Pb Isotopic Tracing Research Articles

Geochemical accumulation and source tracing of heavy metals in arable soils from a black shale catchment, southwestern China

Heavy metal enrichment in soils has been linked to the weathering of lithologies with high geochemical backgrounds, such as black shale. Therefore, this study conducted a typical sampling of surface soils in a black shale catchment in southwestern China to characterize the accumulation and sources of the heavy metals As, Cd, Co, Cr, Cu, Ni, Pb, Zn, Mo and Tl. Elevated concentrations of most heavy metals in the soils underlain by black shale are determined to exceed the regional soil background values, even the risk screening values, especially for Mo, As and Cd. Sequential extraction analysis, together with previous results, reveals that most heavy metals in soils are mainly bound in the residual fraction (> 65 %) as a result of the fixation of stable aluminosilicates (e.g., clay minerals). In contrast, Cd mainly occurs in relatively labile proportions as exchangeable (24.42 %), carbonate (24.48 %) and Fe/Mn oxide fractions (26.60 %) due to the non-specific adsorption of soil colloids and the precipitation of carbonates and Fe/Mn oxides. Pb isotopic tracing and APCS/MLR receptor model suggest that heavy metals in the urban surface soils (SG1) have a mixed source of black shale weathering, vehicle exhaust and agricultural input, while heavy metals in the rural surface soils (SG2) are a geogenic source of black shale weathering. Overall, this study provides new insights into contamination management, land use planning and health risk assessment in regions with high geochemical backgrounds.

Lead isotopic fingerprinting as a tracer to identify the sources of heavy metals in sediments from the Four Rivers’ inlets to Dongting Lake, China

In this study, Pb isotopic composition of bulk sediments and 1 M HCl leachates/residues of samples from the Four Rivers’ inlets to Dongting Lake (China) was determined to identify and differentiate the source of Pb inputs. Results highlighted that Xiangjiang river (XY-QS) sediments were highly enriched in Pb with less radiogenic Pb isotopes (e.g., 206Pb/207Pb ratios of 1.1830 ± 0.003), indicating the predominance of anthropogenic Pb inputs. In contrast, sediments of the Zijiang, Yuanjiang and Lishui rivers (ZD-LH) were moderately enriched in Pb and exhibited more radiogenic Pb (e.g., 206Pb/207Pb ratios of 1.1880 ± 0.008). Results from 1 M HCl extraction of XY-QS sediments illustrated that anthropogenic Pb was removed, which resulted in differentiation of 206Pb/207Pb isotope ratios between leachates (1.1740 ± 0.005) and residues (1.1846 ± 0.008), however, this difference was not observed in ZD-LH sediments (leachates: 1.1887 ± 0.009; residues: 1.1887 ± 0.008). Residual Pb isotope ratios suggested that Pb isotopic composition of lithologically inherited Pb in inlet sediments was similar, which was attributed to mixing, hydrological sorting, and averaging of different Pb sources from diverse geological settings. Pb isotopic tracing showed that Pb in XY-QS sediments resulted from the mixing of two end member sources, an anthropogenic source (less radiogenic Pb) from downstream ore smelting and upstream ore mining activities (53%) and a lithological source (37%) from granite through weathering. In contrast, Pb in ZD-LH sediments resulted from the mixing of multiple sources including Pb from upstream mining activities (20%), coal combustion (20%), and lithologically inherited Pb (60%) while surface sediments from the Yuanjiang river contained Pb from diesel oil usage (50%). Results from this study highlight the utility of a Pb isotope approach for identifying and differentiating Pb source inputs in diverse sediments from the Four River inlets to Dongting Lake (China).

Distribution of Pb isotopes in different chemical fractions in bed sediments from lower reaches of the Xiangjiang River, Hunan province of China

This paper reports Pb isotopes in different fractions following the three step BCR and 1 M HCl extractions on river sediments from lower reaches of the Xiangjiang river in China, and highlights the importance of Pb isotopes in heavy metal contamination assessment. Lead concentrations and Pb isotopes in bulk sediments and sediment fractions (leachates and residues) from the river were analysed using ICP-MS techniques. Results showed that sediments were highly enriched with Pb with enrichment factors >5.5, while Pb in sediments was dominated by reducible and residual Pb fractions, residing mainly in Fe-oxide and silicate minerals. Pb isotopes in sediments was characterized by radiogenic Pb produced from the decay of uranium and thorium with 206Pb/207Pb ratios of 1.1744 for less radiogenic Pb and 1.1816 for more radiogenic Pb. The leachates and residues from BCR extraction generally had similar Pb isotope compositions, of which the 206Pb/207Pb ratios were 1.1798 ± 0.002 and 1.1844 ± 0.008 respectively. Differentiation of Pb isotopes between BCR leachates and residues was insignificant. However, differentiation between leachates and residues using 1 M HCl extraction was significant, as shown by average 206Pb/207Pb ratios of 1.1746 ± 0.005 and 1.1858 ± 0.008 for leachates and residues respectively. Pb isotopic tracing suggests that Pb in sediments from Zhuzhou section arose from the mixing of anthropogenic Pb from coal combustion (39%) and mining-smelting for Pb-Zn ores (58%); while Pb in sediments from Xiangtan, Changsha and Xiangyin sections arose from the mixing of anthropogenic Pb from mining-smelting for Pb-Zn ores (54%), and lithologically inherited Pb from granite weathering (35%) with a small amount of contribution from coal combustion (10%). The present study suggests that the BCR extraction scheme was not appropriate for ecological risk assessment of heavy metal contamination in mining-impacted (ore-Pb dominated) river sediments.

Source identification of the geochemical anomaly from the fine-grained soil survey in the Nuheting sandstone-type uranium deposit, Erlian Basin, north China

Sedimentary basins in the arid areas of northern China have great potential to aid the discovery of new sandstone-type uranium deposits. A fine-grained (<75 μm) soil survey covering an area of approximately 6400 km2 has been undertaken to explore the concealed sandstone-type uranium deposit in Erlian Basin, north China. Displaying an obvious geochemical anomaly, the Nuheting (NHT) sandstone-type uranium deposit has been chosen for detailed studies of the source of geochemical anomaly, using lead (Pb) isotopic tracing and nanoparticle observation. Fine-grained soils are divided into three groups according to their spatial distance to the NHT uranium deposit which are soils above deposit, proximal soils and distal soils. Using analysis of variance (ANOVA), Pb isotope ratios of these soils show significant difference between proximal and distal samples. Deep mineralization and regional faults may give rise to the difference of radiogenic Pb isotopes. In addition, the widely observed Mo-bearing nanoparticles provide evidence that fine-grained soils contain signature of deep uranium ore. The characteristics of Pb isotope and nanoparticles indicate that accumulation of radiogenic Pb isotopes in the fine-grained soils is resulted from the concealed NHT uranium deposit. The transport and evaporation of groundwater has led to the vertical migration of geochemical signature from the deep to the surface. The fine-grained soil survey shows promise as an effective exploration technique for the sandstone-type uranium deposit in arid areas.

Geochemistry, risk assessment, and Pb isotopic evidence for sources of heavy metals in stream sediments around the Ulukışla Basin, Niğde, southern Turkey

Concentrations of selected elements (Al, Fe, Mn, Mo, As, Cd, Cu, Cr, Ni, Co, Pb, Sb, and Zn) and Pb isotope ratios were determined in 53 sediments from Alihoca, Gümüş, Horoz, and Çakıt streams around the south-central Taurides (Ulukışla Basin), Niğde, which is a known mining province in Turkey. Several pollution and risk assessment indices were used to assess possible heavy metal pollution in the stream sediments and the associated potential ecological risks. Concentrations of As, Cd, Cu, Cr, Ni, Co, Pb, Sb, and Zn were elevated in the streams located near ancient mines, active mines, and slag piles in the area, suggesting an influence from mining activities. The pollution assessment indices indicated that the sediments were significantly polluted by As, Cd, Sb, Zn, and Pb and moderately polluted by Cu, Ni, Cr, and Co. The sediments show very high potential ecological risk with As, Cd, Sb, and Pb as the principal contributors. Ni, Cr, As, Pb, Zn, and Cd exceeded the probable effect concentrations in most of the samples implying that their concentrations may frequently affect sediment-dwelling organisms. Multivariate statistical analyses indicate that the accumulation of heavy metals in the stream sediments is due to an interplay of anthropogenic activities (mining and agrochemical application) and geogenic processes (weathering of bedrocks and supergene alteration of base metal-rich mineralization). Pb isotopic tracing indicates that total Pb in the sediments (206Pb/207Pb = 1.09–1.29) is primarily from weathering and dissolution of ultrapotassic rocks (206Pb/207Pb up to 1.20) and galena (206Pb/207Pb up to 1.21) from the Pb-Zn-Au deposits in the area with some anthropogenic input from mine slag piles (206Pb/207Pb = 1.10).

The mobility of thallium in sediments and source apportionment by lead isotopes

Thallium (Tl) is a very toxic heavy metal. As a part of ongoing investigations, the mobility, sources and fate of Tl were investigated for sediments from a watershed in the northern part of the Pearl River, South China, whose catchment has been seriously impacted by large-scale PbZn smelting activities onshore. A wide dispersion of severe Tl contamination was observed throughout the depth profiles. A modified IRMM (Institute for Reference Materials and Measurements, Europe) sequential extraction procedure of a selected depth profile uncovered an exceptionally high enrichment of Tl in geochemically-mobile fractions (i.e., weak-acid-exchangeable, reducible and oxidizable fractions), on average 5.94 ± 2.19 mg/kg (74.6% ± 5.1% of the total Tl content) not only in the surface sediments but also in deep sediments. The proximal quantitative source apportionment using Pb isotopic fingerprinting technique indicated that a majority (80%–90%) of Tl contamination along the depth profiles is anthropogenically derived from the PbZn smelting wastes. The results highlight the pivotal role of smelting activities in discharging huge amounts of geochemically-mobile Tl to the sediments down to approximately 1 m in length, which is quantitatively evidenced by Pb isotopic tracing technique. Lead isotopes combined with distribution of Tl and Pb contents identified a potential marker for a point source from the PbZn smelter in the river catchment, which also provides a theoretical framework for source apportionment of metal contamination in a larger river/marine system and in other sulfide mining/smelting areas likewise.

Tracing environmental lead sources on the Ao mountain of China using lead isotopic composition and biomonitoring

Atmospheric lead (Pb) and other trace metals can transport over long distance and deposit on remote alpine ecosystems. In this work, the soil profiles, litter and dominant mosses along a large altitude were collected on Ao Mountain, Central China, to obtain the spatial distributions of Pb in these materials, decipher the possible factors controlling the distribution, and quantitatively distinguish the natural versus anthropogenic sources of Pb through the Pb isotopic tracing and biomonitoring. The results show that soil Pb concentrations (mg/kg) decreased significantly with depth, and they were markedly higher in the O (42.6 ± 2.7) and A (36.4 ± 2.2) horizons than in the litter (7.20 ± 1.9) and mosses (28.0 ± 3.9). The Pb enrichment in the surface soils (O and A horizons), litter and mosses existed in the relatively high altitudes, which was attributed to the influences from atmospheric wet deposition, plants, soil physicochemical properties and human activity. The Pb isotopic ratios identified the Pb sources as originating mainly from Chinese coal combustion, mining and smelting. Atmospheric Pb from southeastern, southwestern and northwestern regions could be deposited in the alpine ecosystem by long distance atmospheric transport. The anthropogenic Pb reached over 50% in the O and A horizons, and over 70% in the litter and mosses, which corresponded to the concentrations of 26.9, 17.7, 5.92 and 21.2 mg/kg, respectively. The results indicate that the mutual effects of climate and regional human activity could increase the Pb accumulation in remote alpine ecosystems.

Human health risk assessment and source analysis of metals in soils along the G324 Roadside, China, by Pb and Sr isotopic tracing

Metal pollution was studied along the G324 roadside in Xiamen, southeast China, based on the soil profile and the different distances from the road. A range of metal concentrations were determined using ICP-MS and evaluated using enrichment factors, human health risk assessment and potential ecological risk index. The pollution sources in the soil were examined using multivariate statistical analysis and Pb-Sr isotope tracing technology. The results showed that the high soil metal contents were mainly distributed at the depth of 0-30m, and the distance from the highway of 0-7m. In both topsoils and profile soils, Cd had the biggest ecological risk. According to the human health risk assessment, there is no risk for human health in the roadside. The multivariate statistical analysis showed that the surface soil was clearly affected by the traffic factors; however, the profile soil was not only influenced by the traffic factors, but also by the industrial production. The results of analysis of Pb isotopic compositions showed that in the profile, the binary mixing of two major Pb sources (parent material and vehicle exhaust), the contribution rates were 78.29% and 21.71% on average, respectively. In topsoil, at a distance of 0-7m away from the roadside, the two sources were also parent material (75.96%) and vehicle exhaust (24.04%). At 31-300m from the roadside, the main sources were parent material (73.85%) and coal (26.15%). The combined Pb-Sr isotope tracing pollution sources confirm the Pb isotope analysis.

Monitoring steel bridge renovation using lead isotopic tracing

Monitoring removal of lead (Pb) paint from steel structures usually involves analysis of environmental samples for total lead and determination of blood Pb levels of employees involved in the Pb paint removal. We used high precision Pb isotopic tracing for a bridge undergoing Pb paint removal to determine if Pb in the environmental and blood samples originated from the bridge paint. The paint system on the bridge consisted of an anti-corrosive red Pb primer top-coated with a Micaceous Iron Oxide (MIO) alkyd. Analysis of the red Pb primer gave uniform isotopic ratios indicative of Pb from the geologically-ancient Broken Hill mines in western New South Wales, Australia. Likewise waste abrasive material, as anticipated, had the same isotopic composition as the paint. The isotopic ratios for other samples lay on 2 separate linear arrays on a207Pb/204Pb versus 206Pb/204Pb diagram, one largely defined by gasoline and the majority of the ambient air data, and the other by data for one sample each of gasoline and ambient air and underwater sediments. Isotopic ratios in background ambient air samples for the project were characteristic of leaded gasoline. Air sampling during paint removal showed a contribution of paint Pb ranging from about 20 to 40%. Isotopic ratios in the blood of 8 employees prior to the commencement of work showed that 6 of these had been previously exposed to the Broken Hill Pb possibly from earlier bridge paint removal projects. One subject appeared to have increased exposure to Pb probably from the paint renovations.

Chemical characteristics and Pb isotopic compositions of PM2.5 in Nanchang, China

In mid-September 2013, PM2.5 samples were collected at six sites in Nanchang, Jiangxi Province, China, to quantify nine water-soluble ions (Ca2+, Mg2+, K+, Na+, NH4+, SO42−, Cl−, F−, NO3−), 29 trace elements (Ba, Zn, Pb, Ni, Mo, Cr, Cu, Sr, Sb, Rb, Cd, Bi, Zr, V, Ga, Li, Y, Nb, W, Cs, Tl, Sc, Co, U, Hf, In, Re, Be, and Ta), and to characterize Pb isotopic ratios (207Pb/206Pb, 208Pb/206Pb, and 207Pb/204Pb) for identifying the main source(s) of Pb. The results showed that the average daily PM2.5 concentration (53.16±24.17) μg/m3 was within the secondary level of the Chinese ambient air quality standard. The combined concentrations of SO42−, NH4+, and NO3− to total measured water-soluble ion concentrations in PM2.5 ranged from 79.40% to 95.18%, indicating that anthropogenic sources were significant. Coal combustion and vehicle emissions were both contributors to PM2.5 based on the NO3−/SO42− ratios. Wushu School experienced the lowest concentrations of PM2.5 and most trace elements among the six sampling sites. Enrichment factor results showed that Tl, Cr, In, Cu, Zn, Pb, Bi, Ni, Sb, and Cd in PM2.5 were affected by anthropogenic activities. Cluster analysis suggested that Cd, Sb, Pb, Re, Zn, Bi, Cs, Tl, Ga, and In were possibly related to coal combustion and vehicle exhaust, while Ni, Nb, Cr, and Mo may have originated from metal smelting. Pb isotopic tracing showed that coal dust, cement dust, road dust and construction dust were the major Pb sources in PM2.5 in Nanchang. Combined, these sources contributed an average of 72.51% of the Pb measured, while vehicle exhaust accounted for 27.49% of Pb based on results from a binary Pb isotope mixed model.

Characteristics and Source Apportionment of Metals in the Dustfall of Quanzhou City

Concentrations of 23 metal elements in the dustfall collected from different functional areas of Quanzhou City, China, were determined. Several methods were applied to assess the enrichment degree, pollution level and potential ecological risk of the above elements. The sources of the above elements were analyzed based on the multivariate statistical analysis combining Pb and Sr isotopic tracing technology. The results showed that the concentrations of metals in the dustfall presented significant spatial difference. The results of enrichment factor and geo-accumulation index indicated that Cd, Hg, Zn, Ca, Pb, Cu, Ni and Sr showed relatively higher enrichment degree and pollution level. The results of ecological risk index showed that the comprehensive ecological risk of heavy metals was very high in the dustfall of all functional areas with the sequence of industrial area>heavy traffic area >commercial area >residential area >scenic area >agricultural area. Cd and Hg showed extremely high potential ecological risk, and they contributed 95.56% to the comprehensive potential ecological risk index. The multivariate statistical analysis demonstrated that the elements of V, Fe, Ba, Bi, Ni, Sr, Pb, Cs, Sc, Zn, Cd were mainly from industrial and vehicle emissions; Th, U, Rb, Y, Ti were mainly derived from soil dust; Li, Mn, Cu, Hg, Cr, Co, Ca were mainly from coal combustion. The contribution ranges of parent soil, coal combustion and vehicle emission to the Pb in the dustfall were 29.41%-64.00%, 22.53%-60.48% and 3.13%-13.47%, respectively, as calculated by a ternary hybrid model; The plots of 87Sr/86Sr vs 1/Sr showed that Sr in the dustfall was dominated by coal combustion and vehicle emission.

Heavy metal pollution and Pb isotopic tracing in the intertidal surface sediments of Quanzhou Bay, southeast coast of China

Concentrations of 16 heavy metals and Pb isotopic ratios in the intertidal surface sediments of Quanzhou Bay were determined to study the pollution level of heavy metals and the sources of Pb. The results showed that most concentrations of Cd, Sn, Mn, Cu, Zn, Cr, Pb, Hg, Ni, Co, Cs, Fe and V were higher than the background values, while most concentrations of Ti, Sb and Sr were lower than the background values. The mean concentrations of Cu, Zn, Pb, Cr and Cd exceeded the first-grade criteria of Chinese marine sediment quality. The geo-accumulation indexes revealed that the sediments had been polluted by some heavy metals. The results of Pb isotopic tracing indicated that the total Pb in the sediments were mainly from parent material, industrial emission and vehicle exhaust with the mean contributions of 38.2%, 51.3% and 10.5%, respectively, calculated by a three-end-member model of Pb isotopic ratios.

Lead distribution and possible sources along vertical zone spectrum of typical ecosystems in the Gongga Mountain, eastern Tibetan Plateau

A total of 383 samples from soil, plant, litterfall and precipitation in four typical ecosystems of Gongga Mountain were collected. Pb concentrations of samples were measured and analyzed. The results showed mean Pb concentrations in different soil layers were in the order of O > A > C, and mean Pb concentrations of the aboveground parts of plant was 3.60 ± 2.54 mg kg−1, with the minimum value of 0.77 mg kg−1 and the maximum value of 10.90 mg kg−1. Pb concentrations in soil's O-horizon and A-horizon showed a downward trend with increasing elevation (the determination coefficient R2 was 0.9478, 0.7918 and 0.9759 respectively). In contrast to other soil layers, the level of Pb concentrations in O-horizon (incomplete decomposition) was significantly high. Litterfall decomposition, atmospheric deposition and the unique climate could be main factors leading high Pb accumulation in soil's O-horizon. What's more, significant correlation (R2 = 0.8126, P < 0.05) was found between Pb concentrations in fine roots and soil's A-horizon confirms that fine roots could adsorb and accumulate Pb materials in soil. In general, the fact that Pb inputted into the typical ecosystems in the Gongga Mountain via long-range transportation and deposition of the atmosphere from external Pb sources could be confirmed by the HYSPLIT model and the ratio of CPb/CAl in plants (leaves) and CPb/CAl in litterfall. The mining activities and increasing anthropogenic activities (tourism development) could be main sources of Pb in this area. In order to better understand Pb sources and eco-risks of these typical ecosystems, litterfall decomposition characteristics, biomass of productivity of forest ecosystem, Pb isotopic tracing among air mass, twigs, leaves, litterfall and O-horizon soil in this vertical belt should also be taken into consideration.

Atmospheric pollution in an urban environment by tree bark biomonitoring – Part II: Sr, Nd and Pb isotopic tracing

The harmful effect of manmade particles on natural processes and human health is documented by a large number of studies showing a positive correlation between particulate matter (PM) concentration and health effects. Diminution of this health risk necessitates among others the precise knowledge of the particle sources, their physical and chemical properties and their dissemination in the environment. Pb isotope ratios have been successfully used during the past decades as tracers of anthropogenic Pb disseminated in the biosphere. Here we show that tree bark biomonitoring with lead (Pb), strontium (Sr) and neodymium (Nd) isotope ratios as tracers allow a thorough analysis of the impacts of industrial and other anthropogenic emissions on the urban environment. This is the first comprehensive multi-isotope tracer study of atmospheric pollution in an urban environment allowing to identify and to integrate the different plume paths of emissions in a digital map system. This innovative approach might become an important tool for environmental management and policy-making processes dealing especially with risks and surveillance of air quality in the urban environment.

Application of Pb isotopic tracing technique to constraining the source of Pb in the West Lake Longjing tea

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 gradually 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 environmental media (soil, atmosphere, water) in Hangzhou. With the aggravation of Pb pollution, the Pb isotopic composition gradually changed from the natural background (soil residues) to the direction of automobile exhaust. This phenomenon 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.

Tracing the spatial distribution and mobility of metal/metalloid contaminants in Oxisols in the vicinity of the Nkana copper smelter, Copperbelt province, Zambia

The copper mining and smelting activities in the Copperbelt province (Zambia) left enormous pollution related to the disposal sites for mining/smelting waste (tailings, slags) and to the continuous deposition of smelter stack particulates in the soil systems. Topsoils in the vicinity of the Nkana copper smelter were studied in order to assess the spatial distribution of metal/metalloid contaminants (As, Co, Cu, Pb, Zn) in a 32-km 2 zone around the smelter ( n = 196 soil samples). The bulk concentrations of metal/metalloid contaminants were determined by ICP techniques, supplemented by the determination of the Pb isotopic composition of selected samples measured by quadrupole-based ICP-MS. The spatial distribution of the major contaminants indicated the highest contamination NW of the smelter stack, corresponding to the prevailing wind direction in the area. The highest metal/metalloid concentrations in the topsoils were: 255 mg As kg − 1 , 27,410 mg Cu kg − 1 , 606 mg Co kg − 1 , 480 mg Pb kg − 1 and 450 mg Zn kg − 1 . Lead isotopes helped to differentiate the extent of metallic pollution and indicated the mixing of three major pollution sources (given as 206Pb/ 207Pb ratios): smelting activities (1.19–1.28), petrol combustion (1.07–1.09) and regional background (deep soil horizons, ca. 1.35) To assess the vertical mobility of these inorganic contaminants, a 110-cm-deep profile in Oxisol in a highly polluted zone in the near vicinity of the Nkana smelter was sampled and studied by combination of bulk chemical analysis, sequential extraction procedure (SEP) and Pb isotopic tracing. Investigation of the soil profile indicated that the contamination is mostly located in the uppermost soil horizons enriched in organic matter (< 10 cm). Based on SEP, the isotopic composition and knowledge of smelter activities in the area, it was predicted that anthropogenic Pb (corresponding to a concentration of 1 mg kg − 1 , i.e., approx. 1.5% of total Pb) exhibited downward migration in the soil profile with estimated penetration rate of 1.36 cm year − 1 . Copper, being substantially bound in the exchangeable fraction, also showed significant mobility in the profile. As a result, the sources of anthropogenic emissions in the Kitwe smelting area represent an important source of mobile (and potentially bioavailable) metals.

Characteristics and genesis of Gangdese porphyry copper deposits in the southern Tibetan Plateau: Preliminary geochemical and geochronological results

Porphyry-type Cu (Mo, Au) deposits have been discovered along the Gangdese magmatic arc in the southern Tibetan Plateau. Extensive field investigations and systematic studies of geochemistry, S–Pb isotopic tracing, together with Re–Os and 40Ar/ 39Ar isotopic dating indicate that the mineralisation of the copper belt is genetically related to emplacement of late orogenic granitic porphyries during the post-collisional crustal relaxation period of the Late Himalayan epoch. These porphyries are petrochemically K-enriched and belong to shoshonitic to high-K calc-alkaline series. They display enrichment of large ion lithophile elements (LILE) Rb, K, U, Th, Sr, Pb and depletion of high field strength elements (HFSE) Nb, Ta, Ti and the heavy rare earth elements (HREE) and Y without Eu anomalies. These characteristics demonstrate that subduction played a dominant role in their petrogenesis and residual garnet was left in the magma sources. Pb isotope data show a linear correlation in the plumbotectonic framework diagram ranging from orogenic Pb in the eastern segment of the copper belt to mantle Pb in the western segment. These constitute a mixing line of the Indian Oceanic MORB with Indian Oceanic sediments and suggest that the porphyry magmas were dominantly derived from partial melting of subducted oceanic crusts mixed with a minor quantity of sediments and mantle wedge components. The Gangdese porphyry copper polymetallic belt has alteration characteristics and zonation typical of porphyry-type copper deposits which include potassic alteration (K-feldspathisation and biotitisation), silicification, sericitisation, and propylitisation. Mineralisation mainly occurs in strongly altered granitic cataclasite at the exo-contact with veinlet-disseminated textures. The porphyries themselves are weakly mineralised with disseminated pyrite and chalcopyrite. The copper deposits contain simple ore mineral associations consisting of chalcopyrite, pyrite, bornite, molybdenite, sphalerite and oxidised minerals of malachite, covellite and molybdite. During supergene oxidation, primary ores underwent secondary enrichment to form economic orebodies with Cu grade ranging from 1% to 5%. Ore sulphides of the copper belt display S and Pb isotopic compositions identical to the ore-bearing porphyries. Their δ 34S values vary between − 3.8‰ and + 2.4‰ and are typical of mantle sulphur. The 206Pb/ 204Pb, 207Pb/ 204Pb, and 208Pb/ 204Pb ratios vary in the ranges: 18.106 to 18.752, 15.501 to 15.638, and 37.394 to 39.058, respectively, and yielded radiogenetic lead-enriched signatures. Twelve molybdenite samples from the copper belt yielded isochron ages of 14.76 ± 0.22 Ma and 13.99 ± 0.16 Ma for the Nanmu and Chongjiang deposits and model ages of 13.5 to 13.6 Ma for the Lakang'e deposit. Meanwhile, 40Ar/ 39Ar isotopic dating of two biotite phenocrysts from the Chongjiang and Lakang'e deposits give plateau ages of 13.5 ± 1.0 Ma and 13.42 ±0.10 Ma, respectively. During the geodynamic evolution of the Gangdese collision-orogenic belt, intrusion of the ore-bearing porphyries took place just before the rapid uplift and E–W extension of the southern Plateau. And the ore-forming process may have occurred simultaneously with the uplift and extension (14 ± 0.1 Ma).

Melt components derived from a subducted slab in late orogenic ore-bearing porphyries in the Gangdese copper belt, southern Tibetan plateau

A porphyry-type Cu (Mo, Au) polymetallic ore belt extends in an E–W direction for >400 km along the Gangdese magma arc in the southern Tibetan plateau. Extensive field investigations and systematic geochemical study, combined with S and Pb isotopic tracing, indicate that Cu polymetallic mineralization of the copper belt is genetically related to late orogenic granitic porphyries formed in a late Himalayan crustal extension stage (18–14 Ma). Geochemistry of the porphyries shows the essential characteristics of adakite and suggests a dominant role of subduction-related components in their genesis. The genesis of these ore-bearing porphyries is mainly related to melt components derived from subducted slabs and has little relationship with fluids released from them. Pb isotopes show a clear linear array in the plumbotectonics model and are manifested by a progressive variation from orogenic Pb in the east segment of the copper belt to mantle Pb in the west segment, forming a mixing line of Indian Oceanic MORB and Indian Oceanic sediments. This suggests that the porphyry magma dominantly originated from partial melting of subducted oceanic crust and was mixed with a minor melts of sediments and mantle wedge components.

U-Pb isotopic geochemistry of the post-collisional mafic-ultramafic rocks from the Dabie Mountains

The U-Pb isotope geochemical study of the pyroxenite-gabbro intrusion in the Dabie Mountains shows that the post-collisional mafic-ultramafic rocks of the Dabie Mountains are characterized by relative high Pb contents, low U contents and low U/Pb ratios. These characters may be results of interaction between lithosphere or depleted asthenospheric mantle (DMM) and lower crust, but have nothing to do with mantle plume and subducted continental crust. It was first observed that some samples with lower 206 Pb/ 204 Pb and higher 207 Pb/ 204 Pb ratios show typical characters of the LOMU component. The Pb, Sr, and Nd isotopic tracing shows that three components are needed in the source of the Zhujiapu pyroxenite-gabbro intrusion. They could be old enriched sub-continental lithospheric mantle (LOMU component), lower crust and depleted asthenospheric mantle. The crust-mantle interaction process producing primitive magma of post-collisional mafic-ultramafic rocks in the Dabie Mountains could be described by a lithospheric delamination and magma underplating model. After continent-continent collision, delamination of the thickened lithosphere induced the upwelling of depleted asthenospheric mantle, which caused partial melting of asthenospheric mantle and residual sub-continental lithospheric mantle. The basaltic magma produced in this process underplated in the boundary between the crust and mantle and interacted with lower crust resulting in the geochemical characters of both enriched lithospheric mantle and lower crust.

Application of Pb isotopic mapping to environment evaluation in China

Quantitative criterion of Pb pollution sources and levels from Pb isotopic tracing must depend on the establishment of a natural Pb isotopic background. Lead isotopic mapping for Continental China and the neighborhood sea areas is being completed. Seven major isotopic provinces in the continent (Cathaysia, Indochina, Yangtze, North China, Northeast China, North Xinjiang and Tibet) have been identified. The Pb isotopic mapping in the South China Sea shows two depositing areas; sediments from the Red River is related to the Indochina geochemical province; sediments from the Pearl River system is related to the Cathaysia geochemical province. Pb isotopic evidence indicates that the major Pb pollution sources of aerosols in the Eastern China are from local Pb–Zn–Cu resource consumption in various industries. The Pb pollution from aerosols, eolian dusts, and acid leachable components in soils and sediments around the South China Sea shows two major sources: application of lead metal in various industries and automobile exhausts.