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Background Developing eco-friendly antioxidant and antimicrobial substances originating from biomass residues has recently attracted considerable interest. In this study, two lignosulfonates and various oxidized water-soluble lignins were investigated for their antioxidant properties, as assessed by ABTS, DPPH and Folin-Ciocalteu methods, and their antimicrobial activity against some bacterial strains responsible for human pathologies. Results The lignosulfonates showed the largest antiradical/antimicrobial capacity, whereas the other substrates were less effective. The observed antioxidant/antibacterial properties were positively correlated with lignin aromatic/phenolic content. The positive correlation between antiradical and antimicrobial activities suggests that lignin scavenging capacity was also involved in its antibacterial activity. A greater antimicrobial performance was generally observed against Gram-positive bacterial strains, and it was attributed to the intrinsic larger susceptibility of Gram-positive bacteria to lignin phenols. A significant though lesser inhibitory activity was also found against Escherichia coli. Conclusion Our results confirmed the dependence of lignin antioxidant/antibacterial power on its extraction method and chemical structure, as well as on the type of bacterial strains. Identifying the relationship between lignin molecular composition and its antioxidant/antibacterial features represents an advance on the potential future use of renewable and eco-compatible lignin materials in nutraceutical, pharmaceutical and cosmetic sectors. © 2021 Society of Chemical Industry.

The molecular composition of water-soluble lignins isolated from four non-food bioenergy crops (cardoon CAR, eucalyptus EUC, and two black poplars RIP and LIM) was characterized in detail, and their potential bioactivity towards maize germination and early growth evaluated. Lignins were found to not affect seed germination rates, but stimulated the maize seedling development, though to a different extent. RIP promoted root elongation, while CAR only stimulated the length of lateral seminal roots and coleoptile, and LIM improved only the coleoptile development. The most significant bioactivity of CAR was related to its large content of aliphatic OH groups, C-O carbons and lowest hydrophobicity, as assessed by (31)P-NMR and (13)C-CPMAS-NMR spectroscopies. Less bioactive RIP and LIM lignins were similar in composition, but their stimulation of maize seedling was different. This was accounted to their diverse content of aliphatic OH groups and S- and G-type molecules. The poorest bioactivity of the EUC lignin was attributed to its smallest content of aliphatic OH groups and largest hydrophobicity. Both these features may be conducive of a EUC conformational structure tight enough to prevent its alteration by organic acids exuded from vegetal tissues. Conversely the more labile conformational arrangements of the other more hydrophilic lignin extracts promoted their bioactivity by releasing biologically active molecules upon the action of exuded organic acids. Our findings indicate that water-soluble lignins from non-food crops may be effectively used as plant biostimulants, thus contributing to increase the economic and ecological liability of bio-based industries.

Water-soluble humic-like lignins from energy crops had been previously shown to significantly improve plant development due to their chemical composition and supramolecular arrangement. Here, humic-like lignins isolated from Giant Reed were tested in several bioassays to verify whether the biostimulation was due to a hormone-mimic (auxin- and gibberellin-like) activity. The water-soluble lignins were applied on tomato seeds harboured with the auxin reporter DR5::GUS (β-glucuronidase), to visualize the auxin responses in roots. Moreover, auxin- or gibberellin (GA)-mimetic activities were assessed by the Audus test on watercress and chicory seeds, respectively, with increasing concentrations of water-soluble lignin. The latter showed a significant GA-like effect, whereas it did not produce auxin-like activity at any assayed concentration. The water-soluble lignins may either directly function as GA on plant and seed development or positively perturb GA-related hormonal balances, thereby influencing GA-mediated physiological mechanisms. These findings suggest that humic-like residual lignins from energy crops may be useful in intensified sustainable agriculture as seed germination enhancers and biostimulants of plant growth.

The sorption of Cu and Pb added alone or in mixture in the absence or presence of low-molecular mass aliphatic acids (LMMAAs): oxalic, citric or glutamic acid onto a synthetic goethite at different pH values (from 3.0 to 5.5) was studied. Copper showed a higher affinity for goethite than lead both in absence or presence of LMMAAs. By increasing the initial organic ligand/metal molar ratio from 0 to 10, the adsorption of both the metals on the iron oxide initially increased and then decreased or remained constant. In the presence of oxalic acid the adsorption of Cu on the surfaces of goethite increased by increasing ratio up to 2–4 and then decreased. Citric acid showed a similar effect but the amounts of Cu fixed were lower. Glutamic acid had the lowest effect on the adsorption of this element onto goethite. Adsorption of Pb was strongly affected by citric acid. The amounts of Pb fixed onto the surfaces of goethite increased up to molar ratio 4 and then slightly decreased. On the contrary, oxalic and glut...

The competitive sorption of Cu, Cr and Pb on a ferrihydrite and two synthetic organomineral complexes, obtained by coprecipitating iron with different quantities of oxalate and tartrate were studied. Greater amounts (μmol/m2) of heavy metals were sorbed onto the organomineral complexes than ferrihydrite, the higher the carbon content in the samples the greater the sorption of heavy metals. Lead was sorbed much more and more tightly than Cr and Cu on the sorbents. In binary systems, the sorption and the inhibitive efficiency of one metal (M1) to the other (M2) were affected by the nature of the metal, initial M2/M1 molar ratio, addition sequence of M1 and M2, and residence time. Lead showed a much greater capacity to inhibit the sorption of the other two metals, whereas the opposite was true for Cu. In ternary systems, when equimolar amounts of each metal were added, the sorbents were covered with more than 50% by Pb alone. However, even in the presence of large excess of Pb and Cr, considerable extent of Cu sorption still occurred regardless of sorbent types, indicating that some sorption sites on each sorbent had a high affinity for Cu. The results of this study would contribute to further our current understanding on the mobility of multi heavy metals in soils and related environments.

Background Liquid-state 31P-NMR spectroscopy becomes progressively an important role for studying phosphorus (P) dynamics in soil. Soils of different origin and organic matter content were used to optimize sample preparation and re-dissolution procedures to improve characterization of P species in soil by 31P-NMR spectroscopy. The efficiency of P extraction from an untreated fresh soil was compared to that from freeze-dried and air-dried soil samples. Results A freeze-drying pretreatment not only provided the greatest extraction yields of total and organic P from both farmland and forest soils but also enhanced the intensity of signals for inorganic and organic P species in 31P-NMR spectra, except for polyphosphates. Re-dissolution of freeze-dried soil extracts in relatively dilute alkaline solution and addition of a small aliquot of concentrated HCl to the NMR tube prior to analysis improved the quality of NMR spectra. Finally, the visibility of relatively weak P signals, such as for phosphorus diesters, phosphonates, polyphosphate, phospholipids, and DNA were reproducibly enhanced when 31P-NMR spectra were generated after at least 15 h of acquisition time. Conclusion The optimized procedure presented here ensured the greatest detectability of inorganic and organic P species by liquid-state P-NMR spectroscopy in soil extracts.

The molecular composition of soil organic matter (SOM) in three agricultural fields under different managements, was evaluated by off-line thermochemolysis followed by gas chromatography mass spectrometry analysis (THM-GC-MS). While this technique enabled the characterization of SOM components in coarse textured soil, its efficiency in heavy textured soils was seriously affected by the interference of clay minerals, which catalyzed the formation of secondary artifacts in pyrolysates. Soil demineralization with hydrofluoric acid (HF) solutions effectively improved the reliable characterization of organic compounds in clayey soils by thermochemolysis, while did not alter significantly the results of coarse textured soil. A wide range of lignin monomers and lipids molecules, of plant and microbial origin, were identified in the pyrograms of HF treated soils, thereby revealing interesting molecular differences between SOM management practices. Our results indicated that clay removal provided by HF pretreatment enhanced the capacity of thermochemolysis to be a valuable and accurate technique to study the SOM dynamics also in heavy-textured and OC-depleted cultivated soils.

Arsenic pollution is currently a major health issue because As is toxic for human beings, animals, and plants. Knowledge of As mobility is therefore important to assess health risk. The sorption of arsenite and arsenate on metal oxides in the presence of various anionic ligands is closely linked to the mobility, bioavailability, and risk. It was reported that the sorption mechanisms and characteristics of arsenite and arsenate on Al-oxides were different from that on Fe-oxides. Previous work reports the sorption of arsenite and arsenate on Fe-oxides in the presence of ligands. Whereas there is few knowledge on the sorption of arsenite and arsenate by Al-oxides in the presence of ligands. Here, we studied the sorption of arsenite and arsenate on amorphous Al-oxide by batch experiments. We tested the effect of organic ligands: oxalate, malate, tartrate, citrate; and inorganic ligands: sulfate, phosphate, selenate, selenite. Results show that amorphous Al-oxide has more sorption affinity for arsenate than arsenite. The inhibition of As sorption by ligands at pH 6 is higher for arsenite than arsenate. For arsenite, the As sorption inhibition decreases in the order phosphate, citrate, malate, selenite, oxalate, tartrate, sulfate, and selenate. For arsenate, the As sorption inhibition decreases in the order phosphate, malate, citrate, selenite, tartrate, oxalate, sulfate, and selenate.

The influence of compost on the growth of bean plants irrigated with As-contaminated waters and its influence on the mobility of As in the soils and the uptake of As (as NaAs III O 2 ) by plant components was studied at various compost application rates (3·10 4 and 6·10 4 kg ha −1 ) and at three As concentrations (1, 2 and 3 mg kg −1 ). The biomass and As and P concentrations of the roots, shoots and beans were determined at harvest time, as well as the chlorophyll content of the leaves and nonspecific and specifically bound As in the soil. The bean plants exposed to As showed typical phytotoxicity symptoms; no plants however died over the study. The biomass of the bean plants increased with the increasing amounts of compost added to the soil, attributed to the phytonutritive capacity of compost. Biomass decreased with increasing As concentrations, however, the reduction in the biomass was significantly lower with the addition of compost, indicating that the As phytotoxicity was alleviated by the compost. For the same As concentration, the As content of the roots, shoots and beans decreased with increasing compost added compared to the Control. This is due to partial immobilization of the As by the organic functional groups on the compost, either directly or through cation bridging. Most of the As adsorbed by the bean plants accumulated in the roots, while a scant allocation of As occurred in the beans. Hence, the addition of compost to soils could be used as an effective means to limit As accumulation in crops from As-contaminated waters.

This paper describes the sorption of arsenate on Al-Mg and Fe-Mg layered double hydroxides as affected by pH and varying concentrations of inorganic and organic ligands, and the effect of residence time on the desorption of arsenate by ligands. The capacity of ligands to inhibit the fixation of arsenate followed the sequence: nitrate < nitrite < sulphate < selenite < tartrate < oxalate < phosphate on Al-Mg-LDH and nitrate < sulphate ≈ nitrite < tartrate < oxalate < selenite ≪ phosphate on Fe-Mg-LDH. The inhibition of arsenate sorption increased by increasing the initial ligand concentration and was greater on Al-Mg-LDH than on Fe-Mg-LDH. The longer the arsenate residence time on the LDH surfaces the less effective the competing ligands were in desorbing arsenate from sorbents. A greater percentage of arsenate was removed by phosphate from Al-Mg-LDH than from Fe-Mg-LDH, due to the higher affinity of arsenate for iron than aluminum.

We studied the sorption of As(III) and As(V) onto ferrihydrite as affected by pH, nature and concentration of organic [oxalic (OX), malic (MAL), tartaric (TAR), and citric (CIT) acid] and inorganic [phosphate (PO(4)), sulphate (SO(4)), selenate (SeO(4)) and selenite (SeO(3))] ligands, and the sequence of anion addition. The sorption capacity of As(III) was greater than that of As(V) in the range of pH 4.0-11.0. The capability of organic and inorganic ligands in preventing As sorption follows the sequence: SeO(4) ≈ SO(4) < OX < MAL ≈ TAR < CIT < SeO(3) ≪ PO(4). The efficiency of most of the competing ligands in preventing As(III) and As(V) sorption increased by decreasing pH, but PO(4) whose efficiency increased by increasing pH. In acidic systems all the competing ligands inhibited the sorption of As(III) more than As(V), but in alkaline environments As(III) and As(V) seem to be retained with the same strength on the Fe-oxide. Finally, the competing anions prevented As(III) and As(V) sorption more when added before than together or after As(III) or As(V).

The competitive sorption among Cu, Pb and Cr in ternary system on Na-montmorillonite at pH 3.5, 4.5 and 5.5 and at different heavy metal concentrations, and the effect of varying concentrations of Al, Fe, Ca and Mg on the sorption of heavy metals were studied. Competitive sorption of Cu, Pb and Cr in ternary system on montmorillonite followed the sequence of Cr ≫ Cu > Pb. Moreover, the competition was weakened by the increase of pH while was intensified by the increase of heavy metal concentration. The sorption of heavy metal on montmorillonite was inhibited by the presence of Ca and Mg, while Al and Fe showed different patterns in affecting heavy metal sorption. Aluminum and Fe generally inhibited the sorption of heavy metal when the pH and/or concentration of major elements were relatively low. However, promoting effects on heavy metal sorption by Al and Fe were found at relatively high pH and/or great concentration of major elements. The inhibition of major elements on heavy metal sorption generally followed the order of Al > Fe > Ca ≥ Mg, while Fe was more efficient than Al in promoting the sorption of heavy metals. These findings are of fundamental significance for evaluating the mobility of heavy metals in polluted environments.

In this study we have investigated the uptake and distribution of arsenic (As) and phosphate (Pi) in roots, shoots, and grain of wheat grown in an uncontaminated soil irrigated with solutions containing As at three different concentrations (0.5, 1 and 2 mg l−1) and in the presence or in the absence of P fertilization. Arsenic in irrigation water reduced plants growth and decreased grain yield. When Pi was not added (P−), plants were more greatly impacted compared to the plus Pi (P+) treatments. The differences in mean biomass between P− and P+ treatments at the higher As concentrations demonstrated the role of Pi in preventing As toxicity and growth inhibition. Arsenic concentrations in root, shoot and grain increased with increasing As concentration in irrigation water. It appears that P fertilization minimizes the translocation of As to the shoots and grain whilst enhancing P status of plant. The observation that P fertilization minimises the translocation of arsenic to the shoots and grain is interesting and may be useful for certain regions of the world that has high levels of As in groundwater or soils.

We have studied: (i) the sorption of arsenate on Mg-Al layered double hydroxides (LDHs) containing chloride (LDH-Cl) or carbonate (LDH-CO(3)) in the absence or presence of phosphate; (ii) the competitive sorption of arsenate and phosphate as affected by reaction time and pH and; (iii) the desorption of arsenate previously sorbed on the LDH by phosphate. The LDH samples were uncalcined (LDH-Cl-20 and LDH-CO(3)-20) or calcined at 450 degrees C (LDH-Cl-450 and LDH-CO(3)-450). More phosphate than arsenate was sorbed onto all the minerals but LDH-Cl-450 sorbed much lower amounts of both the ligands than LDH-Cl-20; vice versa LDH-CO(3)-450 showed a capacity to sorb arsenate and phosphate much greater than LDH-CO(3)-20. XRD analysis showed that arsenate was included into the layer spaces of LDH-Cl-20, but not in those of LDH-CO(3)-20. Competition in sorption between arsenate and phosphate was affected by pH, reaction time, surface coverage and sequence of addition of the ligands. Phosphate showed a greater affinity for LDHs than arsenate. The final arsenate sorbed/phosphate sorbed molar ratio increased with reaction time or by adding arsenate before phosphate, but decreased by increasing pH and by adding phosphate before arsenate. The effect of reaction time on the desorption of arsenate by phosphate was also studied.