The current socio-economic, environmental and public health challenges that countries are facing clearly need common-defined strategies to inform and support our transition to a sustainable economy. ...Here, the technology-critical elements (which includes Ga, Ge, In, Te, Nb, Ta, Tl, the Platinum Group Elements and most of the rare-earth elements) are of great relevance in the development of emerging key technologies—including renewable energy, energy efficiency, electronics or the aerospace industry. In this context, the increasing use of technology-critical elements (TCEs) and associated environmental impacts (from mining to end-of-life waste products) is not restricted to a national level but covers most likely a global scale. Accordingly, the European COST Action TD1407: Network on Technology-Critical Elements (NOTICE)—from environmental processes to human health threats, has an overall objective for creating a network of scientists and practitioners interested in TCEs, from the evaluation of their environmental processes to understanding potential human health threats, with the aim of defining the current state of knowledge and gaps, proposing priority research lines/activities and acting as a platform for new collaborations and joint research projects. The Action is focused on three major scientific areas: (i) analytical chemistry, (ii) environmental biogeochemistry and (iii) human exposure and (eco)-toxicology.
The possible environmental impact of the recent increase in use of a group of technology-critical elements (Nb, Ta, Ga, In, Ge and Te) is analysed by reviewing published concentration profiles in ...environmental archives (ice cores, ombrotrophic peat bogs, freshwater sediments and moss surveys) and evaluating temporal trends in surface waters. No increase has so far been recorded. The low potential direct emissions of these elements, resulting from their absolute low production levels, make it unlikely that the increasing use of these elements in modern technology has any noticeable effect on their environmental concentrations on a global scale. This holds particularly true for those of these elements that are probably emitted in relatively high amounts from other human activities (i.e., coal combustion and non-ferrous smelting), such as In, the most studied element of the group.
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•The increased use of technology-critical elements may disturb their natural cycles.•No effect linked to new uses recorded for less-studied TCE (Ta, Nb, Ga, In, Ge, Te).•Changes due to indirect emissions (coal consumption, smelters) may be predominant.
Microbial mats and microbialites are essential tools for reconstructing early life and its environments. To better understand microbial trace element cycling, a microbial mat was collected from the ...sinkhole systems of the western shores of the Dead Sea, a dynamic environment exhibiting diverse extreme environments. Intense arsenic enrichment was measured (up to 6.5 million times higher than current concentrations in water, and 400 times the bulk concentration in the mat). Arsenic was found predominantly as As(V) in organic molecules, as shown by XANES spectra and high‐resolution elemental mapping. Arsenic cycling genes obtained from metagenomic analysis were associated with arsenic detoxification, supporting an active mechanism of As(V) uptake, As(III) efflux and organoarsenic accumulation in the extracellular polymeric substances (EPS) of the mat. Thus, we propose that such localized As enrichment can be attributed to a transient increase in As(V) concentrations in the circulating subsurface water of the Dead Sea shore and its subsequent incorporation into organoarsenic molecules through microbial detoxification processes. Our data set supports the possibility of metalloid enrichment recorded in very localized facies due to rapid geogenic fluctuations in the chemistry of the water flowing over a biofilm. In this context, this example calls for caution in interpreting metal(loid) enrichment in organic matter‐rich layers and microbialites of Paleoproterozoic origin. Arsenic signatures in Precambrian organic matter and carbonate rocks may host biosignatures, including evidence for extracellular polymeric substances, As‐binding and detoxification processes, without supporting arsenotrophy. However, they provide clues to better assess the paleoenvironmental conditions at the time of microbial mat formation.
Plain Language Summary
Microbial mats and microbialites are like time machines helping us learn about ancient life and its environments. We collected a microbial mat from the unique Dead Sea’s sinkholes, where life thrives in extreme conditions. In this mat, we found for the first time in this area a staggering 6.5 million‐fold increase in arsenic, an element toxic to life. By closely studying the genes and chemistry of this microbial mat, we discovered that microbes were striving to clean up this excess arsenic in a sort of natural detoxification process. It seems that a temporary spike in arsenic levels in the Dead Sea water triggered this clean‐up work, which eventually stored the arsenic safely in the mat away from the microbial cells. Our findings suggest that in the past, when microbial mats were one of the only ecosystems on Earth, changes in the water flowing over mats like this one could have caused similar accumulations of metals. Therefore, when scientists study ancient fossilized microbial layers, these discoveries can help us look into the past and understand the chemical and biological conditions under which these ancient microbial mats formed.
Key Points
Intense arsenic enrichment is detected for the first time around the Dead Sea
Arsenic is accumulated in the organic matter of a microbial mat as methylated organoarsenic
The enrichment results from microbial detoxification and may be fossilized
Increases in dissolved organic carbon (DOC) concentrations have often been reported in rivers and lakes of the Northern Hemisphere over the last few decades. High-quality organic carbon (OC) ...concentration data have been used to study the change in DOC and total (TOC) organic carbon concentrations in the main rivers of Switzerland (Rhône, Rhine, Thur and Aar) between 1974 and 2010. These rivers are characterized by high discharge regimes (due to their Alpine origin) and by running in populated areas. Small long term trends (a general statistically significant decrease in TOC and a less clear increase in DOC concentrations), on the order of 1% of mean OC concentration per year, have been observed. An upward trend before 1999 reversed direction to a more marked downward trend from 1999 to 2010. Of the potential causes of OC temporal variation analysed (water temperature, dissolved reactive phosphorus and river discharge), only discharge explains a significant, albeit still small, part of TOC variability (8–31%), while accounting for barely 2.5% of DOC variability. Estimated anthropogenic TOC and DOC loads (treated sewage) to the rivers could account for a maximum of 4–20% of the temporal trends. Such low predictability is a good example of the limitations faced when studying causality and drivers behind small variations in complex systems. River export of OC from Switzerland has decreased significantly over the period. Since about 5.5% of estimated NEP of Switzerland is exported by the rivers, riverine OC fluxes should be taken into account in a detailed carbon budget of the country.
•High-quality organic carbon data used to study long-term trends in Switzerland•A statistically significant decrease in TOC and a less clear increase in DOC observed•Trend change in all rivers: upward until 1999, stronger downward 1999–2010•Riverine OC fluxes should be taken into account in carbon budgets of the country
Determining antimony speciation is essential to understand its environmental behaviour and potential (eco)toxicological effects. Absence of Gradients and Nernstian Equilibrium Stripping (AGNES) is an ...electroanalytical technique that has been applied up to date to the determination of the free metal ion concentrations of Zn(II), Cd(II), Pb(II) and In(III). In this work, the first application of AGNES to the measurement of the concentration of one particular species of Sb(III) in aqueous solution is developed. The extensive hydrolysis of this element, even at low pH, suggests the convenience of performing calibrations and AGNES measurements in terms of the Sb(OH)3(aq) concentration, rather than the “free” ion. A new preconcentration factor, Y′, is also introduced as the ratio between Sb0 in the amalgam and Sb(OH)3(aq) in the solution. Y′ dependence on pH is evaluated with calibrations at different pH values. The experimental values of Sb(OH)3(aq) obtained with AGNES in the titration of antimony with the organic ligand oxalate agree very well with the values predicted with the complexation constants recently reported. This promising methodology opens the way to tackle antimony speciation with AGNES in other systems.
•AGNES technique has been applied for the first time to Sb(III) speciation.•Due to the high hydrolysis of antimony, Sb(OH)3 is determined rather than free.•The specifically defined preconcentration factor (or gain) depends on pH.•Sb(OH)3 measured in presence of oxalate agrees well with literature values.
Evaluation of time series of organic carbon (OC) concentrations in lakes is useful for monitoring some of the effects of global change on lakes and their catchments. Isolating the evolution of ...autochthonous and allochthonous lake OC might be a useful way to differentiate between drivers of soil and photosynthetic OC related changes. However, there are no temporal series for autochthonous and allochthonous lake OC. In this study, a new approach has been developed to construct time series of these two categories of OC from existing dissolved organic carbon (DOC) data. First, temporal series (longer than ten years) of OC have been compiled for seven big Swiss lakes and another 27 smaller ones and evaluated by using appropriate non-parametric statistical methods. Subsequently, the new approach has been applied to construct time series of autochthonous and allochthonous lake OC in the seven big lakes. Doing this was possible because long term series of DOC concentrations at different depths are available for these lakes.
Organic carbon concentrations generally increase in big lakes and decrease in smaller ones, although only in some cases are these trends statistically significant. The magnitude of the observed changes is generally small in big lakes (<1% annual change) and larger in smaller lakes. Autochthonous DOC concentrations in big lakes increase or decrease depending on the lake and the station but allochthonous DOC concentrations generally increase. This pattern is consistent with an increase in the OC input from the lakes' catchments and/or an increase in the refractoriness of the OC in question, and with a temporal evolution of autochthonous DOC depending on the degree of recovery from past eutrophication of each particular lake. In small lakes, OC dynamics are mainly driven by decreasing biological productivity, which in many, but not all cases, outweighs the probable increase of allochthonous OC.
•Compilation and analysis of time series of organic carbon (OC) in 34 Swiss lakes•New approach developed for obtaining allochthonous and autochthonous OC time series.•Total OC concentrations generally increase in big lakes and decrease in smaller ones.•Autochthonous OC decreases or increases depending on the lake.•Allochthonous OC increases in eight of nine big lake stations studied.
Until now, descriptions of intracellular biomineralization of amorphous inclusions involving alkaline‐earth metal (AEM) carbonates other than calcium have been confined exclusively to cyanobacteria ...(Couradeau et al., 2012). Here, we report the first evidence of the presence of intracellular amorphous granules of AEM carbonates (calcium, strontium, and barium) in unicellular eukaryotes. These inclusions, which we have named micropearls, show concentric and oscillatory zoning on a nanometric scale. They are widespread in certain eukaryote phytoplankters of Lake Geneva (Switzerland) and represent a previously unknown type of non‐skeletal biomineralization, revealing an unexpected pathway in the geochemical cycle of AEMs. We have identified Tetraselmis cf. cordiformis (Chlorophyta, Prasinophyceae) as being responsible for the formation of one micropearl type containing strontium (Ca,SrCO3), which we also found in a cultured strain of Tetraselmis cordiformis. A different flagellated eukaryotic cell forms barium‐rich micropearls (Ca,Ba)CO3. The strontium and barium concentrations of both micropearl types are extremely high compared with the undersaturated water of Lake Geneva (the Ba/Ca ratio of the micropearls is up to 800,000 times higher than in the water). This can only be explained by a high biological pre‐concentration of these elements. The particular characteristics of the micropearls, along with the presence of organic sulfur‐containing compounds—associated with and surrounding the micropearls—strongly suggest the existence of a yet‐unreported intracellular biomineralization pathway in eukaryotic micro‐organisms.
This paper describes several possible interactions among the different types of organic and inorganic aquatic colloids, based on our present knowledge of their size, electric charge, and ...conformation. The physicochemical properties of the different groups of colloids are described. Emphasis is placed on the various types of organic components, including fulvic compounds. Subsequently, the role of each colloid class is discussed with respect to homoaggregation (aggregation within a given colloid class) and heteroaggregation (aggregation among different colloid types). On the basis of a synthesis of literature reports, microscopic observations of natural colloids, experimental results obtained with model systems, and numerical simulations, it is concluded that the formation of aggregates in aquatic systems can be understood by mainly considering the roles of three types of colloids: (i) compact inorganic colloids; (ii) large, rigid biopolymers; and (iii) either the soil-derived fulvic compounds or their equivalent in pelagic waters, aquagenic refractory organic matter. In most natural aquatic systems, the small (few nanometers) fulvic compounds will stabilize the inorganic colloids whereas the rigid biopolymers (0.1−1 μm) will destabilize them. The concentration of stable colloids in a particular aquatic system will depend on the relative proportions of these three components.
A simple method is described for the rapid and reliable determination of ultratrace concentrations of Sb(III) and Sb(V) in seawater by differential pulse anodic stripping voltammetry. It is based on ...the well-known dependence of Sb(III)/Sb(V) voltammetric response on acidity conditions. Under our optimised conditions (0.5
mol
l
−1 HCl for Sb(III) and 5
mol
l
−1 HCl for total Sb, respectively): (i) a detection limit of 11
ng
l
−1 is obtained for a 10 min deposition time; (ii) no prior elimination of organic matter is needed; and (iii) antimony can be determined in the presence of natural copper levels. Particular care has been taken in order to understand the chemical processes taking place in all the solutions and reactions involved in the sampling and measuring procedures. Our results revealed the need to consider (i) the effect of photooxydation of synthetic and seawater samples on Sb speciation; and (ii) the stability of Sb(III) both in seawater samples and in the analytical solutions.
Knowledge of antimony redox kinetics is crucial in understanding the impact and fate of Sb in the environment and optimizing Sb removal from drinking water. The rate of oxidation of Sb(III) with H2O2 ...was measured in 0.5 mol L-1 NaCl solutions as a function of Sb(III), H2O2, pH, temperature, and ionic strength. The rate of oxidation of Sb(III) with H2O2 can be described by the general expression: −dSb(III)/dt = kSb(III)H2O2H+-1 with log k = −6.88 (±0.17) k: min-1. The undissociated Sb(OH)3 does not react with H2O2: the formation of Sb(OH)4 - is needed for the reaction to take place. In a mildly acidic hydrochloric acid medium, the rate of oxidation of Sb(III) is zeroth order with respect to Sb(III) and can be described by the expression −dSb(III)/dt = kH2O2H+Cl- with log k = 4.44 (±0.05) k: L2 mol-2 min-1. The application of the calculated rate laws to environmental conditions suggests that Sb(III) oxidation by H2O2 may be relevant either in surface waters with elevated H2O2 concentrations and alkaline pH values or in treatment systems for contaminated solutions with millimolar H2O2 concentrations.
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