Organic matter stabilization and phosphorus activation during vegetable waste composting: Multivariate and multiscale investigation.

The conversion of organic matter and P in the waste composting process affects the efficiency of the composted product. However, the addition of microbial inoculants may improve the conversion characteristics of organic matter and P. In this study, straw-decomposing microbial inoculant (SDMI) was added to investigate its effects on the organic matter stabilization and phosphorus activation during the composting of vegetable waste (VWs). Aliphatic carboxyl-containing compounds were degraded during composting, but the stability of the organic matter and P was improved. The addition of SDMI promoted the degradation of dissolved organic carbon by 81.7 % and improved P stability and thermal stability of organic matter. Hedley sequential P fractionation showed a decrease in the H2O-P proportion by >12 % and increased in the HCl-P proportion by >4 % by the end of composting. Stable forms of P, such as AlPO4 and iron-containing phosphate, were the main forms of P in the final compost. The results provide a basis for producing high-quality vegetable compost products and improving the reutilization potential of VWs.

Molecular composition and possible transformations of labile soil organic matter fractions in Mediterranean arable soils: Relevance and implications.

With the increased global interest in sequestering carbon in soil, it is necessary to understand the composition of different pools of soil organic matter (SOM) that cycle over suitably short timeframes. To explore in detail the chemical composition of agroecologically relevant yet distinct fractions of SOM, the light fraction of SOM (LFOM), the 53-µm particulate organic matter (POM), and the mobile humic acid (MHA) fractions were sequentially extracted from agricultural soils and characterized using both 13C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy and also Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The NMR results showed a decrease in the O-alkyl C region assigned to carbohydrates (51-110 ppm) and an increase in the aromatic region (111-161 ppm) proceeding from the LFOM to the POM and then to the MHA fraction. Similarly, based on the thousands of molecular formulae assigned to the peaks detected by FT-ICR-MS, condensed hydrocarbons were dominant only in the MHA, while aliphatic formulae were abundant in the POM and LFOM fractions. The molecular formulae of the LFOM and POM were mainly grouped in the high H/C lipid-like and aliphatic space, whereas a portion of the MHA compounds showed an extremely high (17-33, average of 25) double bond equivalent (DBE) values, corresponding to low H/C values of 0.3-0.6, representative of condensed hydrocarbons. The labile components appeared most pronounced in the POM (93% of formulae have H/C ≥ 1.5) similar to the LFOM (89% of formulae have H/C ≥ 1.5) but in contrast to the MHA (74% of formulae have H/C ≥ 1.5). The presence of both labile and recalcitrant components in the MHA fraction suggests that the stability and persistence of soil organic matter is influenced by a complex interaction of physical, chemical, and biological factors in soil. Understanding the composition and distribution of different SOM fractions can provide valuable insights into the processes that govern carbon cycling in soils, which can help inform strategies for sustainable land management and climate change mitigation.

Pandemic COVID-19 ends but soil pollution increases: Impacts and a new approach for risk assessment.

For three years, a large amount of manufactured pollutants such as plastics, antibiotics and disinfectants has been released into the environment due to COVID-19. The accumulation of these pollutants in the environment has exacerbated the damage to the soil system. However, since the epidemic outbreak, the focus of researchers and public attention has consistently been on human health. It is noteworthy that studies conducted in conjunction with soil pollution and COVID-19 represent only 4 % of all COVID-19 studies. In order to enhance researchers' and the public awareness of the seriousness on the COVID-19 derived soil pollution, we propose the viewpoint that "pandemic COVID-19 ends but soil pollution increases" and recommend a whole-cell biosensor based new method to assess the environmental risk of COVID-19 derived pollutants. This approach is expected to provide a new way for environmental risk assessment of soils affected by contaminants produced from the pandemic.

Aquaculture sediments amended with biochar improved soil health and plant growth in a degraded soil.

Sustainable and safe management of aquaculture sediments is of great concern. Biochar (BC) and fishpond sediments (FPS) are rich in organic carbon and nutrients and thus can be used as soil amendments; however, it is not fully explored how the biochar amended fishpond sediments can affect soil properties/fertility and modulate plant physiological and biochemical changes, particularly under contamination stress. Therefore, a comprehensive investigation was carried out to explore the effects of FPS and BC-treated FPS (BFPS) on soil and on spinach (Spinacia oleracea L.) grown in chromium (Cr) contaminated soils. Addition of FPS and BFPS to soil caused an increase in nutrients content and reduced Cr levels in soil, which consequently resulted in a significant increase in plant biomass, chlorophyll pigments, and photosynthesis, over the control treatment. The most beneficial effect was observed with the BFPS applied at 35 %, which further increased the antioxidant enzymes (by 2.75-fold, at minimum), soluble sugars by 24.9 %, and upregulated the gene expression activities. However, the same treatment significantly decreased proline content by 74.9 %, Malondialdehyde by 65.6 %, H2O2 by 65.1 %, and Cr concentration in spinach root and shoot tissues. Moreover, the average daily intake analysis showed that BFPS (at 35 %) could effectively reduce human health risks associated with Cr consumption of leafy vegetables. In conclusion, these findings are necessary to provide guidelines for the reutilization of aquaculture sediments as an organic fertilizer and a soil amendment for polluted soils. However, more future field studies are necessary to provide guidelines and codes on aquaculture sediments reutilization as organic fertilizer and soil amendment for polluted soils, aiming for a more sustainable food system in China and globally, with extended benefits to the ecosystem and human.

Enhancing microplastics biodegradation during composting using livestock manure biochar.

Biodegradation of microplastics (MPs) in contaminated biowastes has received big scientific attention during the past few years. The aim here is to study the impacts of livestock manure biochar (LMBC) on the biodegradation of polyhydroxyalkanoate microplastics (PHA-MPs) during composting, which have not yet been verified. LMBC (10% wt/wt) and PHA-MPs (0.5% wt/wt) were added to a mixture of pristine cow manure and sawdust for composting, whereas a mixture without LMBC served as the control (CK). The maximum degradation rate of PHA-MPs (22-31%) was observed in the thermophilic composting stage in both mixtures. LMBC addition significantly (P < 0.05) promoted PHA-MPs degradation and increased the carbon loss and oxygen loading of PHA-MPs compared to CK. Adding LMBC accelerated the cleavage of C-H bonds and oxidation of PHA-MPs, and increased the O-H, CO and C-O functional groups on MPs. Also, LMBC addition increased the relative abundance of dominant microorganisms (Firmicutes, Proteobacteria, Deinococcus-Thermus, Bacteroidetes, Ascomycota and Basidiomycota) and promoted the enrichment of MP-degrading microbial biomarkers (e.g., Bacillus, Thermobacillus, Luteimonas, Chryseolinea, Aspergillus and Mycothermus). LMBC addition further increased the complexity and connectivity between dominant microbial biomarkers and PHA-MPs degradation characteristics, strengthened their positive relationship, thereby accelerated PHA-MPs biodegradation, and mitigated the potential environmental and human health risk. These findings provide a reference point for reducing PHA-MPs in compost and safe recycling of MPs contaminated organic wastes. However, these results should be validated with other composting matrices and conditions.

The significance of eighteen rice genotypes on arsenic accumulation, physiological response and potential health risk.

Rice is an important food crop that is susceptible to arsenic (As) contamination under paddy soil conditions depending on As uptake characteristics of the rice genotypes. Here we unveiled the significance of eighteen (fine and coarse) rice genotypes against As accumulation/tolerance, morphological and physiological response, and antioxidant enzymes-enabled defense pathways. Arsenic significantly affected rice plant morphological and physiological attributes, with relatively more impacts on fine compared to coarse genotypes. Grain, shoot, and root As uptake were lower in fine genotypes (0.002, 0.020, and 0.032 mg pot-1 DW, respectively) than that of coarse (0.031, 0.60, and 1.2 mg pot-1 DW, respectively). Various biochemical (pigment contents, hydrogen peroxide, lipid peroxidation) and defense (antioxidant enzymes) plant parameters indicated that the fine genotypes, notably Kainat and Basmati-385, possessed the highest As tolerance. Arsenic-induced risk indices exhibited greater hazard quotient (up to 1.47) and carcinogenic risk (up to 0.0066) for coarse genotypes compared to the fine ones, with the greatest risk for KSK-282. This study elaborates the pivotal role of genotypic variation among rice plants in As accumulation, which is crucial for mitigating the associated human health risk. Further research is required on molecular aspects, e.g., genetic sequencing, to examine rice genotypes variation in defense mechanisms to As contamination.

Microbial inoculants and struvite improved organic matter humification and stabilized phosphorus during swine manure composting: Multivariate and multiscale investigations.

The combined effects of microbial inoculants (MI) and magnesium ammonium phosphate (MAP; struvite) on organic matter (OM) biodegradation and nutrients stabilization during biowaste composting have not yet been investigated. Therefore, the effects of MI and MAP on OM stability and P species during swine manure composting were investigated using geochemical and spectroscopic techniques. MI promoted the degradation of carbohydrates and aliphatic compounds, which improved the degree of OM mineralization and humification. MI and MAP promoted the redistribution of P fractions and species during composting. After composting, the portion of water-soluble P decreased from 50.0% to 23.0%, while the portion of HCl-P increased from 18.5% to 33.5%, which mean that MI and MAP can stabilize P and mitigate its potential loss during composting. These findings indicate that MI can be recommended for enhancing OM biodegradation and stabilization of P during biowastes composting, as a novel trial for the biological waste treatment.

Herbal plants- and rice straw-derived biochars reduced metal mobilization in fishpond sediments and improved their potential as fertilizers.

Fishpond sediments are rich in organic carbon and nutrients; thus, they can be used as potential fertilizers and soil conditioners. However, sediments can be contaminated with toxic elements (TEs), which have to be immobilized to allow sediment reutilization. Addition of biochars (BCs) to contaminated sediments may enhance their nutrient content and stabilize TEs, which valorize its reutilization. Consequently, this study evaluated the performance of BCs derived from Taraxacum mongolicum Hand-Mazz (TMBC), Tribulus terrestris (TTBC), and rice straw (RSBC) for Cu, Cr, and Zn stabilization and for the enhancement of nutrient content in the fishpond sediments from San Jiang (SJ) and Tan Niu (TN), China. All BCs, particularly TMBC, reduced significantly the average concentrations of Cr, Cu, and Zn in the overlying water (up to 51% for Cr, 71% for Cu, and 68% for Zn) and in the sediments pore water (up to 77% for Cr, 76% for Cu, and 50% for Zn), and also reduced metal leachability (up to 47% for Cr, 60% for Cu, and 62% for Zn), as compared to the control. The acid soluble fraction accounted for the highest portion of the total content of Cr (43-44%), Cu (38-43%), and Zn (42-45%), followed by the reducible, oxidizable, and the residual fraction; this indicates the high potential risk. As compared with the control, TMBC was more effective in reducing the average concentrations of the acid soluble Cr (15-22%), Cu (35-53%), and Zn (21-39%). Added BCs altered the metals acid soluble fraction by shifting it to the oxidizable and residual fractions. Moreover, TMBC improved the macronutrient status in both sediments. This work provides a pathway for TEs remediation of sediments and gives novel insights into the utilization of BC-treated fishpond sediments as fertilizers for crop production.

Addition of walnut shells biochar to alkaline arable soil caused contradictory effects on CO2 and N2O emissions, nutrients availability, and enzymes activity.

Mitigation of greenhouse gas (GHGs) emissions and improving soil health using biochar (BC) shall help achieving the UN-Sustainable Development Goals. The impacts of walnut shells biochar (WSB) pyrolyzed at different temperatures on CO2 and N2O emission and soil health have not been yet sufficiently explored. We investigated the effects of addition of WSB pyrolyzed at either 300 °C (WSB-300), 450 °C (WSB-450), or at 600 °C (WSB-600) to alkaline soil on CO2 and N2O emissions, nutrients availability, and soil enzymes activities in a 120-day incubation experiment. Cumulative N2O emissions were reduced significantly as compared to the control, by 64.9%, 50.6%, and 36.4% after WSB-600, WSB-450 and WSB-300, respectively. However, the cumulative CO2 emissions increased, over the control, as follows: WSB-600 (50.7%), WSB-450 (68.6%), and WSB-300 (73.4%). Biochar addition, particularly WSB-600 significantly increased soil pH (from 8.1 to 8.34), soil organic C (SOC; from 8.6 to 22.3 g kg-1), available P (from 21.0 to 60.5 mg kg-1), and K (181.0-480.5 mg kg-1), and activities of urease, alkaline phosphatase, and invertase. However, an opposite pattern was observed with NH4+, NO3-, total N and ß-glucosidase activity after WSB application. The WBS produced from high temperature pyrolysis can be used for N2O emissions mitigation and improvement of soil pH, SOC, available P and K, and activities of urease, alkaline, phosphatase. However, WBS produced from low temperature pyrolysis can be used to promote N availability and ß-glucosidase; however, these findings should be verified under different field and climatic conditions.

Removal of potentially toxic elements from contaminated soil and water using bone char compared to plant- and bone-derived biochars: A review.

Conversion of hazardous waste materials to value-added products is of great interest from both agro-environmental and economic points of view. Bone char (BC) has been used for the removal of potentially toxic elements (PTEs) from contaminated water, however, its potential BC for the immobilization of PTEs in contaminated water and soil compared to bone (BBC)- and plant (PBC)-derived biochars has not been reviewed yet. This review presents an elaboration for the potentials of BC for the remediation of PTEs-contaminated water and soil in comparison with PBC and BBC. This work critically reviews the preparation and characterization of BC, BBC, and PBC and their PTEs removal efficiency from water and soils. The mechanisms of PTE removal by BC, BBC, and PBC are also discussed in relation to their physicochemical characteristics. The review demonstrates the key opportunities for using bone waste as feedstock for producing BC and BBC as promising low-cost and effective materials for the remediation of PTEs-contaminated water and soils and also elucidates the possible combinations of BC and BBC aiming to effectively immobilize PTEs in water and soils.

Improving the humification and phosphorus flow during swine manure composting: A trial for enhancing the beneficial applications of hazardous biowastes.

Improving the recovery of organic matter and phosphorus (P) from hazardous biowastes such as swine manure using acidic substrates (ASs) in conjunction with aerobic composting is of great interest. This work aimed to investigate the effects of ASs on the humification and/or P migration as well as on microbial succession during the swine manure composting, employing multivariate and multiscale approaches. Adding ASs, derived from wood vinegar and humic acid, increased the degree of humification and thermal stability of the compost. The 31P nuclear magnetic resonance spectroscopy and X-ray absorption near-edge structure analyses demonstrated compost P was in the form of struvite crystals, Ca/Al-P phases, and Poly-P (all inorganic P species) as well as inositol hexakisphosphate and Mono-P (organophosphorus species). However, the efficiency of P recovery could be improved by generating more struvite by adding the ASs. The flows among nutrient pools resulted from the diversity in the dominant microbial communities in different composting phases after introducing the ASs and appearance of Bacillus spp. in all phases. These results demonstrate the potential value of ASs for regulating and/or improving nutrients flow during the composting of hazardous biowastes for producing higher quality compost, which may maximize their beneficial benefits and applications.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review.

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.

Earthworms as candidates for remediation of potentially toxic elements contaminated soils and mitigating the environmental and human health risks: A review.

Global concerns towards potentially toxic elements (PTEs) are steadily increasing due to the significant threats that PTEs pose to human health and environmental quality. This calls for immediate, effective and efficient remediation solutions. Earthworms, the 'ecosystem engineers', can modify and improve soil health and enhance plant productivity. Recently, considerable attention has been paid to the potential of earthworms, alone or combined with other soil organisms and/or soil amendments, to remediate PTEs contaminated soils. However, the use of earthworms in the remediation of PTEs contaminated soil (i.e., vermiremediation) has not been thoroughly reviewed to date. Therefore, this review discusses and provides comprehensive insights into the suitability of earthworms as potential candidates for bioremediation of PTEs contaminated soils and mitigating environmental and human health risks. Specifically, we reviewed and discussed: i) the occurrence and abundance of earthworms in PTEs contaminated soils; ii) the influence of PTEs on earthworm communities in contaminated soils; iii) factors affecting earthworm PTEs accumulation and elimination, and iv) the dynamics and fate of PTEs in earthworm amended soils. The technical feasibility, knowledge gaps, and practical challenges have been worked out and critically discussed. Therefore, this review could provide a reference and guidance for bio-restoration of PTEs contaminated soils and shall also help developing innovative and applicable solutions for controlling PTEs bioavailability for the remediation of contaminated soils and the mitigation of the environment and human risks.

Wheat and maize-derived water-washed and unwashed biochar improved the nutrients phytoavailability and the grain and straw yield of rice and wheat: A field trial for sustainable management of paddy soils.

A field experiment was carried out to evaluate the effects of different biochars on grain yield and phytoavailability and uptake of macro- and micro-nutrients by rice and wheat grown in a paddy soil in a rotation. Soil was treated with i) maize raw (un-washed) biochar (MRB), ii) maize water-washed biochar (MWB), iii) wheat raw biochar (WRB) or iv) wheat water-washed biochar (WWB) and untreated soil was used as control (CF). Inorganic fertilizers were applied to all soils while biochar treated soils received 20 ton ha-1 of designated biochar before rice cultivation in rice-wheat rotation. The WRB significantly (P < 0.05) increased rice grain yield and straw by up to 49%, compared to the CF. Biochar addition, particularly WRB, significantly increased the availability of N, P, K and their content in the grain (26-37%) and straw (22-37%) of rice and wheat. Also, the availability and grain content of Fe, Mn, Zn, and Cu increased significantly after biochar addition, particularly after the WRB, due to WRB water dissolved C acting as a carrier for micronutrients in soil and plant. However, the water-washing process altered biochar properties, particularly the water extractable C, which decreased its efficiency. Both wheat- and maize-derived biochars, particularly the WRB, are recommended to improve nutrients availability and to improve grain yield in the rice-wheat rotation agro-ecosystem. These results shed light on the importance of crop straw transformation into an important source for soil C and nutrients necessary for sustainable management of wheat-rice agro-ecosystem. However, with the current and future alternative energy demands, the decision on using crop biomass for soil conservation or for bioenergy becomes a challenge reliant on regulatory and policy frameworks.

Effects of sheep bone biochar on soil quality, maize growth, and fractionation and phytoavailability of Cd and Zn in a mining-contaminated soil.

Biochar prepared from various feedstock materials has been utilized in recent years as a potential stabilizing agent for heavy metals in smelter-contaminated soils. However, the effectiveness of animal bone-derived biochar and its potential for the stabilization of contaminants remains unclear. In the present study, sheep bone-derived biochar (SB) was prepared at low (500 °C; SBL) and high temperatures (800 °C; SBH) and amended a smelter-contaminated soil at 2, 5, and 10% (w/w). The effects of SB on soil properties, bioavailable Zn and Cd and their geochemical fractions, bacterial community composition and activity, and the response of plant attributes (pigments and antioxidant activity) were assessed. Results showed that the SBH added at 10% (SBH10) increased soil organic carbon, total nitrogen, and phosphorus, and also increased the oxidizable and residual Zn and Cd fractions at the expense of the bioavailable fractions. The SBH10 lowered the Zn and Cd contents in maize roots (by 57 and 60%) and shoot (by 42 and 61%), respectively, compared to unamended control. Additionally, SBH10 enhanced urease (98%) and phosphates (107%) activities, but reduced dehydrogenase (58%) and ß-glucosidase (30%) activities. Regarding the effect of the pyrolysis temperature, SBH enhanced the activity of Acidobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Verrucomicrobia, Chlorobi, and Microgenomates, but reduced Actinobacteria and Parcubacteria in comparison to SBL. However, only the SBL10 reduced the Proteobacteria community (by 9%). In conclusion, SB immobilized Zn and Cd in smelter-affected soils, enhanced the bacterial abundance and microbial function (urease, phosphates), and improved plant growth. However, validation of the results, obtained from the pot experiment, under field conditions is suggested.

Bone-derived biochar improved soil quality and reduced Cd and Zn phytoavailability in a multi-metal contaminated mining soil.

Reusing by-products such as cow bones in agriculture can be achieved thorough pyrolysis. The potential of bone-derived biochar as a promising material for metals immobilization in contaminated mining soils has not yet been sufficiently explored. Therefore, cow bones were used as biochar feedstock were pyrolyzed at 500 °C (CBL) and 800 °C (CBH) and. The two biochars were applied to a mine contaminated soil at 0 (control), 2.5, 5 and 10%, w/w, dosages; then, the soils were incubated and cultivated by maize in the greenhouse. Cadmium (Cd) and zinc (Zn) bioavailability and their sequentially extracted fractions (acid soluble, reducible, oxidizable, and residual fraction), soil microbial function, and plant health attributes were analyzed after maize harvesting. Bone-derived biochar enhanced the content of dissolved organic carbon (up to 74%), total nitrogen (up to 26%), and total phosphorus (up to 27%) in the soil and improved the plant growth up to 55%, as compared to the control. The addition of CBL altered the acid soluble fraction of both metals to the residual fraction and, thus, reduced the content of Zn (55 and 40%) and Cd (57 and 67%) in the maize roots and shoots, respectively as compared to the control. The CBL enhanced the ß-glucosidase (51%) and alkaline phosphatase activities (71%) at the lower doses (2.5-5%) as compared to control, while the activities of these enzymes decreased with the higher application doses. Also, CBL improved the antioxidants activity and maize growth at the 2.5-5% application rate. However, the activity of the dehydrogenase significantly decreased (77%), particularly with CBH. We conclude that CBL, applied at 2.5-5% dose, can be utilized as a potential low cost and environmental friendly amendment for stabilization of toxic metals in contaminated mining soils and producing food/feed/biofuel crops with lower metal content.

Green remediation of toxic metals contaminated mining soil using bacterial consortium and Brassica juncea.

Microorganism-assisted phytoremediation is being developed as an efficient green approach for management of toxic metals contaminated soils and mitigating the potential human health risk. The capability of plant growth promoting Actinobacteria (Streptomyces pactum Act12 - ACT) and Firmicutes (Bacillus subtilis and Bacillus licheniformis - BC) in mono- and co-applications (consortium) to improve soil properties and enhance phytoextraction of Cd, Cu, Pb, and Zn by Brassica juncea (L.) Czern. was studied here for the first time in both incubation and pot experiments. The predominant microbial taxa were Proteobacteria, Actinobacteria and Bacteroidetes, which are important lineages for maintaining soil ecological activities. The consortium improved the levels of alkaline phosphatase, ß-D glucosidase, dehydrogenase, sucrase and urease (up to 33%) as compared to the control. The bacterial inoculum also triggered increases in plant fresh weight, pigments and antioxidants. The consortium application enhanced significantly the metals bioavailability (DTPA extractable) and mobilization (acid soluble fraction), relative to those in the unamended soil; therefore, significantly improved the metals uptake by roots and shoots. The phytoextraction indices indicated that B. juncea is an efficient accumulator of Cd and Zn. Overall, co-application of ACT and BC can be an effective solution for enhancing phytoremediation potential and thus reducing the potential human health risk from smelter-contaminated soil. Field studies may further credit the understanding of consortium interactions with soil and different plant systems in remediating multi-metal contaminated environments.

Streptomyces pactum addition to contaminated mining soils improved soil quality and enhanced metals phytoextraction by wheat in a green remediation trial.

Streptomyces pactum (Act12), an agent of a gentle in situ remediation approach, has been recently used in few works in phytoextraction trials; however, the impact of Act12 on soil quality and metal phytoavailability has not been assessed in multi-metal contaminated soils. Consequently, here we assessed the potential impact of Act12 on the wheat (Triticum aestivum L.) growth, antioxidants activity, and the metal bioavailability in three industrial and mining soils collected from China and contained up to 118, 141, 339, and 6625 mg Cd, Cu, Pb, and Zn kg-1 soil, respectively. The Act12 was applied at 0 (control), 0.75 (Act-0.75), 1.50 (Act-1.5), and 2.25 (Act-2.25) g kg-1 (dry weight base) to the three soils; thereafter, the soils were cultivated with wheat (bio-indicator plant) in a pot experiment. The addition of Act12 (at Act-1.5 and Act-2.25) promoted wheat growth in the three soils and significantly increased the content of Cd, Cu, and Zn in the roots and shoots and Pb only in the roots (up to 121%). The Act12-induced increase in metals uptake by wheat might be attributed to the associated decrease in soil pH and/or the increase of metal chelation and production of indole acetic acid and siderophores. The Act12 significantly decreased the antioxidant activities and lipid peroxidation in wheat, which indicates that Act12 may mitigate metals stress in contaminated soils. Enhancing metals phytoextraction using Act12 is a promising ecofriendly approach for phytoremediation of metal-contaminated mining soils that can be safely utilized with non-edible plants and/or bioenergy crops.

Fe/Mn- and P-modified drinking water treatment residuals reduced Cu and Pb phytoavailability and uptake in a mining soil.

Management of industrial hazardous waste is of great concern. Recently, aluminum rich drinking water treatment residuals (Al-WTR) received considerable attention as a low-cost immobilizing agent for toxic elements in soils. However, the suitability and effectiveness of modified Al-WTR as stabilizing agent for toxic metals such as Cu and Pb in mining soil is not assessed yet. We examined the impact of different doses (0, 0.5, 1.5, and 2.5%) of raw and Fe/Mn- and P- modified Al-WTR on the bioavailability and uptake of Cu and Pb by ryegrass in Cu and Pb contaminated mining soil. The addition of Fe/Mn-and P- modified Al-WTR to the soil reduced significantly the concentrations of Pb (up to 60% by Fe/Mn-Al-WTR and 32% by P-Al-WTR) and Cu (up to 45% by Fe/Mn-Al-WTR and 18% by P-Al-WTR) in the shoots and roots of ryegrass as compared to raw Al-WTRs and untreated soil. Our results demonstrate that modification of the raw Al-WTR increased its pH, CEC, specific surface area, active functional groups (Fe-O and Mn-O), and thus increased its immobilization efficiency. Our results highlight the potential of the modified Al-WTR, particularly the Fe/Mn-Al-WTR, for the remediation of Cu and Pb contaminated soils and recommend field scale verification.

Influence of crop rotation, tillage and fertilization on chemical and spectroscopic characteristics of humic acids.

The changes in soil organic matter composition induced by anthropogenic factors is a topic of great interest for the soil scientists. The objective of this work was to identify possible structural changes in humic molecules caused by a 2-year rotation of durum wheat with faba bean, lasted for a decade, and conducted with different agricultural practices in a Mediterranean soil. Humic acids (HA) were extracted at three depths (0-30, 30-60 and 60-90 cm) from a Mediterranean soil subjected to different tillage (no tillage, minimum tillage and conventional tillage), crops (faba bean and wheat), and fertilization. The changes in HA quality were assessed by several chemical (ash, yield and elemental analysis) and spectroscopic techniques (solid-state 13C nuclear magnetic resonance, Fourier transform infrared and fluorescence). The results suggest that the different agronomic practices strongly affected the quality of HA. Smaller but more aromatic molecules were observed with depth, while the fertilization induced the formation of simpler and less aromatic molecules due to the enhanced decomposition processes. Under no tillage, more stable humic molecules were observed due to the less soil aeration, while under conventional tillage larger and more aromatic molecules were obtained. Compared to wheat, more aromatic and more oxidized but less complex molecules were observed after faba bean crop. The inorganic fertilization accelerates the decomposition of organic substances rather than their stabilization. At the end of each crop cycle, humic matter of different quality was isolated and this confirms the importance of the rotation practice to guarantee a diversification of the soil organic matter with time. Finally, no tillage induces the formation of more stable humic matter.