SciCombinator

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Concept: Humus

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Eco-toxicological or bioassay tests have been intensively discussed as tools for the evaluation of soil quality. Tests using soil organisms, including microarthropods and plants, allow direct estimates to be made of important soil characteristics and functions. In this study we compared the results obtained by two in vitro standard bioassays following ISO or OECD guidelines: (i) the short term-chronic phytotoxicity germination and root elongation test using three different plant species Cucumis sativus L. (Cucurbitaceae), Lepidium sativum L. (Brassicaceae), and Medicago sativa L. (Fabaceae) and (ii) the inhibition of reproduction of Folsomia candida (Collembola) by soil pollutants to investigate the toxicity of a serpentine soil present in the Italian Apennines, rich in heavy metals such as Ni, Cr, and Co. In addition, microarthropod communities were characterised to evaluate the effects of metal contents on the soil fauna in natural conditions. Abundances, Acari/Collembola ratio, biodiversity indices and the QBS-ar index were calculated. Our results demonstrate that the two in vitro tests distinguish differences correlated with metal and organic matter contents in four sub-sites within the serpentinite. Soil fauna characterisation, not previously performed on serpentine soils, revealed differences in the most vulnerable and adapted groups of microarthropods to soil among the four sub-sites: the microarthropod community was found to be rich in term of biodiversity in the sub-site characterised by a lower metal content and a higher organic matter content and vegetation.

Concepts: Plant, Soil, Heavy metal music, Humus, Organic matter, Cannabis sativa, Serpentine group, Serpentine soil

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To enhance colloidal stability of nano zero-valent iron (NZVI) used for groundwater remediation, the surfaces of such NZVI can be modified via coating with organic stabilizers. These surface stabilizers can electrostatically, sterically, or electrosterically stabilize NZVI suspensions in water, but their efficacy is affected by the presence of humic acid (HA) in groundwater. In this study, the effect of HA on the colloidal stability of NZVI coated with three types of stabilizers (i.e., polyacrylic acid (PAA), Tween-20 and starch) was evaluated. Differing stability behaviors were observed for different surface-modified NZVIs (SM-NZVI) in the presence of HA. Fluorescence spectroscopic analysis probed the possible interactions at the SM-NZVI-HA interface, providing a better understanding of the effect of HA on SM-NZVI stability. The adsorption of HA on the surface of PAA-modified NZVI via complexation with NZVI (rather than the PAA stabilizer) enhanced the electrosteric repulsion effect, increasing the stability of the particles. However, for NZVI modified with Tween-20 or starch, HA could interact with the surface stabilizer and apparently play a “bridge” role among the particles, which might induce aggregation of the particles. Therefore, the stability behavior of NZVI modified with Tween-20 or starch might have resulted from the combined effect of “bridging” and “electrosteric” exerted by HA.

Concepts: Spectroscopy, Water, Stabilizer, Water purification, Colloid, Behavior, Humus, Flocculation

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The aim of this study is to investigate how the presence of Cu influences tebuconazole (Teb) sorption onto contrasting soil types and two important constituents of the soil sorption complex: hydrated Fe oxide and humic substances. Tebuconazole was used in commercial form and as an analytical-grade chemical at different Teb/Cu molar ratios (1:4, 1:1, 4:1, and Teb alone). Increased Cu concentrations had a positive effect on tebuconazole sorption onto most soils and humic substances, probably as a result of Cu-Teb tertiary complexes on the soil surfaces. Tebuconazole sorption increased in the following order of different Teb/Cu ratios 1:4 > 1:1 > 4:1 > without Cu addition, with the only exception for the Leptosol and ferrihydrite. The highest K ( f ) value was observed for humic substances followed by ferrihydrite, the Cambisol, the Arenosol, and the Leptosol. The sorption of analytical-grade tebuconazole onto all matrices was lower, but the addition of Cu supported again tebuconazole sorption. The Teb/Cu ratio with the highest Cu addition (1:4) exhibited the highest K ( f ) values in all matrices with the exception of ferrihydrite. The differences in tebuconazole sorption can be attributed to the additives present in the commercial product. This work proved the importance of soil characteristics and composition of the commercially available pesticides together with the presence of Cu on the behavior of tebuconazole in soils.

Concepts: Water purification, Soil, Ratio, Copper, Chelation, Humus, Humic acid, Soil classification

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Organic matter is known to accumulate high amounts of metals/metalloids, enhanced during the process of decomposition by heterotrophic biofilms (with high fixation capacity for metals/metalloids). The colonization by microbes and the decay rate of the organic matter depends on different litter properties. Main litter properties affecting the decomposition of organic matter such as the nutrient ratios and the content of cellulose, lignin and phenols are currently described to be changed by silicon availability. But less is known about the impact of silicon availability during plant growth on elemental fixation during decay. Hence, this research focuses on the impact of silicon availability during plant growth on fixation of 42 elements during litter decay, by controlling the litter properties. The results of this experiment are a significantly higher metal/metalloid accumulation during decomposition of plant litter grown under low silicon availability. This may be explained by the altered litter properties (mainly nutrient content) affecting the microbial decomposition of the litter, the microbial growth on the litter and possibly by the silicon double layer, which is evident in leaf litter with high silicon content and reduces the binding sites for metals/metalloids. Furthermore, this silicon double layer may also reduce the growing biofilm by reducing the availability of carbon compounds at the litter surface and has to be elucidated in further research. Hence, low silicon availability during plant growth enhances the metal/metalloid accumulation into plant litter during aquatic decomposition.

Concepts: Photosynthesis, Bacteria, Organism, Ecology, Chemical element, Carbon, Humus, Detritus

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This study sought to evaluate the efficacy of aerobic and anaerobic composting of inoculated banana peels, and assess the agronomic value of banana peel-based compost. Changes in the chemical composition under aerobic and anaerobic conditions were examined for four formulations of banana peel-based wastes over a period of 12weeks. The formulations i.e. plain banana peel (B), and a mixture with either cow dung (BC), poultry litter (BP) or earthworm (BE) were separately composted under aerobic and anaerobic conditions under laboratory conditions. Inoculation with either cow dung or poultry litter significantly facilitated mineralization in the order: BP>BC>B. The rate of decomposition was significantly faster under aerobic than in anaerobic composting conditions. The final composts contained high K (>100gkg(-1)) and TN (>2%), indicating high potential as a source of K and N fertilizer.

Concepts: Nitrogen, Waste management, Humus, Compost, Composting, Manure, Anaerobic exercise, Vermicompost

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Kinetics of humic acid (HA) adsorption onto soil minerals (kaolinite and hematite) has been investigated under various conditions. The influence of ionic strength, pH, and solution cations on the rate of adsorption has been studied. The rate and the amount of adsorbed humic acid onto soil minerals increased with increasing ionic strength, decreasing pH, and in the presence of Ca(2+) as background electrolyte. The adsorption equilibrium data showed that adsorption behavior of humic acid could be described more reasonably by Freundlich adsorption isotherm than Langmiur adsorption isotherm. Pseudo first order and pseudo second order kinetic models were used to evaluate the kinetic data and the rate constants. The results explained that humic acid adsorption on hematite and kaolinite was more conforming with pseudo second order kinetics.

Concepts: Soil, Adsorption, Rate equation, Colloidal chemistry, Freundlich equation, Humus, Humic acid, Weathering

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The significance of natural organic matter (NOM, both humic acid and alginate) on the transport and deposition kinetics of ZnO nanoparticles (NPs) in irregular quartz sand was examined by direct comparison of both breakthrough curves and retained profiles with NOM present in NPs suspension versus those obtained without NOM. Packed column experiments were conducted in both NaCl and CaCl(2) solutions under a series of environmentally relevant ionic strengths. Under all examined conditions, breakthrough plateaus with NOM even at concentration as low as 1 mg L(-1) of total organic carbon (TOC) were higher than those without NOM, indicating that presence of NOM in NPs suspensions enhanced ZnO NPs transport. Although hyper-exponential retained profiles were observed both in the presence and absence of NOM, the amount of retained ZnO NPs acquired in the presence of NOM decreased slowly as the transport distance increased. Straining induced by concurrent aggregation is found to cause the hyper-exponential decrease. In the presence of NOM, electrosteric interaction effectively reduced the ZnO NPs deposition on collector surfaces and NPs-NPs aggregation. Subsequently, the amount of NPs that jammed in the column inlet in the absence of NOM were markedly decreased, which therefore exhibited as flatter retained profiles.

Concepts: Soil, Zinc, Organic chemistry, Humus, Humic acid, Organic matter, Natural organic matter, Total organic carbon

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Interactions of organic pollutants with soil organic matter can be studied by adsorption of the pollutants on well-characterized soil samples with constant mineralogy but different organic matter compositions. Therefore, the objectives of the current study are establishing a set of different, well-characterized soil samples by systematic modifications of their organic matter content and molecular composition and prove these modifications by advanced complementary analytical techniques. Modifications were done by off-line pyrolysis and removal/addition of hot-water extracted organic fraction (HWE) from/to the original soil sample. Both pyrolysis-field ionization mass spectrometry (Py-FIMS) and synchrotron-based C- and N- X-ray absorption near-edge structure spectroscopy (XANES) were applied to investigate the composition of the soil organic matter. These complementary analytical methods in addition to elemental analysis agreed in showing the following order of organic matter contents: pyrolyzed soil

Concepts: Mass spectrometry, Soil, Analytical chemistry, Carboxylic acid, Organic chemistry, Organic compounds, Humus, Organic matter

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Per- and poly fluorinated alkyl substances (PFASs), notably perfluorooctanoic acid (PFOA), contaminate many ground and surface waters and are environmentally persistent. The performance limitations of existing remediation methods motivate efforts to develop effective adsorbents. Here we report a β-cyclodextrin (β-CD)-based polymer network with higher affinity for PFOA compared to powdered activated carbon, along with comparable capacity and kinetics. The β-CD polymer reduces PFOA concentrations from 1 μg L(-1) to <10 ng L(-1), at least 7 times lower than the 2016 U.S. EPA advisory level (70 ng L(-1)), and was regenerated and reused multiple times by washing with MeOH. The performance of the polymer is unaffected by humic acid, a component of natural organic matter that fouls activated carbons. These results are promising for treating PFOA-contaminated water and demonstrate the versatility of β-CD-based adsorbents.

Concepts: Hydrogen, Polymer, Soil, Carbon, Organic chemistry, Activated carbon, Humus, Fluorocarbon

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Bacterial activity and physiological diversity were characterized in mining and milling impacted soils collected from three abandoned uranium mine sites, Senokos, Buhovo and Sliven, using bacterial dehydrogenase activity and Biolog (EcoPlate) tests. The elemental composition of soils revealed high levels of uranium and heavy metals (sum of technogenic coefficients of contamination; TCCsum) pollution as follows: Sliven (uranium - 374mg/kg; TCCsum - 23.40) >Buhovo (uranium - 139.20mg/kg; TCCsum - 3.93) >Senokos (uranium - 23.01mg/kg; TCCsum - 0.86). The physiological profiles of the bacterial community level were site specific, and indicated intensive utilization of polyols, carbohydrates and carboxylic acids in low and medium polluted environments, and i-erithrytol and 2-hydroxy-benzoic acid in the highly polluted environment of Sliven waste pile. Enzymes which take part in the biodegradation of recalcitrant substances were more resistant to pollution than these from the pathways of the easily degradable carbon sources. The Shannon index indicated that the physiological diversity of bacteria was site specific but not in line with the levels of pollution. A general tendency of increasing the importance of the number of utilizable substrates to bacterial physiological diversity was observed at less polluted sites, whereas in highly polluted sites the evenness of substrate utilization rate was more significant. Dehydrogenase activity was highest in Senokos upper soil layer and positively correlated (p<0.01) with the soil organic matter content. The bacterial activity (EcoPlate) and physiological diversity (Shannon index) correlated significantly and negatively with As, Cu, Zn, Pb and U, and Co, Cr, Ni and Mn, respectively. We concluded that the observed site specific shifts in bacterial communities were complex due to both the environmental peculiarities and the bacterial tolerance to the relevant level of pollution, rather than a strong indication of uranium and heavy metals toxicity.

Concepts: Enzyme, Soil, Uranium, Pollution, Lead, Heavy metal music, Humus, Uranium mining