Vermiremediation of metal(loid)s via Eichornia crassipes phytomass extraction: A sustainable technique for plant amelioration

Emerging concern of nano-pollution in agro-ecosystem: Flip side of nanotechnology

Nanomaterials (NMs) have proven to be a game-changer in agriculture, showcasing their potential to boost plant growth and safeguarding crops. The agricultural sector has widely adopted NMs, benefiting from their small size, high surface area, and optical properties to augment crop productivity and provide protection against various stressors. This is attributed to their unique characteristics, contributing to their widespread use in agriculture. Human exposure from various components of agro-environmental sectors (soil, crops) NMs residues are likely to upsurge with exposure paths may stimulates bioaccumulation in food chain. With the aim to achieve sustainability, nanotechnology (NTs) do exhibit its potentials in various domains of agriculture also have its flip side too. In this review article we have opted a fusion approach using bibliometric based analysis of global research trend followed by a holistic assessment of pros and cons i.e. toxicological aspect too. Moreover, we have also tried to analyse the current scenario of policy associated with the application of NMs in agro-environment.

Sustainable water management in rice cultivation reduces arsenic contamination, increases productivity, microbial molecular response, and profitability

Arsenic (As) and silicon (Si) are two structurally competitive natural elements where Si minimises As accumulation in rice plants, and based on this two-year field trial, the study proposes adopting alternating wetting and drying (AWD) irrigation as a sustainable water management strategy allowing greater Si availability. This field-based project is the first report on AWD's impact on As-Si distribution in fluvio-alluvial soils of the entire Ganga valley (24 study sites, six divisions), seasonal variance (pre-monsoon and monsoon), rice plant anatomy and productivity, soil microbial diversity, microbial gene ontology profiling and associated metabolic pathways. Under AWD to flooded and pre-monsoon to monsoon cultivations, respectively, greater Si availability was achieved and As-bioavailability was reduced by 8.7 ± 0.01-9.2 ± 0.02% and 25.7 ± 0.09-26.1 ± 0.01%. In the pre-monsoon and monsoon seasons, the physiological betterment of rice plants led to the high rice grain yield under AWD improved by 8.4 ± 0.07% and 10.0 ± 0.07%, proving the economic profitability. Compared to waterlogging, AWD evidences as an optimal soil condition for supporting soil microbial communities in rice fields, allowing diverse metabolic activities, including As-resistance, and active expression of As-responsive genes and gene products. Greater expressions of gene ontological terms and complex biochemical networking related to As metabolism under AWD proved better cellular, genetic and environmental responsiveness in microbial communities. Finally, by implementing AWD, groundwater usage can be reduced, lowering the cost of pumping and field management and generating an economic profit for farmers. These combined assessments prove the acceptability of AWD for the establishment of multiple sustainable development goals (SDGs).

Selenium - An environmentally friendly micronutrient in agroecosystem in the modern era: An overview of 50-year findings

Agricultural productivity is constantly being forced to maintain yield stability to feed the enormously growing world population. However, shrinking arable and nutrient-deprived soil and abiotic and biotic stressor (s) in different magnitudes put additional challenges to achieving global food security. Though well-defined, the concept of macro, micronutrients, and beneficial elements is from a plant nutritional perspective. Among various micronutrients, selenium (Se) is essential in small amounts for the life cycle of organisms, including crops. Selenium has the potential to improve soil health, leading to the improvement of productivity and crop quality. However, Se possesses an immense encouraging phenomenon when supplied within the threshold limit, also having wide variations. The supplementation of Se has exhibited promising outcomes in lessening biotic and abiotic stress in various crops. Besides, bulk form, nano-Se, and biogenic-Se also revealed some merits and limitations. Literature suggests that the possibilities of biogenic-Se in stress alleviation and fortifying foods are encouraging. In this article, apart from adopting a combination of a conventional extensive review of the literature and bibliometric analysis, the authors have assessed the journey of Se in the "soil to spoon" perspective in a diverse agroecosystem to highlight the research gap area. There is no doubt that the time has come to seriously consider the tag of beneficial elements associated with Se, especially in the drastic global climate change era.

A Critical Review on the Vermicomposting of Organic Wastes as a Strategy in Circular Bioeconomy: Mechanism, Performance, and Future Perspectives

AbstractTo meet the current need for sustainable development, vermicomposting (VC), a natural, eco-friendly, and cost-effective technology, can be a wise selection for the bioconversion of organic wastes into value-added by-products. However, no one has tried to establish the VC technology as an economically sustainable technology by exploring its linkage to circular bioeconomy. Even, no researcher has made any effort to explore the usability of the earthworms (EWs) as a protein supplement while assessing the economic perspectives of VC technology. Very few studies are available on the greenhouse gas (GHG) emission potential of VC technology. Still, the contribution of VC technology towards the non-carbon waste management policy is not yet explored. In the current review, a genuine effort has been made to inspect the contribution of VC technology towards the circular bioeconomy, along with evaluating its capability to bioremediate the organic wastes generated from domestic, industrial, and agricultural premises. The potential of the EWs as a protein source has also been explored to strengthen the contribution of VC technology towards the circular bioeconomy. Moreover, the linkage of the VC technology to the non-carbon waste management policy has been comprehensively demonstrated by highlighting its carbon sequestration and GHG emission potentials during the treatment of organic wastes. It has been observed that the cost of food production was reduced by 60--70% by replacing chemical fertilizers with vermicompost. The implication of the vermicompost significantly lessened the harvesting period of the crops, thereby helping the farmers attain higher profits by cultivating more crops in a single calendar year on the same plot. Furthermore, the vermicompost could hold the soil moisture for a long time, lessening the water demand up to 30-40%, which, in turn, reduced the frequency of irrigation. Also, the replacement of the chemical fertilizers with vermicompost resulted in a 23% increment in the grapes' yield, engendering an extra profit of up to 110000 rupees/ha. In Nepal, vermicompost has been produced at a cost of 15.68 rupees/kg, whereas it has been sold to the local market at a rate of 25 rupees/kg as organic manure, ensuring a net profit of 9.32 rupees/kg of vermicompost. EWs embraced 63% crude protein, 5-21% carbohydrates, 6-11% fat, 1476 kJ/100 g of metabolizable energy, and a wide range of minerals and vitamins. EWs also contained 4.11, 2.04, 4.43, 2.83, 1.47, and 6.26  g/kg (on protein basis) of leucine, isoleucine, tryptophan, arginine, histidine, and phenylalanine, respectively, enhancing the acceptability of the EW meal (EWM) as the protein supplement. The inclusion of 3 and 5% EWM in the diet of broiler pullets resulted in a 12.6 and 22.5% increase in their feed conversion ratio (FCR), respectively after one month. Similarly, when a 100% fish meal was substituted by 50% EWM and 50% fish meal, the FCR and growth rate of Parachanna obscura were increased substantially. The VC of maize crop residues mixed with pig manure, cow dung, and biochar, in the presence of Eisenia fetida EWs, yielded only 0.003-0.081, 0-0.17, and 130.40-189.10 g CO₂-eq.kg^-1 emissions of CO₂, CH₄, and N₂O, respectively. Similarly, the VC of tomato stems and cow dung ensured 2.28 and 5.76 g CO₂-eq.kg^-1 CO₂ emissions of CH₄ and N₂O, respectively. Additionally, the application of vermicompost at a rate of 5 t/ha improved the soil organic carbon proportion and aggravated carbon sequestration. The land application of vermicompost improved micro-aggregation and cut down the tillage, reducing GHG emissions and triggering carbon sequestration. The significant findings of the current review suggest that VC technology potentially contributes to the concept of circular bioeconomy, substantially negotiates potential GHG emissions, and complies with the non-carbon waste management policy, reinforcing its acceptability as an economically sound and environmentally benevolent organic waste bioremediation alternative.

Iron oxide doped rice biochar reduces soil-plant arsenic stress, improves nutrient values: An amendment towards sustainable development goals

Arsenic (As) contamination in paddy soils and its further translocation to the rice is a serious global issue. Arsenic loading to the rice depends on soil physico-chemical parameters and agronomic practices. To minimize this natural threat, as a natural substance, rice straw was used to produce rice biochar (RBC) and doped with iron oxide (IO) nanoparticles, another eco-friendly composite. In this study, RBC was used at three different concentrations- 0.5%, 1%, and 1.5% alone as well as conjugated with fixed 20 ppm IO nanoparticles. These treatments were compared with the control soil and control plants that had only As in the setup, without any amendments. The application of these treatments was efficient in reducing soil As bioavailability by 43.9%, 60.5%, and 57.3% respectively. Experimental data proved a significant percentage of As was adsorbed onto the RBC + IO conjugate. Further, the 1% RBC + IO conjugate was found to be the best treatment in terms of making soil macro-nutrients bioavailable. Rice seedlings grown under this treatment was more stress tolerant and produced less antioxidant enzymes and stress markers compared to the control plants grown under As-stress only. Rice plants from these different growth setups were observed for internal anatomical integrity and found that the RBC alone and RBC + IO conjugate, both improved the internal vascular structure compared to the control plants. To minimize soil As stress in crops, IO-doped RBC was proven to be the best sustainable amendment for improving soil-crop quality and achieving the proposed motto of Sustainable Development Goals by the United Nations.

Transcriptome analysis reveals candidate genes involved in multiple heavy metal tolerance in hyperaccumulator Sedum alfredii

Sedum alfredii Hance is a perennial herb native to China that can particularly be found in regions with abandoned Pb/Zn mines. It is a Cd/Zn hyperaccumulator that is highly tolerant to Pb, Cu, Ni, and Mn, showing potential for phytoremediation of soils contaminated with multiple heavy metals. A better understanding of how this species responds to different heavy metals would advance the phytoremediation efficiency. In this study, transcriptomic regulation of S. alfredii roots after Cd, Zn, Pb, and Cu exposure was analyzed to explore the candidate genes involved in multi-heavy metal tolerance. Although Zn and Cd, Pb and Cu had similar distribution patterns in S. alfredii, distinct expression patterns were exhibited among these four metal treatments, especially about half of the differentially expressed genes were upregulated under Cu treatment, suggesting that it utilizes distinctive and flexible strategies to cope with specific metal stress. Most unigenes regulated by Cu were enriched in catalytic activity, whereas the majority of unigenes regulated by Pb had unknown functions, implying that S. alfredii may have a unique strategy coping with Pb stress different from previous cognition. The unigenes that were co-regulated by multiple heavy metals exhibited functions of antioxidant substances, antioxidant enzymes, transporters, transcription factors, and cell wall components. These metal-induced responses at the transcriptional level in S. alfredii were highly consistent with those at the physiological level. Some of these genes have been confirmed to be related to heavy metal absorption and detoxification, and some were found to be related to heavy metal tolerance for the first time in this study, like Metacaspase-1 and EDR6. These results provide a theoretical basis for the use of genetic engineering technology to modify plants by enhancing multi-metal tolerance to promote phytoremediation efficiency.

Enhanced phytoremediation of Metal(loid)s via spiked ZVI nanoparticles: An urban clean-up strategy with ornamental plants

The increasing industrialization and urbanization are also triggering environmental pollution, mostly unnoticed, in the case of soil pollution due to uncontrolled contamination by toxic elemental dispersion. The present study focused on this aspect and studied the clean-up of urban soil in a low-cost and eco-friendly way to restrict arsenic (As), lead (Pb) and mercury (Hg) contamination. Four potential ornamental plants, Catharanthus roseus (vinca), Cosmos bipinnatus (cosmos), Gomphrena globose (globosa) and Impatiens balsamina (balsamina) were used along with zero valent iron (ZVI) nanoparticles (Fe NPs) for remediation of the soil spiked with As (70 mg kg-1), Pb (600 mg kg-1) and Hg (15 mg kg-1) in a 60 d pot experiment. All plants were divided into four groups viz. control, spiked, spiked+20 mg kg-1 ZVI NP and spiked+50 mg kg-1 ZVI NP. FTIR and SEM were used for ZVI NP characterization. Soil and plant analyses and elemental assessments were done using ICP-MS, XRF and SEM. Among the four plants, cosmos showed the maximum accumulation of toxic elements (41.24 ± 0.022 mg kg-1 As, 139.15 ± 11.2 mg kg-1 Pb and 15.57 ± 0.27 mg kg-1 Hg) at 60 d. The application of ZVI NP at 20 mg kg-1 dosage was found to further augment plants' potential for metal(loid)s accumulation without negatively hampering their growth. Cosmos were observed to reduce soil As from 81.35 ± 1.34 mg kg-1 to 28.16 ± 1.38 mg kg-1 (65.38%), Pb from 1132.47 ± 4.66 to 516.09 ± 3.15 mg kg-1 (54.42%) and Hg from 17.35 ± 0.88 to 6.65 ± 0.4 mg kg-1 (61.67%) at 60 d in spiked + 20 mg kg-1 ZVI NP treatment. Balsamina was the most sensitive plant and showed the least metal(loid)s accumulation. In conclusion, three of these plants are potent enough to use together for a better and enhanced removal of toxic elements from the contaminated soil with cosmos to be the best amongst these in urban areas.

Vermiremediation of engine oil contaminated soil employing indigenous earthworms, Drawida modesta and Lampito mauritii

Engine oil consists of hazardous substances that adversely affect the environment and soil quality. Bioremediation (employing organisms) is an appropriate technique to mitigate engine oil pollution. In the present study, the earthworm species, Drawida modesta (epigeic) and Lampito mauritii (anecic) were used to restore the soil polluted with polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs) from used engine oil. Four treatments were set up in addition to positive and negative controls. A maximum of 68.6% PAHs and 34.3% TPHs removal in the treatment with soil (1 kg), cow dung (50 g), used engine oil (7.5 mL) and earthworms was recorded after 60 days. Undoubtedly, earthworms effectively removed PAHs and TPHs from the oil-contaminated soil. PAHs were more strongly accumulated in D. modesta (16.25 mg kg^-1) than in L. mauritii (13.25 mg kg^-1). Further, histological analysis revealed the epidermal surface irregularity, cellular disintegration, and cellular debris in earthworms. The pH (6.3%), electrical conductivity (12.7%), and total organic carbon (35.4%) were significantly (at P < 0.05) decreased after 60 days; while, total nitrogen (62%), total potassium (76.2%), and total phosphorus (19.2%) were substantially increased at the end of the experiment. The seed germination assay with fenugreek indicates that germination percentage (95%), and germination index (179), were dramatically increased in earthworm inoculated treatments when compared to the negative control (without earthworms). The results reveal that there is a great scope for utilizing the earthworms, D. modesta and L. mauritii for the bioremediation of soils contaminated with PAHs and TPHs.

Arsenic dynamics and flux assessment under drying-wetting irrigation and enhanced microbial diversity in paddy soils: A four year study in Bengal delta plain

Arsenic (As) assessment in agricultural soils and corresponding crops is necessary from the global health safety perspective. To the best of our knowledge, we are reporting for the first time, As flux determining parametric equations for paddy field with seasonal rice cultivation under conventional flooding and dry-wet irrigation approaches. Rigorous field experiments and measuring quantitative parameters, flushed out or percolated into the deeper soil As flux was assessed. A wintery (boro)-monsoonal (aman) study from 2016 to 2019 has been conducted showing the efficiency of dry-wet irrigation on reduction of soil As bioavailability. The reduction in boro was 52.4% in 2016 to 64.8% in 2019 while in aman, it was 61% in 2016 to 74.9% in 2019. Low bioavailability was correlated to plant's internal vascular structure that was found more rigid and firm in dry-wet field grown plants. Observed soil physico-chemical parameters clearly influenced As bioavailability as well as soil microbial community. Assessment of microbial diversity using metagenomics under altered water regime was done by population analysis, relative abundance, species richness, Krona chart comparison. Dry-wet field was found to be more diverse and enriched in microbial community than that of the flooded soil indicating an affective reduction of As bioavailability under biotic-abiotic factors.

An assessment of arsenic hazard in groundwater-soil-rice system in two villages of Nadia district, West Bengal, India

The present study measured arsenic (As) concentrations in soil, groundwater and rice grain samples in two villages, Sarapur and Chinili, under Chakdaha block, Nadia district, West Bengal, India. This study also included a survey of the two villages to understand the knowledge among villagers about the As problem. Soil and groundwater samples were collected from fields in two villages while rice grain samples were collected from villagers' houses. The results revealed the presence of As in higher concentrations than the maximum permissible limit of As in drinking water (10 µg L^-1 and 50 µg L^-1 by WHO and Indian standard, respectively) in groundwater [124.50 ± 1.11 µg L^-1 (Sarapur) and 138.20 ± 1.34 µg L^-1 (Chinili)]. The level of As in soil was found to range from 47.7 ± 0.14 to 49.3 ± 0.19 mg Kg^-1 in Sarapur and from 57.5 ± 0.25 to 62.5 ± 0.44 mg Kg^-1 in Chinili which are also higher than European Union maximum acceptable limit in agricultural soil (i.e. 20 mg Kg^-1). The analysis of As in rice grains of five varieties, collected from residents of two villages, showed the presence of higher than recommended safe level of As in rice by FAO/WHO (0.2 mg Kg^-1). The As concentration order was Gosai (0.95 ± 0.044 mg kg^-1), Satabdi (0.79 ± 0.038 mg kg^-1), Banskathi (0.60 ± 0.026 mg kg^-1), Kunti (0.47 ± 0.018 mg kg^-1) and Ranjit (0.29 ± 0.021 mg kg^-1). Importantly, Gosai and Satabdi were the most popular varieties being consumed by local people. The data of consumption of rice per day in the survey was used for the measurement of average daily dose and hazard quotient. It was seen that the As hazard was negatively correlated to the age of residents. Therefore, children and toddlers were at higher risk of As exposure than elderly people. In addition, people with skin related As toxicity symptoms were also cited in the two villages. The study emphasized the severity of As problem in remote areas of West Bengal, India where people consume As tainted rice due to lack of awareness about the As problem and associated health issues.

Ultra-structure alteration via enhanced silicon uptake in arsenic stressed rice cultivars under intermittent irrigation practices in Bengal delta basin

The study implements a periodical intermittent water cycle during rice cultivation providing insight potential in minimizing soil bio-available arsenic. Soil As concentrations were 34 ± 0.49 and 72.03 ± 0.54 mg kg-1 As respectively in two selected fields with rice cultivars gosai and satabdi, in comparison to 42.26 ± 0.37 and 83.69 ± 0.48 mg kg-1 in continuously flooded field soil, determined through ICP-MS. The study found higher translocation of silicon from soil to rice plant parts under intermittent irrigation having pH range of 7.6-9.4 and greater availability of soil organic content that in turn release more labile silicon from soil to aqueous phase for plant accumulation. This increased uptake of silicon strengthens rice shoots, nodes and leaf xylem-phloem integrity compared to conventional continuously flooded rice cultivation approach, suppressing the arsenic translocation, as observed under FE-SEM real-time imaging. Fresh plants were analysed for bioaccumulation and translocation factors of arsenic and silicon to justify the enhanced silicon uptake under proposed practice. Plant stress regulator enzymes viz. malondialdehyde (MDA), total protein, superoxide dismutase (SOD), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) from both conditions and found to be better in intermittent method over conventional practice with higher productivity.

Soil amendments enhanced the growth of Nicotiana alata L. and Petunia hydrida L. by stabilizing heavy metals from wastewater

Due to the non-degradable nature of heavy metals (HMs), the industrial effluent, whether treated or untreated, carrying HMs, eventually end up into the water bodies, soil, and sediments. Numerous countermeasures were applied, but the use of ornamental plants for the stress mitigation associated with HMs on the environment is a neglected research domain. The composition of wastewater influences bioremediation strategies. As the wastewater is contaminated with multiple HMs, many lab studies, with the plants, failed in the industrial field. This work focuses on the potential of Nicotiana alata L. and Petunia hydrida L. against multiple HMs contaminated synthetic wastewater. To improve plant tolerance, soil amendments (biochar, compost, and moss, each at 5% v/v in soil) were used, individually and in combination. After 6 weeks of the exposure, plant physiological, biochemical and enzymatic parameters, as well as the distribution of HMs, (Cd, Cr, Cu, Pb, Mn, Ni, and Zn) in the plant (flower, leaves, root, and shoot) and soil, were measured. The HMs uptake positivity influenced the malondialdehyde content, hydrogen peroxide content and electrolyte leakage, while negatively to photosynthetic pigments, and resulted in increased catalase, guaiacol peroxidase, glutathione s-transferase, ascorbate peroxidase, while reduced superoxide dismutase activity. It was found that all amendments improved the plant growth by metal stabilization, and best results were obtained with the combined application of biochar + compost + moss. So, HMs stabilization can be achieved by growing ornamental plants, like Nicotiana alata L. and Petunia hydrida L. along with soil amendments.