Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion

Discrimination of metal contaminant sources in river sediments influenced by mining and smelting activities using stable Pb and Zn isotopes

To determine the sources and pathways of lead (Pb) and zinc (Zn) in river sediments contaminated with metals from mining and smelting activities, metal concentrations and Pb and Zn isotope ratios were measured in river water and sediment, and potential metal contaminant samples (imported Zn concentrates, smelting wastes, soils around the smelter, mine ores, and riverside tailings). Zn and cadmium (Cd) concentrations in river water and sediment samples were 30- and 11-25-fold higher, respectively, near the smelter than upstream, while a 6-fold increase in sediment Pb concentrations was detected over the same region. Sediment samples near the smelter (207Pb/206Pb = 0.8638 and 208Pb/206Pb = 2.0960) were observed to have a different Pb isotopic composition from upstream of the smelter (207Pb/206Pb = 0.8322 and 208Pb/206Pb = 2.0502), with δ66Zn values increasing from -0.01 to 0.82‰. Analysis of Pb and Zn isotopes and concentrations revealed that dust-contaminated soils were a major Pb source, and baseline sediments were found to be contaminated by regional mining tailings. For Zn in sediments, the main Zn sources were groundwater-derived Zn (δ66Zn = 1.02 ± 0.43‰, n = 4), dust-contaminated soils (δ66Zn = -0.18 ± 0.08‰, n = 3), and tailings-contaminated sediments (δ66Zn = 0.01 ± 0.07‰, n = 10). Endmember mixing model results showed that dust-contaminated soils contributed 78% and 64% of sediment Pb and Zn, respectively, within 2 km of the Zn smelter, decreasing to negligible levels after 47.1 km downstream. Downstream of the smelter, groundwater-derived Zn contributed 54% of sediment Zn, whereas tailings contaminated sediments contributed 70% and 25% of Pb and Zn, respectively.

Identification of atmospheric particulate matter derived from coal and biomass burning and from non-exhaust traffic emissions using zinc isotope signatures

Improving urban air quality is a global challenge. To implement successful abatement measures that reduce atmospheric particulate matter (APM) and associated metal concentrations, precise source apportionment is needed. For this, apportioning contributions from coal and biomass burning and differentiating these from non-exhaust traffic emissions in urban APM is critical. Recent studies characterising the metal isotope composition of urban APM, and potential source materials suggested that non-traditional isotope systems could prove unique fingerprinting tools. Zinc isotopes should be able to separate APM derived from uncontrolled combustion (fly ash, isotopically heavy) from non-exhaust traffic sources (tyre and brake wear, intermediate) and from controlled industrial emissions (flue gas, light). To test this hypothesis, we determined zinc isotope ratios of APM (TSP, PM_2.5, PM₁) in Beijing (coal combustion for residential heating) and Varanasi (biomass burning in pre-monsoon periods). In Beijing, δ⁶⁶Zn_Lyon values of PM_2.5 ranged from -0.41 to +1.01‰ in 2015 (avg = +0.25 ± 0.50‰, n = 19). Aerosols (including TSP, PM_2.5 and PM₁ samples) from the heating period were significantly (t-test, p < 0.001) heavier (avg = +0.90 ± 0.12‰, n = 7) than those from the non-heating period (avg = +0.14 ± 0.36‰, n = 23). Average δ⁶⁶Zn_Lyon values of PM_2.5 in Varanasi in spring 2015 were +0.82 ± 0.11‰ (n = 4). Extent and direction of isotope fractionation is in line with that expected from theoretical models and the isotope signatures observed agree with previously determined ratios of source materials. Our study links for the first time comprehensively the heavy zinc isotope compositions in APM to coal and biomass burning and shows that zinc isotope compositions of aerosols can discriminate between non-exhaust traffic and combustion sources.

Spatial and temporal trends in δ66Zn and 206Pb/207Pb isotope ratios along a rural transect downwind from the Upper Silesian industrial area: Role of legacy vs. present-day pollution

Transect sampling is an under-exploited tool in isotope studies of atmospheric pollution. Few studies have combined Zn and Pb isotope ratios to investigate whether atmospheric pollution at a receptor site is dominated by a different anthropogenic source of each of these toxic elements. It has been also unclear whether pollution abatement strategies in Central Europe have already resulted in regionally well-mixed background isotope signature of atmospheric Zn and Pb. Zinc and lead isotope ratios were determined in snow collected along a rural transect downwind from the Upper Silesian industrial area (southern Poland). Spatial and temporal gradients in δ⁶⁶Zn and ²⁰⁶Pb/²⁰⁷Pb ratios at four sites were compared with those of ore and coal collected in eight Czech and Polish mining districts situated at distances of up to 500 km. Snow pollution was extremely high 8 km from Olkusz in 2011 (1670 μg Zn L^-1; 240 μg Pb L^-1), sharply decreased between 2011 and 2018, and remained low in 2019-2021. Snow pollution was lower at sites situated 28-68 km from Olkusz. Across study sites, mean δ⁶⁶Zn and ²⁰⁶Pb/²⁰⁷Pb ratios of snow were -0.13‰ and 1.155, respectively. With an increasing distance from Olkusz, the δ⁶⁶Zn values first increased and then decreased, while the ²⁰⁶Pb/²⁰⁷Pb ratios first decreased and then increased. The δ⁶⁶Zn values in snow plotted closer to those of Upper Silesian ores (-0.20‰) than to the δ⁶⁶Zn values of Upper Silesian stone coal (0.52‰), showing predominance of smelter-derived over power-plant derived Zn pollution. The ²⁰⁶Pb/²⁰⁷Pb ratios of Upper Silesian coal (1.171) and Upper Silesian ores (1.180) were higher compared to those of snow. A²⁰⁶Pb/²⁰⁷Pb vs.²⁰⁸Pb/²⁰⁷Pb plot identified legacy pollution from leaded gasoline as the low-radiogenic mixing end-member. Across the transect sites, only the last sampling campaign exhibited a high degree of isotope homogenization for both Zn and Pb.

"Non-traditional" stable isotopes applied to the study of trace metal contaminants in anthropized marine environments

The advent of Multicollector ICP-MS inaugurated the analysis of new metal isotope systems, the so-called "non-traditional" isotopes. They are now available tools to study geochemical and ecotoxicological aspects of marine metal contamination and hence, to push the frontiers of our knowledge. However, such applications are still in their infancy, and an accessible state-of-the-art describing main applications, obstacles, gaps, and directions for further development was missing from the literature. This paper fills this gap and aims to encourage the marine scientific community to explore the contributions of this newly available information for the fields of chemical risk assessment, biomonitoring, and trophic transfer of metal contaminants. In the current "Anthropocene" epoch, metal contamination will continue to threaten marine aquatic ecosystems, and "non-traditional" isotopes can be a valuable tool to detect human-induced changes across time-space involving metal contaminants, and their interaction with marine biota.

Metal stable isotopes in transplanted oysters as a new tool for monitoring anthropogenic metal bioaccumulation in marine environments: The case for copper

Metal release into the environment from anthropogenic activities may endanger ecosystems and human health. However, identifying and quantifying anthropogenic metal bioaccumulation in organisms remain a challenging task. In this work, we assess Cu isotopes in Pacific oysters (C. gigas) as a new tool for monitoring anthropogenic Cu bioaccumulation into marine environments. Arcachon Bay was taken as a natural laboratory due to its increasing contamination by Cu, and its relevance as a prominent shellfish production area. Here, we transplanted 18-month old oysters reared in an oceanic neighbor area into two Arcachon Bay mariculture sites under different exposure levels to continental Cu inputs. At the end of their 12-month long transplantation period, the oysters' Cu body burdens had increased, and was shifted toward more positive δ⁶⁵Cu values. The gradient of Cu isotope compositions observed for oysters sampling stations was consistent with relative geographic distance and exposure intensities to unknown continental Cu sources. A binary isotope mixing model based on experimental data allowed to estimate the Cu continental fraction bioaccumulated in the transplanted oysters. The positive δ⁶⁵Cu values and high bioaccumulated levels of Cu in transplanted oysters support that continental emissions are dominantly anthropogenic. However, identifying specific pollutant coastal source remained unelucidated mostly due to their broader and overlapping isotope signatures and potential post-depositional Cu isotope fractionation processes. Further investigations on isotope fractionation of Cu-based compounds in an aqueous medium may improve Cu source discrimination. Thus, using Cu as an example, this work combines for the first time a well-known caged bivalve approach with metal stable isotope techniques for monitoring and quantifying the bioaccumulation of anthropogenic metal into marine environments. Also, it states the main challenges to pinpoint specific coastal anthropogenic sources utilizing this approach and provides the perspectives for further studies to overcome them.

Catchment Runoff in Industrial Areas Exports Legacy Pollutant Zinc from the Topsoil Rather than Geogenic Zn

In highly industrialized, densely populated parts of Central Europe, mobilization of legacy Zn pollution from forest ecosystems may negatively affect the quality of water resources. To test this hypothesis, we determined the ⁶⁶Zn/⁶⁴Zn isotope ratios of 15 Zn reservoirs and fluxes in an acidified, spruce die-back affected mountain-slope catchment in northern Czech Republic. The δ⁶⁶Zn values of precipitation, organic horizon, and runoff were statistically indistinguishable. In contrast, δ⁶⁶Zn values of bedrock orthogneiss and mineral soil were significantly different from δ⁶⁶Zn values of runoff. The magnitude of within-site Zn isotope fractionations appeared to be relatively small. Despite the large potential source of Zn in bedrock, runoff exported mostly young pollutant Zn that had been temporarily stored in the organic horizon. This conclusion was corroborated by comparing Zn input-output mass balances in the polluted northern catchment and in a relatively unpolluted catchment situated 250 km to the south. Seven-times higher Zn export via runoff at the northern site was controlled by a combination of 10-times higher atmospheric Zn input and five-times higher DOC leaching, compared to the southern site. In industrial areas, atmospherically deposited Zn is leached from headwater catchments in a direct analogy to leaching of highly toxic pollutant Pb.

Possible application of stable isotope compositions for the identification of metal sources in soil

Metals in soil are potentially harmful to humans and ecosystems. Stable isotope measurement may provide "fingerprint" information on the sources of metals. In light of the rapid progress in this emerging field, we present a state-of-the-art overview of how useful stable isotopes are in soil metal source identification. Distinct isotope signals in different sources are the key prerequisites for source apportionment. In this context, Zn and Cd isotopes are particularly helpful for the identification of combustion-related industrial sources, since high-temperature evaporation-condensation would largely fractionate the isotopes of both elements. The mass-independent fractionation of Hg isotopes during photochemical reactions allows for the identification of atmospheric sources. However, compared with traditionally used Sr and Pb isotopes for source tracking whose variations are due to the radiogenic processes, the biogeochemical low-temperature fractionation of Cr, Cu, Zn, Cd, Hg and Tl isotopes renders much uncertainty, since large intra-source variations may overlap the distinct signatures of inter-source variations (i.e., blur the source signals). Stable isotope signatures of non-metallic elements can also aid in source identification in an indirect way. In fact, the soils are often contaminated with different elements. In this case, a combination of stable isotope analysis with mineralogical or statistical approaches would provide more accurate results. Furthermore, isotope-based source identification will also be helpful for comprehending the temporal changes of metal accumulation in soil systems.

Trace metal dynamics in an industrialized Brazilian river: A combined application of Zn isotopes, geochemical partitioning, and multivariate statistics

The Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (δ^66/64Zn_JMC ≈ + 0.30‰) and anthropogenic (δ^66/64Zn_JMC ≈ + 0.15‰) end members. The lighter δ^66/64Zn_JMC values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds.

Zinc isotope composition as a tool for tracing sources and fate of metal contaminants in rivers

Zinc is a ubiquitous metal, acting both as an essential and a toxic element to organisms depending on its concentration and speciation in solution. Human activities mobilize and spread large quantities of zinc broadly in the environment. Discriminating the natural and various anthropogenic zinc sources in the environment and understanding zinc's fate at a catchment scale are key challenges in preserving the environment. This review presents the state of the art in zinc isotope studies applied to environmental purposes at a river-basin scale. Even though the study of zinc isotopes remains less developed than more "traditional" lead isotopes, we can assess their potential for being a relevant tracer of zinc in the environment. We present the principles of zinc isotope measurements from collecting samples to mass spectrometry analysis. To understand the fate of zinc released in the environment by anthropogenic activities, we summarize the main processes governing zinc distribution between the dissolved and solid phases, with a focus on the isotope fractionation effects that can modify the initial signature of the various zinc sources. The signatures of zinc isotopes are defined for the main natural sources of zinc in the environment: bulk silicate earth (BSE), zinc sulfide ore deposits, and coal signatures. Rivers draining natural environments define the "geological background for surface water", which is close to the BSE value. We present the main anthropogenic sources (metallurgical waste, effluents, fertilizers, etc.) with their respective isotope signatures and the main processes leading to these specific isotope characteristics. We discuss the impact of the various anthropogenic zinc emissions based on the available studies based on zinc isotopes. This literature review points out current knowledge gaps and proposes future directions to make zinc isotopes a relevant tracer of zinc (and associated trace metals) sources and fate at a catchment scale.

Zinc isotopic variation of water and surface sediments from the German Elbe River

Recent studies suggested the use of the isotopic composition of Zn as a possible tracer for anthropogenic Zn emissions. Nevertheless, studies mainly focused on sampling areas of a few km² with well-characterized anthropogenic Zn emissions. In contrast, this study focused on analyzing a large sample set of water and sediment samples taken throughout the course of the Elbe River, a large, anthropogenically impacted river system located in Central Europe. The primary objective was to evaluate the use of the isotopic composition of Zn to trace anthropogenic Zn emission on a large regional scale. In total 18 water and 26 surface sediment samples were investigated, covering the complete course of over 700 km of the German Elbe between the German/Czech border and the German North Sea, including six tributaries. Stable isotope abundance ratios of Zn were assessed by multi-collector inductively coupled plasma mass spectrometry (MC ICP-MS) in water filtrates (<0.45 µm) and total digests of the sieved surface sediment fraction (<63 µm) after analyte/matrix separation using Bio-Rad AG MP-1 resin via a micro-column approach and application of a ⁶⁴Zn/⁶⁷Zn double spike. Measured isotopic compositions of δ⁶⁶Zn/⁶⁴Zn_IRMM-3702 ranged from -0.10 ‰ to 0.32 ‰ for sediment samples, and from -0.51 ‰ to 0.45 ‰ for water samples. In comparison to historical data some tributaries still feature high mass fractions of anthropogenic Zn (e.g. Mulde, Triebisch) combined with δ⁶⁶Zn/⁶⁴Zn_IRMM-3702 values higher than the lithogenic background. The dissolved δ⁶⁶Zn/⁶⁴Zn_IRMM-3702 values showed a potential correlation with pH. Our results indicate that biogeochemical processes like absorption may play a key role in natural Zn isotopic fractionation making it difficult to distinguish between natural and anthropogenic processes.

Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago

Sourcing and understanding the fate of anthropogenic metals in a historical contamination context is challenging. Here we combined elemental and isotopic (Pb, Zn, Cu) analyses with X-ray Absorption Spectroscopy (XAS) measurements (Zn) to trace the fate, in undisturbed soil profiles, of historical metal contamination emitted by a 167-year-old Pb-Ag smelter decommissioned 100 years ago located in the Calanques National Park (Marseilles, France). Lead isotopic measurements show that entire soil profiles were affected by 74 years of Pb emissions up to ~7 km from the smelter under the main NNW wind, and indicate particulate transfer down to 0.8 m at depth. This vertical mobility of anthropogenic Pb contrasts with previous studies where Pb was immobilized in surface horizons. The contribution of anthropogenic Pb to the total Pb concentration in soil was estimated at 95% in surface horizons, and 78% in the deepest horizons. Zinc isotopic signatures of past emissions that are enriched in light isotopes compared to the natural geological background (-0.70 ± 0.04‰ and -0.15 ± 0.02‰, respectively), were detected only in the surface horizons of the studied soils. Using XAS analyses, we showed that anthropogenic Zn was transformed and immobilized in surface horizons as Zn-Layered Double Hydroxide, thus favoring the enrichment in heavy isotopes in these surface horizons. No clear evidence of copper contamination by the smelter was found and Cu isotopes point to a bedrock origin and a natural distribution of Cu concentrations.

Historical records, distributions and sources of mercury and zinc in sediments of East China sea: Implication from stable isotopic compositions

The distribution and source of mercury (Hg) and zinc (Zn) in surface sediments from East China Sea (ECS) were studied using stable isotopes. Hg concentrations in surface sediments varied from 12.6 to 133.2 ng g^-1. Zn concentrations ranged between 45.9 and 133.6 ng g^-1. Hydrodynamic circulation and sedimentary process within the ECS were the dominant factors controlling the distribution and fate of heavy metals, referring from relationships of Hg and Zn concentrations and total organic carbon (TOC) and clay contents. Spatial variations in Hg isotopic compositions (δ²⁰²Hg) were observed in the ECS, with δ²⁰²Hg ranging from -1.86 to -0.83‰ and Δ¹⁹⁹Hg ranging from -0.07 to +0.26‰. The high δ²⁰²Hg values and relatively negative Δ¹⁹⁹Hg values in estuarine and inner shelf sites indicated that the riverine inputs from Yangtze River played an important role in delivering Hg to ECS. In contrast, Hg isotopic signatures in outer shelf sediments had relatively low δ²⁰²Hg and positive Δ¹⁹⁹Hg, implying that atmospheric Hg deposition could be relatively dominant source for Hg. Moreover, application of zinc isotopes to trace anthropogenic sources has been tested, with δ⁶⁶Zn ranging from 0.20 to 0.67‰. The results showed significant variations of δ⁶⁶Zn in the ECS, implying that Zn isotope compositions can be tracers of anthropogenic sources. Using these Hg isotope compositions, the source attributions of sediments in ECS were estimated based on a mixing model, suggesting that river-dominated inputs, discharging pollutants from industrial sources, and atmospheric deposition could dominate in the occurrence and fate of Hg in sediments of ECS.

Assessment of Metal Immission in Urban Environments Using Elemental Concentrations and Zinc Isotope Signatures in Leaves of Nerium oleander

A thorough understanding of spatial and temporal emission and immission patterns of air pollutants in urban areas is challenged by the low number of air-quality monitoring stations available. Plants are promising low-cost biomonitoring tools. However, source identification of the trace metals incorporated in plant tissues (i.e., natural vs anthropogenic) and the identification of the best plant to use remain fundamental challenges. To this end, Nerium oleander L. collected in the city of Zaragoza (NE Spain) has been investigated as a biomonitoring tool for assessing the spatial immission patterns of airborne metals (Pb, Cu, Cr, Ni, Ce, and Zn). N. oleander leaves were sampled at 118 locations across the city, including the city center, industrial hotspots, ring-roads, and outskirts. Metal concentrations were generally higher within a 4 km radius around the city center. Calculated enrichment factors relative to upper continental crust suggest an anthropogenic origin for Cr, Cu, Ni, Pb, and Zn. Zinc isotopes showed significant variability that likely reflects different pollution sources. Plants closer to industrial hotspots showed heavier isotopic compositions (δ⁶⁶Zn_Lyon up to +0.70‰), indicating significant contributions of fly ash particles, while those far away were isotopically light (up to -0.95‰), indicating significant contributions from exhaust emissions and flue gas. We suggest that this information is applied for improving the environmental and human risk assessment related to the exposure to air pollution in urban areas.

Discovery and ramifications of incidental Magnéli phase generation and release from industrial coal-burning

Coal, as one of the most economic and abundant energy sources, remains the leading fuel for producing electricity worldwide. Yet, burning coal produces more global warming CO₂ relative to all other fossil fuels, and it is a major contributor to atmospheric particulate matter known to have a deleterious respiratory and cardiovascular impact in humans, especially in China and India. Here we have discovered that burning coal also produces large quantities of otherwise rare Magnéli phases (Ti _x O_2x-1 with 4 ≤ x ≤ 9) from TiO₂ minerals naturally present in coal. This provides a new tracer for tracking solid-state emissions worldwide from industrial coal-burning. In its first toxicity testing, we have also shown that nanoscale Magnéli phases have potential toxicity pathways that are not photoactive like TiO₂ phases, but instead seem to be biologically active without photostimulation. In the future, these phases should be thoroughly tested for their toxicity in the human lung.Solid-state emissions from coal burning remain an environmental concern. Here, the authors have found that TiO2 minerals present in coal are converted into titanium suboxides during burning, and initial biotoxicity screening suggests that further testing is needed to look into human lung consequences.

A critical examination of the possible application of zinc stable isotope ratios in bivalve mollusks and suspended particulate matter to trace zinc pollution in a tropical estuary

The application of zinc (Zn) isotopes in bivalve tissues to identify zinc sources in estuaries was critically assessed. We determined the zinc isotope composition of mollusks (Crassostrea brasiliana and Perna perna) and suspended particulate matter (SPM) in a tropical estuary (Sepetiba Bay, Brazil) historically impacted by metallurgical activities. The zinc isotope systematics of the SPM was in line with mixing of zinc derived from fluvial material and from metallurgical activities. In contrast, source mixing alone cannot account for the isotope ratios observed in the bivalves, which are significantly lighter in the contaminated metallurgical zone (δ⁶⁶Zn_JMC = +0.49 ± 0.06‰, 2σ, n = 3) compared to sampling locations outside (δ⁶⁶Zn_JMC = +0.83 ± 0.10‰, 2σ, n = 22). This observation suggests that additional factors such as speciation, bioavailability and bioaccumulation pathways (via solution or particulate matter) influence the zinc isotope composition of bivalves.

Stable isotope composition of mercury forms in flue gases from a typical coal-fired power plant, Inner Mongolia, northern China

Mercury forms emitted from coal combustion via air pollution control devices are speculated to carry different Hg isotope signatures. Yet, their Hg isotope composition is still not reported. Here, we present the first onsite Hg isotope data for gaseous elemental Hg (GEM) and gaseous oxidized Hg (GOM) of flue gases from a typical lignite-fired power plant (CFPP). Significant mass dependent fractionation (MDF) and insignificant mass independent fractionation (MIF) are observed between feed coal and coal combustion products. As compared to feed coal (δ²⁰²Hg=-2.04±0.25‰), bottom ash, GEM and GOM in flue gases before and after wet flue gas desulfurization system significantly enrich heavy Hg isotopes by 0.7-2.6‰ in δ²⁰²Hg, while fly ash, desulfurization gypsum and waste water show slight but insignificant enrichment of light Hg isotopes. GEM is significantly enriched heavy Hg isotopes compared to GOM and Hg in fly ash. Our observations verify the previous speculation on Hg isotope fractionation mechanism in CFPPs, and suggest a kinetically-controlled mass dependent Hg isotope fractionation during transformation of Hg forms in flue gases. Finally, our data are compared to Hg isotope compositions of atmospheric Hg pools, suggesting that coal combustion Hg emission is likely an important atmospheric Hg contributor.

Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime

Copper (Cu) and zinc (Zn) isotope ratios can be used to fingerprint sources and dispersion pathways of pollutants in the environment. Little is known, however, about the potential of δ⁶⁵Cu and δ⁶⁶Zn values in liquid and solid forms of atmospheric deposition to distinguish between geogenic, industrial, local and remote sources of these potentially toxic base metals. Here we present Cu-Zn deposition fluxes at 10 mountain-top sites in the Czech Republic, a region affected by extremely high industrial emission rates 25 years ago. Additionally, we monitored isotope composition of Cu and Zn in vertical and horizontal atmospheric deposition at two sites. We compared δ⁶⁵Cu and δ⁶⁶Zn values in snow and rime, extracted by diluted HNO₃ and concentrated HF. Cu and Zn isotope signatures of industrial pollution sources were also determined. Cu and Zn deposition fluxes at all study sites were minute. The mean δ⁶⁵Cu value of atmospheric deposition (-0.07‰) was higher than the mean δ⁶⁵Cu value of pollution sources (-1.17‰). The variability in δ⁶⁵Cu values of atmospheric deposition was lower, compared to the pollution sources. The mean δ⁶⁶Zn value of atmospheric deposition (-0.09‰) was slightly higher than the mean δ⁶⁶Zn value of pollution sources (-0.23‰). The variability in δ⁶⁶Zn values of atmospheric deposition was indistinguishable from that of pollution sources. The largest isotope differences (0.35‰) were observed between the insoluble and soluble fractions of atmospheric deposition. These differences may result from different sources of Cu/Zn for each fraction. The difference in isotope composition of soluble and insoluble particles appears to be a promising tool for pollution provenance studies in Central Europe.

Isotopic Tracing of Thallium Contamination in Soils Affected by Emissions from Coal-Fired Power Plants

Here, for the first time, we report the thallium (Tl) isotope record in moderately contaminated soils with contrasting land management (forest and meadow soils), which have been affected by emissions from coal-fired power plants. Our findings clearly demonstrate that Tl of anthropogenic (high-temperature) origin with light isotope composition was deposited onto the studied soils, where heavier Tl (ε(205)Tl ∼ -1) naturally occurs. The results show a positive linear relationship (R(2) = 0.71) between 1/Tl and the isotope record, as determined for all the soils and bedrocks, also indicative of binary Tl mixing between two dominant reservoirs. We also identified significant Tl isotope variations within the products from coal combustion and thermo-desorption experiments with local Tl-rich coal pyrite. Bottom ash exhibited the heaviest Tl isotope composition (ε(205)Tl ∼ 0), followed by fly ash (ε(205)Tl between -2.5 and -2.8) and volatile Tl fractions (ε(205)Tl between -6.2 and -10.3), suggesting partial Tl isotope fractionations. Despite the evident role of soil processes in the isotope redistributions, we demonstrate that Tl contamination can be traced in soils and propose that the isotope data represent a possible tool to aid our understanding of postdepositional Tl dynamics in surface environments for the future.

New Insights from Zinc and Copper Isotopic Compositions into the Sources of Atmospheric Particulate Matter from Two Major European Cities

This study reports spatial and temporal variability of Zn and Cu isotopes in atmospheric particulate matter (PM) collected in two major European cities with contrasting atmospheric pollution, Barcelona and London. We demonstrate that nontraditional stable isotopes identify source contributions of Zn and Cu and can play a major role in future air quality studies. In Barcelona, samples of fine PM were collected at street level at sites with variable traffic density. The isotopic signatures ranged between -0.13 ± 0.09 and -0.51 ± 0.05‰ for δ(66)ZnIRMM and between +0.04 ± 0.20 and +0.33 ± 0.15‰ for δ(65)CuAE633. Copper isotope signatures similar to those of Cu sulfides and Cu/Sb ratios within the range typically found in brake wear suggest that nonexhaust emissions from vehicles are dominant. Negative Zn isotopic signatures characteristic for gaseous emissions from smelting and combustion and large enrichments of Zn and Cd suggest contribution from metallurgical industries. In London, samples of coarse PM collected on the top of a building over 18 months display isotope signatures ranging between +0.03 ± 0.04 and +0.49 ± 0.02‰ for δ(66)ZnIRMM and between +0.37 ± 0.17 and +0.97 ± 0.21‰ for δ(65)CuAE633. Heavy Cu isotope signatures (up to +0.97 ± 0.21‰) and higher enrichments and Cu/Sb ratios during winter time indicate important contribution from fossil fuel combustion. The positive δ(66)ZnIRMM signatures are in good agreement with signatures characteristic for ore concentrates used for the production of tires and galvanized materials, suggesting nonexhaust emissions from vehicles as the main source of Zn pollution.