In recent years, heavy metal pollution has become a global environmental problem and poses a great threat to the health of people and ecosystems. Therefore, strategies for the effective remediation of Cd from contaminated soil are urgently needed. In this study, ryegrass was utilized as a remediation plant, and its remediation potential was enhanced through the application of Citric Acid (CA) in conjunction with Bacillus megaterium (B. megaterium). The P3 treatment (CA + Bacillus megaterium) exhibited a significantly higher efficiency in promoting cadmium extraction by ryegrass, resulting in a 1.79-fold increase in shoot cadmium accumulation compared to the control group (CK) with no Bacillus megaterium or CA. Moreover, the P3 treatment led to an increased abundance of Actinobacteriota, Acidobacteriota, and Patescibacteria in the rhizosphere. The concentration of amino derivatives (such as betaine, sulfolithocholylglycine, N-alpha-acetyl-lysine, glycocholic acid, arginyl-threonine) showed significant upregulation following the P3 treatment. In summary, this study proposes a viable approach for phytoremediation of soil contaminated with cadmium by harnessing the mobilizing abilities of soil bacteria.
Our aim was to gain a comprehensive understanding of the mechanisms involved in phytoremediation. These findings contribute to the existing knowledge by providing insights into the mechanism of phytoremediation in Cd-contaminated soil. They are expected to serve as a theoretical foundation for further elucidation of the phytoremediation mechanisms employed in Cd-contaminated soil.

Sunflower (Helianthus annuus) can potentially be used for uranium (U) phytoremediation. However, the factors influencing the absorption of U and its subsequent distribution within plant tissues remain unclear, including the effect of silicon (Si) which is known to increase metal tolerance. Here, using hydroponics, the effect of Si on the distribution and speciation of U in sunflower was examined using synchrotron-based X-ray fluorescence and fluorescence-X-ray absorption near-edge spectroscopy. It was found that ∼88 % of U accumulates within the root regardless of treatments. Without the addition of Si, most of the U appeared to bind to epidermis within the roots, whereas in the leaves, U primarily accumulated in the veins. The addition of Si alleviated U phytotoxicity and decreased U concentration in sunflower by an average of 60 %. In the roots, Si enhanced U distribution in cell walls and impeded its entry into cells, likely due to increased callose deposition. In the leaves, Si induced the sequestration of U in trichomes. However, Si did not alter U speciation and U remained in the hexavalent form. These results provide information on U accumulation and distribution within sunflower, and suggest that Si could enhance plant growth under high U stress.

Particulate matter (PM) is one of the most hazardous atmospheric pollutants. Several plant species show high potential to reduce air pollutants and are widely used as green belts to provide clean outdoor spaces for human well-being. However, high PM concentrations cause physiological changes and stress in plants. In this study, 11 species of Thai native perennial plants were exposed to PM generated from tobacco smoke. Wrightia religiosa (Teijsm. & Binn.) Benth. ex Kurz, Bauhinia purpurea DC. ex Walp. and Tectona grandis L.f. reduced PM effectively (which is in the typical range of 43.95 to 52.97%) compared to other plant species. In addition, the responses of perennial plants under PM stress at the proteomic level were also evaluated. Proteomic analysis of these three plant species showed that plants respond negatively to high PM concentrations, such as reducing several photosynthetic-related proteins and increasing plant stress response proteins. To improve PM phytoremediation efficiency and reduce plant stress from PM, perennial plant-microbe interactions were investigated. W. religiosa was inoculated with Acinetobacter indicus PS1, and high biosurfactant-producing strains clearly showed a higher PM removal efficiency than non-inoculated plants (9.48, 9.5 and 12.6% for PM1.0, PM2.5 and PM10, respectively). Inoculating W. religiosa with A. indicus PS1 maintained chlorophyll a and b concentrations. Moreover, the malondialdehyde (MDA) concentration of W. religiosa inoculated with A. indicus PS1 was lower than that of non-inoculated W. religiosa. The leaf wax content (µg/cm2) and biosurfactant (µg/cm2) of W. religiosa inoculated with A. indicus PS1 were also higher than those of non-inoculated W. religiosa. This study clearly showed that inoculating plants with A. indicus PS1 can help plants remediate PM and improve their PM stress response.

Rare earth elements (REEs) comprises of a uniform group of lanthanides and scandium (Sc) and yttrium (Y) finding their key importance in agriculture sectors, electronic and defense industries, and renewable energy production. The immense application of REEs as plant growth promoters has led to their undesirable accumulation in the soil system raising concerns for REE pollution as upcoming stresses. This review mainly addresses the chemistry of REEs, uptake and distribution and their biphasic responses in plant systems and possible plausible techniques that could mitigate/alleviate REE contamination. It extends beyond the present understanding of the biphasic impacts of rare earth elements (REEs) on physio-biochemical attributes. It not only provides landmarks for further exploration of the interrelated phytohormonal and molecular biphasic nature but also introduces novel approaches aimed at mitigating their toxicities. By delving into innovative strategies such as recycling, substitution, and phytohormone-assisted mitigation, the review expands upon existing knowledge of REEs whilst also offering pathways to tackle the challenges associated with REE utilization.

Polycyclic aromatic hydrocarbons (PAHs) are phytotoxic, which can limit their phytoremediation. When the ability of plants to phytoremediation PAHs is compromised, the application of plant growth regulators can enhance the growth of the plants. This study aimed to determine the best plant growth regulator (1-naphthalene acetic acid, 6-benzyladenine, or thidiazuron) to enhance the phytoremediation ability of sweet grass (Pennisetum purpureum cv. Mahasarakham) when grown in weather PAH-contaminated soil. In a greenhouse study, 0.01 mg/l thidiazuron resulted in the highest growth of sweet grass when compared to the other tested plant growth regulators (dry shoot weight 24.11 ± 1.28 g and dry root weight 0.70 ± 0.02 g). Sweet grass was grown in soil contaminated with PAH, which demonstrated the toxicity to sweet grass by reducing the total chlorophyll (1.01 µg/g fresh weight) and carotenoid (0.28 µg/g fresh weight) contents with proline increased (6.63 µg/g fresh weight). Meanwhile, total chlorophyll, carotenoid, and proline content in leaves of sweet grass grown in non-contaminated soil were 1.68, 0.44, and 5.23 µg/g fresh weight, respectively. When sweet grass was used to phytoremediate PAHs, there were reductions in acenaphthylene (4.69 ± 0.50%), acenaphthene (10.69 ± 1.47%), and phenanthrene (3.61 ± 0.07%), which compared to levels of over 30% in non-planted soil. For the three PAHs, the bioconcentration factors were 1.6 to 2.4, but the translocation factors were below 1, showing limited movement to the aerial parts of the plant, thereby suggesting that the main mechanism is rhizoremediation. Sweet grass is an excellent candidate for PAH remediation, especially when thidiazuron is applied to relieve plant stress.
Thidiazuron at 0.01 mg/l was the best plant growth regulator to stimulate the growth of sweet grass when compared to 1-naphthalene acetic acid and 6-benzyladenine. Sweetgrass enhanced the removal of acenaphthylene, acenaphthene, and phenanthrene from contaminated soil. A possible mechanism for polycyclic aromatic hydrocarbon (PAH) remediation was rhizoremediation, as the accumulation of PAH in sweet grass biomass was limited, and the translocation factor from the root to the shoot was lower than 1. Thidiazuron may indirectly enhance the PAH phytoremediation by sweet grass via increased plant tolerance to PAH toxicity.

Limited open areas for urban agriculture and greenery have led to the search for innovative, sustainable growing media to strengthen the food supply and improve atmospheric quality for a resilient city. Rampant land developments have caused soil to become increasingly scarce. Sewage sludge incineration ash (SSIA), the by-product of waste-to-energy (WtE) incineration of sewage sludge, is a major municipal waste containing phosphorus-fertilizing nutrients. For the first time, we investigated the novel application of SSIA as a soilless plant-growing medium with built-in fertilizer. SSIA outperformed topsoil in bulk density, water-holding capacity, porosity, and nutrient content. However, it was found that SSIA has a high salinity and should be treated first. Wheatgrass (Triticum aestivum L.), a fast-growing glycophyte, thrived in the desalinated SSIA, showing growth and nutrient content comparable to the topsoil case. Simultaneously, it demonstrated phytoremediation. The SSIA residue was then recycled into cementitious materials, using desalinating water for mixing. SSIA upcycle into a growing medium facilitates urban resource management by utilizing nutrients in sewage waste for eco-friendly plant cultivation, benefiting urban agriculture and greenery. It is also a prudent valorization step before further recycling SSIA to reduce landfill requirements.

Background: The application of phytoremediation by utilizing plants has been used to control oil pollution in waters. One of the plants that can act as a phytoremediator is the hyacinth because this plant can reduce various pollutants including petroleum hydrocarbons. This study aims to study the reduction ability of petroleum hydrocarbons at different concentrations including improving water quality. Methods: This study consisted of one treatment (petroleum hydrocarbon) consisting of five factors with three replicates. The treatments consisted of 10 ppm (E1), 30 ppm (E2), 50 ppm (E3), 70 ppm (E4), 90 ppm (E5), and (E0) without aquatic plants as controls. The treatments were observed daily and measured from the first day (D-1), the seventh day (D-7), and the 14 th day (D-14). The water quality in each treatment was also measured, such as water temperature, pH, and dissolved oxygen. Results: The results showed that the hyacinth plant was able to reduce hydrocarbon in terms of total petroleum hydrocarbon (TPH) by 79% while it was only between 17-27% naturally without the hyacinth. The reduction of TPH in the water was in line with the decrease of chlorophyll in the leaves of hyacinths, and it was followed by the increase of dissolved oxygen in the water media. Conclusions: In conclusion, hyacinths can reduce petroleum hydrocarbons and they can improve the water quality as well.

Fifteen poplar varieties were used in a field trial to investigate the phytoremediation efficiency, stress resistance, and wood property of poplar hybrid varieties with diverse genetic backgrounds under the composite pollution of heavy metals. The coefficient of variation and clone repeatability for growth traits and Cd concentration were large. The Cd accumulation of poplar varieties 107 and QHQ reached 1.9 and 1.7 mg, respectively, followed by QHB, Ti, 69, and Pa, in which Cd accumulation reached 1.3 mg. Most of the intra-specific hybrid varieties (69, QH1, SL4, T3, and ZL46) had low Cd concentrations and small biomass, resulting in weak Cd accumulation and low phytoremediation efficiency for Cd-polluted soil. By contrast, the inter-sectional and inter-specific hybrid varieties exhibited better growth performance and accumulated higher concentrations of heavy metals than the intra-specific hybrids. The bioconcentration factor and translocation factor of Hg, As, and Pb were less than 1, indicating that poplars have low phytoremediation efficiency for these heavy metals. The hybrids between section Aigeiros and Tacamahaca (QHQ and QHB) and the inter-specific hybrid 107 within section Aigeiros were more resistant to composite heavy metal stress than the other poplar varieties were partially because of their high levels of free proline that exceeded 93 μg·g-1 FW. According to the correlation analysis of the concentrations of the different heavy metals, the poplar roots absorbed different heavy metals in a cooperative manner, indicating that elite poplar varieties with superior capacity for accumulating diverse heavy metals can be bred feasibly. Compared with the intra-specific hybrid varieties, the inter-sectional (QHQ and QHB) and inter-specific (107) hybrid varieties had higher pollution remediation efficiency, larger biomass, higher cellulose content, and lower lignin content, which is beneficial for pulpwood. Therefore, breeding and extending inter-sectional (QHQ and QHB) and inter-specific hybrid varieties can improve the phytoremediation of composite pollution.

Pollution of arable land with heavy metals is a worldwide problem. Cadmium (Cd) is a toxic metal that poses a severe threat to humans\' and animals\' health and lives. Plants can easily absorb Cd from the soil, and plant-based food is the main means of exposure to this hazardous element for humans and animals. Phytoremediation is a promising plant-based approach to removing heavy metals from the soil, and plant growth-promoting micro-organisms such as the fungi Trichoderma can enhance the ability of plants to accumulate metals. Inoculation of Avena sativa L. (oat) with Trichoderma viride enhances germination and seedling growth in the presence of Cd and, in this study, the growth of 6-month-old oat plants in Cd-contaminated soil was not increased by inoculation with T. viride, but a 1.7-fold increase in yield was observed. The content of Cd in oat shoots depended on the Cd content in the soil. Still, it was unaffected by the inoculation with T. viride. A. sativa metallothioneins (AsMTs) participate in plant-fungi interaction, however, their role in this study depended on MT type and Cd concentration. The inoculation of A. sativa with T. viride could be a promising approach to obtaining a high yield in Cd-contaminated soil without increasing the Cd content in the plant.

Toxic metals cause risks to the ecological environment. Typha latifolia L. is a good candidate to clean potentially toxic metals contaminated water or soil. However, limited research investigated the impact of environmental factors (e.g., pH, soil substrate, flood duration) on metal accumulations in cattails. In this study, cattails were cultured in soils flooded with artificial wastewater with varying pH (5, 7 or 9) and different levels of Cr, Cd and Zn for four weeks to investigate the interactions between environmental conditions and metal uptake in cattails. The metal content in biomass were measured by an inductively coupled plasma-optical emission spectrometer.
More Zn (>10,000 mg/kg dry biomass) entered plants compared to Cd and Cr (<1,000 mg/kg dry biomass). Approximately 80% of Zn from solutions with 50 mg/L Cd, 25 mg/L Cr, 250 mg/L Zn were removed by cattails. Most Cd and Cr were sorbed onto soils. Cattails exhibited relatively consistent performance in removing metals from wastewater with initial pH of 5, 7 or 9. The pH of all the solutions ended close to neutral after 4 weeks. More research is needed to further understand the influence of environmental conditions on metal uptakes in plants to improve phytoremediation efficiency.
It is the first study to evaluate metal accumulation in cattails cultured in soils flooded with artificial wastewater with varying pH and different levels of metals.This project investigated the interactions between growth conditions (e.g., pH, soil substrate, flooding) and different metal uptake in cattails, which was not conducted in previous research.