Release of Particulate Iron Sulfide during Shale-Fluid Interaction.

During hydraulic fracturing, a technique often used to extract hydrocarbons from shales, large volumes of water are injected into the subsurface. Although the injected fluid typically contains various reagents, it can become further contaminated by interaction with minerals present in the rocks. Pyrite, which is common in organic-rich shales, is a potential source of toxic elements, including arsenic and lead, and it is generally thought that for these elements to become mobilized, pyrite must first dissolve. Here, we use atomic force microscopy and environmental scanning electron microscopy to show that during fluid-rock interaction, the dissolution of carbonate minerals in Eagle Ford shale leads to the physical detachment, and mobilization, of embedded pyrite grains. In experiments carried out over a range of pH, salinity, and temperature we found that in all cases pyrite particles became detached from the shale surfaces. On average, the amount of pyrite detached was equivalent to 6.5 × 10-11 mol m-2 s-1, which is over an order of magnitude greater than the rate of pyrite oxidation expected under similar conditions. This result suggests that mechanical detachment of pyrite grains could be an important pathway for the mobilization of arsenic in hydraulic fracturing operations and in groundwater systems containing shales.

Assembly of clay mineral platelets, tactoids, and aggregates: Effect of mineral structure and solution salinity.

Clay mineral properties, together with solution chemistry, control the assembly of clay platelets into hierarchical structures, including tactoids and aggregates. We studied the effect of salinity on the assembly of kaolinite, illite, and montmorillonite at three critical scales: platelet, tactoid, and aggregate, using cryogenic scanning electron microscopy (cryo-SEM), atomic force microscopy (AFM) and cryo-transmission EM (cryo-TEM), respectively. Cyro-SEM images coupled with original alignment analysis indicate that the degree of aggregate alignment in an ionized solution was significantly higher than in deionized water. Furthermore, upon increasing platelet-platelet bonding energy (montmorillonite > illite > kaolinite), tactoid size increased, packing was less ordered, and aggregate alignment decreased. AFM measurements showed that an increase in ionic-strength caused a decrease in the Young's modulus of the clays, indicating higher tactoid alignment, since, disordered structures, comprising various platelet orientations, are stiffer than highly-aligned structures. We successfully measured distances <1 nm, for both kaolinite and montmorillonite by cryo-TEM, directly demonstrating that increasing ionic-strength reduces platelet-platelet distances. The outcome of this study offers a new approach and methodology to study fundamental colloid-assembly which will trigger future studies investigating additional parameters affecting assembly such as, temperature, solution pH, natural organic matter, and anthropogenic activity.

Origin of lead in eight Central European peat bogs determined from isotope ratios, strengths, and operation times of regional pollution sources.

Lead originating from coal burning, gasoline burning, and ore smelting was identified in 210Pb-dated profiles through eight peat bogs distributed over an area of 60,000 km2. The Sphagnum-dominated bogs were located mainly in mountainous regions of the Czech Republic bordering with Germany, Austria, and Poland. Basal peat 14C-dated at 11,000 years BP had a relatively high 206Pb/207Pb ratio (1.193). Peat deposited around 1800 AD had a lower 206Pb/207Pb ratio of 1.168-1.178, indicating that environmental lead in Central Europe had been largely affected by human activity (smelting) even before the beginning of the Industrial Revolution. Five of the sites exhibited a nearly constant 206Pb/207Pb ratio (1.175) throughout the 19th century, resembling the "anthropogenic baseline" described in Northern Europe (1.17). At all sites, the 206Pb/207Pb ratio of peat decreased at least until 1980; at four sites, a reversal to more radiogenic values (higher 206Pb/207Pb), typical of easing pollution, was observed in the following decade (1980-1990). A time series of annual outputs for 14 different mining districts dispersing lead into the environment has been constructed for the past 200 years. The production of Ag-Pb, coal, and leaded gasoline peaked in 1900, 1980, and 1980, respectively. In contrast to other European countries, no peak in annual Pb accumulation rates was found in 1900, the year of maximum ore smelting. The highest annual Pb accumulation rates in peat were consistent with the highest Pb emission rates from coal-fired power plants and traffic (1980). Although maximum coal and gasoline production coincided in time, their isotope ratios were unique. The mean measured 206Pb/207Pb ratios of local coal, ores, and gasoline were 1.19, 1.16, and 1.11, respectively. A considerable proportion of coal emissions, relative to gasoline emisions, was responsible for the higher 206Pb/207Pb ratios in the recent atmosphere (1.15) compared to Western Europe (1.10). As in West European countries, the gasoline sold in the Czech Republic during the Communist era (1948-1989) contained an admixture of low-radiogenic Precambrian lead from Australia.

Association between SARS-Cov-2 infection during pregnancy and adverse pregnancy outcomes: a re-analysis of data from Wei et al. (2021).

BackgroundWei et al. have published a meta-analysis (MA) which aimed to "evaluate the association between SARS-CoV-2 infection during pregnancy and adverse pregnancy outcomes". Using classical random-effects model, they found that SARS-CoV-2 infection was associated with preeclampsia, preterm birth and stillbirth. Performing MA with low event rates or with few studies may be challenging as MA relies on several within and between study distributional assumptions. Methodsto assess the robustness of the results provided by Wei et al., we performed a sensitivity analysis using several frequentist and Bayesian meta-analysis methods. We also estimated fragility indexes. ResultsFor eclampsia (patients with Covid-19 vs without), the confidence intervals of most frequentist models contain 1. All beta-binomial models (Bayesian) lead to credible intervals containing 1. The prediction interval, based on DL method ranges from 0.75 to 2.38. The fragility index is 2 for the DL method. For preterm, the confidence (credible) intervals exclude 1. The prediction interval is broad, ranging from 0.84 to 20.61. The fragility index ranges from 27 to 10. For stillbirth, the confidence intervals of most frequentist models contain 1. Six Bayesian MA models lead to credible intervals containing 1.The prediction interval ranges from 0.52 to 8.49. The fragility index is 3. InterpretationGiven the available data and the results of our broad sensitivity analysis, we can only suggest that SARS-CoV-2 infection during pregnancy is associated to preterm, and may be associated to preeclampsia. For stillbirth, more data are needed as none of the Bayesian analyses are conclusive.