Soil aeration - The relationship between redox potential and air-filled pores

Soil water contents are variable with impact on oxygen diffusion rates and redox potentials (EH). When water saturated soils become aerated, a switch from reducing to oxidizing conditions occurs. However, only limited information are available at which air-filled pore volume (ε) this dramatic shift happens. Therefore, undisturbed soil cores were taken by steel cylinders from the topsoils of a Fluvisol and a Gleysol that differed in soil structure and clay content. After submergence in the laboratory, the samples were sealed by a glass dome to exclude oxygen and to achieve strongly reducing conditions (EH < -100 mV). We aerated the sample on demand by removal of glass plugs in the dome and consecutively measured EH by platinum-(Pt) tipped electrodes and ε by pressure head readings on hourly basis. We propose to use the terms: i) εPt reaction, to indicate the air-filled pore volume at which a response of the Pt-tipped electrode due to contact with oxygen occurs (i.e., EH increase > 5 mV h-1), and ii) εPt aeration, to indicate when oxidizing soil conditions are present (i.e., EH > 300 mV at pH 7). These characteristic εPt reaction values were at 0.036±0.013 cm3 cm–3 for the Fluvisol and at 0.048±0.017 cm3 cm–3 for the Gleysol whereas εPt aeration values were at 0.047±0.005 and at 0.085±0.002 cm3 cm–3, respectively. This study provided important information to determine the aeration status of a soil when, e.g., ε is known but EH measurements are absent

Wer bremst verliert - Antimon in Straßenrandböden

Seit dem weitreichenden Verbot von Asbest in den 1980er Jahren wurde verstärkt das Halbmetall Antimon (Sb) in Bremsbelägen von PKW und LKW verwendet. Im Zuge des Bremsvorganges wird dieses in Form von Feinstaub freigesetzt und straßennah in die Böden eingetragen. Grundsätzlich sind Antimoneinträge in Böden negativ zu bewerten, da das Halbmetall toxische Wirkungen hervorrufen kann. Um die räumliche Verteilung von Antimon und seinen Bindungsformen in Straßenrandböden zu untersuchen, wurden 5 parallele Transekte mit jeweils 7 Entfernungen und 4 Probentiefen entlang einer Kölner Kreisstraße (Verkehrsaufkommen ca. 9.600 Fahrzeuge pro Tag) beprobt. Neben einer allgemeinen physikochemischen Charakterisierung der Bodenproben wurden ihre königswasser-löslichen Antimongehalte bestimmt. Zusätzlich wurde an einem Transekt eine sequentielle Extraktion nach Wenzel et al. 2001 durchgeführt, um die Bindungsformen von Antimon zu ermitteln. Die Antimongehalte nahmen von bis zu 6,18 g kg–1 unmittelbar am Straßenrand bis auf 0,513 g kg–1 in 10 m Entfernung ab. Ebenfalls konnte eine deutliche Abnahme mit der Bodentiefe (0 bis 30 cm) festgestellt werden. Dieses Verteilungsmuster deutet auf den Verkehr als Antimoneintragsquelle hin. Als Hinweis auf einen durch den Bremsabrieb metallener Bremsscheiben dominierten Eintrag wurde die magnetische Suszeptibilität gemessen. Allerdings lieferte der Korrelationskoeffizient (Spearman) von Antimon gegenüber der magnetischen Suszeptibilität 0,423 (p = 0,023) nur einen eher schwachen Beleg. Die ursprünglich für Arsen entwickelte sequentielle Extraktion ließ sich reproduzierbar ebenfalls für Antimon anwenden. Anhand dieser konnten im Wesentlichen drei Trends der Bindungsformen erfasst werden: i) spezifisch gebundenes Antimon (Fraktion 2: 0,05 mol l–1 (NH4)H2P2O4) konnte lediglich innerhalb 1 m Entfernung zur Straße und mit der Bodentiefen abnehmenden Gehalten nachgewiesen werden, ii) der Anteil an schwachkristallinen Eisenoxiden gebundenem Antimon (Fraktion 3: 0,2 mol l–1 (NH4)2-Oxalatpuffer; pH 3,25) nahm signifikant mit steigender Entfernung zur Straße ab, während iii) die prozentualen Gehalte in den starkkristallinen Eisenoxiden (Fraktion 4: 0,2 mol l–1 (NH4)2-Oxalatpuffer + 0,1 mol l–1 Ascorbinsäure; pH 3,25) und in der Residualphase (Fraktion 5: Königswasser) zunahmen

Organische Überzüge auf Eisenoxiden und Chloriten

Die Adsorption von organischer Substanz an Bodenminerale kann die Eigenschaften der Mineraloberfläche und damit deren Reaktivität vollständig verändern. In welchem Ausmaß Mineraloberflächen im Boden mit organischer Substanz bedeckt sind und woraus diese neuen organischen Oberflächen zusammengesetzt sind ist Gegenstand unserer Untersuchungen. Das Vorhandensein und die Zusammensetzung organischer Überzüge auf Fe-Oxiden (und falls vorhanden Tonmineralen) wurde mit Rasterkraftmikroskopie (AFM) und räumlich aufgelöster Röntgenabsorptionsspektroskopie (STXM mit NEXAFS an der C K-Kante und der Fe L-Kante) analysiert. Die untersuchten Fe-Oxide stammten aus drei Systemen mit unterschiedlichem organischem Ausgangsmaterial: (1) synthetische Goethite, die mit Biofilmen in Kontakt gebracht wurden, (2) natürliche Fe-Oxide, die in einem Quellaustritt, vermutlich unter starker mikrobieller Beteiligung, ausgefällt wurden und (3) Goethit-dominierte natürliche Fe-Oxide aus dem Go-Horizont eines Brauneisengleys. Unsere Auswertung ist noch nicht abgeschlossen. Erste Ergebnisse zeigen, dass das mit den Fe-Oxiden assoziierte organische Material aus den drei Milieus sehr unterschiedlich zusammengesetzt ist: Überzüge auf den Oxiden aus Biofilmen werden von Proteinen und Alkyl C dominiert. Die Überzüge auf den Fe-Oxiden aus der Quelle sind im Vergleich dazu wesentlich reicher an Aryl C und O-Alkyl C, jedoch ärmer an Alkyl C. Die Überzüge der Fe-Oxide aus dem Brauneisengley sind dagegen reich an Alkyl C und Carbonyl C. Im Brauneisengley sind zusätzlich zu den Fe-Oxiden auch Chlorite vorhanden. Auf diesen ist das NEXAFS-C-Signal wesentlich schwächer als auf den Oxiden. Gleichzeitig detektiert das AFM auf den Chloriten eine deutlich höhere Adhäsion zwischen Spitze und Mineral als auf den Fe-Oxiden. Wir nehmen daher an, dass die Chlorite weniger organisches Material binden als die Fe-Oxide. In den kommenden Monaten werden wir uns der räumlichen Homogenität bzw. Heterogenität der Überzüge widmen und die räumliche Verteilung von C, N, P und S in den Überzügen per NanoSIMS beschreiben

Passive Sampling to Scale Wastewater Surveillance of Infectious Disease: Lessons Learned From COVID-19

Much of what is known and theorized concerning passive sampling techniques has been developed considering chemical analytes. Yet, historically, biological analytes, such as Salmonella typhi, have been collected from wastewater via passive sampling with Moore swabs. In response to the COVID-19 pandemic, passive sampling is re-emerging as a promising technique to monitor SARS-CoV-2 RNA in wastewater. Method comparisons and disease surveillance using composite, grab, and passive sampling for SARS-CoV-2 RNA detection have found passive sampling with a variety of materials routinely produced qualitative results superior to grab samples and useful for sub-sewershed surveillance of COVID-19. Among individual studies, SARS-CoV-2 RNA concentrations derived from passive samplers demonstrated heterogeneous correlation with concentrations from paired composite samples ranging from weak (R2 = 0.27, 0.31) to moderate (R2 = 0.59) to strong (R2 = 0.76). Among passive sampler materials, electronegative membranes have shown great promise with linear uptake of SARS-CoV-2 RNA observed for exposure durations of 24 to 48 h and in several cases RNA positivity on par with composite samples. Continuing development of passive sampling methods for the surveillance of infectious diseases via diverse forms of fecal waste should focus on optimizing sampler materials for the efficient uptake and recovery of biological analytes, kit-free extraction, and resourceefficient testing methods capable of rapidly producing qualitative or quantitative data. With such refinements passive sampling could prove to be a fundamental tool for scaling wastewater surveillance of infectious disease, especially among the 1.8 billion persons living in low-resource settings served by non-traditional wastewater collection infrastructure

Maize Field Study Reveals Covaried Microbiota and Metabolic Changes in Roots over Plant Growth

Plant roots are colonized by microorganisms from the surrounding soil that belong to different kingdoms and form a multikingdom microbial community called the root microbiota. Despite their importance for plant growth, the relationship between soil management, the root microbiota, and plant performance remains unknown. Here, we characterize the maize root-associated bacterial, fungal, and oomycetal communities during the vegetative and reproductive growth stages of four maize inbred lines and the pht1;6 phosphate transporter mutant. These plants were grown in two long-term experimental fields under four contrasting soil managements, including phosphate-deficient and -sufficient conditions. We showed that the maize root-associated microbiota is influenced by soil management and changes during host growth stages. We identified stable bacterial and fungal root-associated taxa that persist throughout the host life cycle. These taxa were accompanied by dynamic members that covary with changes in root metabolites. We observed an inverse stable-to-dynamic ratio between root-associated bacterial and fungal communities. We also found a host footprint on the soil biota, characterized by a convergence between soil, rhizosphere, and root bacterial communities during reproductive maize growth. Our study reveals the spatiotemporal dynamics of the maize root-associated microbiota and suggests that the fungal assemblage is less responsive to changes in root metabolites than the bacterial community

Standardizing data reporting in the research community to enhance the utility of open data for SARS-CoV-2 wastewater surveillance

SARS-CoV-2 RNA detection in wastewater is being rapidly developed and adopted as a public health monitoring tool worldwide. With wastewater surveillance programs being implemented across many different scales and by many different stakeholders, it is critical that data collected and shared are accompanied by an appropriate minimal amount of meta-information to enable meaningful interpretation and use of this new information source and intercomparison across datasets. While some databases are being developed for specific surveillance programs locally, regionally, nationally, and internationally, common globally-adopted data standards have not yet been established within the research community. Establishing such standards will require national and international consensus on what meta-information should accompany SARS-CoV-2 wastewater measurements. To establish a recommendation on minimum information to accompany reporting of SARS-CoV-2 occurrence in wastewater for the research community, the United States National Science Foundation (NSF) Research Coordination Network on Wastewater Surveillance for SARS-CoV-2 hosted a workshop in February 2021 with participants from academia, government agencies, private companies, wastewater utilities, public health laboratories, and research institutes. This report presents the primary two outcomes of the workshop: (i) a recommendation on the set of minimum meta-information that is needed to confidently interpret wastewater SARS-CoV-2 data, and (ii) insights from workshop discussions on how to improve standardization of data reporting

Wastewater surveillance for bacterial targets: current challenges and future goals

Wastewater-based epidemiology (WBE) expanded rapidly in response to the COVID-19 pandemic. As the public health emergency has ended, researchers and practitioners are looking to shift the focus of existing wastewater surveillance programs to other targets, including bacteria. Bacterial targets may pose some unique challenges for WBE applications. To explore the current state of the field, the National Science Foundation-funded Research Coordination Network (RCN) on Wastewater Based Epidemiology for SARS-CoV-2 and Emerging Public Health Threats held a workshop in April 2023 to discuss the challenges and needs for wastewater bacterial surveillance. The targets and methods used in existing programs were diverse, with twelve differentdifferentdifferenttargets and nine different methods listed. Discussions during the workshop highlighted the challenges in adapting existing programs and identified research gaps in four key areas: choosing new targets, relating bacterial wastewater data to human disease incidence and prevalence, developing methods, and normalizing results. To help with these challenges and research gaps, the authors identified steps the larger community can take to improve bacteria wastewater surveillance. This includes developing data reporting standards and method optimization and validation for bacterial programs. Additionally, more work is needed to understand shedding patterns for potential bacterial targets to better relate wastewater data to human infections. Wastewater surveillance for bacteria can help provide insight into the underlying prevalence in communities, but much work is needed to establish these methods

Chromate adsorption from chromite ore processing residue eluates by three Indian soils

Chromite ore processing residue (COPR) is a harmful waste of the chromate (CrO42-) extraction roasting process. Nevertheless, deposition of COPR in uncontrolled surface landfills is still common practice in some countries. Leaching of carcinogenic CrO42- and contamination of groundwater is a key environmental risk arising from COPR sites. The objective of this study was to evaluate the adsorption behaviour of CrO42- from COPR eluates by soils. Prior to the adsorption experiments, batch studies at varying solid- to- liquid ratios were performed to evaluate the solubility of CrO42- from COPR. Chromate adsorption experiments were carried out in a batch system with eluates obtained from two different Indian COPRs to assess potential groundwater contamination by CrO42-. Three soils that originate from the surroundings of COPR dumping sites were chosen in order to provide realistic adsorption conditions. The data were evaluated with the Freundlich and Langmuir equation. Chromate adsorption was inhibited because of the high pH of both of the soils (pH 6.7 to 7.2) and the eluates (pH 12.3) as well as the high carbonate concentration of the eluates. The extent and behaviour of CrO42- adsorption from both eluates was similar. The main difference between the eluates was the solubility of CrO42- from COPR and thus the initial CrO42- concentration. The results presented in this study provide an improved understanding of the mobility of CrO42 in the affected area, which is important because the local population uses the groundwater not only for the needs of livestock but also as drinking water

Molybdate adsorption from steel slag eluates by subsoils

Steel slags are industrial by-products which are generated in large amounts worldwide, e.g. 150-230 x 106 Mg in 2012, and which are partly used for construction. Molybdenum (Mo) can be added during steel processing in order to harden the steel. The objective of this study was to evaluate the adsorption behaviour of molybdate (MoO2,-) from slag eluates in subsoils. Molybdate batch adsorption experiments were carried out with eluates obtained from two different kinds of steel slags (i) LD slag (Linz-Donawitz operation, LDS) and (ii) electric arc furnace slag (EAF) to assess the risk that may arise from the contamination of groundwater by the leaching of molybdate. Six different subsoils were chosen in order to provide a wide range of chemical properties (pH 4.0-7.6; dithionite-extractable Fe 0.7314.7 g Molybdate adsorption experiments were carried out at the pH of the steel slag eluates (pH 11-12) as well as at pH values adjusted to the soil pH. The data were evaluated with the Freundlich equation. Molybdate adsorption exhibited a maximum near pH 4 for steel slag eluates adjusted to the soil pH, and decreased rapidly with increasing pH until adsorption was virtually zero at pH > 11. Adsorption was greater for soils with high amounts of dithionite-extractable Fe oxides. The extent and behaviour of molybdate adsorption from both eluates was similar. After a reaction time of 24 h, the pH of the EAF slag eluate was lower than that of the LD steel slag eluate, which was caused by different acid buffer capacities. Some soils were able to decrease the pH of the EAF slag eluates by about 4 pH units, enhancing the adsorption of molybdate. Transport simulations indicated that molybdate discharge is low in acidic soils. (C) 2013 Elsevier Ltd. All rights reserved