Phytoremediation of Pollutants: Applicability and Future Perspective.

Environmental pollution is a global issue since it is spreading worldwide, affecting entire ecosystems [...].

Use of Biostimulants as a New Approach for the Improvement of Phytoremediation Performance-A Review.

Environmental pollution is one of the most pressing global issues, and it requires priority attention. Environmental remediation techniques have been developed over the years and can be applied to polluted sites, but they can have limited effectiveness and high energy consumption and costs. Bioremediation techniques, on the other hand, represent a promising alternative. Among them, phytoremediation is attracting particular attention, a green methodology that relies on the use of plant species to remediate contaminated sites or prevent the dispersion of xenobiotics into the environment. In this review, after a brief introduction focused on pollution and phytoremediation, the use of plant biostimulants (PBs) in the improvement of the remediation effectiveness is proposed. PBs are substances widely used in agriculture to raise crop production and resistance to various types of stress. Recent studies have also documented their ability to counteract the deleterious effects of pollutants on plants, thus increasing the phytoremediation efficiency of some species. The works published to date, reviewed and discussed in the present work, reveal promising prospects in the remediation of polluted environments, especially for heavy metals, when PBs derived from humic substances, protein and amino acid hydrolysate, inorganic salts, microbes, seaweed, plant extracts, and fungi are employed.

Phytodepuration of Nitrate Contaminated Water Using Four Different Tree Species.

Water pollution by excessive amounts of nitrate (NO3-) has become a global issue. Technologies to clean up nitrate-contaminated water bodies include phytoremediation. In this context, this research aimed to evaluate four tree species (Salix alba L., Populus alba L., Corylus avellana L. and Sambucus nigra L.) to remediate nitrate-contaminated waters (100 and 300 mg L-1). Some physiological parameters showed that S. alba L. and P. alba L. increased particularly photosynthetic activity, chlorophyll content, dry weight, and transpired water, following the treatments with the above NO3- concentrations. Furthermore, these species were more efficient than the others studied in the phytodepuration of water contaminated by the two NO3- levels. In particular, within 15 days of treatment, S. alba L. and P. alba L. removed nitrate quantities ranging from 39 to 78%. Differently, C. avellana L. and S. nigra L. did not show particular responses regarding the physiological traits studied. Nonetheless, these species removed up to 30% of nitrate from water. In conclusion, these data provide exciting indications on the chance of using S. alba L. and P. alba L. to populate buffer strips to avoid NO3- environmental dispersion in agricultural areas.

Blue:Red LED Light Proportion Affects Vegetative Parameters, Pigment Content, and Oxidative Status of Einkorn (Triticum monococcum L. ssp. monococcum) Wheatgrass.

This work aimed to study the effect of some light spectra on the growth, oxidative state, and stress of einkorn wheatgrass (Triticum monococcum L. ssp. monococcum). To this end, six light treatments, having the same total incident photon flux density (PFD) of 200 µmol m-2 s-1, were applied to einkorn and compared: only blue light; only red; three blue:red combinations, at different proportions of total PFD (75:25%, 50:50%, and 25:75%, respectively); and a wide spectrum, taken as a control treatment, composed of blue (18% of PFD), red (18%), and intermediate wavelengths (64%). Light treatments affected the contents of pigments (chlorophylls and carotenes), hydrogen peroxide (H2O2), and malondialdehyde (MDA). These results revealed the changes in the oxidative status of wheatgrass, in response to the different light treatments. However, the dichromatic light with blue ≥50% of the total PFD appeared to be the best combination, guarantying good wheatgrass yield, increasing pigment content, and reducing H2O2 and MDA when compared to the other light treatments. Our findings also contribute to explaining the available literature on the effect of these kinds of light on the increase in phenolic compounds and antioxidant activity in einkorn wheatgrass.

Phytoremediation and detoxification of xenobiotics in plants: herbicide-safeners as a tool to improve plant efficiency in the remediation of polluted environments. A mini-review.

Phytoremediation is a widely studied and applied technology, based on the use of plants and their associated microorganisms to decontaminate polluted sites. In recent years, different strategies have been investigated to improve the phytoremediation efficiency of the selected plants. In this context, some studies have shown that herbicide-safeners, chemicals applied to crops to enhance their tolerance to herbicides, can increase the phytoremediation of soils and water polluted by organic and inorganic contaminants. Safeners, by inducing the xenobiotic detoxification and the antioxidant metabolism in plants, can enhance their removal potential in the cleaning process. In this review, after a short survey of phytoremediation technologies and the biochemical mechanisms activated by plants to tolerate and detoxify heavy metals and herbicides, the use of herbicide-safeners as a tool to increase the phytoremediation performance is reviewed and discussed.

Effects of Megafol on the Olive Cultivar 'Arbequina' Grown Under Severe Saline Stress in Terms of Physiological Traits, Oxidative Stress, Antioxidant Defenses, and Cytosolic Ca2.

Salinity is one of the most impacting abiotic stresses regarding crop productivity and quality. Among the strategies that are attracting attention in the protection of crops from abiotic stresses, there is the use of plant biostimulants. In this study, Megafol (Meg), a commercial plant biostimulant, was tested on olive plants subjected to severe saline stress. Plants treated with salt alone showed substantial reductions in biomass production, leaf net photosynthesis (Pn), leaf transpiration rate (E), stomatal conductance (gs), and relative water content (RWC). In addition, samples stressed with NaCl showed a higher sodium (Na+) content in the leaves, while those stressed with NaCl and biostimulated with Meg increased the potassium (K+) content in the leaves, thus showing a higher K+/Na+ ratio. Salinity caused the accumulation of significant quantities of hydrogen peroxide (H2O2) and malondialdehyde (MDA) due to decreases in the activity of antioxidant enzymes, namely superoxide dismutase (SOD - EC 1.15.1.1), ascorbate peroxidase (APX - EC 1.11.1.11), guaiacol peroxidase (GPX - EC 1.11.1.9), and catalase (CAT - EC 1.11.1.6). When olive plants under saline stress were biostimulated with Meg, the plants recovered and showed physiological and biochemical traits much improved than salt stressed samples. Finally, Meg exhibited Ca2+-chelating activity in olive pollen grains, which allowed the biostimulant to exert this beneficial effect also by antagonizing the undesirable effects of hydrogen peroxide on Ca2+ metabolism.

Application of a Plant Biostimulant To Improve Maize (Zea mays) Tolerance to Metolachlor.

Plant biostimulants (PBS) increase crop productivity and induce beneficial processes in plants. Although PBS can stimulate plant tolerance to some abiotic stresses, their effect in improving crop resistance to herbicide injuries has barely been investigated. Therefore, a study on the effect of a biostimulant (Megafol) on maize (Zea mays L.) tolerance to a chloro-acetanilide herbicide (metolachlor) was carried out. We found that Megafol reduced the negative effects of metolachlor on maize. Indeed, biostimulated samples showed increases in germination, biomass production, Vigor index, and EC50 (effective concentration causing 50% reductions to roots and aerial biomass) with respect to the samples treated with metolachlor alone. Furthermore, plants treated with the herbicide in combination with Megafol showed lower levels of malondialdehyde (MDA). Antioxidant enzymes, namely, ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and catalase (CAT), were assayed in samples treated with metolachlor alone or in combination with Megafol, and higher enzymes activities were found in biostimulated plants. The results of this study open the perspective of using Megafol, as well as other suitable plant biostimulants, in improving the crop's capacity to cope with injuries and unwanted effects that herbicide could cause to these species.

The treatment of duckweed with a plant biostimulant or a safener improves the plant capacity to clean water polluted by terbuthylazine.

Water pollution is becoming alarming since thousands contaminants are dispersed in the aquatic environments, and agricultural practices, for the massive use of pesticides, are contributing to exacerbating this problem. In this context, a research aimed at investigating the ability of duckweed (Lemna minor), a free-floating aquatic species widespread throughout the world, to remediate water polluted with five different concentrations of a herbicide - terbuthylazine (TBA) - was carried out. In addition, duckweed was treated with a plant biostimulant and a safener with the aim of increasing the plant's capacity to tolerate and remove the TBA from the water. The results evidenced that the herbicide affected the duckweed already at the lower concentrations, reducing its capacity to proliferate and the area of its fronds. On the contrary, when the TBA treatments were performed in combination with the biostimulant or the safener the average area of the fronds was affected of lesser extents, compared to the plants treated with the herbicide only. Antioxidant enzymes, namely ascorbate peroxidases (APX) and catalases (CAT), were investigated and it was found that the biostimulated and safened duckweed showed increased activities of these enzymes, compared to the plants treated with TBA only. At last, some phytofiltration experiments were planned. The biostimulated and safened duckweed removed more TBA from polluted water than the plants treated with the herbicide alone. In conclusion, this research showed that duckweed is suitable for cleaning water polluted with TBA and this potential can be successfully improved by treating the species with a biostimulant or a safener.

Interference of three herbicides on iron acquisition in maize plants.

The use of herbicides to control weed species could lead to environmental threats due to their persistence and accumulation in the ecosystems and cultivated fields. Nonetheless, the effect of these compounds on plant mineral nutrition in crops has been barely investigated. This study aimed at ascertaining the effect of three herbicides (S-metolachlor, metribuzin and terbuthylazine) on the capacity of maize to acquire iron (Fe). Interferences on plant growth and reductions on the Fe contents were found in the plants treated. Furthermore, root cell viability and functionality losses were ascertained following the treatments, which, in turn, decreased the amount of phytosiderophores (PSs) released by the roots. An investigation carried out in greater depth on root apices of treated plants using an FE-SEM (Scanning Electron Microscope) coupled with EDX (Energy Dispersive X-ray) indicated that the reductions on Fe content started in this part of the roots. Lastly, decreases were found also in copper (Cu+2), zinc (Zn+2) and manganese (Mn+2) content in root apices.

Combination of aquatic species and safeners improves the remediation of copper polluted water.

In the last decades, many anthropogenic activities have resulted in heavy metal contamination of freshwaters and surrounding environments. This poses serious threats to human health. Phytoremediation is a cost-effective technology which is useful for remediating polluted soils and water. Recently, the use of aquatic free-floating plants has been proposed to remediate polluted water. In this context, a study on the capacity of two aquatic plants, Lemna minor (duckweed) and Salvinia auriculata (salvinia), to remediate Cu+2 (Cu) polluted water was carried out. Initially, the species were exposed to different copper concentrations (1, 5, 10, 20 and 50µmolL-1) in order to assess Cu+2 toxicity to the plants. In addition, plants were treated with two safeners (benoxacor and dichlormid), with the aim of pointing out any safening effect of these compounds on the aquatic species. Toxicity tests showed that safened plants had a greater Cu resistance, especially at the higher Cu doses. Finally, unsafened and safened plants were tested in the decontamination of water polluted by copper (1.2mgL-1). In general, duckweed removed higher amounts of Cu from polluted water than salvinia, and, surprisingly, for both the species the safeners significantly increased the plants' capacity to remove the metal from the polluted waters. Lastly, an HPLC-based method was developed and standardized to monitor the residual amounts of the two safeners in the water. While dichlormid was completely absorbed by duckweed within few days after the treatments, some residual amounts of both safeners were found in salvinia vegetated water after two weeks. In conclusion, the results of this research show that the use of aquatic species in combination with safeners is an attractive and reliable tool to make plants more effective in phytoremediation of water polluted with metals (or other toxic compounds).

Effect of three safeners on sulfur assimilation and iron deficiency response in barley (Hordeum vulgare) plants.

BACKGROUND: Safeners are agrochemicals used in agriculture to protect crops from herbicide injuries. They act by stimulating herbicide metabolism. As graminaceous plants, to cope with iron (Fe) deficiency, activate sulfur (S) metabolism and release huge amounts of Fe-chelating compounds, or phytosiderophores (PSs), we investigated, in barley plants (Hordeum vulgare, L.) grown in Fe deficiency, the effects of three safeners on two enzymes of S assimilation, cysteine (Cys) and glutathione (GSH), and PS release. Finally, we monitored the root Fe content in plants treated with the most effective safener. RESULTS: Generally, all the safeners activated S metabolism and increased Cys and GSH contents. In addition, the safened plants excreted higher levels of PSs. Given that mefenpyr-diethyl (Mef) was the most effective in causing these effects, we assessed the Fe concentration in Mef-treated barley and found higher Fe levels than those in untreated plants. CONCLUSION: The three safeners, in different ways but specifically, activated S reductive metabolism and regulated Cys and GSH contents, PS release rate and Fe content (Mef-treated barley). The results of this research provide new indications of the biochemical and physiological mechanisms involved in the safening action. © 2016 Society of Chemical Industry.

Use of two grasses for the phytoremediation of aqueous solutions polluted with terbuthylazine.

The capacity of two grasses, tall fescue (Festuca arundinacea) and orchardgrass (Dactylis glomerata), to remove terbuthylazine (TBA) from polluted solutions has been assessed in hydroponic cultures. Different TBA concentrations (0.06, 0.31, 0.62, and 1.24 mg/L) were chosen to test the capacity of the two grasses to resist the chemical. Aerial biomass, effective concentrations (to cause reductions of 10, 50, and 90% of plant aerial biomass) and chlorophylls contents of orchardgrass were found to be more affected. Tall fescue was found to be more capable of removing the TBA from the growth media. Furthermore, enzymes involved both in the herbicide detoxification and in the response to herbicide-induced oxidative stress were investigated. Glutathione S-transferase (GST, EC. 2.5.1.18) and ascorbate peroxidase (APX, EC. 1.11.1.11) of tall fescue were found to be unaffected by the chemical. GST and APX levels of orchardgrass were decreased by the treatment. These negative modulations exerted by the TBA on the enzyme of orchardgrass explained its lower capacity to cope with the negative effects of the TBA.

Nitrate removal from polluted water by using a vegetated floating system.

Nitrate (NO3(-)) water pollution is one of the most prevailing and relevant ecological issues. For instance, the wide presence of this pollutant in the environment is dramatically altering the quality of superficial and underground waters. Therefore, we set up a floating bed vegetated with a terrestrial herbaceous species (Italian ryegrass) with the aim to remediate hydroponic solutions polluted with NO3(-). The floating bed allowed the plants to grow and achieve an adequate development. Ryegrass was not affected by the treatments. On the contrary, plant biomass production and total nitrogen content (N-K) increased proportionally to the amount of NO3(-) applied. Regarding to the water cleaning experiments, the vegetated floating beds permitted to remove almost completely all the NO3(-) added from the hydroponic solutions with an initial concentration of 50, 100 and 150 mg L(-1). Furthermore, the calculation of the bioconcentration factor (BCF) indicated this species as successfully applicable for the remediation of solutions polluted by NO3(-). In conclusion, the results highlight that the combination of ryegrass and the floating bed system resulted to be effective in the remediation of aqueous solutions polluted by NO3(-).

Iron deficiency in barley plants: phytosiderophore release, iron translocation, and DNA methylation.

All living organisms require iron (Fe) to carry out many crucial metabolic pathways. Despite its high concentrations in the geosphere, Fe bio-availability to plant roots can be very scarce. To cope with Fe shortage, plants can activate different strategies. For these reasons, we investigated Fe deficient Hordeum vulgare L. plants by monitoring growth, phytosiderophores (PS) release, iron content, and translocation, and DNA methylation, with respect to Fe sufficient ones. Reductions of plant growth, roots to shoots Fe translocation, and increases in PS release were found. Experiments on DNA methylation highlighted significant differences between fully and hemy-methylated sequences in Fe deficient plants, with respect to Fe sufficient plants. Eleven DNA bands differently methylated were found in starved plants. Of these, five sequences showed significant alignment to barley genes encoding for a glucosyltransferase, a putative acyl carrier protein, a peroxidase, a ß-glucosidase and a transcription factor containing a Homeodomin. A resupply experiment was carried out on starved barley re-fed at 13 days after sowing (DAS), and it showed that plants did not recover after Fe addition. In fact, Fe absorption and root to shoot translocation capacities were impaired. In addition, resupplied barley showed DNA methylation/demethylation patterns very similar to that of barley grown in Fe deprivation. This last finding is very encouraging because it indicates as these variations/modifications could be transmitted to progenies.

Italian ryegrass for the phytoremediation of solutions polluted with terbuthylazine.

The phytoextraction capacity of Italian ryegrass (Lolium multiflorum L.) to remove terbuthylazine (TBA) from aqueous solution has been assessed using a plant-based biotest (RHIZOtest). Three TBA concentrations (0.5, 1.0 and 2.0 mg L(-1)) were chosen to evaluate the tolerance capacity of the ryegrass. Even though the treatments negatively affected plants, they were able to remove up to 30-40% of TBA. In addition, some enzymatic activities involved in the response to TBA-induced stress were determined. Glutathione S-transferase (GST) has been activated with a TBA-dose dependent trend; ascorbate peroxidase (APX) activities have been induced within the first hours after the treatments, followed by decreases or disappearance in plants exposed to two higher dosages. In conclusion, this case-study highlights that the combination of ryegrass and RHIZOtest resulted to be effective in the remediation of aqueous solutions polluted by TBA.