Abstract: Paintings are complex objects containing many different chemical compounds that can react over time. The degradation of arsenic sulfide pigments causes optical changes in paintings. The main degradation product was thought to be white arsenolite (As2O3), but previous research also showed the abundant presence of As(V) species. In this study, we investigate the influence of the presence of a medium on the degradation mechanism of orpiment (As2S3) using synchrotron radiation (SR)-based tomographic transmission X-ray microscopy, SR-based micro-X-ray fluorescence, and Xray absorption near edge structure spectroscopy. Upon direct illumination of dry orpiment powder using UV-visible light, only the formation of As2O3 was observed. When As2S3 was surrounded by a medium and illuminated, As2O3 was only observed in the area directly exposed to light, while As(V) degradation species were found elsewhere in the medium. Without accelerated artificial light aging, As(V)(aq) species are formed and migrate throughout the medium within weeks after preparation. In both scenarios, the As(V) species form via intermediate As(III)(aq) species and the presence of a medium is necessary. As(V)(aq) species can react with available cations to form insoluble metal arsenates, which induces stress within the paint layers (leading to, e.g., cracks and delamination) or can lead to a visual change of the image of the painting.

Abstract: Biosensing platforms are answering the increasing demand for analytical tools for environmental monitoring of small molecules, such as per- and polyfluoroalkyl substances (PFAS). By transferring toxicological findings in bioreceptor design we can develop innovative pathways for biosensor design. Indeed, toxicological studies provide fundamental information about PFAS-biomolecule complexes that can help evaluate the applicability of the latter as bioreceptors. The toolbox of native mass spectrometry (MS) can support this evaluation, as shown by the two case studies reported in this work. The analysis of model proteins’ (i.e. albumin, haemoglobin, cytochrome c and neuroglobin) interactions with well-known PFAS, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), demonstrated the potential of this native MS screening approach. In the first case study, untreated albumin and delipidated albumin were compared in the presence and absence of PFOA confirming that the delipidation step increases albumin affinity for PFOA without affecting protein stability. In the second case study, the applicability of our methodology to identify potential bioreceptors for PFOS/PFOA was extended to other proteins. Structurally related haemoglobin and neuroglobin revealed a 1 : 1 complex, whereas no binding was observed for cytochrome c. These studies have value as a proof-of-concept for a general application of native MS to identify bioreceptors for toxic compounds.

Abstract: Selenium is determined in the ng g−1 to μg g−1 range in biological and environmental samples. A wet digestion procedure was optimized with respect to volatility losses and recovery yields, by using 75Se metabolically incorporated into rat organs. Selenium is preconcentrated from the digestion liquid by a two-step reduction with 4 M HCl and ascorbic acid. The colloidal selenium formed is adsorbed on activated carbon and filtered on a Nucleopore membrane for measurement by energy-dispersive x-ray fluorescence. Almost complete recovery was obtained, and the detection limit was 20 ng, corresponding to 10 ng g−1 for a 2-g sample. Biological reference materials were analyzed with satisfactory results, and the accuracy of the method was good.

Abstract: Heritage-related guidelines and standards recommend stable climatic conditions, since these contribute to the extension of heritage collections life. As a result, numerous museums and other heritage institutions implement (expensive) mitigation measures to achieve stable conditions. Nevertheless, temperature and relative humidity fluctuations are often still observed. This contribution demonstrates that the analysis of temperature and humidity peaks and drops helps to identify hazards which cause fluctuations in different frequency ranges. This hazard identification provides information on the type of mitigation actions that are required in the near future and in which order they need to be implemented. The approach is illustrated with a case study. A 22 month monitoring campaign was performed in a chapel in the center of Antwerp (Belgium) where the climatic conditions are controlled with a heating, ventilation and air conditioning (HVAC) system. Low-, mid- and high-frequency fluctuations were separated and discussed for their hazards.

Abstract: A diffusive sampling method for the determination of gaseous acetic and formic acids, using a radial symmetry diffusive sampler, has been optimised for a 7-day exposure time in this study. Sampling rate determinations were performed on data obtained from a dynamic exposure chamber, simulating the indoor conditions of an empty, closed, room, at room temperature and minimal wind speed. Analysis has been performed by means of ion chromatography. The sampling rates for formic acid concentrations of 128 ìg m−3 and 1248 ìg m−3 were determined to be 91.2 ± 3.9 ml min−1 and 111.6 ± 2.8 ml min−1, respectively. The acetic acid sampling rate was independent of the concentration in the range 160 ìg m−31564 ìg m−3, and amounted to 97.3 ± 3.1 ml min−1. Experimentally determined sampling rates showed deviations of 3% for acetic acid, and 321% for formic acid, in relation to theoretically derived values. The blank values were as low as 1.69 ± 0.07 ìg for formic acid and 1.21 ± 0.14 ìg for acetic acid, and detection limits lower than 0.5 ìg m−3 could be achieved, which is an improvement of 9899% compared to previously validated diffusive sampling methods. This study describes the first step of an extended validation program in which the applicability of these types of samplers for the measurement of organic acids will be validated and optimised for the environmental conditions typical for museum showcases.

Abstract: K X-ray fluorescence cross-sections of Cu, Y and Ba elements were measured in CuO, Y(2)O(3), BaCO(3) Compounds and YBa(2)Cu(3)O(7-delta) superconductor samples (nonreacted agent, calcined and sintered states). A superconductor sample of YBa(2)Cu(3)O(7-delta) was prepared by using a solid-state reaction technique. The samples were excited by gamma rays of energy 59.5 keV from a (241)Am radioisotope source. The Cu, Y and Ba K X-ray intensities counted with a Si(Li) detector were measured in different solid-state conditions. The obtained values of K X-ray fluorescence cross-section were compared with the theoretical values of pure Cu, Y and Ba elements. We found that the K X-ray fluorescence cross-section of Cu, Y and Ba in YBa(2)Cu(3)O(7-delta) sample is changed in different solid-state conditions, depending on the mixture (nonreacted agent), calcined and sintered states. (c) 2008 Elsevier Ltd. All rights reserved.

Abstract: There is a type of filament that forms dosed contours encircling regions of one polarity of magnetic field, while the surrounding region has the opposite polarity One distribution of ring-filaments has sizes 2R = 40,000 to 160,000 km with the maximum around 100,000 km; the other distribution (with filaments and filament channels) has bigger sizes, with a maximum around 300,000 km. At low and mid latitudes the radial component B-rs (radial for the Sun) in the region outlined by filaments varies from 50 to 100 gauss, while the longitudinal component B-phi varies from 10 to 30 gauss. The total current inside the filament is 10(10) – 10(11) A, the ratio R/a approximate to 5 to 10, the magnetic flux crossing the surface is approximate to 10(21) – 10(22) MX; th, magnetic energy is approximate to 10(29) – 10(31) erg. Polar ring-filaments at latitudes 60 degrees-80 degrees are related to the polar magnetic field reversal and the quasi-flare processes at the poles during the field reversal. Correlation between B-rs and B-phi for the polar filament bands cannot be satisfactorily explained. A theoretical model using the conservation laws is used to study the relations between the various fields, currents, etc, of shrinking polar ring-filaments and their evolution. According to this theory ring-filaments should rise higher above the photosphere when shrinking. However, observations show that the height lowers. Presumably the discrepancy is due to the lack of dissipation in the model.

Abstract: Herein, an isothermal padlock probe-based assay for the simple and portable detection of pathogens coupled with a glucose oxidase (GOx)-based electrochemical readout is reported. Infectious diseases remain a constant threat on a global scale, as in recurring pandemics. Rapid and portable diagnostics hold the promise to tackle the spreading of diseases and decentralising healthcare to point-of-care needs. Ebola, a hypervariable RNA virus causing fatalities of up to 90% for recent outbreaks in Africa, demands immediate attention for bedside diagnostics. The design of the demonstrated assay consists of a rolling circle amplification (RCA) technique, responsible for the generation of nucleic acid amplicons as RCA products (RCPs). The RCPs are generated on magnetic beads (MB) and subsequently, connected via streptavidin-biotin bonds to GOx. The enzymatic catalysis of glucose by the bound GOx allows for an indirect electrochemical measurement of the DNA target. The RCPs generated on the surface of the MB were confirmed by scanning electron microscopy, and among other experimental conditions such as the type of buffer, temperature, concentration of GOx, sampling and measurement time were evaluated for the optimum electrochemical detection. Accordingly, 125 μg mL−1 of GOx with 5 mM glucose using phosphate buffer saline (PBS), monitored for 1 min were selected as the ideal conditions. Finally, we assessed the analytical performance of the biosensing strategy by using clinical samples of Ebola virus from patients. Overall, this work provides a proof-of-concept bioassay for simple and portable molecular diagnostics of emerging pathogens using electrochemical detection, especially in resource-limited settings.

Abstract: Nutrient losses in our food chain severely surpass our planetary boundaries. Resource recovery can contribute to mitigation, for instance through converting wastewater resources to microbial protein for animal feed. Wastewater typically holds a complex mixture of organics, posing a challenge to selectively produce heterotrophic biomass. Ensuring the product's quality could be achieved by anaerobic generation of volatile fatty acids (VFAs) followed by photoheterotrophic production of purple non-sulfur bacteria (PNSB) with infrared light. This study aimed to determine the most suitable PNSB culture for VFA conversion and map the effect of acetate, propionate, butyrate and a VFA mixture on growth and biomass yield. Six cultures were screened in batch: (i) Rhodopseudomonas palustris, (ii) Rhodobacter sphaeroides, (iii) Rhodospirillum rubrum, (iv) a 3-species synthetic community (i+ii+iii), (v) a community enriched on VFA holding Rb. capsulatus, and (vi) Rb. capsulatus (isolate v). The VFA mixture elevated growth rates with a factor 1.32.5 compared to individual VFA. Rb. capsulatus showed the highest growth rates: 1.82.2 d−1 (enriched) and 2.33.8 d−1 (isolated). In a photobioreactor (PBR) inoculated with the Rb. capsulatus enrichment, decreasing sludge retention time (SRT) yielded lower biomass concentrations, yet increased productivities, reaching 1.7 g dry weight (DW) L−1 d−1, the highest phototrophic rate reported thus far, and a growth rate of up to 5 d−1. PNSB represented 2657% of the community and the diversity index was low (37), with a dominance of Rhodopseudomonas at long SRT and Rhodobacter at short SRT. The biomass yield for all cultures, in batch and reactor cultivation, approached 1 g CODBiomass g−1 CODRemoved. An economic estimation for a two-stage approach on brewery wastewater (load 2427 kg COD d−1) showed that 0.5 d SRT allowed for the lowest production cost ( 10 kg−1 DW; equal shares for capex and opex). The findings strengthen the potential for a novel two-stage approach for resource recovery from industrial wastewater, enabling high-rate PNSB production.

Abstract: Extended producer responsibility (EPR) schemes have effectively increased the plastic waste that is separately collected. However, due to the structure of the recycling industry, EPR cannot increase recycling rates up to the target levels.Additional policy instruments to increase recycling rates such as recycled content targets, green dot fees bonus for recycled content, recycling targets and taxes on non-recycled plastic packaging have been discussed on a political level in the last years. However, very little research has quantitatively studied the effectiveness of these policy interventions.Using a partial equilibrium model, this paper examines the effectiveness of the implementation of the aforementioned policy instruments to increase recycling rates and the impact on different stakeholders of the value chain: plastic producers, consumers, producer responsibility organization and recyclers.Results show that direct interventions (recycled content standards and recycling targets) have the benefit of decoupling the recycling industry from external markets such as the oil market. They can be a good starting point to increase recycling, but in the long term they may be restricting by not presenting incentives to achieve recycling levels beyond the targeted amounts and by limiting technological innovation. On the contrary, eco-nomic interventions such as a green dot fee bonus or a packaging tax create economic incentives for recycling. However, these incentives are diminished by the lower perceived quality of packaging with higher recycled content levels.

Abstract: The evaluation of nucleation rates from molecular dynamics trajectories is hampered by the slow nucleation time scale and impact of finite size effects. Here, we show that accurate nucleation rates can be obtained in a very general fashion relying only on the free energy barrier, transition state theory, and a simple dynamical correction for diffusive recrossing. In this setup, the time scale problem is overcome by using enhanced sampling methods, in casu metadynamics, whereas the impact of finite size effects can be naturally circumvented by reconstructing the free energy surface from an appropriate ensemble. Approximations from classical nucleation theory are avoided. We demonstrate the accuracy of the approach by calculating macroscopic rates of droplet nucleation from argon vapor, spanning 16 orders of magnitude and in excellent agreement with literature results, all from simulations of very small (512 atom) systems.

Abstract: Nitrification and denitrification, the key biological processes for thermophilic nitrogen removal, have separately been established in bioreactors at 50 °C. A well-characterized set of kinetic parameters is essential to integrate these processes while safeguarding the autotrophs performing nitrification. Knowledge on thermophilic nitrifying kinetics is restricted to isolated or highly enriched batch cultures, which do not represent bioreactor conditions. This study characterized the stoichiometry and kinetics of two thermophilic (50 °C) nitrifying communities. The most abundant ammonia oxidizing archaea (AOA) were related to the Nitrososphaera genus, clustering relatively far from known species Nitrososphaera gargensis (95.5% 16S rRNA gene sequence identity). The most abundant nitrite oxidizing bacteria (NOB) were related to Nitrospira calida (97% 16S rRNA gene sequence identity). The nitrification biomass yield was 0.200.24 g VSS g−1 N, resulting mainly from a high AOA yield (0.160.20 g VSS g−1 N), which was reflected in a high AOA abundance in the community (5776%) compared to NOB (511%). Batch-wise determination of decay rates (AOA: 0.230.29 d−1; NOB: 0.320.43 d−1) rendered an overestimation compared to in situ estimations of overall decay rate (0.0260.078 d−1). Possibly, the inactivation rate rather than the actual decay rate was determined in batch experiments. Maximum growth rates of AOA and NOB were 0.120.15 d−1 and 0.130.33 d−1 respectively. NOB were susceptible to nitrite, opening up opportunities for shortcut nitrogen removal. However, NOB had a similar growth rate and oxygen affinity (0.150.55 mg O2 L−1) as AOA and were resilient towards free ammonia (IC50 > 16 mg NH3-N L−1). This might complicate NOB outselection using common practices to establish shortcut nitrogen removal (SRT control; aeration control; free ammonia shocks). Overall, the obtained insights can assist in integrating thermophilic conversions and facilitate single-sludge nitrification/denitrification.

Abstract: We calculate bubble nucleation rates in a Lennard-Jones fluid through explicit molecular dynamics simulations. Our approach-based on a recent free energy method (dubbed reweighted Jarzynski sampling), transition state theory, and a simple recrossing correction-allows us to probe a fairly wide range of rates in several superheated and cavitation regimes in a consistent manner. Rate predictions from this approach bridge disparate independent literature studies on the same model system. As such, we find that rate predictions based on classical nucleation theory, direct brute force molecular dynamics simulations, and seeding are consistent with our approach and one another. Published rates derived from forward flux sampling simulations are, however, found to be outliers. This study serves two purposes: First, we validate the reliability of common modeling techniques and extrapolation approaches on a paradigmatic problem in materials science and chemical physics. Second, we further test our highly generic recipe for rate calculations, and establish its applicability to nucleation processes.

Abstract: Stimulated anaerobic dechlorination is generally considered a valuable step for the remediation of aquifers polluted with chlorinated ethenes (CEs). Correct simulation and prediction of this process in situ, however, require good knowledge of the associated biological reactions. The aim of this study was to evaluate the dechlorination reaction in an aquifer contaminated with trichloroethene (TCE) and its daughter products, discharging into the Zenne River. Different carbon sources were used in batch cultures and these were related to the dechlorination reaction, together with the monitored biomarkers. Appropriate kinetic formulations were assessed. Reductive dechlorination of TCE took place only when external carbon sources were added to microcosms, and occurred concomitant with a pronounced increase in the Dehalococcoides mccartyi cell count as determined by 16S rRNA gene-targeted qPCR. This indicates that native dechlorinating bacteria are present in the aquifer of the Zenne site and that the oligotrophic nature of the aquifer prevents a complete degradation to ethene. The type of carbon source, the cell number of D. mccartyi or the reductive dehalogenase genes, however, did not unequivocally explain the observed differences in degradation rates or the extent of dechlorination. Neither first-order, Michaelis-Menten nor Monod kinetics could perfectly simulate the dechlorination reactions in TCE spiked microcosms. A sensitivity analysis indicated that the inclusion of donor limitation would not significantly enhance the simulations without a clear process understanding. Results point to the role of the supporting microbial community but it remains to be verified how the complexity of the microbial (inter)actions should be represented in a model framework. (C) 2013 Elsevier B.V. All rights reserved.

Abstract: Daily and seasonal variation in the total elemental, organic carbon (OC) and elemental carbon (EC) content and mass of PM2.5 were studied at industrial, urban, suburban and agricultural/rural areas. Continuous (optical Dustscan, standard tapered element oscillating micro-balance (TEOM), TEOM with filter dynamics measurement system), semi-continuous (Partisol filter-sampling) and non-continuous (Dekati-impactor sampling and gravimetry) methods of PM2.5 mass monitoring were critically evaluated. The average elemental fraction accounted for 26% of the PM2.5 mass measured by gravimetry. Metals, like K, Mn, Fe, Cu, Zn and Pb were strongly inter-correlated, also frequently with non-metallic elements (P, S, Cl and/or Br) and EC/OC. A high OC/EC ratio (29) was generally observed. The total carbon content of PM2.5 ranged between 3 and 77% (averages: 1232%), peaking near industrial/heavy trafficked sites. Principal component analysis identified heavy oil burning, ferrous/non-ferrous industry and vehicular emissions as the main sources of metal pollution. This work compares various aerosol monitoring methods to characterize PM2.5 over six locations of different anthropogenic activities over Northern Belgium.