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.

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.

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.

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.

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.

Soil microbial response to tetracycline in two different soils amended with cow manure.

High amounts of antibiotics are introduced in the soil environment by manure amendment, which is the most important spreading route in soil, with a potential ecotoxicological impact on the environment. The objectives of this study were (a) to assess the tetracycline (Tc) bioavailability in a clay and in a sandy soil, and (b) to evaluate the effects of the Tc and cow manure on the structure and function of soil microbial communities. Clay and sandy soils were spiked with Tc at the concentrations of 100 and 500 mg Tc kg(-1) soil, and were amended or not with cow manure. The clay soil showed greater Tc sorption capacity and bioavailable Tc was between 0.157 and 4.602 mg kg(-1) soil. Tc dose and time-dependent effects on soil microbial communities were investigated by fluorescein diacetate activity, phospholipid fatty acids analysis, as well as by Biolog community level physiological profile and microbial counts at 2, 7 and 60 days after Tc and/or manure addition. The added Tc caused detrimental effect on the microbial activity and structure, particularly in the short term at the highest concentrations. However, the Tc effect was transient' it decreased after 7 days and totally disappeared within 60 days. Cow manure shifted the bacterial structure in both soils, increased the microbial activity in clay soil and contributed to recover the microbial structure in Tc-spiked manure treatments.

Soil sorption and leaching of active ingredients of Lumax® under mineral or organic fertilization.

The study describes the soil sorption of the herbicide Lumax®, composed of S-metolachlor (MTC), terbuthylazine (TBZ), and mesotrione (MST), as influenced by mineral and organic fertilizers. The investigation was performed on a sandy soil of an agricultural area designated as a Nitrate Vulnerable Zone, where mineral and organic fertilizers were applied for many years. Two organic fertilizers, cattle manure and slurry, respectively, and a mineral fertilizer with a nitrification inhibitor, Entec®, were compared. According to the experiments, performed with a batch method, the sorption conformed to Freundlich model. The extent of sorption of Lumax® ingredients was closely related to their octanol-water partition coefficient Kow. The respective desorption was hysteretic. Leaching trials were carried out by using water or solutions of DOM or Entec® as the eluants. Only the elution with the mineral fertilizer promoted the leaching of Lumax® active ingredients.

Influence of the isomerism on the sorption of imazamethabenz-methyl by soil.

The sorption of meta and para isomers of the herbicide imazamethabenz-methyl, methyl 6-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-m- or p-toluate, by three soils and soil organic matter, was studied. Sorption isotherms conformed to the Freundlich equation. It was found that pH was the main factor influencing the adsorption in all of the systems. The highest level of sorption was measured on soils with low pH and high organic carbon content. Moreover, at low pH value, the soil rich in smectite clays, favoured the sorption of meta rather than para isomer. The higher affinity of clay surfaces for the meta isomer of the herbicide is due to the stabilization of the meta protonated form by resonance. At all pH values, the sorption on soil organic matter did not differ between two isomers.

Sorption behavior of sulfamethazine on unamended and manure-amended soils and short-term impact on soil microbial community.

In this study we investigated the sorption of sulfamethazine (SMZ) in two soils with different physico-chemical properties and the sulfonamide short-term influence on the microbial community structure and function. The presence of manure increased the SMZ sorption, the uppermost level being measured on soil with the lower pH and the higher manure content allowed by the Italian regulation. The sulfonamide desorption was hysteretic on both soils. SMZ addition to soil at the concentration of 53.6 µg/g had a significant short-term negative impact on readily culturable bacteria, potential metabolic activity (Biolog CLPP) and soil enzyme activity. Moreover, a shift of the culturable microbial populations towards a lower bacteria/fungi ratio was observed after SMZ addition. Despite the observed SMZ effects disappeared almost completely after 7 day, structural changes of microbial communities were still present in SMZ-treated soils. The results presented are remarkable since previous studies addressing the SMZ impact on soil microbial parameters failed to highlight any significant effect of the sulfonamide on microbial abundance and diversity.

Direct and indirect photolysis of two quinolinecarboxylic herbicides in aqueous systems.

The photodegradation of two quinolinecarboxylic herbicides, 7-chloro-3-methylquinoline-8-carboxylic acid (QMe) and 3,7-dichloroquinoline-8-carboxylic acid (QCl), was studied in aqueous solution at different irradiation wavelengths. The effect of sunlight irradiation was investigated also in the presence of titanium dioxide (TiO(2)). UV irradiation degraded rapidly QMe affording 7-chloro-3-methylquinoline (MeQ) through a decarboxylation reaction. The reaction rate was lower in the presence of dissolved organic carbon (DOC) because of the adsorption of the herbicide on the organic components. Instead, QCl was stable under both UV light and sunlight irradiation. The irradiation of QMe or QCl solutions with simulated sunlight in the presence of TiO(2) produced the complete mineralization of the two herbicides.

Direct and indirect photolysis of cyhalofop in aqueous systems.

The photodegradation of the aryloxyphenoxy propionic herbicide cyhalofop-butyl (2R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]butylpropanoate (CyB), and of its primary metabolite (2R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoic acid (CyA) was studied in water at different irradiation wavelengths. The sunlight irradiation was investigated also in the presence of humic acid (HA), Fe oxide, titanium dioxide (TiO2) and zinc oxide (ZnO) as photocatalysts. CyB and CyA were rapidly degraded by UV irradiation. CyB afforded the butyl ester of 2-[3-(4-cyano-2-fluorophenyl)-4-hydroxy-phenoxy]propanoic acid (CyI), a metabolite arising from a photo-Fries rearrangement. Instead, CyA yielded (R)-2-4-(4-carboxyl-2-fluorophenoxy)phenoxypropanoic acid (CyD), a dicarboxylic acid arising from the photo-hydrolysis of cyano group via amide. CyB was stable in simulated sunlight also in the presence of the catalysts tested. The irradiation of a CyA solution, in the presence of HA or Fe oxide, with simulated sunlight did not produce any significant degradation. In the same experimental conditions, CyA was totally mineralized in the presence of TiO2 and ZnO.

Effects of a municipal sewage sludge amendment on triasulfuron soil sorption and wheat growth.

The influence of municipal sewage sludge (SL) as a soil amendment on the sorption and activity of the herbicide triasulfuron (TRS, [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide]) was studied. Weed control was checked in a greenhouse on a wheat (Triticum turgidum L. subsp. durum) crop. At the highest SL amount allowed by Italian regulation, TRS sorption onto soil increased by 7 times and weed control was unaffected. A vegetative bloom and an early heading phase were noted. To compare inorganic fertilization (N, P, and K) and SL amendment, a greenhouse fertilization experiment was carried out. The SL-amended crop developed larger leaf surfaces, higher biomass, and a forward heading compared to that fertilized with N, P, and K. The SL hormone-like activity was evaluated by measuring auxin- and gibberellin-like activity of sewage sludge.

Fenhexamid adsorption behavior on soil amended with wine lees.

The adsorption of fenhexamid (FEN) [N-(2,3-dichloro-4-hydroxyphenyl)-1-methylcyclohexanecarboxamide] on vineyard soil amended with wine lees (WL) produced by vinery was studied. The adsorption extent depends on WL fraction. The addition of the centrifuged solid lees (SWL) increases the FEN adsorption on soil. Most likely, the organic insoluble fraction formed mainly by dead fermentation yeasts is responsible for the observed increase. The adsorption measured on some deactivated yeasts of wine fermentation shows that Saccharomyces cerevisiae are the most active in FEN retention. On the other hand, the soil amendment with whole WL decreases considerably the fungicide adsorption. This opposite effect may be the result of FEN hydrophobic bonds with the dissolved organic matter of lees that keeps fungicide in solution. This hypothesis is substantiated by the increased FEN solubility in the supernatant of centrifuged wine lees (LWL). The results of soil column mobility confirm that the elution with LWL increases the mobility of FEN in soil.

Hydrolysis and adsorption of cyhalofop-butyl and cyhalofop-acid on soil colloids.

A study was undertaken to investigate the stability of cyhalofop-butyl (2 R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]butylpropanoate (CyB), an aryloxyphenoxy-propionic herbicide, at different pH values. The hydrolysis of CyB was faster in nonsterile than in sterile water. In sterile medium, CyB degraded only to (2 R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoic acid (CyA), whereas in nonsterile water, also the metabolites (2 R)-2-[4-(4-carbamoyl-2-fluorophenoxy)phenoxy]propanoic acid (CyAA) and (2 R)-2-[4-(4-carboxyl-2-fluorophenoxy)phenoxy]propanoic acid (CyD) were detected. The adsorption of CyB onto clays, iron oxide, and dissolved organic matter (DOM), using a batch equilibrium method, was also studied. A lipophilic bond is responsible for CyB adsorption on DOM. CyB was adsorbed on Fe(III)- and Ca-clays through hydrogen bonding between the carbonyl oxygen and water surrounding the exchangeable cations. In the interlayer of K-clay, CyB was hydrolyzed to CyA, which remained adsorbed therein as a monomer. The acid CyA was adsorbed only by the Fe-oxide through complexation. The CyA-Fe-oxide complex was stable and did not undergo degradation.