ecosystem, and that anthropogenic Pb strongly influences Pb cycling. Although the Japanese cedar ecosystem has a shallow forest floor, very little atmospherically derived Pb migrated downward over 10 cm in depth.  相似文献   

5.
Southern Ocean aerosols were collected at the Cape Grim Baseline Air Pollution Station from onshore air under baseline conditions between February 1999 and April 2000. Thermal ionization techniques (TIMS) and isotope dilution mass spectrometry (IDMS) were used to measure the isotopic composition and concentration of lead in the air giving concentrations as low as 0.6 ± 0.1 pg · m−3. Air collected under baseline conditions for 12 months (May 1999-April 2000) yielded an overall lead concentration of 11.0 ± 0.2 pg · m−3 and isotopic composition of 206Pb/207Pb = 1.154, 208Pb/207Pb = 2.387 and 206Pb/204Pb = 17.93. The range in isotopic ratios was consistent with the mixing of lead from major population centers in the Southern Hemisphere in the mid to high latitudes, except for the presence of highly radiogenic lead in some samples. Contributions from radiogenic lead of up to ∼0.8% were observed. Three periods with the highest percentage contribution of radiogenic lead (>0.5%) were investigated in more detail, and 4-d back-trajectories and radon concentrations were used to help identify the sources. The sources are probably associated with the mining and processing of uranium rich ores in southern Africa and possibly South Australia.  相似文献   

6.
This paper dealt with the Pb contents and Pb isotopic composition of the West Lake Longjing tea. The results showed that in the tea leaves, from young leaf →old leaf →tea limb, the Pb contents tend to increase gradu-ally from 1.63 →4.84 →6.07×10-6, wich revealed that the Pb was accumulated gradually in the tea. After cleaned, the Pb contents of tea leaves were significantly reduced. This indicated that the deposits on the surface of tea leaves made a great contributuion to Pb contents. The survey results for soils in the relevant tea gardens showed that soil from the Longjing tea garden has higher Pb contents, with an average level of 49.6×10-6, two times those of common soils (24×10-6) in China. Results of the systematic analysis for tea, tea garden soil and the samples with the relevant background of the Pb isotopic composition displayed that the Pb isotopic ratio of tea is 206Pb/207Pb=1.164±0.005 (2σ). The ratio of 206Pb/207Pb for the soil gradually decreased from residue phase, soil dilute acid extract phase, and then to urban topsoil, i.e., 1.175 →1.171 →1.170. The 208Pb/(206Pb+207Pb) ratios also show a similar variation trend. 206Pb/207Pb ratios in the samples with the relevant background were: vehicle exhaust, 1.124; coal-combustion, 1.156; atmosphere, 1.168; and water, 1.166. Comparative studies have shown that Pb pollution is popular in the environ-mental media (soil, atmosphere, water) in Hangzhou. With the aggravation of Pb pollution, the Pb isotopic composi-tion gradually changed from the natural background (soil residues) to the direction of automobile exhaust. This phe-nomenon could illustrate that the pollution source was the vehicle exhaust, while the coal-combustion contributed little to environmental pollution in Hangzhou. The Pb of the Longjing tea came mostly from soluble phase Pb in the polluted soil. Moreover, secondary pollution was caused by vehicle exhaust.  相似文献   

7.
杭州市土壤铅污染的铅同位素示踪研究   总被引：27，自引：0，他引：27       下载免费PDF全文
根据杭州市40个土壤全铅和38个可溶相铅的统计分析,土壤中全铅平均含量为49.6×10-6,可溶相铅平均为21.4×10-6,城区表土的全铅高达76.1×10-6,显著高于全国土壤平均值。分析结果还显示,从农村→远郊→近郊→公路旁,土壤可溶相铅含量逐渐增加,且土壤的可溶相铅含量与深度具明显的负相关关系。表明杭州市土壤受到了不同程度的铅污染,污染程度由农村→远郊→近郊→公路旁→城区有明显的增高趋势。通过对茶园土壤中可溶相铅、残渣态铅及城区表土全铅的同位素组成对比分析发现,从土壤残渣态(代表土壤背景)→土壤可溶相→城区表层土壤全铅206Pb/207Pb比值有明显的降低。208Pb/(206Pb+207Pb)也有类似的变化趋势。将土壤与杭州市的汽车尾气、大气等环境样品进行对比发现,随着土壤受污染程度的增加,铅同位素组成逐渐向汽车尾气铅漂移,表明汽车尾气排放的铅为其主要污染源。  相似文献   

8.
The Pb contents and 206Pb/207Pb and 208Pb/206Pb isotopic ratios were studied in the soils and wines (2004 harvest) of three vineyard areas of the Czech Republic. The areas differ in their geological basements and anthropogenic loading. The isotopic compositions of wine in areas with intensive industry (Most, North Bohemia 206Pb/207Pbwine = 1.178 ± 0.004) and the agricultural areas of Central Bohemia (Roudnice nad Labem 206Pb/207Pbwine = 1.176 ± 0.007) are similar to the Pb isotopic composition of airborne particulate material typical of polluted and industrial environments (206Pb/207Pb = 1.17–1.19). The isotopic composition of wine from Prague (206Pb/207Pbwine = 1.174 ± 0.003) is different from that of the soil, which was severely contaminated in the past by vehicular Pb (206Pb/207Pbsoil = 1.147–1.168). This fact shows that interception of airborne Pb by plants is greater than its uptake by the root system.  相似文献   

9.
Isotopic evidence for the source of lead in the North Pacific abyssal water   总被引：1，自引：0，他引：1  
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.  相似文献   

10.
Lead (Pb) isotopic compositions and concentrations, and barium (Ba) and indium (In) concentrations have been determined at monthly resolution in five Law Dome (coastal Eastern Antarctica) ice core sections dated from ∼1757 AD to ∼1898 AD. ‘Natural’ background Pb concentrations in ∼1757 AD average ∼0.2 pg g−1 and can be attributed to mineral dust and volcanic emissions, with 206Pb/207Pb ratios reaching up to 1.266 ± 0.002. From ∼1887 AD to ∼1898 AD, Pb concentrations reached ∼5 pg g−1 and 206Pb/207Pb ratios decreased to 1.058 ± 0.001 as a result of additional inputs of Pb from anthropogenic sources. Seasonal variability in the late 1880s has been investigated by decoupling volcanic Pb from the total measured Pb concentrations, revealing spring and autumn maxima, and consistent winter minima, in anthropogenic Pb and mineral dust (Ba) concentrations. We link this variability to the annual cycle in the position and strength of the Antarctic Circumpolar Trough and, the Southern Ocean westerly winds to the north of the trough region. During the autumn and spring seasons, these systems increase in strength, transporting more impurity laden air from the Southern Hemisphere continental regions to Eastern Antarctica and Law Dome. As this Pb is isotopically identical to that emitted from south-eastern Australia (Broken Hill, Port Pirie) this implies a relatively direct air trajectory pathway from southern Australia to Law Dome (Eastern Antarctica).  相似文献   

11.
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.  相似文献   

12.
Economic reform in China since 1978 has accelerated economic development nationwide hugely, but has also brought about some environmental pollution. In order to identify the primary Pb source to the atmosphere in the central Guizhou region, Pb isotopic ratios in the acid soluble fraction of sediment from Hongfeng Lake were investigated. Lead isotopes in the lake sediments record the history of regional atmospheric Pb pollution. Before the economic reform in 1978, the 208Pb/206Pb and 206Pb/207Pb ratios in the leachates of lake sediments were constant, with a range of 2.0060 to 2.0117 and of 1.2314 to 1.2355, respectively. In the early period of economic reform (1978 to 1988), with the rapid industrial growth in Guizhou province, the acid soluble Pb isotope ratios in the lake sediments changed sharply: the 208Pb/206Pb ratios increased from 2.0212 to about 2.05, while the 206Pb/207Pb ratios decreased from 1.2251 to 1.2060. Emissions from Pb-ore-related industries are suggested to be the major pollution source of Pb in this period. Due to output from a local power plant since 1988, the isotope ratios of the acid soluble Pb in sediments in 1990s are characterized by a little higher radiogenic Pb (208Pb/206Pb = 2.0340–2.0400; 206Pb/207Pb = 1.2122–1.2158) than for the 1980s.  相似文献   

13.
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).  相似文献   

14.
Three soil profiles taken from the Hartwood Research Station in Central Scotland have been analyzed using chemical digestion and extraction techniques to investigate the chemical association of heavy metals deposited from the atmosphere. Total digestion, EDTA extraction and the BCR (Bureau Communitaire de Reference) sequential extraction procedure were used. In addition, lead isotope ratios in the whole soils and in the fractions from the sequential extraction procedure were measured using thermal ionisation mass spectrometry. All the digestion and extraction procedures gave clear indication of enhanced concentrations of heavy metals in surface soils, in particular for lead and zinc. Whereas total digestion gave a good indication of the heavy metal status of the soils, the extraction procedures were necessary to provide information on chemical association of the metals with soil components, information needed to understand the soil processes involved in mobilization of metals. Lead isotope analysis of the whole soils revealed a consistent picture of lower 206Pb/207Pb ratios in surface soils (1.140-1.147) than in soils at 20-30 cm depth (1.182-1.190). The steady progression from the lower to higher ratios down the profile was clear indication that anthropogenic lead had penetrated to some degree into the deeper soils. The combination of sequential extraction and lead isotope analysis proved to be a powerful approach to studying this effect in more detail and showed that the fractions extractable from 20 to 30 cm soils contained lead with much lower 206Pb/207Pb ratios (1.174-1.178) than the residual fraction (1.196-1.200). As the extractable fractions contained ≥85% of the lead in the soil, a substantial portion of lead at 20-30 cm depth was of anthropogenic origin. The 206Pb/207Pb ratios of 1.174-1.178 found in the extractable fractions suggested that the mobile component of the anthropogenic lead was that deposited before the introduction of leaded petrol.  相似文献   

15.
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.  相似文献   

16.
Extreme U and Pb isotope variations produced by disequilibrium in decay chains of 238U and 232Th are found in calcite, opal/chalcedony, and Mn-oxides occurring as secondary mineral coatings in the unsaturated zone at Yucca Mountain, Nevada. These very slowly growing minerals (mm my−1) contain excess 206Pb and 208Pb formed from excesses of intermediate daughter isotopes and cannot be used as reliable 206Pb/238U geochronometers. The presence of excess intermediate daughter isotopes does not appreciably affect 207Pb/235U ages of U-enriched opal/chalcedony, which are interpreted as mineral formation ages.Opal and calcite from outer (younger) portions of coatings have 230Th/U ages from 94.6 ± 3.7 to 361.3 ± 9.8 ka and initial 234U/238U activity ratios (AR) from 4.351 ± 0.070 to 7.02 ± 0.12, which indicate 234U enrichment from percolating water. Present-day 234U/238U AR is ∼1 in opal/chalcedony from older portions of the coatings. The 207Pb/235U ages of opal/chalcedony samples range from 0.1329 ± 0.0080 to 9.10 ± 0.21 Ma, increase with microstratigraphic depth, and define slow long-term average growth rates of about 1.2-2.0 mm my−1, in good agreement with previous results. Measured 234U/238U AR in Mn-oxides, which pre-date the oldest calcite and opal/chalcedony, range from 0.939 ± 0.006 to 2.091 ± 0.006 and are >1 in most samples. The range of 87Sr/86Sr ratios (0.71156-0.71280) in Mn-oxides overlaps that in the late calcite. These data indicate that Mn-oxides exchange U and Sr with percolating water and cannot be used as a reliable dating tool.In the U-poor calcite samples, measured 206Pb/207Pb ratios have a wide range, do not correlate with Ba concentration as would be expected if excess Ra was present, and reach a value of about 1400, the highest ever reported for natural Pb. Calcite intergrown with opal contains excesses of both 206Pb and 207Pb derived from Rn diffusion and from direct α-recoil from U-rich opal. Calcite from coatings devoid of opal/chalcedony contains 206Pb and 208Pb excesses, but no appreciable 207Pb excesses. Observed Pb isotope anomalies in calcite are explained by Rn-produced excess Pb. The Rn emanation may strongly affect 206Pb-238U ages of slow-growing U-poor calcite, but should be negligible for dating fast-growing U-enriched speleothem calcite.  相似文献   

17.
Soil O and C horizon samples (N = 752) were collected at a sample density of 1 site/36 km2 in Nord-Trøndelag and parts of Sør-Trøndelag (c. 25,000 km2), and analysed for Pb and three of the four naturally occurring Pb isotopes (206Pb, 207Pb and 208Pb) in a HNO3/HCl extraction. Soil O and C horizons are decoupled in terms of both Pb concentrations and Pb isotope ratios. In the soil C horizon the Grong-Olden Culmination, a continuous exposure of the Precambrian crystalline basement across the general grain of the Caledonian orogen, is marked by a distinct 206Pb/207Pb isotope ratio anomaly. No clear regional or even local patterns are detected when mapping the Pb isotope ratios in the soil O horizon samples. Variation in the isotope ratios declines significantly from the soil C to the O horizon. On average, Pb concentrations in the O horizon are four times higher and the 206Pb/207Pb isotope ratio is shifted towards a median of 1.15 in comparison to 1.27 in the C horizon. It is demonstrated that natural processes like weathering in combination with plant uptake need to be taken into account in order to distinguish anthropogenic input from natural influences on Pb concentration and the 206Pb/207Pb isotope ratio in the soil O horizon.  相似文献   

18.
Knowledge of the cause and source of Pb pollution is important to abate environmental Pb pollution by taking source-related actions. Lead isotope analysis is a potentially powerful tool to identify anthropogenic Pb and its sources in the environment. Spatial information on the variation of anthropogenic Pb content and anthropogenic Pb sources in rural topsoils is remarkably limited. This study presents results of a survey of approximately 350 topsoil samples from rural locations covering the entire Netherlands, for which the bulk geochemical and Pb isotope compositions were determined. The specific aim of this study is to determine the anthropogenic Pb sources in the topsoils from rural areas in The Netherlands. The spatial distribution of anthropogenic Pb in soils in The Netherlands will be explained in terms of land use and pollution sources.Nearly all studied topsoils display Pb contents that exceed the amount expected based on the soil lithology. The range in Pb isotope ratios of the additional Pb fraction in rural Dutch topsoils is established at 1.056–1.199, 2.336–2.486 and 0.452–0.490 for 206Pb/207Pb, 207Pb/208Pb and 206Pb/208Pb, respectively. Five land use types are distinguished (forest, open nature, moor, arable land and grassland) with distinct isotopic compositions for added Pb. Additional Pb in soils of natural areas (forest, open nature and moor) has on average lower 206Pb/207Pb, 208Pb/207Pb and 206Pb/208Pb ratios than the agricultural soils (arable land and grassland). Additional Pb in both natural area soils and agricultural soils is interpreted to be of anthropogenic origin: most likely a mixture of coal/galena, incinerator ashes and gasoline Pb. The dominant sources of additional Pb in the topsoil of open nature areas are most likely incinerator ash and gasoline Pb. In contrast, the on average higher 206Pb/207Pb, 208Pb/207Pb and 206Pb/208Pb ratios of additional Pb in agricultural soils are most likely caused by the presence of animal manure and N–P fertilizers.Several areas are observed with notably high additional Pb contents (26–211 mg/kg on an organic matter-free basis) in the topsoil. The largest area is the Randstad area, which has the highest population and traffic density, and hosts a considerable fraction of the Dutch chemical industry. Two other areas with high additional Pb contents in the topsoil are located near the Dutch borders and are most likely influenced by German and Belgian chemical industries. The topsoils in the coastal dunes and southern, central and northern forests are characterized by relatively low additional Pb contents (<10 mg/kg on an organic matter-free basis). The population, traffic and chemical industry density is low in these areas and no fertilizers are applied.  相似文献   

19.
The results of our combined U-Pb, Rb-Sr, and Sm-Nd isotope study of mare basalt 10017 contribute to the understanding of the petrogenetic processes involved in the origin of geochemical diversity in lunar mare basalt sources, as well as the U-Pb isotope systematics of the Moon. The Rb-Sr, Sm-Nd, and 238U-206Pb isotope systems yield concordant crystallization ages of 3.633 ± 0.057 Ga, 3.678 ± 0.069 Ga, and 3.616 ± 0.098 Ga, respectively. The 235U-207Pb isochron yields an older, though still concordant, age of 3.80 ± 0.12 Ga. Neither the 206Pb-207Pb system nor U-Pb concordia system yields an age for 10017 that is concordant with the age determined from the Sm-Nd, Rb-Sr, and 238U-206Pb systems. The initial 87Sr/86Sr of 10017 is 0.69941 ± 7 and the initial εNd is +3.2 ± 0.4. Initial Pb isotopic compositions, determined from the U-Pb isochrons, are 206Pb/204Pbi = 31 ± 11 and 207Pb/204Pbi = 34 ± 15. Together, these initial Pb compositions constrain the μ value of the 10017 source to be 70 ± 30, assuming a single-stage Pb growth model. This is considerably lower than μ values typically estimated for mare basalt sources (∼100-600). Regardless, the μ values calculated for the sources of mare basalts, as well as other lunar samples, show a range that is larger than can be explained by fractionation of U from Pb solely by crystallization of silicate phases and ilmenite during magma ocean solidification and formation of lunar mantle sources. The U-Pb isotope systematics may reflect late-stage formation of a sulfide phase, which strongly fractionates Pb from U but has minimal effect on Rb/Sr or Sm/Nd compositions, during crystallization of the lunar magma ocean.  相似文献   

20.
In situ U-Pb isotopic measurements were carried out by ion microprobe on the Zr-rich accessory minerals zirconolite [CaZrTi2O7], tranquillityite [Fe82+(ZrY)2Ti3Si3O24] and baddeleyite [ZrO2] in low-K, high-Ti mare basalt 10047 collected during the Apollo 11 mission. The analysed minerals are concentrated in pockets of late-stage mesostasis that comprises an intergrowth of silica, barian K-feldspar and Si-Al-K glass, from a phaneritic, subophitic, basalt comprising mainly pyroxene, plagioclase, ilmenite, cristobalite and troilite. Most Zr-rich minerals are unaltered, however, some tranquillityite is replaced by a complex intergrowth of zirconolite, baddeleyite, ilmenite and fayalite, suggesting that the mineral became unstable during crystallization. Several baddeleyite crystals have also undergone alteration to secondary zircon. Zirconolite was analysed in thin section 10047,11 and tranquillityite and baddeleyite in 10047,227, using a ∼6 μm primary ion beam. Both zirconolite and tranquillityite have significant U and low initial Pb contents, and are highly suitable for Pb/Pb dating. Fifteen analyses of zirconolite give a 207Pb/206Pb age of 3708 ± 7 Ma (207Pb/206Pb:204Pb/206Pb isochron; 95% confidence, including renormalisation of ratios) and twenty-five analyses of tranquillityite give 3710 ± 6 Ma. The 207Pb/206Pb dates are consistent with each other and refine results from an earlier study. Baddeleyite data were less precise, mainly due to lower secondary ionisation efficiency. Our results show that zirconolite and tranquillityite can provide precise isotopic dates and, given their presence in other samples, they represent important U-Pb chronometers for refining lunar geology.  相似文献   

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