Divergent Temporal Trends of Mercury in Arctic Char from Paired Lakes Influenced by Climate‐related Drivers

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Abstract

Climate-driven changes including rising air temperatures, enhanced permafrost degradation, and altered precipitation patterns can have profound effects on contaminants, such as mercury (Hg), in High Arctic lakes. Two physically similar lakes, East Lake and West Lake at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut, Canada are being affected by climate change differently. Both lakes have experienced permafrost degradation in their catchments; however, West Lake has also undergone multiple underwater Mass Movement Events (MME; beginning in fall 2008), leading to a sustained 50-fold increase in turbidity. This provided the unique opportunity to understand the potential impacts of permafrost degradation and other climate-related effects on Hg concentrations and body condition of landlocked Arctic char (Salvelinus alpinus), an important sentinel species across the Circum-Arctic. The objectives of this work were to assess temporal trends in char Hg concentrations and to determine potential mechanisms driving the trends. There was a significant decrease in Hg concentrations in East Lake char averaging 6.5 %/y and 3.8 %/y for length-adjusted and age- adjusted means, respectively, from 2008 to 2019. Conversely, in West Lake there was a significant increase, averaging 7.9 %/y and 8.0 %/y for length-adjusted and age-adjusted mean Hg concentrations, respectively, for 2009 to 2017 (last year with sufficient sample size). The best predictors of length-adjusted Hg concentrations in West Lake were carbon and nitrogen stable isotope ratios, indicating a shift in diet including possible dietary starvation brought on by the profound increase in lake turbidity. This work provides an example of how increasing lake turbidity, a likely consequence of climate warming in Arctic lakes, may influence fish condition and Hg concentrations.

Oxidative Stress Contributes to Flumioxazin‐Induced Cardiotoxicity in Zebrafish Embryos

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ABSTRACT

Flumioxazin is a widely applicated herbicide in the control of aquatic plants. Current evidence suggested that flumioxazin could induce cardiac defects (ventricular septal defects) in vertebrates, but the underlining mechanisms remain unclear. Because of the inhibitory effect of flumioxazin on polyphenol oxidase (PPO), the assumption is made that flumioxazin-induced cardiotoxicity is caused by oxidative stress. The results show that flumioxazin induced cardiac malformations and abnormal gene expression associated with cardiac development. Cardiac malformations include pericardium edema, cardiac linearization, elongated heart, cardiomegaly, cardiac wall hypocellularity, myocardial cell atrophy into granular, and a significant gap between the myocardial intima and the adventitia. An increase in oxidative stress and apoptosis was observed in the cardiac region of zebrafish after exposure to flumioxazin. Antioxidant astaxanthin reversed the cardiac malformations, excessive ROS production and expression of genes for cardiac developmental and apoptosis regulation induced by flumioxazin. In addition, flumioxazin also activated AHR signaling pathway genes (ahr2, cyp1a1, and cyp1b1) and increased porphyrins concentration. In conclusion, the results suggest that excessive ROS production, which could be mediated through AHR, led to apoptosis, contributing to the cardiotoxicity of flumioxazin in zebrafish embryos.

INCREASED ENDOCRINE ACTIVITY OF XENOBIOTIC CHEMICALS AS MEDIATED BY METABOLIC ACTIVATION

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ABSTRACT

The US EPA is faced with long lists of chemicals that require hazard assessment. This research is part of a larger effort to develop in vitro assays and QSARs applicable to untested chemicals on US EPA inventories through study of estrogen receptor (ER) binding and estrogen mediated gene expression in fish. The current effort investigates metabolic activation of chemicals resulting in increased estrogenicity. Phenolphthalin (PLIN) was shown not to bind rainbow trout (Oncorhynchus mykiss) ER (rtER) in a competitive binding assay but vitellogenin (Vtg) expression was induced in trout liver slices exposed to 10-4 and 10-3.7 M PLIN. Phenolphthalein (PLEIN), metabolite of PLIN, was subsequently determined to be formed when slices were exposed to PLIN. PLEIN binds rtER with a relative binding affinity (RBA) to 17β-estradiol of 0.020%. Slices exposed to PLEIN expressed Vtg mRNA at 10-4.3, 10-4, and 10-3.7 M, with no detectable PLIN present. Thus, Vtg expression noted in PLIN slice exposures was explained by metabolism to PLEIN in trout liver slices. A second model chemical, 4,4’-methylenedianiline (MDA) was not shown to bind rtER but did induce Vtg mRNA production in tissue slices at 10-4.3, 10-4, and 10-3.7 M in amounts nearly equal to reference estradiol induction, thus indicating metabolic activation of MDA. A series of experiments were performed to identify a potential metabolite responsible for the observed increase in activity. Potential metabolites hydroxylamine-MDA, nitroso-MDA, azo-MDA, or azoxy-MDA were not observed. However, acetylated-MDA was observed and tested in both ER-binding and tissue slice Vtg induction assays.

Research Priorities for the Environmental Risk Assessment of Per‐ and Polyfluorinated Substances

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Abstract

Per- and polyfluorinated substances (PFAS) are a group of thousands of ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases toward specific compounds, environmental compartments, and organisms. The aim of our study was therefore to highlight current developments and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases and found that knowledge of the environmental fate of PFAS is based on the analysis of <1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter remain largely understudied. The bioavailability, bioaccumulation, and food web transfer studies of PFAS also focus on a very limited number of compounds and are biased toward aquatic biota, predominantly fish, and less frequently aquatic invertebrates and macrophytes. The available ecotoxicity data revealed that only a few PFAS have been well studied for their environmental hazards, and that PFAS ecotoxicity data are also strongly biased toward aquatic organisms. Ecotoxicity studies in the terrestrial environment are needed, as well as chronic, multigenerational, and community ecotoxicity research, in light of the persistency and bioaccumulation of PFAS. Finally, we identified an urgent need to unravel the relationships among sorption, bioaccumulation, and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to allow predictions of exposure, bioaccumulation, and toxicity. Environ Toxicol Chem 2023;00:1–15. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Trace Elements and Consequent Ecological Risks in Mining‐Influenced Streams of Appalachia

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Abstract

Appalachian (eastern USA) coal surface mines fracture geologic materials, causing release of both major ions and trace elements to water via accelerated weathering. When elevated above natural background, trace elements in streams may produce adverse effects on biota via direct exposure from water and sediment and via dietary exposure in food sources. Other studies have found elevated water concentrations of multiple trace elements in Appalachia's mining-influenced streams. Except for Se, trace-element concentrations in abiotic and biotic media of Appalachian mining-influenced streams are less well known. We analyzed environmental media of headwater streams receiving alkaline waters from Appalachian coal mines for eight trace elements (Al, As, Cd, Cu, Ni, Sr, V, and Zn) and assessed the potential consequent ecological risks. Streamwater, particulate media (sediment, biofilm, leaf detritus), and benthic macroinvertebrates (primary consumers, secondary consumers, crayfish) were sampled from six mining-influenced and three reference streams during low-flow conditions in two seasons. Dissolved Cu, Ni, and Sr were higher in mining-influenced streams than in reference streams; Ni, Sr, and Zn in fine sediments and Ni in macroinvertebrates were also elevated relative to reference-stream levels in samples from mining-influenced streams. Seasonal ratios of mining-influenced stream concentrations to maximum concentrations in reference streams also demonstrated mining-influenced increases for several elements in multiple media. In most media, concentrations of several elements including Ni were correlated positively. All water-column dissolved concentrations were below protective levels, but fine-sediment concentrations of Ni approached or exceeded threshold-effect concentrations in several streams. Further study is warranted for several elements (Cd, Ni, and Zn in biofilms, and V in macroinvertebrates) that approached or exceeded previously established dietary-risk levels. Environ Toxicol Chem 2023;00:1–15. © 2023 SETAC.

Meta‐Analysis Comparing Nominal and Measured Concentrations of Perfluorooctanoic Acid and Perfluorooctane Sulfonate in Aquatic Toxicity Studies Across Various Experimental Conditions

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Abstract

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are among the most frequently detected chemicals among the per- and polyfluoroalkyl substances in aquatic environments. Because of their high detection frequency, persistence, and potential toxicity, interest in both PFOA and PFOS has increased in recent years. However, a substantial number of PFOA and PFOS toxicity tests only report nominal, or unmeasured, treatment concentrations, which may complicate the determination of protective values. In addition, previous literature has indicated that differences between nominal and measured concentrations of both PFOA and PFOS could be linked to experimental conditions (e.g., feeding regimes for test organisms, test vessel material [glass or plastic], use of solvent, and the presence of substrate). Therefore, this critical review examined whether nominal and measured concentrations were in close agreement with each other among the current PFOA and PFOS aquatic toxicity literature and if experimental conditions were associated with any observed differences. Nominal and measured concentrations in the current PFOA and PFOS aquatic toxicity literature generally displayed a high degree of linear correlation and relatively low median percent differences. Correlations between measured and nominal concentrations were >0.98 for PFOA and >0.95 for PFOS in freshwater tests across experimental conditions. For saltwater tests, correlations of >0.84 were observed for PFOA and PFOS (separate and combined) across experimental conditions. While measured PFOA and PFOS toxicity tests are generally preferred, the present meta-analysis demonstrated that experimental conditions had little influence on observed discrepancies between nominal and measured concentrations, with the exception of PFOS saltwater tests and PFOA and PFOS freshwater studies that contained substrate. Unmeasured tests with these conditions should be considered carefully based on project needs, with the caveat that the data sets for these two experimental conditions were limited. Environ Toxicol Chem 2023;00:1–13. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Immunological Exploration of Helicobacter pylori Serotype O2 O‐antigen by Using A Synthetic Glycan Library

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Comprehensive Summary

Helicobacter pylori (H. pylori) infection is a threat to human health. The lipopolysaccharide (LPS) O-antigen holds promise for developing vaccines. It is meaningful to explore the immunological activity of oligosaccharides with different lengths and frameshifts for antigen development. Herein, a glycan library of H. pylori O2 O-antigen containing eight fragments is constructed. After screening with anti-H. pylori O2 LPS sera and patients’ sera by glycan microarray, the disaccharide HPO2G-2b and trisaccharide HPO2G-3a show strong antigenicity and then are separately conjugated with carrier protein CRM197. Both glycoconjugates elicit a robust immunoglobulin G (IgG) immune response in rabbits. The anti-HPO2G-3a IgG antibodies possess a much stronger binding affinity with the LPS and bacteria of H. pylori O2 than the anti-HPO2G-2b IgG antibodies. There is no cross-reaction between both sera IgG antibodies with LPS and bacteria of H. pylori O1, O6, and E. coli. The results demonstrate the trisaccharide HPO2G-3a is a promising candidate for H. pylori vaccine development.

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Fluorine Substitution of TCNQ Alters the Redox‐Driven Catalytic Pathway for the Ferricyanide‐Thiosulfate Reaction

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Fluorine Substitution of TCNQ Alters the Redox-Driven Catalytic Pathway for the Ferricyanide-Thiosulfate Reaction

Fluorination of TCNQ tunes the redox potential and can alter catalytic mechanisms. Accordingly, TCNQF4 1− and TCNQF2 1− can act as catalysts for the ferrocyanide-thiosulfate reaction via the same mechanism, which differs from that found for TCNQ. CuTCNQFn (n=0, 4) coordination polymers have sufficient solubility in water to act as catalysts via homogeneous pathways. This study challenges perceptions of insolubility being correlated with heterogeneous pathways.


Abstract

Mechanistic variation in catalysis through substituent-based redox tuning is well established. Fluorination of TCNQ (TCNQ=tetracyanoquinodimethane) provides ~850 mV variation in the redox potentials of the and (n=0, 2, 4) processes. With , catalysis of the kinetically very slow ferrocyanide-thiosulfate redox reaction in aqueous solution occurs via a mechanism in which the catalyst is reduced to when reacting with which is oxidised to . Subsequently, reacts with to form and reform the catalyst, in another thermodynamically favoured process. An analogous mechanism applies with as a catalyst. In contrast, since the reaction of with is thermodynamically unfavourable, an alternative mechanism is required to explain the catalytic activity observed in this non-fluorinated system. Here, upon addition of , reduction of to occurs with concomitant oxidation of to , which then acts as the catalyst for oxidation. Thermodynamic data explain the observed differences in the catalytic mechanisms. (n=0, 4) also act as catalysts for the ferricyanide-thiosulfate reaction in aqueous solution. The present study shows that homogeneous pathways are available following addition of these dissolved materials. Previously, these (n=0, 4) coordination polymers have been regarded as insoluble in water and proposed as heterogeneous catalysts for the ferricyanide-thiosulfate reaction. Details and mechanistic differences were established using UV-visible spectrophotometry and cyclic voltammetry.

Impact of Top Electrodes (Cu, Ag, and Al) on Resistive Switching behaviour of Cu‐rich Cu2ZnSnS4 (CZTS) Ideal Kesterite

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Impact of Top Electrodes (Cu, Ag, and Al) on Resistive Switching behaviour of Cu-rich Cu2ZnSnS4 (CZTS) Ideal Kesterite

The resistive switching behaviour of Cu2ZnSnS4 material on ITO substrate with three different top electrodes (Cu, Ag, and Al) and work function is demonstrated. The Ag top electrode-based resistive random-access memory device shows more stable resistive switching than the ones with Cu and Al top electrode.


Abstract

Cu2ZnSnS4 (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO/Glass is investigated up to 102 cycles. The stability of all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 103 sec in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 102 cycles with 30 msec switching width shows stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu+ in CZTS plays a decisive role in resistive switching with Al electrode. Further, the impedance spectroscopy measurements suggest that Cu+ and Ag+ diffusion is the main source for the resistive switching with Cu and Ag electrodes.

Identification of in situ generated iron‐vacancy induced oxygen evolution reaction kinetics on cobalt iron oxyhydroxide

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Comprehensive Summary

Developing highly efficient and low-cost electrocatalysts towards oxygen evolution reaction (OER) is essential for the practical application in water electrolyzers and rechargeable metal-air batteries. Although Fe-based oxyhydroxides are regarded as the state-of-the-art non-noble OER electrocatalysts, the origin of performance enhancement derived from Fe doping still remains a hot topic of considerable discussion. Herein, we demonstrate that in situ generated Fe vacancies in the pristine CoFeOOH catalyst through a pre-conversion process during alkaline OER results from dynamic Fe dissolution, identifying the origin of Fe-vacancy-induced enhanced OER kinetics. Density functional theory (DFT) calculations and experimental results including X-ray absorption fine-structure spectroscopy, in situ UV-Vis spectroscopy, and in situ Raman spectroscopy reveal that the Fe vacancies could significantly promote the d-band center and valence states of adjacent Co sites, alter the active site from Fe atom to Co atom, accelerate the formation of high-valent active Co4+ species, and reduce the energy barrier of the potential-determining step, thereby contribute to the significantly enhanced OER performance.

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