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Povzetek: The COVID-19 pandemic has increased the use of disposable plastics, including medical masks, which have become a necessity in our daily lives. As these are often improperly disposed of, they represent an important potential source of microplastics in the environment. We prepared microplastics from polypropylene medical masks and characterised their size, shape, organic chemical leaching, and acute toxicity to the planktonic crustacean Daphnia magna. The three layers of the masks were separately milled and characterised. Each of the inner frontal, middle filtering, and outer layers yielded different types of microplastics: fibres were obtained from the inner and outer layer, but irregular fragments from the middle layer. The shape of the obtained microplastics differed from the initial fibrous structure of the intact medical mask layers, which indicates that the material is deformed during cryo-milling. The chemical compositions of plastics-associated chemicals also varied between the different layers. Typically, the inner layer contained more chemicals related to antimicrobial function and flavouring. The other two layers also contained antioxidants and their degradation products, plasticisers, cross-linking agents, antistatic agents, lubricants, and non-ionic surfactants. An acute study with D. magna showed that these microplastics do not cause immobility but do physically interact with the daphnids. Further long-term studies with these microplastics are needed using a suite of test organisms. Indeed, studies with other polypropylene microplastics have shown numerous adverse effects on other organisms at concentrations that have already been reported in the environment. Further efforts should be made to investigate the environmental hazards of polypropylene microplastics from medical masks and how to handle this new source of environmental burden.
Ključne besede: COVID-19 pandemic, plastics-associated chemicals, Daphnia magna, fibres, fragments, nanofibres, polypropylene microplastics, single-use plastic
Objavljeno v DiRROS: 05.05.2023; Ogledov: 344; Prenosov: 214
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Povzetek: The durability of Portland cement mortars is often affected by environmental factors, which can cause physicochemical and mechanical degradation processes. In this study, the performance of three products, calcium acetoacetate and calcium tetrahydrofurfuryloxide dissolved in two different solvents developed and tested as stone consolidants, was evaluated in terms of crack filling or sealing and consolidation. Realistic cracks were induced in quasibrittle cement mortar prisms using a custom-designed test rig. The effectiveness and the performance of the considered treatments, investigated on specimens, were evaluated by optical and scanning electron microscopy, colourimetry, water absorption rate, ultrasonic pulse velocity, and surface hardness measurements. Results revealed that, in the examined conditions, the products were more suitable as surface consolidants than as crack fillers.
Ključne besede: cement mortars, 20th century architecture conservation, calcium acetoacetate, calcium alkoxide, concrete repair, open access
Objavljeno v DiRROS: 04.05.2023; Ogledov: 360; Prenosov: 205
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Povzetek: Simple Summary: Irisin is a known myokine secreted mainly by the muscle that is produced after physical activity. It induces browning in the adipose tissue with a consequent increase in mitochondrial oxidation of lipids and reduction of insulin resistance; thus, it has been hypothesized that irisin was the molecule mediating most of the beneficial effects related to exercise on adipose tissue and consequently on the whole organism. In our study we observed that extreme physical inactivity induces the loss of muscle mass and function, and an increase in the body adipose tissue as expected. However, of note, circulating irisin levels were increased secondary to enhanced irisin synthesis mainly from adipose tissue rather than muscle. In addition, subjects who produced more irisin had reduced muscle impairment. Therefore, our hypothesis is that there is negative feedback within the muscle-adipose tissue crosstalk, specifically not only does the muscle influence the adipose tissue through irisin during exercise, but also the adipose tissue protects the muscle during inactivity.Abstract: The detrimental effect of physical inactivity on muscle characteristics are well known. Irisin, an exercise-induced myokine cleaved from membrane protein fibronectin type III domain-containing protein-5 (FNDC5), mediates at least partially the metabolic benefits of exercise. This study aimed to assess the interplay between prolonged inactivity, circulating irisin, muscle performance, muscle fibers characteristics, as well as the FNDC5 gene expression (FNDC5ge) in muscle and adipose tissue among healthy subjects. Twenty-three healthy volunteers were tested before and after 14 days of Bed Rest, (BR). Post-BR circulating levels of irisin significantly increased, whereas body composition, muscle performance, and muscle fiber characteristics deteriorated. Among the subjects achieving the highest post-BR increase of irisin, the lowest reduction in maximal voluntary contraction and specific force of Fiber Slow/1, the highest increase of FNDC5ge in adipose tissue, and no variation of FNDC5ge in skeletal muscle were recorded. Subjects who had the highest FNDC5ge in adipose tissue but not in muscle tissue showed the highest circulating irisin levels and could better withstand the harmful effect of BR.
Ključne besede: physical inactivity, bed rest, FNDC5 gene expression, myokines, sarcopenia, muscles fiber
Objavljeno v DiRROS: 07.07.2022; Ogledov: 732; Prenosov: 401
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Povzetek: Unloading induces rapid skeletal muscle atrophy and functional decline. Importantly, force is lost at a much higher rate than muscle mass. We aimed to investigate the early determinants of the disproportionate loss of force compared to that of muscle mass in response to unloading. Ten young participants underwent 10 days of bed rest (BR). At baseline (BR0) and at 10 days (BR10), quadriceps femoris (QF) volume (VOL) and isometric maximum voluntary contraction (MVC) were assessed. At BR0 and BR10 blood samples and biopsies of vastus lateralis (VL) muscle were collected. Neuromuscular junction (NMJ) stability and myofibre innervation status were assessed, together with single fibre mechanical properties and sarcoplasmic reticulum (SR) calcium handling. From BR0 to BR10, QFVOL and MVC decreased by 5.2% (P = 0.003) and 14.3% (P < 0.001), respectively. Initial and partial denervation was detected from increased neural cell adhesion molecule (NCAM)-positive myofibres at BR10 compared with BR0 (+3.4%, P = 0.016). NMJ instability was further inferred from increased C-terminal agrin fragment concentration in serum (+19.2% at BR10, P = 0.031). Fast fibre cross-sectional area (CSA) showed a trend to decrease by 15% (P = 0.055) at BR10, while single fibre maximal tension (force/CSA) was unchanged. However, at BR10 SR Ca2+ release in response to caffeine decreased by 35.1% (P < 0.002) and 30.2% (P < 0.001) in fast and slow fibres, respectively, pointing to an impaired excitation%contraction coupling. These findings support the view that the early onset of NMJ instability and impairment in SR function are eligible mechanisms contributing to the greater decline in muscle force than in muscle size during unloading.
Ključne besede: Ca2+ dynamics, muscle atrophy, neuromuscular junction instability, sarcoplasmic reticulum, single fibre atrophy, single fibre contractile impairment, unloading
Objavljeno v DiRROS: 16.06.2021; Ogledov: 1113; Prenosov: 1090
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Povzetek: The relatively poor simulation of the below-ground processes is a severe drawback for many ecosystem models, especially when predicting responses to climate change and management. For a meaningful estimation of ecosystem production and the cycling of water, energy, nutrients and carbon, the integration of soil processes and the exchanges at the surface is crucial. It is increasingly recognized that soil biota play an important role in soil organic carbon and nutrient cycling, shaping soil structure and hydrological properties through their activity, and in water and nutrient uptake by plants through mycorrhizal processes. In this article, we review the main soil biological actors (microbiota, fauna and roots) and their effects on soil functioning. We review to what extent they have been included in soil models and propose which of them could be included in ecosystem models. We show that the model representation of the soil food web, the impact of soil ecosystem engineers on soil structure and the related effects on hydrology and soil organic matter (SOM) stabilization are key issues in improving ecosystem-scale soil representation in models. Finally, we describe a new core model concept (KEYLINK) that integrates insights from SOM models, structural models and food web models to simulate the living soil at an ecosystem scale.
Ključne besede: soil fauna, model, Soil Organic Matter, SOM, hydrology, pore size distribution, PSD, soil biota, ecosystem
Objavljeno v DiRROS: 23.09.2020; Ogledov: 1457; Prenosov: 1217
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