Application of Cu isotopes to identify Cu sources in soils impacted by multiple anthropogenic activities

Copper (Cu) is an important micronutrient for animals and plants, but it is toxic at high concentrations in soil. Soils adjacent to industrial areas would be subjected to severe Cu pollution. Identifying Cu sources in the surface environment is crucial for understanding their pollution level and fate. This study investigated Cu content, isotope composition of topsoils, and two soil profiles with varying levels of Cu contamination and related potential Cu sources in southwest China. The difference in Cu isotope compositions of tailing (1.29 ± 0.08 ‰), smelting fly ash (0.04 ± 0.03 ‰), coal (2.44 ± 0.09 ‰), coal-burning fly ash (0.34 ± 0.03 ‰), and geogenic soil (0.10 ± 0.03 ‰) enabled us to distinguish anthropogenic Cu from geogenic Cu. The plot of δ65Cu and 1/Cu demonstrates that Cu of the polluted soils was from three end-members: the smelting fly ash, the vehicle exhaust, and the background soils. Based on the mass balance model, we calculated that the fly ash from smelting was the major anthropogenic source, contributing approximately 29 % of Cu contamination in soils, and the diesel exhaust was another important source, with a contribution rate of approximately 25 %. Additionally, soil profile results suggest that anthropogenic Cu could transport through soil profiles and influence Cu content and isotope signatures of subsurface soils, at least to a depth of ∼60 cm. Finally, our research indicates that Cu isotopes could be a promising tool for tracing industrial pollution, as significant Cu isotope fractionation would occur during the smelting process. Our research highlights the contribution of smelting and diesel exhaust to Cu contamination in the soils in a representative mining area. These findings serve as a scientific foundation for the development of policy for pollution control in industrial-affected regions.

Alzheimer's Disease and Age-Related Changes in the Cu Isotopic Composition of Blood Plasma and Brain Tissues of the APPNL-G-F Murine Model Revealed by Multi-Collector ICP-Mass Spectrometry

Alzheimer's' disease (AD) is characterized by the formation of β-amyloid (Aβ) plaques and neurofibrillary tangles of tau protein in the brain. Aβ plaques are formed by the cleavage of the β-amyloid precursor protein (APP). In addition to protein aggregations, the metabolism of the essential mineral element Cu is also altered during the pathogenesis of AD. The concentration and the natural isotopic composition of Cu were investigated in blood plasma and multiple brain regions (brain stem, cerebellum, cortex, and hippocampus) of young (3-4 weeks) and aged (27-30 weeks) APP^NL-G-F knock-in mice and wild-type controls to assess potential alterations associated with ageing and AD. Tandem inductively coupled plasma-mass spectrometry (ICP-MS/MS) was used for elemental analysis and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for high-precision isotopic analysis. The blood plasma Cu concentration was significantly altered in response to both age- and AD-related effects, whereas the blood plasma Cu isotope ratio was only affected by the development of AD. Changes in the Cu isotopic signature of the cerebellum were significantly correlated with the changes observed in blood plasma. The brain stem showed a significant increase in Cu concentration for both young and aged AD transgenic mice compared with healthy controls, whereas the Cu isotopic signature became lighter as a result of age-related changes. In this work, ICP-MS/MS and MC-ICP-MS provided relevant and complementary information on the potential role of Cu in ageing and AD.

Copper migration and isotope fractionation in a typical paddy soil profile of the Yangtze Delta

To decipher Cu migration in paddy soils, which is important for understanding Cu supply in rice cultivation, Cu concentrations and isotope compositions were measured in a paddy soil profile in Suzhou, Eastern China, in the central Yangtze Delta. The results show that the variations in δ⁶⁵Cu values and Cu concentrations are not coupled along the profile. From top to bottom, the δ⁶⁵Cu values show small variations (0.07 ± 0.03‰ to 0.25 ± 0.01‰) in the upper layers (Ap-Br1), with a decrease in the subsurface Br2 layer (from 0.16 ± 0.04‰ to -0.19 ± 0.02‰), are almost homogeneous in the transitional Br3-BCrg layers (-0.01 ± 0.01‰ to -0.10 ± 0.02‰), and further decrease to -0.33 ± 0.01‰ in the permanently submerged G1 and G2 layers. Copper concentrations in the Ap layer show some fluctuations (25.8 to 29.0 μg/g), increase in the Br2 and Br3 layers (23.9 μg/g to 31.9 μg/g), and then decrease to 15.1 μg/g in the lower layers. The lack of coupling between δ⁶⁵Cu values and Cu concentrations may be ascribed to various physicochemical conditions in different layers. In the upper layers, Cu(I) enriched in light isotopes migrates downward with soil solutions under flooded conditions, leaving the soils of the Ap and Br1 layers enriched in heavy Cu isotopes. In the Br2 layer, the readsorption of light Cu isotopes on clay minerals results in decreased δ⁶⁵Cu values and increased Cu concentrations. In the Br3-BCrg layers, Cu(I) can be oxidized to Cu(II). The homogeneous Cu isotopes in these layers may mainly result from equilibrium adsorption of Cu on clay minerals. The decreased δ⁶⁵Cu values and Cu concentrations in the G layer are mainly attributed to groundwater transport in this layer. This study represents the Cu isotope variations in a paddy soil profile and the possible mechanism of Cu isotope fractionation.

The geochemical behavior of Cu and its isotopes in the Yangtze River

Copper (Cu) isotopes can be a useful tool to constrain the interaction of water and the environment, but they have not been widely applied to riverine research in the preceding decades. Isotopically heavy Cu in rivers (global average: about +0.7‰) compared to rocks (at about 0‰) has been attributed to: a) the mobilization of heavy Cu during oxidative weathering, and b) partitioning between an isotopically heavy, organically complexed dissolved pool, and an isotopically light pool adsorbed to particulates. Here, we report Cu concentrations and isotope ratios of the main stream of the Yangtze River and its several tributaries. We find that the Yangtze River exhibits anomalously heavy Cu isotope compositions compared to other rivers: δ⁶⁵Cu_{NIST 976} of dissolved Cu for the main stream, from Chongqing to Nanjing, ranges from +0.59 to +1.65‰, while the tributaries vary from +0.48 to +1.20‰. A negative correlation is observed between Cu concentrations and Cu isotope compositions. We attribute the anomalous Cu isotope geochemistry of the Yangtze River to two key features of the basin: first, the influence of the Three Gorges Dam (TGD), and second, the presence of extensive Cu sulphide deposits close to the lower reaches of the river. In the upper reaches, downstream towards the TGD, δ⁶⁵Cu values increase as Cu concentrations decrease, reflecting the preferential adsorption of light Cu by sedimenting particulate phases. δ⁶⁵Cu values continue to increase to a maximum of +1.65‰ in the middle reaches, at Guangxingzhou. The lower reaches, from Jiujiang to Tongling, are characterized by less positive values of δ⁶⁵Cu (at about +0.60‰), due to the oxidative weathering of Cu sulphide deposits. The overall Cu-δ⁶⁵Cu trend in the river reflects mixing of these waters from the lower reaches, influenced by Cu sulphides, with waters from upstream, which have lower Cu concentrations and elevated δ⁶⁵Cu values.

Experiments on Cu-isotope fractionation between chlorine-bearing fluid and silicate magma: implications for fluid exsolution and porphyry Cu deposits

Hydrothermal fluid is essential for transporting metals in the crust and mantle. To explore the potential of Cu isotopes as a tracer of hydrothermal-fluid activity, Cu-isotope fractionation factors between Cl-bearing aqueous fluids and silicate magmas (andesite, dacite, rhyolite dacite, rhyolite and haplogranite) were experimentally calibrated. Fluids containing 1.75-14 wt.% Cl were mixed together with rock powders in Au₉₅Cu₅ alloy capsules, which were equilibrated in cold-seal pressure vessels for 5-13 days at 800-850°C and 2 kbar. The elemental and Cu-isotopic compositions of the recovered aqueous fluid and solid phases were analyzed by (LA-) ICP-MS and multi-collector inductively coupled plasma mass spectrometry, respectively. Our experimental results show that the fluid phases are consistently enriched in heavy Cu isotope (⁶⁵Cu) relative to the coexisting silicates. The Cu-isotope fractionation factor (Δ⁶⁵Cu_FLUID-MELT) ranges from 0.08 ± 0.01‰ to 0.69 ± 0.02‰. The experimental results show that the Cu-isotopic fractionation factors between aqueous fluids and silicates strongly depend on the Cu speciation in the fluids (e.g. CuCl(H₂O), CuCl₂ ^- and CuCl₃ ^2-) and silicate melts (CuO_1/2), suggesting that the exsolved fluids may have higher δ⁶⁵Cu than the residual magmas. Our results suggest the elevated δ⁶⁵Cu values in Cu-enriched rocks could be produced by addition of aqueous fluids exsolved from magmas. Together with previous studies on Cu isotopes in the brine and vapor phases of porphyry deposits, our results are helpful for better understanding Cu-mineralization processes.

Lighter serum copper isotopic composition in patients with early non-alcoholic fatty liver disease

Objective

The occurrence of non-alcoholic fatty liver disease (NAFLD) is globally increasing. To challenge the current incidence of NAFLD, non-invasive markers that could identify patients at risk or monitor disease progression are an important need. Copper intake and organ copper concentrations have earlier been linked to NAFLD progression, but serum copper does not adequately represent the disease state. Cu atoms occur under the form of two stable isotopes, ⁶³Cu and ⁶⁵Cu, and the ratio of both (expressed as δ⁶⁵Cu, in  ‰) in blood serum has been shown to be altered in chronic liver disease. To assess whether the Cu isotope ratio might predict disease occurrence and progression of NAFLD, the serum Cu isotopic composition of patients with different stages of NAFLD was determined.

Results

Our results showed that serum δ⁶⁵Cu values were lower in NAFLD patients, already at the level of simple steatosis, and remained stable during further disease progression. ROC analysis shows an almost perfect diagnostic ability of serum δ⁶⁵Cu values for NAFLD, but no discrimination between different severity degrees could be made. Therefore, the serum Cu isotopic composition might show potential for early diagnosis of NAFLD patients.

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

The copper (Cu) content and isotopic composition were studied in soils and in pine tree rings at locations close to and far from the Cu smelter, located at Kitwe, Zambia. The soil in the remote area contained 25-75mgkg^-1 Cu, whereas the soil close to the smelter contained 207-44,000mgkg^-1 Cu. The δ⁶⁵Cu at the remote area and close to the smelter varied in the range -0.40 to -0.11‰, and -0.44 to 0.01‰ respectively. The δ⁶⁵Cu of the surface soil at both profiles (-0.44 to -0.40‰) is similar to the isotopic composition of the concentrates processed in the smelter (-0.75 to -0.45‰), i.e. both locations are affected by Cu ore dust. The increase in the δ⁶⁵Cu in the direction towards the centre of the profile is caused by the oxidative dissolution of Cu(I) from ore minerals, during which heavier Cu is released. In deeper parts of the profile, there is a slight decrease in δ⁶⁵Cu because of easier mobilisation of the lighter isotope. The tree rings at the two locations differ in the total contents and isotopic composition. At the less contaminated site, the Cu contents equal 0.4 to 1.1mgkg^-1 while, at the polluted site, the Cu contents vary in the range 3 to 47mgkg^-1. Whereas, at the less contaminated location, the tree rings are substantially enriched in lighter Cu (δ⁶⁵Cu=-0.76 to -2.2‰), at locations close to the smelter the tree rings have an isotopic composition (-0.31 to -0.88‰) similar to that of the contaminated soil or processed ore. The isotopic compositions of the tree rings close to the smelter are affected particularly by interception of dust containing Cu ore. The δ¹³C in tree rings demonstrate the interconnection of acidification and Cu mobility.

Origin and fate of copper in a small Mediterranean vineyard catchment: new insights from combined chemical extraction and δ65Cu isotopic composition

For centuries, many Mediterranean catchments were covered with vineyards in which copper was widely applied to protect grapevines against fungus. In the Mediterranean-type flow regime, brief and intense flood events increase the stream water discharge by up to 10 times and cause soil leaching and storm runoff. Because vineyards are primarily cultivated on steep slopes, high Cu fluxes are discharged by surface water runoff into the rivers. The purpose of this work was to investigate the riverine behavior and transport of anthropogenic Cu by coupling a sequential chemical extraction (SCE) procedure, used to determine Cu partitioning between residual and non-residual fractions, with δ(65)Cu isotopic measurements in each fraction. In the Baillaury catchment, France, we sampled soils (cultivated and abandoned), river bed sediments (BS), suspended particulate matter (SPM), and river water during the flash flood event of February 2009. Copper partitioning using SCE show that most of Cu in abandoned vineyard soil was in the residual phase (>60%) whereas in cultivated soil, BS and SPM, Cu was mostly (>25%) in non-residual fractions, mainly adsorbed onto iron oxide fractions. A small fraction of Cu was associated with organic matter (5 to 10%). Calculated enrichment factors (EF) are higher than 2 and the anthropogenic contribution was estimated between 50 to 85%. Values for δ(65)Cu in bulk samples were similar to bedrock therefore; δ(65)Cu on SCE fractions of superficial soils and SPM allowed for discrimination between Cu origin and distribution. Copper in residual fractions was of natural mineral origin (δ(65)Cu close to local bedrock, +0.07‰). Copper in water soluble fraction of SPM (δ(65)Cu=+0.26‰) was similar to dissolved river Cu (δ(65)Cu=+0.31‰). Copper from fungicide treatment (δ(65)Cu=-0.35‰) was bound to organic matter (δ(65)Cu=-0.20‰) without or with slight isotopic fractioning. A preferential adsorption of (65)Cu onto iron oxides (δ(65)Cu=+0.5‰) is shown.