Phytoavailability Of Metals Research Articles

Enhanced Phytoremediation of Heavy Metals By Soil-applied Organic And Inorganic Amendments: Heavy Metal Phytoavailability, Accumulation, And Metal Recovery

ABSTRACT Phytoremediation, an eco-friendly and cost-effective technique for remediating heavy metal-contaminated soils, can be significantly enhanced through the application of soil amendments. This study investigates the impact of Foliar spraying of both organic (fulvic acid, auxin, Compost, and coconut coir) and inorganic (sulfur) amendments on the phytoavailability, accumulation, and recovery of heavy metals: Arsenic-As, Mercury-Hg, Cadmium-Cd and Lead-Pb in contaminated soils. Field experiment was conducted using hyperaccumulator plant species; T. capensis and H. psittacorum with varying amendment treatments to assess their effectiveness in improving phytoremediation outcomes. The results demonstrate that specific amendments significantly increase heavy metal uptake and translocation within plants by altering soil pH, cation exchange capacity, and microbial activity, thus enhancing metal solubility and bioavailability. Furthermore, the study evaluates the potential of these amendments to not only facilitate metal recovery but also to restore soil health and fertility. The findings underscore the potential of tailored amendment strategies in optimizing phytoremediation processes, offering a sustainable solution for heavy metal remediation in polluted environments.

Effect of intercropping and biochar amendments on lead removal capacity by Corchorus olitorius and Zea mays.

Intercropping is a sustainable strategy recognized for boosting crop production and mitigating heavy metal toxicity in contaminated soils. This study investigates the effects of biochar amendments on Pb-contaminated soil, utilizing monocropping and intercropping techniques with C. olitorius and Z. mays. The research assesses Pb removal capacity, nutrient uptake, antioxidant enzymes, and soil Pb fractionation. In monocropping, the phytoremediation ratio for C. olitorius increased from 16.67 to 27.33%, while in intercropping, it rose from 19.00 to 28.33% with biochar amendments. Similarly, Z. mays exhibited an increased phytoremediation ratio from 53.33 to 74.67% in monocropping and from 63.00 to 78.67% in intercropping with biochar amendments. Intercropping significantly increased the peroxidase (POD) activity in Z. mays roots by 22.53%, and there were notable increases in shoot POD of C. olitorius (11.54%) and Z. mays (16.20%) with biochar application. CAT showed consistent improvements, increasing by 37.52% in C. olitorius roots and 74.49% in Z. mays roots with biochar. Biochar amendments significantly increased N content in soil under sole cropping of Z. mays and intercropping systems. In contrast, Cu content increased by 56.34%, 59.05%, and 79.80% in monocropping (C. olitorius and Z. mays) and intercropping systems, respectively. This suggests that biochar enhances nutrient availability, improving phytoremediation efficacy in Pb-contaminated soil. Phyto availability of trace metals (Zn, Mn, Cu, and Fe) exhibited higher levels with biochar amendments than those without. The findings indicate that intercropping and biochar amendments elevate antioxidant enzyme levels, reducing reactive oxygen species and mitigating Pb toxicity effects. This approach improves phytoremediation efficiency and holds promise for soil pollution remediation while enhancing nutrient content and crop quality in Pb-contaminated soil.

Alginate-encapsulated biochar as an effective soil ameliorant for reducing Pb phytoavailability to lettuce (Lactuca sativa L.).

The alginate-biochar formulation for metal removal from aquatic environments has been widely tried but its use for lowering phytoavailability of metals in the soil-crop continuum is limited. Biochar has been increasingly used as a soil amendment due to its potential for soil carbon sequestration and sorption capacity. Handling of powdery biochar as a soil top-dressing material is, however, cumbersome and vulnerable to loss by water and wind. In this experiment, biochar powder, which was pyrolyzed from oak trees, was encapsulated into beads with alginate, which is a naturally occurring polysaccharide found in brown algae. Both batch and pot experiments were conducted to examine the effects of the alginate-encapsulated biochar beads (BB), as compared to its original biochar powdery form (BP), on the Pb adsorption capacity and phytoavailability of soil Pb to lettuce (Lactuca sativa L.). The BB treatment improved reactivity about six times due to a higher surface area (287 m2g-1) and five times due to a higher cation exchange capacity (50 cmolc kg-1) as compared to the BP treatment. The maximum sorption capacity of Pb was increased to 152 from 81mgg-1 because of surface chemosorption. Adsorption of Pb onto BB followed multiple first-order kinetics and comprised fast and slow steps. More than 60% of the Pb was adsorbed in the fast step, i.e., within 3h. Also, the BB treatment, up to the 5% level (w/w), increased soil pH from 5.4 to 6.5 and lowered the phytoavailable fraction of Pb in soil from 5.7 to 0.3mgkg-1. The Pb concentrations in lettuce cultivated at 5% for the BP and BB treatments were similar but 63 and 66% lower, respectively, than those of the control soil. The results showed that the encapsulation of biochar with alginate enhanced adsorption by the biochar.

Assessment of herbaceous community structure for identifying metal-tolerant species at different land uses in and around Varanasi city.

Plant community structure under different land uses provides an important understanding of vegetation dynamics to safeguard future restoration programmes and balance ecosystem services. Therefore, this study was carried out to estimate the alterations in soil properties and contamination by potentially toxic metals at different land uses (industrial, brick kiln, highway, and residential areas) compared to the reference (botanical garden area) site coupled with their subsequent influence on herbaceous community structure, bioconcentration, translocation, and extraction amountof metals in different plant species. Most of the total and phytoavailable metals (Co, Cr, Cd, Cu, Ni, Pb, Mn, and Zn) were higher at the contaminated sites compared to the reference site. The number of herbaceous species was highest at the reference site and minimum at the industrial site. Dominant and tolerant species were Cyanodon dactylon, Croton bonaplandianus, Achyranthus aspera, Malvestrum coromendelianum, Dicanthium annulatum, Nicotiana hindostana, Sporobolus virginicus, and Parthenium hysterophorus, found at the industrial, brick kiln, and highway sites. Based on transfer coefficients, C. bonaplandianus, D. annulatum, and Eleusine indica were recognized as potential accumulators, whereas C. dactylon, Commelina benghalensis, A. aspera, Amaranthus sessilis, and M. coromendelianum were found as excluder species for different metals. The identified tolerant herbaceous species could be used for future phytoremediation strategies and the prevention of hazardous risks to living components of contaminated sites.

Simultaneous immobilization of multiple heavy metal(loid)s in contaminated water and alkaline soil inoculated Fe/Mn oxidizing bacterium

Two strains of Fe/Mn oxidizing bacteria tolerant to high concentrations of multiple heavy metal(loid)s and efficient decontamination for them were screened. The surface of the bio-Fe/Mn oxides produced by the oxidation of Fe(II) and Mn(II) by Pseudomonas taiwanensis (marked as P4) and Pseudomonas plecoglossicida (marked as G1) contains rich reactive oxygen functional groups, which play critical roles in the removal efficiency and immobilization of heavy metal(loid)s in co-contamination system. The isolated strains P4 and G1 can grow well in the following environments: pH 5-9, NaCl 0-4%, and temperature 20-30°C. The removal efficiencies of Fe, Pb, As, Zn, Cd, Cu, and Mn are effective after inoculation of the strains P4 and G1 in the simulated water system (the initial concentrations of heavy metal(loid) were 1 mg/L), approximately reaching 96%, 92%, 85%, 67%, 70%, 54% and 15%, respectively. The exchangeable and carbonate bound As, Cd, Pb and Cu are more inclined to convert to the Fe-Mn oxide bound fractions in P4 and G1 treated soil, thereby reducing the phytoavailability and bioaccessible of heavy metal(loid)s. This research provides alternatives method to treat water and soil containing high concentrations of multi-heavy metal(loid)s.

The Effect of Cadmium Tolerant Plant Growth Promoting Rhizobacteria on Plant Growth Promotion and Phytoremediation: A Review.

Cadmium (Cd) is a heavy metal of considerable toxicity with destructive impacts on plants, microbes and environments. Its toxicity is due to mishandling and manual hazards in plants and is primarily observed within the soil to cause decline of plants and microbial activity inside the rhizosphere. Cadmium accumulation in crops and the probability of Cd entering the food chain are grave for public health in the worldwide. Cadmium toxicity leads to depletion in seed germination, initial seedling growth, plant biomass, chlorosis, necrosis, hindrance of photosynthetic machinery and other physiological and biological activities in plants. Cadmium triggers the reactive oxygen species (ROS) that influences gene mutation and DNA damage that affects the cell cycle and cell division. Cd toxicity altered the levels ofphenolic compounds,carbohydrates, glycinebetaine, proline and organic acids incrops. Under stress conditions, the plant growth promoting rhizobacteria (PGPR) have various properties such as enzymatic activities, plant growth hormones production, phosphate solubilization, siderophores production and chelating agents that help the plants tolerate against Cd stress and also increase phenolic compound levels and osmolytes. Hence, this review highlights the crucial role of cadmium tolerant PGPR for crop production, declining metal phytoavailability and enhancing morphological and physiological boundaries of plants under stress conditions. It could be an environment friendly and cost effective technology under sustainable crop production.

Is the co-application of self-produced compost and natural zeolite interesting to reduce environmental and toxicological availability in metal-contaminated kitchen garden soils?

Composting can turn organic waste into a valuable soil amendment that can improve physical, chemical, and biological soil quality. Compost amendments can also contribute to the remediation of areas anthropogenically degraded by metals. However, it is well known that compost, particularly self-produced compost, can show enrichment in metals. An experimental study was conducted to examine the short- and long-term distribution and the mobility of metals in soils amended with a self-produced compost when it was added alone or in combination with different doses of a natural zeolite to soil. The aim was also to study the interest of managing moderately metal-contaminated kitchen garden soils by assessing the chemical extractability, phytoavailability, and oral bioaccessibility of metals. When zeolite was added to compost alone, it had the tendency to better reduce extractability of Cd and Zn at 25%, and those of Pb at 15%. When the self-produced compost alone or in co-application with zeolite at these doses was applied to soils, the results showed (1) a decrease of NH4NO3-extractable Zn; (2) a reduction of Pb environmental availability, but not Pb bioaccessibility, and (3) an increase of ryegrass biomass. Nevertheless, the risk posed by the self-produced compost was minimal when applied at the proper rate (0.6%w/w). In the selected experimental conditions, the study recommends that self-produced compost be mixed with 15% zeolite to maximize vegetal biomass and minimize environmental risk. The question of sustainability of the results with repeated compost addition is also raised.

Phytoextraction of nickel, lead, and chromium from contaminated soil using sunflower, marigold, and spinach: comparison of efficiency and fractionation study.

Heavy metals in soil pose a serious threat through their toxic effect on the human food chain. Phytoremediation is a clean and green potentially cost-effective technology in remediating the heavy metal-contaminated soil. However, the efficiency of phytoextraction is very often limited by low phytoavailability of heavy metals in soil, slow growth, and small biomass production of hyper-accumulator plants. To solve these issues, accumulator plant(s) with high biomass production and amendment(s) which can solubilize metals in soil is required for better phytoextraction. A pot experiment was conducted to assess the efficiency of phytoextraction of sunflower, marigold, and spinach as affected by the incorporation of Sesbania (solubilizer) and addition of gypsum (solubilizer) in nickel (Ni)-, lead (Pb)-, and chromium (Cr)-contaminated soil. A fractionation study was conducted to study the bioavailability of the heavy metals in contaminated soil after growing the accumulator plants and as affected by using soil amendments (Sesbania and gypsum). Results showed that marigold was the most efficient among the three accumulator plants in phytoextraction of the heavy metals in the contaminated soil. Both sunflower and marigold were able to reduce the bioavailability of the heavy metals in the post-harvest soil, which was reflected in their (heavy metals) lower concentration in subsequently grown paddy crop (straw). The fractionation study revealed that carbonate and organically bound fractions of the heavy metals control the bioavailability of the heavy metals in the experimental soil. Both Sesbania and gypsum were not effective in solubilizing the heavy metals in the experimental soil. Therefore, the possibility of using Sesbania and gypsum for solubilizing heavy metals in contaminated soil is ruled out.

Geochemical analyses of metal(loid) fractions do not predict plant uptake behavior: Are plant bioassays better tools to predict mine rehabilitation success?

Management of metal(loid) tailings at historic sites presents environmental hazards usually requiring rehabilitation to mitigate pollution risks. Strategies employed include capping or establishing vegetation directly, which requires tailings assessments to determine suitable rehabilitation approaches. Assessments are typically geochemical analyses, but plant based approaches may provide a more accurate measure of revegetation success although they are often limited to germination indices. This study uses the plant bioassay (Rhizotest™) with common geochemical assessment to predict plant uptake of metal(loid)s and the subsequent likely rehabilitation success. Pb/Zn tailings from five legacy sites within the UK and Ireland were characterized for pH, EC, water soluble and CaCl2-extractable content and aqua regia extractable content. Uptake of Sb, As, Cd, Cu, Ca, Mg, Mn, Zn, Pb was determined in shoots and roots of Lolium perenne.Total Zn, Pb, Sb, Cd and As in tailings ranged from 694 to 2683 mg kg−1, 1252 to 8072 mg kg−1, 14 to 148 mg kg−1, 1.3 to 44 mg kg−1 and 1.3 to 45 mg kg−1, respectively. The only correlation found between total and water soluble or CaCl2-extractable metal(loid) contents was for Cd, where r = 0.8 for total and CaCl2-extractable fractions. Limited uptake and translocation risk was identified for major contaminants Zn and Pb in most tailings samples but in some cases exceedance of phytotoxic threshold values occurred that was not reflected in geochemical analysis. Crucially, although total Cd and Sb content was relatively low (< 20 mg kg−1) in some tailings, elevated plant content for some samples highlights phytotoxic risk from minor elements. Results indicate that screening based on geochemical content is not sufficiently predictive of metal(loid) phytoavailability to reliably inform mine rehabilitation strategies. We therefore strongly recommend that geochemical analyses are supplemented with plant based bioassay to plan mine tailings revegetation and reduce risk of wider ecosystem metal(loid) transfer.

Lactic acid bacteria promoted soil quality and enhanced phytoextraction of Cd and Zn by mustard: A trial for bioengineering of toxic metal contaminated mining soils

Microbial-assisted phytoremediation provides a green approach for remediation of metal contaminated soils. However, the impacts of mono and co-applications of lactic acid bacteria (LAB) on soil biochemical properties and phytoavailability of toxic metals in contaminated mining soils have not yet been sufficiently examined. Consequently, here we studied the effects of Lactobacillus plantarum (P), Lactobacillus acidophilus (A), and Lactobacillus rhamnosus (R) applications alone and in combination on soil enzyme activities and bioavailability and uptake of Cd and Zn by mustard (Brassica juncea) in a smelter-contaminated soil under greenhouse conditions. Among the studied bacteria, P was the most tolerant to Cd-and-Zn contamination. As compared to control, R increased the fresh and dry weight of mustard plants by 53.5% and 63.2%, respectively. Co-application of P + A increased the chlorophyll content by 28.6%, as compared to control. Addition of LAB to soil increased the activity of soil urease, alkaline phosphatase and β-D glucosidase increased by 1.86-fold (P + R), 1.80-fold (R) and 55.16% (P + R), respectively. Application of P + A + R enhanced catalase activity (19.3%) and superoxide dismutase activity (51.2%), while addition of A alone increased peroxidase activity (POD: 15.7%). Addition of P alone and together with A (P + A) enhanced Cd and Zn phytoextraction by mustard shoots up to 51.5% and 52.5%, respectively. We conclude that the single and/or co-application of LAB decreased soil pH, promoted plant growth, antioxidant and enzyme activities, and enhanced the phytoavailability of Cd and Zn in the studied contaminated soil. These findings might be an aid for enhancing the phytoremediation of Cd and Zn using LAB and mustard as a bioenergy crop, which may offer new ideas for field treatment of toxic metals contaminated soils.

Biochar Is Not Durable for Remediation of Heavy Metal-Contaminated Soils Affected by Acid-Mine Drainage

Biochar is a soil conditioner for enhancing plant growth and reducing plants’ uptake of heavy metals. However, the protonation of biochar surfaces in acid soils can weaken the capacity of biochar to reduce the phytoavailability of soil-borne heavy metals over time. The aim of this study was to test this hypothesis by performing a plant-growth experiment with five harvest cycles to examine the durability of rice-straw biochar for the remediation of an acidic-mine-water-contaminated soil. The application of the biochar significantly reduced the phytoavailability of the heavy metals and inhibited the plant uptake of cationic heavy metals but not anionic Cr. The beneficial effects of the biochar were weakened with the increasing number of harvest cycles caused by the gradual protonation of the biochar surfaces, which resulted in the desorption of the adsorbed heavy metals. The weakening capacity of the biochar to reduce the heavy-metal uptake by the vegetable plants was more evident for Cu, Zn, and Pb compared to Ni and Cd. The experimental results generally confirmed the hypothesis. It was also observed that the bioaccessible amount of various metals in the edible portion of the vegetable was also reduced as a result of the biochar application.

Effects of solid waste-based soil conditioner and arbuscular mycorrhizal fungi on crop productivity and heavy metal distribution in foxtail millet (Setaria italica)

Shanxi is a large coal-producing province, and it also produces a lot of solid waste. Solid waste can leach heavy metals, which can harm soil and affect food security at the beginning of the food chain. To investigate the impacts of solid waste-based soil conditioner (SWSC) and arbuscular mycorrhizal fungi (AMF) on millet safety and crop production, a field experiment with foxtail millet (Setaria italica) was conducted in Tunliu. The results of this study demonstrate that SWSC + AMF, SWSC and AMF can increase millet yield by 28.0%, 27.1% and 19.5%, respectively, compared with CK. This is mainly due to increased mycorrhizal infection. Besides, the pollution index (Pi) and the Nemerow-integrated pollution index (PN) of the soil with SWSC and AMF were both below 0.7, indicating safe pollution levels. The application of AMF and SWSC inhibits plants from absorbing heavy metals from the soil and reduces the TFroot/soil of the millet. SWSC + AMF application inhibited the transfer of heavy metals from the roots to the upper part of the ground and reduced the TFshoot/root of the millet. The TFgrain/soil of the millet was below 1. The HQ and HI of the millet grains did not exceed 1, indicating the absence of a potential health risk. Therefore, SWSC combined with AMF is applicable for millet production in Tunliu, and the combined treatment can decrease heavy metal phytoavailability and post-harvest transfer risks. This work provides a way to utilize solid waste while also improving millet yields in dry farming. Based on the review, we suggested future researches to better understand the mechanisms of SWSC + AMF long-term application to promote awareness on its role over time through alterations in its surface chemistry, soil microbial community and environmental implications.

Challenges in Reducing Phytotoxicity of Metals in Soils Affected by Non-Ferrous Smelter Operations

Lime is one of the effective agents for reducing the phytoavailability of metals in contaminated acidic soils. However, previous studies have shown that lime alone cannot reduce metal phytotoxicity to the desired extent in such soils. The goal of this study was to evaluate the effect of different amendment combinations (lime with and without Feand/or Mn-based amendments) on plant growth. A sample of Histosol (0-5 cm) was collected around a Cu/Ni smelter near Monchegorsk, Murmansk region, exhibiting total Cu and Ni concentrations in the soil of 6418 and 2293 mg kg-1, respectively. Likewise, a sample of forest litter (0-15 cm) was collected around a Cu smelter near Revda, Sverdlovsk region, exhibiting total Cu concentration in the soil of 5704 mg kg-1. Fe-Mn oxides were sourced from ferromanganese nodules in the Gulf of Finland, and iron powder was used as a precursor for iron oxides. Perennial ryegrass was grown in pots for 21 days under controlled laboratory conditions. Two dolomite doses were tested: 5% w/w (giving a soil pH of 6.5) and 20% w/w (giving a soil pH of 7.4). Over-liming stunted plant growth; therefore, the dolomite dose was set at 5% in the further experiments of the study. Importantly, the addition of 0.5% and 1% of Fe-Mn-oxides or iron powder did not improve the efficacy of the lime amendment in promoting plant growth in the soils. Therefore, the issue of reducing plant exposure to metals remained unresolved in the soils under study.

Effect of Vermiculite Soil Amendment on Immobilization of Selected Heavy Metals of Rhizospheric Zone of Maize

ABSTRACT The elevated level of metals in the soil increases the assimilation of these metals by plants causing a serious health risk to humans. A series of pot experiments were conducted to study Pb, Cu, and Zn uptake by Zea mays to investigate the role of vermiculite for metals immobilization in the soil root zone. The metals accumulation was decreased (13.17% to 29.21% in above-ground parts and 4.18% to 69.74% in roots) and total plant biomass increased (1.43% in control soil and 10.54% in polluted soil) in vermiculite amended soils. The effective immobilization of metals in vermiculite amended soil was revealed by decreased values of translocation factors for root-stalk and subsequently for stalk-leaves under varying metal concentrations. Vermiculite amendment to soil had no observable effect on the chemical structure while there were few changes in the functional group of the soil structure. The study reveals that vermiculite can be amended to the soil for reducing phytoavailability of toxic metals to plant uptake and in return flow processes for controlling food-chain contamination and groundwater pollution without compromising with crop production.

Stabilization of metals in sludge-amended soil using red mud and its effects on yield and oil quality of Brassica juncea cultivar Kranti.

Prolonged application of sewage-sludge may cause excessive accumulation of metal(oid)s in soil, leading to phytotoxic effects. Spread of contaminants in soil can probably be hindered by using an effective metal(oid) stabilizer. Pot experiment in open field conditions was conducted for five months to evaluate the metal(oid) (Al, Cu, Zn, Cd and Cr) stabilization potential of red mud (RM) in sludge-amended soil and its effects on growth, yield, oil quality parameters and metal(oid) accumulations in Brassica juncea cultivar Kranti. The test plant was grown at different RM concentrations (0, 5, 10 and 15% w/w) in sludge-amended soil (soil/sludge: 2:1 w/w). As the total and phytoavailable metal(oid) concentrations in sludge were high, its application increased their concentrations in soil compared to the control (no RM and sludge). Increasing RM concentrations in sludge-amended soil effectively stabilized Cd followed by Cr, Cu, Zn and Al, leading to their reduced contents in plants coupled with enhanced growth performance and yield. Maximum plant (root and shoot) biomass (14.9%) and seed yield (40.4%) were found in 10% RM treatment, whereas oil content showed substantial increase with increasing RM treatments in sludge-amended soil. Mustard oil showed low rancidification, high long-chain fatty acids, saturated and polyunsaturated (ω-3 and ω-6) fatty acids within FAO ranges for edible oils under varying RM treatments compared to sludge-amended soil. Furthermore, high oleic and low erucic acid contents in mustard oil indicated a better oil quality under different RM treatments. Metal(oid) contents in seeds under different red mud treatments were within FAO/WHO limits for consumption. Thus, RM applications preferably 5 and 10% (w/w) in sludge-amended soil might be effective in stabilization of metal(oid)s using B. juncea cultivar Kranti coupled with better yield, improved oil quality and metal(oid)s within limits for human consumption.

A comparison between the function of Serendipita indica and Sinorhizobium meliloti in modulating the toxicity of zinc oxide nanoparticles in alfalfa (Medicago sativa L.).

Zinc oxide nanoparticles (ZnO-NPs) are among the most commonly used nano-fertilizers (NF). However, elevated levels of ZnO-NPs in soil may affect plant growth and development due to its potential toxicity when accumulated in large amounts in plant tissues. This research was conducted using an in situ rhizobox system with the aims of evaluating zinc uptake from nano-zinc oxide amended rhizosphere soil by alfalfa plant and the effect of plant growth-promoting microorganisms on alleviating the phytotoxicity of ZnO-NPs. Treatments included microbial inoculations (Sinorhizobium meliloti, Serendipita indica) and different ZnO-NP concentrations (0, 400, and 800 mg kg-1) with three replications. The results indicated that S. indica minimized the phytotoxicity of ZnO-NPs to alfalfa by enhancing growth rate and decreasing zinc (Zn) translocation from root to shoot. Compared with plants inoculated with S. meliloti, co-inoculation with S. indica increased the shoot dry weight by 18.33% and 8.05% at 400 and 800 mg kg-1 ZnO-NPs, respectively. However, at the highest level of ZnO-NPs (800 mg kg-1), root inoculation of S. indica and S. indica + S. meliloti decreased Zn translocation factor by 60.2% and 44.3% compared to S. meliloti, respectively. Furthermore, a distinct relation between tolerance of S. indica-colonized plant to ZnO-NPs and the ability of S. indica in inhibiting or retarding degradation of polyunsaturated lipids through prevention of excess reactive oxygen species formation was observed. Malondialdehyde content of inoculated plants with S. indica either alone or in combination with S. meliloti was significantly lower than non-inoculated plants (p< 0.01). Zn-induced oxidative stress was mitigated by S. indica through enhanced activities of catalase and peroxidase enzymes. The findings of the present study indicate the potential use of endophytes fungus S. indica for ensuring food safety and security, and human health in heavy metal-polluted soil by reducing the phytoavailability of heavy metals in the aerial parts of the host plants.

Variations in phytoremediation potential and phytoavailability of heavy metals in different Salix genotypes subjected to seasonal flooding

Climate-related flooding poses a potential challenge to phytoremediation of metal polluted areas. In the present study, uptake, translocation and accumulation of heavy metals (Cd, Zn and Cu), and their phytoavailability in six flood-tolerant Salix genotypes were investigated under simulated seasonal flooding conditions (non-flooding conditions were kept as the control). Plants were cultivated in a greenhouse with open windows using the soil polluted with Cd, Zn and Cu for 110 days. All the control (non-flooded) genotypes did not exhibit visible toxic symptoms, whereas the flooded genotypes showed leaf chlorosis and developed both lenticels and adventitious roots. Biomass production and metal accumulation in tissues varied with Salix genotypes. The flooded genotypes dramatically decreased aerial biomass production compared with corresponding non-flooded genotypes. All the control Salix genotypes showed relatively high accumulation for Cd, Zn and Cu in aerial parts due to high EDTA-extractable metals in the rhizosphere, exhibiting phytoextraction features. In contrast, the flooded genotypes drastically decreased uptake, translocation, accumulation, and extraction capacities for Cd, Zn and Cu in aerial parts, differing with genotypes, and tended to phyto-stabilize them in roots, especially Cu. This study indicated that flooding is a leading factor on phytoremediation efficiency for contaminated sites with willows.

Effects of biochar derived from sewage sludge and sewage sludge/cotton stalks on the immobilization and phytoavailability of Pb, Cu, and Zn in sandy loam soil

Co-pyrolysis of sewage sludge and straws has been used to improve the pore structure and reduce the ecological risks of heavy metals in sewage sludge-derived biochars. However, to date, no study has focused on the effects of biochar derived from sewage sludge/straws on the immobilization and phytoavailability of heavy metals in soil. Here, we studied the effects of biochar derived from sewage sludge/cotton stalks (SCB) and that derived from sewage sludge alone (SSB) on the remediation of sandy loam soil contaminated by Pb, Cu, and Zn. SCB amendment decreased the bioavailable forms of Pb, Cu, and Zn in the soil by 19.0%, 34.9%, and 18.2%, respectively, and reduced their accumulation in ryegrass by 28.6%, 50.1%, and 30.0%, respectively, compared with those by SSB amendment. Furthermore, SCB amendment transformed more metals from the acid-soluble fraction to the oxidizable fraction than SSB amendment, indicating that complexation played a more critical role in SCB amendment than in SSB amendment. Both biochar amendments effectively improved soil water holding capacity, increased the supply of available P, N, and K, and promoted ryegrass growth. The findings of this study show the benefits of SCB over SSB for the remediation of heavy metal-contaminated soil.

Long-term effects of biochar on trace metals accumulation in rice grain: A 7-year field experiment

Biochar (BC) is an emerging amendment for minimizing the phytoavailability of trace metals in soil-crop system, but its relevant durability and mechanism are unclear. A 7-year field study was conducted in double rice paddy land of mid-subtropical China. Wheat straw BC was once applied at rates of 24 and 48 Mg ha−1 (LBC and HBC, respectively). Results showed that the increase in soil total organic C (TOC, 41.1–54.6%), pH (0.41–0.86 units) and cation exchange capacity (13.7–23.3%) for the HBC was kept for 14, 11 and 4 seasons (p < 0.05), respectively. Meanwhile, the reduction in soil CaCl2-extractable Cd, Pb, Zn and Mn (29.5–61.6%, 38.2–81.0%, 36.5–70.7%, 19.1–56.7%, respectively, p < 0.05) was maintained for 9–11 seasons. And, the reduction in grain Cd, Pb, Zn and Mn (23.0–59.5%, 15.2–49.8%, 17.5–22.9%, 13.4–34.2%, respectively, p < 0.05) was maintained for 4–6 seasons. Similar but weaker effects were observed for the LBC. And, their durable periods (except for TOC) for the LBC were about 1/3–1/2 of those for the HBC. Phytoavailability of Cd, Pb, Zn and Mn in soil-rice system was negatively correlated with soil pH and TOC (p < 0.05). Therefore, the immobilization durability of the BC on trace metals in soil-rice system are mainly attributed to the primary fixation of stable microstructure and functional groups, and mediated by the associated changes in soil pH. Alkaline materials should be taken as supplemental agents to strengthen the immobilization durability of the BC on trace metals in soil-rice system.

Short-Term Aging of Pod-Derived Biochar Reduces Soil Cadmium Mobility and Ameliorates Cadmium Toxicity to Soil Enzymes and Tomato.

Contamination of agricultural soil with cadmium (Cd) has become a global concern because of its adverse effects on ecohealth and food safety. Soil amendment with biochar has become one of the phytotechnologies to reduce soil metal phyto-availability and its potential risks along the food chain. Biochar, derived from cocoa pod, was evaluated in soil Cd fractions (exchangeable, reducible, oxidizable, and residual) by modified Commission of the European Communities Bureau of Reference sequential extraction and its efficacy to ameliorate Cd toxicity to soil enzymes and leaf bioactive compounds. A pot experiment was conducted using Cd-spiked soil at 10 mg/kg with tomato (Solanum lycopersicum L.) at a biochar application rate of 1 and 3% (w/w) for 6 wk. The addition of biochar significantly reduced (p < 0.05) the exchangeable, reducible, and residual fractions by at least approximately 23%, with a consequential decrease in Cd root uptake and transport within tomato tissues. The activity of soil enzymes (catalase, dehydrogenase, alkaline phosphatase, and urease) was affected by Cd toxicity. However, with the exception of dehydrogenase, biochar application significantly enhanced the activity of these enzymes, especially at the 3% (w/w) rate. As for the secondary metabolites we studied, Cd toxicity was observed for glutathione, terpenoids, and total phenols. However, the biochar application rate of 1% (w/w) significantly ameliorated the effects of toxicity on the secondary metabolites. In conclusion, biochar demonstrated the potential to act as a soil amendment for Cd immobilization and thereby reduce the bioavailability of Cd in soil, mitigating food security risks. Environ Toxicol Chem 2021;40:3306-3316. © 2020 SETAC.