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1.
Promises and potential of in situ nano-phytoremediation strategy to mycorrhizo-remediate heavy metal contaminated soils using non-food bioenergy crops (Vetiver zizinoides & Cannabis sativa).
Khan, AG
International journal of phytoremediation. 2020;(9):900-915
Abstract
Heavy metals (HMs) in soil, air, and water environments effect human health. These HMs cannot be degraded in soil and they can only be transformed from one state to another. Food and energy resources such as coal, oil, petrol, etc. are gradually diminishing due to ever increasing demand and consumption, world faces crisis. There is an urgent need to address these problems by reclaiming the waste/polluted land for food and energy production. Various physicochemical remediation strategies are being proposed, developed, and tested but they are all very costly and only applicable to small contaminated sites. During the past two decades or so, plant-based phytoremediation technology is rapidly evolving as a promising new tool to address the issue with the potential to remediate HM contaminated soils in a sustainable manner. Plants, labeled as phyto-tolerant or phyto-accumulators, surviving on such contaminated soils reduce the toxicity by preventing their translocation or destroying the contaminants by sequestration by synthesizing thiol-containing HM-binding proteins (nano-molecules) and peptides (phytochelators or PCs) which modulate internal levels of metal concentration between deficient and toxic levels. But such plants are very slow growing, producing small biomass, and the process taking a long time to effectively remediate such soils. To overcome limitations of using such plants, plants capable of high biomass production and tolerating multiple HMs, such as non-food bioenergy crops (Vetiver and Hamp), are required. This plant-based remediation strategy can further be enhanced with the use of both plants and rhizosphere microbes like arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria. The combination of three components, i.e. high biomass producing plant, soil, and its rhizosphere harboring plant growth-promoting rhizobial (PGPR) microbiota, particularly AMF, will further improve the process of nano-phytoremediation of HM contaminated soils. This mini review focuses on how phytoremediation, nanotechnology, AMF and PGPR technologies can be merged together to form an integrated nano-mycorrhizo-phytoremediation (NMPR) strategy which synergistically achieve the goal of remediation of soil contaminants and improve the phytoremediation performance of bioenergy plants grown on HM polluted soils. This review also identifies the urgent need to conduct field-scale application of this strategy and use it as potential tool for reestablishing plant cover and population diversity during restoration of derelict land post-industrial/mining activities.
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2.
Microbes involved in arsenic mobilization and respiration: a review on isolation, identification, isolates and implications.
Mazumder, P, Sharma, SK, Taki, K, Kalamdhad, AS, Kumar, M
Environmental geochemistry and health. 2020;(10):3443-3469
Abstract
Microorganisms play an important role in arsenic (As) cycling in the environment. Microbes mobilize As directly or indirectly, and natural/geochemical processes such as sulphate and iron reduction, oxidative sulphide mineral dissolution, arsenite (AsO33-) oxidation and arsenate (AsO43-) respiration further aid in As cycle in the environment. Arsenate serves as an electron donor for the microbes during anaerobic conditions in the sediment. The present work reviews the recent development in As contamination, various As-metabolizing microbes and their phylogenetic diversity, to understand the role of microbial communities in As respiration and mobilization. It also summarizes the contemporary understanding of the intricate biochemistry and molecular biology of natural As metabolisms. Some successful examples of engineered microbes by harnessing these natural mechanisms for effective remediation are also discussed. The study indicates that there is an exigent need to have a clear understanding of environmental aspects of As mobilization and subsequent oxidation-reduction by a suitable microbial consortium.
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3.
Antibiotic-contaminated wastewater irrigated vegetables pose resistance selection risks to the gut microbiome.
Gudda, FO, Waigi, MG, Odinga, ES, Yang, B, Carter, L, Gao, Y
Environmental pollution (Barking, Essex : 1987). 2020;:114752
Abstract
Wastewater reuse in food crop irrigation has led to agroecosystem pollution concerns and human health risks. However, there is limited attention on the relationship of sub-lethal antibiotic levels in vegetables and resistance selection. Most risk assessment studies show non-significant toxicity, but overlook the link between antibiotics in crops and propagation of gut microbiome resistance selection. The review highlights the risk of antibiotics in treated water used for irrigation, uptake, and accumulation in edible vegetable parts. Moreover, it elucidates the risks to the adaptive resistance selection of the gut microbiome from sub-lethal antibiotic levels, as a result of dietary contaminated vegetables. Experiments have reported that bacterial resistance selection is possible at concentrations that are several hundred-folds lower than lethal effect levels on susceptible cells. Consequently, mutants selected at low antibiotic levels, such as those from vegetables, are fitter and more resistant compared to those selected at high concentrations. Necessary standardization, such as the development of minimum acceptable antibiotic limits allowable in food crop irrigation water, with a focus on minimum selection concentration, and not only toxicity, has been proposed. Wastewater irrigation offers environmental benefits and can contribute to food security, but it has non-addressed risks. Research gaps, future perspectives, and frameworks of mitigating the potential risks are discussed.
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4.
The mechanisms of biochar interactions with microorganisms in soil.
Gorovtsov, AV, Minkina, TM, Mandzhieva, SS, Perelomov, LV, Soja, G, Zamulina, IV, Rajput, VD, Sushkova, SN, Mohan, D, Yao, J
Environmental geochemistry and health. 2020;(8):2495-2518
Abstract
Biochar, a carbonaceous material, is increasingly used in the remediation of the anthropogenically polluted soils and the restoration of their ecological functions. However, the interaction mechanisms among biochar, inorganic and organic soil properties and soil biota are still not very clear. The effect of biochar on soil microorganisms is very diverse. Several mechanisms of these interactions were suggested. However, a well acceptable mechanism of biochar effect on soil microorganisms is still missing. Therefore, efforts were made to examine and proposed a mechanism of the interactions between biochar and microorganisms, as well as existing problems of biochar impacts on main groups of soil enzymes, the composition of the microbiota and the detoxification (heavy metals) and degradation (polycyclic aromatic hydrocarbons) of soil pollutants. The data on the process of biochar colonization by microorganisms and the effect of volatile pyrolysis products released by biochar on the soil microbiota were analysed in detail. The effects of biochar on the physico-chemical properties of soils, the content of mineral nutrients and the response of microbial communities to these changes are also discussed. The information provided here may contribute to the solution of the feasibility, effectiveness and safety of the biochar questions to enhance the soil fertility and to detoxify pollutants in soils.
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5.
Biological approaches of fluoride remediation: potential for environmental clean-up.
Katiyar, P, Pandey, N, Sahu, KK
Environmental science and pollution research international. 2020;(12):13044-13055
Abstract
Fluoride (F), anion of fluorine which is naturally present in soil and water, behaves as toxic inorganic pollutant even at lower concentration and needs immediate attention. Its interaction with flora, fauna and other forms of life, such as microbes, adversely affect various physiochemical parameters by interfering with several metabolic pathways. Conventional methods of F remediation are time-consuming, laborious and cost intensive, which renders them uneconomical for sustainable agriculture. The solution lies in cracking down this environmental contaminant by adopting economic, eco-friendly, cost-effective and modern technologies. Biological processes, viz. bioremediation involving the use of bacteria, fungi, algae and higher plants that holds promising alternative to manage F pollution, recover contaminated soil and improve vegetation. The efficiency of indigenous natural agents may be enhanced, improved and selected over the hazardous chemicals in sustainable agriculture. This review article emphasizes on various biological approaches for the remediation of F-contaminated environment, and exploring their potential applications in environmental clean-up. It further focuses on thorough systemic study of modern biotechnological approaches such as gene editing and gene manipulation techniques for enhancing the plant-microbe interactions for F degradation, drawing attention towards latest progresses in the field of microbial assisted treatment of F-contaminated ecosystems. Future research and understanding of the molecular mechanisms of F bioremediation would add on to the possibilities of the application of more competent strains showing striking results under diverse ecological conditions.
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6.
Prospects and applications of plant growth promoting rhizobacteria to mitigate soil metal contamination: A review.
Guo, J, Muhammad, H, Lv, X, Wei, T, Ren, X, Jia, H, Atif, S, Hua, L
Chemosphere. 2020;:125823
Abstract
The rapid increase in world population has generated the issues of hunger, poverty, food insecurity and malnutrition. To meet the challenge of increased food production of better quality, the farmers were compelled to use more chemical fertilizers, especially in developing countries. The higher use of chemical fertilizers interrupts the food chain through eutrophication, the polluting air and soil by incorporating metals. Trace metals have a deleterious effect on soil microbial and plant growth. To minimize metal toxicity and maximize the production of food, there are different approaches that can lead to lessen the use of chemical fertilizers. Plant growth promoting rhizobacteria (PGPR) are capable to enhance the plant growth and can remediate metal contaminated soils. PGPR has the ability to improve food production with diverse attributes e.g. producing siderophores that promote rhizosphere trace metal sequestration and production of organic and inorganic acids thus affecting trace metal bioavailability and plant induced systemic tolerance (IST) to limit the crop metal accumulation. In this review paper, we have discussed the biological approach which is environmentally friendly and cost-effective mean for metal polluted soils and gives some new insights for safety use of PGPR in trace metal contaminated fields.
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7.
Biochar-bacteria-plant partnerships: Eco-solutions for tackling heavy metal pollution.
Harindintwali, JD, Zhou, J, Yang, W, Gu, Q, Yu, X
Ecotoxicology and environmental safety. 2020;:111020
Abstract
Over the past 30 years, the ever-rising demands of the modern and growing population have led to the rapid development of agricultural and industrial sectors worldwide. However, this expansion has exposed the environment to various pollutants including heavy metal (HM)s. Almost all HMs are serious toxicants and can pose serious health risks to living organisms in addition to their bioaccumulative and non-biodegradable nature. Different techniques have been developed to restore the ecological functions of the HM-contaminated soil (HMCS). However, the major downfalls of the commonly used remediation technologies are the generation of secondary wastes, high operating costs, and high energy consumption. Phytoremediation is a prominent approach that is more innocuous than the existing remediation approaches. Some microbes-plant interactions enhance the bioremediation process, with heavy metal resistant-plant growth promoting bacteria (HMRPGPB) being widely used to assist phytoremediation of HMs. However, the most common of all major microbial assisted-phytoremediation disturbances is that the HM-contaminated soil is generally deficient in nutrients and cannot sustain the rapid growth of the applied HMRPGPB. In this case, biochar has recently been approved as a potential carrier of microbial agents. The biochar-HMRPGPB-plant association could provide a promising green approach to remediate HM-polluted sites. Therefore, this review addresses the mechanisms through which biochar and HMRPGPB can enhance phytoremediation. This knowledge of biochar-HMRPGPB-plant interactions is significant with respect to sustainable management of the HM-polluted environment in terms of both ecology and economy, and it offers the possibility of further development of new green technologies.
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8.
Endophyte-assisted phytoremediation: mechanisms and current application strategies for soil mixed pollutants.
He, W, Megharaj, M, Wu, CY, Subashchandrabose, SR, Dai, CC
Critical reviews in biotechnology. 2020;(1):31-45
Abstract
Phytoremediation uses plants and associated microbes to remove pollutants from the environment and is considered a promising bioremediation method. Compared with well-described single contaminant treatments, the number of studies reporting phytoremediation of soil mixed pollutants has increased recently. Endophytes, including bacteria and fungi, exhibit beneficial traits for the promotion of plant growth, stress alleviation, and biodegradation. Moreover, endophytes either directly or indirectly assist host plants to survive high concentrations of organic and inorganic pollutants in the soil. Endophytic microorganisms can also regulate the plant metabolism in different ways, exhibiting a variety of physiological characteristics. This review summarizes the taxa and physiological properties of endophytic microorganisms that may participate in the detoxification of contaminant mixtures. Furthermore, potential biomolecules that may enhance endophyte mediated phytoremediation are discussed. The practical applications of pollutant-degrading endophytes and current strategies for applying this valuable bio-resource to soil phytoremediation are summarized.
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9.
Growing food in polluted soils: A review of risks and opportunities associated with combined phytoremediation and food production (CPFP).
Haller, H, Jonsson, A
Chemosphere. 2020;:126826
Abstract
Innumerable private households and small-scale producers currently operate on polluted soils. Phytoremediation is one of the most cost-effective remediation options but as a stand-alone technology, it is often not lucrative enough to make it appealing for farmers, especially in economically vulnerable regions. Economic incentives are crucial for remediation projects to materialise and synergies can be obtained by integrating phytoremediation with other profitable activities including food production. This review aims to synthesise state-of-the-art scientific data to provide a general understanding of opportunities and risks for sustainable remediation of agricultural soil by the use of combined phytoremediation and food production (CPFP). The results show that strategies based on CPFP may be appropriate options for most pollutants in virtually all climatic or socioeconomic contexts but a number of challenges need to be surpassed. The challenges include remediation-technological issues such as undeveloped post-harvest technology and inadequate soil governance. The need for remediation solutions for polluted fields is increasingly urgent since many farmers currently operate on polluted land and the scarcity of soil resources as the human population continuously increases will inevitably force more farmers to cultivate in contaminated areas. We conclude that, although large scale CPFP has not yet reached technological maturity, appropriate combinations of soil types, plant species/cultivars, and agronomic practices together with thorough monitoring of the pollutants' pathways can potentially allow for safe food production on polluted soil that restricts the transfer of a number of pollutants to the food chain while the soil pool of pollutants is gradually reduced.
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10.
Mercury methylation in rice paddy and accumulation in rice plant: A review.
Zhao, L, Meng, B, Feng, X
Ecotoxicology and environmental safety. 2020;:110462
Abstract
The bioavailability and toxicity of mercury (Hg) are dependent on its chemical speciation, in which methylmercury (MeHg) is the most toxic compound. Inorganic Hg can be transformed into MeHg in anaerobic conditions. Subsequent accumulation and biomagnification in the food chain pose a potential threat to human health. Previous studies have confirmed that paddy soil is an important site for MeHg production, and rice fields are an important source of MeHg in terrestrial ecosystems. Rice (Oryza sativa L.) is recently confirmed as a potential bioaccumulator plant of MeHg. Understanding the behaviour of Hg in rice paddies is important, particularly the mechanisms involved in Hg sources, uptake, toxicity, detoxification, and accumulation in crops. This review highlights the issue of MeHg-contaminated rice, and presents the current understanding of the Hg cycling in the rice paddy ecosystem, including the mechanism and processes of Hg species accumulation in rice plants and Hg methylation/demethylation processes in rice paddies and the primary controlling factors. The review also identified various research gaps in previous studies and proposes future research objectives to reduce the impact of Hg-contamination in rice crops.