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Emissions of volatile organic sulfur (S), selenium (Se), bromine (Br), and iodine (I) species from aquatic ecosystems represent an important source of these elements into the atmosphere. Available methods to measure these species are either not sensitive enough or not automated, which hinder a full understanding of species distribution and production mechanisms. Here, we present a sensitive and high-throughput method for the simultaneous and comprehensive quantification of S, Se, Br, and I volatile organic species in atmospheric and aqueous samples using a preconcentration step onto sorbent tubes and subsequent analysis by thermal desorption coupled to gas chromatography and inductively coupled plasma mass spectrometry (TD-GC-ICPMS). Selected commercially available sorbent tubes, consisting of mixed porous polymer and graphitized black carbon, offered the highest trapping capacity and lowest loss of species when stored at -20 degrees C for 28 days after sampling. After optimization of the TD-GC-ICP-MS method, absolute detection limits were better than 3.8 pg, 9.1 fg, 313 fg, and 50 fg, respectively, for S, Se, Br, and I species. As a proof of concept, the concentrations of target species were determined in aqueous and continuously collected atmospheric samples during a cruise in the Baltic and North Seas. Moreover, unknown S, Br, and I volatile species were detected in both aqueous and atmospheric samples demonstrating the full potential of the method. ISSN:1520-6882 ISSN:0003-2700

The Modular Multiplatform Compatible Air Measurement System (MoMuCAMS) is a newly developed in situ aerosol and trace gas measurement payload for lower atmospheric vertical profiling in extreme environments. MoMuCAMS is a multiplatform compatible system, primarily designed to be attached to a helikite, a rugged tethered balloon type that is suitable for operations in cold and windy conditions. The system addresses the need for detailed vertical observations of atmospheric composition in the boundary layer and lower free-troposphere, especially in polar and alpine regions. These regions are known to frequently experience strong temperature inversions, preventing vertical mixing of aerosols and trace gases, and therefore reducing the representativeness of ground-based measurements for the vertical column, causing a large informational gap. The MoMuCAMS encompasses a box that houses instrumentation, a board computer to stream data to the ground for inflight decisions, and a power distribution system. The enclosure has an internal volume of roughly 100 L and can accommodate various combinations of instruments within its 20 kg weight limit. This flexibility represents a unique feature, allowing the simultaneous study of multiple aerosol properties (number concentration, size distribution, cluster ions, optical properties, chemical composition and morphology), as well as trace gases (e.g. CO, CO2, O3, N2O) and meteorological variables (e.g., wind speed and direction, temperature, relative humidity, pressure) . To the authors’ knowledge, it is the first tethered balloon based system equipped with instrumentation providing a full size distribution for aerosol particles starting from 8 nm, which is vital to understanding atmospheric processes of aerosols and their climate impacts through interaction with direct radiation and clouds. MoMuCAMS has been deployed during two field campaigns in Swiss Alpine valleys in winter and fall 2021. It has been further deployed in Fairbanks, Alaska (USA) in January–February 2022, as part of the ALPACA (Alaskan Layered Pollution and Chemical Analysis) campaign and in Pallas, Finland, in September–October 2022, as part of the PaCE2022 (Pallas Cloud Experiment) study. The system flew successfully at temperatures of −36° C, in wind speeds above 15 m s−1 and in clouds. Here we present a full characterization of the specifically developed inlet system and novel, hitherto not yet characterized, instruments, most notably a miniaturized scanning electrical mobility spectrometer and a near-infrared carbon monoxide monitor. Three cases from one of the Swiss Alpine studies are presented to illustrate the capability of MoMuCAMS to perform high-resolution measurements with different instrumental setups. We show two case studies with surface-based inversions in the morning that allowed for observation of aerosol and trace gas dynamics in evolving boundary layer conditions. The vertical structure of the boundary layer featured in both cases a surface layer (SL) with a top between 50 and 70 m above ground level, dominated by traffic emissions leading to particle number concentrations up to seven times higher than in the residual layer above. Following sunrise, turbulent mixing led to rapid development of a mixed boundary layer and dilution of the SL within one to two hours. The third case study illustrates the capability of the system to perform aerosol sampling at a chosen altitude over several hours, long enough in low aerosol concentrations environments to perform chemical analyses. Trace elements were analyzed using inductively coupled plasma tandem mass spectrometry. The samples were also analyzed under a scanning electron microscope with energy dispersive x-ray and a transmission electron microscope to gain additional insights into their morphology and chemical composition. Such analyses are suitable to gain deeper insights into particles’ origins, and their physical and chemical transformation in the atmosphere. Overall, MoMuCAMS is an easily deployable tethered balloon payload with high flexibility, able to cope with the rough conditions of extreme environments. Compared to uncrewed aerial vehicles (drones) it allows to observe aerosol processes in detail over multiple hours providing insights on their vertical distribution and processes, e.g. in clouds, that were difficult to obtain beforehand.

Biological N2 fixation was key to the expansion of life on early Earth. The N2-fixing microorganisms and the nitrogenase type used in the Proterozoic are unknown, although it has been proposed that the canonical molybdenum-nitrogenase was not used due to low molybdenum availability. We investigate N2 fixation in Lake Cadagno, an analogue system to the sulfidic Proterozoic continental margins, using a combination of biogeochemical, molecular and single cell techniques. In Lake Cadagno, purple sulfur bacteria (PSB) are responsible for high N2 fixation rates, to our knowledge providing the first direct evidence for PSB in situ N2 fixation. Surprisingly, no alternative nitrogenases are detectable, and N2 fixation is exclusively catalyzed by molybdenum-nitrogenase. Our results show that molybdenum-nitrogenase is functional at low molybdenum conditions in situ and that in contrast to previous beliefs, PSB may have driven N2 fixation in the Proterozoic ocean., Nature Communications, 12 (1), ISSN:2041-1723

Selenium (Se) is an essential dietary element for humans and animals, and the atmosphere is an important source of Se to soils. However, estimates of global atmospheric Se fluxes are highly uncertain. To constrain these uncertainties, we use a global model of atmospheric Se cycling and a database of more than 600 sites where Se in aerosol has been measured. Applying Bayesian inference techniques, we determine the probability distributions of global Se emissions from the four major sources: anthropogenic activities, volcanoes, marine biosphere, and terrestrial biosphere. Between 29 and 36 Gg of Se are emitted to the atmosphere every year, doubling previous estimates of emissions. Using emission parameters optimized by aerosol network measurements, our model shows good agreement with the aerosol Se observations (R2 = 0.66), as well as with independent aerosol (0.59) and wet deposition measurements (0.57). Both model and measurements show a decline in Se over North America in the last two decades because of changes in technology and energy policy. Our results highlight the role of the ocean as a net atmospheric Se sink, with around 7 Gg yr–1 of Se transferred from land through the atmosphere. The constrained Se emissions represent a substantial step forward in understanding the global Se cycle., Environmental Science & Technology, 54 (12), ISSN:0013-936X, ISSN:1520-5851

Even though lake sediments are globally important organic carbon (OC) sinks, the controls on long-term OC storage in these sediments are unclear. Using a multiproxy approach, we investigate changes in diatom, green algae, and vascular plant biomolecules in sedimentary records from the past centuries across five temperate lakes with different trophic histories. Despite past increases in the input and burial of OC in sediments of eutrophic lakes, biomolecule quantities in sediments of all lakes are primarily controlled by postburial microbial degradation over the time scales studied. We, moreover, observe major differences in biomolecule degradation patterns across diatoms, green algae, and vascular plants. Degradation rates of labile diatom DNA exceed those of chemically more resistant diatom lipids, suggesting that chemical reactivity mainly controls diatom biomolecule degradation rates in the lakes studied. By contrast, degradation rates of green algal and vascular plant DNA are significantly lower than those of diatom DNA, and in a similar range as corresponding, much less reactive lipid biomarkers and structural macromolecules, including lignin. We propose that physical shielding by degradation-resistant cell wall components, such as algaenan in green algae and lignin in vascular plants, contributes to the long-term preservation of labile biomolecules in both groups and significantly influences the long-term burial of OC in lake sediments., PNAS Nexus, 1 (3), ISSN:2752-6542

Photodegradation processes play an important role in releasing elements tied up in biologically refractory forms in the environment, and are increasingly being recognized as important contributors to biogeochemical cycles. While complete photo-oxidation of dissolved organic carbon (to CO2) and dissolved organic phosphorous (to PO43-) has been documented, the analogous photoproduction of sulfate from dissolved organic sulfur (DOS) has not yet been reported. Recent high-resolution mass spectrometry studies showed a selective loss of organic sulfur during photodegradation of dissolved organic matter, which was hypothesized to result in the production of sulfate. Here, we provide evidence of ubiquitous production of sulfate, methanesulfonic acid (MSA), and methanesulfinic acid (MSIA) during photodegradation of DOM samples from a wide range of natural terrestrial environments. We show that photochemical production of sulfate is generally more efficient than the production of MSA and MSIA, as well as volatile S-containing compounds such as CS2 and COS. We also identify possible molecular precursors for sulfate and MSA, and we demonstrate that a wide range of relevant classes of DOS compounds (in terms of S oxidation state and molecular structure) can liberate sulfate upon photosensitized degradation. This work suggests that photochemistry may play a more significant role in the aquatic and atmospheric fate of DOS than currently believed.

The essential elements selenium (Se) and iodine (I) are often present in low levels in terrestrial diets, leading to potential deficiencies. Marine I and Se emissions and subsequent atmospheric wet deposition has been suggested to be an important source of I and Se to soils and terrestrial food chains. However, the contribution of recycled moisture of continental origin to I and Se to precipitation has never been analyzed. Here we report concentrations and speciation of I and Se, as well as of bromine (Br), sulfur (S), and DOC-δ13C signatures for weekly collected precipitation samples (in the period of April 2015 to September 2016) at two high altitude sites, i.e., Jungfraujoch (JFJ; Switzerland) and Pic du Midi (PDM; France). Analysis of precipitation chemistry and moisture sources indicate combined marine and continental sources of precipitation and Se, I, Br, and S at both sites. At JFJ, concentrations of I and Se were highest when continental moisture sources were dominant, indicating important terrestrial sources for these elements. Furthermore, correlations between investigated elements and DOC-δ13C, particularly when continental moisture source contributions were high, indicate a link between these elements and the source of dissolved organic matter, especially for I (JFJ and PDM) and Se (JFJ). ISSN:0013-936X ISSN:1520-5851

Rare Earth Elements (REEs) are used in increasing amounts in technical applications and consumer products. However, to date, the contribution of industrial sources to the loads of individual REEs in wastewater streams have not been quantified. Here, we determine the REE contents in sludge collected from 63 wastewater treatment plants (WWTPs) across Switzerland. To quantify the industrial fraction of individual REEs in the sewage sludge, we develop two complementary approaches, based on REE ratios and REE pattern fitting. Unspecific (background) inputs, with REE patterns similar to the averaged REE pattern of soils collected across Switzerland, dominate the REE budget of most WWTPs. A few WWTPs receive significant REE inputs from specific industrial sources. Based on population equivalents of Switzerland, we estimate a total annual load of 4200 kg Cerium (Ce, 0.5 g Ce year-1 capita-1), with an industrial contribution of 2000 kg year-1. The latter agrees with estimates of probabilistic mass flow models for engineered nanoscale CeO2 particles discharged to the sewer network. About 7 kg year-1 of Samarium (Sm,total for Switzerland: 184 kg year-1 or 0.02 g Sm year-1 capita-1) and 3 kg year-1 of Europium (Eu,total for Switzerland: 44 kg year-1 or 0.005 g Eu year-1 capita-1) are assigned to industrial inputs from single WWTPs. Gadolinium (Gd) is used in the form of a stable complex as contrast agent in magnetic resonance imaging. Assuming 10% removal of Gd during wastewater treatment, we calculate an annual discharge of 90 kg of Gd from one individual WWTP to surface waters. WWTPs with exceptionally high industrial inputs of specific REEs warrant detailed investigations to identify the respective sources and to assess whether REE concentrations in effluents are elevated to the same degree., Water Research X, 11, ISSN:2589-9147

Lake sediments are globally important organic carbon (OC) sinks. Biomolecule chemical reactivity, adsorption and physical shielding have been suggested as important factors in controlling OC degradation rates in sediments. Yet, few studies have investigated the relative importance of these variables, or traced how OC from different organismal sources changes over time due to source-dependent variations in degradation rates.We investigate the factors that control organic biomolecule degradation based on analyses of eukaryotic DNA, biomarkers, and (macro)molecule compositions (using pyrolysis-GC/MS) in sediments of five lakes in central Switzerland that differ in trophic state. We specifically target biomolecules of dominant phytoplankton groups (diatoms, green algae), and terrestrial vascular plants. We show that the decay rates of diatom DNA are significantly higher than those of diatom lipid biomarkers and (macro)molecules, consistent with the higher chemical reactivity of DNA. However, the decay rates of green algal DNA and vascular plant DNA are much slower than those of diatom DNA and similar in magnitude to their corresponding membrane lipids and (macro)molecules. In the case of vascular plant biomolecules (DNA, lignin, polyaromatic compounds), no significant biomolecule degradation was detected over the time scales studied (1-5 centuries).Our results suggest that chemical reactivity and physical shielding, but not adsorption, are key variables controlling organic biomolecule decay in the lakes studied. In the case of green algae and vascular plants, greater chemical resistance of cell wall structural components to microbial attack appears to facilitate long-term preservation of even highly reactive, intramolecular compounds, such as DNA. These findings have important implications for the use of sedimentary eukaryotic DNA records to reconstruct past environmental changes.

The cycling of phosphorus in terrestrial and aquatic systems is tightly coupled to the redox-cycling of iron (Fe). The oxidation of dissolved Fe(II) in natural waters leads to the precipitation of amorphous to poorly crystalline Fe(III)-solids that can bind phosphate (P) and other nutrients as well as toxic compounds. The EU project P-TRAP is aimed at developing methods to reduce diffuse P inputs into surface waters to mitigate eutrophication, by using Fe-rich byproducts from water treatment (https://h2020-p-trap.eu/). Within this project, we study mechanistic aspects of the formation and transformation of P-containing Fe(III)-precipitates and their implications for P retention in soils and water filters.Freshly formed Fe(III)-precipitates are metastable and can transform into more stable phases over time. This may lead to the release of co-precipitated P. In laboratory experiments, we assessed how Ca, Mg, silicate (Si) and P impact on the formation and transformation of Fe oxidation products (at 0.5 mM Fe) and their P retention in synthetic bicarbonate-buffered groundwater. The time-resolved experiments were performed in electrolyte solutions containing Na, Ca, or Mg as electrolyte cation, without or with Si (at molar Si/Fe of 1), and P (P/Fe of 0.3 and 0.05). Changes in dissolved element concentrations over time were linked to changes in the structure and composition of the Fe(III)-solids; with Fe coordination probed by X-ray absorption spectroscopy, mineralogy by X-ray diffraction, and nano-scale morphology and composition heterogeneity by transmission electron microscopy with energy-dispersive X-ray detection.The freshly-formed Fe(III)-precipitates were mixtures of amorphous Fe(III)-phosphate with either poorly-crystalline lepidocrocite (without Si) or Si-containing ferrihydrite (with Si). Increases in dissolved P during aging were largest in Na electrolytes without Ca, Mg or Si, and were linked to the transformation of amorphous Fe(III)-phosphate into lepidocrocite with a lower P retention capacity than Fe(III)-phosphate. In Ca- and to a lesser extent Mg-containing electrolytes, the Ca or Mg stabilized the amorphous Fe(III)-phosphate and thereby reduced P release over time. The presence of Si increased initial P uptake and inhibited P release during aging by causing the formation of Si-ferrihydrite with higher P sorption capacity than lepidocrocite formed in the absence of Si. In conclusion, the extents to which P is trapped by fresh Fe(III)-precipitates and released during aging can be attributed to the individual and coupled impacts of Ca, Mg and Si on Fe(III)-precipitate structure, stability and transformation.In continuing work, we aim to expand our work to study how organic compounds impact on the formation and colloidal stability of Fe(III)-precipitates and P retention.

Geogenic arsenic (As) contamination of groundwater is a health threat to millions of people worldwide, particularly in alluvial regions of South and Southeast Asia. Mitigation measures are often hindered by high heterogeneities in As concentrations, the cause(s) of which are elusive. Here we used a comprehensive suite of stable isotope analyses and hydrogeochemical parameters to shed light on the mechanisms in a typical high-As Holocene aquifer near Hanoi where groundwater is advected to a low-As Pleistocene aquifer. Carbon isotope signatures (δ13C-CH4, δ13C-DOC, δ13C-DIC) provided evidence that fermentation, methanogenesis and methanotrophy are actively contributing to the As heterogeneity. Methanogenesis occurred concurrently where As levels are high (>200 µg/L) and DOC-enriched aquitard pore water infiltrates into the aquifer. Along the flowpath to the Holocene/Pleistocene aquifer transition, methane oxidation causes a strong shift in δ13C-CH4 from -87‰ to +47‰, indicating high reactivity. These findings demonstrate a previously overlooked role of methane cycling and DOC infiltration in high-As aquifers., Water Research, 200, ISSN:0043-1354, ISSN:1879-2448

Atmospheric deposition is a major source of the nutrients sulfur and selenium to agricultural soils. Air pollution control and cleaner energy production have reduced anthropogenic emissions of sulfur and selenium, which has led to lower atmospheric deposition fluxes of these elements. Here, we use a global aerosol-chemistry-climate model to map recent (2005–2009) sulfur and selenium deposition, and project future (2095–2099) changes under two socioeconomic scenarios. Across the Northern Hemisphere, we find substantially decreased deposition to agricultural soils, by 70 to 90% for sulfur and by 55 to 80% for selenium. Recent trends in sulfur and selenium concentrations in USA streams suggest that catchment mass balances of these elements are already changing due to the declining atmospheric supply. Sustainable fertilizer management strategies will need to be developed to offset the decrease in atmospheric nutrient supply and ensure future food security and nutrition, while avoiding consequences for downstream aquatic ecosystems., Communications Earth & Environment, 2 (1), ISSN:2662-4435

Mercury (Hg) pollution threatens ecosystems and human health. Wastewater treatment plants (WWTPs) play a key role in limiting Hg discharges from wastewaters to rivers and lakes, but large-scale studies to estimate Hg loads and discharge at national levels are scarce. We assessed the concentration, flux, speciation, and removal of Hg in municipal wastewater throughout Switzerland by investigating 64 WWTPs in a pre-study and a subset of 28 WWTPs in the main study. We also studied the behavior and pathways of Hg along the various treatment steps in a state-of-the-art WWTP. The resulting dataset, representative of industrialized countries, provides an overview of (i) current Hg concentration ranges, (ii) average per capita loads, and (iii) wastewater Hg inputs into surface waters. The results allowed estimation of a total Hg (THg) load in Swiss wastewater of 130 ± 30 kg THg/year (15.7 mg/capita/y), of which 96 ± 4% is retained in sewage sludge. About 4.7 ± 0.5 kg THg/year (0.57 mg/capita/y) is discharged with the treated wastewater into surface waters. This corresponds to only 1.5–3% of the THg load carried by the major Swiss rivers, indicating that >95% of riverine Hg originates from other sources. Extrapolation to the population of Europe would yield a total amount of 11,700 kg THg/year in raw wastewater, with some 480 kg THg/year discharged to surface waters. Monomethyl mercury on average accounted for 0.23% of THg, and its fraction remained constant along the different treatment steps. ISSN:0043-1354 ISSN:1879-2448

In a recent study, we showed that photodegradation of dissolved organic sulfur (DOS) from a wide range of natural terrestrial environments releases sulfate (SO42–) and other small and highly oxidized S-containing compounds as degradation products, similar to what had already been reported for dissolved organic carbon, nitrogen and phosphorous. However, the underlying chemical mechanism of photoproduction of sulfate is still unknown.To fill this knowledge gap, we selected cysteine as a DOS model compound and we investigated its photodegradation to sulfate using model sensitizers as the source of singlet oxygen (1O2) and triplet excited states (3Sens*), two photochemically produced reactive species ubiquitous in sunlit surface waters. Using a combination of steady-state photochemistry experiments, kinetic modeling and mechanistic knowledge from the biochemistry literature, we reconstructed the molecular events that likely lead to the release of sulfate. We found that the release of SO2 via triplet-sensitized fragmentation of cysteine sulfinic acid, a 1O2 degradation product of cysteine, is a key step in the reaction mechanism. In the presence of oxygen and a photosensitizer, SO2 is then rapidly oxidized to SO42–.Interestingly, nowadays there is great interest in the atmospheric chemistry community on the same transformation (i.e., aqueous phase oxidation of SO2 to SO42–) in the context of extreme haze events. Triplet-induced SO2 oxidation has already been proposed as a potential aqueous phase reaction that might explain the mismatch between measured and modelled sulfate concentrations, but the mechanism of this process is still not established. Our work provides an example of how mechanistic knowledge gained on the (photo)chemical behaviour of dissolved organic matter in aquatic systems can offer insights on processes occurring in atmospheric aqueous phases.

Groundwater is a much safer and more dependable source of drinking water than surface water. However, natural (geogenic) hazardous elements can contaminate groundwater and lead to severe health problems in consumers. Arsenic concentrations exceeding the WHO drinking water guideline of 10 μg/L globally affect over 220 million people and can cause arsenicosis (skin lesions and cancers). Fluoride, while preventing caries at low concentrations, has detrimental effects when above the WHO drinking water guideline of 1.5 mg/L and puts several hundred million people at risk of dental and skeletal fluorosis. In this article, we report on the geochemistry and occurrence of arsenic and fluoride in groundwater and on the development of global and regional risk maps that help alert governments and water providers to take appropriate mitigation measures for the provision of safe drinking water. We then summarize research on the removal of arsenic and fluoride from drinking water, focusing on adapted technologies for water treatment. Finally, we discuss the applicability of various measures in a larger context and future challenges in reaching the goal of access to safe drinking water for all., Chimia, 74 (7-8), ISSN:0009-4293

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01–6.63 μmol/L) and redox states, reaching from suboxic to anoxic conditions (Eh of +159 to −4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO3− and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6–189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.

The number and quantities of trace elements used in industry, (high-tech) consumer products, and medicine are rapidly increasing, but the resulting emissions and waste streams are largely unknown. We assessed the concentrations of 69 elements in digested sewage sludge and effluent samples from 64 municipal wastewater treatment plants as well as in major rivers in Switzerland. This data set, representative of an entire industrialized country, presents a reference point for current element concentrations, average per-capita fluxes, loads discharged to surface waters, and economic waste-stream values. The spatial distribution of many individual elements could be attributed either to predominant geogenic or to anthropogenic inputs. Per-capita element fluxes ranged from 1 mg day–1 (e.g., Zn, Sc, Y, Nb, and Gd) and >1 g day–1 (e.g., for P, Fe, and S). Effluent loads of some elements contributed significantly to riverine budgets (e.g., 24% for Zn, 50% for P, and 83% for Gd...

Geogenic arsenic (As) contamination of groundwater poses a major threat to global health, particularly in Asia. To mitigate this exposure, groundwater is increasingly extracted from low-As Pleistocene aquifers. This, however, disturbs groundwater flow and potentially draws high-As groundwater into low-As aquifers. Here we report a detailed characterisation of the Van Phuc aquifer in the Red River Delta region, Vietnam, where high-As groundwater from a Holocene aquifer is being drawn into a low-As Pleistocene aquifer. This study includes data from eight years (2010–2017) of groundwater observations to develop an understanding of the spatial and temporal evolution of the redox status and groundwater hydrochemistry. Arsenic concentrations were highly variable (0.5–510 μg/L) over spatial scales of, Science of The Total Environment, 717, ISSN:0048-9697, ISSN:1879-1026

Marine emissions of dimethyl sulfide (DMS) to the atmosphere play a fundamental role in the global sulfur (S) cycle and have important consequences for the Earth's radiative balance. In the ocean, DMS is mainly produced by marine algae and bacteria via cleavage of the precursor compound dimethylsulfoniopropionate (DMSP). Here, we studied the reaction between DMS and the strong oxidant hypobromous acid (HOBr), which is also produced by marine algae. Further, reactions between DMS oxidation products and HOBr were studied. The second-order rate constants were determined in competition kinetic experiments using sulfite as a competitor. In addition, we developed a new HPLC-ICP-MS/MS method to identify and quantify the oxidation products of DMS and related compounds. We found that HOBr reacts very fast with DMS to dimethyl sulfoxide (DMSO), with a second-order rate constant of 1.6 × 10

Despite its importance in biological processes and its influence on metal bioavailability, the biogeochemical cycle of dissolved organic sulfur (DOS) in aquatic systems is still poorly understood. Recent high-resolution mass spectrometry (HRMS) studies showed a selective loss of organic sulfur during photodegradation of dissolved organic matter (DOM), which was hypothesized to result in the production of sulfate. Here, we provide evidence of ubiquitous production of sulfate, methanesulfonic acid (MSA) and methanesulfinic acid (MSIA) during photodegradation of DOM samples from a wide range of natural terrestrial environments. We show that photochemical production of sulfate is generally at least one order of magnitude more efficient than the production of MSA and MSIA, as well as volatile S-containing compounds (i.e., CS2and COS). We also identify possible molecular precursors for sulfate and MSA, and we demonstrate that a wide range of relevant classes of DOS compounds (in terms of S oxidation state and molecular structure) can liberate sulfate upon photosensitized degradation. This work indicates that photochemistry plays a more significant role in the aquatic and atmospheric cycle of DOS than currently believed.

International audience; The speciation of highly-diluted elements by X-ray absorption spectroscopy in a diverse range of materials is extremely challenging, especially in biological matrices such as articular cartilage. Here we show that using a high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) technique coupled to an array of crystal analyzers, selenium speciation down to 400 ppb (μg/kg) within articular cartilage can be demonstrated. This is a major advance in the speciation of highly-diluted elements through X-ray absorption spectroscopy and opens new possibilities to study the metabolic role of selenium and other elements in biological samples.

SOCOL-AERv1 was developed as an aerosol–chemistry–climate model to study the stratospheric sulfur cycle and its influence on climate and the ozone layer. It includes a sectional aerosol model that tracks the sulfate particle size distribution in 40 size bins, between 0.39 nm and 3.2 µm. Sheng et al. (2015) showed that SOCOL-AERv1 successfully matched observable quantities related to stratospheric aerosol. In the meantime, SOCOL-AER has undergone significant improvements and more observational datasets have become available. In producing SOCOL-AERv2 we have implemented several updates to the model: adding interactive deposition schemes, improving the sulfate mass and particle number conservation, and expanding the tropospheric chemistry scheme. We compare the two versions of the model with background stratospheric sulfate aerosol observations, stratospheric aerosol evolution after Pinatubo, and ground-based sulfur deposition networks. SOCOL-AERv2 shows similar levels of agreement as SOCOL-AERv1 with satellite-measured extinctions and in situ optical particle counter (OPC) balloon flights. The volcanically quiescent total stratospheric aerosol burden simulated in SOCOL-AERv2 has increased from 109 Gg of sulfur (S) to 160 Gg S, matching the newly available satellite estimate of 165 Gg S. However, SOCOL-AERv2 simulates too high cross-tropopause transport of tropospheric SO2 and/or sulfate aerosol, leading to an overestimation of lower stratospheric aerosol. Due to the current lack of upper tropospheric SO2 measurements and the neglect of organic aerosol in the model, the lower stratospheric bias of SOCOL-AERv2 was not further improved. Model performance under volcanically perturbed conditions has also undergone some changes, resulting in a slightly shorter volcanic aerosol lifetime after the Pinatubo eruption. With the improved deposition schemes of SOCOL-AERv2, simulated sulfur wet deposition fluxes are within a factor of 2 of measured deposition fluxes at 78 % of the measurement stations globally, an agreement which is on par with previous model intercomparison studies. Because of these improvements, SOCOL-AERv2 will be better suited to studying changes in atmospheric sulfur deposition due to variations in climate and emissions., Geoscientific Model Development, 12 (9), ISSN:1991-9603, ISSN:1991-959X

An estimated 0.5–1 billion people globally have inadequate intakes of selenium (Se), due to a lack of bioavailable Se in agricultural soils. Deposition from the atmosphere, especially through precipitation, is an important source of Se to soils. However, very little is known about the atmospheric cycling of Se. It has therefore been difficult to predict how far Se travels in the atmosphere and where it deposits. To answer these questions, we have built the first global atmospheric Se model by implementing Se chemistry into an aerosol–chemistry–climate model, SOCOL-AER. In the model, we include information from the literature about the emissions, speciation, and chemical transformation of atmospheric Se. Natural processes and anthropogenic activities emit volatile Se compounds, which oxidize quickly and partition to the particulate phase. Our model tracks the transport and deposition of Se in 7 gas-phase species and 41 aerosol tracers. However, there are large uncertainties associated with many of the model's input parameters. In order to identify which model uncertainties are the most important for understanding the atmospheric Se cycle, we conducted a global sensitivity analysis with 34 input parameters related to Se chemistry, Se emissions, and the interaction of Se with aerosols. In the first bottom-up estimate of its kind, we have calculated a median global atmospheric lifetime of 4.4 d (days), ranging from 2.9–6.4 d (2nd–98th percentile) given the uncertainties of the input parameters. The uncertainty in the Se lifetime is mainly driven by the uncertainty in the carbonyl selenide (OCSe) oxidation rate and the lack of tropospheric aerosol species other than sulfate aerosols in SOCOL-AER. In contrast to uncertainties in Se lifetime, the uncertainty in deposition flux maps are governed by Se emission factors, with all four Se sources (volcanic, marine biosphere, terrestrial biosphere, and anthropogenic emissions) contributing equally to the uncertainty in deposition over agricultural areas. We evaluated the simulated Se wet deposition fluxes from SOCOL-AER with a compiled database of rainwater Se measurements, since wet deposition contributes around 80 % of total Se deposition. Despite difficulties in comparing a global, coarse resolution model with local measurements from a range of time periods, past Se wet deposition measurements are within the range of the model's 2nd–98th percentile at 79 % of background sites. This agreement validates the application of the SOCOL-AER model to identifying regions which are at risk of low atmospheric Se inputs. In order to constrain the uncertainty in Se deposition fluxes over agricultural soils we should prioritize field campaigns measuring Se emissions, rather than laboratory measurements of Se rate constants.

Biogenic selenium (Se) emissions play a major role in the biogeochemical cycle of this essential micronutrient. Microalgae may be responsible for a large portion of these emissions via production of methylated Se compounds that volatilize into the atmosphere. However, the biochemical mechanisms underlying Se methylation in microalgae are poorly understood. Here, we study Se methylation by Chlamydomonas reinhardtii, a model freshwater alga, as a function of uptake and intracellular Se concentrations and present a biochemical model that quantitatively describes Se uptake and methylation. Both selenite and selenate, two major inorganic forms of Se, are readily internalized by C. reinhardtii, but selenite is accumulated around ten times more efficiently than selenate due to different membrane transporters. With either selenite or selenate as substrates, Se methylation was highly efficient (up to 89% of intracellular Se) and directly coupled to intracellular Se levels (R(2) > 0.92) over an intracellular concentration range exceeding an order of magnitude. At intracellular concentrations exceeding 10 mM, intracellular zerovalent Se was formed. The relationship between uptake, intracellular accumulation, and methylation was used by the biochemical model to successfully predict measured concentrations of methylated Se in natural waters. Therefore, biological Se methylation by microalgae could significantly contribute to environmental Se cycling.

This study identifies causes of rising arsenic (As) concentrations over 17 years in an inter-montane aquifer system located just north of the Trans-Mexican-Volcanic-Belt in the Mesa central physiographic region that is extensively developed by long-screened production wells. Arsenic concentrations increased by more than 10 µg/L in 14% (3/22) of re-sampled wells. Similarly, in a larger scale analysis wherein As concentrations measured in 137 wells in 2016 were compared to interpolated, baseline concentrations from 246 wells in 1999, As concentrations rose more than 10 µg/L in 30% of wells. Between 1999 and 2016, the percentage of all wells sampled in each basin-wide sampling campaign exceeding the World Health Organization's 10 µg/L drinking water limit increased from 38 to 64%. Principal Components Analysis (PCA), step-wise multiple regression, and Random Forest modeling (RF) revealed that high As concentrations are closely associated with high pH and temperature, and high concentrations of fluoride (F), molybdenum (Mo), lithium (Li), sodium (Na) and silica (Si), but low calcium (Ca) and nitrate (NO3) concentrations. Pumping-induced mixing with hot, geothermally impacted groundwater generates alkaline water through hydrolysis of silicate minerals. The rising pH converts oxyanion sorption sites from positive to negative releasing As (and Mo) to pore waters. The negative correlation between nitrate and As concentrations can be explained by conservative mixing of shallow, young groundwater with geothermally influenced groundwater. Therefore water carrying an anthropogenic contaminant dilutes water carrying geogenic contaminants. This process is enabled by long well screens. Over-exploitation of aquifers in geothermal regions for agriculture can drive As concentrations in water from production wells to toxic levels even as the total dissolved solids remain low.

Carbohydrates serve as structural materials, energy storage compounds, and energy carriers in organisms and provide insights into the dominant sources and the degradation state of organic matter (OM). Several studies have analyzed dissolved and/or particulate carbohydrates in the environment, often with the aim of studying particular carbohydrate groups of interest. These studies have often employed different acids and hydrolytic conditions, making comparisons across studies a challenge. Here, we introduce a sequential acid hydrolysis protocol for the comprehensive extraction, quantification and compositional investigation of carbohydrates in sediment samples. This protocol has four acid hydrolysis steps that sequentially increase in extraction strength, where each subsequent hydrolysis step is performed on the unextracted remains previously hydrolyzed. The four hydrolysis steps consist of 1 M HCl for 2 h at (1) room temperature, (2) 50 °C, and (3) 105 °C, followed by incubation for 8 h using (4) 6 M HCl and 105 °C. Based on tests using diverse carbohydrate standard compounds, the protocol recovers most di- and oligosaccharides and soluble polysaccharides during the initial hydrolysis steps, whereas the recovery of most insoluble polysaccharides is highest during the final extraction step. Applying this protocol to different sediment types shows that recoveries of neutral sugars, amino sugars and sugar alcohols are on average ~60% higher than with a reference one-step extraction method using only hydrolysis with hot 6 M HCl. This sequential extraction protocol thus provides an important new tool for the quantitative and compositional analysis of carbohydrates in aquatic sediments.

© 2015 Elsevier B.V. Biologically produced volatile alkylated Se and S compounds play an important role in the global biogeochemical Se and S cycles are important constituents of odorous industrial emissions and contribute to (off )flavors in food and beverages. This study presents a fully automated direct immersion solid phase microextraction (DI SPME) method coupled with capillary gas chromatography mass spectrometry (GC/MS) for the simultaneous quantification of 10 volatile alkylated Se and S compounds in complex aqueous media. Instrumental parameters of the SPME procedure were optimized to yield extraction efficiencies of up to 96 from complex aqueous matrices. The effects of sample matrix composition and analyte transformation during sample storage were critically assessed. With the use of internal standards and procedural calibrations the DI SPME GC/MS method allows for trace level quantification of volatile Se and S compounds in the ng/L range (e.g. down to 30 ng/L dimethyl sulfide and 75 ng/L dimethyl selenide). The applicability and robustness of the presented method demonstrate that the method may be used to quantify volatile Se and S compounds in complex aqueous samples such as industrial effluents or food and beverage samples.

© 2015 by the authors; licensee MDPI Basel Switzerland. Selenium (Se) is an essential element for humans and animals which occurs ubiquitously in the environment. It is present in trace amounts in both organic and inorganic forms in marine and freshwater systems soils biomass and in the atmosphere. Low Se levels in certain terrestrial environments have resulted in Se deficiency in humans while elevated Se levels in waters and soils can be toxic and result in the death of aquatic wildlife and other animals. Human dietary Se intake is largely governed by Se concentrations in plants which are controlled by root uptake of Se as a function of soil Se concentrations speciation and bioavailability. In addition plants and microorganisms can biomethylate Se which can result in a loss of Se to the atmosphere. The mobilization of Se across soil plant atmosphere interfaces is thus of crucial importance for human Se status. This review gives an overview of current knowledge on Se cycling with a specific focus on soil plant atmosphere interfaces. Sources speciation and mobility of Se in soils and plants will be discussed as well as Se hyperaccumulation by plants biofortification and biomethylation. Future research on Se cycling in the environment is essential to minimize the adverse health effects associated with unsafe environmental Se levels.

While the impact of arsenic in irrigated agriculture has become a major environmental concern in Bangladesh, to date there is still a limited understanding of arsenic in Bangladeshi paddy soils at a landscape level. A soil survey was conducted across ten different physiographic regions of Bangladesh, which encompassed six types of geomorphology (Bil, Brahmaputra floodplain, Ganges floodplain, Meghna floodplain, Karatoya-Bangali floodplain and Pleistocene terrace). A total of 1209 paddy soils and 235 matched non-paddy soils were collected. The source of irrigation water (groundwater and surface water) was also recorded. The concentrations of arsenic and sixteen other elements were determined in the soil samples. The concentration of arsenic was higher in paddy soils compared to non-paddy soils, with soils irrigated with groundwater being higher in arsenic than those irrigated with surface water. There was a clear difference between the Holocene floodplains and the Pleistocene terraces, with Holocene floodplain soils being higher in arsenic and other elements. The results suggest that arsenic is most likely associated with less well weathered/leached soils, suggesting it is either due to the geological newness of Holocene sediments or differences between the sources of sediments, which gives rise to the arsenic problems in Bangladeshi soils.

Deficiencies of micronutrients, including essential trace elements, affect up to 3 billion people worldwide. The dietary availability of trace elements is determined largely by their soil concentrations. Until now, the mechanisms governing soil concentrations have been evaluated in small-scale studies, which identify soil physicochemical properties as governing variables. However, global concentrations of trace elements and the factors controlling their distributions are virtually unknown. We used 33,241 soil data points to model recent (1980–1999) global distributions of Selenium (Se), an essential trace element that is required for humans. Worldwide, up to one in seven people have been estimated to have low dietary Se intake. Contrary to small-scale studies, soil Se concentrations were dominated by climate–soil interactions. Using moderate climate-change scenarios for 2080–2099, we predicted that changes in climate and soil organic carbon content will lead to overall decreased soil Se concentrations, particularly in agricultural areas; these decreases could increase the prevalence of Se deficiency. The importance of climate–soil interactions to Se distributions suggests that other trace elements with similar retention mechanisms will be similarly affected by climate change.

Selenium (Se) is an essential trace element for maintaining homeostasis in humans and is characterized by a narrow range of recommended dietary intake levels. The main dietary sources of Se are food crops and therefore human intake levels largely depend on total concentrations and forms of Se in those food products. Important factors controlling Se uptake by plants are concentrations and speciation of Se in soils. Generally, Se concentrations in soils are driven by gradients in chemical and physical variables, which are in turn controlled by multiple biotic and abiotic processes that simultaneously span multiple spatial and temporal scales. This chapter discusses the factors and processes that control soil Se distributions on different spatial scales (i.e. from molecular to global scales) and how these gradients can be affected over time. In addition, it discusses how increased environmental scales lead to increased interactions among multi-scale factors and processes as well as to non-linear patterns between soil Se concentrations and environmental variables. Finally, it will be discussed how these patterns can be analyzed using sophisticated statistical techniques and how multi-scale variables and their interactions can be used to make predictions of soil Se concentrations in areas where this information is not available.

Atmospheric processes play an important role in the supply of the trace element selenium (Se) as well as other essential trace elements to terrestrial environments, mainly via wet deposition. Here we investigate whether the marine biosphere can be identified as a source of Se and of other trace elements in precipitation samples. We used artificial neural network (ANN) modeling and other statistical methods to analyze relationships between a high-resolution atmospheric deposition chemistry time series (March 2007-January 2009) from Plynlimon (UK) and exposure of air masses to marine chlorophyll a and to other source proxies. Using ANN sensitivity analyses, we found that higher air mass exposure to marine productivity leads to higher concentrations of dissolved organic carbon (DOC) in rainfall. Furthermore, marine productivity was found to be an important but indirect factor in controlling Se as well as vanadium (V), cobalt (Co), nickel (Ni), zinc (Zn), and aluminum (Al) concentrations in atmospheric deposition, likely via scavenging by organic compounds derived from marine organisms. Marine organisms may thus play an indirect but important role in the delivery of trace elements to terrestrial environments and food chains.

The western part of the Chalkidiki peninsula in Northern Greece is a geothermally active area that contains high levels of naturally derived arsenic in its alkaline groundwaters (up to 3760 μg/L). Near wells, equilibration of these groundwaters with atmospheric carbon dioxide leads to the precipitation of travertines that contain very high levels of arsenic (up to 913 mg/kg). To determine the mechanism of arsenic uptake in these travertines, we analyzed two different types of travertine from this region using both bulk and micro-focused X-ray absorption spectroscopy (XAS and μ-XAS) and micro-focused X-ray fluorescence spectroscopy (μ-XRF). Bulk XAS showed that in all of the studied samples arsenic is present in the pentavalent oxidation state (arsenate). μ-XRF analyses indicated that arsenic is closely associated with the calcite matrix and that it generally does not correlate well with iron. The arsenic K-edge XAS spectra of all samples closely matched each other and closely resembled a reference spectrum for arsenate coprecipitated with calcite (rather than adsorbed or pure calcium arsenate). Iron on the other hand was found to be mainly present as a constituent of clay minerals, of presumably detrital origin, suggesting that iron-(hydr)oxides were not sufficiently abundant to act as major scavengers for arsenic in the Chalkidiki travertines. We estimated that calcite in these travertines could sequester at least 25% of aqueous arsenic in the form of As(V) and thus immobilize a substantial part of arsenic present in the geothermal groundwaters. These results may also be relevant for other areas where geothermal groundwaters carry arsenic to the surface and possibly as well for arsenic geochemistry in other environments with CO2-enriched water.

Microbial selenium (Se) bioremediation is based on conversion of water soluble, toxic Se oxyanions to water insoluble, elemental Se. Formed biogenic elemental Se is of nanometer size, hampering straightforward separation from the aqueous phase. This study represents the first systematic investigation on colloidal properties of pure biogenic Se suspensions, linking electrophoretic mobility (ζ-potential) to column settling behavior. It was demonstrated that circumneutral pH, commonly applied in bioremediation, is not appropriate for gravitational separation due to the negative ζ-potential preventing agglomeration. Mono/di/trivalent counter cations and acidity (protons) were used to screen efficiently the intrinsic negative charge of biogenic Se suspensions at circumneutral pH. Fast settling was induced by La(3+) addition in the micromolar range (86.2 ± 3.5% within 0.5 h), whereas considerably higher concentrations were needed when Ca(2+) or Na(+) was used. Colloidal stability was furthermore studied in different model waters. It was demonstrated that surface waters as such represent a fragile system regarding colloidal stability of biogenic Se suspensions (ζ-potential ∼ -30 mV), whereas dissolved organic matter increases colloidal stability. In marine waters, biogenic Se is colloidally destabilized and is thus expected to settle, representing a potential sink for Se during transport in the aquatic environment.

Selenium (Se) is of key importance to human health with a very narrow concentration range of optimal dietary intake. Due to the inherent analytical challenge linked with the low natural abundance, information on precise and accurate Se speciation in deficient environments is hardly existent. This study presents a novel approach to determine Se species-specifically at ultratraces, by online coupling of a preconcentration (trap) column to an ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) system. It is demonstrated that with this robust and work/time efficient method, the predominant selenium oxyanions, selenite (Se(IV)) and selenate (Se(VI)), can be quantified down to 7.3 and 8.3 picogram total Se, respectively, in an overall analytical time of 420 s, only. The applicability for environmental samples was proven on pristine volcanic ashes collected from seven different volcanoes. The high sensitivity of the novel approach allowed to determine speciation in samples that were strongly depleted in total selenium (0.05 mg kg(-1) Se) with only minor fractions of Se mobilized (i.e., less than 10% of the total selenium was leached in 10 out of 12 samples). The studied samples showed considerate differences in selenium speciation, with selenite and selenate co-occurring in most samples. The fact that the studied sample leachates had a wide range of pH (3.78-9.55) and major anion/cation composition underlines the versatility and wide potential application range of the method presented.

International audience; Quantification and speciation of volatile selenium (Se) fluxes in remote areas has not been feasible previously, due to the absence of a simple and easily transportable trapping technique that preserves speciation. This paper presents a chemo-trapping method with nitric acid (HNO3) for volatile Se species, which preserves speciation of trapped compounds. The recovery and speciation of dimethylselenide (DMSe) and dimethyl diselenide (DMDSe) entrained through both concentrated nitric acid and hydrogen peroxide (H2O2) were compared by HPLC-ICP-MS and HPLC-HG-AFS analyses. It was demonstrated that trap reproducibility was better for nitric acid and a recovery of 65.2 ± 1.9% for DMSe and 81.3 ± 3.9% for DMDSe was found in nitric acid traps. HPLC-ES-MS identified dimethyl selenoxide (DMSeO) as the trapped product of DMSe. Methylseleninic acid (MSA) was identified to be the single product of DMDSe trapping. These oxidized derivatives have a high stability and low volatility, which makes nitric acid a highly attractive trapping liquid for volatile Se species and enables reconstruction of the speciation of those species. The presented trapping method is simple, quantifiable, reproducible, and robust and can potentially be applied to qualitatively and quantitatively study Se volatilization in a wide range of natural environments.