Lead isotope and trace element composition of urban soils in Mongolia

Lead (Pb) pollution in and around Ulaanbaatar is of national concern, given that the Mongolian capital is home to nearly half of the country’s entire population. By comparison, Mongolian countryside is a pristine environment because of its sparse population and low industrial activity. The concentration of Pb in urban soils (average of 39.1 mg kg^–1) was twice the values found (average 18.6 mg kg^–1) in background territories (i.e., Mongolian rural sites). Furthermore, Pb contamination was examined by using Pb stable isotopic composition, and covariance of Pb isotopic ratios showed two groups between rural and urban soils as pristine and disturbed sites. The ²⁰⁶Pb/²⁰⁷Pb ratio, the most prominent fingerprint for Pb pollution, was 1.163–1.185 for the urban whereas values for rural soils (1.186–1.207) were analogue to the regional Pb isotopic signatures. Local coal sources and their combustion products, one of the potential Pb pollution sources in Ulaanbaatar, have significant radiogenic properties in terms of Pb isotopic composition and revealed an average of 1.25 for ²⁰⁶Pb/²⁰⁷Pb and 19.551 for ²⁰⁶Pb/²⁰⁴Pb ratios. Thus, contributions from coal firing activity to Pb pollution lower than it was assumed, and smaller range of these values measured in urban soils may be attributed to the mixing of less radiogenic Pb as a constituent of the leaded gasolines.     

On the Isotopic Composition of Pb in Cloud Waters in Central Germany. A Source Discrimination Study

Fifty seven (57) cloud water samples collected in 1 hr intervals during 9cloud events in 1997 at the summit of the Brocken (altitude 1142 m) in Central Germany were analyzed for their Pb concentrations and isotopic compositions. For comparison, filterdusts of such possible emitters as power plants, cement factories, waste incinerators, cars and others were also studied.Profiles over many hours reveal changes in composition correlatedwith changes in the origin of the air masses. Five main groups ofpossible sources of the Pb can be distinguished: most importantare (1) the European standard pollution ESP dominating the continent from Germany over France to Scandinavia and (2) industrial Pb (and soot from car exhausts) followed by (3) urban waste incinerators as well as (4) perhaps ores from Norilsk/Siberia, and, somewhat uncertain, (5) ores from PaleozoicEuropean deposits. Local and daily varying anthropogenic emissions of the sources (2–5) cause scatter of the points around the ESP correlation line. In soils all these variationsand individual signatures are levelled out so that specific sources of pollution cannot be identified anymore. Geogenic Pbfrom rocks and soils is the same as that from power plants and cement factories. It is one of the two nominal end components making up the mixture of the ESP. The less radiogenic end component of this mix which must contain Pb from very old deposits is somewhat elusive: none of the large Archaic or Proterozoic deposits could be identified. Most probably numerous sources contribute to this Pb. Pb from leaded gasoline seems to be absent or is hidden under the five components dominating the composition of the Pb in the European environment. This probably reflects phasing out of such gasoline in most European countries. The Pb in the clouds may contain a small component of old Proterozoic or even Archaic Pb, but it can also be modelled with Paleozoic Pb.     

Periglacial transport distance of Pb derived from small-scale ore veins in the Rhenish Slate Mountains

The spatial extent of metal contamination caused by small-scale ore veins is increased by periglacial solifluction. Our objectives were (1) to examine the spatial distribution of Pb in cover beds that migrated over Pb ore veins, (2) to calculate the transport distance of ore-derived Pb, and (3) to determine controls on the transport distance.We examined six transects (320-775 m long) in the Rhenish Slate Mountains in West Germany. The transects included four west-exposed and two east-exposed slopes with inclinations between 2-20°. All transects were forest-covered and located at 280-450 m above sea level. Soils were Dystric Cambisols and Stagnic Luvisols. Samples of 120 B horizons developed in the sediments of the last ice age (Wuerm) were analyzed for total Pb concentrations and partly also ²⁰⁶Pb/²⁰⁷Pb ratios. The Pb concentrations ranged from 20 to 135 mg kg^− 1. The spatial Pb distribution suggested that 14 (out of 18) sampling points showing local Pb concentration maxima contained Pb from ore veins upslope. With a two-end-member-mixing model using ²⁰⁶Pb/²⁰⁷Pb isotope ratios of the ore (²⁰⁶Pb/²⁰⁷Pb ratio: 1.1828) as one end member and of the native substrate (a mixture of slate and loess; ²⁰⁶Pb/²⁰⁷Pb ratio: 1.2254 ± 0.0072) as the other we confirmed that the 14 Pb peaks originated from the ore, because they contained 76-100% of ore-derived Pb. By the use of a geographic information system, the transport distance of this Pb was determined to range between 30 and 110 m. Silt concentrations (Pearson r = − 0.69) and the relief curvature (Cramér's V = 0.60) were major controls on the transport distance. Our study demonstrates that Pb ore veins can increase native soil Pb concentrations in soil derived from the periglacial drift of the last ice age (Wuerm) up to a distance of more than 100 m.     

Quantification of anthropogenic lead in Slovak forest and arable soils along a deposition gradient with stable lead isotope ratios

Isotope ratios of Pb may provide the opportunity to determine the contribution of Pb from a point source to Pb concentrations in soil. Our objective was to quantify the contribution of anthropogenic Pb to total Pb and chemical Pb fractions in contaminated soil profiles with the help of ²⁰⁶Pb/²⁰⁷Pb isotope ratios. We sampled 5 forest and 5 arable Cambisols along a transect from a Cu smelter and determined Pb concentrations and ²⁰⁶Pb/²⁰⁷Pb isotope ratios in total digests of all horizons and in 7 chemical fractions of the A horizons. In the organic layer under forest, Pb concentrations decreased from 2155 mg kg^—1 at 1.1 km distance from the smelter to 402 mg kg^—1 at 8 km distance; in the Ap horizons, it decreased from 126 to 72 mg kg^—1. In the total digests, ²⁰⁶Pb/²⁰⁷Pb isotope ratios could be explained by simple mixing of smelter‐ and background‐Pb as indicated by the correlation between the inverse of the Pb concentration and the ²⁰⁶Pb/²⁰⁷Pb ratio (r = 0.93). The mean proportion of smelter‐Pb in soil horizons decreased with depth from 87% (Oi) to 21% (C) under forest and from 64% (A) to 30% (B) in the arable soils. The smelter‐Pb proportions in the B horizons ranged from 6 to 66% and were independent of the distance from the smelter indicating variable leaching rates. The ²⁰⁶Pb/²⁰⁷Pb ratios in the chemical fractions could not be explained by a simple mixing model. Thus, the ²⁰⁶Pb/²⁰⁷Pb ratios may be used to determine the contribution of anthropogenic Pb in total digests but not in chemical Pb fractions.     

Historical change of soil Pb content and Pb isotope signatures of the cultural layers in urban Nanjing

Soils in urban areas are often artificially formed and preserved as cultural layers in which soil materials are mixed with artifacts. The vertical change of soil properties denotes the historical change of human activities, and therefore, urban soil can be considered as a record of history of urban development. We studied a deep profile of urban soil (600 cm) in Nanjing, China, by intensively sampling at every 5 cm. Soil samples were analyzed for lead content. Charcoal from several layers was found and was dated using ¹⁴C to recognize archaeological cultural layers that might be formed in different Chinese dynasties. Pb isotope ratios were determined by thermal ionization mass spectrometry (TIMS) technology. The study found that artificial deposition, i.e., the formation of cultural layer started about 1700 years ago and lasted until recently. All cultural layers above the original loess were heavily contaminated by Pb with total content varying from 100 mg kg^− 1 to more than 2000 mg kg^− 1. There were several historical periods in which Pb content peaked, indicating significant contamination by human activities, such as ancient ore smelting for various purposes and use of Pb-containing materials for handicraft manufacture. Various Pb isotope ratios of the cultural layers differed substantially from that of the original undisturbed loess in the deepest position. ²⁰⁶Pb/²⁰⁷Pb value decreased gradually from the bottom layer to top layer, although with occasional exceptions, indicating a long-lasting mixing of extraneous sources of Pb during the entire history since ca. 300 A.D. In comparison with the isotope ratios of lead ores of different sources and that of aerosols, it was illustrated that the source of Pb in cultural layers might come from lead ores of southern China in the earlier dynasties, while Pb from north China might have contributed to the Pb source in the more recent years, suggested by the lowering of ²⁰⁶Pb/²⁰⁷Pb ratio in the near-surface cultural layers. However, the impact of petrol burning on cultural layers was basically excluded, considering the relatively short history of petroleum use in this area.     

Tracing Pb Pollution Penetration in Temperate Podzols

We combine high‐resolution soil sampling with lead (Pb) analyses (concentrations and stable isotopes) in two temperate podzols, together with previous data obtained with selective Al and Fe dissolution techniques. We aim to assess how atmospheric Pb is incorporated into the soils during pedogenesis. Partial least squares modelling for Pb concentrations shows that the podzolization process has the largest effect on Pb concentration (80·3% of the variance). The proportion of inorganic secondary compounds, the input of fresh organic matter from the soil surface and the relative abundance of Fe versus Al are responsible for a small part of the Pb concentration variance. Lead isotopic composition (²⁰⁶Pb/²⁰⁷Pb ratios) depends on soil organic matter content either fresh/poorly humified (57·3% of the variance) or humified (24·7% of the variance). The Pb linked to inorganic compounds and the overall podzolization process play a minor role in isotopic signature (5·3 and 3·7% of the variance respectively). Soil pH appears to be the controlling variable of the different transport and retention mechanisms. The relatively low isotopic ratios observed in spodic horizons result from geogenic Pb released through the preferential dissolution of the isotopically distinct most weatherable minerals of the parent material in the eluvial horizons, which undergoes downward mobilization. An accurate knowledge of soil reactive components and formation mechanisms is essential to a correct diagnose of the scope of Pb pollution and a more effective design of remediation strategies. Copyright © 2017 John Wiley & Sons, Ltd.     

Lead Isotopic and Metallic Pollution Record in Tree Rings from the Copperbelt Mining�CSmelting Area, Zambia

The composition of tree rings and soils was studied at several locations affected by smelting and transportation in the vicinity of Kitwe (Copperbelt, Zambia). The contents of cobalt (Co), copper (Cu), manganese (Mn), and lead (Pb) and the ²⁰⁶Pb/²⁰⁷Pb isotope ratios in the tree rings were interpreted in relation to potential sources of contamination such as smelter production, acidification of the environment, soil composition, raw material processing, and atmospheric suspended particulate matter (SPM). The highest Co contents in the tree rings correspond to maximum ore production in the mid-1970s. Acidification through SO₂ emissions is documented in the increased Mn contents from the mid-1980s. The isotopic composition of the tree rings of the studied tree species varies in the interval 1.16?C1.34 and the youngest parts of all the studied trees exhibit a low ²⁰⁶Pb/²⁰⁷Pb ratio (<1.17). The soil isotope composition varies in the range ²⁰⁶Pb/²⁰⁷Pb?=?1.18?C1.35. The Pb isotope composition in the soils and tree rings was formed by a combination of lithogenic Pb (²⁰⁶Pb/²⁰⁷Pb????1.3), Pb in processed ores (²⁰⁶Pb/²⁰⁷Pb????1.2), and SPM (automobile) Pb (²⁰⁶Pb/²⁰⁷Pb??1.1). As the soils in the distant region have high ²⁰⁶Pb/²⁰⁷Pb ratios (>1.3) in the whole profile and simultaneously the youngest parts of the tree rings of tree species growing in this soil have a low ²⁰⁶Pb/²⁰⁷Pb ratio (<1.17), it can be assumed that the Pb in the youngest parts of the tree species is derived from absorption of SPM Pb through the bark rather than root uptake. The absence of Pb with a low ²⁰⁶Pb/²⁰⁷Pb ratio in soils in the distant area is probably affected by fires in the herbaceous and bush undergrowth and plant litter, which prevents Pb from biomass from entering the soil and mobilize it back into the atmosphere.     

Investigation of Past and Present Multi-metal Input along Two Highways of British Columbia, Canada, Using Lead Isotopic Signatures

A multi-media monitoring field investigation, which included atmospheric, road sediment and soil samples, was carried out at two highway study sites to identify past and present Pb sources. Past Pb anthropogenic sources such as paint and leaded gasoline were linked to significant Pb accumulation in roadside soils at both sites through Pb isotopic analyses. This was achieved by identifying the distinct Pb isotopic composition in older versus newer Pb accumulation at different depths across the soil profile. Older Pb accumulations exhibited lower ²⁰⁶Pb/²⁰⁷Pb isotopic ratios, consistent with Canadian Pb-bearing ores, whereas newer Pb accumulations reflected a mixture of the ²⁰⁶Pb/²⁰⁷Pb ratios of road sediment samples, with the Pb isotopic signature of uncontaminated soil. Isotopic analyses were also helpful in identifying road sediment as an important current source of Pb in roadside soils, by comparing the isotopic signatures derived from road sediment and atmospheric dustfall. The known association of Pb with anthropogenic sources was used to indirectly relate other metals (Cu, Mn, Zn) to the same source by the Enrichment Ratio method. Significant positive correlations at the 90–95% confidence level were found between Cu, Zn and Pb Enrichment Ratios in roadside and dust deposition samples. Weaker correlations were found between Mn and Pb, at the highway study site with the least amount of traffic. However, correlations between these two metals were significant at the 90% confidence level for the busier highway site highlighting Mn potential anthropogenic source. An isotopic tracer study is suggested to further investigate the process of Mn redistribution in the environment due to exhaust fuel emissions. More research is needed regarding the potential impact from using a Mn-based fuel additive.     

A Comparison of Tree Rings and Peat Deposit Geochemical Archives in the Vicinity of a Lead Smelter

The content of Pb, Cd, Mn, K, Ca, Mg and ²⁰⁶Pb/²⁰⁷Pb isotope ratios in spruce tree rings (Picea abies) and peat cores from the Brdy Hills area (10 km W of the Pb smelter) were compared with those in spruce tree rings in the vicinity of the Pb smelter. Maximum Pb content in tree rings (up to 60 mg kg^?1 Pb) corresponds to a peak of metallurgical production in the mid 1970s and highest smelter emissions in the early 1970s. The Pb concentration curves obtained from peat deposit profiles closely correlate with the Pb concentrations in tree rings at both sampling sites. The small differences between the individual tree cores, with the identical general trend, may be attributed to the difference in distance from the smelter and the altitude of each sampling site. Similar behaviour to Pb can be observed for Cd and Ca. Lead isotope composition in tree rings (²⁰⁶Pb/²⁰⁷Pb ~1.143–1.174) is controlled mainly by the smelter emissions (²⁰⁶Pb/²⁰⁷Pb ~1.16–1.17), with the exception of the youngest segments from the more distant locality from the smelter, which yield isotopic signatures corresponding to car-emission Pb (²⁰⁶Pb/²⁰⁷Pb ~1.143–1.150). Higher content of Mn, Mg and Ca in tree rings corresponding to the 1970s and 1980s may be related to soil chemistry changes caused by acid deposition. In addition, an increase in K, Mg (and in some cases also Mn) in the youngest part of wood cores corresponds to the physiological processes in sapwood, and may be influenced by a decrease in Pb in organic soil horizons, which limited the cycling of basic inorganic nutrients.     

Trace metals in sediments and aquatic plants from the Xiangjiang River, China

Purpose

The metal concentrations and Pb isotopic composition in sediments and plants from the Xiangjiang River, China, were investigated to understand the contamination and potential toxicity of metals in sediments; to determine the accumulation and distribution of metals in plant tissues; and to trace the possible pollution source of Pb in sediments and plants.

Materials and methods

Sediments and plants were collected from 43 sampling sites in the study region. After sediments were air-dried and passed through a 63-??m sieve, they were acid-digested and DTPA-extracted for determination of total and bioavailable metals. The plants were separated into roots, leaves, and stems; dried; cut into pieces; and digested with HNO₃?CH₂O₂. Metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) and Pb isotopic composition were analyzed by inductively coupled plasma-mass spectrometry.

Results and discussion

Maximum As, Cd, Cr, Cu, Ni, Pb, and Zn concentrations in sediments were 47.18, 55.81, 129.5, 161.6, 160.4, 430.7, and 1,098.8?mg?kg^?1, respectively. The bioavailable fractions of As, Cd, Cu, Pb, and Zn had significant linear relationship with their corresponding total contents in sediments while no significant relationship was observed between bioavailable and total contents of Cr and Ni. In general, plant tissues showed higher As, Cd, Cu, Pb, and Zn concentrations and lower Cr and Ni concentrations compared with sediments. The ²⁰⁶Pb/²⁰⁷Pb ratios decreased in the order of total > bioavailable > stems ?? leaves > roots. A strong linear correlation was observed between the ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁶Pb/²⁰⁷Pb ratios of the plant tissues, sediments, and the possible pollution sources of Pb in the Xiangjiang River.

Conclusions

As, Cd, Cu, Pb, and Zn demonstrated higher contamination levels in sediments and plants compared with Cr and Ni. Cd had highest potential ecological risk. The Pb from anthropogenic sources with low ²⁰⁶Pb/²⁰⁷Pb ratios was preferentially associated with the bioavailable fractions in sediments and accumulated in roots. The Pb in plant tissues is mainly derived from the Pb in sediment and is taken up through the sediment-to-root pathway.     

The flux of Cd,Cu, Pb and Zn in mining polluted soils

The monitoring of heavy metal deposition onto soils surrounding old Pb-Zn mines in two locations in the UK has shown that relatively large amounts of Cd, Pb, Zn and, in one case, Cu are entering the soil annually. Small particles of ore minerals in windblown mine tailings were found to be contributing up to 1.46 g m^?2 yr^?1 of Pb, 1.41 g m^?2 yr^?1 of Zn and 0.027 g m^?2 yr^?1 of Cd. However, when these inputs from bulk deposition are compared with the concentrations of the same metals within the soil profiles it is apparent that relatively little long-term accumulation is occurring. Metals are being lost from the soil profiles, probably through leaching. A calculated relative retention parameter gave values that ranged from 0.01 to 0.17 for Cd, 0.11 to 0.19 for Zn, 0.32 to 0.63 for Cu and over 1 for Pb. These relative retention values were found to follow the order of electronegativity of the elements concerned: Pb>Cu>Zn>Cd. Distribution coefficient (Kd) values quantifying the adsorptive capacity of the mine soils for Cd and Pb showed marked differences for the two metals (12 to 69 cm³ g^?1 for Cd and 14 to 126 cm³ g^?1 for Pb) and may, in part, account for the two to one hundred-fold variation in the relative retention parameter for the different metals within these soils.     

Contributions of different parent materials in soils developed from periglacial cover‐beds

Soils frequently develop from mixtures of different parent materials. We quantified the contributions of different parent materials to the substrate for recent soil development using trace metal concentrations and Pb isotope ratios as input data for end‐member mixing analyses (EMMAs). We examined six transects (320–775 m) at two sites in the Rhenish Slate Mountains. Soil types ranged from acid Cambisols to stagnic Luvisols developed from periglacial cover‐beds. Sixteen O, 11 A, 120 B and 10 C horizons were analysed for total trace metal concentrations and partly also ²⁰⁶Pb:²⁰⁷Pb ratios. Most metal concentrations in the B horizons were in the background range, except for Pb, which partly had elevated concentrations of up to 135 mg kg⁻¹. The depth distribution of metal concentrations and ²⁰⁶Pb:²⁰⁷Pb ratios suggested that metals deposited from the atmosphere had hardly reached the B horizons. A principal component analysis (PCA) of the trace element concentrations in the 120 B horizons identified four main metal sources of the B horizons, which we interpreted as bedrock (slate), loess, Laacher See tephra (LST) resulting from the last volcanic eruption in the Eifel mountains and ore veins. The slate was characterized by Cr and Zn, the loess by Zr, the LST by Nb and the ore veins by Pb. Based on EMMAs with four end‐members using two different sets of tracers (Set 1: concentration ratios of Zr:Cr, Nb:Cr, Pb:Cr, Set 2: Zr:Zn, Nb:Zn, and Pb:Zn), slate, loess and LST contributed, on average, 39–40, 22–24 and 37–38%, respectively, at Site 1 and 19–21, 53–63 and 18–26%, respectively, at Site 2. In contrast, the ore contribution was consistently estimated at 0%. An additional EMMA with two end‐members based on the ²⁰⁶Pb:²⁰⁷Pb ratios estimated the contribution of the ore at 0.02%. We conclude that EMMAs based on trace element concentrations and isotope ratios provide a tool for determining the contribution of different parent materials to the substrate from which soils develop, at least at a small regional scale and if an appropriate tracer that distinguishes all the considered substrates is found.     

Using isotopic tracers in lake sediments to assess atmospheric transport of lead in Eastern Canada

The isotopic composition of lead pollution in the environment provides information as to the source of emission. The ²⁰⁶Pb/²⁰⁷Pb ratio for Canadian industrial emissions (1.153±0.005) is significantly less than U.S. industrial emissions (1.213±0.008) making it possible to determine the relative contributions of emissions from both countries within Eastern North America by means of a simple isotopic mixing model. Profundal sediments in lakes chronicle contaminant inputs and are therefore useful monitors of environmental pollution. Surface sediment from 32 sediment cores across Quebec and Ontario, Canada were analyzed for ²⁰⁶Pb^/207Pb to ascertain the relative proportions of Pb emission from Canada and the U.S.A. Data show that U.S. contributions to the total lead burden in surficial sediments across much of southern Quebec and Ontario are often in excess of 50%. Local sources were particularly important in the Eastern Township region of Quebec which lies 200 km south east of the city of Montreal. The results are discussed in relation to the major sources of industrial lead emissions in North America.     

Distribution of anthropogenic lead estimated by Pb isotopic composition in the upper layers of soil from a mixed forest at Dinghushan, southern China

Purpose

The heavy metal lead (Pb) is toxic to living organisms. Forest soils are important sinks for heavy metals generated by human activities. The forest at Dinghushan of southern China has experienced long-term exposure to atmospheric pollutants from the Pearl River Delta (PRD). The objectives of this research were (a) to determine the vertical and temporal distribution of Pb in the forest soil at Dinghushan, (b) to determine whether dilute acid extraction could be used to identify anthropogenic sources of Pb in forest soil, and (c) to determine the main anthropogenic contributors to soil Pb.

Materials and methods

Lead concentrations and isotopes were measured in two sets of forest soil samples. One set consisted of archived samples from 0 to 20 cm depth collected annually from 1997 to 2010. The other set was collected throughout three profiles sampled at 5-cm intervals to the bedrock (85 cm depth) in 2011. The soil samples were air-dried, ground, and passed through a 100-mesh polyethylene sieve. Lead in the samples was digested with concentrated acid (HNO₃?+?HClO₄, 4:1?v/v) or extracted with dilute acid (1 M HCl with a soil/solution ratio of 1:10) and was measured with an inductively coupled plasma mass spectrometer.

Results and discussion

Concentrations of Pb obtained both by total digestion and dilute acid extraction decreased with soil depth in the profile samples and increased over time in the archived ones. Soils at 0–20 cm depth had Pb concentrations of more than twice of the local soil background value. In all soil samples, the ^206/207Pb ratios was lower and the ^206/204Pb, ^207/204Pb, and ^208/204Pb ratios were higher with the dilute acid extraction than with the strong-acid digestion, indicating that dilute acid extraction could be used to distinguish between anthropogenic and geogenic Pb. Comparison of the Pb isotope ratios in the samples with those in the main pollutants from the PRD indicated that coal combustion and industrial emission were the main contributors to the forest soil Pb at Dinghushan.

Conclusions

The forest soil (0–20 cm depth) at Dinghushan was contaminated by Pb. Dilute acid extraction could be used to identify anthropogenic Pb sources. From 1997 to 2010, the main contributors of anthropogenic Pb to the forest soil at Dinghushan were coal combustion and industrial emission. Measures that control Pb emission from coal combustion and industrial activity, changes in coal consumption, and re-adjustments of industry development in the PRD should reduce Pb contamination of forest soil.     

Lead Concentrations,Isotope Ratios,and Source Apportionment in Road Deposited Sediments,Honolulu, Oahu,Hawaii

Anthropogenic contributions of lead to the urban environment havebeen dominated by combustion of leaded gasoline. A number of studies have used lead concentrations in road deposited sediments(RDSs) to infer automobile contributions. However, few studies have combined concentration data, enrichment ratios, and lead isotope ratio data into a comprehensive picture of lead contamination of road sediments. An urban, non-industrialized basin, in Oahu, Hawaii, was selected for investigation. Twenty RDSsamples were collected throughout the 11 km² system, with anundisturbed soil profile sampled to a depth of 30 cm to documentbackground lead levels.Median lead concentrations from a weak (cold) HCl digestion and a hot nitric acid digestion were 3 and 7 mg kg^-1 for thebackground soil, and 256 and 303 mg kg^-1 for RDSs. The median Pb enrichment ratio (HCl digestion) for RDSs was 129, witha range from 24 to 883. All the data collected point to a highlycontaminated environment.Lead isotope ratios from potential sources were examined relativeto those observed for RDSs in the system. Host geological rocks,paint, and long-range aerosol transport were ruled-out as significant sources based on an examination of isotope ratios andpotential loadings to road sediments. Leaded gasoline wasidentified as the major contributor to present-day road sedimentsbased on their radiogenic nature, with mean ²⁰⁶Pb/²⁰⁴Pb = 18.787 ± 0.096 (95% confidence interval), ²⁰⁷Pb/²⁰⁴Pb = 15.847± 0.074, ²⁰⁸Pb/²⁰⁴Pb= 38.836 ± 0.221, and ²⁰⁶Pb/²⁰⁷Pb = 1.184 ± 0.009. The contribution of gasoline additives to RDS for two periods, pre-1968 and post-1968, were estimated using ²⁰⁶Pb/²⁰⁷Pb ratios. The average contribution of post-1968 lead to RDSs was 59%, with a range from 32 to 81%. To explain the mixed age of lead in the RDSs, we suggest that erosional processes have mobilized sediment from roadside reservoirs in the basin that have accumulated automobile emissions primarily since the 1930s. The significant shift in useof radiogenic (J-type) ores, mostly from Missouri, USA, have allowed us to fingerprint and apportion lead in RDSs of thissystem.     

Isotopic Record of Lead Contamination in Alluvial Soils and Tree Rings on Recent Floodplains (Southern Québec, Canada)

Current and past industrial pollution leaves many traces in the environment, in particular along rivers in industrial and urban areas. The isotopic analysis of the lead found in soils and tree rings offers a kind of environmental archive for presenting a portrait of the pollutant distribution in the environment in both spatial and temporal terms. This study is an attempt to identify and compare the source of contamination found in soils and tree rings located along two rivers affected by pollution over several years. Specifically, the focus is on the pattern of lead concentrations and lead isotopic signatures (206Pb/207Pb, 208Pb/206Pb, and 206Pb/204Pb) detected in soils and tree rings located on polluted floodplains. The concentration of Pb in overbank sediments does not rise with the increasing distance downstream from the point source (mining area), suggesting that significant fluvial transport of the pollutant particles over 80 km is involved. For the soil profiles, Pb concentration levels range between 12.32 and 149.13 mg/kg, with the highest concentrations found at the base of the profiles (>1 m). For the lead isotope ratios in the soil profiles, the values obtained range from 0.851 to 0.872 (206Pb/207Pb), 2.081 to 2.111 (208Pb/206Pb), and 0.547 to 0.562 (206Pb/204Pb). The tree ring analysis of red ash (Fraxinus pennsylvanica Marsh.) shows average lead concentrations of 0.63 μg/g, and the lead values of all the tree specimens range between 0.03 and 11.38 μg/g. Pb concentrations varied greatly between the specimens in selected sites and lead isotope ratios in the tree rings showed a strong variability in the time series, particularly from 1945 to 1970. The greater number of variations in the lead concentration rates and isotopic ratios suggest that many more events associated with pollution and contamination have in fact occurred in this area. The study demonstrates the utility of combining stable isotope analyses (soils and tree rings) to examine the source and dispersion of contaminant Pb in fluvial systems by providing reliable and robust indicators for the detection of environmental changes on a local and regional scale.     

Comparative assessment of the contents of magnetic spherules, 137Cs, and 210Pb in soils as applied for the estimation of soil erosion

The contents of magnetic spherules and ¹³⁷Cs and ²¹⁰Pb isotopes were determined in gray forest soils of the Novosil Agroforest Experimental Station in Orel oblast (central part of European Russia). The spatial variability in the contents of these substances was studied, and their distribution in the soil profiles and along soil transects within the afforested and cultivated slopes was analyzed. Factors and processes favoring the accumulation of magnetic spherules and ¹³⁷Cs and ²¹⁰Pb isotopes in the soils, as well as their removal from the soils, were revealed. Similarities and distinctions in the patterns of their behavior were interpreted. Prospects for the combined use of these three tracers to estimate the rates of soil erosion and sediment deposition on the soil surface were tested.     

Evaluation of Pb Phytoremediation Potential in Buddleja asiatica and B. paniculata

The phytoremediation potential for Pb of Buddleja asiatica (a wild species) and a closely related cultivated species, B. paniculata, was investigated by means of field survey, hydroponic and pot experiments, and field trial experiments. Field surveys showed that B. asiatica had an extraordinary accumulation capacity and tolerance for Pb. Plants grown in soil with 2,369.8–206,152 mg kg^?1 total Pb accumulated 1,835.5–4,335.8 mg kg^?1 Pb in their shoots. Under hydroponic conditions (10, 20 mg l^?1 Pb), both B. asiatica and B. paniculata showed unusually high concentrations of Pb in their roots (12,133–21,667 mg kg^?1) and increased biomass production. A pot experiment in a greenhouse without any soil amendments was conducted on three different soils with various Pb contents (10,652, 31,304, 89,083 mg kg^?1) for 3 months. The results showed that both species of Buddleja had an increase in the biomass similar to the control plants. There was a slight decrease in survival rates of plants grown in soil with 89,083 mg kg^?1 Pb content. A field trial experiment was conducted for 6 months at three sites around the Pb mine area in which plants were provided with Osmocote fertilizer. Both Buddleja species showed 100% survival, increased biomass production and phytoextraction capacity (TF 1.1–2.3) when grown in soil with Pb content of 94,584–101,405 mg kg^?1. Plants accumulated 2,273–3,675 mg kg^?1 Pb in their shoots. The results suggest these Buddleja plants are suitable for use in the phytoremediation of Pb-contaminated soil.     

苏南经济快速发展区昆山市土壤铅形态含量及其影响因素

以地处苏南经济快速发展区的江苏省昆山市为典型区,采集水稻土及传统蔬菜地和保护栽培蔬菜地土壤样品126个,采用多元统计回归分析方法,定量研究几种因素对农田土壤各形态铅含量的影响。结果表明:土壤有效态铅平均含量为3.75 mg·kg-1,土壤全铅平均含量为27.42 mg·kg-1,土壤铅的活化率平均为15.64%。土壤各形态铅含量相对大小为残渣态(15.35 mg·kg-1)>有机质结合态(6.68 mg·kg-1)>铁锰氧化物结合态(4.27 mg·kg-1)>碳酸盐结合态(0.76 mg·kg-1)>可交换态(0.36 mg·kg-1),残渣态含量明显高于其他形态,占49.79%。pH是影响可交换态铅含量和铁锰氧化物结合态铅含量的最主要因素,均达极显著负相关水平。全铅含量是影响碳酸盐结合态铅含量和残渣态铅含量的最主要因素,达极显著正相关水平。有机质含量是影响有机质结合态铅含量的最主要因素,达极显著正相关水平。pH也是影响有机质结合态铅含量的重要因素。     

Potential of Borago officinalis, Sinapis alba L. and Phacelia boratus for Phytoextraction of Cd and Pb from Soil

Heavy metal phytoextraction is a soil remediation technique, which makes use of plants in removing contamination from soil. The plants must thus be tolerant to heavy metals, adaptable to soil and climate characteristics, and able to take up large amounts of heavy metals. Most of the high biomass productive plants such as, maize, oat and sunflower are plants, which do not grow in cold climates or need intensive care. In this study three “weed” plants, Borago officinalis; Sinapis alba L. and Phacelia boratus were investigated for their ability to tolerate and accumulate high amounts of Cd and Pb. Pot experiments were performed with soil containing Cd and Pb at concentrations of up to 180 mg kg^?1 and 2,400 mg kg^?1 respectively. All three plants showed high levels of tolerance. Borago officinalis; and Sinapis alba L. accumulated 109 mg kg^?1 and 123 mg kg^?1 Cd, respectively at the highest Cd spiked soil concentration. Phacelia boratus reached a Cd concentration of 42 mg kg^?1 at a Cd soil concentration of 100 mg kg^?1. In the case of Pb, B. officinalis and S. alba L. displayed Pb concentrations of 25 mg kg^?1 and 29 mg kg^?1, respectively at the highest Pb spiked soil concentration. Although the Pb uptake in P. boratus reached up to 57 mg kg^?1 at a Pb spiked soil concentration of 1,200 mg kg^?1, it is not suitable for phytoextraction because of its too low biomass.