Techno-economic analysis of phytoremediation: A strategic rethinking

Lead toxicity in plants: mechanistic insights into toxicity, physiological responses of plants and mitigation strategies

Soil toxicity is a major environmental issue that leads to numerous harmful effects on plants and human beings. Every year a huge amount of Pb is dumped into the environment either from natural sources or anthropogenically. Being a heavy metal it is highly toxic and non-biodegradable but remains in the environment for a long time. It is considered a neurotoxic and exerts harmful effects on living beings. In the present review article, investigators have emphasized the side effects of Pb on the plants. Further, the authors have focused on the various sources of Pb in the environment. Investigators have emphasized the various responses including molecular, biochemical, and morphological of plants to the toxic levels of Pb. Further emphasis was given to the effect of elevated levels of Pb on the microbial population in the rhizospheres. Further, emphasized the various remediation strategies for the Pb removal from the soil and water sources.

Ecological risk of per-and polyfluorinated alkyl substances in the phytoremediation process: a case study for ecologically keystone species across two generations

The potential ecological risk of per- and polyfluorinated alkyl substances (PFASs) in phytoremediation has raised social concerns, promoting a need to better understand their distribution and risks in the recovery process of aquatic plants. Herein, we aim to fill this knowledge gap by investigating the distribution and ecotoxicological effects of PFASs on the structure and function of water-macrophyte-sediment microcosm systems. Among the entire system, 63.0 %-73.1 % PFOA was found in sediments and submerged plants, however, 52.5 %-53.0 % of PFPeA and 47.0 %-47.5 % of PFBS remained in the water under different treatments. PFOA was more bioavailable than the other substances, as demonstrated by the bioaccumulation factors (BAF) with ranges exposed to PFPeA and PFBS. Bioaccumulation PFASs induced plant oxidative stress which generates enzymes to suppress superoxide, and disturbed the processes of lysine biosynthesis, in which allysine, meso-2,6-diaminoheptanedioate, and Nsuccinyl-2-amino-6-ketopimelate were downregulated. PFASs were detected in the propagator (turions) of an ecological restoration species, where short-chain PFASs (70.1 % and 45.7 % for 2 or 20 μg/L PFAS exposure, respectively) were found to spread further into new individuals and profoundly influence ecological processes shaping populations. PFASs significantly enhanced the number of microbial species in the sediment, but the degree of differentiation in the microbial community structure was not significantly different. This study enhances our understanding of the ecological mechanisms of PFASs in the water-macrophyte-sediment systems and potential threats to the recovery process of macrophytes.

Improving peanut growth and cadmium phytoextraction capacity by inoculating Bacillus megaterium and Trichoderma harzianum

Arachis hypogaea L. (peanut) is an economic crop with abundant biomass and remarkable capacity for cadmium (Cd) uptake. In a two-year field experiment, the translocation and accumulation mechanisms of Cd in peanuts were investigated following inoculation of Bacillus megaterium (BM) and Trichoderma harzianum (TH). The results demonstrated that inoculating BM and TH enhanced both biomass and Cd concentration in peanut roots and shoots compared with those of the CK treatment. There was no statistically significant difference observed in kernel biomass between peanut plants inoculated with TH and the CK treatment. The inoculation of BM and TH increased the Cd concentration in the soluble fraction of peanut roots by 24.36% and 102.78%, thus promoting Cd translocation from roots to shoots. Additionally, inoculating BM and TH resulted in a 31.75% and 52.88% elevation in Cd concentration within the leaf cell walls, thereby facilitating the accumulation of Cd within the shoots. Simultaneously, inoculating BM and TH enhanced the concentration of highly bioavailable Cd forms in peanuts. The accumulation of Cd in shoots is the primary factor determining the phytoextraction capacity in peanut, and inoculation of TH resulted in a 16.35-54.54% increase in shoot biomass and an enhancement of 99.10-99.95% in shoot Cd concentration. Therefore, inoculating TH can enhance the phytoextraction capacity for Cd in peanuts, particularly the production of economically valuable components (kernels), without compromising production.

Co-treatment of agri-food waste streams using black soldier fly larvae (Hermetia illucens L.): A sustainable solution for rural waste management

The management of rural waste, particularly agri-food waste, poses a major challenge to the ecosystem health. This study investigated the efficacy of black soldier fly larvae (Hermetia illucens L., BSFL) bioconversion for agri-food waste under independent treatment or co-treatment strategies using chicken manure and food waste as a model system. The results showed a synergistic effect of co-treating agri-food waste from different sources. The co-treatment strategy enhanced bioconversion efficiency, resulting in a 1.31-fold waste reduction rate and a 1.93-fold bioconversion rate. Additionally, larval growth performance and biomass quality of BSFL were improved, while lauric acid and oleic acid were enriched in the larval fat from the co-treatment strategy. 16S rRNA amplicon sequencing revealed that the co-treatment strategy reshaped both the residue and larval gut microbiota, with distinct enrichment of taxonomical biomarkers. Furthermore, under this strategy, metabolic functions of the residue microbiota were significantly activated, especially carbohydrate, amino acid, and lipid metabolism were enhanced by 16.3%, 23.5%, and 20.2%, respectively. The early colonization of lactic acid bacteria (Weisella and Aerococcus) in the residue, coupled with a symbiotic relationship between Enterococcus in the larval gut and the host, likely promoted organic matter degradation and larval growth performance. Scaling up the findings to a national level in China suggests that the co-treatment strategy can increase waste reduction quantity by 86,329 tonnes annually and produce more larval protein and fat with a market value of approximately US$237 million. Therefore, co-treatment of agri-food waste streams using BSFL presents a sustainable solution for rural waste management that potentially contributes to the achievement of SDG2 (Zero Hunger), SDG3 (Good Health and Well-Being), and SDG12 (Responsible Consumption and Production).

The power of green: Harnessing phytoremediation to combat micro/nanoplastics

Plastic pollution and its potential risks have been raising public concerns as a global environmental issue. Global plastic waste may double by 2030, posing a significant challenge to the remediation of environmental plastics. In addition to finding alternative products and managing plastic emission sources, effective removal technologies are crucial to mitigate the negative impact of plastic pollution. However, current remediation strategies, including physical, chemical, and biological measures, are unable to compete with the surging amounts of plastics entering the environment. This perspective lays out recent advances to propel both research and action. In this process, phytoaccumulation, phytostabilization, and phytofiltration can be applied to reduce the concentration of nanoplastics and submicron plastics in terrestrial, aquatic, and atmospheric environments, as well as to prevent the transport of microplastics from sources to sinks. Meanwhile, advocating for a more promising future still requires significant efforts in screening hyperaccumulators, coupling multiple measures, and recycling stabilized plastics from plants. Phytoremediation can be an excellent strategy to alleviate global micro/nanoplastic pollution because of the cost-effectiveness and environmental sustainability of green technologies.

Soil application of graphitic carbon nitride nanosheets alleviate cadmium toxicity by altering subcellular distribution, chemical forms of cadmium and improving nitrogen availability in soybean (Glycine max L.)

Cadmium (Cd)-contamination impairs biological nitrogen fixation in legumes (BNF), threatening global food security. Innovative strategies to enhance BNF and improve plant resistance to Cd are therefore crucial. This study investigates the effects of graphitic carbon nitride nanosheets (g-C3N4 NSs) on soybean (Glycine max L.) in Cd contaminated soil, focusing on Cd distribution, chemical forms and nitrogen (N) fixation. Soybean plants were treated with 100 mg kg-1 g-C3N4 NSs, with or without 10 mg kg-1 Cd for 4 weeks. Soil addition of g-C3N4 NSs alleviated Cd toxicity and promote soybean growth via scavenging Cd-mediated oxidative stress and improving photosynthesis. Compared to Cd treatment, g-C3N4 NSs increased shoot and root dry weights under Cd toxicity by 49.5% and 63.4%, respectively. g-C3N4 NSs lowered Cd content by 35.7%-54.1%, redistributed Cd subcellularly by increasing its proportion in the cell wall and decreasing it in soluble fractions and organelles, and converted Cd from high-toxicity to low-toxicity forms. Additionally, g-C3N4 NSs improved the soil N cycle, stimulated nodulation, and increased the N-fixing capacity of nodules, thus increasing N content in shoots and roots by 12.4% and 43.2%, respectively. Mechanistic analysis revealed that g-C3N4 NSs mitigated Cd-induced loss of endogenous nitric oxide in nodules, restoring nodule development. This study highlights the potential of g-C3N4 NSs for remediating Cd-contaminated soil, reducing Cd accumulation, and enhancing plant growth and N fixation, offering new insights into the use of carbon nanomaterials for soil improvement and legume productivity under metal(loid)s stress.

Biotechnological approaches for enhancement of heavy metal phytoremediation capacity of plants

Heavy metals are extremely hazardous for human health due to their toxic effects. They are non-biodegradable in nature, thus remain in the environment and enter and accumulate in the human body through biomagnification; hence, there is a serious need of their remediation. Phytoremediation has emerged as a green, sustainable, and effective solution for heavy metal removal and many plant species could be employed for this purpose. Plants are able to sequester substantial quantity of heavy metals, in some cases thousands of ppm, due to their robust physiology enabling high metal tolerance and anatomy supporting metal ion accumulation. Identification and modification of potential target genes involved in heavy metal accumulation have led to improved phytoremediation capacity of plants at the molecular level. The introduction of foreign genes through genetic engineering approaches has further enhanced phytoremediation capacity manifolds. This review gives an insight towards improving the phytoremediation efficiency through a better understanding of molecular mechanisms involved, expression of different proteins, genetic engineering approaches for transgenic production, and genetic modifications. It also comprehends novel omics tools such as genomics, metabolomics, proteomics, transcriptomics, and genome editing technologies for improvement of phytoremediation ability of plants.

Halophilic archaea as tools for bioremediation technologies

Haloarchaea are extremophilic microorganisms belonging to the Archaea domain that require high salt concentrations to be alive, thus inhabiting ecosystems like salty ponds, salty marshes, or extremely salty lagoons. They are more abundantly and widely distributed worldwide than initially expected. Most of them are grouped into two families: Halobacteriaceae and Haloferacaceae. The extreme conditions under which haloarchaea survive contribute to their metabolic and molecular adaptations, thus making them good candidates for the design of bioremediation strategies to treat brines, salty water, and saline soils contaminated with toxic compounds such as nitrate, nitrite, oxychlorates such as perchlorate and chlorate, heavy metals, hydrocarbons, and aromatic compounds. New advances in understanding haloarchaea physiology, metabolism, biochemistry, and molecular biology suggest that biochemical pathways related to nitrogen and carbon, metals, hydrocarbons, or aromatic compounds can be used for bioremediation proposals. This review analyses the novelty of the most recent results showing the capability of some haloarchaeal species to assimilate, modify, or degrade toxic compounds for most living beings. Several examples of the role of these microorganisms in the treatment of polluted brine or salty soils are also discussed in connection with circular economy-based processes. KEY POINTS: • Haloarchaea are extremophilic microorganisms showing genuine metabolism • Haloarchaea can metabolise compounds that are highly toxic to most living beings • These metabolic capabilities are useful for designing soil and water bioremediation strategies.

Advances in amelioration of air pollution using plants and associated microbes: An outlook on phytoremediation and other plant-based technologies

Globally, air pollution is an unfortunate aftermath of rapid industrialization and urbanization. Although the best strategy is to prevent air pollution, it is not always feasible. This makes it imperative to devise and implement techniques that can clean the air continuously. Plants and microbes have a natural potential to transform or degrade pollutants. Hence, strategies that use this potential of living biomass to remediate air pollution seem to be promising. The simplest future trend can be planting suitable plant-microbe species capable of removing air pollutants like SO2, CO2, CO, NOX and particulate matter (PM) along roadsides and inside the buildings. Established wastewater treatment strategies such as microbial fuel cells (MFC) and constructed wetlands (CW) can be suitably modified to ameliorate air pollution. Green architecture involving green walls and green roofs is facile and aesthetic, providing urban ecosystem services. Certain microbe-based bioreactors such as bioscrubbers and biofilters may be useful in small confined spaces. Several generative models have been developed to assist with planning and managing green spaces in urban locales. The physiological limitations of using living organisms can be circumvent by applying biotechnology and transgenics to improve their potential. This review provides a comprehensive update on not just the plants and associated microbes for the mitigation of air pollution, but also lists the technologies that are available and/or can be modified and used for air pollution control. The article also gives a detailed analysis of this topic in the form of strengths-weaknesses-opportunities-challenges (SWOC). The strategies mentioned in this review would help to attain corporate Environmental Social and Governance (ESG) and Sustainable Development Goals (SDGs), while reducing carbon footprint in the urban scenario. The review aims to emphasise that urbanization is possible while tackling air pollution using facile, green techniques involving plants and associated microbes.

Reducing Heavy Metal Contamination in Soil and Water Using Phytoremediation

The increase in industrialization has led to an exponential increase in heavy metal (HM) soil contamination, which poses a serious threat to public health and ecosystem stability. This review emphasizes the urgent need to develop innovative technologies for the environmental remediation of intensive anthropogenic pollution. Phytoremediation is a sustainable and cost-effective approach for the detoxification of contaminated soils using various plant species. This review discusses in detail the basic principles of phytoremediation and emphasizes its ecological advantages over other methods for cleaning contaminated areas and its technical viability. Much attention has been given to the selection of hyperaccumulator plants for phytoremediation that can grow on heavy metal-contaminated soils, and the biochemical mechanisms that allow these plants to isolate, detoxify, and accumulate heavy metals are discussed in detail. The novelty of our study lies in reviewing the mechanisms of plant-microorganism interactions that greatly enhance the efficiency of phytoremediation as well as in discussing genetic modifications that could revolutionize the cleanup of contaminated soils. Moreover, this manuscript discusses potential applications of phytoremediation beyond soil detoxification, including its role in bioenergy production and biodiversity restoration in degraded habitats. This review concludes by listing the serious problems that result from anthropogenic environmental pollution that future generations still need to overcome and suggests promising research directions in which the integration of nano- and biotechnology will play an important role in enhancing the effectiveness of phytoremediation. These contributions are critical for environmental scientists, policy makers, and practitioners seeking to utilize phytoremediation to maintain the ecological stability of the environment and its restoration.

Trends in phytoremediation of heavy metals-contaminated soils: A Web of science and CiteSpace bibliometric analysis

Heavy metals pollution in soils is an urgent environmental issue worldwide. Phytoremediation is a green and eco-friendly way of remediating heavy metals. However, a systematic overview of this field is limited, and little is known about future development trends. Therefore, we used CiteSpace software to conduct bibliometric and visual analyses of published literature in the field of phytoremediation of heavy metals in soils from the Web of Science core collection and identified research hotspots and development trends in this field. Researchers are paying increased attention to phytoremediation of heavy metals in soils, especially environmental researchers. A total of 121 countries or regions, 3790 institutions, 4091 funded organisations and 15,482 authors have participated in research in this area. China, India, and Pakistan are the largest contributors. There has been extensive cooperation between countries, institutions, and authors worldwide, but there is a lack of cooperation among top authors. 'Calcareous soil', 'Co-contaminated soil' and 'Metal availability' are the most intensively investigated topics. 'EDTA', 'Plant growth-promoting Rhizobacteria', 'Photosynthesis', 'Biochar' and 'Phytoextraction' are research hotspots in this field. In addition, more and more researchers are beginning to pay attention to research on co-contaminated soil, metal availability, chelating agents, and microbial-assisted phytoremediation. In summary, bibliometric, and visual analyses in the field of phytoremediation of heavy metals in soils identifies probable directions for future research and provides a resource through which to better understand this rapidly advancing subject.