Green rust formation and reactivity with arsenic species

Elevated levels of arsenic (As) in soils and groundwaters remain a pressing global challenge due to its widespread occurrence and distribution, high toxicity and mobility. In oxygen-limited subsurface conditions, redox-active mineral phases can be important substrates in controlling the fate and mobility of As in the environment. Among these redox-active minerals, green rust (GR) phases, an Fe(II)-Fe(III)-bearing layered double hydroxide, have been shown to be able to sequester a wide range of toxic metals and metalloids, including As. However, very little is known regarding how GR phases interact with As species and what is the fate of the immobilized As under dynamic geochemical conditions. GR phases are suggested to form through the transformation of metastable iron mineral phases in non-sulfidic, reducing environments. However, the exact mechanism and pathway of this transformation, as well as the fate of mineral-associated As (i.e. whether it is re-released back into the groundwater by desorption, dissolution or redox transformation) is not yet known but critically needed for modelling As cycling in contaminated environments. To address these knowledge gaps, I conducted a series of experimental geochemical studies and combined them with various laboratory- and synchrotron-based solid and liquid phase characterization methods to examine the interaction between GR sulfate (GRSO4) and As species [As(III) and As(V)]. Specifically, I performed several batch experiments under anoxic and near-neutral pH conditions to determine As-GR interaction mechanisms during GR formation and transformation. Moreover, I also quantified how these transformation reactions affect the toxicity and mobility of As species in contaminated environments. From the batch adsorption experiments, I showed that synthetic GRSO4 can adsorb up to 160 and 105 mg of As(III) and As(V) per g of solid, respectively. These adsorption capacities are among the highest reported for iron (oxyhydr)oxides that form in soils and groundwaters. Results from this study also show that As removal by GRSO4 can be inhibited by several geochemical parameters such as pH, high ionic strength, presence of co-existing inorganic ions (e.g., Mg2+, PO43-, Si) and low temperature. I also employed an integrated nano-scale solid-state characterization approach to elucidate As-GRSO4 interactions. Specifically, I combined scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray (EDX) spectroscopy together with bulk synchrotron-based X-ray techniques including high energy X-ray total scattering, pair distribution function (PDF) analysis and X-ray absorption spectroscopy (XAS). With these, I was able to directly visualize and pinpoint As binding sites at the GR surface sites and to identify the binding mechanism for both As(III) and As(V). In the case of As(III)-reacted GR, STEM-EDX maps showed that As(III) were preferentially adsorbed at the GR crystal edges, primarily as bidentate binuclear (2C) inner-sphere surface complexes based from the differential PDF and As K-edge XAS data. For the As(V)-reacted GR, As(V) was sequestered as a newly-formed As-bearing mineral phase parasymplesite and as adsorbed As(V) species at the GR edges (in 2C geometry). To assess the fate of As in subsurface environments, I studied As during GR formation and transformation to quantify As uptake and/or its potential release back into solution and the stability of GR and other Fe (oxhydr)oxide phases in this process. During the Fe2+-induced transformation of As(V)-bearing ferrihydrite, I followed the changes in aqueous behavior and speciation of As, as well as the changes in composition of the Fe mineral phases, as a function of varying Fe2+(aq)/Fe(III)solid ratios (0.5, 1 ,2). In all the ratios tested, GRSO4, goethite and lepidocrocite formed in the early stages of transformation (≤ 2h). However, at low ratios (<2), the initially formed GRSo4 and/or lepidocrocite disappeared as the reaction progressed, leaving goethite and unreacted ferrihydrite after 24 h. At an Fe2+(aq)/Fe(III)solid ratio of 2, GRSO4 was formed and remained in the solids until the end of the 24-h transformation, with goethite and unreacted ferrihydrite. The initial As(V) was partially reduced to As(III) by the surface-associated Fe2+-GT redox couple, and extent of reduction increased from 34 to 44% as Fe2+(aq)/Fe(III)solid ratios increased. Despite this reduction to the more mobile and more toxic As(III) species, no significant As release was observed during the mineral transformation reactions. Finally, I tested the long-term stability and reactivity of GR by aging synthetic GRSO4 in pristine and As-spiked natural groundwater at ambient (25 °C) and low (4 °C) temperatures. The spiked As in the groundwater was completely removed after 120 days at 25 °C while the removal rate was ~2 times slower at 4 °C with only ~66% As removal after 120 days. On the other hand, the stability of synthetic GRSO4 in groundwater was strongly affected by the presence of adsorbed As species and temperature. At ambient temperature, the initial GRSO4 aged in As-free groundwater was converted to GRCO3 by ion exchange within a few days and both GR phases eventually transformed to magnetite after 120 days. Remarkably, both the addition of As species in groundwater and lowering the temperature increased long-term GRSO4 stability through the inhibition of (a) ion exchange in the GRSO4 interlayer (i.e., slower conversion to GRCO3) and (b) transformation of GR to magnetite. Moreover, a synergistic stabilization effect was observed with both As addition and low temperature, significantly enhancing GR stability up to a year. Overall, the work presented in this thesis clearly emphasizes the potential role of GR phases in controlling the mobility and toxicity of As species in subsurface environments. Specifically, I contributed to the fundamental understanding of the reactions involving As(III) and As(V) at GR surfaces, elucidating the relevant binding mechanisms and visualizing specific binding sites of immobilized As species. This work also identified critical geochemical factors that affect As removal and GR formation and transformation under anoxic and circum-neutral pH conditions. More importantly, I was able to show the enhanced long-term stability of GR in natural groundwaters and its prolonged reactivity for As sequestration

Past, present and future global influence and technological applications of iron-bearing metastable nanominerals

Iron-bearing nanominerals such as ferrihydrite, schwertmannite, and green rust behave as metastable precursors leading to the formation of more thermodynamically stable iron mineral phases (e.g., jarosite, goethite, hematite, and magnetite). However, this transformation may last from days to tens or even hundreds of years, making them the most predominant iron-bearing minerals at environmental conditions and at the human time scale. The present review characterizes ferrihydrite, schwertmannite, and green rust nanominerals according to their main physical and chemical properties, and at both nano- and meso-scales. It also presents a comprehensive review of the multiple past and present Earth environments where these nanominerals have played, and still play, a pivotal role in the geochemistry, mineralogy and environmental nanogeosciences of these environments. Finally, the present and future technological applications of these nanominerals as well as their role in the generation of a more sustainable human-Earth relationship is discussed, with a special emphasis on their use in new circular economies and green based technologies

Past, present and future global influence and technological applications of iron-bearing metastable nanominerals

Iron-bearing nanominerals such as ferrihydrite, schwertmannite, and green rust behave as metastable precursors leading to the formation of more thermodynamically stable iron mineral phases (e.g., jarosite, goethite, hematite, and magnetite). However, this transformation may last from days to tens or even hundreds of years, making them the most predominant iron-bearing minerals at environmental conditions and at the human time scale. The present review characterizes ferrihydrite, schwertmannite, and green rust nanominerals according to their main physical and chemical properties, and at both nano- and mesoscales. It also presents a comprehensive review of the multiple past and present Earth environments where these nanominerals have played, and still play, a pivotal role in the geochemistry, mineralogy and environmental nanogeosciences of these environments. Finally, the present and future technological applications of these nanominerals as well as their role in the generation of a more sustainable human- Earth relationship is discussed, with a special emphasis on their use in new circular economies and green based technologies.This research was partially supported by Advanced Mining Technology Center (AMTC) from Universidad de Chile; National Agency for Research and Development, ANID, through ANID-PIA Project AFB180004. MAC was financially supported by the Spanish Ministry of Science and Innovation through the Program Ramon y Cajal 2019, Grant RYC2019-026496-I. J.P.H.P. acknowledges the funding from the European Union’s Horizon 2020 Marie Skłodowska-Curie Innovative Training Network (grant no. 675219) and Helmholtz Recruiting Initiative (award no. I-044-16- 01). MPA was financially supported by the Junta de Andalucía through the Emergia Program 2020. Funding for open access charge: Universidad de Huelva / CBUA

Deep weathering in the semi-arid Coastal Cordillera, Chile

The weathering front is the boundary beneath Earth’s surface where pristine rock is converted into weathered rock. It is the base of the “critical zone”, in which the lithosphere, biosphere, and atmosphere interact. Typically, this front is located no more than 20 m deep in granitoid rock in humid climate zones. Its depth and the degree of rock weathering are commonly linked to oxygen transport and fluid flow. By drilling into fractured igneous rock in the semi-arid climate zone of the Coastal Cordillera in Chile we found multiple weathering fronts of which the deepest is 76 m beneath the surface. Rock is weathered to varying degrees, contains core stones, and strongly altered zones featuring intensive iron oxidation and high porosity. Geophysical borehole measurements and chemical weathering indicators reveal more intense weathering where fracturing is extensive, and porosity is higher than in bedrock. Only the top 10 m feature a continuous weathering gradient towards the surface. We suggest that tectonic preconditioning by fracturing provided transport pathways for oxygen to greater depths, inducing porosity by oxidation. Porosity was preserved throughout the weathering process, as secondary minerals were barely formed due to the low fluid flow

Association of Genetic Variants With Primary Open-Angle Glaucoma Among Individuals With African Ancestry.

Importance:Primary open-angle glaucoma presents with increased prevalence and a higher degree of clinical severity in populations of African ancestry compared with European or Asian ancestry. Despite this, individuals of African ancestry remain understudied in genomic research for blinding disorders. Objectives:To perform a genome-wide association study (GWAS) of African ancestry populations and evaluate potential mechanisms of pathogenesis for loci associated with primary open-angle glaucoma. Design, Settings, and Participants:A 2-stage GWAS with a discovery data set of 2320 individuals with primary open-angle glaucoma and 2121 control individuals without primary open-angle glaucoma. The validation stage included an additional 6937 affected individuals and 14 917 unaffected individuals using multicenter clinic- and population-based participant recruitment approaches. Study participants were recruited from Ghana, Nigeria, South Africa, the United States, Tanzania, Britain, Cameroon, Saudi Arabia, Brazil, the Democratic Republic of the Congo, Morocco, Peru, and Mali from 2003 to 2018. Individuals with primary open-angle glaucoma had open iridocorneal angles and displayed glaucomatous optic neuropathy with visual field defects. Elevated intraocular pressure was not included in the case definition. Control individuals had no elevated intraocular pressure and no signs of glaucoma. Exposures:Genetic variants associated with primary open-angle glaucoma. Main Outcomes and Measures:Presence of primary open-angle glaucoma. Genome-wide significance was defined as P &lt; 5 × 10-8 in the discovery stage and in the meta-analysis of combined discovery and validation data. Results:A total of 2320 individuals with primary open-angle glaucoma (mean [interquartile range] age, 64.6 [56-74] years; 1055 [45.5%] women) and 2121 individuals without primary open-angle glaucoma (mean [interquartile range] age, 63.4 [55-71] years; 1025 [48.3%] women) were included in the discovery GWAS. The GWAS discovery meta-analysis demonstrated association of variants at amyloid-β A4 precursor protein-binding family B member 2 (APBB2; chromosome 4, rs59892895T&gt;C) with primary open-angle glaucoma (odds ratio [OR], 1.32 [95% CI, 1.20-1.46]; P = 2 × 10-8). The association was validated in an analysis of an additional 6937 affected individuals and 14 917 unaffected individuals (OR, 1.15 [95% CI, 1.09-1.21]; P &lt; .001). Each copy of the rs59892895*C risk allele was associated with increased risk of primary open-angle glaucoma when all data were included in a meta-analysis (OR, 1.19 [95% CI, 1.14-1.25]; P = 4 × 10-13). The rs59892895*C risk allele was present at appreciable frequency only in African ancestry populations. In contrast, the rs59892895*C risk allele had a frequency of less than 0.1% in individuals of European or Asian ancestry. Conclusions and Relevance:In this genome-wide association study, variants at the APBB2 locus demonstrated differential association with primary open-angle glaucoma by ancestry. If validated in additional populations this finding may have implications for risk assessment and therapeutic strategies

Photography-based taxonomy is inadequate, unnecessary, and potentially harmful for biological sciences

The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009; Cianferoni & Bartolozzi 2016; Amorim et al. 2016). This question was again raised in a letter supported by 35 signatories published in the journal Nature (Pape et al. 2016) on 15 September 2016. On 25 September 2016, the following rebuttal (strictly limited to 300 words as per the editorial rules of Nature) was submitted to Nature, which on 18 October 2016 refused to publish it. As we think this problem is a very important one for zoological taxonomy, this text is published here exactly as submitted to Nature, followed by the list of the 493 taxonomists and collection-based researchers who signed it in the short time span from 20 September to 6 October 2016

Studies of the mass composition of cosmic rays and proton-proton interaction cross-sections at ultra-high energies with the Pierre Auger Observatory

In this work, we present an estimate of the cosmic-ray mass composition from the distributions of the depth of the shower maximum (Xmax) measured by the fluorescence detector of the Pierre Auger Observatory. We discuss the sensitivity of the mass composition measurements to the uncertainties in the properties of the hadronic interactions, particularly in the predictions of the particle interaction cross-sections. For this purpose, we adjust the fractions of cosmic-ray mass groups to fit the data with Xmax distributions from air shower simulations. We modify the proton-proton cross-sections at ultra-high energies, and the corresponding air shower simulations with rescaled nucleus-air cross-sections are obtained via Glauber theory. We compare the energy-dependent composition of ultra-high-energy cosmic rays obtained for the different extrapolations of the proton-proton cross-sections from low-energy accelerator data

Study of downward Terrestrial Gamma-ray Flashes with the surface detector of the Pierre Auger Observatory

The surface detector (SD) of the Pierre Auger Observatory, consisting of 1660 water-Cherenkov detectors (WCDs), covers 3000 km2 in the Argentinian pampa. Thanks to the high efficiency of WCDs in detecting gamma rays, it represents a unique instrument for studying downward Terrestrial Gamma-ray Flashes (TGFs) over a large area. Peculiar events, likely related to downward TGFs, were detected at the Auger Observatory. Their experimental signature and time evolution are very different from those of a shower produced by an ultrahigh-energy cosmic ray. They happen in coincidence with low thunderclouds and lightning, and their large deposited energy at the ground is compatible with that of a standard downward TGF with the source a few kilometers above the ground. A new trigger algorithm to increase the TGF-like event statistics was installed in the whole array. The study of the performance of the new trigger system during the lightning season is ongoing and will provide a handle to develop improved algorithms to implement in the Auger upgraded electronic boards. The available data sample, even if small, can give important clues about the TGF production models, in particular, the shape of WCD signals. Moreover, the SD allows us to observe more than one point in the TGF beam, providing information on the emission angle

Investigating multiple elves and halos above strong lightning with the fluorescence detectors of the Pierre Auger Observatory

ELVES are being studied since 2013 with the twenty-four FD Telescopes of the Pierre Auger Observatory, in the province of Mendoza (Argentina), the world’s largest facility for the study of ultra-high energy cosmic rays. This study exploits a dedicated trigger and extended readout. Since December 2020, this trigger has been extended to the three High levation Auger Telescopes (HEAT), which observe the night sky at elevation angles between 30 and 60 degrees, allowing a study of ELVES from closer lightning. The high time resolution of the Auger telescopes allows us to upgrade reconstruction algorithms and to do detailed studies on multiple ELVES. The origin of multiple elves can be studied by analyzing the time difference and the amplitude ratio between flashes and comparing them with the properties of radio signals detected by the ENTLN lightning network since 2018. A fraction of multi-ELVES can also be interpreted as halos following ELVES. Halos are disc-shaped light transients emitted at 70-80 km altitudes, appearing at the center of the ELVES rings, due to the rearrangement of electric charges at the base of the ionosphere after a strong lightning event