Trace Metal Enrichment Research Articles

Nature of Devonian anoxic events based on multiproxy records from Panthalassa, NW Canada

Causes and controls of Middle-Late Devonian anoxic and biotic events are highly debated, and our results from the oceanographically open black-shale succession called the Horn River Group (HRG) provide elucidations. These strata are overall lean in siliciclastics and enriched in authigenic U, Mo, V, and planktogenic organic matter. We focus on three major event horizons within the HRG. Within new conodont constraints, these horizons are correlated to the global Frasnes-Manticoceras, basal punctata, and late punctata events. Two major characteristics of these three events are positive δ13Corg excursions of ~2.0–3.0‰ amplitude and U, Mo, V enrichment, which indicate pulses of severe anoxia within the basin. Trace-metal enrichment horizons are offset from associated isotopic excursions, indicating a time lag of ~80–125 ky between the onset of the δ13C excursion and the onset of severe anoxia. We demonstrate that these events are robust and traceable in off-bank anoxic facies across the entire basin, including remote locations ≥400 km away from the study area. The onsets of three major δ13C excursions are coupled with the thin spikes of elemental mercury and siliciclastic content. Our observations align with the hypothesis that Middle-Late Devonian anoxic events were triggered by pulses of large-scale volcanism through the same pathway as classical Mesozoic oceanic anoxic events. No rigorous evidence exists that land plants could drive shelfal seas into anoxia and mass extinctions.

Productivity-induced redox transition within the Niobrara formation, western Interior seaway, Colorado

Deposition of organic rich shale/marl within the Niobrara Formation during the Coniacian to Santonian Ocean anoxic event (OAE 3) within the Western Interior Seaway presents a unique record of variable organic carbon burial under a greenhouse climate. In order to understand the mechanisms behind the changes from low to high organic carbon burial, and how this high burial rate was sustained for over 3 Ma, productivity within the surface waters and subsequent preservation of organic matter within the sediments were investigated in this study. Based on the multiproxy approach adopted herein, the sedimentary record of the Niobrara Formation in northern Colorado can be separated into two distinct intervals: Interval 1 and Interval 2. Interval 1 is bioturbated, organic lean and oxic, with low to moderate trace metal enrichment except for Mn. Interval 2 is laminated, organic-rich, more enriched in trace metals U, V and Mo, and less enriched in Mn, typical of anoxia during deposition. The transition from oxic to anoxic conditions coincides with greater enrichments in TOC, Cu and Ni, suggesting enhanced productivity is associated with redox transitions within the Niobrara Formation. These local changes in productivity and redox conditions are sudden and coincide with recurring iron (Fe) and phosphorus (P)-rich bentonites, evidence of ash deposition that could have enhanced nutrient supply, productivity and accumulation of organic carbon. Consequently, perturbations of the global carbon cycle associated with OAE 3 were inferred to have occurred in Interval 2.High total Fe, total sulfur, Fe/Al, and trace metal enrichments in Interval 2 are intrinsically linked to prevalence of anoxic bottom-water conditions which enhanced burial of pyrite and organic matter. Results from productivity proxies and Fe–S–C ternary plots show that Fe limitation on pyrite formation under anoxic porewater enhanced organic carbon burial and preservation. This implies Fe enrichment within the sediments favored pyrite formation instead of organic matter sulfidization, leading to a complex relationship between S and organic carbon in the marine sediments during Niobrara deposition.

Geological, geochemical and fluid inclusion features of Kömürlükdere and Göçükdibi Cu-Zn ore (Central Pontides, Turkey): Implications for their genesis

The Kömürlükdere and Göçükdibi Cu-Zn ores are located in the Central Pontide orogenic belt, where Besshi-type deposits (such as Hanönü, Zeybek, Sayyayla [Kastamonu]) have been discovered in last two decades. The Göçükdibi and Kömürlükdere ores are hosted in metabasites and quartz schist that belong to the Middle Jurassic Kunduz metamorphic rocks in the accretionary complex in the Central Pontides. The ore bodies show stratiform features, parallel to schistosity, within an alternation of metabasite and quartz schist succession. The average thicknesses of the ore zone and ore levels within the ore zone are 12 m and 3 cm, respectively. The ore bodies contain chalcopyrite, sphalerite, and magnetite, with dominant pyrite formed during the ore formation phase. Meanwhile, hematite, covellite, malachite, and goethite minerals formed during the supergene processes.Microprobe studies showed that the Fe and Cd content of sphalerite varies from 0.08 to 1.12 wt%, indicating Fe-poor sphalerite, and 0.08–0.27 wt%, respectively. The Zn/Cd ratios (average 274.4 for Kömürlükdere, 288.6 for Göçükdibi) of the sphalerite are comparable to those of the worldwide volcanogenic-massive sulfide (VMS) ore system related to andesitic-basaltic source rocks. The Co/Ni ratio (mean 3.2) of pyrite shows volcanogenic pyrite.The average δ34S of the stratiform pyrites is 3.9 ‰ (ranging from 2.06 ‰ to 5.34 ‰), indicating that the sulfur comes from a large homogeneous source, possibly magmatic. The average homogenization temperature (Th) and salinity of fluid inclusions obtained from quartz and sphalerite are 313 °C and 7.7 % equiv. NaCl, respectively, and similar to those of the global VMS deposits.The metabasites contain an average of 164 ppm Cu, 127 ppm Zn, and 2.2 ppm Sb, which shows enrichment several times greater than the background value of the basalts. Meanwhile the ore levels contain an average 0.23 % and 0.83 % Cu and Zn values, respectively. The trace metal enrichment of associated metabasites and the ore zones is evident for elements such as Cu, Zn, Cd, As, and Sb, indicating that they both precipitated in the same basin as syngenetic, and that there was repeated pulses of metal-rich fluids exhaled into the basin.Field observations and analytical data (mineral chemistry, sulfur isotope, fluid inclusion, etc.) show that the Kömürlükdere and Göçükdibi Cu-Zn ore bodies occurred as Besshi-type deposits within the Middle Jurassic Central Pontide Supercontinent, which developed in the marine environment appropriate to the accretionary complex located along the southern margin of Eurasia.

Maastrichtian Anoxia and Its Influence on Organic Matter and Trace Metal Patterns in the Southern Tethys Realm of Egypt during Greenhouse Variability.

Maastrichtian organic-rich sediments of Egypt were deposited under a warm greenhouse climate along the stable African shelf. This study presents an integrated analysis of the geochemical, mineralogical, and palynological data from Maastrichtian organic-rich sediments in the northwest Red Sea region of Egypt. The aim of the study is to assess the impact of anoxia on the enrichment of organic matter and trace metals and to reconstruct a model for the formation of these sediments. The sediments are hosted within the Duwi and Dakhla formations, covering an interval of ∼1.14-2.39 million years. Our data indicate variable bottom-water oxygen-level conditions for early and late Maastrichtian sediments. The C-S-Fe systematics and redox geochemical proxies (e.g., V/(V + Ni), Ni/Co, and Uauthigenic) suggest dysoxic to anoxic depositional conditions for the late and early Maastrichtian organic-rich sediments, respectively. The early Maastrichtian sediments contain abundant small-sized framboids (average = 4.2-5.5 μm), suggesting anoxic conditions, while the late Maastrichtian sediments have larger framboids (average = 4-7.1 μm), indicating dysoxic conditions. The palynofacies analyses reveal the high abundance of amorphous organic matter and confirm the predominance of anoxic conditions during deposition of these organic-rich sediments. The early Maastrichtian organic-rich sediments have a significant Climate concentration of Mo, V, and U, indicating high biogenic production rates and distinct preservation conditions. Additionally, the data imply that oxygen deficiency conditions and low sedimentation rates were the main factors controlling the preservation of organic matter in the studied sediments. Overall, our study provides insights into the environmental conditions and processes that led to the formation of the Maastrichtian organic-rich sediments in Egypt.

Composition, distribution and enrichment of trace metals in sediments from the muddy area off the southern Shandong Peninsula in the Northwestern South Yellow Sea of China since 10,000 years

We analyzed ten trace metals (Cu, Pb, Zn, Cr, Cd, Hg, As, Ni, V, Co and Ni) in sediments of the upper 14.98 m of core WHZK01 from the muddy area off the Shandong Peninsula, northwestern South Yellow Sea, to analyze their content, vertical distribution, and the enrichment status. Except for Hg and As, the other metals (Cu, Pb, Zn, Cr, Cd, Ni, V, Co and Ni) were mainly controlled by grain size. When the sediment particle size became smaller, the metal content reached a high level. Moreover, oxides and hydroxides of Al, Ti, Fe, and Mn also contributed to the metal enrichments due to their strong adsorption to the metals. Over the past four stages of 10–7 kyr BP, 7–4.5 kyr BP, 4.5–2.5 kyr BP, and 2.5 kyr BP to date, the metal values have shown a trend of increasing – fluctuating to high values – decreasing – re-increasing, respectively. However, since 4.5 kyr BP, Hg concentrations have been on an increasing trend, associated with the release of large amounts of contaminants into the environment from ancient human metal mining and smelting activities. As concentrations, despite the fluctuating changes, have remained relatively stable at high levels since 5.5 kyr BP, associated with their high background values.

Trace Metal(loid) Migration from Road Dust to Local Vegetables and Tree Tissues and the Bioaccessibility-Based Health Risk: Impacts of Vehicle Operation-Associated Emissions.

Traffic activities release large amounts of trace metal(loid)s in urban environments. However, the impact of vehicle operation-associated emissions on trace metal(loid) enrichment in road dust and the potential migration of these trace metal(loid)s to the surrounding environment remain unclear. We evaluated the contamination, sequential fraction, and bioaccessibility of trace metal(loid)s in urban environments by assessing their presence in road dust, garden vegetables, and tree tissues, including bark and aerial roots, at a traffic-training venue impacted by vehicle operation emissions and, finally, calculated the bioaccessibility-based health risk. The results indicated a significant accumulation of trace metal(loid)s in road dust, with the highest lead (Pb), cadmium (Cd), and antimony (Sb) concentrations in the garage entrance area due to higher vehicle volumes, frequent vehicle starts and stops, and lower speeds. Aerial roots exposed to hill start conditions exhibited the highest Pb, Zn, and Sb levels, potentially caused by high road dust resuspension, confirming that this tree tissue is an appropriate bioindicator. Sequential extraction revealed high percentages of carbonate-, Fe/Mn oxide-, and organic/sulphide-associated fractions of Pb, copper (Cu), and zinc (Zn) in road dust, while most Cd, Cr, Ni, and Sb occurred as residual fractions. According to the potential mobilizable fractions in sequential extraction, the in vitro gastrointestinal method could be more suitable than the physiologically based extraction test to evaluate the bioaccessibility-related risk of traffic-impacted road dust. The bioaccessibility-based health risk assessment of the road dust or soil confirmed no concern about noncarcinogenic risk, while the major risk originated from Pb although leaded gasoline was prohibited before the venue establishment. Furthermore, the cancer risks (CRs) analysis showed the probable occurrence of carcinogenic health effects from Cd and Ni to adults and from Cd, Cr, and Ni to children. Furthermore, the Cd and Pb concentrations in the edible leaves of cabbage and radish growing in gardens were higher than the recommended maximum value. This study focused on the health risks of road dust directly impacted by vehicle emissions and provides accurate predictions of trace metal(loid) contamination sources in the urban environment.

Geochemical Contamination, Speciation, and Bioaccessibility of Trace Metals in Road Dust of a Megacity (Guangzhou) in Southern China: Implications for Human Health.

Road dust has been severely contaminated by trace metals and has become a major health risk to urban residents. However, there is a lack of information on bioaccessible trace metals in road dust, which is necessary for an accurate health risk assessment. In this study, we collected road dust samples from industrial areas, traffic intersections, and agricultural fields from a megacity (Guangzhou), China, and conducted a geochemical enrichment, speciation, and bioaccessibility-based health risk assessment of trace metals. In comparison with local soil background values, the results revealed a significant accumulation of trace metals, including Zn, Cd, Cu, and Pb in the road dust, which is considered moderate to heavy pollution. Sequential extraction indicated that most trace metals in the road dust were primarily composed of a Fe/Mn oxide-bound fraction, carbonate-bound fraction, and residual fraction, while the dominant fraction was the organic matter-bound fraction of Cu, and the residual fractions of As, Cr, and Ni. The in vitro gastrointestinal (IVG) method revealed that high percentages of Zn, Cd, Cu, and As were bioaccessible, suggesting the possible dissolution of trace metals from adsorbed and carbonate-associated fractions in road dust exposed to the biological fluid matrix. The IVG bioaccessibility-based concentration largely decreased the noncarcinogenic health risk to a negligible level. Nevertheless, the entire population is still exposed to the cumulative probability of a carcinogenic risk, which is primarily contributed to by As, Cd, Cr, and Pb. Future identification of the exact sources of these toxic metals would be helpful for the appropriate management of urban road dust contamination.

Meso- and microplastic distribution and spatial connections to metal contaminations in highly cultivated and urbanised floodplain soilscapes – a case study from the Nidda River (Germany)

Floodplain soilscapes act as temporary sinks in the environment and are nowadays affected by multiple contaminant accumulations and exposures, including different trace metals and plastics. Despite increasing knowledge about the occurrence and behaviour of plastics at the interface between aquatic and terrestrial systems, there are still major uncertainties about the spatial distribution of plastics, their sources and deposition, as well as spatial relationships with other contaminants. Our recent case study addresses these questions, using the example of a river system ranging from rural to urban areas. Based on a geospatial sampling approach we obtained data about soil properties, metal contents via ICP-MS analyses, and particle-based (171 μm – 52 mm) plastic contents, analysed using sodium chloride density separation, visual fluorescence identification and ATR-FTIR analysis. We found plastic contents of 0.00–35.82 p kg− 1 and zero to moderate metal enrichments. Levels of both contaminations occur in the lower range of known concentrations in floodplain soils and show a different spatial distribution along the river course and in the floodplain cross-section. Furthermore, we found that plastic enrichment occurs in the uppermost soil layers, while trace metal enrichment is equally distributed over depth, indicating different sources like flood dynamics and agricultural practice during different deposition periods. Finally, direct short to long-term anthropogenic impacts, like floodplain restoration or tillage may affect plastic enrichments, raising questions for future research directions within floodplain soilscapes.

Processes of Enrichment of Trace Metals for High-Tech Applications in Hydrothermal Veins of the Ruhr Basin and the Rhenish Massif, Germany

ABSTRACTThe increasing demand for high-tech trace elements supports the need for systematic investigations of their primary occurrences. Mineralogy and trace element characteristics of hydrothermal base-metal veins from the Ruhr Basin (Ruhrgebiet) and the Rhenish Massif (Bergisches Land) in Germany were studied by energy-dispersive X-ray fluorescence mapping, laser ablation-ICP-mass spectrometry, and electron microprobe analyses. Quantitative trace element analysis proves elevated concentrations of Ge and Ga in sphalerite from the Ruhrgebiet. In addition to about 6 Mt of sphalerite-dominated ore, a potential of about 10 t of Ge is indicated to be concentrated in the Auguste Victoria and Graf-Moltke base-metal deposits in the Ruhrgebiet. Assessments on physicochemical fluid properties and metal sources using vitrinite reflectance analysis and host rock investigation indicate a genetic link between the Carboniferous carbonaceous rocks (hosting a number of coal seams) and significant trace metal enrichment in the veins. Gallium enrichment, outlining primary growth zones in ore stage 1 sphalerite, is facilitated by the alteration of Al-bearing minerals in adjacent host rocks due to intense fluid/rock interaction. Reduced Ga and very low In concentrations in ore stage 2 may reflect sealed fluid pathways or changes in the fluid properties. The high level of organic matter in the system probably supported enrichment of Ge in the hydrothermal fluids. The constantly high levels of fixation of Ge in sector zoning patterns of the sphalerite during both ore stages indicate a continuous supply. Elevated contents of Sb together with Cu, As, and Pb in sectors of the sphalerite grains point to a local enrichment of nanometer-scale inclusions of sulfosalt-like phases. Sphalerite of both districts and even of the two ore stages in the Ruhrgebiet shows variations in δ34S isotope compositions due to varying sulfur sources. Both the host rock composition and the presence of organic matter contributed to the trace metal enrichment in the Ruhrgebiet base-metal sulfides as compared to the low contents typical of base-metal ore from the Bergisches Land.

Trace Metal Enrichment in the Colloidal Fraction in Soils Developing on Abandoned Mine Spoils

The release of colloid-bound trace metals from abandoned coal mine spoils can potentially be a significant source of contamination during weathering. We examined the size-dependent enrichment of trace metals in mine spoil samples using centrifugation and acid extraction to compare metal loading in the bulk and colloid fractions. A combination of X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and focused ion beam (FIB) sectioning of selected colloids for transmission electron microscopy (TEM) analyses was used to determine the morphology and elemental and mineral composition at the micro- and nanoscales. In contrast to bulk soils, primary Fe-sulfides (up to 11%) and secondary Fe(III)-bearing phases (up to 5%) were a significant portion of the colloid mineralogy. Secondary Fe-(hydro)oxides and (hydroxy)sulfates were enriched with Mn, Ni, Cu, and Zn, and these metals showed stronger correlations with Fe in the colloid fraction (R2 of 0.58, 0.77, 0.94, and 0.81, respectively) than in the bulk fraction (R2 of 0.40, 0.09, 0.84, and 0.62, respectively), indicating that Fe-bearing colloids are likely major trace-metal-bearing phases. The results from this study will help to design better remediation projects for abandoned mine spoils to better account for a potentially underappreciated mode of contaminant transport.

A Chelating Resin of EDTA-Type Modified Cross-Linking Polystyrene to Preconcentrate Trace Metals for Seawater Detection.

The determination of trace metals in seawater is an important project of marine environmental monitoring. However, the presence of many alkali metal ions with high concentration, such as sodium ion, seriously interferes with the detection limit and accuracy of atomic absorption spectrometry (AAS, flame/graphite furnace integrated). The conventional chemical methods for the enrichment of trace metals are complex, and low boiling point organic solvents are used. In this paper, a kind of commercial cross-linked polystyrene resin microspheres was chloromethylated and aminated to introduce EDTA-type amino polycarboxylic groups and then loaded in a column as the absorption filler. A set of seawater pretreatment and enrichment devices was designed and assembled. The enriching process and conditions of trace Cu, Zn, Pb, and Cd in standard seawater were studied. 10 g of the modified resin could enrich the equivalent seawater and remove successfully the light metal ions. pH = 5∼9 and 0.2 mL/min of the flow rate were the suitable conditions for preconcentration. The enriched metal ions in the eluent were analyzed on the AAS. Compared with the conventional solvent method, the novel material and enrichment device have high preconcentration efficiency, strong anti-interference ability, and low cost and could be directly applied for routine seawater detection.

Intensive ocean anoxia and large δ13Ccarb perturbations during the Carnian Humid Episode (Late Triassic) in Southwest China

The Carnian Humid Episode (CHE) represents a dramatic dry to wet climate transition in the Late Triassic. Manifestations of this climate shift and its associated biological and environmental responses are not fully understood. Here, we carried out carbonate carbon isotope, trace metal, and pyrite framboid analyses at Wolonggang in southwest China to trace palaeoenvironmental changes during this critical interval. The CHE at Wolonggang is marked by the development of fine laminated carbonaceous siltstones and black shales overlying the intensely bioturbated Zhuganpo limestone deposited in the latest Julian 1. This lithological change is accompanied by two negative δ 13 C carb excursions, a strong enrichment of redox-sensitive trace metals U and Mo, and the development of abundant small pyrite framboids with an average diameter < 5 μm. The sedimentary and geochemical evidence collectively suggest a sharp decrease in carbonate production and a major carbon cycle disturbance, coinciding with the onset of intense ocean anoxia and the mass mortality of burrowing faunas. Unlike other areas in the western Tethys, the aftermath of the CHE at Wolonggang is characterized by long-lasting ocean anoxia, with weak carbonate production persisting at least to the late Tuvalian. This is evidenced by the deposition of finely laminated silty carbonates, marls, and carbonaceous siltstones with rare benthic fossils in the Wayao Formation. Our study suggests that anoxic-euxinic environments widely developed along the southwest margins of the Yangtze Platform and in the Nanpanjiang Basin, probably contributing to the loss of marine faunas during the CHE. • Sedimentary and bio-chemostratigraphic investigations were carried out in a key Carnian section in SW China. • Carbon cycle instability was seen during the Carnian Humid Episode. • Anoxia was basin-wide and long-lasting during the CHE and its aftermath. • Warming and anoxia played key roles in the loss of marine faunas during Carnian.

Evaluation of alkalinity sources to Cryogenian cap carbonates, and implications for cap carbonate formation models

Current cap carbonate formation models invoke a number of different alkalinity sources for the Neoproterozoic deglacial ocean (e.g., weathering alkalinity, hydrothermal alkalinity, microbial sulfate reduction (MSR) alkalinity, and methane oxidation alkalinity). Assessment of the competing models depends in part on an evaluation of their proposed alkalinity source(s). In the Nanhua rift basin of South China, recently discovered Sturtian cap carbonates on horsts have the potential to address this issue owing to sedimentological and geochemical differences between them and correlative deepwater deposits from adjacent grabens. Cap carbonates at three sites in northeastern Guizhou Province, China were selected for petrographic, XRD, XRF, ICP-MS, in-situ LA-ICP-MS, and Sr and Nd isotope analyses to evaluate the conditions and processes under which they formed: (1) JJS, a high-energy shallow-water (platform) setting that accumulated white laminated dolostone and pisolitic grainstone, (2) ZK01, an intermediate-depth (upper slope) setting that accumulated dark-gray laminated dolostone, and (3) ZK4207, a deep-water (basinal) setting that accumulated organic-rich Mn‑carbonates of the basal Datangpo Formation. The salinity proxy B/Ga records brackish conditions at JJS (4.7 ± 1.2) versus fully marine conditions at ZK01 (7.5 ± 0.8) and ZK4207 (9.1 ± 2.0). Hydrothermal influences, as proxied by high Eu/Eu*, trace-metal (Co, Ni, Cu, V) enrichments, and radiogenic SrNd isotopic compositions, were strong in the latter sections but absent at JJS. These observations document the existence in the post-Sturtian Nanhua Basin of a reduced-salinity surface layer presumably containing a large glacial meltwater component and lacking hydrothermal inputs, and a fully marine deep watermass subject to strong hydrothermal inputs. Carbonate δ13C variation between JJS (−2 to +2‰), ZK01 (−4 to 0‰), and ZK4207 (−7 to −6‰) records a pronounced vertical carbon-isotope gradient in the Nanhua Basin, consistent with elevated marine productivity in the context of strong salinity/density stratification. Massive inputs of alkalinity from meltwater sources are supported by a ∼ 3.5× greater flux to surface-layer dolomitic cap carbonates than to basinal Mn‑carbonates during the Sturtian deglaciation, although strong correlations between intermediate/deep-water carbonates and hydrothermal proxies imply that basin-floor vents were an additional source of alkalinity. Our study provides insight into the mechanisms of formation of cap carbonates generally, with implications for both Sturtian and Marinoan cap carbonate deposits on other cratons.

Paleoenvironmental redox evolution of Ediacaran-Cambrian restricted seas in the core of West Gondwana: Insights from trace-metal geochemistry and stratigraphy of the Bambuí Group, east Brazil

The sedimentary evolution of the Bambuí foreland basin system in the interior of West Gondwana is marked by periods of connection and isolation from the global ocean during the late Neoproterozoic and early Paleozoic. To understand the link between these periods and seawater redox conditions, we present an integrated study of trace-metal geochemistry and stratigraphy of the carbonate-siliciclastic rocks from the two lowermost second order transgressive-regressive sequences of the Bambuí Group, east Brazil. The basal 2nd-order sequence trace-metal pattern shows a progressive decrease of mass fractions of Co, Cr, Ni, Cu, Mo, U, V, Zn, and Cd, concomitant with a progressive decrease of Al and Fe contents and Mo/TOC ratios. Among all these elements, only Cd, Mo and U mass fractions seem to be less or not affected by detrital influence, so they can be used as reliable redox proxies for the paleoenvironmental analysis of the studied Bambuí strata. Moreover, normalization to aluminum shows a progressive increase of trace-metal enrichments for Cd and Mo in the order of 0.1–10 times and for U in the order of 1–100 times, accompanied by a progressive increase of organic carbon content upward section. These changes in sedimentary trace-metal patterns provide evidence for the chemical evolution of basinal deep-waters, whose conditions changed progressively from suboxic-anoxic to anoxic-euxinic at the basal transgressive-regressive sequence. We suggest that the paleomarine system represented by the basal Bambuí Group has probably evolved as an intracontinental silled basin recording changes in seawater chemistry associated with redox variations and restricted hydrographic conditions. Sedimentary trace-metal patterns indicate that Bambuí epeiric sea was initially in communication with open ocean followed by the marine restriction during the transgressive and regressive cycles, respectively. This resulted in a long deepwater residence time and chemical evolution of deep watermass as a response to tectonic pulses and consequent sea-level variations during the restricted stage. Under anoxic-euxinic conditions of seawater, trace metals scarcity and micronutrient fixation limitation would have impacted nitrate bioavailability, preventing the evolution of early benthic metazoans in the Bambuí paleomarine system during the late Ediacaran and early Cambrian.

Trace metal enrichment and sediment quality in coastal-urban rivers along the Indian Ocean coast, Dar es Salaam, Tanzania

Trace metal enrichment and sediment quality in coastal-urban rivers along the Indian Ocean coast, Dar es Salaam, Tanzania

Hydrothermal activity and associated subsurface processes at Niuatahi rear-arc volcano, North East Lau Basin, SW Pacific: Implications from trace elements and stable isotope systematics in vent fluids

Hydrothermal activity is abundant in the area between the North Eastern Lau Spreading Center and the Tofua intra-oceanic island arc with multiple active sites in the rear-arc at the Mata and Niuatahi volcanoes. We report geochemical data for high-temperature vent fluids sampled from within the caldera of Niuatahi volcano. Hydrothermal fluids were sampled from three vent sites: South Central, Southwestern Cone and Northern Cone located in water depths between 1607 and 1699 m. Maximum temperatures of 334 °C were measured and pH values were as low as 2.8. The vent fluids were characterized by depletions in Mg, SO4 and U as well as an enrichment of (trace) metals (e.g., Fe, Mn, K, Li) and dissolved gases (e.g., H2S, CO2, H2) relative to seawater. Water-rock ratios calculated based on concentrations (K, Li, Rb, Cs, REE) and isotope ratios (δ7Li, δ11B, 87Sr/86Sr) suggest fluid-rock interactions under rock-dominated conditions at all three vent sites.The South Central vents lie closest to the site of most recent volcanic activity in the Niuatahi caldera. Vent fluids are characterized by relatively low Cl concentrations (as low as 292 mmol/kg) that are indicative of sub-critical phase separation. These fluids also had the lowest pH values (2.8–3.1), highest H2S and lowest H2, CH4 and CO2 concentrations of the three sites. The δD and δ18O values suggest that H2O and CO2 were added in small amounts by subduction-related volcanic vapors. However, there was no evidence for magmatic SO2 input in the vent fluids at the time of sampling in 2018. Vent fluids from the Northern and Southwestern Cone sites on the caldera ring fault had a similar chemical composition, despite being situated at opposite sides of the caldera. Fluids from these sites had lower Fe/Mn ratios (<1) and H2S concentrations than those from South Central suggesting that they were affected by subsurface cooling and sulfide precipitation. This study indicates variations of the Niuatahi hydrothermal vent sites depending on the location within the caldera with variable effects of fluid-rock interaction and magmatic input on fluid compositions in agreement with previous work on fluid S isotopes and sulfides.

Variability of sulfur isotopes and trace metals in pyrites from the upper oceanic crust of the South China Sea basin, implications for sulfur and trace metal cycling in subsurface

The circulation of seawater within the oceanic crust promotes cycling of metals and sulfur, as well as development of the subsurface biosphere. Characterization of the full spectrum of sulfide geochemistry in the altered oceanic crust is critical for a complete understanding of global cycling of sulfur and metals, while those in off-axis hydrothermal circulation have received less attention. This study applied a combination of in-situ sulfur isotopic and trace metal analyses to study the pyrite geochemical features in altered basalts of the South China Sea basin. This contribution unravels a detailed picture of the cycling of sulfur and metals in the subsurface. Such cycling is likely to be co-controlled by the hydrothermal and microbial activities when oceanic crusts transit from on-axis to off-axis hydrothermal systems.A total of five groups of pyrites associated with distinct mineral assemblages, morphologies, trace metal enrichment and sulfur isotopic values were observed in altered basalts. Pyrite disseminated (type 1) within the background hydrothermal alteration is characterized by δ34S values close to zero, with relative enrichment of trace metals (> 500 ppm), such as Ni, Co, and Cu. This type of pyrite is most likely to precipitate from upwelling high-temperature hydrothermal fluids when they ascended towards the seafloor. Sulfur was mainly derived from magmatic sulfides. Linear regression analyses of trace metal contents in disseminated pyrite show various strong positive correlations between trace metals reflecting a series of metal mobility processes, including incorporation into pyrite and leaching directly from sulfides or silicate minerals. Additionally, a population of pyrite has δ34S values ranging from +4 to +8 ‰ and low trace element contents, which reveals precipitation conditions where the ascending high-temperature hydrothermal fluids have mixed with significant amounts of seawater-sourced fluids. This group of pyrites is either formed by the replacement of silicates as patchy texture (type 2) or are exclusively associated with epidote‑carbonate veins (type 3). Furthermore, strongly positive δ34S signatures are observed within framboidal pyrite (type 4) (δ34S up to +57 ‰) and within overgrown euhedral pyrite (type 5) (δ34S up to +24 ‰). These unprecedented isotopically-heavy framboidal pyrite in modern oceanic crust presents a well-preserved organic matter framework, which is interpreted as a consequence of microbial sulfate reduction activities based on current observations. The extremely positive values of the sulfur isotopes could be produced by Rayleigh isotopic fractionation when ~77% sulfate (assumed with an initial seawater sulfate δ34S of 21%) is consumed by microorganisms in closed systems, in this case, the cavities in the altered basalt. The microorganisms meanwhile may enhance the sequestration of trace metals into pyrite, possibly through microbial metabolisms or detoxification processes. The positive δ34S values of overgrown euhedral pyrite (type 5) are interpreted to be mainly introduced by the involvement of seawater-derived sulfur or inherited from the framboidal pyrite.The various isotopic and elemental signatures in these five types of pyrites could be linked to either the hydrothermal or microbial processes occurring within the upper oceanic crust in the South China Sea basin. Both processes are critical to the metal and sulfur cycling in subsurface and should be considered jointly in future studies. Additionally, our results exemplify the potential roles of microorganisms, not only in accumulating trace metals in sulfides in the subsurface but also as a potential biosignature to reveal microbial activities in similar environments in the early Earth.

Trace metals enrichment and potential ecological risk in sediments of the Sepetiba Bay (Rio de Janeiro, SE Brazil)

The Sepetiba Bay (SB; SE Brazil) has been severely affected by growing of urbanization and industrial activity. This work aims to analyze the evolution of contamination by metals of sediments in SB. The results show a marked increasing trend in the concentrations of potentially toxic elements (PTEs), which is consistent with the rapid populational and industrial growth, mostly since 1970 CE. The remobilization and redistribution of sediments by currents have contributed to the dispersion of metals from the main source of pollutants to relatively distant regions. “Moderately to strongly polluted” sediments are also recorded in some sites in deeper sedimentary layers (namely in preindustrial periods), probably due to lithologic sources of the sediments. The concentrations of PTEs in SB are relatively high when compared with those found globally and in other Brazilian water bodies. Samples of high-resolution sediment cores confirmed that potential ecological risk to the coastal system is influenced not only through human actions but also by natural causes.

Trace metal enrichment in a tidally influenced, rural tributary of the upper Chesapeake Bay

Trace metals in sediments from the Chester River, a tidal tributary of the upper Chesapeake Bay with a predominantly rural, agricultural watershed, were investigated to better understand distributions and potential sources of metals. Sediments were analyzed for Al, Fe, Ni, Cr, Cu, Zn, As, Ag, Cd and organic C. Concentrations exceeded sediment toxicity guidelines in 44% of samples for Pb, and >20% for As, Ni, Cr, and Cu. Median enrichment factors (EF) for Cd, Ag, Pb, As and Zn were elevated above natural background levels. Nickel, Cu, Zn, and Cd exhibited significant differences in EF medians between the upper, middle, and lower segments of the river. Cadmium and As enrichments are presumably from application of inorganic and organic fertilizers in the watershed. Active marinas are likely an important source of metal enrichment, especially for Cu. The data underscore how land use in rural watersheds contributes to metals loading in aquatic systems.

Influence of different seabird species on trace metals content in Antarctic soils.

The behavior and feeding habits of different species of seabirds can influence the enrichment of trace metals in Antarctic soils. This study aimed to evaluate the influence of different species of seabirds on the concentrations of potentially toxic metals in Antarctic soils. For this, we collected soil samples in areas influenced by penguins, kelp gulls, and giant petrels. We analyzed the concentration of total organic carbon (TOC), total nitrogen (TN), available phosphorus (P) and metals by three different methods of extraction: USEPA 3051A, Mehlich-1, and distilled water. The concentrations of Cr and Hg presented positive correlations with P, TOC, and TN by the USEPA 3051A method, indicating the biotransport of these metals by seabirds. Soils influenced by penguins showed higher levels of P, TOC, TN, Cr, and Hg. Comparing the results from the different extractors, we found that Hg had the highest relative levels in the exchangeable fraction and the soil solution. Therefore, the soils with the influence of penguins present higher levels of biotransported trace metals, but this does not necessarily mean that these birds have a higher biotransport potential, since the concentration of trace metals in these soils may be related to their degree of ornithogenesis.