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Phytoremediation of Polluted Environments: Current Status and Future Directions

A special issue of International Journal of Environmental Research and Public Health (ISSN 1660-4601). This special issue belongs to the section "Environmental Science and Engineering".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 60061

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Guest Editor
Scotland's Rural College, West Mains Road, The King's Buildings, Edinburgh EH9 3JG, UK
Interests: phytoremediation; phytomining; plant metal hyperaccumulation; ecosystem services

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Guest Editor
Centre for Functional Ecology-Science for People & the Planet, Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal
Interests: plant-microbe interactions; mycorrhiza; plant beneficial bacteria; sustainable agriculture; phytoremediation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Tackling environmental pollution is one of the greatest challenges of our time. The ever-growing contamination of soil, water, and air has taken a severe toll on the planet and constitutes a major threat to public health. In this backdrop, a plant-based technology known as phytoremediation has emerged as a low-cost, sustainable, and green alternative to the often costly, impractical, and environmentally hazardous conventional solutions. Approximately three decades after its formal inception, phytoremediation has profited from numerous breakthroughs that have improved its effectiveness and broadened the array of potential applications. From mine tailings to wetlands, and oil spill sites to derelict industrial areas, phytoremediation has steadily become one of the most prolific research fields in environmental science, bridging disciplines like plant, soil, and water sciences, microbiology, and genetics, to list but a few.

This Special Issue aims to gather the foremost developments in phytoremediation of terrestrial and aquatic environments afflicted by organic and inorganic contamination. We also welcome novel research on any phytoremediation-related subjects (e.g., plant metal hyperaccumulation; bioindication; phytomining; bioremediation), as well as high-quality reviews. Potential topics include but are not limited to:

  • Phytoremediation of metal polluted soils and waters;
  • Phytoremediation of soils and waters contaminated with organic compounds;
  • Phytoremediation of saline soils;
  • Amendments-enhanced phytoremediation of polluted soils;
  • Bacteria and mycorrhiza-assisted phytoremediation;
  • Phytoremediation of polluted air;
  • Modelling of phytoremediation processes.
Dr. Luís A. B. Novo

Dr. Rui S. Oliveira
Guest Editors

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Keywords

  • phytoremediation
  • metal pollution
  • phytoextraction
  • phytostabilization
  • organic pollution
  • plant growth-promoting bacteria
  • phytodesalination
  • constructed wetlands
  • soil amendments

Published Papers (16 papers)

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17 pages, 2253 KiB  
Article
Screening of Emerging Pollutants (EPs) in Estuarine Water and Phytoremediation Capacity of Tripolium pannonicum under Controlled Conditions
by Ariel E. Turcios, Marie Hielscher, Bernardo Duarte, Vanessa F. Fonseca, Isabel Caçador and Jutta Papenbrock
Int. J. Environ. Res. Public Health 2021, 18(3), 943; https://doi.org/10.3390/ijerph18030943 - 22 Jan 2021
Cited by 8 | Viewed by 3290
Abstract
The increasing number of pharmaceuticals in the environment and their difficult biodegradation, can lead to bioaccumulation in different trophic compartments. Their bioaccumulation can have negative consequences, especially in the generation of bacterial resistance by antibiotics, but also in the impairment of plant and [...] Read more.
The increasing number of pharmaceuticals in the environment and their difficult biodegradation, can lead to bioaccumulation in different trophic compartments. Their bioaccumulation can have negative consequences, especially in the generation of bacterial resistance by antibiotics, but also in the impairment of plant and animal metabolism. The Tejo estuary in Portugal is the habitat for many plant and animal species, which are also prone to this type of contamination. Therefore, in the present study different classes of emerging pollutants (EPs) were surveyed in water samples in the Tejo estuary, including antibiotics, anticonvulsants, antidepressants, lipid-lowering drugs, anti-inflammatory drugs, beta-blockers and analgesics. According to the results, only four compounds were detected in water samples collected at the three selected salt marshes, including carbamazepine, fluoxetine hydrochloride, venlafaxine hydrochloride and acetaminophen. Having the detected substances as a basis, a subsequent study was performed aiming to investigate the uptake and biodegradation capacity of halophytes, using Tripolium pannonicum as a model plant cultivated under controlled conditions with different concentrations of the found EPs. This experimental approach showed that T. pannonicum was able to uptake and degrade xenobiotics. Moreover, the application of sulfamethazine, as a model antibiotic, showed also that this species can uptake and degrade this compound, although the degradation rate and process proved to be compound-specific. This was also confirmed using crude plant extracts spiked with the different EPs. Thus this species is a potential candidate for the remediation of marine water and sediments contaminated with environmentally-significant EPs. Full article
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24 pages, 32675 KiB  
Article
Long-Term Heavy Metal Retention by Mangroves and Effect on Its Growth: A Field Inventory and Scenario Simulation
by Anh Nguyen, Otto Richter, Bao V.Q. Le, Nguyen Thi Kim Phuong and Kim Chi Dinh
Int. J. Environ. Res. Public Health 2020, 17(23), 9131; https://doi.org/10.3390/ijerph17239131 - 07 Dec 2020
Cited by 12 | Viewed by 3338
Abstract
The ability of mangroves in taking up and storing heavy metal (HM) helps in reducing HM pollution. However, HMs likewise adversely affect the growth of mangroves. We assess the effects of the long-term soil HMs enrichment on the growth of Rhizophora apiculata forest [...] Read more.
The ability of mangroves in taking up and storing heavy metal (HM) helps in reducing HM pollution. However, HMs likewise adversely affect the growth of mangroves. We assess the effects of the long-term soil HMs enrichment on the growth of Rhizophora apiculata forest in the Can Gio Mangrove Forest (Southern Vietnam) in different environmental conditions of soil salinity, ground elevation, and tree density based on a novel set of measured data. These data were analyzed and were used to calibrate and validate for a tree growth model with influencing factors salinity, elevation, tree density, and heavy metals content. Three scenario simulations were performed to predict the mangrove dynamics under different levels of heavy metal pollution in combined environmental conditions of salinity and elevation. Simulation results show the decline of total forest biomass from 1,750,000 tons (baseline scenario with no HM pollution) down to 850,000 tons and 350,000 tons for the current HM pollution and double HM pollution scenarios, respectively. Both data analysis and simulations have shown that although mangroves can assist in reducing HM pollution, the quality and health of this ecosystem will be severely affected if the environment is excessively polluted. In addition, a data-and-model driven management tool is devised for the sustainable management of the mangrove environmental resources. Full article
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23 pages, 4989 KiB  
Article
Mitigation of Nickel Toxicity and Growth Promotion in Sesame through the Application of a Bacterial Endophyte and Zeolite in Nickel Contaminated Soil
by Muhammad Naveed, Syeda Sosan Bukhari, Adnan Mustafa, Allah Ditta, Saud Alamri, Mohamed A. El-Esawi, Munazza Rafique, Sobia Ashraf and Manzer H. Siddiqui
Int. J. Environ. Res. Public Health 2020, 17(23), 8859; https://doi.org/10.3390/ijerph17238859 - 28 Nov 2020
Cited by 37 | Viewed by 3150
Abstract
Nickel (Ni) bioavailable fraction in the soil is of utmost importance because of its involvement in plant growth and environmental feedbacks. High concentrations of Ni in the soil environment, especially in the root zone, may retard plant growth that ultimately results in reduced [...] Read more.
Nickel (Ni) bioavailable fraction in the soil is of utmost importance because of its involvement in plant growth and environmental feedbacks. High concentrations of Ni in the soil environment, especially in the root zone, may retard plant growth that ultimately results in reduced plant biomass and yield. However, endophytic microorganisms have great potential to reduce the toxicity of Ni, especially when applied together with zeolite. The present research work was conducted to evaluate the potential effects of an endophytic bacterium Caulobacter sp. MN13 in combination with zeolite on the physiology, growth, quality, and yield of sesame plant under normal and Ni stressed soil conditions through possible reduction of Ni uptake. Surface sterilized sesame seeds were sown in pots filled with artificially Ni contaminated soil amended with zeolite. Results revealed that plant agronomic attributes such as shoot root dry weight, total number of pods, and 1000-grains weight were increased by 41, 45, 54, and 65%, respectively, over control treatment, with combined application of bacteria and zeolite in Ni contaminated soil. In comparison to control, the gaseous exchange parameters (CO2 assimilation rate, transpiration rate, stomatal- sub-stomatal conductance, chlorophyll content, and vapor pressure) were significantly enhanced by co-application of bacteria and zeolite ranging from 20 to 49% under Ni stress. Moreover, the combined utilization of bacteria and zeolite considerably improved water relations of sesame plant, in terms of relative water content (RWC) and relative membrane permeability (RMP) along with improvement in biochemical components (protein, ash, crude fiber, fat), and micronutrients in normal as well as in Ni contaminated soil. Moreover, the same treatment modulated the Ni-stress in plants through improvement in antioxidant enzymes (AEs) activities along with improved Ni concentration in the soil and different plant tissues. Correlation and principal component analysis (PCA) further revealed that combined application of metal-tolerant bacterium Caulobacter sp. MN13 and zeolite is the most influential strategy in alleviating Ni-induced stress and subsequent improvement in growth, yield, and physio-biochemical attributes of sesame plant. Full article
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21 pages, 3813 KiB  
Article
Livestock Wastewater Treatment in Constructed Wetlands for Agriculture Reuse
by Sofia Dias, Ana P. Mucha, Rute Duarte Crespo, Pedro Rodrigues and C. Marisa R. Almeida
Int. J. Environ. Res. Public Health 2020, 17(22), 8592; https://doi.org/10.3390/ijerph17228592 - 19 Nov 2020
Cited by 19 | Viewed by 3694
Abstract
The aim of this study focused on the evaluation of constructed wetlands (CWs) microcosms, on a laboratory scale, for the removal of metals from a pig industry effluent while maintaining effluent organic matter and nutrients levels for its later used as a fertilizer. [...] Read more.
The aim of this study focused on the evaluation of constructed wetlands (CWs) microcosms, on a laboratory scale, for the removal of metals from a pig industry effluent while maintaining effluent organic matter and nutrients levels for its later used as a fertilizer. CWs with different macrophytes (Phragmites australis and Typha latifolia) and different substrates (light expanded clay aggregate and lava rock) were tested. Results showed high removals of metals during CWs treatment, with removal rates reaching >80% for Cd, Cr, Cu, Fe, Mn, and Zn after 2 days of treatment in CWs planted with T. latifolia and >60% in CWs planted with P. australis. Significant differences were only found between substrates for Fe and Mn in CWs with P. australis. Removal of organic matter (through chemical oxygen demand (COD)) was >77%, with no significant differences between substrates or plants. Removals of ammonium and phosphate ions ranged between 59–84% and 32–92%, respectively, in CWs with P. australis and 62–75% and 7–68% in CWs with T. latifolia, with no significant differences between substrates. Overall, CWs showed potential to be efficient in removing toxic contaminants, as metals, while maintaining moderated levels of nutrients, allowing the use of reclaimed water in agriculture, namely as fertilizer. If one aims for a short CW treatment, CW planted with T. latifolia and expanded clay as substrate could be the more suitable choice. Full article
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20 pages, 4213 KiB  
Article
Physiological Response of Populus balsamifera and Salix eriocephala to Salinity and Hydraulic Fracturing Wastewater: Potential for Phytoremediation Applications
by Michael A. Bilek, Raju Y. Soolanayakanahally, Robert D. Guy and Shawn D. Mansfield
Int. J. Environ. Res. Public Health 2020, 17(20), 7641; https://doi.org/10.3390/ijerph17207641 - 20 Oct 2020
Cited by 5 | Viewed by 2259
Abstract
Natural and anthropogenic soil degradation is resulting in a substantial rise in the extension of saline and industrially-polluted soils. Phytoremediation offers an environmentally and economically advantageous solution to soil contamination. Three growth trials were conducted to assess the stress tolerance of native Canadian [...] Read more.
Natural and anthropogenic soil degradation is resulting in a substantial rise in the extension of saline and industrially-polluted soils. Phytoremediation offers an environmentally and economically advantageous solution to soil contamination. Three growth trials were conducted to assess the stress tolerance of native Canadian genotypes of Populus balsamifera L., Salix eriocephala Michx., and one hybrid willow (S. discolor × S. dasyclados) to salinity and hydraulic fracturing (fracking) wastewater. Thirty-three genotypes were grown in NaCl or fracking wastewater solutions between 0 and 7 mS−1 over a period of 3–4 months. P. balsamifera was observed to be relatively salt-intolerant compared to S. eriocephala and hybrid willow, which is likely caused by an inability of P. balsamifera to restrict Na+ translocation. Photosynthesis and transpiration decreased with salinity treatments, and severe reductions occurred with exposure to fracking solutions. Raffinose and stachyose content was tripled in leaf and root tissues. In willows, Na+ was primarily confined to root tissues, Cl accumulated up to 5% dry weight in leaves, and K+ was translocated from roots to leaves. Willow genotypes CAM-2 and STL-2 displayed the greatest maintenance of growth and resistance to necrotic symptoms in all trials, suggesting that these genotypes may be useful for practical application and further field study. Full article
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16 pages, 3738 KiB  
Article
Successful Outcome of Phytostabilization in Cr(VI) Contaminated Soils Amended with Alkalizing Additives
by Maja Radziemska, Agnieszka Bęś, Zygmunt M. Gusiatin, Łukasz Sikorski, Martin Brtnicky, Grzegorz Majewski, Ernesta Liniauskienė, Václav Pecina, Rahul Datta, Ayla Bilgin and Zbigniew Mazur
Int. J. Environ. Res. Public Health 2020, 17(17), 6073; https://doi.org/10.3390/ijerph17176073 - 20 Aug 2020
Cited by 6 | Viewed by 2271
Abstract
This study analysed the effect of three alkalizing soil amendments (limestone, dolomite chalcedonite) on aided phytostabilization with Festuca rubra L. depending on the hexavalent chromium (Cr(VI)) level in contaminated soil. Four different levels of Cr(VI) were added to the soil (0, 50, 100 [...] Read more.
This study analysed the effect of three alkalizing soil amendments (limestone, dolomite chalcedonite) on aided phytostabilization with Festuca rubra L. depending on the hexavalent chromium (Cr(VI)) level in contaminated soil. Four different levels of Cr(VI) were added to the soil (0, 50, 100 and 150 mg/kg). The Cr contents in the plant roots and above-ground parts and the soil (total and extracted Cr by 0.01 M CaCl2) were determined with flame atomic absorption spectrometry. The phytotoxicity of the soil was also determined. Soil amended with chalcedonite significantly increased F. rubra biomass. Chalcedonite and limestone favored a considerable accumulation of Cr in the roots. The application of dolomite and limestone to soil contaminated with Cr(VI) contributed to a significant increase in pH values and was found to be the most effective in reducing total Cr and CaCl2-extracted Cr contents from the soil. F. rubra in combination with a chalcedonite amendment appears to be a promising solution for phytostabilization of Cr(VI)-contaminated areas. The use of this model can contribute to reducing human exposure to Cr(VI) and its associated health risks. Full article
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22 pages, 7471 KiB  
Article
The Role of Mangroves in the Retention of Heavy Metal (Chromium): A Simulation Study in the Thi Vai River Catchment, Vietnam
by Anh Nguyen, Bao V.Q Le and Otto Richter
Int. J. Environ. Res. Public Health 2020, 17(16), 5823; https://doi.org/10.3390/ijerph17165823 - 12 Aug 2020
Cited by 20 | Viewed by 4597
Abstract
In this study, chromium (Cr) retention by the mangroves in the Thi Vai catchment located in the south of Vietnam was simulated using a coupled model of the hydrodynamic model Delft3D with Cr transport and a model for the uptake of Cr by [...] Read more.
In this study, chromium (Cr) retention by the mangroves in the Thi Vai catchment located in the south of Vietnam was simulated using a coupled model of the hydrodynamic model Delft3D with Cr transport and a model for the uptake of Cr by mangroves. This coupled model was calibrated and validated using data from four hydrodynamic stations and data from phytoremediation studies. To analyze the effect of mangroves on reducing Cr pollution, three scenarios were run by the model. Scenario 1 (SC1) is based on the actual situation concerning discharges and the distribution of mangroves. Scenario 2 (SC2) simulates the deterioration of the actual situation by deforestation on the west bank and the establishment of more industrial zones on the east bank. Scenario 3 (SC3) simulates an eco-friendly development comprising the channeling of wastewater through constructed wetlands with mangroves prior to the discharge into the river. Simulation results showed that the total Cr uptake by mangroves in SC3 was higher than in the other two scenarios. In total, 33 kg Cr in water were absorbed by the constructed wetlands in SC3 within one month. The simulation results helped in overcoming the difficulties and challenges in assessing the capacity of mangrove forests on the retention of chromium at catchment scale. Full article
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21 pages, 11920 KiB  
Article
Functional Trait-Based Screening of Zn-Pb Tolerant Wild Plant Species at an Abandoned Mine Site in Gard (France) for Rehabilitation of Mediterranean Metal-Contaminated Soils
by Isabelle Laffont-Schwob, Jacques Rabier, Véronique Masotti, Hélène Folzer, Lorène Tosini, Laurent Vassalo, Marie-Dominique Salducci and Pascale Prudent
Int. J. Environ. Res. Public Health 2020, 17(15), 5506; https://doi.org/10.3390/ijerph17155506 - 30 Jul 2020
Cited by 3 | Viewed by 2225
Abstract
The selection of plant species at mine sites is mostly based on metal content in plant parts. Recent works have proposed referring to certain ecological aspects. However, plant traits for plant metal-tolerance still need to be accurately assessed in the field. An abandoned [...] Read more.
The selection of plant species at mine sites is mostly based on metal content in plant parts. Recent works have proposed referring to certain ecological aspects. However, plant traits for plant metal-tolerance still need to be accurately assessed in the field. An abandoned Zn-Pb mine site in Gard (France) offered the opportunity to test a set of ecological criteria. The diversity of micro-habitats was first recorded through floristic relevés and selected categorical and measured plant traits were compared for plant species selection. The floristic composition of the study site consisted in 61 plant species from 31 plant families. This approach enabled us to focus on seven wild plant species naturally growing at the mining site. Their ability to form root symbioses was then observed with a view to phytostabilization management. Four species were considered for phytoextraction: Noccaea caerulescens (J. et C. Presl) FK Meyer, Biscutella laevigata L., Armeria arenaria (Pers.) Schult. and Plantago lanceolata L. The metal content of their aerial and root parts was then determined and compared with that of soil samples collected at the same site. This general approach may lead to the development of a knowledge base for assessment of the ecological restoration trajectory of the site and can help in plant selection for remediation of other metal-rich soils in the Mediterranean area based not only on metal removal but on ecological restoration principles. Full article
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18 pages, 9022 KiB  
Article
Relief Role of Lysine Chelated Zinc (Zn) on 6-Week-Old Maize Plants under Tannery Wastewater Irrigation Stress
by Rehan Ahmad, Wajid Ishaque, Mumtaz Khan, Umair Ashraf, Muhammad Atif Riaz, Said Ghulam, Awais Ahmad, Muhammad Rizwan, Shafaqat Ali, Saad Alkahtani and Mohamed M. Abdel-Daim
Int. J. Environ. Res. Public Health 2020, 17(14), 5161; https://doi.org/10.3390/ijerph17145161 - 17 Jul 2020
Cited by 16 | Viewed by 3292
Abstract
Tannery wastewater mainly comes from leather industries. It has high organic load, high salinity, and many other pollutants, including chromium (Cr). Tannery wastewater is generally used for crop irrigation in some areas of Pakistan and worldwide, due to the low availability of good [...] Read more.
Tannery wastewater mainly comes from leather industries. It has high organic load, high salinity, and many other pollutants, including chromium (Cr). Tannery wastewater is generally used for crop irrigation in some areas of Pakistan and worldwide, due to the low availability of good quality of irrigation water. As tannery wastewater has many nutrients in it, its lower concentration benefits the plant growth, but at a higher concentration, it damages the plants. Chromium in tannery wastewater accumulates in plants, and causes stress at physiological and biochemical levels. In recent times, the role of micronutrient-amino acid chelated compounds has been found to be helpful in reducing abiotic stress in plants. In our present study, we used lysine chelated zinc (Zn-lys) as foliar application on maize (Zea mays L.), growing in different concentrations of tannery wastewater. Zinc (Zn) is required by plants for growth, and lysine is an essential amino acid. Maize plants were grown in tannery wastewater in four concentrations (0, 25%, 50%, and 100%) and Zn-lys was applied as a foliar spray in three concentrations (0 mM, 12.5 mM, and 25 mM) during plant growth. Plants were cautiously harvested right after 6 weeks of treatment. Foliar spray of Zn-lys on maize increased the biomass and improved the plant growth. Photosynthetic pigments such as total chlorophyll, chlorophyll a, chlorophyll b and contents of carotenoids also increased with Zn-lys application. In contrast to control plants, the hydrogen peroxide (H2O2) contents were increased up to 12%, 50%, and 68% in leaves, as well as 16%, 51% and 89% in roots at 25%, 50%, and 100% tannery water application, respectively, without Zn-lys treatments. Zn-lys significantly reduced the damages caused by oxidative stress in maize plant by decreasing the overproduction of H2O2 and malondialdehyde (MDA) in maize that were produced, due to the application of high amount of tannery wastewater alone. The total free amino acids and soluble protein decreased by 10%, 31% and 64% and 18%, 61% and 122% at 25%, 50% and 100% tannery water treatment. Zn-lys application increased the amino acids production and antioxidant activities in maize plants. Zn contents increased, and Cr contents decreased, in different parts of plants with Zn-lys application. Overall, a high concentration of tannery wastewater adversely affected the plant growth, but the supplementation of Zn-lys assertively affected the plant growth and enhanced the nutritional quality, by enhancing Zn and decreasing Cr levels in plants simultaneously irrigated with tannery wastewater. Full article
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19 pages, 7309 KiB  
Article
Can Green Walls Reduce Outdoor Ambient Particulate Matter, Noise Pollution and Temperature?
by Naomi Paull, Daniel Krix, Fraser Torpy and Peter Irga
Int. J. Environ. Res. Public Health 2020, 17(14), 5084; https://doi.org/10.3390/ijerph17145084 - 14 Jul 2020
Cited by 30 | Viewed by 5110
Abstract
Green walls have previously demonstrated the capacity to reduce particulate matter (PM), noise pollution, and temperature conditions in manipulative experiments and computational models. There is, however, minimal evidence that green walls can influence ambient environmental conditions, especially taking into account the variable environmental [...] Read more.
Green walls have previously demonstrated the capacity to reduce particulate matter (PM), noise pollution, and temperature conditions in manipulative experiments and computational models. There is, however, minimal evidence that green walls can influence ambient environmental conditions, especially taking into account the variable environmental conditions encountered in situ. The aim of this paper was to determine if green walls have a quantitative effect on ambient air quality in an urban environment. Ambient PM, noise, and temperature were recorded at 12 green wall and adjacent reference wall locations across a dense urban centre, over a 6-month period. The results indicated that PM levels and temperature did not significantly differ between the green wall and reference wall sites. Ambient noise at the green wall sites, however, was significantly lower than at the reference wall locations. It is suggested that mechanically assisted, or ‘active’ green wall systems may have a higher PM and temperature reduction capacity, and if so, they will be more valuable for installation in situ compared to standard passive systems, although this will require further research. Full article
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20 pages, 2658 KiB  
Article
Temporal Evolution of PAHs Bioaccessibility in an Aged-Contaminated Soil during the Growth of Two Fabaceae
by Marie Davin, Elisa Renard, Kévin Lefébure, Marie-Laure Fauconnier and Gilles Colinet
Int. J. Environ. Res. Public Health 2020, 17(11), 4016; https://doi.org/10.3390/ijerph17114016 - 05 Jun 2020
Cited by 7 | Viewed by 2044
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are health-concerning organic compounds that accumulate in the environment. Bioremediation and phytoremediation are studied to develop eco-friendly remediation techniques. In this study, the effects of two plants (Medicago sativa L. and Trifolium pratense L.) on the PAHs’ bioaccessibility [...] Read more.
Polycyclic aromatic hydrocarbons (PAHs) are health-concerning organic compounds that accumulate in the environment. Bioremediation and phytoremediation are studied to develop eco-friendly remediation techniques. In this study, the effects of two plants (Medicago sativa L. and Trifolium pratense L.) on the PAHs’ bioaccessibility in an aged-contaminated soil throughout a long-term rhizoremediation trial was investigated. A bioaccessibility measurement protocol, using Tenax® beads, was adapted to the studied soil. The aged-contaminated soil was cultured with each plant type and compared to unplanted soil. The bioaccessible and residual PAH contents were quantified after 3, 6 and 12 months. The PAHs’ desorption kinetics were established for 15 PAHs and described by a site distribution model. A common Tenax® extraction time (24 h) was established as a comparison basis for PAHs bioaccessibility. The rhizoremediation results show that M. sativa developed better than T. pratense on the contaminated soil. When plants were absent (control) or small (T. pratense), the global PAHs’ residual contents dissipated from the rhizosphere to 8% and 10% of the total initial content, respectively. However, in the presence of M. sativa, dissipation after 12 months was only 50% of the total initial content. Finally, the PAHs’ bioaccessible content increased more significantly in the absence of plants. This one-year trial brought no evidence that the presence of M. sativa or T. pratense on this tested aged-contaminated soil was beneficial in the PAH remediation process, compared to unplanted soil. Full article
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14 pages, 2214 KiB  
Article
N-Fertilizer (Urea) Enhances the Phytoextraction of Cadmium through Solanum nigrum L.
by Arosha Maqbool, Shafaqat Ali, Muhammad Rizwan, Muhammad Saleem Arif, Tahira Yasmeen, Muhammad Riaz, Afzal Hussain, Shamaila Noreen, Mohamed M. Abdel-Daim and Saad Alkahtani
Int. J. Environ. Res. Public Health 2020, 17(11), 3850; https://doi.org/10.3390/ijerph17113850 - 29 May 2020
Cited by 15 | Viewed by 3342
Abstract
Heavy metal contamination is currently a major environmental concern, as most agricultural land is being polluted from municipal discharge. Among various other pollutants, cadmium (Cd), one of the most harmful heavy metals, enters into the food chain through the irrigation of crops with [...] Read more.
Heavy metal contamination is currently a major environmental concern, as most agricultural land is being polluted from municipal discharge. Among various other pollutants, cadmium (Cd), one of the most harmful heavy metals, enters into the food chain through the irrigation of crops with an industrial effluent. In the present study, a pot experiment was designed to assess the effect of different nitrogen (N)-fertilizer forms in the phytoremediation of Cd through Solanum nigrum L. Two types of N fertilizers (NH4NO3 and urea) were applied to the soil in different ratios (0:0, 100:0, 0:100, and 50:50 of NH4NO3 and urea, individually) along with different Cd levels (0, 25, and 50 mg kg−1). The plants were harvested 70 days after sowing the seeds in pots. Cadmium contamination significantly inhibited the growth of leaves and roots of S. nigrum plants. Cadmium contamination also induced oxidative stress; however, the application of N-fertilizers increased the plant biomass by inhibiting oxidative stress and enhancing antioxidants’ enzymatic activities. The greatest plant growth was observed in the urea-treated plants compared with the NH4NO3-treated plants. In addition, urea-fed plants also accumulated higher Cd concentrations than NH4NO3-fed plants. It is concluded that urea is helpful for better growth of S. nigrum under Cd stress. Thus, an optimum concentration of N-fertilizers might be effective in the phytoremediation of heavy metals through S. nigrum. Full article
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15 pages, 2734 KiB  
Article
Cataloging of Cd Allocation in Late Rice Cultivars Grown in Polluted Gleysol: Implications for Selection of Cultivars with Minimal Risk to Human Health
by Qiang Lin, Wenbin Tong, Bilal Hussain, Yasir Hamid, Min Lu, Zhenli He and Xiaoe Yang
Int. J. Environ. Res. Public Health 2020, 17(10), 3632; https://doi.org/10.3390/ijerph17103632 - 21 May 2020
Cited by 7 | Viewed by 2359
Abstract
Cadmium (Cd) is a toxic trace metal that has polluted 20% of agricultural land in China where its concentration exceeds the standards for Chinese farmland. Plants are capable of accumulating Cd and other trace metals, but this capacity varies with species and cultivars [...] Read more.
Cadmium (Cd) is a toxic trace metal that has polluted 20% of agricultural land in China where its concentration exceeds the standards for Chinese farmland. Plants are capable of accumulating Cd and other trace metals, but this capacity varies with species and cultivars within a species. Rice is a staple food consumed by half of the global population. In order to select safe late rice cultivars that are suitable late rice cultivars that can be cultivated in for growing in slightly contaminated soil, a two-year field experiment was conducted with 27 in the first year and 9 late rice cultivars in the second year. The results showed that plant Cd concentrations varied among the cultivars, with high magnitudes of variation occurred in straw and grains. Five genotypes including LR-12, LR-17, LR-24, LR-25 and LR-26 were identified as low accumulators for the first year while LR-15 and LR-17 were identified as promising cultivars based on Cd concentration in the polished rice grains (<0.02 mg kg−1 DW). In addition, these cultivars had favorable traits, including mineral nutrition and grain yield. Therefore, these genotypes should be considered for cultivation in slightly or moderately Cd contaminated soils. Full article
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16 pages, 2300 KiB  
Article
Screening of Heavy Metal-Immobilizing Bacteria and Its Effect on Reducing Cd2+ and Pb2+ Concentrations in Water Spinach (Ipomoea aquatic Forsk.)
by Tiejun Wang, Xiaoyu Wang, Wei Tian, Lunguang Yao, Yadong Li, Zhaojin Chen and Hui Han
Int. J. Environ. Res. Public Health 2020, 17(9), 3122; https://doi.org/10.3390/ijerph17093122 - 30 Apr 2020
Cited by 6 | Viewed by 3070
Abstract
Microbial immobilization is considered as a novel and environmentally friendly technology that uses microbes to reduce heavy metals accumulation in plants. To explore microbial resources which are useful in these applications, three water spinach rhizosphere soils polluted by different levels of heavy metals [...] Read more.
Microbial immobilization is considered as a novel and environmentally friendly technology that uses microbes to reduce heavy metals accumulation in plants. To explore microbial resources which are useful in these applications, three water spinach rhizosphere soils polluted by different levels of heavy metals (heavy pollution (CQ), medium pollution (JZ), and relative clean (NF)) were collected. The community composition of heavy metal-immobilizing bacteria in rhizosphere soils and its effects on reducing the Cd2+ and Pb2+ concentrations in water spinach were evaluated. Four hundred strains were isolated from the CQ (belonging to 3 phyla and 14 genera), JZ (belonging to 4 phyla and 25 genera) and NF (belonged to 6 phyla and 34 genera) samples, respectively. In the CQ sample, 137 strains showed a strong ability to immobilize Cd2+ and Pb2+, giving Cd2+ and Pb2+ removal rates of greater than 80% in solution; Brevundimonas, Serratia, and Pseudoarthrobacter were the main genera. In total, 62 strains showed a strong ability to immobilize Cd2+ and Pb2+ in the JZ sample and Bacillus and Serratia were the main genera. A total of 22 strains showed a strong ability to immobilize Cd2+ and Pb2+ in the NF sample, and Bacillus was the main genus. Compared to the control, Enterobacter bugandensis CQ-7, Bacillus thuringensis CQ-33, and Klebsiella michiganensis CQ-169 significantly increased the dry weight (17.16–148%) of water spinach and reduced the contents of Cd2+ (59.78–72.41%) and Pb2+ (43.36–74.21%) in water spinach. Moreover, the soluble protein and Vc contents in the shoots of water spinach were also significantly increased (72.1–193%) in the presence of strains CQ-7, CQ-33 and CQ-169 compared to the control. In addition, the contents of Cd and Pb in the shoots of water spinach meet the standard for limit of Cd2+ and Pb2+ in vegetables in the presence of strains CQ-7, CQ-33 and CQ-169. Thus, the results provide strains as resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables. Full article
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Review

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37 pages, 2975 KiB  
Review
Phytoremediation and Microorganisms-Assisted Phytoremediation of Mercury-Contaminated Soils: Challenges and Perspectives
by Emanuela D. Tiodar, Cristina L. Văcar and Dorina Podar
Int. J. Environ. Res. Public Health 2021, 18(5), 2435; https://doi.org/10.3390/ijerph18052435 - 02 Mar 2021
Cited by 49 | Viewed by 9278
Abstract
Mercury (Hg) pollution is a global threat to human and environmental health because of its toxicity, mobility and long-term persistence. Although costly engineering-based technologies can be used to treat heavily Hg-contaminated areas, they are not suitable for decontaminating agricultural or extensively-polluted soils. Emerging [...] Read more.
Mercury (Hg) pollution is a global threat to human and environmental health because of its toxicity, mobility and long-term persistence. Although costly engineering-based technologies can be used to treat heavily Hg-contaminated areas, they are not suitable for decontaminating agricultural or extensively-polluted soils. Emerging phyto- and bioremediation strategies for decontaminating Hg-polluted soils generally involve low investment, simple operation, and in situ application, and they are less destructive for the ecosystem. Current understanding of the uptake, translocation and sequestration of Hg in plants is reviewed to highlight new avenues for exploration in phytoremediation research, and different phytoremediation strategies (phytostabilization, phytoextraction and phytovolatilization) are discussed. Research aimed at identifying suitable plant species and associated-microorganisms for use in phytoremediation of Hg-contaminated soils is also surveyed. Investigation into the potential use of transgenic plants in Hg-phytoremediation is described. Recent research on exploiting the beneficial interactions between plants and microorganisms (bacteria and fungi) that are Hg-resistant and secrete plant growth promoting compounds is reviewed. We highlight areas where more research is required into the effective use of phytoremediation on Hg-contaminated sites, and conclude that the approaches it offers provide considerable potential for the future. Full article
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16 pages, 853 KiB  
Review
Heavy-Metal Phytoremediation from Livestock Wastewater and Exploitation of Exhausted Biomass
by Monika Hejna, Elisabetta Onelli, Alessandra Moscatelli, Maurizio Bellotto, Cinzia Cristiani, Nadia Stroppa and Luciana Rossi
Int. J. Environ. Res. Public Health 2021, 18(5), 2239; https://doi.org/10.3390/ijerph18052239 - 24 Feb 2021
Cited by 31 | Viewed by 4220
Abstract
Sustainable agriculture is aimed at long-term crop and livestock production with a minimal impact on the environment. However, agricultural practices from animal production can contribute to global pollution due to heavy metals from the feed additives that are used to ensure the nutritional [...] Read more.
Sustainable agriculture is aimed at long-term crop and livestock production with a minimal impact on the environment. However, agricultural practices from animal production can contribute to global pollution due to heavy metals from the feed additives that are used to ensure the nutritional requirements and also promote animal health and optimize production. The bioavailability of essential mineral sources is limited; thus, the metals are widely found in the manure. Via the manure, metallic ions can contaminate livestock wastewater, drastically reducing its potential recycling for irrigation. Phytoremediation, which is an efficient and cost-effective cleanup technique, could be implemented to reduce the wastewater pollution from livestock production, in order to maintain the water conservation. Plants use various strategies for the absorption and translocation of heavy metals, and they have been widely used to remediate livestock wastewater. In addition, the pollutants concentrated in the plants can be exhausted and used as heat to enhance plant growth and further concentrate the metals, making recycling a possible option. The biomass of the plants can also be used for biogas production in anaerobic fermentation. Combining phytoremediation and biorefinery processes would add value to both approaches and facilitate metal recovery. This review focuses on the concept of agro-ecology, specifically the excessive use of heavy metals in animal production, the various techniques and adaptations of the heavy-metal phytoremediation from livestock wastewater, and further applications of exhausted phytoremediated biomass. Full article
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