Combined biochar and wheat-derived endophytic bacteria reduces cadmium uptake in wheat grains in a metal-polluted soil.

In this study, two wheat-derived cadmium (Cd)-immobilizing endophytic Pseudomonas paralactis M14 and Priestia megaterium R27 were evaluated for their effects on wheat tissue Cd uptake under hydroponic conditions. Then, the impacts of the biochar (BC), M14+R27 (MR), and BC+MR treatments on wheat Cd uptake and the mechanisms involved were investigated at the jointing, heading, and mature stages of wheat plants under field-plot conditions. A hydroponic experiment showed that the MR treatment significantly decreased the above-ground tissue Cd content compared with the M14 or R27 treatment. The BC+MR treatment reduced the grain Cd content by 51.5%-67.7% and Cd translocation factor at the mature stage of wheat plants and increased the organic matter-bound Cd content by 31%-75% in the rhizosphere soils compared with the BC or MR treatment. Compared with the BC or MR treatment, the relative abundances of the biomarkers associated with Gemmatimonas, Altererythrobacter, Gammaproteobacteria, Xanthomonadaceae, Phenylobacterium, and Nocardioides in the BC+MR-treated rhizosphere microbiome decreased and negatively correlated with the organic matter-bound Cd contents. In the BC+MR-treated root interior microbiome, the relative abundance of the biomarker belonging to Exiguobacterium increased and negatively correlated with the Cd translocation factor, while the relative abundance of the biomarker belonging to Pseudonocardiaceae decreased and positively correlated with the Cd translocation factor. Our findings suggested that the BC+MR treatment reduced Cd availability and Cd transfer through affecting the abundances of these specific biomarkers in the rhizosphere soil and root interior microbiomes, leading to decreased wheat grain Cd uptake in the contaminated soil.

Bioaccessibility and health risk assessment of hydrophobic organic pollutants in soils from four typical industrial contaminated sites in China.

There have been reports of potential health risks for people from hydrophobic organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated hydrocarbons (PCHs), and organophosphate flame retardants (OPFRs). When a contaminated site is used for residential housing or public utility and recreation areas, the soil-bound organic pollutants might pose a threat to human health. In this study, we investigated the contamination profiles and potential risks to human health of 15 PAHs, 6 PCHs, and 12 OPFRs in soils from four contaminated sites in China. We used an in vitro method to determine the oral bioaccessibility of soil pollutants. Total PAHs were found at concentrations ranging from 26.4 ng/g to 987 ng/g. PCHs (0.27‒14.3 ng/g) and OPFRs (6.30‒310 ng/g) were detected, but at low levels compared to earlier reports. The levels of PAHs, PCHs, and OPFRs released from contaminated soils into simulated gastrointestinal fluids ranged from 1.74% to 91.0%, 2.51% to 39.6%, and 1.37% to 96.9%, respectively. Based on both spiked and unspiked samples, we found that the oral bioaccessibility of pollutants was correlated with their logKow and molecular weight, and the total organic carbon content and pH of soils. PAHs in 13 out of 38 contaminated soil samples posed potential high risks to children. When considering oral bioaccessibility, nine soils still posed potential risks, while the risks in the remaining soils became negligible. The contribution of this paper is that it corrects the health risk of soil-bound organic pollutants by detecting bioaccessibility in actual soils from different contaminated sites.

Oxygen atmosphere enhances ball milling remediation of petroleum-contaminated soil and reuse as adsorptive/catalytic materials for wastewater treatment.

Ball milling is an environmentally friendly technology for the remediation of petroleum-contaminated soil (PCS), but the cleanup of organic pollutants requires a long time, and the post-remediation soil needs an economically viable disposal/reuse strategy due to its vast volume. The present paper develops a ball milling process under oxygen atmosphere to enhance PCS remediation and reuse the obtained carbonized soil (BCS-O) as wastewater treatment materials. The total petroleum hydrocarbon removal rates by ball milling under vacuum, air, and oxygen atmospheres are 39.83%, 55.21%, and 93.84%, respectively. The Langmuir and pseudo second-order models satisfactorily describe the adsorption capacity and behavior of BCS-O for transition metals. The Cu2+, Ni2+, and Mn2+ adsorbed onto BCS-O were mainly bound to metal carbonates and metal oxides. Furthermore, BCS-O can effectively activate persulfate (PDS) oxidation to degrade aniline, while BCS-O loaded with transition metal (BCS-O-Me) shows better activation efficiency and reusability. BCS-O and BCS-O-Me activated PDS oxidation systems are dominated by 1O2 oxidation and electron transfer. The main active sites are oxygen-containing functional groups, vacancy defects, and graphitized carbon. The oxygen-containing functional groups and vacancy defects primarily activate PDS to generate 1O2 and attack aniline. Graphitized carbon promotes aniline degradation by accelerating electron transfer. The paper develops an innovative strategy to simultaneously realize efficient remediation of PCS and sequential reuse of the post-remediation soil.

Nitrogen utilization efficiency assessment during bioremediation of petroleum-contaminated loess soils: insights from metagenomic analysis.

Nitrogen addition is commonly used to remediate total petroleum hydrocarbons (TPH) in petroleum-contaminated soils. However, acceptable exogenous nitrogen dosages and their utilization efficiency for the degradation of hydrocarbons in oil-polluted soils are not well understood. This study compared the hydrocarbon bioremediation capacity by applying different doses of NH4Cl as a stimulant in soils contaminated with TPH at 8553 and 17090 mg/kg. The results showed acceptable exogenous nitrogen levels ranging from 60 to 360 mg N/kg soil, and the optimal nitrogen dosage for TPH remediation was 136 mg N/kg in soils with different TPH concentrations. The nitrogen availability efficiency (NAE) and nitrogen polarization factor availability (NPFA) in the 136 mg N/kg addition treatments were 6.69 and 20.47 mg/mg in 8533 mg/kg TPH-polluted soil, and 6.03 and 31.11 mg/mg in 17090 mg/kg TPH-polluted soil, respectively. Metagenomic analysis revealed that the application of 136 mg/kg nitrogen facilitated ammonia oxidation and nitrite reduction to nitric oxide, and induced soil microorganisms to undergo regulatory or adaptive changes in energy supply and metabolic state, which could aid in restoring the ecological functions of petroleum-contaminated soils. These findings underscore that 136 mg/kg of nitrogen dosage application is optimal for remediation of petroleum-contaminated soils irrespective of the TPH concentrations. This exogenous nitrogen application dosage for TPH remediation aligns with the nitrogen requirements for crop growth in agriculture.

Migration of fluoranthene, phenanthrene, and pyrene in soil environment during the growth of Brassica rapa subsp. chinensis.

The escalating concern surrounding fluoranthene (FLN), phenanthrene (Phe), and pyrene (Pyr), underscores the urgency to investigate their dynamics in the context of agricultural ecosystems. Brassica rapa subsp. chinensis (Bok choy), a globally consumed vegetable, holds particular significance in this scenario. This study explores the migration and transformation of FLN, Phe, and Pyr from soil to Brassica rapa subsp. chinensis during its growth. The germination rates of seeds in these treatments varied, with soil+Bok choy and soil+FLN+Bok choy treatments showing higher rates (77.8 %), while soil+mix+Bok choy exhibited the lowest rate (11.1 %) after 3 days. Analyzing the distribution of FLN, Phe, and Pyr in Brassica rapa subsp. chinensis parts after 30 days revealed a sequence of accumulation in stem> root> leaf. This study provides information on practical implications for regulating the soil-plant migration and transformation of FLN, Phe, and Pyr, offering valuable insights for migration of PAHs pollution in agricultural settings.

The dynamic response mechanism of crops to manganese uptake and transfer mediated by different intercropping crop attributes.

BACKGROUND: An issue of pressing concern is the manganese contamination in farmland soils adjacent to industrial areas. To address this, intercropping hyperaccumulator plants with crops emerges as a sustainable approach to ensuring food security. This study aims to investigate the influence of intercropping Sedum alfredii with maize or soybean on their growth and the dynamics of manganese accumulation through field experiments. RESULTS: The results showed that compared with monoculture, the Sedum alfredii-maize intercropping system exhibited a land equivalent ratio (LER) of 1.89, signifying a 71.13% augmentation in bioaccumulation amount (BCA). Additionally, it led to a significant reduction in manganese content in various organs, ranging from 17.05% to 25.50%. However, the Sedum alfredii-soybean intercropping system demonstrated a LER of 1.94, accompanied by a 66.11% increase in BCA, but did not significantly reduce the manganese content in the roots, stems, and pods of soybeans. Furthermore, manganese accumulation in maize and soybean grains was primarily attributed to the aboveground translocation of manganese. The intercropping effect on blocking manganese absorption of maize during growth and maturity is primarily attributed to the earlier manganese accumulation in intercropped maize by 2.63 to 4.35 days, and a reduction of 21.95% in the maximum manganese accumulation rate. CONCLUSIONS: The study found that manganese accumulation dynamics vary significantly depending on the crop family. Intercropping Sedum alfredii with maize enhances land-use efficiency and reduces manganese uptake by crops, making it a promising strategy for remediating manganese-contaminated farmland near industrial areas. © 2024 Society of Chemical Industry.

Effect of AC electric field on enhancing phytoremediation of Cd-contaminated soils in different pH soils.

To increase the efficiency of phytoremediation to clean up heavy metals in soil, assisted with alternating current (AC) electric field technology is a promising choice. Our experiments utilized the hyperaccumulator Sedum alfredii Hance and the fast-growing, high-biomass willow (Salix sp.). We investigated the efficiency of AC field combined with S. alfredii-willow intercropping for removing Cd from soils with different pH values. In the AC electric field treatment with S. alfredii-willow intercropping, the available Cd content in acidic soil increased by 50.00% compared to the control, and in alkaline soil, the increase was 100.00%. Furthermore, AC electric field promoted Cd uptake by plants in both acidic and alkaline soils, with Cd accumulation in the aboveground increased by 20.52% (P < 0.05) and 11.73%, respectively. In conclusion, the integration of AC electric fields with phytoremediation demonstrates significant favorable effectiveness.

Efficient removal of Cr(VI) from contaminated kaolin and anolyte by electrokinetic remediation with foamed iron anode electrode and acetic acid electrolyte.

Combined electrokinetic remediation employing reducing agents represents an extensively utilized approach for the remediation of hexavalent chromium (Cr(VI))-contaminated soil. In this investigation, electrokinetic remediation of artificially contaminated kaolin was conducted utilizing a separate circulation system for the anolyte, with a 0.5M solution of acetic acid (HAc) as the electrolyte and foamed iron serving as the anode. The experimental outcomes demonstrated that employing HAc as the electrolyte enhances the electromigration of Cr(VI) and establishes an acidic milieu conducive to the reduction of Cr(VI) by foamed iron, thereby facilitating the rapid reduction of Cr(VI) accumulated in the anolyte through electrokinetic remediation. In the self-prepared contaminated kaolin, the initial concentration of Cr(VI) was 820.26 mg/L. Following the remediation process under optimal experimental conditions, the concentration was significantly reduced to 11.6 mg/L, achieving a removal efficiency of Cr(VI) in the soil of 98.59%. In the optimal experimental setup, the Cr(VI) concentration in the anolyte was reduced to 0.05 mg/L, which is below the EPA's Safe Drinking Water Act standard for Cr(VI) content of 0.1 mg/L. The removal mechanism of Cr(VI) from the electrolyte primarily involves reduction, precipitation, and co-precipitation, with the foamed iron playing a predominant role. HAc and foamed iron exhibit a synergistic effect. The findings of this study substantiate that the integration of foamed iron with HAc is efficacious for the electrokinetic remediation of soil contaminated with Cr(VI).

Reduction of the exchangeable cadmium content in soil by appropriately increasing the maturity degree of organic fertilizers.

To enhance the remediation effect of heavy metal pollution, organic fertilizers with different maturity levels were added to cadmium-contaminated soil. The remediation effect was determined by evaluating the form transformation and bioavailability of cadmium in heavy metal-contaminated soil. -Results showed that when the maturity was 50%, although the soil humus (HS) content increased, it didn't contribute to reducing the bioavailability of soil Cd. Appropriately increasing the maturity (GI ≥ 80%), the HS increased by 113.95%∼157.96%, and reduced significantly the bioavailability of soil Cd, among the exchangeable Cd decreased by 16.04%∼33.51% (P < 0.01). The structural equation modeling (SEM) revealed that HS content is a critical factor influencing the transformation of Cd forms and the reduction of exchangeable Cd accumulation; the HS and residual Cd content were positively correlated with the maturity (P < 0.01), while exchangeable Cd content was negatively correlated with maturity (P < 0.01), and the correlation increased with increasing maturity. In summary, appropriately increasing the maturity (GI ≥ 80%) can increase significantly HS, promote the transformation of exchangeable Cd into residual Cd, and ultimately enhance the effectiveness of organic fertilizers in the remediation of soil Cd pollution. These results provide a new insight into the remediation of Cd-contaminated soil through organic fertilizer as soil amendment in Cd-contaminated soil.

Biochar remediates cadmium and lead contaminated soil by stimulating beneficial fungus Aspergillus spp.

An in-depth understanding of the micro-ecological mechanisms underlying the remediation of heavy metal-contaminated soils by biochar amendment is crucial for enhancing the efficacy of biochar-microbe combination. Nevertheless, this remediation mechanism remains elusive. Consequently, we performed a pot experiment to investigate the effects of biochar on soil fungal communities in a cadmium (Cd) and lead (Pb) contaminated soil. The results demonstrated that the amendment of biochar derived from rice straw significantly reshaped soil fungal communities, leading to the enrichment of members of the genus Aspergillus, which was found to correlate significantly with the remediation of heavy metal-contaminated soil. A representative of the targeted Aspergillus species (strain F8) was successfully isolated. The results of the pot experiments demonstrated that the inoculation with the isolate F8 can promote plant growth, immobilize soil Cd and Pb, and decrease tomato plant uptake of Cd and Pb. These results indicate that the enrichment of specific taxa induced by biochar amendment is associated with the remediation of heavy metal-contaminated soil. Therefore, this study provides new evidence to support the indirect mechanism of biochar in the remediation of heavy metal-contaminated soil by reshaping the soil microbiome.

Hg2+ removal characteristics of a strain of mercury-tolerant bacteria screened from heavy metal-contaminated soil in a molybdenum-lead mining area.

In this study, the mercury-tolerant strain LTC105 was isolated from a contaminated soil sample collected from a molybdenum-lead mine in Luanchuan County, Henan Province, China. The strain was shown to be highly resistant to mercury, with a minimum inhibitory concentration (MIC) of 32 mg·L-1. After a 24-h incubation in LB medium with 10 mg·L-1 Hg2+, the removal, adsorption, and volatilization rates of Hg2+ were 97.37%, 7.3%, and 90.07%, respectively, indicating that the strain had significant influence on mercury removal. Based on the results of Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), the investigation revealed that the primary function of LTC105 was to encourage the volatilization of mercury. The LTC105 strain also showed strong tolerance to heavy metals such as Mn2+, Zn2+, and Pb2+. According to the results of the soil incubation test, the total mercury removal rate of the LTC105 inoculation increased by 16.34% when the initial mercury concentration of the soil was 100 mg·L-1 and by 62.28% when the initial mercury concentration of the soil was 50 mg·kg-1. These findings indicate that LTC105 has certain bioremediation ability for Hg-contaminated soil and is a suitable candidate strain for microbial remediation of heavy metal-contaminated soil in mining areas.

Straw removal reduces Cd availability and rice Cd accumulation in Cd-contaminated paddy soil: Cd fraction, soil microorganism structure and porewater DOC and Cd.

The impacts of straw removal on rice Cd absorption, behaviour of Cd and microbial community in rhizosphere soil were investigated in paddy fields over two consecutive seasons. The results of the experiments in two fields revealed that straw removal promoted the transformation of soil Cd from acid-extractable and oxidisable fraction to residual fraction and reduced soil DTPA-Cd content with the reduction in DOC and Cd ions in soil porewater, thereby decreasing Cd content in rice. Specifically, the Cd content in brown rice was below 0.2 mg·kg-1 when all rice straw and roots were removed in the slightly Cd-contaminated soils. The α-diversity of soil microbial communities was less influenced by continuous straw removal, ß-diversity was altered and the relative abundances of Anaeromyxobacter, Methylocystis and Mycobacterium microbes were increased. Redundancy analysis and network analysis exhibited that soil pH predominantly influenced the microbial community. Path analysis revealed that the Cd content in brown rice could be directly influenced by the soil Total-Cd and DTPA-Cd, as well as soil pH and OM. Straw removal, including roots removal, is an economical and effective technique to reduce Cd accumulation in rice plants.

Microplastics in heavy metal-contaminated soil drives bacterial community and metabolic changes.

Microplastic (MP) and heavy metal pollution in soil are global issues. When MPs invade the soil, they combine with heavy metals and adversely affect soil organisms. Six common MPs-polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and polytetrafluoroethylene-were selected for this study to examine the effects of various concentrations and MP types on the physicochemical properties, bacterial community, and soil metabolism of heavy metal-contaminated soil. MP enhanced predation and competition among heavy metal-contaminated soil bacteria. Heavy metal-MPs alter metabolites in lipid metabolism, other pathways, and the bacterial community. MP treatment promotes energy production and oxidative stress of soil bacteria to resist the toxicity of heavy metals and degrade MP pollution. In conclusion, MP treatment changed the metabolism of the microbiome in heavy metal-contaminated soil and increased the abundance of Proteobacteria that responded to MPs and heavy metal pollution by 11.54 % on average. This study explored bacteria for the ecological regeneration and provided ideas for MPs and heavy metal-contaminated soil remediation.

Mechanisms of enhancing MgO for stabilization/solidification of Pb-contaminated red clay through CO2 sequestration.

Pb-contaminated soil poses significant environmental and health risks as well as soil stability issues. Research on sandy soils highlights CO2-enhanced reactive MgO as a promising solution for improving the solidification of Pb-contaminated soils. However, carbonation effects can differ markedly between soil types owing to varying soil properties. In this study, we evaluated the effects of CO2-enhanced reactive MgO on the engineering and environmental characteristics of Pb-contaminated red clay and explored its mechanism of carbonation solidification. The results showed that CO2-enhanced reactive MgO increased the strength of Pb-contaminated red clay to over 3 MPa within 1 h, which was approximately 25 times the strength of untreated soil (0.2 MPa) and significantly higher than that of reactive MgO-treated, uncarbonated soil (0.8 MPa). The pH of the carbonated soil (9-10) facilitated Pb2+ immobilization, and the increase over the initial parameter elevated the electrical conductivity value. Moreover, CO2-enhanced reactive MgO reduced the Pb2+ leaching concentration to below 0.1 mg/L, even at high Pb concentrations (10,000 mg/kg). Pb2+ transformed into lead carbonates during the carbonation process, with the hydrated magnesium carbonates forming a dense internal structure. This solidification mechanism included chemical precipitation, physical adsorption, and encapsulation. Notably, the carbonation time should be controlled within 1 h to prevent soil expansion. Together, these findings support the potential of CO2-enhanced reactive MgO for efficient and low-carbon application in the solidification of Pb-contaminated red clay.

Response of petroleum-contaminated soil to chemical oxidation combined with biostimulation.

In this study, a microcosm experiment was conducted to investigate the effects of Na2S2O8 preoxidation combined with biostimulation on petroleum-contaminated soil remediation. The response of microbial community during this process was explored using BIOLOG ECO microplate carbon utilization method and 16 s rDNA high-throughput sequencing. The results showed that use of 10 mg/g Na2S2O8 removed 19.8 % of the petroleum hydrocarbons, reduced soil biotoxicity and did not affect soil microbial activity compared to other concentrations. Therefore, sodium persulfate of ca. 10 mg/g was used to oxidize petroleum in soil before the biostimulation experiment with organic and inorganic fertilizers. Our finding showed that the content of total petroleum hydrocarbons (TPHs) in soil was reduced by 43.3 % in inorganic fertilizer treatment after 60 days. The results of BIOLOG ECO microplate carbon utilization analysis and 16 S rDNA high-throughput sequencing further confirmed that biostimulation quickly restored the microbial activities in oxidant treated soil. The main marker bacteria in chemical oxidation combined with biostimulation remediation were Arthrobacter and Paenarthrobacter, and their relative abundances were both significantly negatively correlated with the content of petroleum hydrocarbons in soil.

Intraspecific variation in tomato: Impact on production quality and cadmium phytoremediation efficiency in intercropping systems with hyperaccumulating plant.

Intercropping with hyperaccumulators can facilitate the safe utilization of cadmium-contaminated soil. However, the effectiveness of this approach is influenced by plant species and varieties, which necessitates research on optimal plant consortia. In this study, 8 tomato varieties (3 cherry tomatoes and 5 common large-fruit tomatoes) were intercropped with Sedum alfredii in a moderately Cd-contaminated vegetable field. The results showed that the Cd concentration in the fruits of common large-fruit tomato varieties under monoculture was 1.03-1.50 mg/kg, while that in the fruits of cherry tomato varieties was 0.67-0.71 mg/kg. After intercropping with S. alfredii, the fruit Cd concentrations of Hangza 501, Hangza 503, and Hangza 108 decreased by 16.42 %, 19.72 %, and 6.76 %, respectively, while those of the other varieties significantly increased, except for those of Hangza 8. In contrast, the shoot Cd concentration of cherry tomatoes was greater than that of large-fruit tomatoes under monoculture. Furthermore, a significant increase in the shoot Cd concentration was noted in the Hangza 501, Hangza 503 and Hangza 603 plants following intercropping. Additionally, intercropping with S. alfredii increased the concentration of soluble sugars in the fruits of Hangza 8, Hangza 501, Hangza 503 and Hangza 603 by 4.66 %, 17.91 %, 10.60 % and 17.88 %, respectively. Intercropping with tomatoes resulted in a decrease in both the biomass and Cd uptake of S. alfredii. Interestingly, the inhibitory effect on S. alfredii was less pronounced when intercropped with cherry tomatoes than when intercropped with large-fruit tomatoes. Among the intercropping treatments, S. alfredii exhibited the greatest total Cd accumulation (0.06 mg/plant) when intercropped with Hangza 503. In conclusion, the cherry tomato variety Hangza 503 was the most suitable for intercropping with S. alfredii and can be used safely for vegetable production and simultaneous phytoremediation of polluted soil. Our findings suggest that strategic selection of tomato varieties can optimize the effectiveness of "phytoextraction coupled with agro-safe production" technology for managing soil Cd concentrations.

Genotype of pioneer plant Miscanthus is not a key factor in the structure of rhizosphere bacterial community in heavy metal polluted sites.

Miscanthus is a common pioneer plant with abundant genetic variation in abandoned mines in southern China. However, the extent to which genetic differentiation among species modulates rhizosphere bacterial communities remains unclear. Miscanthus samples were collected from 26 typical abandoned heavy-metal mines with different soil types in southern China, tested using 14 pairs of simple sequence repeats (SSR) primers, and classified into two genotypes based on Nei's genetic distance. The structure and diversity of rhizosphere bacterial communities were examined using 16 S rRNA sequencing. The results showed that among the factors affecting the rhizosphere bacterial community structure of Miscanthus samples, the role of genotype was not significant, and geographical conditions were the most important factors, followed by pH and total organic carbon (TOC). The process of rhizospheric community assembly varied among different genotypes; however, the recruited species and their abundances were similar. Collectively, we provided an approach based on genetic differentiation to quantify the relative contribution of genotypes to the rhizosphere bacterial community, demonstrating that genotypes contribute less than soil conditions. Our findings provide new insights into the role of host genetics in the ecological processes of plant rhizosphere bacterial communities in abandoned mines and provide theoretical support for microbe-assisted phytoremediation.

Toward a more realistic estimate of exposure to chromium and nickel in soils of geogenic and/or anthropogenic origin: importance of oral bioaccessibility.

To enhance risk assessment for contaminated sites, incorporating bioavailability through bioaccessibility as a corrective factor to total concentration is essential to provide a more realistic estimate of exposure. While the main in vitro tests have been validated for As, Cd, and/or Pb, their potential for assessing the bioaccessibility of additional elements remains underexplored. In this study, the physicochemical parameters, pseudototal Cr and Ni concentrations, soil phase distribution, and oral bioaccessibility of twenty-seven soil samples were analysed using both the ISO 17924 standard and a simplified test based on hydrochloric acid. The results showed wide variability in terms of the concentrations (from 31 to 21,079 mg kg-1 for Cr, and from 26 to 11,663 mg kg-1 for Ni) and generally low bioaccessibility for Cr and Ni, with levels below 20% and 30%, respectively. Bioaccessibility variability was greater for anthropogenic soils, while geogenic enriched soils exhibited low bioaccessibility. The soil parameters had an influence on bioaccessibility, but the effects depended on the soils of interest. Sequential extractions provided the most comprehensive explanation for bioaccessibility. Cr and Ni were mostly associated with the residual fraction, indicating limited bioaccessibility. Ni was distributed in all phases, whereas Cr was absent from the most mobile phase, which may explain the lower bioaccessibility of Cr compared to that of Ni. The study showed promising results for the use of the simplified test to predict Cr and Ni bioaccessibility, and its importance for more accurate human exposure evaluation and effective soil management practices.

Impact of low molecular weight organic acids on heavy metal(loid) desorption in biochar-amended paddy soil.

Low molecular weight organic acids (LMWOAs) are important soil components and play a key role in regulating the geochemical behavior of heavy metal(loid)s. Biochar (BC) is a commonly used amendment that could change LMWOAs in soil. Here, four LMWOAs of oxalic acid (OA), tartaric acid (TA), malic acid (MA), and citric acid (CA) were evaluated for their roles in changing Cd and SB desorption behavior in contaminated soil with (S1-BC) or without BC (S1) produced from Paulownia biowaste. The results showed that OA, TA, MA, and CA reduced soil pH with rising concentrations, and biochar partially offset the pH reduction by LMWOAs. The LMWOAs reduced Cd desorption from the soil at low concentrations but increased Cd desorption at high concentrations, and CA was the most powerful in this regard. The LMWOAs had a similar effect on Sb desorption, and CA was the most effective species of LMWOAs. Adding BC to the soil affects Cd and Sb dynamics by reducing the Cd desorption but increasing Sb desorption from the soil and increasing the distribution coefficient (Kd) values of Cd but lowering the Kd values of Sb. This study helped understand the effects of LMWOAs on the geochemical behavior of Cd and Sb in the presence of biochar, as well as the potential risks of biochar amendment in enhancing Sb desorption from contaminated soil.

Enhancing biodegradation of vegetable oil-contaminated soil with soybean texturized waste, spent mushroom substrate, and stabilized poultry litter in microcosm systems.

Industrial activities contribute to environmental pollution, particularly through unregulated effluent discharges, causing adverse effects on ecosystems. Vegetable oils, as insoluble substances, exacerbate this pollution, forming impermeable films and affecting the oxygen transfer, leading to serious habitat disruption. Organic wastes, such as soybean texturized waste, spent mushroom substrate, and stabilized poultry litter, were assessed for their efficacy in enhancing the degradation of vegetable oil in contaminated soil. For this purpose, contaminated soil was amended with each of the wastes (10% w/w) using microcosm systems, which were monitored physico-chemically, microbiologically and toxicologically. Results indicate that the wastes promoted significant oil degradation, achieving 83.1, 90.7, and 86.2% removal for soybean texturized waste, spent mushroom substrate, and stabilized poultry litter, respectively, within a 90-day period. Additionally, they positively influenced soil microbial activity, as evidenced by increased levels of culturable microorganisms and hydrolytic microbial activity. While bioassays indicated no phytotoxicity in most cases, soybean texturized waste exhibited inhibitory effects on seed germination and root elongation of Lactuca sativa. This study significantly enhances our comprehension of remediation techniques for sites tainted with vegetable oils, highlighting the critical role of organic waste as eco-friendly agents in soil restoration. Emphasizing the practical implications of these findings is imperative to underscore the relevance and urgency of addressing vegetable oil contamination in soil. Moving forward, tailored strategies considering both contaminant characteristics and soil ecosystem traits are vital for ensuring effective and sustainable soil remediation.