Copper isotopic record in soils and tree rings near a copper smelter, Copperbelt, Zambia

Wood anatomy and dendrochronological potentiality of some woody shrubs from the southern Mediterranean coast in Egypt

In tropical and subtropical regions, much research is still required to explore the dendrochronological potential of their trees. This study aims to evaluate the anatomical structure and dendrochronological potential of three Mediterranean desert shrubs in Egypt (Lycium schweinfurthii var. schweinfurthii, L. europaeum, and Calligonum polygonoides subsp. comosum) supported by X-ray density. The results showed that the target species had distinct growth rings at macroscopic and microscopic levels. The vessel traits reflected the adaptability of each species with the prevailing arid climate conditions. After the exclusion of the non-correlated series, we obtained three site chronologies that cover the years 2013-2022 for L. schweinfurthii, 2012-2022 for L. europaeum, and 2011-2022 for C. comosum. The mean series intercorrelation was 0.746, 0.564, and 0.683 for L. schweinfurthii, L. europaeum, and C. comosum, respectively. The EPS (expressed population signal) values ranged from 0.72 to 0.80, while the SNR (species-to-noise ratio) ranged from 9.1 to 21.5. Compiling all series of L. schweinfurthii raised the EPS value to 0.86. The chronologies developed for the studied species were relatively short since we dealt with multi-stemmed shrubs. The average percentage difference between latewood density (LWD) and earlywood density (EWD) in C. comosum, L. europaeum, and L. schweinfurthii were 11.8% ± 5.5, 5.2%± 1.87, and 3.6% ± 1.86, respectively. X-ray densitometry helped in the precise determination of the ring borders of the studied species. The relationships between the radial growth of the studied species and the climate variables were weak to moderate but mostly not significant (i.e., r < 0.7). Generally, the radial growth of the target species had a weak to moderate positive correlation with temperature and precipitation during the wet season (winter), while negatively correlated with temperature for the rest of the year, particularly in summer. Our data agrees with earlier findings that ring formation starts at the beginning of the long vegetative stage, then the rest of the assimilated carbohydrates are directed to the flowering and fruiting at the end of the vegetative stages. For more efficient dendrochronological studies on subtropical and Mediterranean trees, we recommend carrying out xylogenesis studies, collection of phenological data, sampling 45-80 trees per species, using new techniques, and choosing homogeneous and close sites for wood sampling.

Emerging applications of high-precision Cu isotopic analysis by MC-ICP-MS

As a component of many minerals and an essential trace element in most aerobic organisms, the transition metal element Cu is important for studying reduction-oxidation (redox) interactions and metal cycling in the total environment (lithosphere, atmosphere, biosphere, hydrosphere, and anthroposphere). The "fractionation" or relative partitioning of the naturally occurring "heavy" (⁶⁵Cu) and "light" (⁶³Cu) isotope between two coexisting phases in a system occurs according to bonding environment and/or as a result of a slight difference in the rate at which these isotopes take part in physical processes and chemical reactions (in absence of equilibrium). Due to this behaviour, Cu isotopic analysis can be used to study a range of geochemical and biological processes that cannot be elucidated with Cu concentrations alone. The shift between Cu⁺ and Cu²⁺ is accompanied by a large degree of Cu isotope fractionation, enabling the Cu isotope to be applied as a vector in mineral exploration, tracer of origin, transport, and fate of metal contaminants in the environment, biomonitor, and diagnostic/prognostic marker of disease, among other applications. In this contribution, we (1) discuss the analytical protocols that are currently available to perform Cu isotopic analysis, (2) provide a compilation of published δ⁶⁵Cu values for matrix reference materials, (3) review Cu isotope fractionation mechanisms, (4) highlight emerging applications of Cu isotopic analysis, and (5) discuss future research avenues.

Copper isotope ratios allowed for quantifying the contribution of coal mining and combustion to total soil copper concentrations in China

The most prominent source of Cu contamination in soils is metal mining and processing, partly since the Middle Age. However, coal mining and combustion can also cause (some) Cu contamination. We studied the distribution of Cu concentrations and isotope ratios in soils of the Huaibei coal mining area. The contribution of the coal mining and combustion to total Cu concentrations in soil was determined with a two-end-member mixing model based on the distinct δ⁶⁵Cu values of the Cu emitted from coal mining and combustion and in native soil. The mean Cu concentration of 75 mg kg^-1 exceeded the local soil background value (round to 22.13 mg kg^-1). The similar δ⁶⁵Cu value of grass near the coal mining and combustion operation as in gangue and flying ash indicated a superficial Cu contamination. Mining input was the dominant source of Cu in the contaminated soils, contributing up to 95% and on average 72% of the total Cu in the topsoils. The mining-derived Cu was leached to a depth of 65 cm, where still 29% of the Cu could be attributed to the mining emissions. Grasses showed lower δ⁶⁵Cu values than the topsoils, because of the preferential uptake of light Cu isotopes. However, the Δ⁶⁵Cu_grass-soil was lower in the contaminated than the uncontaminated area because of superficial adsorption of isotopically heavy Cu from the mining emissions. Overall, in this study the distinct δ⁶⁵Cu values of the mining-derived Cu emissions and the native soil allowed for the quantification of the mining-derived Cu and had already reached the subsoil and contaminated the grass by superficial adsorption in only 60 years of mining operation.

Bioaccumulation of Cu, Fe, Mn and Zn in native Brachystegia longifolia naturally growing in a copper mining environment of Mufulira, Zambia

Heavy metal contamination in the soil and the subsequent accumulation in Brachystegia longifolia were investigated as a function of the wind direction and distance from a copper mine in Mufulira, Zambia. Soil and leaves of B. longifolia were collected along transects up to 12 km downwind and 19 km upwind. The total concentration of trace elements in the soil and leaves was determined through _pXRF. Plant-available Cu, Fe, Mn, and Zn were extracted in a Mehlich III solution and analyzed using ICP-AES. The degree of soil contamination illustrates that Cu and Fe from the copper mine strongly pollute Mufulira and the surrounding forests. Bioavailable Cu, Fe, Mn, and Zn reduced with increasing distance from the mine. An average of 296 mg/kg Cu, 2337 mg/kg Fe, 1101 mg/kg Mn, and 109 mg/kg Zn were recorded in leaves at the most polluted site. Similarly, 55.21 mg/kg Cu, 516.4 mg/kg Fe, 3196 mg/kg Mn, and 154 mg/kg Zn were recorded at an unpolluted site 19 km upwind. The concentration of Cu and Fe reduced significantly with increasing distance, while Mn and Zn increased significantly. It was further established that B. longifolia leaves accumulated Mn (× 38) and Zn (× 15) more than their respective total concentration in the soil. The concentrations of Cu and Fe found in leaves near the mine, as well as the Mn concentration in leaves across the study sites, could be stressful for B. longifolia tree growth.

Metal distribution, bioavailability and isotope variations in polluted soils from Lower Swansea Valley, UK

Soils in the Lower Swansea Valley, (United Kingdom) contain elevated level of metals, enough to cause direct or indirect effects on human health. This study assesses the severity of soil pollution and bioavailability of Cu and other metals (Ni, Zn, Co, Pb and Cr) in soils with various distances from a Ni refinery. We compare Cu concentrations in operationally defined soil fractions (bioavailable, bound to Fe/Mn oxide and incorporated in organic matter) with other metals (Ni, Zn, Pb, Co, Cr) usually occurring in ores used in metallurgic processes and report their pollution and geoaccumulation indices (PI and I_geo). Further, we use Cu stable isotope ratios (δ⁶⁵Cu) to trace the fate and mobility of Cu in soils. Our data suggest a point source of contamination for some of the heavy metals including Ni (I_geo = 1.9), Zn (I_geo = 0.28) and Cu (I_geo = 3.6) near the Ni refinery. However, Co (I_geo = 0.15) and Pb (I_geo = 3.3) contaminations are likely to be linked to different sources. No elevated Cr levels (I_geo= -0.07) occur in any of the studied soils. All soil metals are predominantly associated with organic matter (>50%) which  reduces their bioavailibility and thus their risk for ecological and human health. The Cu isotope data show that Cu in soil organic matter is enriched in ⁶⁵Cu, while the lighter isotopes (⁶³Cu) remain in the dissolved bioavailable Cu fraction (Δ⁶⁵Cu_{organic-bioavailable} is +0.12 ± 0.13‰). This suggests the preferential complexation of ⁶⁵Cu with soil organic matter after dissolution of Cu deposited to the soil. Thus, Cu isotope data can effectively indicate pathways of metal migration in polluted soils.

The what, how, why, and when of dendrochemistry: (paleo)environmental information from the chemical analysis of tree rings

The chemical analysis of tree rings has attracted the interest of researchers in the past five decades in view of the possibility of exploiting this biological indicator as a widely available, high-resolution environmental archive. Information regarding the surrounding environment can be derived either by directly measuring environmental variables (nutrient availability, presence of pollutants, etc.) or by exploiting proxies (e.g. paleoclimatic and paleoenvironmental reconstructions). This review systematically covers the topic and provides a critical view on the reliability of dendrochemical information. First, we introduce the determinable chemical species, such as major elements, trace metals, isotopic ratios, and organic compounds, together with a brief description of their uptake mechanisms and functions in trees. Subsequently, we present the possibilities offered by analytical techniques in the field of tree ring analysis, focusing on direct methods and recent developments. The latter strongly improved the details of the accessible information, enabling the investigation of complex phenomena associated with plant life and encouraging the direct analysis of new analytes, particularly minor organic compounds. With regard to their applications, dendrochemical proxies have been used to trace several processes, such as environmental contamination, paleoclimate reconstruction, global environmental changes, tree physiology, extreme events, ecological trends, and dendroprovenance. Several case studies are discussed for each proposed application, with special emphasis on the reliability of tracing each process. Starting from the reviewed literature data, the second part of the paper is devoted to the critical assessment of the reliability of tree ring proxies. We provide an overview of the current knowledge, discuss the limitations of the inferences that may be drawn from the dendrochemical data, and provide recommendations for the best practices to be used for their validation. Finally, we present the future perspectives related to the advancements in analytical instrumentation and further extension of application fields.

Impacts of smelter atmospheric emissions on forest nutrient cycles: Evidence from soils and tree rings

Although the environmental impacts of metal atmospheric emissions from point sources such as smelter have been extensively studied, very few studies have attempted to understand the influence of those emissions on nutrient cycles in the surrounding forests. This study investigates nutrient variations in space and time along with trace metals by statistical analysis of tree-ring series combined with the characterization of element concentrations in soil horizons. The research focuses on the Horne smelter (Rouyn Noranda, Québec, Canada), because it released high atmospheric emissions of metals and gases between 1928 and 1990s. Tree-ring Sr/Mn ratios, and Mn and Sr z-score series reveal that surface soil pH recovered progressively within the 45 km footprint of the smelter since the end of acidic deposition in the late 1970s. The influence of acidic deposition on the current soil pH has become negligible. In other words, element bioavailability and root assimilation have changed through time due to soil acidification at proximal sites. The detrended tree-ring elemental series during the last century also suggest that summer temperatures partly control the elemental bioavailability to trees in soils. Moreover, tree-ring Zn and Mg series appear as key environmental indicators of metal deposition from the smelter. This research confirms previous findings indicating that elemental concentrations in black and white spruce trees may be used to evaluate the potential influence of smelter emissions on nutrient cycles. For a future informed and adaptive management of forests, understanding the potential modifications of nutrient regimes caused by anthropogenic contaminations is critical, especially in the context of global warming.

Role of temperature, wind, and precipitation in heavy metal contamination at copper mines: a review

The increasing demand for minerals pressurizing the mining authorities to extract low-grade ore results in more mining waste and degradation of the environment. The main aim of review was to understand the role of climatic factors (temperature, wind, and precipitation) in dispersal and mobility of heavy metals in soil, water, and vegetation in Cu mining region. The major source of contamination in the mining sector is tailings, overburden rocks, and abandoned mines. The contaminates or fine particles of sulfide-rich mining waste follow two major pathways for the dispersal: aerial and leaching. Sulfides on exposure to oxygen and water generate acid mine drainage which results in leaching of heavy metals. The pit water of abandoned mines is also a cause of concern which contaminates the groundwater resources. Climatic factors such as temperature, precipitation, and wind significantly influence the paths of contaminate dispersal. In arid/semi-arid regions, high temperature forms fine-grained efflorescence salts on tailings or exposed surficial mines which are carried away by strong winds/water and contaminates the surroundings. In wet regions, the leaching of heavy metals from both tailings and overburden rocks sulfides results in environmental contamination. The application of impermeable layers is highly recommended. The climatic factors (temperature, wind, and precipitation) significantly control the dispersal and mobility of heavy metals in Cu mining region. The implementation of waste management policies and pollution control technologies is recommended after considering the climatic factors.

The Influence of Environmental Pollution and Drought on the Satisfaction With Life of Entrepreneurs in Zambia’s Mining Sector

Following contemporary trends of entrepreneurship research, measures of entrepreneurship, in terms of corporate social responsibility in relation to business performance (as an indicator of welfare, which is monetary well-being), has been investigated abundantly in developing countries. However, the consequences of climate change and natural disasters, such as environmental pollution and drought, have hardly been studied on the satisfaction with life (i.e., well-being) of entrepreneurs in developing countries. Therefore based on questionnaires administered to 132 entrepreneurs in the mining sector of the Copperbelt Province and North-Western Province of Zambia (i.e., the developing country context of this study), this chapter shows that environmental pollution and drought have a negative effect on satisfaction with life. Moreover, environmental pollution and drought have negative effects on both business’ profitability and decision-making. The results involve contributions to the existing literature and practical suggestions for entrepreneurs, policymakers, and educators.

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.

Thallium stable isotope fractionation in white mustard: Implications for metal transfers and incorporation in plants

We studied thallium (Tl) isotope fractionation in white mustard grown hydroponically at different Tl doses. Thallium isotope signatures in plants indicated preferential incorporation of the light ²⁰³Tl isotope during Tl uptake from the nutrient solution. Negative isotope fractionation was even more pronounced in dependence on how much the available Tl pool decreased. This finding corresponds to the concept of isotope overprinting related to a high contamination level in the growing media (solution or soil). Regarding Tl translocation in plants, we observed a large Tl isotope shift with an enrichment in the heavy ²⁰⁵Tl isotope in the shoots relative to the roots in treatments with low/moderate solution Tl concentrations (0.01/0.05 mg Tl/L), with the corresponding α^205/203Tl fractionation factors of ˜1.007 and 1.003, respectively. This finding is probably a consequence of specific (plant) reactions of Tl replacing K in its cycle. The formation of the S-coordinated Tl(I) complexes, potentially affecting both Tl accumulation and Tl isotope fractionation in plants, however, was not proven in our plants, since we did not have indication for that on the basis of X-ray absorption spectroscopy, suggesting that Tl was mainly present as free/hydrated Tl⁺ ion or chemically bound to O-containing functional groups.

Tracing Copper Migration in the Tongling Area through Copper Isotope Values in Soils and Waters

Copper mining in Tongling has occurred since the Bronze Age, and this area is known as one of the first historic places where copper has been, and is currently, extracted. Multiple studies have demonstrated, through concentrated work on soils and waters, the impact of mining in the area. Here we present copper isotope values of 13 ore samples, three tailing samples, 20 water samples (surface and groundwater), and 94 soil samples (15 different profiles ranging in depth from 0–2 m) from proximal to distal (up to 10 km) locations radiating from a tailings dam and tailings pile. Oxidation of the copper sulfide minerals results in isotopically heavier oxidized copper. Thus, copper sourced from sulfide minerals has been used to trace copper in mining and environmental applications. At Tongling, higher copper isotope values (greater than 1 per mil, which are interpreted to be derived from copper sulfide weathering) are found both in waters and the upper portions of soils (5–100 cm) within 1 km of the source tailings. At greater than 1 km, the soils do not possess heavier copper isotope values; however, the stream water samples that have low copper concentrations have heavier values up to 6.5 km from the source. The data suggest that copper derived from the mining activities remains relatively proximal in the soils but can be traced in the waters at greater distances.

Thallium contamination of desert soil in Namibia: Chemical, mineralogical and isotopic insights

We studied arid desert soils from Namibia (Rosh Pinah) that were contaminated with up to 7 mg kg^-1 of thallium (Tl) via dust emitted from a local flotation tailing dam. Chemical extractions of waste and soil materials indicated that most of the Tl is strongly bound, in accordance with X-ray diffraction and X-ray absorption spectroscopy data that point to the predominant association of Tl with metal sulfides and phyllosilicates. The isotope fractionation factor ε²⁰⁵Tl of the soil samples (from -0.4 to +3.8) shows a positive linear relationship (R² = 0.62) with 1/Tl, indicative for the mixing of two major Tl pools, presumably anthropogenic Tl and geogenic Tl. The ε²⁰⁵Tl value for the topmost soil samples (∼+3) closely matches the ε²⁰⁵Tl value for post-flotation waste particles with a diameter of <0.05 mm, whereas the bulk flotation waste exhibits a significantly larger ε²⁰⁵Tl value (∼+6). These variations are in accordance with predominant atmospheric transfer of Tl from the tailings to the adjacent soils via fine (dust) particles. The identified minimal Tl alteration in soils indicates that only a small part of the Tl could be potentially released and passively enter the vegetation, local population and/or food chain in the long term. From this viewpoint, Tl does not represent such an important environmental concern as other (abundant) contaminants at the locality. Furthermore, there could be a relevance for other alkaline desert soils, including those where Tl pollution plays a major role.