Experimental quantification of the Fe-valence state at amosite-asbestos boundaries using acSTEM dual-electron energy-loss spectroscopy

Determination of the oxidation state and coordination geometry of iron in Fe-bearing minerals expands our knowledge obtained by standard mineralogical characterization. It provides information that is crucial in assessing the potential of minerals to interact with their surrounding environment and to generate reactive oxygen species, which can disrupt the normal function of living organisms. Aberration-corrected scanning transmission electron microscopy dual-electron energy-loss spectroscopy (acSTEM Dual-EELS) has only rarely been applied in environmental and medical mineralogy, but it can yield data that are essential for the description of near-surface and surface mechanisms involved in many environmental and health-related processes. In this study, we have applied the energy loss near-edge structure (ELNES) and L2,3 white-line intensity-ratio methods using both the universal curve and progressively larger integrating windows to verify their effectiveness in satisfactorily describing the valence state of iron at amosite grain boundaries, and, at the same time, to estimate thickness in the same region of interest. The average valence state obtained from acSTEM Dual-EELS and from a simplified geometrical model were in good agreement, and within the range defined by the bulk and the measured surface-valence states. In the specific case presented here, the use of the universal curve was most suitable in defining the valence state of iron at amosite grain boundaries. The study of ELNES revealed an excellent correspondence with the valence state determined by the L2,3 white-line intensity-ratio method through the use of the universal curve, and it seems that the spectra carry some information regarding the coordination geometry of Fe. The combination of visual examination, reconstruction of the grain boundaries through a simple geometrical model, and Dual-EELS investigation is a powerful tool for characterizing the grain boundaries of hazardous minerals and foreseeing their potential activity in an organism, with the possibility to describe toxic mechanisms in a stepwise fashion

Mineral fibres and asbestos bodies in human lung tissue: A case study

One of the open questions regarding the asbestos problem is the fate of the mineral fibres in the body once inhaled and deposited in the deep respiratory system. In this context, the present paper reports the results of an electron microscopy study of both mineral fibres and asbestos bodies found in the lung tissue of a patient who died of malignant mesothelioma due to past occupational exposure. In concert with previous in vivo animal studies, our data provide evidence that amphibole asbestos fibres are durable in the lungs, whereas chrysotile fibres are transformed into a silica-rich product, which can be easily cleared. Amphibole fibres recovered from samples of tissue of the deceased display a high degree of crystallinity but also show a very thin amorphous layer on their surface; 31% of the fibres are coated with asbestos bodies consisting of a mixture of ferroproteins (mainly ferritin). Here, we propose an improved model for the coating process. Formation of a coating on the fibres is a defence mechanism against fibres that are longer than 10 µm and thinner than 0.5 µm, which macrophages cannot engulf. The mature asbestos bodies show signs of degradation, and the iron stored in ferritin may be released and potentially increase oxidative stress in the lung tissue

How Probabilistic Causation Can Account for the Use of Mechanistic Evidence

In a recent paper in this journal, Federica Russo and Jon Williamson argue that an analysis of causality in terms of probabilistic relationships does not do justice to the use of mechanistic evidence to support causal claims. I will present Ronald Giere=s theory of probabilistic causation, and show that it can account for the use of mechanistic evidence (both in the health sciences B on which Russo and Williamson focus B and elsewhere). I also review some other probabilistic theories of causation (of Suppes, Eells and Humphreys) and show that they cannot account for the use of mechanistic evidence. I argue that these theories are also inferior to Giere's theory in other respects

Naturally-Occurring Zirconolites - Analogues for the Long-Term Encapsulation of Actinides in Synroc

The use of natural zirconolites to assess the effect of α-decay damage and geochemical alteration on the release of actinides from HLW wasteforms is critically examined. There is evidence that the natural zirconolites provide a good chemical and radi-ation damage analogy for the HLW wasteforms, but additional work is required to define the geochemical environments in which zirconolite is stable or unstable (e.g., suffering corrosion or chemical alteration, including loss of actinides)

Identifying adequate models in physico-mathematics: Descartes' analysis of the rainbow

The physico-mathematics that emerged at the beginning of the seventeenth century entailed the quantitative analysis of the physical nature with optics, meteorology and hydrostatics as its main subjects. Rather than considering physico-mathematics as the mathematization of natural philosophy, it can be characterized it as the physicalization of mathematics, in particular the subordinate mixed mathematics. Such transformation of mixed mathematics was a process in which physico-mathematics became liberated from Aristotelian constraints. This new approach to natural philosophy was strongly influenced by Jesuit writings and experimental practices. In this paper we will look at the strategies in which models were selected from the mixed sciences, engineering and technology adequate for an analysis of the specific phenomena under investigation. We will discuss Descartes’ analysis of the rainbow in the eight discourse of his Meteorology as an example of carefully selected models for physico-mathematical reasoning. We will further demonstrate that these models were readily available from Jesuit education and literature

Growth and alteration of uranium-rich microlite

Uranium-rich microlite, a pyrochlore-group mineral, occurs in 440 Ma old lithium pegmatites of the Mozambique Belt in East Africa. Microlite exhibits a pronounced growth zoning, with a U-free core surrounded by a U-rich rim (UO{sub 2} up to 17 wt.%). The core exhibits conjugate sets of straight cracks (cleavage planes) which provided pathways for a late-stage U-enriched pegmatitic fluid which interacted with the U-free microlite to produce a distinct U enrichment along the cracks and led to the formation of the U-rich rim. Following the stage of U incorporation into microlite, a second generation of hydrothermal fluids deposited mica along the cleavage planes. Subsequent to these two hydrothermal stages, the host rock was uplifted and subjected to intense low-temperature alteration during which Na, Ca and F were leached from the microlite crystals. This alteration also led to a hydration of microlite, but there is no evidence of U loss. These low-temperature alteration effects were only observed in the U-rich rim which is characterized by a large number of irregular cracks which are most probably the result of metamictization, as indicated by electron diffraction images and powder X-ray patterns. The pyrochlore-group minerals provide excellent natural analogues for pyrochlore-based nuclear waste forms, because samples of variable age and with high actinide contents are available

Epistemic Dependence and Collective Scientific Knowledge

I argue that scientific knowledge is collective knowledge, in a sense to be specified and defended. I first consider some existing proposals for construing collective knowledge and argue that they are unsatisfactory, at least for scientific knowledge as we encounter it in actual scientific practice. Then I introduce an alternative conception of collective knowledge, on which knowledge is collective if there is a strong form of mutual epistemic dependence among scientists, which makes it so that satisfaction of the justification condition on knowledge ineliminably requires a collective. Next, I show how features of contemporary science support the conclusion that scientific knowledge is collective knowledge in this sense. Finally, I consider implications of my proposal and defend it against objections. © 2013 Springer Science+Business Media Dordrecht

Diking, young volcanism and diffuse hydrothermal activity on the southern Mid-Atlantic Ridge: The Lilliput field at 9°33'S

Detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed, at 9 degrees 33'S, the presence of the southernmost active hydrothermal field known so far on the Mid-Atlantic Ridge. The size of the hydrothermal field, which we have named "Lilliput", is about 1000 m x 250 m. It lies in a water depth of 1500 m on a ridge segment (Segment A3) with considerably thickened crust of 11 km. Four relatively small diffuse vent sites occur on a large young (estimated <100 years old) lava flow, partly covering the flow with hydrothermal Fe-oxide/hydroxide sediments. Based on homogeneous major element compositions of ca. 25 lava samples, this flow covers an area of at least 5 km x 0.6 km. The lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds. The volcanic ridge probably represents the surface expression of an underlying dike which fed the flow. Several drained lava pond structures were observed within the flow but only one shows hydrothermal activity. The hydrothermal venting and precipitation of abundant Fe-oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the Lilliput field lie along and almost equidistant from the eastern flank of the supposed dike. Although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years (2005 and 2006), no high-temperature venting associated with Lilliput has been found. in agreement with findings at other ridges with thick crust such as Reykjanes. High magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow-spreading segments with thick crust whereas diffuse venting is abundant. Interestingly, the fauna at the Lilliput vents largely consists of small and apparently juvenile mussels (Bathymodiolus sp.) and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity