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Abstract Microbial mats are commonly observed in estuaries and in salt marshes but they only rarely represent a significant surface involved in salt production. In the Sečovlje salt works in Northern Adriatic, a microbial mat known as the “petola” covers the bottom of salt crystallising pans, highly influencing salt composition and salt production processes. Throughout the year the petola is subjected to numerous co-varying factors that drive changes in its structure and the microbial community. Seasonal modifications were investigated via various methods (cryo-HRSEM, XRD, elemental analysis, carbohydrate content, bacterial community structure). This study provides knowledge on microbial mat compositional characteristics and functional roles in response to seasonal variation in environmental conditions. The in situ characterisation (close-to its natural hydrated state) of the three-dimensional microstructure provides precise information about dominating filamentous cyanobacterium Coleofasciculus chthonoplastes and extracellular polymer secretion (EPS) organisation. This is the first study to address how microbial mat composition and structure, especially 3D EPS network (and microbial diversity), affects the salt production processes within a hypersaline environment. Graphical abstract Unlabelled Image Highlights • Role of a microbial mat called “petola” in traditional Slovenian salt production. • Combination of microscopic, mineralogical, geochemical and biomolecular analyses. • High resolution cryo-scanning electron microscopy. • Petola's 3D organic microtexture impacts salt formation and production. • Magnesium sequestration by cyanobacterial sheaths favours salt purity. [ABSTRACT FROM AUTHOR]

A mesocosm study was conducted to assess the impact of water saturation episodes and of the input of bioavailable organic matter on the biogeochemical cycles of C and N, and on the behavior of metal(loid)s in a soil highly contaminated by the destruction of arsenical shells. An instrumented mesocosm was filled with contaminated soil taken from the “Place-à-Gaz” site. Four cycles of dry and wet periods of about one month were simulated for 276 days. After two dry/wet cycles, organic litter sampled on the site was added above the topsoil. The nitrogen cycle was the most impacted by the wet/dry cycles, as evidenced by a denitrification microbial process in the saturated level. The concentrations of the two most mobile pollutants, Zn and As, in the soil water and in the mesocosm leachate were, respectively, in the 0.3–1.6 mM and 20–110 μM ranges. After 8 months of experiment, about 83 g·m − 3 of Zn and 3.5 g·m − 3 of As were leached from the soil. These important quantities represent < 1% of the solid stock of this contaminant. Dry/wet cycles had no major effect on Zn mobility. However, soil saturation induced the immobilization of As by trapping As V but enhanced As III mobility. These phenomena were amplified by the presence of bioavailable organic matter. The study showed that the natural deposition of forest organic litter allowed a part of the soil's biological function to be restored but did not immobilize all the Zn and As, and even contributed to transport of As III to the surrounding environment. The main hazard of this type of site, contaminated by organo-arsenic chemical weapons, is the constitution of a stock of As that may leach into the surrounding environment for several hundred years. [ABSTRACT FROM AUTHOR]

Destruction of chemical munitions from World War I has caused extensive local top soil contamination by arsenic and heavy metals. The biogeochemical behavior of toxic elements is poorly documented in this type of environment. Four soils were sampled presenting different levels of contamination. The range of As concentrations in the samples was 1937–72,820 mg/kg. Concentrations of Zn, Cu and Pb reached 90,190 mg/kg, 9113 mg/kg and 5777 mg/kg, respectively. The high clay content of the subsoil and large amounts of charcoal from the use of firewood during the burning process constitute an ample reservoir of metals and As-binding materials. However, SEM–EDS observations showed different forms of association for metals and As. In metal-rich grains, several phases were identified: crystalline phases, where arsenate secondary minerals were detected, and an amorphous phase rich in Fe, Zn, Cu, and As. The secondary arsenate minerals, identified by XRD, were adamite and olivenite (zinc and copper arsenates, respectively) and two pharmacosiderites. The amorphous material was the principal carrier of As and metals in the central part of the site. This singular mineral assemblage probably resulted from the heat treatment of arsenic-containing shells. Microbial characterization included total cell counts, respiration, and determination of As(III)-oxidizing activities. Results showed the presence of microorganisms actively contributing to metabolism of carbon and arsenic, even in the most polluted soil, thereby influencing the fate of bioavailable As on the site. However, the mobility of As correlated mainly with the availability of iron sinks. [ABSTRACT FROM AUTHOR]

• Extraterrestrial organic matter is detected by EPR in 3.33 Ga sediments. • It is associated with Ni-Cr-rich ferrite "cosmic" spinel nanoparticles. • A challenge for the research for organic traces of extinct life in Mars. Electron paramagnetic resonance (EPR) analysis of carbonaceous, volcanic, tidal sediments from the 3.33 Ga-old Josefsdal Chert (Kromberg Formation, Barberton Greenstone Belt), documents the presence of two types of insoluble organic matter (IOM): (1) IOM similar to that previously found in Archean cherts from numerous other sedimentary rocks in the world and of purported biogenic origin; (2) anomalous IOM localized in a 2 mm-thick sedimentary horizon. Detailed analysis by continuous-wave-EPR and pulse-EPR reveals that IOM in this layer is similar to the insoluble component of the hydrogenated organic matter in carbonaceous chondrites, suggesting that this narrow sedimentary horizon has preserved organic matter of extraterrestrial origin. This conclusion is supported by the presence in this thin layer of another anomalous EPR signal at g = 3 attributed to Ni-Cr-Al ferrite spinel nanoparticles, which are known to form during atmospheric entry of cosmic objects. From this EPR analysis, it was deduced that the anomalous sedimentary layer originates from deposition, in a nearshore environment, of a cloud of tiny dust particles originating from a flux of micrometeorites falling through the oxygen-poor Archean atmosphere. [ABSTRACT FROM AUTHOR]

Thermal destruction of chemical munitions from World War I led to the formation of a heavily contaminated residue that contains an unexpected mineral association in which a microbial As transformation has been observed. A mesocosm study was conducted to assess the impact of water saturation episodes and input of bioavailable organic matter (OM) on pollutant behavior in relation to biogeochemical parameters. Over a period of about eight (8) months, the contaminated soil was subjected to cycles of dry and wet periods corresponding to water table level variations. After the first four (4) months, fragmented litter from the nearby forest was placed on top of the soil. The mesocosm solid phase was sampled by three rounds of coring: at the beginning of the experiment, after four (4) months (before the addition of OM), and at the end of the experiment. Scanning electron microscopy coupled to energy dispersive X-ray spectroscopy observations showed that an amorphous phase, which was the primary carrier of As, Zn, and Cu, was unstable under water-saturated conditions and released a portion of the contaminants in solution. Precipitation of a lead arsenate chloride mineral, mimetite, in soils within the water saturated level caused the immobilization of As and Pb. Mimetite is a durable trap because of its large stability domain; however, this precipitation was limited by a low Pb concentration inducing that high amounts of As remained in solution. The addition of forest litter modified the quantities and qualities of soil OM. Microbial As transformation was affected by the addition of OM, which increased the concentration of both As(III)-oxidizing and As(V)-reducing microorganisms. The addition of OM negatively impacted the As(III) oxidizing rate, however As(III) oxidation was still the dominant reaction in accordance with the formation of arsenate-bearing minerals. [ABSTRACT FROM AUTHOR]

The burning of chemical weapons in the 1926–1928 period produced polluted technosols with elevated levels of arsenic, zinc, lead and copper. During an eight-month mesocosm experiment, these soils were submitted to two controlled environmental changes, namely the alternation of dry and water-saturated conditions and the addition of fragmented organic forest litter to the surface soil. We investigated, by sequencing the gene coding 16S rRNA and 18S rRNA, (1) the structure of the prokaryotic and eukaryotic community in this polluted technosol and (2) their response to the simulated environmental changes, in the four distinct layers of the mesocosm. In spite of the high concentrations of toxic elements, microbial diversity was found to be similar to that of non-polluted soils. The bacterial community was dominated by Proteobacteria , Acidobacteria and Bacteroidetes , while the fungal community was dominated by Ascomicota. Amongst the most abundant bacterial Operational Taxonomic Units (OTUs), including Sphingomonas as a major genus, some were common to soil environments in general whereas a few, such as organisms related to Leptospirillum and Acidiferrobacter , seemed to be more specific to the geochemical context. Evolution of the microbial abundance and community structures shed light on modifications induced by water saturation and the addition of forest litter to the soil surface. Co-inertia analysis suggests a relationship between the physico-chemical parameters total organic carbon, Zn, NH 4 + and As(III) concentrations and the bacterial community structure. Both these results imply that microbial community dynamics linked to environmental changes should be considered as factors influencing the behavior of toxic elements on former ammunition burning sites. Unlabelled Image • Microbial communities from a soil polluted by ammunition burning were described. • Proteobacteria, Acidobacteria and Bacteriodetes were the dominant phyla. • The main genus, Sphingomonas , is involved in arsenic cycle. • Organic matter supply and water saturation affected community structures. [ABSTRACT FROM AUTHOR]

Mine tailings are major sources of metals and metalloids in the environment, making the physical and geochemical stabilization of tailings a serious environmental challenge. With a view to facilitate the development of covering vegetation and of decreasing the mobility of Pb in the acid tailings of a former Ag–Pb mine, laboratory microcosm experiments were performed to enable comparison of the effectiveness of several treatments. Tailings were mixed with 5% by weight of ochre, an iron-rich material produced during the treatment of a coal mine water, and with cow manure (0, 0.15, 1 and 2% by weight), either solely or in combination. They were then submitted to weekly watering over 84 days. All treatments raised the pH values from 4 to values between 7 and 8 and induced a strong decrease in the total dissolved Pb concentration in the percolating water (from 13 to 15 mg.L−1 to less than 0.5 mg.L−1). Several processes seemed to be involved in the immobilization of Pb by the amendments: precipitation as hydroxide, sulfate, carbonate and phosphate, and adsorption on iron hydroxides. A transient increase was observed in both Pb mobility and functional microbial diversity with 1% and 2% manure, with a peak after 28 days of incubation. This peak corresponded to an Average Well Color Development (AWCD) in Biolog™ Ecoplates increase from 0.5 to 0.8 with 1% manure and from 0.6 to 1.5 with 2% manure. However, at the end of experiment, Pb immobilization was strengthened by 2% manure and microbial functional biodiversity fell back, with AWCD values of 0.5 and 0.8 for 1% and 2% manure, respectively. Other toxic elements present in the tailings, namely As, Zn and Ba, were not strongly mobilized by the treatments, although cow manure slightly increased the leaching of Ba and As, which maximum concentrations in the leaching water reached 65 μg.L−1 Ba and 9 μg.L−1 As. All amendments improved the growth of ryegrass, which maximum dry biomass ranged from 38 mg/microcosm without amendment to 155 mg/microcosm with 0.15% manure. The results provide key information about the biogeochemical processes driving the mobility of Pb, As, Zn and Ba in acid mine tailings during the first 84 days following their amendment with iron-rich ochre and manure. • Ochre from coal mine water treatment increases pH of acid tailings. • Pb is stabilized and As is not mobilized in tailings by ochre and manure amendment. • Manure induces mobilization of Pb for 35 days then its stabilization. • Microbial functional biodiversity is transiently increased by amendment. • Ochre favors short-term growth of ray-grass on tailings. [ABSTRACT FROM AUTHOR]