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Exposure to oxygen and aerobic biological activity during drought periods alters the availability of terminal electron acceptors (TEA) in the peat catotelm layer. We investigated the changes in the electrochemical and chemical characteristics of humic acids (HA) induced by subjecting air-dried sphagnum peat to biological oxidation or reduction during a 90-day incubation experiment. Structural modifications of HAs from anaerobically (HAred) and aerobically (HAox) incubated peat were investigated by ATR-FTIR, UV-vis, and EEM fluorescence spectroscopy. Number and strength of acid groups were characterized by titration, while changes in redox properties were characterized by cyclic voltammetry and quantified by coulometry with mediated electrochemical oxidation (MEO). Exposure to oxygen had small effects, but compared to anaerobic incubation, decreased by 20% the capacity of HA to reduce the radical ion of 2,2'-Azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·-), passing from 2.77 ± 0.13 mmole- gHA-1 in HAred to 2.21 ± 0.10 mmole- gHA-1 in HAox. Pseudo-first-order electron transfer kinetic constants were 13.3 ± 1.2 s-1 for HAox and 16.7 ± 1.4 s-1 for HAred. Alterations in the hydrological status of the catotelm have minor effects on the actual in situ availability of organic TEA, but if coupled to intensified biological activity they may result in significant variations of greenhouse gases emissions. [ABSTRACT FROM AUTHOR]

The Cananéia-Iguape estuarine–lagoon complex (São Paulo state, Brazil) is a natural laboratory to study metal binding by humic substances (HS) in subtropical settings. This transitional environment is evolving into a freshwater environment due to water input from the Ribeira River, funneled through the Valo Grande Canal (Iguape). Past mining activities in the Ribeira River basin and maritime traffic are suspected to be potential sources of trace metals in the system. In this study, the trace metal contents of Free Humic Acids (FHA), Bound Humic Acids (BHA), and Fulvic Acids (FA) extracted from sedimentary organic matter were investigated. Moreover, the sources of HS were traced using their stable carbon isotope compositions and C/N ratios. The results suggested a mixed marine–terrestrial source of FHA, BHA, and FA. Copper and Cr were the most abundant trace metals bound to HS. On average, Cu showed concentrations of 176, 115, and 37.9 μg g−1 in FHA, BHA, and FA, respectively, whereas Cr showed average concentrations of 47.4, 86.3, and 43.9 μg g−1 in FHA, BHA, and FA, respectively. Marine FHA showed the highest binding capacity for trace metals, whereas terrestrial FA derived from the decay of mangrove organic matter showed the lowest binding capacity. [ABSTRACT FROM AUTHOR]

Conversion of conventional farming (CF) to organic farming (OF) is claimed to allow a sustainable management of soil resources, but information on changes induced on dissolved organic matter (DOM) are scarce. Among DOM components, dissolved humic substances (DHS) were shown to possess stimulatory effects on plant growth. DHS were isolated from CF and OF soil leacheates collected from soil monolith columns: first in November (bare soils) and then in April and June (bare and planted soils). DHS caused an enhancement of nitrate uptake rates in maize roots and modulated several genes involved in nitrogen acquisition. The DHS from OF soil exerted a stronger biostimulant action on the nitrate uptake system, but the first assimilatory step of nitrate was mainly activated by DHS derived from CF soil. To validate the physiological response of plants to DHS exposure, real-time RT-PCR analyses were performed on those genes most involved in nitrate acquisition, such as ZmNRT2.1 , ZmNRT2.2 , ZmMHA2 (coding for two high-affinity nitrate transporters and a PM H+-proton pump), ZmNADH:NR , ZmNADPH:NR , and ZmNiR (coding for nitrate reductases and nitrite reductase). All tested DHS fractions induced the upregulation of nitrate reductase (NR), and in particular the OF2 DHS stimulated the expression of both tested transcripts encoding for two NR isoforms. Characteristics of DHS varied during the experiment in both OF and CF soils: a decrease of high molecular weight fractions in the OF soil, a general increase in the carboxylic groups content, as well as diverse structural modifications in OF vs. CF soils were observed. These changes were accelerated in planted soils. Similarity of chemical properties of DHS with the more easily obtainable water-soluble humic substance extracted from peat (WEHS) and the correspondence of their biostimulant actions confirm the validity of studies which employ WEHS as an easily available source of DHS to investigate biostimulant actions on agricultural crops. [ABSTRACT FROM AUTHOR]

The ability of the simultaneously extracted metals/acid volatile sulfides (∑SEM/AVS) index to ascertain environmental risk from potentially toxic elements in calcareous saltmarsh soils was tested using structural equation modeling. This technique allows the detection of both direct and indirect relationships among AVS, SEM, and other soil variables, representing results in a graphical view. The dataset included 90 soil samples from 21 different sites belonging to 6 different saltmarshes and featured a wide range of soil chemicophysical properties. Variables included in the a priori model were hydroperiod, pH, soil redox potential, labile organic carbon, carbonates, total iron, and total amount of potentially toxic elements (PTEs). The best optimized model pointed out the main soil properties that affect AVS accumulation and SEM speciation in these soils. Effect plots of AVS and SEM calculated with the partial linear mixed‐effects models included in the piecewise structural equation modeling showed a significant and positive influence of pH and carbonates on AVS and a highly significant effect of carbonates and labile organic carbon on SEM. Single SEM components were also considered separately, to define the potential contributions of labile organic carbon or carbonates as alternative binding phases. Simultaneously extracted Cu, Ni, and Zn were preferentially bound to carbonates, followed by labile organic carbon, whereas Pb and Cd were easily bound to labile organic carbon. Environ Toxicol Chem 2019;38:2688–2697. © 2019 SETAC [ABSTRACT FROM AUTHOR]

Monitoring of biogenic sulfide is important because acid volatile sulfides (AVS) represent a reactive pool responsible for immobilization of toxic metals. We propose a new sulfide paper sensor method for semiquantitative determination of AVS in which developed color is compared to a reference chart. The method was validated against the ion‐selective microelectrode and the purge‐and‐trap methods. For fieldwork, readings should fall within 1 to 10 μmoles S2–. Considering that the volume of soil used ranged between 1 and 16 cm3, the corresponding soil sulfides concentration range spans from 0.06 to 10 mmoles S2– cm−3. The sulfide paper sensor method is highly suitable for field screening and has sensitivity levels comparable to laboratory methods. Environ Toxicol Chem 2018;37:3025–3031. © 2018 SETAC [ABSTRACT FROM AUTHOR]

Born in Trento (Italy, 2003) for the purpose of standardising vocabulary and units of humus form classification, after publishing a first synthetic classification e-book (Zanella et al. 2011) they do not cover all site conditions in the European area. Although having basic concepts and general lines, the European (and North American, Canadian, the Humus group decided to use its classification for handling global change (Zanella and Ascher-Jenull 2018). The process is detailed in many scientific articles published in three Special Issues (Humusica 1, 2 and 3) of the journal Applied Soil Ecology. Conceptually, the whole of Humusica answers three crucial questions: A) What is soil? Soil is a biological ecosystem. It recycles dead structures and implements mineral material, furnishing more or less re-elaborated organic, mineral and organic-mineral elements to support living organisms. Article chapters: 1. Essential vocabulary; 2. Soil covers all the Earth's surfaces (soil as the seat of processes of organic matter storage and recycling); 3. Soil may be involved in the process of natural evolution (through organisms' process of recycling biomass after death). B) If soil has a biogenic essence, how should it be classified to serve such managerial purposes as landscape exploitation or protection? A useful classification of soil should consider and propose useful references to biologically discriminate soil features. Article chapters: 4. Soil corresponds to a biogenic structure; 5. TerrHum, an App for classifying forest humipedons worldwide (a first attempt to use a smartphone as a field manual for humus form classification). C) How can this soil classification be used for handling the current global change? Using the collected knowledge about the biodiversity and functioning of natural (or semi-natural) soil for reconstructing the lost biodiversity/functioning of heavily exploited or degraded soils. Article chapters: 6. Agricultural soils correspond to simplified natural soils (comparison between natural and agricultural soils); 7. Organic waste and agricultural soils; 8. Is traditional agriculture economically sustainable? Comparing past traditional farm practices (in 1947) and contemporary intensive farm practices in the Venice province of Italy. [ABSTRACT FROM AUTHOR]

Iron (Fe) sources available for plants in the rhizospheric solution are mainly a mixture of complexes between Fe and organic ligands, including phytosiderophores (PS) and water-extractable humic substances (WEHS). In comparison with the other Fe sources, Fe-WEHS are more efficiently used by plants, and experimental evidences show that Fe translocation contributes to this better response. On the other hand, very little is known on the mechanisms involved in Fe allocation in leaves. In this work, physiological and molecular processes involved in Fe distribution in leaves of Fe-deficient Cucumis sativus supplied with Fe-PS or Fe-WEHS up to 5 days were studied combining different techniques, such as radiochemical experiments, synchrotron micro X-ray fluorescence, real-time reverse transcription polymerase chain reaction and in situ hybridization. In Fe-WEHS-fed plants, Fe was rapidly (1 day) allocated into the leaf veins, and after 5 days, Fe was completely transferred into interveinal cells; moreover, the amount of accumulated Fe was much higher than with Fe-PS. This redistribution in Fe-WEHS plants was associated with an upregulation of genes encoding a ferricIII-chelate reductase (FRO), a Fe2+ transporter (IRT1) and a natural resistance-associated macrophage protein (NRAMP). The localization of FRO and IRT1 transcripts next to the midveins, beside that of NRAMP in the interveinal area, may suggest a rapid and efficient response induced by the presence of Fe-WEHS in the extra-radical solution for the allocation in leaves of high amounts of Fe. In conclusion, Fe is more efficiently used when chelated to WEHS than PS and seems to involve Fe distribution and gene regulation of Fe acquisition mechanisms operating in leaves. [ABSTRACT FROM AUTHOR]

A technology for remediation of mine tailings, based on air oxidation of added Fe(II) in solution, was tested by chemical extraction and growing pea (Pisum sativum) plants in a greenhouse experiment. Tailings, from a mine site (Cave del Predil, Italy) with high content of Pb and Zn, were saturated with a 0.5M FeSO4 solution and then air-dried. The acidity released by Fe(II) oxidation was successively neutralized by Ca(OH)2. This treatment was repeated 6 times. Cd, Cu, Ni, Mn, Pb and Zn mobility was assessed by Ca(NO3)2 extraction, and their bio-available fraction either by DTPA-extraction or by plant test. Mobility of Cd, Pb and Zn decreased at the end of 6 cycles by 48, 66 and 67%, respectively, whereas Cu, Mn and Ni were below detection limits. In treated mining tailings, DTPA-extractable Cu, Pb and Zn after 6 cycles of treatment showed a marked decrease of 50, 65 and 38%, respectively. Conversely, extractable Mn and Ni, although present at very low concentrations, slightly increased their bioavailability, and that of Cd did not change significantly. Pea dry matter yield increased significantly after 4 and 6 treatment cycles. Metal concentration in plant tissue at the end of 6 cycles showed a decrease for Cd (53%), Cu (9%), Mn (8%), Pb (35%) and Zn (26%), but a slight increase for Ni. [ABSTRACT FROM AUTHOR]

In membrane treatment of wastewater containing proteins, humic acid influences the rate and extent of fouling. Cations may increase the tendency of foulants to precipitate due to the changes in intermolecular electrostatic interactions. In this paper, we investigated the effect of cations, including ionic charge and size of hydrated ion, on ultrafiltration of the solutions containing the mixture of HA and bovine serum albumin (BSA). All experiments were carried out in an Amicon batch stirred cell using Amicon XM50, XM300, YM 100 ultrafiltration membranes with molecular weight cut-offs of 50 kDa, 300 kDa and 100 kDa, respectively, and Sartorius microfiltration membranes with a nominal pore size of 0.2 μm. Humic substances were extracted from a commercial sample of sphagnum peat from Northern Ireland (Bulrush). In the presence of Ba2+ cations, the HA rejection in the solutions containing HA and BSA was higher compared to the solutions containing Na+ cations. Unlike monovalent cations, divalent cations interact specifically with natural organic matter (NOM) and form metal humic complexes. The binding of divalent cations with natural organic matter is responsible for the development of a dense layer on the membrane surface. Metal cations may also act as a bridge between humic acid and protein. These phenomena result in a higher deposition of substances on the membrane surface leading to lower flux and higher rejection in the presence of divalent metal cations. In addition to the charge, the size of cation plays a role in the deposition process. The solutions containing MgCl2·6H2O are characterizing by higher flux and lower rejection compared to the solution containing BaCl2·2H2O at all ultrafiltration membranes. This phenomenon may be attributed to the size of Mg2+ and Ba2+ ions. [ABSTRACT FROM AUTHOR]