Detecting radioactive particles in complex environmental samples using real-time autoradiography

Radioactive particles often contain very high radioactivity concentrations and are widespread. They pose a potential risk to human health and the environment. Their detection, quantification, and characterization are crucial if we are to understand their impact. Here, we present the use of a real-time autoradiography gaseous detector (using parallel ionization multiplier) to expedite and improve the accuracy of radioactive particle screening in complex environmental samples. First, standard particles were used to assess the detector capabilities (spatial resolution, spectrometry, and artefact contributions), then, we applied the technique to more complex and environmentally relevant samples. The real-time autoradiography technique provides data with a spatial resolution (≲100 µm) suitable for particle analysis in complex samples. Further, it can differentiate between particles predominantly emitting alpha and beta radiation. Here, the technique is applied to radioactive cesium-rich microparticles collected from the Fukushima Daiichi nuclear exclusion zone, showing their accurate detection, and demonstrating the viability of real-time autoradiography in environmental scenarios. Indeed, for more complex samples (radioactive particles in a less radioactive heterogeneous background mix of minerals), the technique permits relatively high selectivity for radioactive particle screening (up to 61.2% success rate) with low false positive percentages (~ 1%).

Bioelectrochemical Systems for Groundwater Remediation: The Development Trend and Research Front Revealed by Bibliometric Analysis

: Due to the deficiency of fresh water resources and the deterioration of groundwater quality worldwide, groundwater remedial technologies are especially crucial for preventing groundwater pollution and protecting the precious groundwater resource. Among the remedial alternatives, bioelectrochemical systems have unique advantages on both economic and technological aspects. However, it is rare to see a deep study focused on the information mining and visualization of the publications in this field, and research that can reveal and visualize the development trajectory and trends is scarce. Therefore, this study summarizes the published information in this field from the Web of Science Core Collection of the last two decades (1999–2018) and uses Citespace to quantitatively visualize the relationship of authors, published countries, organizations, funding sources, and journals and detect the research front by analyzing keywords and burst terms. The results indicate that the studies focused on bioelectrochemical systems for groundwater remediation have had a significant increase during the last two decades, especially in China, Germany and Italy. The national research institutes and universities of the USA and the countries mentioned above dominate the research. Environmental Science & Technology, Applied and Environmental Microbiology, and Water Research are the most published journals in this field. The network maps of the keywords and burst terms suggest that reductive microbial diversity, electron transfer, microbial fuel cell, etc., are the research hotspots in recent years, and studies focused on microbial enrichment culture, energy supply/recovery, combined pollution remediation, etc., should be enhanced in future.

Quantifying Technetium and Strontium Bioremediation Potential in Flowing Sediment Columns

The high-yield fission products ⁹⁹Tc and ⁹⁰Sr are found as problematic radioactive contaminants in groundwater at nuclear sites. Treatment options for radioactively contaminated land include bioreduction approaches, and this paper explores ^99mTc and ⁹⁰Sr behavior and stability under a range of biogeochemical conditions stimulated by electron donor addition methods. Dynamic column experiments with sediment from the Sellafield nuclear facility, completed at site relevant flow conditions, demonstrated that Fe(III)-reducing conditions had developed by 60 days. Sediment reactivity toward ⁹⁹Tc was then probed using a ^99mTc(VII) tracer at <10^-10 mol L^-1 and γ camera imaging showed full retention of ^99mTc in acetate amended systems. Sediment columns were then exposed to selected treatments to examine the effects of different acetate amendment regimes and reoxidation scenarios over 55 days when they were again imaged with ^99mTc. Here, partially oxidized sediments with no further electron donor additions remained reactive toward ^99mTc under relevant groundwater O₂ and NO₃^- concentrations over 55 days. Immobilization of ^99mTc was highest where continuous acetate amendment had resulted in sulfate-reducing conditions. Interestingly, the sulfate reducing system showed enhanced Sr retention when stable Sr²⁺ was added continuously as a proxy for ⁹⁰Sr. Overall, sediment reactivity was nondestructively imaged over an extended period to provide new information about dynamic iron and radionuclide biogeochemistry throughout realistic sediment redox cycling regimes.

Fossilized bioelectric wire - the trace fossil Trichichnus

The trace fossil Trichichnus is proposed as an indicator of fossil bioelectric bacterial activity at the oxic–anoxic interface zone of marine sediments. This fulfils the idea that such processes, commonly found in the modern realm, should be also present in the geological past. Trichichnus is an exceptional trace fossil due to its very thin diameter (mostly less than 1 mm) and common pyritic filling. It is ubiquitous in some fine-grained sediments, where it has been interpreted as a burrow formed deeper than any other trace fossils, below the redox boundary. Trichichnus, formerly referred to as deeply burrowed invertebrates, has been found as remnant of a fossilized intrasediment bacterial mat that is pyritized. As visualized in 3-D by means of X-ray computed microtomography scanner, Trichichnus forms dense filamentous fabric, which reflects that it is produced by modern large, mat-forming, sulfide-oxidizing bacteria, belonging mostly to Thioploca-related taxa, which are able to house a complex bacterial consortium. Several stages of Trichichnus formation, including filamentous, bacterial mat and its pyritization, are proposed to explain an electron exchange between oxic and suboxic/anoxic layers in the sediment. Therefore, Trichichnus can be considered a fossilized “electric wire”.

Self-potential monitoring of a crude oil-contaminated site (Trecate, Italy)

We present a multidisciplinary approach for characterization of a crude oil-contaminated site (Trecate, Italy), integrating geophysical data, such as subsoil electrical potential (in millivolts) and electrical resistivity (in ohm meters) distribution, with hydrogeological and bio-chemical data. Self-potential measurements have been evaluated together with active geoelectrical measurements and hydrological information, to provide spatial and temporal information about the self-potential sources and their possible correlations with the contamination state of the subsoil. Three self-potential surveys (March 2010, October 2010, and March 2011) were conducted at the site, both in the contaminated and uncontaminated regions. The obtained self-potential maps show large time-lapse differences in correspondence of the contaminated area, with positive electrical potential values (up to 50 mV) in spring surveys and an electrical potential dipolar distribution in October (2010) survey (amplitude from -15 to 25 mV). To understand the origin of the measured self-potential signals, a model using vertical dipolar electrical sources was built, taking into account the electrical resistivity distribution deduced from electrical resistivity tomography. The self-potential source identification allows the Trecate contamination state to be better delineated. In particular, two self-potential contributions are superimposed: the electrokinetic mechanism is predominant in spring, while the redox mechanism represents the most important contribution in autumn.