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The Development and Application of a Method to Measure Volatile Antimony Emissions from Soils and Antimony Release from Contaminated Soils
No full textIn the environment, antimony (Sb) is a ubiquitous, but toxic, element. Due to the increased use of Sb in flame retardants, ammunition, as a PET catalyst, and its potential for applications in green energy, the exploitation and associated contamination of Sb has increased and likely will continue to increase. Due to its assumed geochemical similarities to the toxic element arsenic (As), the environmental fate of Sb has become an area of public concern. In general, the biogeochemical cycle of Sb remains to be elucidated with many unknowns. The behavior of inorganic Sb in the aerobic environment is relatively well understood but, Sb behavior in anaerobic environments has been poorly investigated. Even less studied are the microbial-mediated transformations of Sb in the environment such as its methylation and volatilization, although these transformations may have an impact on its mobility and toxicity. Environments susceptible to anoxic conditions (e.g., wetlands) constitute a major part of Earth’s surface and all soils are prone to periodic flooding therefore, the fate of Sb, behavior, and its transformations require further investigation. This dissertation aimed to investigate Sb transformations, such as its volatilization, and release from different soils under laboratory and field conditions from soils susceptible to waterlogging.
First, to investigate Sb volatilization in laboratory and field conditions a method had to be developed that had the following criteria 1) easy to deploy in the field, 2) cost-effective, and 3) user-friendly. Commercially available activated charcoal sorbent tubes (Sb-traps) were tested for their ability to capture stibines (trimethylstibine ((CH3)3Sb) and stibine (SbH3)) produced by hydride generation. The traps were extracted using a closed-vessel aqua regia extraction. The extraction recoveries, as total Sb, were 93.2 ± 2.3% for (CH3)3Sb and 89.6 ± 3.8% for SbH3 with a limit of detection < 2 ng. This method was then applied to microcosm experiments on Swiss shooting range soils to test its ability to capture naturally produced stibines. The 42-day microcosm experiment showed that volatile Sb was only detected in waterlogged conditions, highlighting the importance of waterlogging on volatilization. By amending the waterlogged soils with 5% (w/w) manure a five-fold increase in volatile Sb was produced from the soils. This experiment indicated that common agricultural practices on contaminated soils such as waterlogging, potentially anoxic conditions, and organic-matter amendments (e.g., manuring) strongly influence the formation of stibines from soils by likely stimulating microorganisms in the soil. As the first experiment showed that volatile Sb was only produced under waterlogged conditions, there was a focus in the next experiments on soils commonly impacted by waterlogging.
Rice-paddy soils are agricultural soils impacted by varying hydrologic conditions and rice is an important staple food for many nations. In the second experiment, Sb release from three rice paddies and Sb volatilization from two rice paddies (low and high Sb contaminated sites) was investigated in an Sb-mining region in the field. In the field campaign, porewater Sb was associated with Fe at two sites and with Eh, SO42-, Fe, and Mn at the third site. Volatile Sb was detected (18.1 ± 5.2 to 217.9 ± 160.7 mg ha−1 y−1) in both investigated rice paddies but the high Sb-contaminated site had higher volatile Sb emissions. The same soils from the field campaign were complemented with a 56-day microcosm experiment in the laboratory using two treatments, waterlogging-only and waterlogging with 0.8% (w/w) manure, to better understand the potential drivers of Sb volatilization and release. The lowest-producing soil was the low Sb site from the field campaign which produced relatively negligible volatile Sb. The two high-Sb contaminated soils produced more volatile Sb when manured and agree with the first experiment where agricultural practices may influence Sb inputs to the atmosphere. Volatile Sb in the microcosm was correlated with the surface water Sb concentration indicating that the surface water Sb maybe the source of volatile Sb. The release of Sb in the porewaters was not influenced by manuring, and was always high with the beginning of waterlogging, indicating that with the start of the rice growing season relevant amounts of Sb may be released into waters and pose a risk to the environment. A rapid decrease of porewater Sb was observed in all experiments correlated with a decrease in porewater SO42-, indicating potential sulfide precipitation. In some microcosms, a temporary release of Sb was observed, likely associated with the reductive dissolution of Fe-(oxyhydr)oxides.
The third experiment was a 27-day microcosm experiment investigating Sb release, methylation, and volatilization from two different wetland soils with a high soil Sb (organic-rich wetland) and a low soil Sb (Fe-rich floodplain soil). The Sb release patterns between the two soil types varied. In the organic-rich wetland soil, Sb release was a complex interplay with DOC, SO42-, and Mn while the Fe-rich floodplain soil showed a strong coupling of Sb to the Fe-cycle and potential immobilization by sulfide precipitation. Both soils released environmentally relevant concentrations of Sb to the waters indicating that waterlogging of these soils may pose risk to the surrounding environment. In the porewaters of the organic-rich wetland soil, after 6 days of waterlogging an unknown species was detected. Spiked porewaters with TMSb did not aid in species identification. Additionally, poor column recoveries for the waters indicate the potential formation of retained Sb species. In soil TMSb extractions before and after incubation and the surface waters from the organic-rich wetland soils, a species with a similar retention time as the unknown species in the porewaters was detected. Spiked extracts and surface waters with TMSb overlapped with the unknown species but the identification remained unclear due to potential matrix effects causing a TMSb retention time shift in the samples. These results highlight the importance of future investigations into Sb speciation outside of typical SbIII, SbV, and TMSb analysis. Both soils produced volatile Sb more (organic-rich wetland soil) or comparable (Fe-rich floodplain soil) amounts as the previous experiments even though these soils were not nutrient amended, indicating that naturally high organic carbon may promote volatilization. In this experiment, relationships between volatile Sb production and physicochemical properties of the soils and waters were not detected indicating a more complex, likely microbial, mechanism.
In conclusion, the release of Sb from waterlogged soils is controlled by the Fe and S cycles in rice-paddy and floodplain soils. In organic-rich wetland soils, Sb solubility is a more complex mechanism. By manuring rice-paddy soils there was no impact on the release of Sb, an interesting finding as manuring soils typically enhances the mobility of the geochemically similar element, As. In all soils, except for the Fe-rich floodplain soil, Sb is quickly immobilized in the porewaters likely due to sulfide precipitation. In the floodplain soils, Sb is released with Fe and subsequently immobilized after a longer periodic of waterlogging. All soils released environmentally relevant concentrations of Sb into the waters. Additionally, speciation analysis of the porewaters indicated the presence of an unknown Sb species in the organic-rich wetland soils and highlights the importance of future investigations. Volatile Sb was detected for the first time in the rice-paddies and rice paddy, organic-rich, and floodplain soils microcosms and is influenced by agricultural practices (e.g., waterlogging and manuring) and may represent an important, but overlooked, source of Sb to the atmosphere
Validation and deployment of a quantitative trapping method to measure volatile antimony emissions
Full text linkMicrobial-mediated Sb volatilization is a poorly understood part of the Sb biogeochemical cycle. This is mostly due to a lack of laboratory and field-deployable methods that are capable of quantifying low-level emissions of Sb from diffuse sources. In this study, we validated two methods using a H2O2 -HNO3 liquid chemotrap and an activated coconut shell charcoal solid-phase trap, achieving an absolute limit of detection of 4.6 ng and below 2.0 ng Sb, respectively. The activated charcoal solid-phase trapping method, the most easily operated method, was then applied to contaminated shooting range soils. Four treatments were tested: 1) flooded, 2) manure amended + flooded, 3) 70 % water holding capacity, and 4) manure amendment +70 % water holding capacity, since agricultural practices and flooding events may contribute to Sb volatilization. Volatile Sb was only produced from flooded microcosms and manure amendment greatly influenced the onset and amount of volatile Sb produced. The highest amount of volatile Sb produced, up to 62.1 ng kg−1 d−1, was from the flooded manure amended soil. This suggests that anaerobic microorganisms may potentially be drivers of Sb volatilization. Our results show that polluted shooting range soils are a source of volatile Sb under flooded conditions, which may lead to an increase in the mobility of Sb. Some of these volatile Sb species are toxic and genotoxic, highlighting the role of Sb volatilization on environmental health, especially for individuals living in contaminated areas exposed to wetlands or flooded conditions (e.g., rice paddy agriculture surrounding mining areas). This work paves way for research on Sb volatilization in the environment
Organo-mercury species in a polluted agricultural flood plain: Combining speciation methods and polymerase chain reaction to investigate pathways of contamination.
Full text linkThe analysis of organic mercury (Hg) species in polluted soils is a necessary tool to assess the environmental risk(s) of mercury in contaminated legacy sites. The artificial formation of monomethylmercury (MeHg) during soil extraction and/or analysis is a well-known limitation and is especially relevant in highly polluted areas where MeHg/Hg ratios are notoriously low. Although this has been known for almost 30 years, the thorough characterisation of artificial formation rates is rarely a part of the method development in scientific literature. Here we present the application of two separate procedures (inorganic Hg (iHg) spiking and double-spike isotope dilution analyses (DSIDA)) to determine and correct for artificial Hg methylation in MeHg-selective acid-leaching/organic solvent extraction procedure. Subsequently, we combined corrected MeHg and ethylmercury (EtHg) measurements with PCR amplification of hgcA genes to distinguish between naturally formed MeHg from primary deposited MeHg in soils from a legacy site in a Swiss mountain valley. We found the DSIDA procedure incompatible with the organomercury selective extraction method due to the quantitative removal of iHg. Methylation factors from iHg spiking were in the range of (0.0075 ± 0.0001%) and were consistent across soils and sediment matrices. Further, we suggest that MeHg was deposited and not formed in-situ in two out of three studied locations. Our line of evidence consists of 1) the concomitant detection of EtHg, 2) the elevated MeHg concentrations (up to 4.84 μg kg-1), and 3) the absence of hgcA genes at these locations. The combination of Hg speciation and methylation gene (hgcA) abundance analyses are tools suited to assess Hg pollution pathways at Hg legacy sites
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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