Combining biochar and grass-legume mixture to improve the phytoremediation of soils contaminated with potentially toxic elements (PTEs).

The combination of soil amendments with plants can be a viable option for restoring the functionality of PTEs-contaminated soils. Soil recovery could be further optimized through the mixed cropping of plant species (e.g. legumes and grasses) with different physiological characteristics. The aim of this study was to assess the phytoremediation ability of Vicia villosa Roth. And Lolium rigidum Gaud. Grown alone or in mixture in a soil contaminated with PTEs (C), i.e. Cd (23 mg kg-1), Pb (4473 mg kg-1) and Zn (3147 mg kg-1), and amended with 3% biochar (C + B). Biochar improved soil fertility and changed PTEs distribution, reducing soluble fractions and increasing the more stable ones. The addition of biochar increased the plant biomass of hairy vetch and annual ryegrass, both in monoculture and when in mixture. For example, shoot and root biomass of the C + B intercropped hairy vetch and annual ryegrass increased 9- and 7-fold, and ∼3-fold respectively, compared to the respective C plants. The biochar addition decreased PTE-uptake by both plants, while mixed cropping increased the uptake of PTEs by shoots of hairy vetch grown in C and C + B. The bioaccumulation, translocation factors, and mineralomass showed that hairy vetch and annual ryegrass behaved as phytostabilising plants. PTE mineralomasses proved that mixed cropping in C + B increased the overall capacity of PTE accumulation by plant tissues, particularly the root system. Therefore, the combination of biochar and legumes/grasses mixed cropping could be an effective solution for the recovery of PTEs-contaminated soils and the mitigation of their environmental hazard.

Using biochar for environmental recovery and boosting the yield of valuable non-food crops: The case of hemp in a soil contaminated by potentially toxic elements (PTEs).

Hemp (Cannabis sativa L.) is known to tolerate high concentrations of soil contaminants which however can limit its biomass yield. On the other hand, organic-based amendments such as biochar can immobilize soil contaminants and assist hemp growth in soils contaminated by potentially toxic elements (PTEs), allowing for environmental recovery and income generation, e.g. due to green energy production from plant biomass. The aim of this study was therefore to evaluate the suitability of a softwood-derived biochar to enhance hemp growth and promote the assisted phytoremediation of a PTE-contaminated soil (i.e., Sb 2175 mg kg-1; Zn 3149 mg kg-1; Pb 403 mg kg-1; and Cd 12 mg kg-1). Adding 3% (w/w) biochar to soil favoured the reduction of soluble and exchangeable PTEs, decreased soil dehydrogenase activity (by ∼2.08-fold), and increased alkaline phosphomonoesterase and urease activities, basal respiration and soil microbial carbon (by ∼1.18-, 1.22-, 1.22-, and 1.66-fold, respectively). Biochar increased the abundance of selected soil culturable microorganisms, while amplicon sequencing analysis showed a positive biochar impact on α-diversity and the induction of structural changes on soil bacterial community structure. Biochar did not affect root growth of hemp but significantly increased its aboveground biomass by ∼1.67-fold for shoots, and by ∼2-fold for both seed number and weight. Biochar increased the PTEs phytostabilisation potential of hemp with respect to Cd, Pb and Zn, and also stimulated hemp phytoextracting capacity with respect to Sb. Overall, the results showed that biochar can boost hemp yield and its phytoremediation effectiveness in soils contaminated by PTEs providing valuable biomass that can generate profit in economic, environmental and sustainability terms.

Mixing Compost and Biochar Can Enhance the Chemical and Biological Recovery of Soils Contaminated by Potentially Toxic Elements.

Biochar and compost are able to influence the mobility of potentially toxic elements (PTEs) in soil. As such, they can be useful in restoring the functionality of contaminated soils, albeit their effectiveness can vary substantially depending on the chemical and/or the (micro)biological endpoint that is targeted. To better explore the potential of the two amendments in the restoration of PTE-contaminated soils, biochar, compost (separately added at 3% w/w), and their mixtures (1:1, 3:1, and 1:3 biochar-to-compost ratios) were added to contaminated soil (i.e., 2362 mg kg-1 of Sb and 2801 mg kg-1 of Zn). Compost and its mixtures promoted an increase in soil fertility (e.g., total N; extractable P; and exchangeable K, Ca, and Mg), which was not found in the soil treated with biochar alone. All the tested amendments substantially reduced labile Zn in soil, while biochar alone was the most effective in reducing labile Sb in the treated soils (-11% vs. control), followed by compost (-4%) and biochar-compost mixtures (-8%). Compost (especially alone) increased soil biochemical activities (e.g., dehydrogenase, urease, and ß-glucosidase), as well as soil respiration and the potential catabolic activity of soil microbial communities, while biochar alone (probably due to its high adsorptive capacity towards nutrients) mostly exhibited an inhibitory effect, which was partially mitigated in soils treated with both amendments. Overall, the biochar-compost combinations had a synergistic effect on both amendments, i.e., reducing PTE mobility and restoring soil biological functionality at the same time. This finding was supported by plant growth trials which showed increased Sb and Zn mineralomass values for rigid ryegrass (Lolium rigidum Gaud.) grown on biochar-compost mixtures, suggesting a potential use of rigid ryegrass in the compost-biochar-assisted phytoremediation of PTE-contaminated soils.

Microbial community assembly and chemical dynamics of raw brewers' spent grain during inoculated and spontaneous solid-state fermentation.

Solid-state fermentation (SSF) carried out by microbial bioinoculants is an environmentally friendly technology for the sustainable recovery and valorization of agri-food wastes. Particularly, mesophilic SSF processes allows the production of bio-organic fertilizers enriched with beneficial soil microorganisms. However, the establishment of microbial consortia and the interaction with native waste microbiota still require thoughtful investigations. Here, raw brewers' spent grain (BSG), the main waste from the brewing industry, was subjected to two mesophilic SSF processes (maximum temperature of 35 °C) carried out by a multi-kingdom microbial bioinoculant and the BSG spontaneous microbiota. After 90 days, both SSF processes led to stable organic soil amendments, as indicated by the C:N ratio (10.00 ± 1.4), pH (6.66 ± 0.09), and DOC (8.45 ± 1.2 mg/g) values. Additionally, the fermented BSG showed a high nitrogen content (42.2 ± 3.4 mg/Kg) and biostimulating activities towardLepidium sativumseeds. The monitoring of microbial communities by high-throughput sequencing of 16S and ITS rRNA indicated that BSG samples were enriched in microbial genera with interesting agronomic applications (i.e.,Devosia, Paenibacillum, Trichoderma, Mucor, etc.). Microbial cross-kingdom network analyses suggested that the microbial assembly of BSG was significantly influenced by the bioinoculant, despite the inoculated microbial genera being able to persist in BSG samples only the first week of SSF. This suggests that the study of microbial interactions between exogenous microbial inoculants and waste resident microbiota is required to optimize SSF processes aimed at the recovery and valorization of unprocessed wastes.

Long-term effect of municipal solid waste compost on the recovery of a potentially toxic element (PTE)-contaminated soil: PTE mobility, distribution and bioaccessibility.

Compost from municipal solid waste (MSWC) can represent a resource for the environmental management of soils contaminated with potentially toxic elements (PTEs), since it can reduce their mobility and improve soil fertility. However, the long-term impact of compost on soil recovery has been poorly investigated. To this end, the influence of a MSWC added at different rates (i.e. 1.5, 3.0 and 4.5% w/w) to a multi-PTE-contaminated (e.g. Sb 412 mg kg-1, Pb 2664 mg kg-1 and Zn 7510 mg kg-1) sub-acidic soil (pH 6.4) was evaluated after 6 years since its addition. The MSWC significantly enhanced soil fertility parameters (i.e. total organic carbon, Olsen P and total N) and reduced the PTE labile fractions. The distribution maps of PTEs detected through µXRF analysis revealed the presence of Zn and Pb carbonates in the amended soils, or the formation of complexes between these PTEs and the functional groups of MSWC. A higher oral, inhalation and dermal bioaccessibility of each PTE was detected in the soil fine-grained fractions (< 2 and 2-10 µm) than in coarse particles (10-20 and 20-50 µm). The MSWC amendment generally did not modify the PTE bioaccessibility, while the relative bioaccessibility of cationic PTEs was greater than that of anionic ones (e.g. Cd > Zn > Pb > Sb > As). Pb and Sb showed the highest hazard quotients (e.g. 2.2 and 10 for Sb and Pb, respectively, in children). Overall, the results indicated that the MSWC used can be an effective option for the recovery of PTE-contaminated soils, even in the long term.

DWI-MR and PET-CT Functional Imaging for Boost Tumor Volume Delineation in Neoadjuvant Rectal Cancer Treatment.

BACKGROUND/AIM: T2 weighted magnetic resonance (MR) imaging is the gold standard for locally advanced rectal cancer (LARC) staging. The potential benefit of functional imaging, as diffusion-weighted MR (DWI) and positron emission tomography-computed tomography (PET-CT), could be considered for treatment intensification strategies. Dose intensification resulted in better pathological complete response (pCR) rates. This study evaluated the inter-observer agreement between two radiation oncologists, and the difference in gross tumor volume (GTV) delineation in simulation-CT, T2-MR, DWI-MR, and PET-CT in patients with LARC. PATIENTS AND METHODS: Two radiation oncologists prospectively delineated GTVs of 24 patients on simul-CT (CTGTV), T2-weighted MR (T2GTV), echo planar b1000 DWI (DWIGTV) and PET-CT (PETGTV). Observers' agreement was assessed using Dice index. Kruskal-Wallis test assessed differences between methods. RESULTS: Mean CTGTV, T2GTV, DWIGTV, and PETGTV were 41.3±26.9 cc, 25.9±15.2 cc, 21±14.8 cc, and 37.7±27.7 cc for the first observer, and 42.2±27.9 cc, 27.6±16.9 cc, 19.9±14.9cc, and 34.8±24.3 cc for the second observer, respectively. Mean Dice index was 0.85 for CTGTV, 0.84 for T2GTV, 0.82 for DWIGTV, and 0.89 for PETGTV, representative of almost perfect agreement. Kruskal-Wallis test showed a statistically significant difference between methods (p=0.009). Dunn test showed there were differences between DWIGTV vs. PETGTV (p=0.040) and DWIGTV vs. CTGTV (p=0.008). CONCLUSION: DWI resulted in smaller volume delineation compared to CT, T2-MR, and PET-CT functional images. Almost perfect agreements were reported for each imaging modality between two observers. DWI-MR seems to remain the optimal strategy for boost volume delineation for dose escalation in patients with LARC.

Stabilising fluoride in contaminated soils with monocalcium phosphate and municipal solid waste compost: microbial, biochemical and plant growth impact.

This study evaluated the influence of a municipal solid waste compost (MSWC) and monocalcium phosphate (MCP), alone or combined, on the mobility, toxicity, bioavailability and health risk of fluoride (1000 mg F-·kg-1) in an artificially polluted soil (pH 7.85). The addition of MCP (0.2% w/w) and MSWC (1% w/w) (alone and combined) to the contaminated soil reduced water-soluble (e.g. by more than 50% in MCP and MCP + MSWC-treated soils) and exchangeable F- fractions and increased the residual one. The addition of MSWC and MSWC + MCP to the contaminated soil significantly increased microbial biomass C (SMB-C; 1.3-3.6-fold) while all treatments increased the abundance of culturable heterotrophic bacteria (up to twofold in MSWC + MCP). Overall, dehydrogenase, ß-glucosidase, urease and phosphomonoesterase activities were enhanced in treated soils and positively correlated with SMB-C, but not with labile F-. All treatments increased carrot yield (up to 3.4-fold in MSWC + MCP), while bean growth was significantly enhanced only by MCP and MCP + MSWC (~ twofold). The opposite trend applied for F- uptake which was especially reduced in the edible part of carrot after soil amendment. A limited influence of MCP and MSWC on hazard quotient (HQ), due to bean and carrot consumption, was also recorded (i.e. HQ generally > 1). Results suggest that MCP and MSWC can be used in the recovery of soil chemical, microbial and biochemical status of F-rich agricultural soils. They also indicate that the bean and carrot cultivars employed in this study are likely unsuitable in such soils due to high F- uptake in edible parts.

Impact of Eisenia fetida earthworms and biochar on potentially toxic element mobility and health of a contaminated soil.

This study aimed to evaluate the influence of Eisenia fetida (Savigny), added to an acidic soil contaminated with potentially toxic elements (PTEs; As, Sb, Cd, Pb, Zn) and amended with a softwood-derived biochar (2 and 5% w/w), on the mobility of PTEs and soil health (i.e. nutrient availability, enzyme activity and soil basal respiration). The PTEs bioaccumulation by E. fetida and the acute ecotoxicity effects of the amended soils were also evaluated. The interaction between earthworms and biochar led to a significant increase in soil pH, organic matter, dissolved organic carbon content, cation exchange capacity, and exchangeable Ca compared to the untreated soil. Moreover, the water-soluble and readily exchangeable PTE fraction decreased (with the exception of Sb) between 1.2- and 3.0-fold in the presence of biochar and earthworms. Earthworms, biochar, and their combination, led to a reduction of phosphomonoesterase activity which in soils amended with biochar and earthworms decreased between 2.2- and 2.5-fold with respect to the untreated soil. On the other hand, biochar and earthworms also enhanced soil basal respiration and protease activity. Although the survival rate and the weight loss of E. fetida did not change significantly with the addition of 2% biochar, adding the highest biochar percentage (5%) resulted in a survival rate that was ~2-fold lower and a weight loss that was 2.5-fold higher than the other treatments. The PTE bioaccumulation factors for E. fetida, which were less than 1 for all elements (except Cd), followed the order Cd > As>Zn > Cu > Pb > Sb and were further decreased by biochar addition. Overall, these results highlight that E. fetida and biochar, especially at 2% rate, could be used for the restoration of soil functionality in PTE-polluted environments, reducing at the same time the environmental risks posed by PTEs, at least in the short time.

Microbial and chemical dynamics of brewers' spent grain during a low-input pre-vermicomposting treatment.

The eco-sustainability of industrial processes relies on the proper exploitation of by-products and wastes. Recently, brewers' spent grain (BSG), the main by-product of brewing, was successfully recycled through vermicomposting to produce an organic soil conditioner. However, the pre-processing step there applied (oven-drying) resulted in high costs and the suppression of microbial species beneficial for soil fertility. To overcome these limitations, a low-input pre-processing step was here applied to better exploit BSG microbiota and to make BSG suitable for vermicomposting. During 51 days of pre-treatment, the bacterial and fungal communities of BSG were monitored by denaturing gradient gel electrophoresis (DGGE). Chemical (carbon, nitrogen, ammonium, nitrate content, dissolved organic carbon) and biochemical (dehydrogenase activity) parameters were also evaluated. Mature vermicompost obtained from pre-processed BSG was characterized considering its legal requirements (e.g., absence of pathogens and mycotoxins, lack of phytotoxicity on seeds), microbiota composition, and chemical properties. Results obtained showed that throughout the pre-process, the BSG microbiota was enriched in bacterial and fungal species of significant biotechnological and agronomic potential, including lactic acid bacteria (Weissella, Pediococcus), plant growth-promoting bacteria (Bacillus, Pseudomonas, Pseudoxhantomonas), and biostimulant yeasts (Pichia fermentans, Trichoderma reesei, Beauveria bassiana). Pre-processing increased the suitability of BSG for earthworms' activity to produce high-quality mature vermicompost.

Insights into the fate of antimony (Sb) in contaminated soils: Ageing influence on Sb mobility, bioavailability, bioaccessibility and speciation.

The effect of long-term ageing (up to 700 days) on the mobility, potential bioavailability and bioaccessibility of antimony (Sb) was investigated in two soils (S1: pH 8.2; S2: pH 4.9) spiked with two Sb concentrations (100 and 1000 mg·kg-1). The Sb mobility decreased with ageing as highlighted by sequential extraction, while its residual fraction significantly increased. The concentration of Sb (CDGT), as determined by diffusive gradients in thin films (DGT), showed a reduction in potential contaminant bioavailability during ageing. The DGT analysis also showed that Sb-CDGT after 700 days ageing was significantly higher in S1-1000 compared to S2-1000, suggesting soil pH plays a key role in Sb potential bioavailability. In-vitro tests also revealed that Sb bioaccessibility (and Hazard Quotient) decreased over time. Linear combination fitting of Sb K-edge XANES derivative spectra showed, as a general trend, an increase in Sb(V) sorption to inorganic oxides with ageing as well as Sb(V) bound to organic matter (e.g. up to 27 and 37% respectively for S2-100). The results indicated that ageing can alleviate Sb ecotoxicity in soil and that the effectiveness of such processes can be increased at acidic pH. However, substantial risks due to Sb mobility, potential bioavailability and bioaccessibility remained in contaminated soils even after 700 days ageing.

Evaluation of Cynara cardunculus L. and municipal solid waste compost for aided phytoremediation of multi potentially toxic element-contaminated soils.

The suitability for aided phytoremediation of Cynara cardunculus L. var. altilis and municipal solid waste compost (MSWC) applied at 2% and 4 % rates was evaluated in a multi potentially toxic element (PTE)-contaminated mining soil (Pb ~ 15,383 mg kg-1, Zn ~ 4076 mg kg-1, As ~ 49 mg kg-1, Cd ~ 67 mg kg-1, Cu ~ 181 mg kg-1, and Sb ~ 109 mg kg-1). The growth of C. cardunculus significantly increased with compost amendment and followed the order: MSWC-4% > MSWC-2% > Control. PTE concentrations in the roots of plants grown on amended soils decreased compared with control plants (i.e., less than ~ 82, 94, and 88% for Pb, Zn, and Cd respectively). PTE translocation from roots to shoots depended on both PTE and amendment rate but values were generally low (i.e., < 1). However, PTE mineralomasses were always higher for plants grown on MSWC-amended soils because of their higher biomass production, which favored an overall PTE bioaccumulation in roots and shoots. After plant growth, labile As and Sb increased in amended soils, while labile Pb, Zn, Cu, and Cd significantly decreased. Likewise, dehydrogenase and urease activities increased significantly in planted soils amended with MSWC. Also, the potential metabolic activity and the catabolic versatility of soil microbial communities significantly increased in planted soils amended with MSWC. Overall, our results indicate that C. cardunculus and MSWC can be effective resources for the aided phytoremediation of multi PTE-contaminated soils.

Addition of softwood biochar to contaminated soils decreases the mobility, leachability and bioaccesibility of potentially toxic elements.

Softwood-derived biochar (5% w/w) was added to two mining soils (S1 and S2) contaminated with Cd (4.8-74 mg kg-1), Pb (318-1899 mg kg-1) and Zn (622-3803 mg kg-1), to evaluate its immobilization capabilities towards such potentially toxic elements (PTEs). Biochar addition (S + B) increased soil pH, organic carbon content, extractable phosphorous and calcium. Sequential extractions showed that biochar reduced the labile pools of PTEs (e.g. -29, 55 and 79% of water-soluble and exchangeable Cd, Zn and Pb respectively in S1 + B compared to S1) and at the same time increased their most stable and less mobile fractions. Leaching experiments revealed a significant decrease of DOC, N-NO3-, P and PTEs in biochar-treated soils, and an increase of leached K. Kinetic equations derived from leaching data showed that PTEs in control soils were quickly mobilized, while those in biochar-treated soils needed longer time to leachate. In vitro tests showed that biochar was effective at reducing the bioaccessibility of Cd and Pb in the gastric phase of S2 and that of Zn and Pb in the intestinal phase of S1. The results obtained showed that biochar could be used as alternative amendment for the recovery of PTEs-contaminated soils.

Fragment-based Differential Targeting of PPI Stabilizer Interfaces.

Stabilization of protein-protein interactions (PPIs) holds great potential for therapeutic agents, as illustrated by the successful drugs rapamycin and lenalidomide. However, how such interface-binding molecules can be created in a rational, bottom-up manner is a largely unanswered question. We report here how a fragment-based approach can be used to identify chemical starting points for the development of small-molecule stabilizers that differentiate between two different PPI interfaces of the adapter protein 14-3-3. The fragments discriminately bind to the interface of 14-3-3 with the recognition motif of either the tumor suppressor protein p53 or the oncogenic transcription factor TAZ. This X-ray crystallography driven study shows that the rim of the interface of individual 14-3-3 complexes can be targeted in a differential manner with fragments that represent promising starting points for the development of specific 14-3-3 PPI stabilizers.

Mobility and potential bioavailability of antimony in contaminated soils: Short-term impact on microbial community and soil biochemical functioning.

Antimony (Sb) and its compounds are emerging priority pollutants which pose a serious threat to the environment. The aim of this study was to evaluate the short-term fate of antimonate added to different soils (S1 and S2) with respect to its mobility and impact on soil microbial communities and soil biochemical functioning. To this end, S1 (sandy clay loam, pH 8.2) and S2 (loamy coarse sand, pH 4.9) soils were spiked with 100 and 1000 mg Sb(V) kg-1 soil and left in contact for three months. Sequential extractions carried out after this contact time indicated a higher percentage of labile antimony in the Sb-spiked S1 soils than S2 (e.g. ~13 and 4% in S1 and S2 treated with 1000 mg Sb(V) kg-1 respectively), while the opposite was found for residual (hardly bioavailable) Sb. Also, a reduced number of culturable heterotrophic bacteria was recorded in Sb-spiked S1 soil (compared to the unpolluted S1), while an increased one was found in S2. Heterotrophic fungi followed the opposite trend. Actinomycetes and heat-resistant aerobic bacterial spores showed a variable trend depending on the soil type and Sb(V) treatment. The Biolog community level physiological profile indicated a reduced metabolic activity potential of microbial communities from the Sb-spiked S1 soils (e.g. <50% for Sb-1000 compared to the unpolluted S1), while an increase was recorded for those extracted from the Sb-spiked S2 soils (e.g. >2-fold for Sb-1000). The soil dehydrogenase activity followed the same trend. High-throughput 16S rRNA amplicon sequencing analysis revealed that Sb did not influence the bacterial α-diversity in both soils, while significantly affected the composition of the respective soil bacterial communities. Several phyla (e.g. Nitrosospira Nitrososphaeraceae, Adheribacter) were found positively correlated with the concentration of water-soluble Sb in soil. Overall, the results obtained suggest that the risk assessment in soils polluted with antimony should be a priority especially for alkaline soils where the high mobility of the anionic Sb(OH)6- species can pose, at least in the short-term, a serious threat for soil microbial abundance, diversity and functionality, soil fertility and eventually human health.

Biochar and compost as gentle remediation options for the recovery of trace elements-contaminated soils.

The use of organic-based amendments for gentle remediation options (GRO), i.e. the stabilization of trace elements (TE) in polluted soils and the reduction of their impact on soil microbial and biochemical features, has been constantly growing in last 10 years. To verify the effectiveness of biochar and compost in such context, biochar (1 and 3% w/w), compost (3% w/w) and their combination (compost 2% + biochar 2% w/w) were added to two sub-alkaline soils (FS and MS) contaminated with Sb (41-99 mg kg-1 respectively), As (~18 mg kg-1), and trace metals such as Ni (103-172 mg kg-1 respectively) and Cr (165-132 mg kg-1 respectively). Most of the treatments (especially 3% biochar) reduced labile TE pools (water-soluble and exchangeable) and increased their residual (non-extractable) fractions (e.g. +48, 56, 66, and 68% of residual Sb, As, Cr and Ni in MS-treated soil compared to the untreated control). The amendments addition had both stimulating and inhibiting effects on the activity of soil microbial communities, as shown by the Biolog community level physiological profiles. However, in both soils, 3% biochar produced the highest increase of metabolic potential as well as the use of carboxylic acids and polymers by the soil microbial communities. Likewise, soil dehydrogenase (DHG), ß-glucosidase (ß-GLU) and urease (URE) activities were significantly enhanced in FS and MS soils treated with 3% biochar (e.g. +77, 48, and 17% for DHG, URE and ß-GLU in FS-3% biochar with respect to untreated FS). Overall, the results from this study showed that the amendments investigated (particularly 3% biochar) can be effectively used for GRO of sub-alkaline soils, being able to reduce labile TE and to increase the metabolic potential and actual biochemical activities of the respective soil microbial communities. The manifold environmental implications of such effects are discussed.

Mobility, bioaccessibility and toxicity of potentially toxic elements in a contaminated soil treated with municipal solid waste compost.

The aim of this study was to assess the influence of a municipal solid waste compost (MSWC) on the mobility, bioaccessibility and toxicity of several potentially toxic elements (PTE), i.e. Pb (15,383 mg kg-1), Zn (4076 mg kg-1), Cu (181 mg kg-1), Sb (109 mg kg-1), Cd (67 mg kg-1) and As (49 mg kg-1), present in a contaminated sub-acidic soil (pH = 5.93). The addition of MSWC at 2 and 4% rates significantly decreased the labile fractions of PTE (with the exception of Cu and As) and at the same time increased the residual fractions of Zn and Sb. In-vitro tests also showed that compost amendment was able to decrease Cd and Cu gastric bioaccessibility, with respect to untreated soil (-19 and 13% of Cd and Cu in MSWC-4% respectively), while a significant increase of As intestinal bioaccessibility was recorded. This increment was attributed to the pH rise (up to 7.0) during the in-vitro intestinal phase, which likely favoured a release of the arsenic non-specifically bonded to MSWC. Soil enzyme activities, i.e. dehydrogenase and ß-glucosidase, were significantly enhanced in MSWC-amended soils (i.e. up to ~6.0 and 1.4 times higher in MSWC-4% than in control soil, respectively), as well as soil basal respiration, and the potential metabolic activity and catabolic versatility of soil microbial communities (as assessed by the Biolog ecoplate community level physiological profile). Overall, the results obtained suggested that MSWC, particularly at 4% rate, could be useful to stabilise PTE in sub-acidic contaminated soils and to increase the microbial activity and functionality in these latter soils.

Sb(V) adsorption and desorption onto ferrihydrite: influence of pH and competing organic and inorganic anions.

In this study, we investigated the Sb(V) adsorption on ferrihydrite (Fh) at different pH values, in the presence and absence of common competing anions in soil such as phosphate (P(V)) and arsenate (As(V)). Batch adsorption experiments, carried out at pH 4.5, 6.0, and 7.0, showed a greater affinity of Fh towards P(V) and As(V) with respect to Sb(V), especially at higher pH values, while the opposite was true at acidic pH. The capacity of Fh to accumulate greater amounts of phosphate and arsenate in the 6.0-7.0 pH range was mainly linked to the different acid properties of P(V), As(V), and Sb(V) oxyanions. The Sb(V) adsorption on Fh was highly pH-dependent and followed the following order: pH 4.5 (0.957 mmol·g-1 Fh) > pH 6.0 (0.701 mmol·g-1 Fh) > pH 7.0 (0.583 mmol·g-1 Fh). Desorption of antimonate from Sb(V)-saturated Fh, treated with citric and malic acid solutions, was ~equal to 55, 68, and 76% of that sorbed at pH 4.5, 6.0, and 7.0, respectively, while phosphate, arsenate, and sulfate were able to release significantly lower Sb(V) amounts. The FT-IR spectra revealed substantial absorbance shifts related to the surface hydroxyl groups of Fh, which were attributed to the formation of Fe-O-Sb(V) bonds and supported the formation of inner-sphere bonding between Sb(V) and Fh.

Municipal solid wastes as a resource for environmental recovery: Impact of water treatment residuals and compost on the microbial and biochemical features of As and trace metal-polluted soils.

In this study we evaluated the microbiological and biochemical impact of iron-based water treatment residuals (Fe-WTRs) and municipal solid waste compost (MSWC), alone and combined, on three different soils co-contaminated with arsenic (As) and trace-metals (TM), i.e. Pb, Cu and Zn. Overall, all the amendments considered significantly increased the abundance of culturable heterotrophic bacteria, with MSWC showing the greatest impact across all soils (up to a 24% increase). In most of treated soils this was accompanied by a significant reduction of both the (culturable) fungal/bacterial ratio, and the proportion of culturable As(V)- and As(III)-resistant bacteria with respect to total bacterial population. The catabolic potential and versatility of the resident microbial communities (assessed by community level physiological profile) was highly soil-dependent and substantial increases of both parameters were observed in the amended soils with the higher total As concentration (from approx. 749 to 22,600 mg kg-1). Moreover, both carbon source utilisation profile and 16S rRNA soil metagenome sequencing indicated a significant impact of MSWC and Fe-WTRs on the structure and diversity of soil microbial communities, with Proteobacteria, Actinobacteria and Firmicutes being the most affected taxa. The assessment of selected soil enzyme activities (dehydrogenase, urease and ß-glucosidase) indicated an increase of metabolic functioning especially in soils treated with MSWC (e.g. dehydrogenase activity increased up to 19.5-fold in the most contaminated soil treated with MSWC). Finally, the microbial and biochemical features of treated (and untreated) contaminated soils (i.e. total bacterial counts, catabolic potential and versatility and soil enzyme activities) were highly correlated with the concentrations of labile As and TM in these latter soils and supported a clear role of the tested amendments (especially MSWC) as As- and TM-immobilising agents.

Municipal solid waste compost as a novel sorbent for antimony(V): adsorption and release trials at acidic pH.

The ability of two municipal solid waste composts (MSW-Cs) to sorb antimony(V) in acidic conditions (pH 4.5) was investigated. Sorption isotherms and kinetics showed that both MSW-Cs could sorb antimony(V), even if in different amounts (~ 0.18 and 0.24 mmol g-1 of Sb(V) by MSW-C1 and MSW-C2, respectively). These differences were ascribed to the chemical composition of composts, as well as to the total acidity of their humic substances. The Sb(V) sorption by both MSW-Cs followed a pseudo-second-order kinetic model, while the sorption isotherms data fitted the Freundlich model better than the Langmuir one. The humic acids extracted from composts contributed to 4.26 and 8.24% of Sb(V) sorption by MSW-C1 and MSW-C2 respectively. SEM-EDX spectra of the MSW-C+Sb(V) systems showed a certain association of Ca(II) with Sb(V), while sequential extraction procedures indicated that more than 80% of the Sb(V) sorbed was strongly retained by MSW-Cs. On the other hand, treatment with oxalic acid at pH 4.5 favored the release of more than 98 and 65% of the Sb(V) sorbed by MSW-C1 and MSW-C2 respectively, supporting a possible role of calcium in Sb(V) retention. The results from this study suggest that MSW-Cs could be used as amendments for the in-situ immobilization of Sb(V) in acidic-polluted soils.