Lead isotopes combined with a sequential extraction procedure for source apportionment in the dry deposition of Asian dust and non-Asian dust

Differentiating anthropogenic effects from natural metal(loid) levels in residential soil near a zinc smelter in South Korea

Metal(loid)s pose a significant hazard due to inherent toxicity. Individuals are particularly exposed to metal(loid)s in soil through direct or indirect contact. Identifying metal(loid) sources in soil is required for exposure mitigation to anthropogenic metal(loid)s, while metal(loid)s are natural constitutes of soil. Metal(loid) concentrations and Pb isotopes were determined in residential soil profiles impacted by a Zn smelter to distinguish the anthropogenic effect from natural levels. One hundred sixty-nine core soil samples were collected from depths down to 5.5 m below ground level at 19 sites and were divided into Zn-Cd-As- and As-contaminated groups based on the worrisome level (WL) of soil contamination. The Zn-Cd-As-contaminated group (n = 62) was observed at depths < 1 m, showed high Zn levels (mean of 1168 mg/kg) and Cd and As frequently exceeding WLs, and had low 206Pb/207Pb ratios close to the Zn smelter. In contrast, the As-contaminated group (n = 96) was observed at depths > 1 m, did not have other metals exceeding WLs, and showed a wide range of 206Pb/207Pb ratios far away from the Zn smelter. The results indicated that the pollution sources of Zn-Cd-As- and As-contaminated soils were fugitive dust emissions from smelter stacks and geology, respectively. The metal(loid)s in host rock set geochemical baselines in soil profiles, while smelting activities affected the upper layers over 50 years. This study demonstrated the effectiveness of utilizing the vertical distribution of metal(loid) concentrations and Pb isotopes in soil profiles for distinguishing between anthropogenic and geogenic origins, in combination with baseline assessment.

Analytical study on heavy metal output fluxes and source apportionment of a non-ferrous smelter in southwest China

Abandoned Pb/Zn smelters are often accompanied by a large amount of smelting slag, which is a serious environmental problem. Previous studies have demonstrated that slag deposits pose an environmental threat even if the smelters are shut down. Herein, a Pb/Zn smelter and its impacted zone in GeJiu, Yunnan, China were selected as the study area. The risk and source apportionment of heavy metals (HMs) in the soil of the impacted zone were systematically studied. Based on the hydrogeological features, the migration path and output fluxes of the HMs released from smelting slag to the impacted zone were investigated. The HM contents (Cd, As, Zn, Pb, and Cu) in the soil substantially exceeded the screening values of the Chinese soil standard (GB15618-2018). Based on the results of the Pb isotopic and statistical analyses for source apportionment, the contaminated sites and agricultural irrigation water had a large impact on the HMs of soil. The hydrological analysis results showed that runoff, as an HM migration path under rainfall, continued to affect the environment. The water balance calculations using the Hydrologic Evaluation of Landfill Performance model showed that the rainfall was distributed on site as follows: evaporation (57.35%), runoff (32.63%), and infiltration (10.02%). Finally, the output fluxes were calculated in combination with the leaching experiment. As, Zn, Cd, Pb, and Cu runoff had the output fluxes of 6.1 × 10^-3, 4.2 × 10^-3, 4.1, 1.4 × 10^-2, and 7.2 × 10^-4 mg/kg/y, and infiltration of 1.9 × 10^-3, 1.3 × 10^-3, 1.3, 4.0 × 10^-4, and 2.2 × 10^-4 mg/kg/y, respectively. Therefore, this study offers theoretical and scientific recommendations for effective environmental management and engineering remediation.

Pb Content, Risk Level and Primary-Source Apportionment in Wheat and Rice Grains in the Lihe River Watershed, Taihu Region, Eastern China

This study detailed a complete research from Lead (Pb) content level to ecological and health risk to direct- and primary-sources apportionment arising from wheat and rice grains, in the Lihe River Watershed of the Taihu region, East China. Ecological and health risk assessment were based on the pollution index and US Environmental Protection Agency (EPA) health risk assessment model. A three-stage quantitative analysis program based on Pb isotope analysis to determine the relative contributions of primary sources involving (1) direct-source apportionment in grains with a two-end-member model, (2) apportionment of soil and dustfall sources using the IsoSource model, and (3) the integration of results of (1) and (2) was notedly first proposed. The results indicated that mean contents of Pb in wheat and rice grains were 0.54 and 0.45 mg/kg and both the bio-concentration factors (BCF) were <<1; the ecological risk pollution indices were 1.35 for wheat grains and 1.11 for rice grains; hazard quotient (HQ) values for adult and child indicating health risks through ingestion of grains were all <1; Coal-fired industrial sources account for up to 60% of Pb in the grains. This study provides insights into the management of grain Pb pollution and a new method for its source apportionment.

Mobility of metal(loid)s in roof dusts and agricultural soils surrounding a Zn smelter: Focused on the impacts of smelter-derived fugitive dusts

The mobility of Zn, Cd, Pb, Cu, and As was assessed in an atmospheric environment and soil system near a Zn smelter by performing sequential extraction as well as Pb isotopic and mineralogical analyses for fugitive and roof dusts and agricultural soils. Transmission electron microscopy observations with selected area electron diffraction patterns confirmed that micron-sized roof dusts originated from the Zn smelter. Both fugitive and roof dusts contained zincite, massicot, franklinite, anglesite, and willemite. The sequential extraction of the fugitive dust from the Zn smelter stacks showed that Zn, Cd, and Pb were predominantly bound to the exchangeable (FI), carbonate (FII), and reducible (FIII) fractions, whereas Cu and As were significantly associated with the residual (FV) fraction and had low mobility. The estimation of remobilized concentrations of Zn, Cd, and Pb bound to labile fractions (FI and FII) in the fugitive dust implied their severe environmental and human health risks. In contrast, the studied metal(loid)s in the roof dust had low mobility except for Pb, implying the insignificant risks of roof dusts, although anthropogenic dusts from the Zn smelter significantly impacted FV as well as the non-residual fractions based on the Pb isotopic compositions of geochemical fractions. Similarly, the mobility and bioavailability of the studied metal(loid)s were low in agricultural soils, except for Cd, suggesting a low adverse effect on crops cultivated in the soil. The decrease in labile Cd fractions with depth indicated that the agricultural soil did not retain anthropogenic Cd in the soil subsurface. The mineralogical investigation combined with sequential extraction revealed that the different mobility of Zn, Cd, and Pb between fugitive dusts, roof dusts and agricultural soils resulted from the different solubility of metal-bearing minerals, e.g., zincite, willemite, simonkolleite which were not detected in the residuals of the fugitive dust collected after FIII extraction.

A comprehensive review of biogeochemical distribution and fractionation of lead isotopes for source tracing in distinct interactive environmental compartments

Lead (Pb) is a non-essential and extremely noxious metallic-element whose biogeochemical cycle has been influenced predominantly by increasing human activities to a great extent. The introduction and enrichment of this ubiquitous contaminant in the terrestrial-environment has a long history and getting more attention due to its adverse health effects to living organisms even at very low exposure levels. Its lethal-effects can vary widely depending on the atmospheric-depositions, fates and distribution of Pb isotopes (i.e., ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb &²⁰⁸Pb) in the terrestrial-environment. Thus, it is essential to understand the depositional behavior and transformation mechanism of Pb and the factors affecting Pb isotopes composition in the terrestrial-compartments. Owing to the persistence nature of Pb-isotopic fractions, regardless of ongoing biogeochemical-processes taking place in soils and in other interlinked terrestrial-compartments of the biosphere makes Pb isotope ratios (Pb-IRs) more recognizable as a powerful and an efficient-tool for tracing the source(s) and helped uncover pertinent migration and transformation processes. This review discusses the ongoing developments in tracing migration pathway and distribution of lead in various terrestrial-compartments and investigates the processes regulating the Pb isotope geochemistry taking into account the source identification of lead, its transformation among miscellaneous terrestrial-compartments and detoxification mechanism in soil-plant system. Additionally, this compendium reveals that Pb-pools in various terrestrial-compartments differ in Pb isotopic fractionations. In order to improve understanding of partition behaviors and biogeochemical pathways of Pb isotope in the terrestrial environment, future works should involve investigation of changes in Pb isotopic compositions during weathering processes and atmospheric-biological sub-cycles.

Assessment of trace metal pollution in roof dusts and soils near a large Zn smelter

The spatial extent of dust emissions from a Zn smelter was assessed based on metal concentrations in roof dust samples. In addition, the vertical mobility of metal loads in soils was assessed from metal concentrations and Pb isotopic compositions. Moreover, the source apportionment of metals in the roof dusts and soils was estimated using Pb isotopes. A total of 13 roof dust and 11 smelter dust samples were collected respectively from residential houses and smelter stacks. The vertical distribution in soils was assessed at 10 cm intervals in four sites along the predominant wind direction. High metal concentrations were found in the roof dusts, which were enriched in Zn, Pb, Cd, and Cu by a factor of 48-937, 13-169, 161-3400 and 10-135, respectively, compared to the regional background values of soils, depending on the distance from the smelter. Horizontal extents of the airborne metal transport were estimated to exceed the impact radius (<4 km) calculated by a numerical model. As for soils, the metal concentrations were high in the surface layer and decreased abruptly with depth. The vertical extent of the metal contamination was found up to 60 cm. Considering the operational period of the smelter, the Pb migration rate was 0.4-1.3 cm/year and the farmlands showed higher penetration rates than the other sites, probably due to agricultural practices. The Pb isotope compositions for the contaminated soils lay on a mixing line between the anthropogenic Pb of the smelter and the geogenic Pb of the background soils, which confirmed that the emission and deposition of the airborne particles produced by the smelter contributed to 49-83% of trace metals in the surface soils. Similarly, the Pb isotopic compositions of the roof dusts indicated that most of Pb was derived from the smelter, in particular, from the casting and leaching stacks.

Lead isotopes combined with geochemical and mineralogical analyses for source identification of arsenic in agricultural soils surrounding a zinc smelter

As-contaminated soil samples were chosen to identify As sources near a Zn smelter where Zn contamination in soils was found to be of smelter origin. Based on the As concentrations and Pb isotopic compositions, high As levels in soils were originated from the geogenic source. There was no consistent trend in As concentrations with either depth or distance from the smelter, while the Pb isotopic compositions in soils varied regardless of As levels and were quite different from those of smelter origin. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) suggested that the high As concentrations were due to arsenopyrite and its alteration minerals, which were easily found but heterogeneously distributed within host rocks. A detailed investigation of As levels and Pb isotropic compositions along the predominant wind direction also supported that the As contamination was of geogenic origin unlike the Zn contamination. The atmospheric emissions from the smelter increased the Zn concentrations and decreased the ²⁰⁶Pb/²⁰⁷Pb ratios at surface layers, while the As concentrations occasionally exceeded the worrisome level at deep layers. According to the Pb isotropic compositions, about 21% of the As-contaminated soils were impacted by the smelter, in particular at the surface layer.

The vertical migration and speciation of the Pb in the paddy soil: A case study of the Yangtze River Delta, China

Migration of Pb in the soil can be enhanced by acidification and frequent change of environmental condition. The paddy soil, where the environmental condition such as redox fluctuates frequently due to soil submergence and drainage, may offer a favorable condition for Pb migrating to deeper soil and further contaminate groundwater by leaching or irrigation. To date, not much is known about how quickly Pb migrates in the soil and the relevant transformation of Pb. We use long-term soil profile monitoring, sequential extraction and isotopic measurement to examine the temporal change of concentrations and isotopic ratios of Pb associated with different soil components in the paddy soil profile in the Yangtze River Delta area during 2011-2017. We find that Pb vertical migration in the paddy soil is faster. Pb in the shallow soil may migrate downward up to 60 cm during six years. The migration of Pb is dominated by the carbonate, and secondarily influenced by Fe/Mn oxides. Our results also imply that the mechanism of Pb migration in soils is changing. The mechanism which is now characterized as the carbonate-dominating will be replaced as the Fe/Mn oxides-dominating in the near future as the carbonate in shallow soil is becoming depleted.

Characteristic concentrations and isotopic composition of airborne lead at urban, rural and remote sites in western Korea

Anthropogenic Pb emitted from East Asia, particularly China, is often long-range transported to the east by the prevailing westerlies. To characterize the geographical properties of varying atmospheric Pb concentrations by transboundary and domestic source(s)-related Pb in Korea, closely adjacent to China, the Al and Pb concentrations and the stable Pb isotopic composition were determined in the total suspended particles (TSP) collected at urban (IC), rural (TA), and remote background (JJ) sites in western Korea from August 2015 to October 2016. The annual average Pb concentrations were significantly higher in urban and rural areas (IC, 16.2 ng m^-3 and TA, 11.1 ng m^-3) than in remote area (JJ, 6.41 ng m^-3), showing pronounced seasonal variations with relatively higher concentrations in winter and spring and lower concentrations in summer and autumn. Significantly high enrichment factors (EF) for Pb indicate that anthropogenic contributions are important for this toxic element in TSP. Coupling the Pb isotopic signatures with the air mass back trajectories identified the major potential source regions for individual samples. The results show that during winter, China was the dominant contributor, accounting for 92%, 82%, and 100% of the sampling periods at IC, TA, and JJ, respectively. The Chinese contribution decreased in summer and autumn, whereas the Korean contribution increased, according to the East Asian monsoon system. The Pb concentrations increased by 2.2 (IC), 1.2 (TA) and 1.4 (JJ) times when the Chinese contribution was dominant, compared to the Korea-dominant periods. The Pb isotopic systematics for the samples characterized by the dominant Korean contribution differed substantially between the three sites, implying that the relative importance of various domestic sources varied with geographical areas in western Korea.

Pollution Characteristics of Sb, As, Hg, Pb, Cd, and Zn in Soils from Different Zones of Xikuangshan Antimony Mine

Major sources of pollution during the antimony (Sb) mining and processing are mining waste rock, smelting waste, tailings dam, and underground tunnel wastewater. The aim of the present study was to assess magnitude of pollution from Sb mine by taking four types of samples: soil in the mining waste rock zone, soil in the smelting zone, soil in tailings zone, and soil in underground tunnel wastewater zone. Sixty soil samples from the four zones were taken for experimental work, and the contents and morphological characteristics of the six potentially toxic elements (PTEs) such as Sb, As, Hg, Pb, Cd, and Zn in the soil samples were measured by using a hydride generation atomic fluorescence spectrometer (AFS-9700). The results show that the soil of the mine area is seriously polluted. The average contents of Sb, As, Hg, Pb, Cd, and Zn in the soil reach 1267.20 mg·kg^-1, 94.44 mg·kg^-1, 1.46 mg·kg^-1, 184.19 mg·kg^-1, 8.54 mg·kg^-1, and 1054.11 mg·kg^-1, respectively. There exists good correlation between the PTEs in the soil, with Sb strongly positively correlated with As, Hg, Pb, and Zn. The intensity of pollution is highest in the antimony-smelting zone, where the potential ecological risk index is over 15,000, followed by the tailings zone and mining waste rock zone, with the underground tunnel wastewater zone being the lowest. Using sequential chemical extraction, the elements are associated with the residual fraction, followed by organic-sulfide fraction, and smaller portions in the Fe-Mn oxide, carbonate, and exchangeable fractions. There are great differences in the speciation content of different elements in different sampling zones. The study implicates that Sb-smelting zone is the potential source of PTEs and maximum metals are associated with residual phase, out of which significant portion is associated with mobile fraction or phase.

Using Pb isotope ratios of particulate matter and epiphytic lichens from the Athabasca Oil Sands Region in Alberta, Canada to quantify local, regional, and global Pb source contributions

Ambient air particulate matter (PM) was collected at the Wood Buffalo Environmental Association Bertha Ganter Fort McKay monitoring station in the Athabasca Oil Sand Region (AOSR) in Alberta, Canada from February 2010 to July 2011 as part of an air quality source assessment study. Daily 24-hour duration fine (PM_2.5) and coarse (PM_10-2.5) PM was collected using a sequential dichotomous sampler. 100 pairs of PM_2.5 and PM_10-2.5 were selected for lead (Pb) concentration and isotope analysis. Pb isotope and concentration results from 250 epiphytic lichen samples collected as far as 160 km from surface mining operations in 2008, 2011, and 2014 were analyzed to examine longer term spatial variations in Pb source contributions. A key finding was recognition of thorogenic ²⁰⁸Pb from eastern Asia in the springtime in the PM_2.5 in 2010 and 2011. ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb isotope ratios were used in a three-component mixing model to quantify local, regional, and global Pb sources in the PM and lichen data sets. 47 ± 3% of the Pb in the PM_2.5 at AMS-1 was attributed to sources from eastern Asia. Combined results from PM_10-2.5 and PM_2.5 indicate PM_2.5 Pb contributions from eastern Asia (34%) exceed local AOSR sources of PM_2.5 Pb (20%), western Canada sources of PM_2.5 Pb (19%), and PM_10-2.5 Pb from fugitive dust including oil sands (14%), tailings (10%), and haul roads (3%). The lichen analysis indicates regional sources contribute 46% of the Pb, local sources 32%, and global sources 22% over the 2008-2014 timeframe. Local sources dominate atmospheric Pb deposition to lichens at near field sites (0-30 km from mining operations) whereas regional Pb sources are prevalent at distal sites (30-160 km). The Pb isotope methodology successfully quantified trans-Pacific transport of Pb to the AOSR superimposed over the aerosol footprint of the world's largest concentration of bitumen mining and upgrading facilities.

Source identification of arsenic contamination in agricultural soils surrounding a closed Cu smelter, South Korea

Arsenic sources were identified in As-contaminated soils 4 km-7 km from a closed Cu smelter. Host rocks, heavy minerals in contaminated soils, ore minerals in quartz veins (geogenic sources) and bottom ash from the Cu smelter (an anthropogenic source) were investigated as potential sources. As a result, heavy minerals and bottom ash were found to contain higher As concentrations than the contaminated soils. Some of the host rock samples also showed higher As levels than the contaminated soils. Arsenopyrite was one of the frequently detected ore minerals in quartz veins. The As concentrations in soils did not decrease with soil depth or distance from the smelter. These results imply that the atmospheric emission from the smelter was not a major arsenic source. Based on the geochemical investigation and Pb isotopic analysis, the As contamination was affected by both regional ore mineralization and the host rock, and the influence of the smelter was limited. The spatial analysis of As concentrations and Pb isotopic ratios suggested that As contamination was mainly due to regional ore mineralization. The ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁴Pb ratios of the contaminated soils were plotted on the mixing line between background soils and ore minerals. The source apportionment results indicated a significant contribution of regional ore mineralization (average 52.9 ± 30.3%) to the As contamination. The contribution of this study is that we identified that the major source of soil contamination was of geologic origin despite an anthropogenic source nearby using geochemical and Pb isotopic investigation.

Enrichment and geochemical mobility of heavy metals in bottom sediment of the Hoedong reservoir, Korea and their source apportionment

Physicochemical characteristics of bottom sediment in the Hoedong reservoir were studied to evaluate the effectiveness of the reservoir as traps for trace metals. Roadside soil, stream sediment and background soil were also studied for comparison. Sequential extractions were carried out, and lead isotopic compositions of each extraction were determined to apportion Pb sources. Besides, particle size distribution of roadside soil, and metal concentrations and Pb isotopes of each size group were determined to characterize metal contamination. In result, Zn and Cu were enriched in sediment through roadside soil. The data on metal partitioning implied that Zn posed potential hazards for water quality. Meanwhile, the noticeable reduction of the ²⁰⁶Pb/²⁰⁷Pb isotopic ratio in the acid-soluble fraction in the size group 200 μm - 2 mm of national roadside soil indicated that this size group was highly contaminated by automotive emission with precipitation of acid-soluble secondary minerals during evaporation. Based on the Pb isotopic ratios, the dry deposition of Asian dust (AD) and non-Asian dust (NAD) affected roadside soil, while the effects of AD and NAD on bottom sediment appeared to be low given the low metal concentrations in sediment. Metal concentrations and Pb isotopic compositions indicated that sediments were a mixture of background and roadside soil. Source apportionment calculations showed that the average proportion of traffic Pb in bottom and stream sediments was respectively 34 and 31% in non-residual fractions, and 26 and 28% in residual fraction. The residual fraction of sediments appeared to be as contaminated as the non-residual fractions.

Isotope Tracing of Long-Term Cadmium Fluxes in an Agricultural Soil

Globally widespread phosphate fertilizer applications have resulted in long-term increases in the concentration of cadmium (Cd) in soils. The accumulation of this biotoxic, and bioaccumulative metal presents problems for the management of soil-plant-animal systems, because the magnitude and direction of removal fluxes (e.g., crop uptake, leaching) have been difficult to estimate. Here, Cd isotopic compositions (δ^114/110Cd) of archived fertilizer and soil samples from a 66 year-long agricultural field trial in Winchmore, New Zealand, were used to constrain the Cd soil mass balance between 1959 and 2015 AD, informing future soil Cd accumulation trajectories. The isotopic partitioning of soil Cd sources in this system was aided by a change in phosphate source rocks in 1998 AD, and a corresponding shift in fertilizer isotope composition. The dominant influence of mixing between isotopically distinct Cd end-members was confirmed by a Bayesian modeling approach. Furthermore, isotope mass balance modeling revealed that Cd removal processes most likely increased in magnitude substantially between 2000 and 2015 AD, implying an increase in Cd bioaccumulation and/or leaching over that interval. Natural-abundance stable isotopes are introduced here as a powerful tool for tracing the fate of Cd in agricultural soils, and potentially the wider environment.

Lead chromate detected as a source of atmospheric Pb and Cr (VI) pollution

Spherical black carbon aggregates were frequently observed in dust dry deposition in Daejeon, Korea. They were tens of micrometers in diameter and presented a mixture of black carbon and several mineral phases. Transmission electron microscopy (TEM) observations with energy-dispersive X-ray spectroscopy (EDS) and selected area diffraction pattern (SADP) analyses confirmed that the aggregates were compact and included significant amounts of lead chromate (PbCrO₄). The compositions and morphologies of the nanosized lead chromate particles suggest that they probably originated from traffic paint used in roads and were combined as discrete minerals with black carbon. Based on Pb isotope analysis and air-mass backward trajectories, the dust in Daejeon received a considerable input of anthropogenic pollutants from heavily industrialized Chinese cities, which implies that long-range transported aerosols containing PbCrO₄ were a possible source of the lead and hexavalent chromium levels in East Asia. Lead chromate should be considered to be a source of global atmospheric Pb and Cr(VI) pollution, especially given its toxicity.

Historical record of lead accumulation and source in the tidal flat of Haizhou Bay, Yellow Sea: Insights from lead isotopes

In order to investigate the historical records of lead contamination and source in coastal region of Haizhou Bay, Yellow Sea, a sediment core was collected from tidal flat, dated by (210)Pb and (137)Cs. Lead and its stable isotopic ratios were determined. The profiles of enrichment factor (EF) and Pb isotope ratios showed increasing trend upward throughout the core, correlating closely with the experience of a rapid economic and industrial development of the catchment. According to Pb isotopic ratios, coal combustion emission mainly contributed to the Pb burden in sediments. Based on end-member model, coal combustion emission dominated anthropogenic Pb sources in recent decades contributing from 48% to 67% in sediment. And the contribution of leaded gasoline was lower than 20%. A stable increase of coal combustion source was found in sediment core, while the contribution of leaded gasoline had declined recently, with the phase-out of leaded gasoline in China.