Synergistic Integration of Anammox and Endogenous Denitrification Processes for the Simultaneous Carbon, Nitrogen, and Phosphorus Removal.

The feasibility of a synergistic endogenous partial denitrification-phosphorus removal coupled anammox (SEPD-PR/A) system was investigated in a modified anaerobic baffled reactor (mABR) for synchronous carbon, nitrogen, and phosphorus removal. The mABR comprising four identical compartments (i.e., C1-C4) was inoculated with precultured denitrifying glycogen-accumulating organisms (DGAOs), denitrifying polyphosphate-accumulating organisms, and anammox bacteria. After 136 days of operation, the chemical oxygen demand (COD), total nitrogen, and phosphorus removal efficiencies reached 88.6 ± 1.0, 97.2 ± 1.5, and 89.1 ± 4.2%, respectively. Network-based analysis revealed that the biofilmed community demonstrated stable nutrient removal performance under oligotrophic conditions in C4. The metagenome-assembled genomes (MAGs) such as MAG106, MAG127, MAG52, and MAG37 annotated as denitrifying phosphorus-accumulating organisms (DPAOs) and MAG146 as a DGAO were dominated in C1 and C2 and contributed to 89.2% of COD consumption. MAG54 and MAG16 annotated as Candidatus_Brocadia (total relative abundance of 16.5% in C3 and 4.3% in C4) were responsible for 74.4% of the total nitrogen removal through the anammox-mediated pathway. Functional gene analysis based on metagenomic sequencing confirmed that different compartments of the mABR were capable of performing distinct functions with specific advantageous microbial groups, facilitating targeted nutrient removal. Additionally, under oligotrophic conditions, the activity of the anammox bacteria-related genes of hzs was higher compared to that of hdh. Thus, an innovative method for the treatment of low-strength municipal and nitrate-containing wastewaters without aeration was presented, mediated by an anammox process with less land area and excellent quality effluent.

Sulfur-containing iron carbon nanocomposites activate persulfate for combined chemical oxidation and microbial remediation of petroleum-polluted soil.

In this study, sulfur-containing iron carbon nanocomposites (S@Fe-CN) were synthesized by calcining iron-loaded biomass and utilized to activate persulfate (PS) for the combined chemical oxidation and microbial remediation of petroleum-polluted soil. The highest removal efficiency of total petroleum hydrocarbons (TPHs) was achieved at 0.2% of activator, 1% of PS and 1:1 soil-water ratio. The EPR and quenching experiments demonstrated that the degradation of TPHs was caused by the combination of 1O2,·OH, SO4·-, and O2·-. In the S@Fe-CN activated PS (S@Fe-CN/PS) system, the degradation of TPHs underwent two phases: chemical oxidation (days 0 to 3) and microbial degradation (days 3 to 28), with kinetic constants consistent with the pseudo-first-order kinetics of chemical and microbial remediation, respectively. In the S@Fe-CN/PS system, soil enzyme activities decreased and then increased, indicating that microbial activities were restored after chemical oxidation under the protection of the activators. The microbial community analysis showed that the S@Fe-CN/PS group affected the abundance and structure of microorganisms, with the relative abundance of TPH-degrading bacteria increased after 28 days. Moreover, S@Fe-CN/PS enhanced the microbial interactions and mitigated microbial competition, thereby improving the ability of indigenous microorganisms to degrade TPHs.

The toxic mechanism of tetracycline on root tips in hulless barley (Hordeum vulgare L. var. nudum).

Tetracycline (TC) is a commonly used antibiotic that affects various physiological processes in plants. However, its negative effects on plants remain poorly understood at the molecular level. To ascertain the TC toxicity in the roots, transcriptomic, cytological, and physiological analyses were performed to explore the molecular mechanisms of TC influencing the growth of hulless barley root. At a low concentration (1 mg/L), TC promoted root growth by upregulating the genes related to the flavonoid pathway. At high concentrations (10, 100, and 200 mg/L), TC downregulated genes related to homologous recombination in the root meristem zone and inhibited the mitosis index by 16.4%. Disruption of the DNA repair process can lead to chromosomal aberrations, resulting in a 6.8% C-mitosis rate in the most severe cases. Finally, root growth was inhibited by TC, as evidenced by a reduction in root viability, an increase in reactive oxygen species content, and an inhibition of root length. Cross-comparison of physiological and cytological characterizations and transcriptomic information revealed changes in genetic processes under TC stress. Overall, we present an early genetic strategy to study the significant influence of TC stress on roots.

Competitive adsorption of lead and cadmium onto nanoplastics with different charges: Two-dimensional correlation spectroscopy study.

The competitive adsorption ability and mechanisms of lead (Pb2+) and cadmium (Cd2+) by nanoplastics (NPs) with positive charges (PS-NH2) and negative charges (PS-SO3H) were investigated by using batch adsorption experiments coupled with the two-dimensional correlation spectroscopy (2D-COS) method. The adsorption isotherm results showed that PS-SO3H exhibited a higher adsorption capacity for Pb2+ or Cd2+ compared to PS-NH2. The adsorption affinity of NPs for Pb2+ was higher than that of Cd2+. The competitive adsorption results showed that Pb2+ had a more pronounced negative effect on the adsorption of Cd2+. The adsorption capacities of NPs were affected by the surface charge and solution pH. Electrostatic force was the main factor influencing PS-SO3H to capture Pb2+ and Cd2+, while chelation was the main mechanism between PS-NH2 and metals. The functional groups of NPs played significant roles in the sorption of Pb2+ or Cd2+ according to the FTIR spectra and 2D-COS analysis. This study provided new insights into the impact of NPs on the transport of other pollutants.

Integrative effects of microbial inoculation and amendments on improved crop safety in industrial soils co-contaminated with organic and inorganic pollutants.

Soils co-contaminated by organic and inorganic pollutants usually pose major ecological risks to soil ecosystems including plants. Thus, effective strategies are needed to alleviate the phytotoxicity caused by such co-contamination. In this study, microbial agents (a mixture of Bacillus subtilis, Sphingobacterium multivorum, and a commercial microbial product named OBT) and soil amendments (ß-cyclodextrin, rice husk, biochar, calcium magnesium phosphate fertilizer, and organic fertilizer) were evaluated to determine their applicability in alleviating toxicity to crops (maize and soybean) posed by polycyclic aromatic hydrocarbon (PAHs) and potentially toxic metals co-contaminated soils. The results showed that peroxidase, catalase, and superoxide dismutase activity levels in maize or soybean grown in severely or mildly contaminated soils were significantly enhanced by the integrative effects of amendments and microbial agents, compared with those in single plant treatments. The removal rates of Zn, Pb, and Cd in severely contaminated soils were 49 %, 47 %, and 51 % and 46 %, 45 %, and 48 %, for soybean and maize, respectively. The total contents of Cd, Pb, Zn, and PAHs in soil decreased by day 90. Soil organic matter content, levels of nutrient elements, and enzyme activity (catalase, urease, and dehydrogenase) increased after the amendments and application of microbial agents. Moreover, the amendments and microbial agents also increased the diversity and distribution of bacterial species in the soil. These results suggest that the amendments and microbial agents were beneficial for pollutant purification, improving the soil environment and enhancing both plant resistance to pollutants and immune systems of plants.

How do different arsenic species affect the joint toxicity of perfluorooctanoic acid and arsenic to earthworm Eisenia fetida: A multi-biomarker approach.

Perfluorooctanoic acid (PFOA) and arsenic are widely distributed pollutants and can coexist in the environment. However, no study has been reported about the effects of different arsenic species on the joint toxicity of arsenic and PFOA to soil invertebrates. In this study, four arsenic species were selected, including arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), and dimethylarsinate (DMA). Earthworms Eisenia fetida were exposed to soils spiked with sublethal concentrations of PFOA, different arsenic species, and their binary mixtures for 56 days. The bioaccumulation and biotransformation of pollutants, as well as eight biomarkers in organisms, were assayed. The results indicated that the coexistence of PFOA and different arsenic species in soils could enhance the bioavailability of arsenic species while reducing the bioavailability of PFOA, and inhibit the arsenic biotransformation process in earthworms. Responses of most biomarkers in joint treatments of PFOA and As(III)/As(V) showed more significant variations compared with those in single treatments, indicating higher toxicity to the earthworms. The Integrated Biomarker Response (IBR) index was used to integrate the multi-biomarker responses, and the results also exhibited enhanced toxic effects in combined treatments of inorganic arsenic and PFOA. In comparison, both the biomarker variations and IBR values were lower in joint treatments of PFOA and MMA/DMA. Then the toxic interactions in the binary mixture systems were characterized by using a combined method of IBR and Effect Addition Index. The results revealed that the toxic interactions of the PFOA/arsenic mixture in earthworms depended on the different species of arsenic. The combined exposure of PFOA with inorganic arsenic led to a synergistic interaction, while that with organic arsenic resulted in an antagonistic response. Overall, this study provides new insights into the assessment of the joint toxicity of perfluoroalkyl substances and arsenic in soil ecosystems.

Ecological toxicity of Cd, Pb, Zn, Hg and regulation mechanism in Solanum nigrum L.

This study aimed to investigate the combined ecotoxicological effects of Cd, Pb, Zn, Hg and regulation mechanisms in Solanum nigrum L. In this work, the co-exposure of these four heavy metals hindered the transformation of Cd, Zn, and Hg (except Pb) from available to non-available chemical forms. Individual Cd, Pb, Zn and Hg induced the oxidative damages to S. nigrum L., while their combination further enhanced this ecological toxicity. By internal regulation, the ecological toxicity of metals to S. nigrum L. could be alleviated to a certain extent. Specifically, S. nigrum L. was a hyperaccumulator of Cd with BCF ＞1. Moreover, since BCFroot of Pb, Zn and Hg were all greater than BCFshoot, S. nigrum L. could accumulate Pb, Hg and Zn mainly in plant roots, which was beneficial for the detoxification of plants. Meanwhile, the immobilization by cell wall (the proportions of Cd, Pb, Zn and Hg in the cell wall were 54.46-84.92%, 38.33-49.25%, 48.38-56.19% and 45.97-63.47% in low metal concentration treatments) and the sequestration in vacuole (the proportions of Cd, Pb, Zn, and Hg in the soluble fractions are 50.99-59.00%, 41.05-45.46%, 37.54-61.04% and 33.47-61.35% in high metal concentration treatments) also act as important detoxification pathways. The external regulation was mainly the changes of soil microbial communities influenced by plants. Specifically, the richness and diversity of bacteria in rhizosphere soil were increased, and roots of S. nigrum L. recruited some potentially beneficial microbials. This study provided a theoretical basis and guidance for S. nigrum L. as a phytoremediation plant under combined heavy metal pollution.

Co-Removal Effect and Mechanism of Cr(VI) and Cd(II) by Biochar-Supported Sulfide-Modified Nanoscale Zero-Valent Iron in a Binary System.

This study aimed to explore the co-removal effect and mechanism of Cr(VI) and Cd(II) with an optimized synthetic material. The toxicity and accumulation characteristics of Cr(VI) and Cd(II) encountered in wastewater treatment areas present significant challenges. In this work, a rational assembly of sulfide-modified nanoscale zero-valent iron (SnZVI) was introduced into a biochar (BC), and a Cr(VI)-Cd(II) binary system adsorbent with high efficiency was synthesized. When the preparation temperature of the BC was 600 °C, the molar ratio of S/Fe was 0.3, the mass ratio of BC/SnZVI was 1, and the best adsorption capacities of BC-SnZVI for Cr(VI) and Cd(II) in the binary system were 58.87 mg/g and 32.55 mg/g, respectively. In addition, the adsorption mechanism of BC-SnZVI on the Cr(VI)-Cd(II) binary system was revealed in depth by co-removal experiments, indicating that the coexistence of Cd(II) could promote the removal of Cr(VI) by 9.20%, while the coexistence of Cr(VI) could inhibit the removal of Cd(II) by 43.47%. This work provides a new pathway for the adsorption of Cr(VI) and Cd(II) in binary systems, suggesting that BC-SnZVI shows great potential for the co-removal of Cr(VI) and Cd(II) in wastewater.

Contribution, Composition, and Structure of EPS by In Vivo Exposure to Elucidate the Mechanisms of Nanoparticle-Enhanced Bioremediation to Metals.

Bacterial extracellular polymeric substances (EPS) have been recently found to contribute most for metal removal in nanoenhanced bioremediation. However, the mechanism by which NPs affect EPS-metal interactions is not fully known. Here, Halomonas sp. was employed to explore the role of EPS after in vivo exposure to Cd/Pb and polyvinylpyrrolidone (PVP) coated iron oxide nanoparticles (IONPs, 20 mg L-1) for 72 h. Cd-IONPs produced the highest concentrations of EPS proteins (136.3 mg L-1), while Cd induced the most production of polysaccharides (241.0 mg L-1). IONPs increased protein/polysaccharides ratio from 0.2 (Cd) to 1.2 (Cd-IONPs). The increased protein favors the formation of protein coronas on IONPs surface, which would promote Cd adsorption during NP-metal-EPS interaction. FTIR analysis indicated that the coexistence of Cd and IONPs interacted with proteins more strongly than with polysaccharides. Glycosyl monomer analyses suggested mannose and glucose as target sugars for EPS complexation with metals, and IONPs reduced metal-induced changes in monosaccharide profiles. Protein secondary structures changed in all treatments, but we could not distinguish stresses induced by metals from those by IONPs. These findings provide greater understanding of the role of EPS in NP-metal-EPS interaction, providing a better underpinning knowledge for the application of NP-enhanced bioremediation.

Hydroxypropyl-ß-cyclodextrin improves the removal of polycyclic aromatic hydrocarbons by aerobic granular sludge.

Polycyclic aromatic hydrocarbons (PAHs) as polar organic pollutants, their potential harm to the environment has caused widespread concern. This study describes a simple method to prepare modified aerobic granular sludge (AGS) by hydroxypropyl-ß-cyclodextrin (HP-ß-CD). Using HP-ß-CD modified AGS as the adsorbent, the removal of specific PAHs: Fluoranthene (Fla) reached 95% comparing to 80% of the unmodified AGS. The removal of Fla was related to initial concentration, temperature and ion concentration (Na+, Mg2+). The removal efficiency of Fla reached 96.27%, 94.26% and 93.69%, when initial concentration of Fla was 10, 15 and 20 µmol/L. At temperatures of 15°C, 30°C and 45°C, the removal efficiency of Fla (15 µmol/L) gradually improved from 87.20% to 94.84% and 95.73%. The presence of Na+ and Mg2+ ions led to the deterioration of PAHs removal. With the increase of Na+ and Mg2+ concentrations, the removal efficiency of modified AGS on PAHs decreased by 3.9% and 6.5%, respectively. These findings indicate the potential application of cyclodextrins as the active sites of a complex modified polymer network for PAHs wastewater treatment.

Assessment and projection of environmental impacts of food waste treatment in China from life cycle perspectives.

China produces vast amounts of food waste every year. However, the environmental impact of the current treatment of food waste and its potential for improvement are not very clear. Therefore, this study applied life cycle assessment to compare the current major treatment options for food waste and to systematically quantify the environmental impact of current and future food waste treatment in China based on the amount and treatment mode of food waste. In 2020, 125 million tons (Mt) of food waste was generated in China. Its treatment consumed 30.1 Mt oil-Eq of fossil fuels and 16.7 Mt of freshwater, and released 37.5 Mt of CO2-Eq. A promising finding was that if the proportion of food waste treated by anaerobic digestion exceeded 40% and landfilling was terminated by 2050, most impact categories would be reduced by more than 50%. Although anaerobic digestion is a potentially more environmentally friendly treatment option due to more output of energy and resources, it is worth noting that it consumed more freshwater than incineration and landfilling. Electricity consumption contributed more than 50% of the environmental burden of anaerobic digestion. Therefore, for the upstream of anaerobic digestion, China should further implement policies of waste classification and promote zero-waste cities, so that less impurities and more food waste would enter anaerobic digestion instead of landfills. Whereas downstream, the resource utilization of biogas and digestate enhance should be enhanced so as to strengthen the environmental sustainability of anaerobic digestion.

Preparation of a newly synthesized biopolymer binder and its application to reduce the erosion of tailings.

A new type of binder was developed by grafting casein and ß-glucan to investigate its effect on tailings erosion and plant growth. 6% casein and 2% ß-glucan were recommended as the best ratio of the new biopolymer binder, which had the best effect on the soil utilization of iron tailings. The infrared analysis of the new binder demonstrated that casein and ß-glucan reacted adequately as raw materials. The results of physichemical properties and loss prevention of iron tailings showed that the binder-treated soils demonstrated lower erodibility compared with untreated iron tailings. The particle size of the tailings was increased after the addition of the binder. In treated soil, the content of soil organic matter increased significantly, which provided sufficient nutrients for the plants growing. Compared with natural tailings without binder, plant height, fresh weight, chlorophyll content, and enzyme activity (POD and SOD) were also significantly increased. This study overcame the current defects of biopolymer in soil improvement and provided an environmentally friendly method to prevent the loss of iron tailings and promote its soil utilization efficiency.

Amendments and bioaugmentation enhanced phytoremediation and micro-ecology for PAHs and heavy metals co-contaminated soils.

Co-existence of polycyclic aromatic hydrocarbons (PAHs) and multi-metals challenges the decontamination of large-scale contaminated sites. This study aims to comprehensively evaluate the remediation potential of intensified phytoremediation in coping with complex co-contaminated soils. Results showed that the removal of PAHs and heavy metals is time-dependent, pollution-relevant, and plant-specific. Removal of sixteen PAHs by Medicago sativa L. (37.3%) was significantly higher than that of Solanum nigrum L. (20.7%) after 30 days. S. nigrum L. removed higher amounts of Cd than Zn and Pb, while M. sativa L. uptake more Zn. Nevertheless, amendments and microbial agents significantly increased the phytoremediation efficiency of pollutants and shortened the gap between plants. Cd removal and PAHs dissipation reached up to 80% and 90% after 90 days for both plants. Heavy metal stability in soil was promoted after the intensified phytoremediation. Plant lipid peroxidation was alleviated, regulated by changed antioxidant defense systems (superoxide dismutase, peroxidase, catalase). Soil enzyme activities including dehydrogenase, urease, and catalase increased up to 5-fold. Soil bacterial diversity and structure were changed, being largely composed of Proteobacteria, Actinobacteria, Patescibacteria, Bacteroidetes, and Firmicutes. These findings provide a green and sustainable approach to decontaminating complex-polluted environments with comprehensive improvement of soil health.

Production, Use, and Fate of Phthalic Acid Esters for Polyvinyl Chloride Products in China.

Phthalic acid esters (PAEs) are the most common plasticizers, approximately 90% of which are used in polyvinyl chloride (PVC) products, but they are also endocrine disruptors that have attracted considerable attention. The metabolism of PAEs in PVC products in China from 1958 to 2019 was studied using dynamic material flow analysis. The results showed that the total consumption of PAEs was 29.2 Mt in the past 60 years. By 2019, the in-use stocks of PAEs were 5.0 Mt. Construction materials were always in the leading position with respect to the consumption and in-use stocks of PAEs. A total PAE loss of 22.7 Mt was generated, of which 68.0% remained in waste distributed in landfills (50.1%), storage sites (5.5%), the environment (44.4%), 12.4% was eliminated during waste incineration and open burning, and 19.6% was emitted into the environment. From 1958 to 2019, 496.4, 55.6, and 3905.0 kt of PAEs were emitted into water, air, and soil, respectively. The use and waste treatment stages contributed 79.3 and 19.9% of the emissions of PAEs in the life cycle, respectively. This study systematically analyzed the metabolism of PAEs at the national level over a long-time span, providing useful information on the life cycle management of PAEs.

Insights into the vertical distribution of the microbiota in steel plant soils with potentially toxic elements and PAHs contamination after 60 years operation: Abundance, structure, co-occurrence network and functionality.

Both potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) are widely present in soil contaminated by steel industries. This study assessed the vertical variation (at 20 cm, 40 cm, 60 cm, 80 cm, 120 cm, and 150 cm depth) of bacterial abundance, community structure, functional genes related to PAHs degradation, and community co-occurrence patterns in an old steel plant soils which contaminated by PTEs and PAHs for 60 years. The excessive PAHs and PTEs in steel plant soils were benzo (a) pyrene, benzo (b) fluoranthene, dibenzo (a, h) anthracene, indeno (1,2,3-c, d) pyrene, and lead (Pb). The abundance and composition of bacterial community considerably changed with soil depth in two study areas with different pollution degrees. The results of co-occurrence network analysis indicated that the top genera in blast furnace zone identified as the potential keystone taxa were Haliangium, Blastococcus, Nitrospira, and Sulfurifustis. And in coking zone, the top genera were Gaiella. The predictions of bacterial metabolism function using PICRUSt showed that the PAHs-PTEs contaminated soil still had the potential for PAHs degradation, but most PTEs negatively correlated with PAHs degradation genes. The total sulfur (TS), acenaphthene (ANA), and Zinc (Zn) were the key factors to drive development of bacterial communities in the steel plant soils. As far as we know, this is the first investigation of vertical distribution and interaction of the bacterial microbiota in the aging soils of steel plant contaminated with PTEs and PAHs.

Distribution Characteristics and Risk Assessment of Polycyclic Aromatic Hydrocarbons in Soils of a Steel Enterprise in East China.

To meet the goal of sustainable development, many large steel enterprises in China have been relocated, leaving serious polycyclic aromatic hydrocarbon (PAH) pollution problems at the abandoned sites. In this study, the spatial distribution and potential health risks of PAHs in soils of a large steel enterprise in East China were studied. The total concentrations of 16 PAHs ranged from 93.96 to2.61E + 05 µg/kg. A total of 54.84% of the samples reached the level of severe pollution, with coking plants and iron works showing much more serious problems than other areas. The contribution levels of PAHs with high molecular weights were high, especially those of 4-ring PAHs. The toxic equivalent concentrations exceeded the values recommended by the Canadian guide. The average carcinogenic risk value of the whole region was greater than 10-6, indicating high carcinogenic risk. The above assessment indicates that the area must be remediated before further development occurs.

Biosorption capacity of Mucor circinelloides bioaugmented with Solanum nigrum L. for the cleanup of lead, cadmium and arsenic.

The biosorption and bioaugmentation performances of Mucor circinelloides were investigated under different contact time, initial metal(loid) concentration and species. The microbe-plant interaction appeared synergistic with enhancing plant growth and alleviating oxidative damages induced by lead, cadmium and arsenic. The bioaugmentation with M. circinelloides led to significant immobilization on lead, cadmium and arsenic as indicated by the decreases of metal(loid) transfer and bioavailability in plant-microbe aqueous system. Lead, cadmium and arsenic were mainly allocated on cell wall and a few parts entered into intercellular system, suggesting cell wall adsorption and intracellular bioaccumulation served as the main mechanisms of M. circinelloides. The adsorption kinetics and isotherms on lead, cadmium and arsenic were fitted well with the pseudo-second-order and Langmuir models, with the maximum adsorption capacities of 500, 15.4 and 29.4 mg·g-1 fungal biomass at pH 6.0 and 25 â„ƒ. The optimum initial concentration and contact time were 300-10-20 mg·L-1 and 2 h. This study provides a basis for M. circinelloides as a promising adsorbent and bioaugmented agent for the cleanup of soil/aqueous environment contaminated with lead, cadmium and arsenic.

Resistance effect of flavonols and toxicology analysis of hexabromocyclododecane based on soil-microbe-plant system.

The toxicity characteristics of HBCD and resistance mechanism of flavonols are investigated based on physiological and metagenomic analysis. Toxicology research of HBCD on Arabidopsis thaliana (Col and fls1-3) not only shows the toxic effect of HBCD on plants, but also indicates that flavonols could improve plant resistance to HBCD, including root length, shoot biomass and chlorophyll content. Analysis of eggNOG and GO enrichment demonstrates that HBCD has toxic effect on both gene expression and protein function, which concentrates on energy production - conversion and amino acid transport - metabolism. Differential expressed genes in flavonols-treated groups indicates that flavonols regulate the metabolism of amino acids, cofactors and vitamins, which is involved in plant defense system against oxidative damage caused by HBCD stress. HBCD is believed to affect the synthesis of proteins via genes expression of ribosome biogenesis process. Flavonols could strengthen the plant resistance and alleviate toxic effect under HBCD stress.

Toxicity, migration and transformation characteristics of lead in soil-plant system: Effect of lead species.

Lead (Pb) is a typical hazardous element of high concern in species characteristics involving toxicity, migration and transformation. A greenhouse experiment was conducted using Solanum nigrum L. grown in soils treated by divalent (Pb2+), tetravalent (Pb4+), trimethyl (TML) and triethyl (TEL) lead for 60 days. Results of physio-biochemical parameters indicated Pb toxicity was ranked as TEL > TML > Pb2+ > Pb4+ in a dose-dependent manner, and the correlation levels of organic species were higher than inorganic species. S. nigrum L. adopted phytostabilization strategy through fixing Pb in roots and restricting its transfer to shoots. More phytotoxic Pb was absorbed from soils treated by Pb2+ than Pb4+ as well as TEL than TML. In soils, inorganic Pb species were mainly present in residues while organic Pb species in Fe/Mn oxide and exchangeable fractions. Although most of Pb species in plant existed in the low-bioavailable extractions of 1 M NaCl and 2% HAC, the water-soluble Pb extracted by d-H2O and 80 % ethanol were increased to a large extent under high-level exposure. The occurrence of reduction and (de)alkylation were considered as the major pathways in the biotransformation of Pb species. This study will conduce to the ecological risk management for Pb-contaminated soils.

Combined toxicity and detoxification of lead, cadmium and arsenic in Solanum nigrum L.

A 3-factor-5-level central composite design was conducted to investigate the combined toxicity and detoxification mechanisms of lead (Pb), cadmium (Cd) and arsenic (As) in Solanum nigrum L. The three metal(loid)s exhibited low-dose stimulation and high-dose inhibition on plant length. Analyses of eleven oxidative stress and antioxidant parameters showed all Pb, Cd and As induced oxidative damages, and the co-exposure further enhanced their toxic effects. Pb, Cd and As were mainly accumulated in plant roots and poorly translocated to shoots, being beneficial for metal(loid) detoxification. The results of subcellular fractionation showed that Pb, Cd and As in plant leaves, stems and roots were mainly localized in the cell wall and soluble fractions. Most of Pb and As in soils occurred in residual fraction while Cd in exchangeable fraction. Although single Pb, Cd and As in all plant tissues existed predominantly in 1 M NaCl-soluble form, the d-H2O and 80 % ethanol-soluble forms were increased under the binary or ternary combinations. This study will conduce to the potential use of S. nigrum L. in the phytostablization of soil co-contaminated with Pb, Cd and As.