A systematic review on the bioremediation of metal contaminated soils using biochar and slag: current status and future outlook

Heavy metals contaminated soils are posing severe threats to food safety worldwide. Heavy metals absorbed by plant roots from contaminated soils lead to severe plant development issues and a reduction in crop yield and growth. The global population is growing, and the demand for food is increasing. Therefore, it is critical to identify soil remediation strategies that are efficient, economical, and environment friendly. The use of biochar and slag as passivators represents a promising approach among various physicochemical and biological strategies due to their efficiency, cost-effectiveness, and low environmental impact. These passivators employ diverse mechanisms to reduce the bioavailability of metals in contaminated soils, thereby improving crop growth and productivity. Although studies have shown the effectiveness of different passivators, further research is needed globally as this field is still in its early stages. This review sheds light on the innovative utilization of biochar and slag as sustainable strategies for heavy metal remediation, emphasizing their novelty and potential for practical applications. Based on the findings, research gaps have been identified and future research directions proposed to enable the full potential of passivators to be utilized effectively and efficiently under controlled and field conditions.

NPA-Cu2+ Complex as a Fluorescent Sensing Platform for the Selective and Sensitive Detection of Glyphosate

Glyphosate is a highly effective, low-toxicity, broad-spectrum herbicide, which is extensively used in global agriculture to control weeds and vegetation. However, glyphosate has become a potential threat to human and ecosystem because of its excessive usage and its bio-concentration in soil and water. Herein, a novel turn-on fluorescent probe, N-n-butyl-4-(3-pyridin)ylmethylidenehydrazine-1,8-naphthalimide (NPA), is proposed. It efficiently detected Cu2+ within the limit of detection (LOD) of 0.21 μM and displayed a dramatic turn-off fluorescence response in CH3CN. NPA-Cu2+ complex was employed to selectively and sensitively monitor glyphosate concentrations in real samples accompanied by a fluorescence turn-on mode. A good linear relationship between NPA and Cu2+ of glyphosate was found in the range of 10-100 μM with an LOD of 1.87 μM. Glyphosate exhibited a stronger chelation with Cu2+ than NPA and the system released free NPA through competitive coordination. The proposed method demonstrates great potential in quantitatively detecting glyphosate in tap water, local water from Songhua River, soil, rice, millet, maize, soybean, mung bean, and milk with mild conditions, and is a simple procedure with obvious consequences and no need for large instruments or pretreatment.

Toxic metal phytoextraction potential and health-risk parameters of some cultivated plants when grown in metal-contaminated river sediment of Danube, near an industrial town

Toxic metal phytoextraction potential of some higher plants, the white mustard (Sinapis alba L.), perennial rye grass (Lolium perenne L.) and also two cultivated plants, as green pea (Pisum sativum L. var. Rajnai törpe), radish (Raphanus sativus L. var. Szentesi óriás vaj), was studied in a field experiment, along the river Danube in close vicinity of an industrial town, Dunaújváros, Hungary. Soil/sediment and the various plant organs (leaves, stems and roots) were assessed for the contamination with some potentially toxic elements (PTE), such as the cadmium (Cd), nickel (Ni), copper (Cu), and zinc (Zn). It was found that Cd and Ni concentration was below, while the Cu and Zn elements were above the Hungarian permissible limits in each of the studied soil/sediment samples. Bioconcentration factor (BAF) was less than 1 in the shoot biomass of test plant samples and followed the order of Cu > Zn > Cd and Ni. Phytoremediation potential of selected test plants was found to be rather limited. The translocation factor (TF) was more than 1 for Cu and Zn elements, at each test plants. Cadmium was translocated into the leaves in case of the radish, only. Considering of the potential human daily intake of metals (DIM), it was less than 1 both for the adults and for the children. Health risk index (HRI) values of children, however, were higher than 1 for the Cd in case of radish, and for Zn and Cu in case of the pea. Results suggest that consumption of these plants grown in gardens of contaminated sediments can result in some risks for citizens in the industrial town of Dunaújváros. Further studies are required to identify appropriate plants with greater toxic metal phytoextraction potential.

Speciation of Zn and Cu in Technosol and evaluation of a sequential extraction procedure using XAS, XRD and SEM-EDX analyses

Metal speciation, linked directly to bioaccessibility and lability, is a key to be considered when assessing associated human and environmental health risks originated from anthropogenic activities. To identify the Zn and Cu speciation in the highly contaminated, technogenically transformed soils (Technosol) from the impact zone near the industrial sludge reservoirs of chemical plant (Siverskyi Donets River floodplain, southern Russia), the validity of the BCR sequential extraction procedure using the X-ray absorption fine-structure and X-ray powder diffraction (XRD) analyses was examined after each of the three stages. After the removal of exchange and carbonate-bonded Zn and Cu compounds from Technosol (first stage of extraction), the resulting residual soil showed enrichment in a great diversity of metal compounds, primarily with Me-S and Me-O bonds. The number of compounds with a higher solubility decreased at the subsequent stages of extraction. In the residual soil left over after extracting the first and second fractions, the dominant Zn-S bond appeared as würtzite (hexagonal ZnS) that made up more than 50%, while the Cu-S bond was almost completely represented only by chalcocite (Cu₂S). The XRD analysis revealed the authigenic minerals of metals with S: sphalerite (cubic ZnS), würtzite (hexagonal ZnS), covellite (CuS) and bornite (Cu₅FeS₄). The scanning electron microscopy data confirmed that würtzite was the dominant form of Me with sulfur-containing and carbonate-containing minerals. The Zn-S bond was the main component (57%), whereas the Cu-O bond was dominant in the residual fraction (the fraction after the third-stage extraction). The results revealed that the composition of the residual fractions might include some of the most stable and hard-to-recover metal compounds of technogenic origin. Thus, the application of the novel instrumental methods, coupled with the chemical fractionation, revealed the incomplete selectivity of the extractants in the extraction of Zn and Cu in long-term highly contaminated soils.

Ultrasound-assisted soil washing processes for the remediation of heavy metals contaminated soils: The mechanism of the ultrasonic desorption

Ultrasound-assisted soil washing processes were investigated for the removal of heavy metals (Cu, Pb, and Zn) in real contaminated soils using HCl and EDTA. The ultrasound-assisted soil washing (US/Mixing) process was compared with the conventional soil washing (Mixing) process based on the mechanical mixing. High removal efficiency (44.8% for HCl and 43.2% for EDTA) for the metals was obtained for the most extreme conditions (HCl 1.0 M or EDTA 0.1 M and L:S = 10:1) in the Mixing process. With the aide of ultrasound, higher removal efficiency (57.9% for HCl and 50.0% for EDTA) was obtained in the same extreme conditions and similar or higher removal efficiency (e.g., 54.7% for HCl 0.5 M and L:S = 10:1 and 50.5% for EDTA 0.05 M and L:S = 5:1) was achieved even in less extreme conditions (lower HCl or EDTA concentration and L:S ratio). Therefore, it was revealed that the US/Mixing was advantageous over the conventional Mixing processes in terms of metal removal efficiency, consumption of chemicals, amount of generated washing leachate, and volume/size of washing reactor. In addition, the heavy metals removal was enhanced for the smaller soil particles in the US/Mixing process. It was due to more violent movement of smaller particles in slurry phase and more violent sonophysical effects. In order to understand the mechanism of ultrasonic desorption, the desorption test was conducted using the paint-coated beads with three sizes (1, 2, and 4 mm) for the free and attached conditions. It was found that no significant desorption/removal of paint from the beads was observed without the movement of beads in the water including floatation, collision, and scrubbing. Thus, it was suggested that the simultaneous application of the ultrasound and mechanical mixing could enhance the physical movement of the particles significantly and the very high removal/desorption could be attained.

About plant species potentially promising for phytoextraction of large amounts of toxic trace elements

There is no information yet about plant species capable of accumulating many different metals/metalloids. The plants feasible for phytoremediation aims must grow fast, have high biomass, deep roots, and should accumulate and tolerate a range of toxicants in their aerial parts. In our research, greenhouse and field experiments have been performed to investigate accumulation and tolerance of not well-studied trace elements such as Br, Eu, Sc, Th (and also U) in couch grass and wheat. We compared bioaccumulation abilities of the plants with those of some other plant species grown under the same conditions. Additionally, we tested the effects of inoculation of seeds with Cellulomonas bacteria on phytoextraction of the trace elements from contaminated soils. For determination of elements, we used neutron activation analysis and ICP-MS. It was found that couch grass and wheat can grow in heavily contaminated soils and accumulate different toxic trace elements to levels that exceed physiological requirements typical for most plant species. Infection of seeds with bacteria resulted in a significant increase in the uptake of various trace elements and their translocation to upper plant parts. The use of couch grass and/or wheat, either alone or in combination with microorganisms, is a promising way to phytoextract metals/metalloids from contaminated soils.

Study on the preparation of the hierarchical porous CX-TiO2 composites and their selective degradation of PHE solubilized in soil washing eluent

A series of CX-TiO₂(Carbon Xerogel- TiO₂) composites with a hierarchical porous structure were obtained through the sol-gel method followed by drying and carbonization, and have been applied to treating solubilizing wastewater containing a high concentration of phenanthrene (PHE). The characterizations demonstrated that the CX-TiO₂ exhibits a hierarchical porous structure, with particles of carbon and P25 being uniformly in the matrix. Removal efficiency of CX-TiO₂ on PHE in soil washing eluent (SWE) were evaluated under ultraviolet (UV) irradiation or dark condition, and P25 was employed as the reference. The results revealed that CX-TiO₂(0.2) had the best removal effect on PHE, with the efficiency as high as 97.8% under UV illumination within 15 h. It demonstrated that in the process of PHE removal by CX-TiO₂ whether it was under UV illumination or not, the adsorption plays a dominant role in the early stage. The kinetic behavior of PHE adsorption was fitted using the pseudo-first-order and pseudo-second-order, and Langmuir model and Freundlich models were applied to describe the PHE adsorption isotherms. The results indicating that it was a chemical adsorption process, which was influenced by the interaction between PHE and CX-TiO₂, and PHE is adsorbed on the interface of CX-TiO₂(0.2) in a single layer form, instead of agglomerating in the admicelle. A possible mechanism of removal of solubilized PHE in SWE was speculated, in which both hierarchical porous structure and appropriate micropores size of CX-TiO₂ were indispensable to the selective adsorption and degradation of PHE. Recycling performance certificated that the selective removal efficiency of PHE could still reach 82.09% after five recycles. Thus the excellent performance testified that the CX-TiO₂ have great potential in treating SWE containing solubilized PAHs.

Controls on δ26Mg variability in three Central European headwater catchments characterized by contrasting bedrock chemistry and contrasting inputs of atmospheric pollutants

Magnesium isotope ratios (²⁶Mg/²⁴Mg) can provide insights into the origin of Mg pools and fluxes in catchments where Mg sources have distinct isotope compositions, and the direction and magnitude of Mg isotope fractionations are known. Variability in Mg isotope compositions was investigated in three small, spruce-forested catchments in the Czech Republic (Central Europe) situated along an industrial pollution gradient. The following combinations of catchment characteristics were selected for the study: low-Mg bedrock + low Mg deposition (site LYS, underlain by leucogranite); high-Mg bedrock + low Mg deposition (site PLB, underlain by serpentinite), and low-Mg bedrock + high Mg deposition (site UDL, underlain by orthogneiss). UDL, affected by spruce die-back due to acid rain, was the only investigated site where dolomite was applied to mitigate forest decline. The δ²⁶Mg values of 10 catchment compartments were determined on pooled subsamples. At LYS, a wide range of δ²⁶Mg values was observed across the compartments, from -3.38 ‰ (bedrock) to -2.88 ‰ (soil), -1.48% (open-area precipitation), -1.34 ‰ (throughfall), -1.19 ‰ (soil water), -0.99 ‰ (xylem), -0.95 ‰ (needles), -0.82 ‰ (bark), -0.76 ‰ (fine roots), and -0.76 ‰ (runoff). The δ²⁶Mg values at UDL spanned 1.32 ‰ and were thus less variable, compared to LYS. Magnesium at PLB was isotopically relatively homogeneous. The δ²⁶Mg systematics was consistent with geogenic control of runoff Mg at PLB. Mainly atmospheric/biological control of runoff Mg was indicated at UDL, and possibly also at LYS. Our sites did not exhibit the combination of low-δ²⁶Mg runoff and high-δ²⁶Mg weathering products (secondary clay minerals) reported from several previously studied sites. Six years after the end of liming at UDL, Mg derived from dolomite was isotopically undetectable in runoff.

Factors affecting pluronic-coated iron oxide nanoparticle binding to petroleum hydrocarbon-impacted sediments

Effective targeted delivery of nanoparticle agents may enhance the remediation of soils and site characterization efforts. Nanoparticles coated with Pluronic, an amphiphilic block co-polymer, demonstrated targeted binding behaviour toward light non-aqueous phase liquids such as heavy crude oil. Various factors including coating concentration, oil concentration, oil type, temperature, and pH were assessed to determine their effect on nanoparticle binding to heavy crude oil-impacted sandy aquifer material. Nanoparticle binding was increased by decreasing the coating concentration, increasing oil concentration, using heavier oil types, and increasing temperature, while pH over the range of 5-9 was found to have no effect. Nanoparticle transport and binding in columns packed with clean and oily porous media demonstrated the ability for efficient nanoparticle targeted binding. For the conditions explored, the attachment rate coefficient in columns packed with clean sand was 2.10 ± 0.66 × 10^-4 s^-1; however, for columns packed with oil-impacted sand a minimum attachment rate coefficient of 8.86 ± 0.43 × 10^-4 s^-1 was estimated. The higher attachment rate for the oil-impacted sand system indicates that nanoparticles may preferentially accumulate to oil-impacted zones present at heterogeneous impacted sites. Simulations were used to demonstrate this hypothesis using the set of parameters generated in this effort. This work contributes to our understanding of the application conditions that are required for efficient targeted binding of nanoparticles to crude-oil impacted porous media.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters β^m and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (K_m) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.

Synthetic biology approaches towards the recycling of metals from the environment

Metals are a finite resource and their demand for use within existing and new technologies means metal scarcity is increasingly a global challenge. Conversely, there are areas containing such high levels of metal pollution that they are hazardous to life, and there is loss of material at every stage of the lifecycle of metals and their products. While traditional resource extraction methods are becoming less cost effective, due to a lowering quality of ore, industrial practices have begun turning to newer technologies to tap into metal resources currently locked up in contaminated land or lost in the extraction and manufacturing processes. One such technology uses biology for the remediation of metals, simultaneously extracting resources, decontaminating land, and reducing waste. Using biology for the identification and recovery of metals is considered a much 'greener' alternative to that of chemical methods, and this approach is about to undergo a renaissance thanks to synthetic biology. Synthetic biology couples molecular genetics with traditional engineering principles, incorporating a modular and standardised practice into the assembly of genetic parts. This has allowed the use of non-model organisms in place of the normal laboratory strains, as well as the adaption of environmentally sourced genetic material to standardised parts and practices. While synthetic biology is revolutionising the genetic capability of standard model organisms, there has been limited incursion into current practices for the biological recovery of metals from environmental sources. This mini-review will focus on some of the areas that have potential roles to play in these processes.

Robust Matrix Effect-Free Method for Simultaneous Determination of Legacy and Emerging Per- and Polyfluoroalkyl Substances in Crop and Soil Matrices

Increasing use of emerging per- and polyfluoroalkyl substances (PFASs) has caused extensive concerns around the world. Effective detection methods to trace their pollution characteristics and environmental behaviors in complex soil-crop systems are urgently needed. In this study, a reliable and matrix effect (ME)-free method was developed for simultaneous determination of 14 legacy and emerging PFASs, including perfluorooctanoic acid, perfluorooctane sulfonate, 6 hydrogenous PFASs, 3 chlorinated PFASs, and 3 hexafluoropropylene oxide homologues, in 6 crop (the edible parts) and 5 soil matrices using ultrasonic extraction combined with solid-phase extraction and ultraperformance liquid chromatography-mass spectrometry (MS)/MS. The varieties of extractants and cleanup cartridges, the dosage of ammonia hydroxide, and the ME were studied to obtain an optimal pretreatment procedure. The developed method had high sensitivity and accuracy with satisfactory method detection limits (2.40-83.03 pg/g dry weight) and recoveries (72-117%) of all target analytes in matrices at five concentrations, that is, 0.1, 1, 10, 100, and 1000 ng/g. In addition, the ME of this method (0.82-1.15) was negligible for all PFASs, even considering 11 different matrices. The successful application of the ME-free method to simultaneously determine the legacy and emerging PFASs in crop and soil samples has demonstrated its excellent practicability for monitoring emerging PFASs in soil-crop systems.

Effect of soil type on heavy metals removal in bioelectrochemical system

Microbial fuel cell (MFC) technology is widely used to remediate heavy metal pollution of soil, and the applicability of soils with different physical and chemical properties under micro-electric field has not been studied. In this study, copper was effectively removed in four typical soil-filled MFCs. The removal efficiencies of copper from closed-circuit MFCs filled with paddy, red, black and alluvial soils were 2.9, 1.50, 3.48 and 3.40 times higher than those in the open-circuit control group, respectively. However, the contributions of electromigration and diffusion mechanisms were different under different soil types. The greatest copper removal (19.3 ± 0.8%) was achieved based on electromigration of the electric field inside the paddy soil MFC in 63 days, while the greatest copper removal (25 ± 2%) was achieved under the action of diffusion mechanism inside the red soil MFC. According to redundancy analysis, the removal of copper by electromigration was positively correlated with electricity generation performance and acid extractable Cu content, whereas copper removal based on diffusion was positively related to soil pore volume and acid extractable Cu content. The cation exchange capacity and total organic carbon of soil were negatively correlated with the acid extractable Cu content, and electrical conductivity of soil was positively correlated with the MFC electricity generation performance. Furthermore, the directional movement of protons under an electric field alleviated the issue of soil acidification caused by citric acid.

Enhanced removal of bisphenol A from contaminated soil by coupling Bacillus subtilis HV-3 with electrochemical system

Exposure to endocrine disruptors interferes with the synthesis, release, transport and metabolic activities of hormones, thus impairing human health significantly. Bisphenol A (BpA), an endocrine disruptor, commonly released into the environment by industrial activities and needs immediate attention. This study aims at investigating the process and prospects of deploying bio-electrochemical systems (BES) for the removal of BpA from artificially contaminated soil using Bacillus subtilis HV-3. The BES was setup with desired operating conditions: initial concentration of BpA (80-150 mg/L), pH (3-11) and applied potential voltage (0.6-1.4 V). Under optimized conditions (initial BpA concentration, 100 mg/L; pH 7; and applied voltage 1.0 V), close to 98% degradation of BpA was achieved. The intermediates produced during degradation were analysed using High performance liquid chromatography-Mass spectrometry and the possible degradation pathway was elucidated. Phytotoxicity studies in the remediated soil with Phaseolus mungo confirmed the environmental applicability of the BES system.

Influence of phosphorus on copper phytoextraction via modulating cellular organelles in two jute (Corchorus capsularis L.) varieties grown in a copper mining soil of Hubei Province, China

Soil in mining areas is typically highly contaminated with heavy metals and lack essential nutrients for plants. Phosphorus reduces oxidative stress, improves plant growth, composition, and cellular structure, as well as facilitates the phytoremediation potential of fibrous crop plant species. In this study, we investigated two jute (Corchorus capsularis) varieties HongTieGuXuan and GuBaChangJia cultivated in copper (Cu)-contaminated soil (2221 mg kg^-1), under different applications of phosphorus (0, 30, 60, and 120 kg ha^-1) at both anatomical and physiological levels. At the same Cu concentration, the tolerance index of HongTieGuXuan was higher than that of GuBaChangJia, indicating that HongTieGuXuan may be more tolerant to Cu stress. Although the normal concentration of P (60 kg ha^-1) in the soil improved plant growth, biomass, chlorophyll content, fibre yield and quality, and gaseous exchange attributes. However, high concentration of P (120 kg ha^-1) was toxic to both jute varieties affected morphological and physiological attributes of the plants under same level of Cu. Moreover, Cu toxicity increased the oxidative stress in the leaves of both jute varieties was overcome by the activities of antioxidant enzymes. Furthermore, the high concentration of Cu altered the ultrastructure of chloroplasts, plastoglobuli, mitochondria, and many other cellular organelles in both jute varieties. Thus, phytoextraction of Cu by both jute varieties increased with the increase in P application in the Cu-contaminated soil. This suggests that P application enhanced the phytoremediation potential jute plants and can be cultivated as fibrous crop in Cu-contaminated sites.

Biochar sorption of PFOS, PFOA, PFHxS and PFHxA in two soils with contrasting texture

The ability to immobilise PFAS in soil may be an essential interim tool while technologies are developed for effective long-term treatment of PFAS contaminated soils. Serial sorption experiments were undertaken using a pine derived biochar produced at 750 °C (P750). All experiments were carried out either in individual mode (solution with one PFAS at 5 μg/L) or mix mode (solution with 5 μg/L of each: PFOS, PFOA, PFHxS and PFHxA), and carried out in 2:1 water to soil solutions. Soils had biochar added in the range 0-5% w/w. Kinetic data were fitted to the pseudo-second order model for both amended soils, with equilibrium times ranging 0.5-96 h for all congeners. PFOS sorption was 11.1 ± 4.5% in the loamy sand compared to 69.8 ± 4.9% in the sandy clay loam. While total sorption was higher in the unamended loamy sand than sandy clay loam for PFHxA, PFOA and PFOS, the effect of biochar amendment for each compound was found to be significantly higher in amended sandy clay loam than in amended loamy sand. Application of biochar reduced the desorbed PFAS fraction of all soils. Soil type and experimental mode played a significant role in influencing desorption. Overall, the relationship between sorbent and congener was demonstrated to be highly impacted by soil type, however the unique physiochemical properties of each PFAS congener greatly influenced its unique equilibrium, sorption and desorption behaviour for each amended soil and mode tested.

Mechanistic insights into the enhanced removal of roxsarsone and its metabolites by a sludge-based, biochar supported zerovalent iron nanocomposite: Adsorption and redox transformation

Roxarsone is a phenyl-substituted arsonic acid comprising both arsenate and benzene rings. Few adsorbents are designed for the effective capture of both the organic and inorganic moieties of ROX molecules. Herein, nano zerovalent iron (nZVI) particles were incorporated on the surface of sludge-based biochar (SBC) to fabricate a dual-affinity sorbent that attracts both the arsenate and benzene rings of ROX. The incorporation of nZVI particles significantly increased the binding affinity and sorption capacity for ROX molecules compared to pristine SBC and pure nZVI. The enhanced elimination of ROX molecules was ascribed to synergetic adsorption and degradation reactions, through π-π* electron donor/acceptor interactions, H-bonding, and As-O-Fe coordination. Among these, the predominate adsorption force was As-O-Fe coordination. During the sorption process, some ROX molecules were decomposed into inorganic arsenic and organic metabolites by the reactive oxygen species (ROS) generated during the early stages of the reaction. The degradation pathways of ROX were proposed according to the oxidation intermediates. This work provides a theoretical and experimental basis for the design of adsorbents according to the structure of the target pollutant.

Mechanochemical immobilization of lead contaminated soil by ball milling with the additive of Ca(H2PO4)2

Lead (Pb) pollution in the soil is becoming more and more serious, and lead poisoning incidents also constantly occur. Therefore, the remediation of lead pollution in the soil has attracted widespread attention. In this study, heavy metal lead in soil was remediated by mechanochemical methods. The effects of different ball milling conditions on the toxic leaching concentration and morphological distribution (BCR sequential extraction procedure) of lead in contaminated soil were analyzed, including the addition of calcium dihydrogen phosphate (Ca(H₂PO₄)₂), ball milling time, and ball milling speed. The reaction mechanism was analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and a laser particle size analyzer. The results show that the optimal conditions for mechanochemical immobilization were 10% additive (Ca(H₂PO₄)₂), milling speed of 550 rpm, and ball milling time for 2 h. Under this condition, the toxic leaching concentration of lead from contaminated soil was 4.36 mg L^-1, and in the BCR sequential extraction procedure, Pb was mainly present in the residual fraction (54.96%). The mechanism of mechanochemical solidification of heavy metal lead in soil is that, during the ball milling process, the lead precipitates with Ca(H₂PO₄)₂ to produce dense agglomerates (Pb₃(PO₄)₂ and Pb_xCa_10-x(PO₄)₆(OH)₂), which fixes the lead in the soil and hampers its leaching.

Inoculation of Cd-contaminated paddy soil with biochar-supported microbial cell composite: A novel approach to reducing cadmium accumulation in rice grains

Bioremediation of heavy metal-contaminated soil using metal-resistant microbes is a promising remediation technology. However, as exogenous bacteria sometimes struggle to survive and grow when introduced to new soils, it is important to develop appropriate carriers for microbial populations. In this study, we report a novel approach to remediating Cd-contaminated rice paddy soil using biochar-supported microbial cell composites (BMCs) produced from agricultural waste (cornstalks). Pot experiments showed that amendment with BMC was more efficient at reducing root and grain Cd content than pure bacteria, while improving soil Cd fractionation toward more stabilized and less labile forms. Bacteria in the BMC medium grew more readily with more abundant metabolites than those raised in free cells, probably because biochar provides shelter via porous structures (as confirmed by scanning electron microscopy) as well as additional nutrients. Overall, the improved long-term production of microbial biomass caused by BMC inoculation results in a higher remediation efficiency. Our results demonstrate the feasibility of using biochar as an appropriate carrier for metal-tolerant bacteria to remediate Cd-contaminated paddy fields.

Effect of Soil Washing Solutions on Simultaneous Removal of Heavy Metals and Arsenic from Contaminated Soil

In this study, we investigated the feasibility of using a solution of sulfuric acid and phosphoric acid as an extraction method for soil-washing to remove Cu, Pb, Zn, and As from contaminated soil. We treated various soil particles, including seven fraction sizes, using sulfuric acid. In addition, to improve Cu, Pb, Zn, and As removal efficiencies, washing agents were compared through batch experiments. The results showed that each agent behaved differently when reacting with heavy metals (Cu, Pb, and Zn) and As. Sulfuric acid was more effective in extracting heavy metals than in extracting As. However, phosphoric acid was not effective in extracting heavy metals. Compared with each inorganic acid, As removal from soil by washing agents increased in the order of sulfuric acid (35.81%) < phosphoric acid (62.96%). Therefore, an enhanced mixture solution using sulfuric acid and phosphoric acid to simultaneously remove heavy metals and As from contaminated soils was investigated. Sulfuric acid at 0.6 M was adopted to combine with 0.6 M phosphoric acid to obtain the mixture solution (1:1) that was used to determine the effect for the simultaneous removal of both heavy metals and As from the contaminated soil. The removal efficiencies of As, Cu, Pb, and Zn were 70.5%, 79.6%, 80.1%, and 71.2%, respectively. The combination of sulfuric acid with phosphoric acid increased the overall As and heavy metal extraction efficiencies from the contaminated soil samples. With the combined effect of dissolving oxides and ion exchange under combined washings, the removal efficiencies of heavy metals and As were higher than those of single washings.

Pilot-scale electro-bioremediation of heavily PAH-contaminated soil from an abandoned coking plant site

This study presents a systematic pilot-scale study on removal of PAHs from the abandoned site of Shenyang former Coking Plant in China (total PAH concentration of 5635.60 mg kg^-1 in soil). Three treatments, including the control treatment (without inoculation and electric field), bioremediation (with inoculation), and the electro-bioremediation (with inoculation and electric field), were conducted with a treatment time of 182 days to assess their PAH-removal efficiency. All the treatments were conducted from May to October under natural conditions. Results show that electro-bioremediation enhanced the removal of total PAHs, especially high-ring (>3 rings) PAHs. At 182 days, the degradation extents of total and 4-6-ring PAHs reached 69.1% and 65.9%, respectively, under electro-bioremediation (29.3% and 44.4% higher, respectively, than those under bioremediation alone). After electro-bioremediation, the total toxicity equivalent concentrations of total PAHs and 4-, 5- and 6-ring PAHs reduced 49.0%, 63.7%, 48.2% and 30.1%, respectively. These results indicate that electro-bioremediation not only effectively removed the PAHs but also reduced the health risks of soil in an abandoned coking plant site. In addition, electro-bioremediation with polarity reversal could maintain uniform soil pH, the degradation extent of PAHs and soil microorganism numbers at all sites. The environmental conditions, such as temperature and rainfall, had little influence on the process of electro-bioremediation. These findings suggest that electro-bioremediation may be applied for field-scale remediation of heavily PAH-contaminated soil in abandoned coking plant sites.

Degradation of Carbendazim in Soil: Effect of Sewage Sludge-Derived Biochars

Application of biochar in soils can affect the soil properties and, in turn, the fate of pesticides. Batch experiments were conducted to investigate the effect of sewage sludge-derived biochars on the dissipation of a fungicide carbendazim in soil, and the transformation of carbendazim in soil was also studied. Results showed that the dissipation of carbendazim was fastest in a loamy soil SD with a half-life of 11.0 d among the three kinds of soils tested in this study. A dual effect (both acceleration and inhibition) of sewage sludge-derived biochars on carbendazim degradation in soil was reported. The addition of 10% biochars produced at 700 °C (BC 700) in soil could accelerate the carbendazim degradation, but an inhibitory effect was observed for 10% BC 300 or BC 500. Degradation of carbendazim was significantly inhibited when 0.5 or 5% BC 700 was added in soil but accelerated when the amendment ratio of BC 700 was increased to 10%. Such complex effects of the sewage sludge biochar should be taken into consideration in risk assessment of pesticides and the biochar effects on soil remediation. Eight metabolites of carbendazim were characterized, seven of which were reported in unamended soil for the first time. The metabolic pathways of carbendazim in soil are proposed.

Efficient Degradation of Phenoxyalkanoic Acid Herbicides by the Alkali-Tolerant Cupriavidus oxalaticus Strain X32

Phenoxyalkanoic acid (PAA) herbicides are mainly metabolized by microorganisms in soils, but the degraders that perform well under alkaline environments are rarely considered. Herein, we report Cupriavidus oxalaticus strain X32, which showed encouraging PAA-degradation abilities, PAA tolerance, and alkali tolerance. In liquid media, without the addition of exogenous carbon sources, X32 could completely remove 500 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) or 4-chloro-2-methylphenoxyacetic acid within 3 days, faster than that with the model degrader Cupriavidus necator JMP134. Particularly, X32 still functioned at pH 10.5. Of note, with X32 inoculation, we observed 2,4-D degradation in soils and diminished phytotoxicity to maize (Zea mays). Furthermore, potential mechanisms underlying PAA biodegradation and alkali tolerance were then analyzed by whole-genome sequencing. Three modules of tfd gene clusters involved in 2,4-D catabolism and genes encoding monovalent cation/proton antiporters involved in alkali tolerance were putatively identified. Thus, X32 could be a promising candidate for the bioremediation of PAA-contaminated sites, especially in alkaline surroundings.

Insight into the mechanisms of plant growth promoting strain SNB6 on enhancing the phytoextraction in cadmium contaminated soil

Plant growth-promoting rhizobacteria (PGPR) assisted accumulator has been proposed as a phytoextraction method to clean cadmium (Cd) in contaminated soil, while the mechanisms were few studied regrading PGPR-soil-accumulator as an assemble. In this study, we revealed the possible mechanisms of the plant growth-promotion strain SNB6 on enhancing the Cd phytoextration of vetiver grass by the analysis of the whole genome of SNB6, soil biochemical properties and plant growth response. Results showed that SNB6 encoded numerous genes needed for Cd tolerance, Cd mobilization and plant growth promotion. SNB6 increased HOAc-extractable Cd that showed a positive correlation with Cd uptake in accumulator. In addition, SNB6 improved the biochemical activities (bioavailability of nutritional substances, bacterial count, soil respiration and enzyme activity) in rhizosphere soil. Moreover, the antioxidative enzymes activities of accumulator were significantly enhanced by SNB6. Consequently, SNB6 promoted Cd uptake and biomass of accumulator, thus enhancing the Cd phytoextraction. The maximum Cd extractions in root, stem and leaf reached to 289.47 mg/kg, 88.33 mg/kg and 59.38 mg/kg, respectively. Meanwhile, the total biomass of accumulator was increased by 9.68-45.99% in SNB6 treatment. These findings could be conducive to the understanding the mechanisms of PGPR on enhancing the Cd phytoextraction of accumulator.

Rhizodegradation of Petroleum Oily Sludge-contaminated Soil Using Cajanus cajan Increases the Diversity of Soil Microbial Community

Most components of petroleum oily sludge (POS) are toxic, mutagenic and cancer-causing. Often bioremediation using microorganisms is hindered by the toxicity of POS. Under this circumstance, phytoremediation is the main option as it can overcome the toxicity of POS. Cajanus cajan a legume plant, was evaluated as a phyto-remediating agent for petroleum oily sludge-spiked soil. Culture dependent and independent methods were used to determine the rhizosphere microorganisms' composition. Degradation rates were estimated gravimetrically. The population of total heterotrophic bacteria (THRB) was significantly higher in the uncontaminated soil compared to the contaminated rhizosphere soil with C. cajan, but the population of hydrocarbon-utilizing bacteria (HUB) was higher in the contaminated rhizosphere soil. The results show that for 1 to 3% oily sludge concentrations, an increase in microbial counts for all treatments from day 0 to 90 d was observed with the contaminated rhizosphere CR showing the highest significant increase (p  < 0.05) in microbial counts compared to other treatments. The metagenomic study focused on the POS of 3% (w/w) and based on the calculated bacterial community abundance indices showed an increase in the values for Ace, Cho, Shannon (Shannon-Weaver) and the Simpson's (measured as InvSimpson) indices in CR3 compared to CN3. Both the Simpson's and the Shannon values for CR3 were higher than CN3 indicating an increase in diversity upon the introduction of C. cajan into the contaminated soil. The PCoA plot revealed community-level differences between the contaminated non-rhizosphere control and contaminated rhizosphere microbiota. The PCoA differentiated the two treatments based on the presence or absence of plant. The composition and taxonomic analysis of microbiota-amplified sequences were categorized into eight phyla for the contaminated non-rhizosphere and ten phyla for the contaminated rhizosphere. The overall bacterial composition of the two treatments varied, as the distribution shows a similar variation between the two treatments in the phylum distribution. The percentage removal of total petroleum hydrocarbon (TPH) after 90 days of treatments with 1, 2, 3, 4, and 5% (w/w) of POS were 92, 90, 89, 68.3 and 47.3%, respectively, indicating removal inhibition at higher POS concentrations. As the search for more eco-friendly and sustainable remediating green plant continues, C. cajan shows great potential in reclaiming POS contaminated soil. Our findings will provide solutions to POS polluted soils and subsequent re-vegetation.

EDTA-enhanced electrokinetic remediation of aged electroplating contaminated soil assisted by combining dual cation-exchange membranes and circulation methods

This paper introduces a novel method for ethylenediaminetetraacetic acid (EDTA)-enhanced electrokinetic (EK) remediation by combining dual cation-exchange membranes and circulation methods for an aged electroplating soil contaminated by chrome (Cr), copper (Cu), and nickel (Ni). Three laboratory-scale EK experiments were carried out, including T1, the traditional EK process; T2, the traditional EDTA-enhanced EK process; and T3, the assisted EDTA-enhanced EK process. The results obtained show that removal of Cu and Ni in T3 was 3-10 times higher than after T1 and T2. However, the removal of Cr (total) was small in all experiments because of the high content of Cr(III). T3 eliminated the metal accumulation problem that existed for T1 and T2. Simultaneously, the highly acidified area (pH < 4) was reduced from 80% in T1 and T2 to only 20% in T3. The results obtained in T3 indicate that the chelating effect of EDTA has a greater ability to dissolve oxidizable Cu and Ni in the soil than the acidification effect. Toxicity evaluation confirmed that the soil treated by T3 presented a lower effect on a luminescent bacterium (Photobacterium phosphoreum T3) because soil pH tended to be more neutral after this treatment. This research provides a novel method for removing heavy metals from soil in a more environmentally friendly way and clarifies the cause of the existing problems of low removal efficiency and high accumulation in the traditional EK process.

Goethite-modified biochar restricts the mobility and transfer of cadmium in soil-rice system

Cadmium (Cd) contamination of paddy soils has raised serious concerns for food safety and security. Remediation and management of Cd contaminated soil with biochar (BC) and modified biochar is a cost-effective method and has gained due attention in recent years. Goethite-modified biochar (GB) can combine the beneficial effects of BC and iron (Fe) for remediation of Cd contaminated soil. We probed the impact of different BC and GB amendments on Cd mobility and transfer in the soil-rice system. Both BC and GB effectively reduced Cd mobility and availability in the rhizosphere and improved the key growth attributes of rice. Although BC supply to rice plants enhanced their performance in contaminated soil but application of 1.5% GB to the soil resulted in prominent improvements in physiological and biochemical attributes of rice plants grown in Cd contaminated soil. Sequential extraction results depicted that BC and GB differentially enhanced the conversion of exchangeable Cd fractions to non-exchangeable Cd fractions thus restricted the Cd mobility and transfer in soil. Furthermore, supplementing the soil with 1.5% GB incremented the formation of iron plaque (Fe plaque) and boosted the Cd sequestration by Fe plaque. Increase in shoot and root biomass of rice plants after GB treatments positively correlates with incremented chlorophyll contents and gas exchange attributes. Additionally, the oxidative stress damage in rice plants was comparatively reduced under GB application. These findings demonstrate that amending the soil with 1.5% GB can be a potential remediation method to minimize Cd accumulation in paddy rice and thereby can protect human beings from Cd exposure.

Co-solubilization of polycyclic aromatic hydrocarbon mixtures in aqueous micellar systems and its correlation with FRET for enhanced remediation processes

Surfactant enhanced remediation (SER) is an effective approach for decontaminating the PAH polluted soils. Solubilization and Cosolubilization of Phenanthrene (Ph), Pyrene (Py) and Perylene (Pe) as single, binary and ternary mixtures have been studied employing cationic (CTAB), anionic (SDS), non-ionic surfactant (Brij 30) and block copolymer (P123) micelles. In the single solute solubilization studies, solubility of Pe follows the order Brij 30 > CTAB > SDS whereas Ph or Py followed the order of CTAB > Brij 30 > SDS. In the cosolubilization studies, an increase, decrease or no change in the mutual solubility of PAHs was observed. Synergism in solubilization was observed most in P123 in both binary and ternary PAH mixture where more PAHs could get solubilized in the dense micellar shell region, thereby enhancing the micellar core volume leading to enhanced solubilization of PAHs. The solubilizates as pairs (Ph-Pe and Py-Pe) were further tested for any possible energy transfer in presence of surfactant based restricted host environments using spectrofluorometry and spectrophotometry. Based on the solubilization and cosolubilization an efficient non-radiative energy transfer (FRET) was observed between Ph/Py (donor) and Pe (acceptor) in the non-ionic surfactant system as well as in CTAB-Brij 58 mixed system. The results of this work may improve the effective utilization of surfactants in their correct evaluation for the removal of PAHs from contaminated soils or aquifers treated with SER technology.

An investigation of the effect of operational conditions on a sequential extraction procedure for arsenic in soil in Thailand

Sequential Extraction Procedure (SEP) can be used to evaluate the toxicity characteristics of heavy metals in soil, including arsenic (As), by separating the metals into several different fractions using selective extraction solvents in sequence. To accomplish this separation task, various factors that are known to affect the extraction process should be carefully considered. This research aimed to investigate the effect of the operational conditions on the SEP for As in soil using experimental designs. In the first step, a Plackett-Burman design was used twice to screen the important extraction variables from a total of 19 studied variables. As a result, SSR, extraction time of the first fraction (F1), and concentrations of sodium acetate (NaOAc) in F2 and ammonium oxalate (NH₄Ox) in F6 were identified as significant to the amount of the extracted As. The selected variables were further investigated using a central composite design with response surface methodology. The optimized SEP characterized by 1:75 g:mL of SSR, an extraction time of 7 h 20 min of F1, 0.16 M of NaOAc and 0.11 M of NH₄OAc were applied to extract a sample from contaminated agricultural soil obtained from the north of Thailand. The fractionation result was compared with the result obtained from a previously reported SEP method. It was found that similar extraction results could be achieved (91-97% As recovery). However, the optimized method revealed certain advantages in that it required dramatically less operation time (from 68 h to 32 h) and lower concentrations of the extraction solvents.

Influence of green waste compost on Pb-polluted soil remediation, soil quality improvement, and uptake by Pakchoi cabbage (Brassica campestris L. ssp)

Green waste compost (GWC) has been widely used as organic mulches, growing media, soil organic fertilizer, and amendment in Beijing, China. The aim of this study is to determine the remediation efficiency of GWC on the Pb concentration in soil and uptake by pakchoi cabbage and to assess the activities of dehydrogenase, urease, and catalase after applying GWC. Original soil samples were spiked with Pb (NO₃)₂ of 500 mg/kg, and greenhouse pot experiment was carried out. Three seedlings of pakchoi cabbage (Brassica campestris L. ssp) were planted in plastic pots with mixture of soil amended with three levels of GWC (2%, 5%, and 10%, w/w). Soil and plant samples were collected over 45-day growth, after which Pb concentration and enzyme activities were assessed by laboratory analysis. The available Pb in soil and total Pb in roots and leaves of pakchoi cabbage greatly decreased after adding GWC, associated with significant increases in organic matter, water soluble organic carbon, total nitrogen, and available K and P, whereas pH was not a main factor controlling Pb speciation in this study. Activities of dehydrogenase, urease, and catalase were promoted with addition of GWC because physical properties, high organic matter, and organic carbon content rose by 9-fold, 40%, and 37% at 10% application rate, respectively. In conclusion, GWC could be an alternative option for the remediation of Pb-contaminated soil because of soil quality improvement and Pb reduction in soils and plants, without introducing extra heavy metals compared with other organic amendments.

Development of a carbamate-conjugated catechol ligand and its application to Cs extraction from contaminated soil by using supercritical CO2

Extraction of radioactive Cs from contaminated soil is a crucial aspect of remediation after nuclear accidents. For this purpose, we have developed a new type of ligand, carbamate-conjugated catechol, to assist in metal extraction by using supercritical CO₂ (SCCO₂). The synthesis process for this ligand is relatively simple, and the carbamate-conjugated catechol ligand dissolves well in SCCO₂. The measured ligand distribution coefficient increased according to a power law with an exponent of 1.7 as the ligand concentration increased, indicating that approximately two ligand molecules are needed to extract one Cs ion. The roles of additives (ligand, co-ligand, and water) were limited when they were used separately, but the combination of these additives was important. We tested 27 combinations of these three additives for extracting Cs from artificially contaminated sea sand. A quantitative analysis indicated that the ligand had the strongest influence on Cs extraction, followed by water, and the co-ligand. The carbamate-conjugated catechol ligand was then used for Cs extraction from artificially contaminated real soil. Three types of soil were prepared: coarse soil (particle size = 0.5-1 mm), medium soil (particle size = 0.2-0.5 mm), and fine soil (particle size < 0.2 mm). The Cs fractions extracted from the coarse, medium, and fine soils were measured to be 95%, 91% and 70% of the Cs fraction extracted from sea sand, respectively, which indicates the existence of a surface area effect. Additionally, we suspect that Cs undergoes chemical interaction on the surface of real soil.

Simultaneous immobilization of the cadmium, lead and arsenic in paddy soils amended with titanium gypsum

In situ immobilization of heavy metals in contaminated soils using industrial by-products is an attractive remediation technique. In this work, titanium gypsum (TG) was applied at two levels (TG-L: 0.15% and TG-H: 0.30%) to simultaneously reduce the uptake of cadmium (Cd), lead (Pb) and arsenic (As) in rice grown in heavy metal contaminated paddy soils. The results showed that the addition of TG significantly decreased the pH and dissolved organic carbon (DOC) in the bulk soil. TG addition significantly improved the rice plants growth and reduced the bioavailability of Cd, Pb and As. Particularly, bioavailable Cd, Pb and As decreased by 35.2%, 38.1% and 38.0% in TG-H treatment during the tillering stage, respectively. Moreover, TG application significantly reduced the accumulation of Cd, Pb and As in brown rice. Real-time PCR analysis demonstrated that the relative abundance of sulfate-reducing bacteria increased with the TG application, but not for the iron-reducing bacteria. In addition, 16S rRNA sequencing analysis revealed that the relative abundances of heavy metal-resistant bacteria such as Bacillus, Sulfuritalea, Clostridium, Sulfuricella, Geobacter, Nocardioides and Sulfuricurvum at the genus level significantly increased with the TG addition. In conclusion, the present study implied that TG is a potential and effective amendment to immobilize metal(loid)s in soil and thereby reduce the exposure risk of metal(loid)s associated with rice consumption.

Evaluation of the phytoremediation potential of dominant plant species growing in a chromium salt-producing factory wasteland, China

The metal contents of the soil and plant tissues in a large chromium salt-producing factory wasteland were determined to assess the properties of soil contamination and to identify plant species accumulating a range of heavy metals. Total metal contents in the factory soils presented a high heterogeneity, and the principal contaminants were Cd and Cr. All plant species examined were metal-tolerant, but to different extents. Especially, the maximum accumulation of Cd (15.61 mg kg^-1) and Cr (925.07 mg kg^-1) was found in Melia azedarach L. Subsequently, the Cd and Cr bioaccumulation and diverse physiological properties of M. azedarach seedlings exposed to different concentrations of Cd(II), Cr(VI), or Cd(II) + Cr(VI) in nutrient solutions were further investigated. All treated seedlings were able to survive under heavy metal stress, and the accumulation of both metals in plant tissues increased with elevation of metal exposure strength. M. azedarach showed a BCF greater than 147.56 for Cd and 36.76 for Cr. Meanwhile, the TF was lower than 0.25 for Cd and 0.32 for Cr. The highest bioaccumulation in root tissues was 2708.03 mg kg^-1 Cd and 824.65 mg kg^-1 Cr for seedlings cultured with 20 mg L^-1 Cd(II) or 20 mg L^-1 Cr(VI). Cd and Cr increased each other's uptake in seedlings although a reduced accumulation in roots occurred when exposed to the highest concentration of Cd(II) + Cr(VI) treatment (20 mg L^-1). At either level of concentration, the degree of plant growth inhibition and oxidative damage caused by heavy metals was Cd(II) + Cr(VI) > Cr(VI) > Cd(II). Superoxide dismutase and peroxidase exhibited positive and effective responses to low-Cd(II) or Cr(VI) concentration stress, but their activities decreased with increasing metal exposure strength. The behavior of the non-enzymatic antioxidants (GSH, soluble protein, and proline) in plant involved in the detoxification of ROS induced by metal exposure was correlated well with higher Cd and Cr accumulations. Here, the potentiality of M. azedarach with the capacity to accumulate and stabilize Cd/Cr in metal-contaminated soil by phytoremediation process has been explored.

Phosphorus influence Cd phytoextraction in Populus stems via modulating xylem development, cell wall Cd storage and antioxidant defense

The soils in mining lands with cadmium (Cd) contamination usually are deficient in nutrients. Disclosing how P nutrition and N:P stoichiometric ratio influences Cd accumulation and stress tolerance in stems of Populus spp. will facilitate the phytoremediation of mining sites polluted by Cd. In this study, investigations at the anatomical and physiological levels were conducted using a clone of Populus × euramericana. Both phosphorus deficiency and cadmium exposure inhibited xylem development via reducing cell layers in the xylem. Under P-sufficient condition, appropriate P status and balanced N:P ratio in stem promoted xylem development under Cd exposure via stimulating cell division, which enhanced Cd accumulation in stems. Cd accumulation in cell walls of collenchyma tissues of the stem was enhanced by P application due to increased polysaccharide production and cell wall affinity for Cd. The low P concentrations (0.3-0.4 mg g^-1) and imbalanced N:P ratio under P deficiency inhibited the production of APX and ascorbate-GSH cycle, which increased oxidative stress and lipid peroxidation as indicated by high MDA concentration in stem. Under P-sufficient condition, the interactions between phytohormones and antioxidants play crucial roles in the process of antioxidant defense under Cd exposure. In conclusions, appropriate P addition and balanced N:P ratio enhanced secondary xylem development and promoted cadmium accumulation and stress tolerance in Populus stems, which can benefit the phytoextraction of Cd from Cd-contaminated soil.

Poultry Farms as a Potential Source of Environmental Pollution by Pharmaceuticals

Industrial poultry breeding is associated with the need to increase productivity while maintaining low meat prices. Little is known about its impact on the environment of soil pollution by pharmaceuticals. Breeders routinely use veterinary pharmaceuticals for therapeutic and preventive purposes. The aim of this work was to determine the influence of mass breeding of hens on the soil contamination with 26 pharmaceuticals and caffeine. During two seasons—winter and summer 2019—15 soil samples were collected. Liquid extraction was used to isolate analytes from samples. Extracts were analyzed using ultra-high performance liquid chromatography coupled with tandem mass spectrometry detection (UPLC-MS/MS). The results showed the seasonal changes in pharmaceutical presence in analyzed soil samples. Ten pharmaceuticals (metoclopramide, sulphanilamide, salicic acid, metoprolol, sulphamethazine, nimesulide, carbamazepine, trimethoprim, propranolol, and paracetamol) and caffeine were determined in soil samples collected in March, and five pharmaceuticals (metoclopramide, sulphanilamide, sulphamethazine, carbamazepine, sulfanilamid) in soil samples collected in July. The highest concentrations were observed for sulphanilamide, in a range from 746.57 ± 15.61 ng/g d.w to 3518.22 ± 146.05 ng/g d.w. The level of bacterial resistance to antibiotics did not differ between samples coming from intensive breeding farm surroundings and the reference area, based on antibiotic resistance of 85 random bacterial isolates.

Enhanced passivation of lead with immobilized phosphate solubilizing bacteria beads loaded with biochar/ nanoscale zero valent iron composite

Phosphate solubilizing bacteria (PSBs) can effectively enhance the stability of lead via the formation of insoluble Pb-phosphate compounds. This research presents a bio-beads, which was implemented with the help of a self-designed porous spheres carrier, by immobilized PSBs strains Leclercia adecarboxylata (hereafter referred as L1-5). In addition, the passivation efficiency of lead via bio-beads under different conditions and its mechanism were also investigated in this study. The results indicated that phosphate solubilized by bio-beads could reach 30 mg/L in Ca₃(PO₄)₂ medium containing 1 mM Pb²⁺, and the highest removal rate of Pb²⁺ in beef peptone liquid medium could reach 93%, which is better than that of free bacteria. Furthermore, it was also concluded that the lead could be transformed into stable crystal texture, such as Pb₅(PO₄)₃Cl and Pb₅(PO₄)₃OH. Both hydrophobic and hydrophilic groups in the bio-beads could capture Pb²⁺, which indicated that electrostatic attraction and ion-exchange were also the mechanism of Pb²⁺ adsorption. All the experimental findings demonstrated that this bio-bead could be consider as an efficient way for the lead immobilization in contaminated soil in the future.

Discovery of a novel native bacterium of Providencia sp. with high biosorption and oxidation ability of manganese for bioleaching of heavy metal contaminated soils

Heavy metal removal from contaminated soils is a long-term challenging problem important for global economics, environment, and human health. Marine and freshwater-originated Mn(II)-oxidizing bacteria are considered as the promising bioremediation agents for environmental applications. However, practical application of soil-originated Mn(II)-oxidizing bacteria remains to be developed for contaminated soil remediation. In this work, the Mn(II) biosorption/oxidation mechanism of a new soil-originated bacterium and its bioleaching efficiency of heavy metals from soils was studied in detail. First, we found, isolated and identified a new highly Mn(II)-tolerant bacterial strain Providencia sp. LLDRA6 from heavy metal-contaminated soils. Next, strain LLDRA6 demonstrated its high Mn(II) biosorption capacity in aqueous solution. Then, Mn(II) adsorption by LLDRA6 was largely proven to be a synergistic effect of (i) Mn(II) precipitation on the cell surface, (ii) oxidation of Mn(II) into BioMnO_x on the cell surface, and (iii) intracellular accumulation of insoluble MnCO₃. Finally, combination bioleaching by the bacterium of Providencia sp. LLDRA6 and its formed BioMnO_x was proposed to develop a potential environment-friendly and cost-effective technique to remediate severely heavy metal-contaminated soils. The bioleaching tests demonstrated that the combination of Providencia sp. LLDRA6 and BioMnO_x exhibited an excellent removal efficiency for heavy metals of Pb (81.72%), Cr (88.29%), Cd (90.34%), Cu (91.25%), Mn (56.13%), and Zn (59.83%) from contaminated soils, resulting in an increase of removal efficiency in the range of 1.68-26.4% compared to Providencia sp. LLDRA6 alone. Moreover, the bacterial leachate facilitated the residual fraction of metals to transform into the easily migratory fractions in soils. These findings have demonstrated that strain LLDRA6 has high adsorption ability to remove heavy metals from contaminated soils, thus providing a promising bio-adsorbent for environmental bioremediation.

Relationship between bioelectrochemical copper migration, reduction and electricity in a three-chamber microbial fuel cell

Microbial fuel cells (MFCs) can remove and recover metals in wastewater; however, there are relatively few studies of metal removal from soil by MFCs. In this study, we developed a three-chamber soil MFC consisting of an anode, contaminated soil, and cathode chamber to remove heavy metals from soil. The performance of the soil MFC was investigated by assessing the relationships among current, voltage, and Cu migration, and reduction. The developed soil MFC successfully reduced and removed Cu, and the Cu removal efficiency in the cathode surpassed 90% after only 7 days of operation. External resistance had a remarkable effect on the performance of the soil MFC which was depended on cathodic polarization. The pH in the cathode also depended on the external resistance. Lower external resistance were associated with lower pH values, higher Cu removal efficiencies, and greater amounts removed in the cathode. Based on sequential fractionation, the acid-extractable and reducible fractions were the main fractions that migrated within the three-chamber soil MFC. Enhancing the voltage output in the three-chamber soil MFC by increasing the external resistance promoted Cu migration, enriched Cu near the cathode, and facilitated Cu removal. Therefore, the developed three-chamber soil MFC not only supports heavy metal migration from soil towards the cathode, but can also realize reduction of heavy metals in the cathode by adjusting the current or voltage generated by the soil MFC.

Comparison of humic and fulvic acid on remediation of arsenic contaminated soil by electrokinetic technology

The use of humic acid (HA) and fulvic acid (FA) as reinforcing agents to improve the efficiency of electrokinetic remediation (EKR) were investigated for the first time using an artificially contaminated soil. A series of soil leaching tests and bench-scale EKR experiments were performed to elucidate the mechanisms of As removed from artificially contaminated soil. The characterization of total reducing capacity (TRC) and functional group were carried out to reveal the difference of HA and FA. The observations demonstrated that with 0.1 M NaOH and KCl as the anolyte, using both HA and FA enhanced the efficiency of EKR. After 25 days of EKR, the removal efficiency of TAs in HA/FA-enhanced EKR was about 2.0-3.0 times greater than when unenhanced. Compared to HA, more As was removed in EKR with FA, which has more TRC and oxygen-containing groups. These EKR experimental results, with the support of data obtained from soil leaching test, indicate that competitive adsorption, reductive dissolution and complexation were the reasons why HA and FA promoted the release of As in the soil and further enhanced the remediation efficiency.

Synergistic immobilization of potentially toxic elements (PTEs) by biochar and nanoparticles in alkaline soil

Biochar and nanoparticle (NP) have the ability to sorb potentially toxic elements (PTEs) from soil and reduce toxicity and leaching into water bodies. However, there is need to tailor biochar formulations to soil types. In this study, we investigate the mobility and chemical forms of Cd, Cr, Cu, Ni, and Zn in a spiked, alkaline soil after amendment with combination of NPs (nano-Fe (NF), nano-clay (NC)) and biochars (almond shell 500 °C, walnut shell 400 °C) in different doses (0, 2.5, 5, and 10%). Many previous studies concluded biochar immobilized PTEs due to an increase in soil pH, which can be disregarded here (soil pH 7.9). In a twenty-week column leaching experiment biochar addition significantly decreased PTE leaching and NP addition further immobilized PTEs in most cases. On average almond biochar more effectively reduced Zn leaching and walnut biochar was more effective in decreasing the leaching of Cd, Cr, and Ni (e.g. 5% biochar reduced Cr leaching by 68%). Copper was immobilized effectively by both biochars. Nano-clay combined with walnut biochar performed best in all treatments, in particular for Cd, Ni, and Zn (e.g. 10% walnut biochar only and in combination with NC reduced Zn leaching by 14.2% and 58.5%, respectively). After amendment, PTEs were present in the Fe-Mn oxides, organic and residual fractions and less in the exchangeable fraction, reducing PTE availability and leachability. The results demonstrate that even for cationic PTEs that behave similarly in the environment optimal biochar-mineral formulations can differ.

Levels of heavy metals in soil and vegetables and associated health risks in Mojo area, Ethiopia

Health implications to the population due to the consumption of contaminated vegetables has been a great concern all over the world. In this study, the levels of heavy metals (Cr, Cd, Zn, Fe, Pb, As, Mn, Cu, Hg, Ni and Co) in soil and commonly consumed vegetables from Mojo area in central Ethiopia have been determined using Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) and possible health risks due to the consumptions of the vegetables have also been estimated. The levels of As, Pb, Cd, Zn, Cu, Hg and Co were exceeded the reference level in agricultural soil. Likewise, As, Pb, Cd, Cr and Hg levels exceeded the recommended values in vegetable samples with concentrations ranging from 1.93–5.73, 3.63–7.56, 0.56–1.56, 1.49–4.63 and 3.43–4.23 mg/kg, respectively. It was observed that leafy vegetable (cabbage) has accumulated heavy metals to greater extent compared with tomato. The estimated daily intake (EDI) of toxic metals due to the consumption of the vegetables were below the maximum tolerable daily intake (MTDI). However, the total health quotient (THQ), calculated based on EDI of the heavy metals were found > 1 for As and Hg due to tomato consumption and for As, Hg and Co due to cabbage consumption, suggesting significant health risk. The health index (HI) due to the intake of toxic metals from the consumption of both vegetables were much > 1, with HI values of 7.205 and 15.078 due to tomato and cabbage consumption, respectively. This clearly suggests the possible adverse health effect to adult population from the consumption of tomato and cabbage from the study area. The total cancer risk (TCR) analysis have also revealed the potential adverse cancer risk induced by As, Cd, Hg, and Ni from the consumption of both tomato and cabbage as their TCR values were above the threshold level. Based on the results of this study, there would be a significant health risk (both non-carcinogenic and carcinogenic) to the consumer associated with the consumption of cabbage and tomato being cultivated in Mojo area. Consequently, we recommend a strict regulatory control on the safety of vegetables originated from the study area.

Double surfactants-assisted electromembrane extraction of cyromazine and melamine in surface water, soil and cucumber samples followed by capillary electrophoresis with contactless conductivity detection

BACKGROUND

Cyromazine (CYR) and its main degradation product melamine (MEL) are attracting wide attention due to their potential hazards to the environment and humans. In this work, double surfactants-assisted electromembrane extraction (DS-EME) by Tween 20 and alkylated phosphate was firstly used for purification and extraction of CYR and MEL, and the extract was directly analyzed by capillary electrophoresis with capacitively coupled contactless conductivity detection.

RESULTS

Under the optimum conditions, two targets could be well separated from the main interferences, including common biogenic amines and inorganic cations within 14 min. This developed method was successfully applied to the analyses of surface water, soil and cucumber samples, and the average recoveries were in the range 93.3-112%. DS-EME provided a synergistic purification and enrichment effect for CYR and MEL by adding Tween 20 and alkylated phosphate into donor phase and supporting liquid membrane, respectively. Satisfactory limits of detection [0.2-1.5 ng mL^-1 , signal-to-noise ratio (S/N) = 3] could be obtained in the tested sample matrices, and the corresponding enrichment factors were up to 115∼123 times.

CONCLUSION

This developed method provides an alternative for the simultaneous analysis of CYR and MEL in complex real-world samples. © 2019 Society of Chemical Industry.

A facile pyrolysis synthesis of biochar/ZnO passivator: immobilization behavior and mechanisms for Cu (II) in soil

Waste biomass can be recycled to prepare biochar for soil restoration, in which process soil fertility would not be lost. In this work, biochar was prepared from waste pomelo peel, combined with ZnO, to be used to immobilize Cu(II) in contaminated soil, whose maximum adsorption capacity was up to 216.37 mg g^-1. Due to combination of ZnO, the BET surface area of biochar increased from 2.39 to 18.53 m² g^-1. Meanwhile, the surface functional groups increased, which was conducive to fixation of metal ion on the surface of biochar. Both pseudo-second-order kinetics and Langmuir isotherm model fit the experimental data well. Adsorption was easy to happen since the adsorption site on the surface of biochar/ZnO had a strong affinity with Cu(II). In addition, mechanism investigation indicated that Cu(II) was bond with biochar/ZnO mainly by non-bioavailable state (75.6%) primarily. It inferred that biochar/ZnO was an efficient and promising passivator in reducing heavy metal risk in soil.

Coupling of bioaugmentation and biostimulation to improve lindane removal from different soil types

Lindane is an organochlorine pesticide that, due to its persistence in the environment, is still detected in different matrices. Bioremediation using actinobacteria consortia proved to be promising for the restoration of contaminated soils. Another alternative to remove xenobiotics is to use agricultural residues, which stimulates microbial activity, increasing its capacity to degrade organic pollutants. The present work studies the coupling of sugarcane bagasse biostimulation and bioaugmentation with the actinobacteria consortium composed of Streptomyces sp. A2, A5, A11 and M7 on lindane removal in different soil types. In this sense, factorial designs with three factors (proportion and size of sugarcane bagasse particles, and moisture content) were employed. A response optimizer identified the combination of factors levels that jointly allowed obtaining the maximum lindane removal in the evaluated conditions. In the optimal conditions, the effect of the bioremediation process on soil microbiota was studied by evaluating different parameters. The highest lindane removal percentages were detected in biostimulated microcosms bioaugmented with the microbial consortium, which were accompanied by a decrease in lindane half-life respect to the controls. Also, the bioaugmentation of biostimulated microcosms increased the microbial counts and enhanced soil enzymatic activities, corroborating the bioremediation process efficiency. The survival of the four actinobacteria at the end of the assay confirmed the ability of all Streptomyces strains to colonize amended soils. Bioremediation by simultaneous application of biostimulation with sugarcane bagasse and bioaugmentation with the actinobacteria consortium, in the optimized conditions, represents an efficient strategy to restore lindane contaminated soils.

Simultaneous scavenging of Cr(VI) from soil and facilitation of nutrient uptake in plant using a mixture of carbon microfibers and nanofibers

Plant growth and yield are adversely affected by the uptake of toxic hexavalent chromium (Cr(VI)) from soil. The present study describes a facile technique to minimize the uptake of Cr(VI) by chickpea (Cicer arietinum) plant from soil using microporous activated carbon microfiber (ACF). Simultaneously, nano-sized carbon nanofibers (CNFs), grown over the ACF substrate, are used as an efficient carrier of the Cu micronutrient from soil to root, shoot and leaf of the plants. Adsorption, seed germination and plant growth experiments are performed in Cr-stressed medium. The ACF, used as the adsorbent for Cr(VI) in metal-stressed soil (100 mg Cr kg^-1 of soil) shows the metal loading of ∼23 mg g^-1. Cr(VI) up to 50 mg L^-1 concentration causes no stress during germination of chickpea seeds in Murashige and Skoog (MS) medium. A dose of 500 mg-mixture (treatment) per kg-soil increases root and shoot lengths by 52 and 11%, respectively than the control, during plant growth in the metal-stressed soil, attributed to an effective translocation of Cu-CNF through plant cells. Whereas Cr uptake by plant decrease to ∼46%, Cu uptake increase up to ∼120% in comparison to control by the mixture treatment. Protein and chlorophyll contents also significantly increased (*p < 0.05) with the application of treatment. The data clearly show that the mixture of ACF and Cu-CNF can be successfully used for the simultaneous scavenging of Cr(VI) from soil by adsorption over ACF and increased uptake of Cu by plants using the CNFs as the micronutrient carrier.

Characteristics of PVP-stabilised NZVI and application to dechlorination of soil-sorbed TCE with ionic surfactant

The characteristics of polyvinylpyrrolidone (PVP)-stabilised nano-zero-valent iron (PVP-NZVI) and its application, combined with surfactant, to trichloroethylene (TCE)-contaminated soil were investigated. Two surfactants (cetyltrimethylammonium bromide [CTAB] and sodium dodecyl sulphate [SDS]) were tested for their ability to enhance the remedial activity of PVP-NZVI in 3 h batch experiments. The prepared PVP-NZVI formed nanoparticles ∼70 nm in diameter. The isoelectric point of PVP-NZVI was about 8.51, similar to the initial pH. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that ZVI was the main active component of PVP-NZVI, and carbonised products of the target were observed. The TCE dechlorination efficiency by PVP-NZVI was about 84.73%; the efficiency by PVP-NZVI was about 20% higher when combined with SDS than with CTAB. Therefore, application of PVP-NZVI with SDS represents a potential remediation approach for TCE-contaminated soil.

Hybrid ash/biochar biocomposites as soil amendments for the alleviation of cadmium accumulation by Oryza sativa L. in a contaminated paddy field

A novel ash/biochar (A/B) biocomposite composed of 90% biomass bottom ash from agroforestry biomass direct-fired power plants, 5% animal-derived biochar from carcass pyrolysis, and 5% bentonite as an adhesive was amended in cadmium (Cd)-polluted paddy soil to alleviate cadmium accumulation by Oryza sativa L. Ash increased the soil pH and contributed exogenous available silicon. Biochar with high Ca/P components played an important role in soil cadmium immobilization. A 1-year field experiment with consecutive rice growing seasons (early and late rice) was conducted in Xiangtan, China, to examine the effects of A/B amendment in Cd-contaminated paddy soil. The A/B biocomposite was amended into soil through one-time addition at three application rates (1, 5, and 10 kg/m²). When A/B amendment was ≥5 kg/m², the soil pH increased from 4.11 to more than 6. The available silicon content in the soil even increased by 22.9 times. For early rice soil, the CaCl₂-extractable Cd(II) and toxicity characteristic leaching procedure (TCLP)-extractable Cd(II) decreased by 77.9%-96.1% and 52.4%-70.7%, respectively. A/B remarkably reduced Cd accumulation in rice organs, and this observation was related to A/B treatment rates. Ash and biochar contributed to the inhibition of Cd accumulation in rice organs and Cd translocation from roots to stems. The Cd concentrations in brown rice decreased to 0.11 and 0.12 mg/kg in early and late rice, respectively, and these values were lower than the national food safety standard limit value of China (0.2 mg/kg).

Biochar accelerates the removal of tetracyclines and their intermediates by altering soil properties

Tetracyclines accumulation in soil environment potentially threatens agroecosystem safety. Interestingly, biochar could clean up organic pollutants, but to what extent biochar affects the removal of tetracyclines is unknown. To investigate it, five types of biochars derived from cow manure (CMB) and other four plant materials were respectively added into soils contaminated with a mixture of tetracycline, oxytetracycline, and chlortetracycline for 60-day incubation in the dark. Three parent tetracyclines and their corresponding intermediates (epitetracycline, anhydrotetracycline, epianhydrotetracycline, epioxytetracycline, epichlortetracycline, and demethylchlortetracycline) were respectively determined and named as TTCs, OTCs and CTCs. Obtained results showed biochar especially CMB could effectively remove the antibiotics (P < 0.05). Compared to control, the removal rate of TTCs, OTCs and CTCs respectively increased by up to 10.86%, 10.29% and 10.12% in CMB-added soil. The increased removal rate of the antibiotics after biochar addition was due to the increasing accessibilities for degrading microorganisms via the elevating electrical conductivity. Moreover, biochar addition might stimulate these microbial activities through the increase of C and N supplement. Our results indicate biochar accelerates the removal of tetracyclines and their intermediates by altering soil properties and thus increasing the antibiotics accessibilities, which provide insights into how biochar accelerates the removal for these antibiotics.

Recovery of EDTA from soil-washing wastewater with calcium-hydroxide-enhanced sulfide precipitation

It is cost effective and thermodynamically feasible to recover EDTA and remove potential toxic elements (PTEs) with sulfide precipitation from soil-washing wastewater produced from EDTA washing PTEs-contaminated soil. However, poor solid-liquid separation and EDTA recovery restrict its application due to a large number of fine particles formed during the precipitation process. This study investigated the effect of single factor on PTEs (Cu, Pb, Cd, and Zn) removal and solid-liquid separation from wastewater. The results showed that Zn was the most difficult to remove compared with Cu, Pb, and Cd; with the aid of Ca(OH)₂, Zn removal efficiency was improved from 22.16% to 92.45%, and over 70.98 min, its average rate was 4.2 times that obtained without Ca(OH)₂ dosage; undissolved Ca(OH)₂ adsorbed suspended particles, acted as condensation nucleus, and promoted similar flocculation effect (self-flocculation); dissolved Ca(OH)₂ modified the charge on the surface of suspended particles by changing the zeta potential from -36.77 ± 1.2 mV to -25.39 ± 3.06 mV and weakened the electrostatic repulsion between the suspended particles, and promoted their adsorption and flocculation precipitation, thereby improving the solid-liquid separation. The acid-recovered EDTA was analyzed in the protonated form (H₄EDTA) using Fourier transform infrared (FT-IR) spectroscopy, and it maintained the same ability to extract PTEs from the soil as that of fresh EDTA over several cycles. This indicates that Ca(OH)₂-enhanced sulfide precipitation can effectively treat soil-washing wastewater and recover EDTA and potentially reduce the cost of remediation techniques for PTEs-contaminated soil with EDTA-enhanced soil washing.

Arsenic removal from flooded paddy soil with spontaneous hygrophyte markedly attenuates rice grain arsenic

China ranks the top in global annual rice output. However, extensive mining and smelting has led to elevated arsenic (As) in paddy soils, potentially imperiling local population health and sustainable rice production in the country. Under flooded condition, reductive As mobilization generally occurs, providing a unique advantage for soil As removal. In this study, we explore the depletion magnitude of labile As from paddy soils through cycling of flooding-drainage with three distinct co-strategies, i.e. (1) no soil disturbance with spontaneously established hygrophyte plants, (2) selective fertilization to enhance soil As release, and (3) soil ploughing following each drainage. After 151 days of flooding with periodic drainage, diffusive gradients in thin film (DGT)-labile As through 0-14 cm soil profile with hygrophyte plants growing decreased from initial 292 μg l^-1 to well below the required threshold level (57-77 μg l^-1) for safe rice production. Correspondingly, an average of 22.9% of total soil As was removed, with up to 76.7% of As bound to amorphous Fe hydroxides being stripped in this treatment. In the following rice cultivation, inorganic As in the polished rice from the naturally vegetated treatment (0.15 mg kg^-1) fell successfully below the Chinese food safety standard (0.2 mg kg^-1). The results highlight that As removal from paddy soils with native hygrophyte under shallow flooded condition can decrease soil bioavailable As specifically to safe levels within a relatively short period, and thus provides a novel and quite cost-effective pathway securing rice production.