The effects of simultaneous application of plant growth regulators and bioaugmentation on improvement of phytoremediation of pyrene contaminated soils

Endogenous IAA affected fluoranthene accumulation by regulating H+-ATPase and SOD activity in ryegrass

This study explores the role of endogenous indole-3-acetic acid (IAA) in modulating plant responses to pollution stress and its effect on pollutant accumulation, with a focus on fluoranthene (Flu) in ryegrass. To elucidate the mechanism, we employed an IAA promoter (α-aminobutyric acid [α-AB]) and an IAA inhibitor (naphthylphthalamic acid [NPA]) to regulate IAA levels and analyze Flu uptake characteristics. The experimental setup included a Flu treatment group (ryegrass with Flu addition) and a control group (ryegrass without Flu). Our findings demonstrate that Flu treatment enhanced IAA content and plant growth in ryegrass compared to the control. The Flu+AB treatment further enhanced these effects, while the Flu+NPA treatment exhibited a contrasting trend. Moreover, Flu+AB treatment led to increased Flu accumulation, in contrast to the inhibitory effect observed with Flu+NPA treatment. Flu treatment also enhanced the activities of key antioxidant enzymes (SOD, POD, CAT) and increased soluble sugar and protein levels, indicative of enzymatic and nonenzymatic defense responses, respectively. The Flu+AB treatment amplified these responses, whereas the Flu+NPA treatment attenuated them. Significantly, Flu treatment raised H+-ATPase activity compared to the control, an effect further elevated by Flu+AB treatment and diminished by Flu+NPA treatment. A random forest analysis suggested that Flu accumulation dependency varied under different treatments: it relied more on H+-ATPase activity under Flu+AB treatment and more on SOD activity under Flu+NPA treatment. Additionally, Flu+AB treatment boosted the transpiration rate in ryegrass, thereby increasing the Flu translocation factor, a trend reversed by Flu+NPA treatment. This research highlights crucial factors influencing Flu accumulation in ryegrass, offering potential new avenues for controlling the gathering of contaminants within plant systems.

Foliar application of plant growth regulators for enhancing heavy metal phytoextraction efficiency by Sedum alfredii Hance in contaminated soils: Lab to field experiments

The phytoremediation efficiency of plants in removing the heavy metals (HMs) might be influenced by their growth status and accumulation capacity of plants. Herein, we conducted a lab-scale experiment and a field try out to assess the optimal plant growth regulators (PGRs) including indole-3-acetic acid (IAA)/brassinolide (BR)/abscisic acid (ABA) in improving the phytoextraction potential of Sedum alfredii Hance (S. alfredii). The results of pot experiment revealed that application of IAA at 0.2 mg/L, BR at 0.4 mg/L, and ABA at 0.2 mg/L demonstrated notable potential as optimal dosage for Cd/Pb/Zn phytoextraction in S. alfredii. The findings of subcellular level of Cd/Pb/Zn in leaves showed that IAA (0.2 mg/L), BR (0.4 mg/L) or ABA (0.2 mg/L) promoted the HMs storage in the soluble and cell wall fraction, therefore contributing HMs subcellular compartmentation. In addition, application of PGRs notably enhanced the antioxidant system (SOD, CAT, POD, APX activities) while reducing lipid peroxidation (MDA content) in S. alfredii, consequently improving HMs tolerance and growth of S. alfredii. Moreover, the results of field trial showed that application of BR, IAA, or ABA+BR substantially improved the growth of S. alfredii by inducing plants biomass and augmenting the levels of photosynthetic pigment contents. Notably, ABA+BR noticed the highest theoretical biomass by 42.9 %, followed by IAA (41.6 %), and BR (36.4 %), as compared with CK. Additionally, ABA+BR treatment showed effectiveness in removing the Cd by 103.4 %, while BR and IAA led to a significant increase of Pb and Zn removal by 239 % and 116 %, respectively, when compared with CK. Overall, the results of this study highlights that the foliar application of IAA, BR, or ABA+BR can serve as viable strategy to boosting phytoremediation efficiency of S. alfredii in contaminated soil by improving the biomass and metal accumulation in harvestable parts.

Concentration-dependent mechanisms of fluoranthene uptake by ryegrass

Fluoranthene (Flu) uptake by plants is affected by plant growth and environmental concentration. Although plant growth processes, including substance synthesis and antioxidant enzyme activities, have been reported to regulate Flu uptake, their contributions have been poorly evaluated. Moreover, the effect of Flu concentration is little known. Here, low concentrations (0, 1, 5, and 10 mg/L) and high concentrations (20, 30, and 40 mg/L) of Flu were set to compare the changes in Flu uptake by ryegrass (Lolium multiflorum Lam.). Indices of plant growth (biomass, root length, root area, root tip number, and photosynthesis and transpiration rates), substance synthesis (indole acetic acid [IAA] content), and antioxidant enzyme activities (superoxide dismutase [SOD], peroxidase [POD], and catalase [CAT]) were recorded to unravel the mechanism of Flu uptake. Findings suggested that the Langmuir model fitted Flu uptake by ryegrass well. Flu absorption capacity in the root was stronger than that that in the leaf. Flu bioconcentration and translocation factors increased then reduced with the increase in Flu concentration and reached the maximum value under 5 mg/L Flu treatment. Plant growth and IAA content had the same pattern as before bioconcentration factor (BCF). SOD and POD activities increased then decreased with Flu concentration and reached their highest levels under 30 and 20 mg/L Flu treatments, respectively, whereas CAT activity decreased continuously and reached its lowest level under 40 mg/L Flu treatment. Variance partitioning analysis indicated that IAA content had the greatest significant effect on Flu uptake under low-concentration Flu treatments, whereas antioxidant enzyme activities had the greatest significant effect on Flu uptake under high-concentration Flu treatments. Revealing the concentration-dependent mechanisms of Flu uptake could provide a basis for regulating pollutant accumulation in plants.

The Transcription Factors WRKY41 and WRKY53 Mediate Early Flowering Induced by the Novel Plant Growth Regulator Guvermectin in Arabidopsis thaliana

Flowering is a crucial stage for plant reproductive success; therefore, the regulation of plant flowering has been widely researched. Although multiple well-defined endogenous and exogenous flowering regulators have been reported, new ones are constantly being discovered. Here, we confirm that a novel plant growth regulator guvermectin (GV) induces early flowering in Arabidopsis. Interestingly, our genetic experiments newly demonstrated that WRKY41 and its homolog WRKY53 were involved in GV-accelerated flowering as positive flowering regulators. Overexpression of WRKY41 or WRKY53 resulted in an early flowering phenotype compared to the wild type (WT). In contrast, the w41/w53 double mutants showed a delay in GV-accelerated flowering. Gene expression analysis showed that flowering regulatory genes SOC1 and LFY were upregulated in GV-treated WT, 35S:WRKY41, and 35S:WRKY53 plants, but both declined in w41/w53 mutants with or without GV treatment. Meanwhile, biochemical assays confirmed that SOC1 and LFY were both direct targets of WRKY41 and WRKY53. Furthermore, the early flowering phenotype of 35S:WRKY41 lines was abolished in the soc1 or lfy background. Together, our results suggest that GV plays a function in promoting flowering, which was co-mediated by WRKY41 and WRKY53 acting as new flowering regulators by directly activating the transcription of SOC1 and LFY in Arabidopsis.

Phytoremediation as a potential technique for vehicle hazardous pollutants around highways

With the synchronous development of highway construction and the urban economy, automobiles have entered thousands of households as essential means of transportation. This paper reviews the latest research progress in using phytoremediation technology to remediate the environmental pollution caused by automobile exhaust in recent years, including the prospects for stereoscopic forestry. Currently, most automobiles on the global market are internal combustion vehicles using fossil energy sources as the primary fuel, such as gasoline, diesel, and liquid or compressed natural gas. The composition of vehicle exhaust is relatively complex. When it enters the atmosphere, it is prone to a series of chemical reactions to generate various secondary pollutants, which are very harmful to human beings, plants, animals, and the eco-environment. Despite improving the automobile fuel quality and installing exhaust gas purification devices, helping to reduce air pollution, the treatment costs of these approaches are expensive and cannot achieve zero emissions of automobile exhaust pollutants. The purification of vehicle exhaust by plants is a crucial way to remediate the environmental pollution caused by automobile exhaust and improve the environment along the highway by utilizing the ecosystem's self-regulating ability. Therefore, it has become a global trend to use phytoremediation technology to restore the automobile exhaust pollution. Now, there is no scientific report or systematic review about how plants absorb vehicle pollutants. The screening and configuration of suitable plant species is the most crucial aspect of successful phytoremediation. The mechanisms of plant adsorption, metabolism, and detoxification are reviewed in this paper to address the problem of automobile exhaust pollution.

Mobilization of contaminants: Potential for soil remediation and unintended consequences

Land treatment has become an essential waste management practice. Therefore, soil becomes a major source of contaminants including organic chemicals and potentially toxic elements (PTEs) which enter the food chain, primarily through leaching to potable water sources, plant uptake, and animal transfer. A range of soil amendments are used to manage the mobility of contaminants and subsequently their bioavailability. Various soil amendments, like desorbing agents, surfactants, and chelating agents, have been applied to increase contaminant mobility and bioavailability. These mobilizing agents are applied to increase the contaminant removal though phytoremediation, bioremediation, and soil washing. However, possible leaching of the mobilized pollutants during soil washing is a major limitation, particularly when there is no active plant uptake. This leads to groundwater contamination and toxicity to plants and soil biota. In this context, the present review provides an overview on various soil amendments used to enhance the bioavailability and mobility of organic and inorganic contaminants, thereby facilitating increased risk when soil is remediated in polluted areas. The unintended consequences of the mobilization methods, when used to remediate polluted sites, are discussed in relation to the leaching of mobilized contaminants when active plant growth is absent. The toxicity of targeted and non-targeted contaminants to microbial communities and higher plants is also discussed. Finally, this review work summarizes the existing research gaps in various contaminant mobilization approaches, and prospects for future research.

Auxin regulates growth, photosynthetic efficiency and mitigates copper induced toxicity via modulation of nutrient status, sugar metabolism and antioxidant potential in Brassica juncea

The involvement of auxin (IAA) in growth and development of plants is well known, but its role in the mitigation of metal stress, especially copper (Cu), is not fully understood; therefore, it is time to explore its involvement in minimizing the stress. A pot experiment was conducted to assess the protective function of IAA, applied to the foliage, on photosynthetic machinery, carbohydrate metabolism, and growth of Brassica juncea, grown with Cu (30 or 60 mg kg^-1 of soil). Among the different concentrations (10^-10, 10^-8, or 10^-6 M), 10^-8 M of IAA alone enhanced the photosynthetic characteristics, sugar accumulation and vegetative growth with minimal cellular oxidative stress level. Moreover, the same concentration of auxin was most effective in decreasing the stress levels generated by Cu and maintained it nearly to that of the control in terms of photosynthetic attributes, gas exchange parameters, PSII activity, electron transport rate, and growth attributes. Auxin also maintained the membrane stability and ultrastructure of chloroplast, stomatal morphology with a reduction in malondialdehyde (MDA), electrolyte leakage (EL) and cell death in test plants even under Cu stress. IAA also improved the translocation of Cu from root to the aerial parts, thus enhanced the Cu-reclamation in metal contaminated soils. Our findings suggest that the application of 10^-8 M of IAA maintains the overall growth of plants and may be used as an effective agent to improve growth, photosynthesis and phyto-remediation potential of B. juncea in Cu contaminated soil.

Phytoremediation of a pyrene-contaminated soil by Cannabis sativa L. at different initial pyrene concentrations

This study proposes the phytoremediation of a pyrene (PYR)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted along a 60 days period using three different initial PYR concentrations (i.e., 50, 100 and 150 mg kg TS^-1 of soil) in 300 mL volume pots under greenhouse conditions (18-25 °C and 45-55% humidity). After 60 days of hemp growth and flourishing, the highest PYR removal reached approximately 95% in planted soil, 35% higher than in the unplanted control. PYR accumulation was observed in both roots and aerial parts of the plant, with a higher PYR uptake at increasing initial PYR concentrations in soil. The initial PYR concentration affected the growth and, thus, the phytoremediation potential of C. sativa L., which was the result of different removal mechanisms. Overall, the lowest initial PYR concentration was the one that resulted in the highest PYR removal. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in this study. The highest DHO activity of 66.26 μg INTF g^-1 TS^-1 was observed in the soil spiked with 50 mg PYR·kg TS^-1.

Particularities of Fungicides and Factors Affecting Their Fate and Removal Efficacy: A Review

Systemic fungicide use has increased over the last decades, despite the susceptibility of resistance development and the side effects to human health and the environment. Although herbicides and insecticides are detected more frequently in environmental samples, there are many fungicides that have the ability to enter water bodies due to their physicochemical properties and their increasing use. Key factors affecting fungicide fate in the environment have been discussed, including the non-target effects of fungicides. For instance, fungicides are associated with the steep decline in bumblebee populations. Secondary actions of certain fungicides on plants have also been reported recently. In addition, the use of alternative eco-friendly disease management approaches has been described. Constructed Wetlands (CWs) comprise an environmentally friendly, low cost, and efficient fungicide remediation technique. Fungicide removal within CWs is dependent on plant uptake and metabolism, absorption in porous media and soil, hydrolysis, photodegradation, and biodegradation. Factors related to the efficacy of CWs on the removal of fungicides, such as the type of CW, plant species, and the physicochemical parameters of fungicides, are also discussed in this paper. There are low-environmental-risk fungicides, phytohormones and other compounds, which could improve the removal performance of CW vegetation. In addition, specific parameters such as the multiple modes of action of fungicides, side effects on substrate microbial communities and endophytes, and plant physiological response were also studied. Prospects and challenges for future research are suggested under the prism of reducing the risk related to fungicides and enhancing CW performance.

Roles of exogenous plant growth regulators on phytoextraction of Cd/Pb/Zn by Sedum alfredii Hance in contaminated soils

Plant growth regulators (PGRs) assisted phytoextraction was investigated as a viable phytoremediation technology to increase the phytoextraction efficiency in contaminated soils. This study aimed to evaluate the cadimum (Cd)/lead (Pb)/zinc (Zn) phytoextraction efficiency by a hyperaccumulator Sedum alfredii Hance (S. alfredii) treated with 9 PGRs, including indole-3-acetic acid (IAA), gibberellin (GA₃), cytokinin (CKs), abscisic acid (ABA), ethylene (ETH), brassinosteroid (BR), salicylic acid (SA), strigolactones (SL) and jasmonic acid (JA), in slightly or heavily contaminated (SC and HC, respectively) soil. Results demonstrated that PGRs were able to improve S. alfredii biomass, the most significant increases were observed in GA₃ and SL for HC soil, while for SC soil, IAA and BR exhibited positive effects. The levels of Cd, Pb and Zn in the shoots of S. alfredii treated with ABA and SL were noticeably greater than in the CK treatment in HC soil, while the uptake of metals were increased by IAA and CKs in SC soil. Combined with the results of biomass and metal contents in shoots, we found that ABA showed the highest Cd removal efficiency and the maximum Pb and Zn removal efficiency was observed with GA₃, which was 62.99%, 269.23%, and 41.18%, respectively higher than the control in HC soil. Meanwhile, compared to control, the maximum removal efficiency of Cd by IAA treatment (52.80%), Pb by JA treatment (165.1%), and Zn by BR treatment (44.97%) in the SC soil. Overall, our results suggested that these PGRs, especially, ABA, SL, IAA, BR and GA₃ had great potential in improving phytoremediation efficiency of S. alfredii grown in contaminated soils.

Phytoremediation of pyrene-contaminated soils: A critical review of the key factors affecting the fate of pyrene

Soil contamination by pyrene has increased over the years due to human-related activities, urgently demanding for remediation approaches to ensure human and environment safety. Within this frame, phytoremediation has been successfully applied over the years due to its green and cost-effectiveness features. The scope of this review includes the main phytoremediation mechanisms correlated with the removal of pyrene from contaminated soils and sediments to highlight the impact of different parameters and the supplement of additives on the efficiency of the treatment. Soil organic matter (SOM), plant species, aging time, environmental parameters (pH, soil oxygenation, and temperature) and bioavailability are among the main parameters affecting pyrene removal through phytoremediation. Phytoextraction only accounts for a small part of the entire phytoremediation process, but the addition of surfactants and chelating agents in planted soils could increase pyrene accumulation in plant tissues by 20% as a consequence of the increased pyrene bioavailability. Rhizodegradation is the main phytoremediation mechanism involved due to the activity of bacteria capable of degrading pyrene in the root area. Inoculated-planted soil treatments have the potential to decrease pyrene accumulation in shoots and roots by approximately 30 and 40%, respectively, further stimulating the proliferation of pyrene-degrading bacteria in the rhizosphere. Plant-fungi symbiotic association results in an enhanced accumulation of pyrene in shoots and roots of plants as well as a higher biodegradation. Finally, pyrene removal from soil can be improved in the presence of amendments, such as natural non-ionic surfactants, biochar, and bacterial mixtures.

Integration of RT-qPCR analysis and grey situation decision-making model for evaluating the effects of plant growth regulators on the gene expression in rice seedlings under thiocyanate exposure

Thiocyanate (SCN^-) present in irrigation water can have negative effects on plant growth and crop yields. Addition of plant growth regulators (PGRs) can alleviate toxic stress to plants. In the current study, we established a grey situation decision-making model (GSDM) to integrate the data of RT-qPCR analysis for screening the optimal addition of PGRs to minimise pollution stress. The effects of PGRs (i.e., jasmonic acid [JA], indole-3-acetic acid [IAA] and sodium hydrosulfide [NaHS]) on the abundance of IAA oxidation and conjugation-related genes in rice seedlings under potassium thiocyanate (KSCN) exposure was examined. The results obtained from RT-qPCR analysis can roughly present the mitigating effects of IAA, JA, and NaHS on rice seedlings under KSCN stress. Integration of RT-qPCR analysis and GSDM further quantified the regulatory effects of PGRs. Simulation results showed that the effect of NaHS on the gene expression at KSCN exposure is apparently better than that of JA and IAA. Our study provides a new simple, efficient, and cheap approach to identify the optimal plant growth regulators under the stress of environmental pollution.

Phytotoxicity of petroleum hydrocarbons: Sources, impacts and remediation strategies

Extraction and exploration of petroleum hydrocarbons (PHs) to satisfy the rising world population's fossil fuel demand is playing havoc with human beings and other life forms by contaminating the ecosystem, particularly the soil. In the current review, we highlighted the sources of PHs contamination, factors affecting the PHs accumulation in soil, mechanisms of uptake, translocation and potential toxic effects of PHs on plants. In plants, PHs reduce the seed germination andnutrients translocation, and induce oxidative stress, disturb the plant metabolic activity and inhibit the plant physiology and morphology that ultimately reduce plant yield. Moreover, the defense strategy in plants to mitigate the PHs toxicity and other potential remediation techniques, including the use of organic manure, compost, plant hormones, and biochar, and application of microbe-assisted remediation, and phytoremediation are also discussed in the current review. These remediation strategies not only help to remediate PHs pollutionin the soil rhizosphere but also enhance the morphological and physiological attributes of plant and results to improve crop yield under PHs contaminated soils. This review aims to provide significant information on ecological importance of PHs stress in various interdisciplinary investigations and critical remediation techniques to mitigate the contamination of PHs in agricultural soils.

The effects of exogenous application of melatonin on the degradation of polycyclic aromatic hydrocarbons in the rhizosphere of Festuca

The study aimed to assess the effects of melatonin, a plant growth regulator, on the degradation of phenanthrene (Phe) and pyrene (Py), in the rhizosphere of the Festuca grass. The experiments were divided into the following groups: 1) soil contaminated with Phe and Py, without the Festuca, 2) contaminated soil + Festuca, 3-5), contaminated soil + Festuca + the application of melatonin in three separate doses: 10, 50, or 100 μM. After 90 days, the effects of melatonin supplementation on the degradation of polycyclic aromatic hydrocarbons (PAHs) were analyzed by evaluating the rate of PAHs degradation, the expression of genes encoding salicylaldehyde dehydrogenase (SDH) and glutathione peroxidase (GPX) enzymes in Pseudomonas putida, as well as by measuring the total activity of dehydrogenase and peroxidase enzymes. Our results have shown that in soil contaminated by 300 mg kg^-1 PAHs, application of melatonin (10, 50, 100 μM), resulted in the following increase in the dehydrogenase and peroxidase activity in all three applied doses (19% and 5.7%), (45.3% and 34.3%), (40.9% and 14.3%), respectively in comparison to the control group. The experiment showed that soil supplementation with melatonin at 50 μM, resulted in the highest removal rate of PAHs. According to our results, melatonin demonstrated a potentially favorable role in enhancing plant biomass, as well as an increase in soil bacterial population, and the activity of antioxidative enzymes in P. putida, causing all tested parameters of the soil and the expression of desired genes to be advantageously altered for the degradation of the chosen PAHs.

Exogenous plant growth regulator alleviate the adverse effects of U and Cd stress in sunflower (Helianthus annuus L.) and improve the efficacy of U and Cd remediation

Plant growth regulators (PGRs) are widely used in agricultural activities and have the potential to improve plant growth and plant tolerance against metal stress. PGR-assisted phytoextraction is now an effective and inexpensive method for enhancing the plant removal of toxic metals from soil. In this study, we conducted experiments to determine the effects of PGR treatments on soil uranium (U) and cadmium (Cd) removal by sunflowers as well as their stress response to U and Cd contamination. We found that the plant growth was inhibited by combined U and Cd stress in sunflowers compared with that of the control; however, the application of exogenous PGR had reduced the combined U and Cd stress by stimulating photosynthesis, decreasing the levels of active oxygen and lipid peroxidation, and enhancing the activity of the antioxidant defence systems. Exogenous PGR also increased the uptake of U and Cd by sunflowers and therefore, improved their U and Cd remediation efficiency. Moreover, indoleacetic acid (IAA) was the most effective PGR at removing U and Cd in the soil; the U and Cd removal efficiency was 484.21% and 238.85% higher in the 500 mg L^-1 IAA application compared with that of the control without PGR application, respectively. Furthermore, none of the PGR treatments significantly influenced the available U and Cd contents in soil. Our results, therefore, may provide some detailed understanding on the technologies for the sustainable remediation of U and Cd contaminated soil by the combination of PGR treatments and phytoextraction.

Bioremediation of PAH-contaminated shooting range soil using integrated approaches

Serious contamination of polycyclic aromatic hydrocarbons (PAHs) occurs at outdoor shooting ranges due to the accumulation of clay target fragments containing coal tar or petroleum pitch. These contaminated sites are characterized with high-molecular-weight PAHs that are low in bioavailability and recalcitrant to bioremediation. We evaluated the effectiveness of different remediation strategies, used individually or in combinations, to decontaminate PAHs in a shooting range soil. The treatments included vegetation with bermudagrass [Cynodon dactylon (L.) Pers] or switchgrass [Panicum virgatum]), bioaugmentation of Mycobacterium vanbaalenii PYR-1, and addition of surfactants (Brij-35, rhamnolipid biosurfactant, or Brij-35/sodium dodecyl sulfate mixture). The initial total PAH concentration in the shooting range soil was 373 mg/kg and consisted of primarily high-molecular-weight PAHs (84%). Planting of bermudagrass and switchgrass resulted in 36% and 27% ∑₁₆PAH reduction compared to the non-vegetated control, respectively. Bermudagrass enhanced soil dehydrogenase activity and both vegetation treatments also increased polyphenol oxidase activity. Bioaugmentation of M. vanbaalenii PYR-1 had a significant effect only on the dissipation of high-molecular-weight PAHs, leading to a 15% decrease (∑₁₀PAH) compared to the control. In the non-vegetated soil, Brij-35/sodium dodecyl sulfate mixture increased PAH degradation compared to the no surfactant control. The increased PAH biodegradation in the vegetated and bioaugmented treatments improved lettuce [Lactuca sativa] seed germination, suggesting reduced toxicity in the treated soils. Phytoremediation using bermudagrass or switchgrass with bioaugmentation of M. vanbaalenii PYR-1 was an effective in situ remediation option for shooting range soils with heavy PAH contamination.

The effect of different levels of leachate on phytoremediation of pyrene-contaminated soil and simultaneous extraction of lead and cadmium

Pyrene is one of the 16 group combinations of polyaromatic hydrocarbons, which are known as primary pollutants in the U.S. Environmental Protection Agency (USEPA) list. This study aimed to investigate the cross effect of different levels of landfill leachate on phytoremediation of pyrene-contaminated soil using the sorghum bicolor plant. The study parameters included the presence or absence of the plant, different concentrations of pyrene (150, 300, 500, 750, and 1000 mg kg^-1), time (30, 60, and 90 days), and different levels of irrigation with leachate (0, 30, 50, 70, and 100%). Soil pyrene was measured every 30 days, and heavy metals (lead and cadmium) added to the soil by irrigation with leachate were measured in the soil and the plant at the end of 90 days. According to the results, pyrene removal efficiency after 90 days was 96% in irrigation treatments with 30% leachate in the presence of the plant and 67% in irrigation treatments with tap water in the presence of the plant. In addition, 95% of lead and 49% of cadmium added to the soil by irrigation with 30% leachate were extracted from the soil by the sorghum bicolor. According to the results, by increasing nutrients and number of soil bacteria during the cross treatment, landfill leachate increased the pyrene removal efficiency significantly during phytoremediation (p < 0.006) and the sorghum bicolor plant extracted the lead and cadmium of the leachate. In non-planting treatments, although adding high levels of leachate to the soil significantly improved the pyrene removal, it caused the levels of heavy metals, such as lead and cadmium, to exceed the allowable limit (p < 0.001).

Phytoremediation of cadmium (Cd) and uranium (U) contaminated soils by Brassica juncea L. enhanced with exogenous application of plant growth regulators

This investigation was made to examine the role of indole-3-acetic acid (IAA), gibberellin A3 (GA₃), 6-Benzylaminopurine (6-BA), and 24-epibrassinolide (EBL) in improving stress tolerance and phytoremediation of the cadmium (Cd) and uranium (U) by mustard (Brassica juncea L.). The optimum concentrations of IAA, GA₃, 6-BA, and EBL were determined based on plant biomass production, metal uptake, translocation, and removal efficiency. The biomass and total chlorophyll content decreased under Cd and U stress. Nevertheless, the application of IAA, GA₃, and 6-BA significantly (p < 0.05) increased the growth and total chlorophyll content of mustard. The malondialdehyde (MDA) and H₂O₂ content of mustard were enhanced under Cd and U stress, but they were significantly (p < 0.05) decreased in plant growth regulators (PGRs) treatments (except for EBL). PGRs treatments increased activities of antioxidant enzymes such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, thus reducing the oxidative stress. Furthermore, the shoot uptake of Cd and U of IAA and EBL treatments was significantly (p < 0.05) higher than that of other treatments. IAA and EBL also have more significant effects on the translocation and remediation of Cd and U compared to GA₃ and 6-BA. The removal efficiency of Cd and U reached the maximum in the 500 mg L^-1 IAA treatment, which was 330.77% and 118.61% greater than that in the control (CK), respectively. These results suggested that PGRs could improve the stress tolerance and efficiency of phytoremediation using B. juncea in Cd- and U- contaminated soils.

Do pyrene and Kandelia obovata improve removal of BDE-209 in mangrove soils?

Combined pollution caused by polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) in mangrove wetlands is serious, with their remediation to be been paid more and more attention. However, little is known about the combined impact of PAHs and mangrove species on removal of PBDEs in contaminated soils. In this study, BDE-209 and pyrene were selected and a 9 months experiment was conducted to explore how BDE-209 removal in contaminated soil varied with pyrene addition and Kandelia obovata planting, and to clarify corresponding microbial responses. Results showed that BDE-209 removals in soil induced by pyrene addition or K. obovata planting were significant and stable after 6 months, with the lowest levels of BDE-209 in combined pyrene addition with K. obovata planting. Unexpected, root uptake of BDE-209 in K. obovata was limited for BDE-209 removal in soil, which was verified by lower total amount of BDE-209 bioaccumulated in K. obovata's root. In soil without K. obovata planting, BDE-209 removal caused by pyrene addition coexisted with changed bacterial abundance at phylum Planctomycetes and Chloroflexi, class Planctomycetacia, and genus Blastopirellula. K. obovata-induced removal of BDE-209 in soil may be related to bacterial enrichment in phylum Proteobacteria, class Gammaproteobacteria and genus Ilumatobacter, Gaiella. Thus, in BDE-209 contaminated soil, microbial community responses induced by pyrene addition and K. obovata planting were different at phylum, class and genus levels. This is the first study demonstrating that pyrene addition and K. obovata planting could improve BDE-209 removal, and differently affected the corresponding responses of microbial communities.

Modelling and Optimizing Pyrene Removal from the Soil by Phytoremediation using Response Surface Methodology, Artificial Neural Networks, and Genetic Algorithm

This study aimed to model and optimize pyrene removal from the soil contaminated by sorghum bicolor plant using Response Surface Methodology (RSM) and Artificial Neural Network (ANN) with Genetic Algorithm (GA) approach. Here, the effects of indole acetic acid (IAA) and pseudomonas aeruginosa bacteria on increasing pyrene removal efficiency by phytoremediation process was studied. The experimental design was done using the Box-Behnken Design (BBD) technique. In the RSM model, the non-linear second-order model was in good agreement with the laboratory results. A two-layer Feed-Forward Back-Propagation Neural Network (FFBPNN) model was designed. Various training algorithms were evaluated and the Levenberg Marquardt (LM) algorithm was selected as the best one. Existence of eight neurons in the hidden layer leads to the highest R and lowest MSE and MAE. The results of the GA determined the optimum performance conditions. The results showed that using indole acetic acid and pseudomonas bacteria increased the efficiency of the sorghum plant in removing pyrene from the soil. The comparison obviously indicated that the prediction capability of the ANN model was much better than that of the RSM model.

Regulation of endogenous phytohormones alters the fluoranthene content in Arabidopsis thaliana

Phytohormones are crucial endogenous modulators that regulate and integrate plant growth and responses to various environmental pollutants, including the uptake of pollutants into the plant. However, possible links between endogenous phytohormone pathways and pollutant accumulation are unclear. Here we describe the fluoranthene uptake, plant growth, and superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione S-transferase (GST) activities in relation to different endogenous phytohormones and different levels in Arabidopsis thaliana. Three phytohormone inhibitors-N-1-naphthyl-phthalamic acid (NPA), daminozide (DZ), and silver nitrate (SN)-were used to regulate endogenous auxin, gibberellin, and ethylene levels, respectively. Fluoranthene inhibited plant growth and root proliferation while increasing GST and SOD activity. The three inhibitors reduced fluoranthene levels in Arabidopsis by either affecting plant growth or modulating antioxidant enzyme activity. NPA reduced plant growth and increased CAT activity. SN promoted plant growth and increased POD and CAT activity, whereas DZ increased POD activity.

Effect of salicylic acid and mycorrhizal symbiosis on improvement of fluoranthene phytoremediation using tall fescue (Festuca arundinacea Schreb)

Polycyclic aromatic hydrocarbons are an important group of pollutants that are widely distributed in the environment. The present study aimed to investigate the effect of salicylic acid (a phenolic phytohormone) and mycorrhizal fungi on the growth and phytoremediation ability of tall fescue in the soil contaminated by fluoranthene. The initial concentrations of fluoranthene in this study were 100, 200, and 300 mg kg^-1. The experimental treatments were included: T0 uncultivated soil; T1 cultivated soil with tall fescue; T2 cultivated soil with tall fescue + salicylic acid application; T3 cultivated soil with tall fescue + application of mycorrhizal fungi; T4 cultivated soil with tall fescue + salicylic acid and mycorrhizal fungi application; and P planting tall fescue in uncontaminated soil. The removal of fluoranthene was measured after 90 days. Furthermore, at the end of the experiment, the amount of shoot and root biomass, soil bacteria, and dehydrogenase activity were measured. According to the results, in all levels of contamination, removal of fluoranthene in cultivated treatments significantly was higher than uncultivated treatments. Increasing the concentration of fluoranthene had a negative effect on the shoot and root biomass in different treatments. Salicylic acid and mycorrhizal fungi significantly increased the shoot and root biomass and also the number of soil bacteria, dehydrogenase activity, and fluoranthene removal in T2, T3, and T4 treatments compared to T1. At the highest concentration of fluoranthene, as a result of simultaneous application of salicylic acid and mycorrhizal fungi (T4), the fluoranthene removal increased by 63, 21, 13, and 16% in comparison with T0, T1, T2, and T3, respectively. Based on the results, salicylic acid and mycorrhizal fungi, either alone or in combination, have a significant effect on the improvement of phytoremediation potential in tall fescue.

Enrichment of the soil microbial community in the bioremediation of a petroleum-contaminated soil amended with rice straw or sawdust

Two common organic wastes from agriculture (rice straw) and forestry (sawdust) were applied to a petroleum-contaminated soil to estimate their effectiveness in the removal of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs). Rice straw was the more effective amendment than the other treatments in reducing TPH contents and addition of sawdust resulted in a significant decrease in PAH removal, particularly high-molecular-weight (5-6 ring) PAHs. Principal coordinates analysis (PCoA) indicates that rice straw treatment separated only the bacterial community but sawdust greatly affected both the soil bacterial and fungal communities. Moreover, the abundance of some petroleum degraders such as the bacteria Sphingomonas, Idiomarina and Phenylobacterium and the fungi Humicola, Wallemia and Graphium was promoted by inputs of the two agricultural and forestry wastes. These results highlight the potential of waste applications in accelerating hydrocarbon biodegradation which may be attributed to the enrichment of keystone taxa that show strong positive associations with hydrocarbon degradation.

The application of plant growth regulators to improve phytoremediation of contaminated soils: A review

Soil contamination is one of the most important environmental problems around the world. The transfer of organic contaminants and heavy metals to the food chain is a major threat to human health. Purging these contaminants often involves a lot of energy and complex engineering processes. Phytoremediation technology can be used in various environments, such as water, soil, and air, to reduce or eliminate different contaminants. The major mechanisms involved in phytoremediation include plant extraction, rhizofiltration, plant evaporation, plant stabilization, plant decomposition, and rhizosphere degradation. The efficiency of phytoremediation can be increased through using chelating and acidifying agents, applying electric current in the soil, using organic chemicals and fertilizers, planting transgenic plants, using bacteria, and applying plant growth regulators. Recently, the use of plant growth regulators has been investigated as a suitable method for improving the efficacy of phytoremediation. Effective plant growth regulators to improve phytoremediation include auxins, gibberellins, cytokinins, and salicylic acid. The activity of these materials depends on their concentration, environmental factors that affect their absorption, and the physiological state of the plant. Using these materials increases the biomass of the plant and reduces the negative effects of the presence of contaminants in the plant. The present study aimed to review the latest studies performed on the improvement of phytoremediation using plant growth regulators and their mechanisms.

How autochthonous microorganisms influence physiological status of Zea mays L. cultivated on heavy metal contaminated soils?

The aim of this study was to investigate the effect of autochthonous microorganisms present in soil collected from heavy metal (HM) uncontaminated (Pb ≈ 59 mg kg^-1, Cd ≈ 0.4 mg kg^-1, Zn ≈ 191 mg kg^-1), moderately (Pb ≈ 343 mg kg^-1, Cd ≈ 12 mg kg^-1, Zn ≈ 1876 mg kg^-1), and highly (Pb ≈ 1586 mg kg^-1, Cd ≈ 57 mg kg^-1, Zn ≈ 3280 mg kg^-1) contaminated sites on Zea mays elemental composition, physiological status, and growth parameters. For this purpose, half of the collected soil was sterilized and soil characterization was performed. After 45 days of cultivation, the presence of HM in the soil negatively affected photosynthesis and transpiration rates, relative chlorophyll content, anthocyanins index, chlorophyll fluorescence parameters, and content of oxidative stress products (H₂O₂ and Malondialdehyde) of Zea mays, while soil sterilization had a positive effect on those parameters. Average percentage of colonization of root segments by arbuscular mycorrhiza fungi decreased with an increase of HM contamination in the soil. The increase in shoot concentration of HMs, particularly Cd and Zn, was a result of contaminated soils sterilization. Aboveground biomass of maize cultivated on sterilized soil was 3-fold, 1.5-fold, and 1.5-fold higher for uncontaminated, moderately contaminated and highly contaminated soils respectively when compared to nonsterilized soils. Contrary to our expectation, autochthonous microflora did not improve plant growth and photosynthetic performance; in fact, they had a negative effect on those processes although they did reduce concentration of HMs in the shoots grown on contaminated soils.

Effects of lead and cadmium on photosynthesis in Amaranthus spinosus and assessment of phytoremediation potential

This study assessed the effects of Pb (0, 200, 500, 1000 mg kg^-1) and Cd (0, 5, 15, 30, 50 mg kg^-1) on photosynthesis in Amaranthus spinosus (A. spinosus), as well as the potential for phytoremediation by pot-culture experiment. Exposure to Pb/Cd produced a concentration-dependent decrease in biomass and all photosynthesis parameters, except for non-photochemical quenching, which increased with the metal concentration. The metals accumulated more in roots compared to shoots. The bioconcentration factor (BCF) of Pb was <1 in shoots at all Pb levels, whereas the BCF was <1 in roots at all but the lowest concentration of Pb. Roots extracted Cd from soil at all treatments. The translocation factor of Cd was larger than that of Pb suggesting that Cd is more mobile than Pb in A. spinosus. Amaranthus spinosus displays a high tolerance for both Pb and Cd with regards to growth and photochemical efficiency, but it is more sensitive to Cd than Pb. Amaranthus spinosus accumulates Pb and Cd primarily in the roots and Cd is more bioconcentrated and translocated in comparison to Pb. This investigation shows that A. spinosus has good potential for phytoremediation of soils contaminated by low levels of Cd and Pb.

Combined treatment of contaminated soil with a bacterial Stenotrophomonas strain DXZ9 and ryegrass (Lolium perenne) enhances DDT and DDE remediation

Bioremediation of contaminated soils by a combinational approach using specific bacterial species together with ryegrass is a promising strategy, resulting in potentially highly efficient degradation of organic contaminants. The present study tested the combination of strain DXZ9 of Stenotrophomonas sp. with ryegrass to remove DDT and DDE contaminants from soil under natural conditions in a pot experiment. The strain DXZ9 was successfully colonized in the natural soil, resulting in removal rates of approximately 77% for DDT, 52% for DDE, and 65% for the two pollutants combined after 210 days. Treatment with ryegrass alone resulted in slightly lower removal rates (72 and 48%, respectively, 61% for both combined), while the combination of strain DXZ9 and ryegrass significantly (p < 0.05) improved the removal rates to 81% for DDT and 55% for DDE (69% for both). The half-life of the contaminants was significantly shorter in combined treatment with DXZ9 and ryegrass compared to the control. The remediation was mostly due to degradation of the contaminants, as the net uptake of DDT and DDE by the ryegrass accounted for less than 3% of the total amount in the soil. DDT is reductively dechlorinated to DDD and dehydrochlorinated to DDE in the soil; the metabolites of DDE and DDD were multiple undefined substances. The toxicity of the soil was significantly reduced as a result of the treatment. The present study demonstrates that the bioremediation of soil contaminated with DDT and DDE by means of specific bacteria combined with ryegrass is feasible.

Evaluation and determination of soil remediation schemes using a modified AHP model and its application in a contaminated coking plant

Soil remediation has been considered as one of the most difficult pollution treatment tasks due to its high complexity in contaminants, geological conditions, usage, urgency, etc. The diversity in remediation technologies further makes quick selection of suitable remediation schemes much tougher even the site investigation has been done. Herein, a sustainable decision support hierarchical model has been developed to select, evaluate and determine preferred soil remediation schemes comprehensively based on modified analytic hierarchy process (MAHP). This MAHP method combines competence model and the Grubbs criteria with the conventional AHP. It not only considers the competence differences among experts in group decision, but also adjusts the big deviation caused by different experts' preference through sample analysis. This conversion allows the final remediation decision more reasonable. In this model, different evaluation criteria, including economic effect, environmental effect and technological effect, are employed to evaluate the integrated performance of remediation schemes followed by a strict computation using above MAHP. To confirm the feasibility of this developed model, it has been tested by a benzene workshop contaminated site in Beijing coking plant. Beyond soil remediation, this MAHP model would also be applied in other fields referring to multi-criteria group decision making.