Investigation of arsenic accumulation and biochemical response of in vitro developed Vetiveria zizanoides plants

Vetiver grass cleans up arsenic contaminated field for subsequent safe cultivation of rice with low arsenic in grains: A two year field study

The presence of high concentrations of arsenic (As) in agricultural soils and its subsequent accumulation in rice crop is a serious issue threatening sustainability of agriculture and human health. In the present work, remediation of As contaminated field in Nadia, West Bengal, India was done through the cultivation of Vetiver (Vetiveria zizanoides L. Nash) and the same field was subsequently used for rice (Oryza sativa L.) cultivation. The results showed that V. zizanoides could reduce As concentrations in the field to bring it lower than the maximum permissible limit (20 mg kg-1) in 11 months' time. The rice plants grown in remediated field showed improvement in growth and photosynthesis parameters as compared to that of contaminated field. Importantly, yield related parameters (filled seed, 1000 grain weight, number of panicles etc.) were also significantly higher in remediated field than that in contaminated field. Arsenic concentration in roots, shoot, husk and grains of rice was found to be significantly lower in remediated field than in contaminated field. Grain As decreased from 0.75 to 0.77 μg g-1 dw in contaminated field to 0.15-0.18 μg g-1 dw. In conclusion, replacing rice for single year with V. zizanoides crop can significantly remediate the field and can be a viable option.

Supplementation of Jasmonic acid Mitigates the Damaging Effects of Arsenic Stress on Growth, Photosynthesis and Nitrogen Metabolism in Rice

Experiments were conducted to evaluate the role of exogenously applied jasmonic acid (JA; 0.1 and 0.5 µM) in alleviating the toxic effects of arsenic (As; 5 and 10 µM) stress in rice. Plants treated with As showed considerable decline in growth attributes like height, fresh and dry weight of plant. Arsenic stress reduced the content of δ-amino livulenic acid (δ-ALA), glutamate 1-semialdehyde (GSA), total chlorophylls and carotenoids, with more reduction evident at higher (10 µM) As concentrations, however exogenously supplied JA alleviated the decline to considerable extent. Arsenic stress mediated decline in photosynthetic gas exchange parameters, Fv/Fm (PSII activity) and Rubisco activity was alleviated by the exogenous treatment of JA. Arsenic stress caused oxidative damage which was evident as increased lipid peroxidation, lipoxygenase activity and hydrogen peroxide concentrations however, JA treatment declined these parameters. Treatment of JA improved the activity of nitrate reductase and glutamate synthase under unstressed conditions and also alleviated the decline triggered by As stress. Activity of antioxidant enzymes assayed increased due to As stress, and the supplementation of JA caused further increase in their activities. Moreover, the content of proline, free amino acids and total phenols increased significantly due to JA application under stressed and unstressed conditions. Treatment of JA increased the content of nitrogen and potassium while as reduced As accumulation significantly.

Root chemistry and microbe interactions contribute to metal(loid) tolerance of an aromatic plant - Vetiver grass

Aromatic plants, such as vetiver grass (Chrysopogon zizanioides), possess strong abilities to resist environmental stresses. However, whether such abilities stem from the interaction between specific chemical characteristics and the associated microbes in roots and rhizosphere remains unclear. We conducted pot experiments to analyze stress-tolerant parameters, organic compounds, and bacterial communities in roots and rhizosphere of vetiver under typical metal(loid) stress [cadmium (Cd), arsenic (As), or Cd + As] over time. The results showed that the vetiver displayed limited toxic symptoms in terms of oxidative stress-antioxidant balance and chlorophyll content. The root low-molecular-weight organic acids (LMWOAs), fatty acids, and sterols were highly sensitive to growth stage (increased from the 4-month to the 8-month stage), and less sensitive to metal(loid) stress. The sugar contents in the rhizosphere soils also notably increased over time. Such endo and rhizosphere chemical changes strongly correlated with and enriched the functional bacteria including Streptomyces, which can resist stress and promote plant growth. The compound-bacteria interaction highly depended on growth stage. Vetiver demonstrated a progressive adaptation to stresses through metabolite modulation and cellular defense reinforcement. Our study evidenced that vetiver shapes the interaction between organic compounds and bacterial community in the root-soil interface and provides notable stress-resistant functions.

Endofungal Rhizobium species enhance arsenic tolerance in colonized host plant under arsenic stress

Arsenic (As) is a toxic metalloid that is present in natural surroundings in many forms with severe consequences to sustainable agriculture and human health. Plant growth-promoting Rhizobia have been found involved in the induction of plant tolerance under various biotic and abiotic stresses. An endofungal Rhizobium species associated with arbuscular mycorrhizal fungi (AMF) Serendipita indica deploy beneficial role in the promotion of plant growth and tolerance against various biotic and abiotic stresses. In the current study, we have determined the role of endofungal Rhizobium species in protection of host plant growth under As stress. We observed that endofungal Rhizobium species strain Si001 tolerate AsV up to 25 mM and its inoculation enhances tomato seed germination and seedling growth. A hyper-colonization of Rhizobium species Si001 in tomato roots was observed under As stress and results in modulation of GSH and proline content with reduced ROS. Rhizobium species Si001 colonization in host plant recovered pigment contents (chlorophyll-a and chlorophyll-b up to 189.5% and 192%, respectively), photosynthesis (157%), and water use efficiency (166%) compared to As-treated plants. Interestingly, bacterial colonization results in 40% increased As accumulation in the root, while a reduction in As translocation from root to shoot up to 89% was observed as compared to As treated plants. In conclusion, endofungal Rhizobium species Si001 association with the host plant may improve plant health and tolerance against As stress with reduced As accumulation in the crop produce.

Uncovering the phytochemicals of root exudates and extracts of lead (Pb) tolerant Chrysopogon zizanioides (L.) Roberty in response to lead contamination and their effect on the chemotactic behavior of rhizospheric bacteria

The chemical composition of root exudates and root extracts from Chrysopogon zizanioides (L.) Roberty cv KS-1 was determined in the presence of lead [Pb(II)]. Hitherto, no information is available in the literature concerning the phytochemical components of root exudates of C. zizanioides. Significantly higher concentrations of total carbohydrates (26.75 and 42.62% in root exudates and root extract, respectively), reducing sugars (21.46 and 56.11% in root exudates and root extract, respectively), total proteins (9.22 and 23.70% in root exudates and root extract, respectively), total phenolic acids (14.69 and 8.33% in root exudates and root extract, respectively), total flavonoids (14.30 and 12.28% in root exudates and root extract, respectively), and total alkaloids (12.48 and 7.96% in root exudates and root extract, respectively) were observed in samples from plants growing under Pb(II) stress in comparison to the respective controls. GC-MS profiling showed the presence of a diverse group of compounds in root exudates and extracts, including terpenes, alkaloids, flavonoids, carotenoids, plant hormones, carboxylic/organic acids, and fatty acids. Among the detected compounds, many have an important role in plant development, regulating rhizosphere microbiota and allelopathy. Furthermore, the results indicated that C. zizanioides exudates possess a chemotactic response for rhizospheric bacterial strains Bacillus licheniformis, Bacillus subtilis, and Acinetobacter junii Pb1.

Influence of Clay Mineral Amendments Characteristics on Heavy Metals Uptake in Vetiver Grass (Chrysopogon zizanioides L. Roberty) and Indian Mustard (Brassica juncea L. Czern)

Phytoremediation is limited when heavy metals reduce soil quality and, subsequently, inhibit plant growth. In this study, we evaluated the use of attapulgite and bentonite as amendments in soil contaminated with multiple metals, to improve the phytoremediation capacity of Vetiver grass and Indian mustard. A 21-day greenhouse study was undertaken, to investigate plant tolerance in heavy-metal-contaminated soil, as well as heavy-metal absorption in plant roots and shoots. The results showed a generally higher root-uptake rate for Cr, Cu, Co, Ni, and Zn in Vetiver grass. Overall, the highest absorption for Ni, Cr, Co, Cu, and Zn was 1.37, 2.79, 1.39, 2.48 and 3.51 mg/kg, respectively, in the roots of Vetiver grass. Clay minerals inhibited the translocation of some heavy metals. The addition of attapulgite improved the phytoremediation capacity of Vetiver for Ni, Cr, and Co, while bentonite improved Vetiver’s absorption of Cu and Zn. The translocation factor for Ni in one of the attapulgite treatments was 2, indicating that attapulgite improved the phytoextraction of Ni by Vetiver grass. Our results confirm that attapulgite at 2.5% (w/w) can successfully improve the phytostabilization of heavy metals by Vetiver grass. Indian mustard showed no significant metal uptake that could be detected by inductively coupled plasma optical emission spectrometry (ICP-OES), despite the addition of attapulgite and bentonite. This research contributes to the knowledge repository of suitable amendments that improve the phytoremediation properties of Vetiver grass.

Cannabis sativa L. and Brassica juncea L. grown on arsenic-contaminated industrial soil: potentiality and limitation for phytoremediation

Phytoremediation represents a natural method to remove contaminants from soil. The goal of this study was to investigate the potential of phosphate-assisted phytoremediation by two energy crops, Cannabis sativa L. and Brassica juncea L., for the sustainable remediation of heavily arsenic-contaminated industrial soil. The two species were investigated for uptake, translocation, and physiological effects of arsenic and phosphate in a microcosm test. Although C. sativa and B. juncea were symptomless when grown in arsenic-contaminated soil, an important reduction of biomass (50 and 25%, respectively) was observed as a stress marker. Phytotoxicity and cytotoxicity effects promoted by contaminated soils were investigated in both the species and a model plant for ecotoxicity studies, Vicia faba L., which is the most developed model to test genotoxicity effects in terms of chromosomal aberration and micronuclei presence. The higher amount of arsenic was found in C. sativa and B. juncea roots (on average 1473 and 778 mg kg^-1, respectively), but both species were able to uptake and translocate arsenic in leaves and stems, up to 47.0 and 189 mg kg^-1, respectively. Phosphate treatment had no effect on arsenic uptake in none of the crop, but significantly improved the plant performance. Biomass production resulted similar to that of B. juncea control plants. Antioxidant enzymatic activities and photosynthetic performance responded differently in the two crops. The present investigation provides new insight for a proficient selection of the most suitable crop species for sustainable phytomanagement of a highly polluted As-contaminated site by coupled phytoremediation-bioenergy approach.

Growth and biosorption of Purple guinea and Ruzi grasses in arsenic contaminated soils

Increasing mining and industrial discharge of untreated wastewater, as well as excessive use of fertilizers for agricultural purposes, and heavy metal contamination in soil have become one of the serious environmental problems worldwide. In the present study, pot experiments were conducted to evaluate the influence of arsenic contamination and other factors on the growth and development of local forage grasses like Purple guinea and Ruzi grasses under controlled conditions. Influence of arsenic concentration, soil properties, and fertilizers on biosorption and withstanding potential of grasses was studied using model soil and real-time arsenic-contaminated mine soil. High arsenic contents in soil significantly affected the growth as well as biomass production of grasses and declined the overall biomass production concerning exposure durations. Purple guinea and Ruzi grasses showed growth tolerance in arsenic-contaminated soils with concentrations of 100 and 150 mg/kg respectively. Grass species, soil compositions, and properties, fertilizers, growth duration, etc. potentially influenced arsenic accumulation in grasses. Both local forage grasses showed <1 bio-accumulation factor (BAF) and bio-concentration factor (BCF) after 45 days that indicates the minimum harvesting time of 45 days, and biosorption rate was found significant to the exposure duration. Maximum translocation factor (TF) values observed in Purple guinea and Ruzi grasses were 0.65 and 0.95, respectively which are < 1, therefore, these local forage grasses could be labeled as arsenic-metallophytes and ability to tolerate high levels of heavy metals without much biosorption. The results confirmed that local forage grasses have much growth tolerance potential against arsenic in real-time mine soil with desired fertilizers and these species could be used for sustainable management of ecological health of the Thung Kum gold mine area in Thailand.

A comprehensive review of adaptations in plants under arsenic toxicity: Physiological, metabolic and molecular interventions

Arsenic (As) is recognized as a toxic metalloid and a severe threat to biodiversity due to its contamination. Soil and groundwater contamination with this metalloid has become a major concern. Large fractions of cultivable lands are becoming infertile gradually due to the irrigation of As contaminated water released from various sources. The toxicity of As causes the generation of free radicals, which are harmful to cellular metabolism and functions of plants. It alters the growth, metabolic, physiological, and molecular functions of the plants due to oxidative burst. Plants employ different signaling mechanisms to face the As toxicity like phosphate cascade, MAPK (Mitogen-Activated Protein Kinase), Ca-calmodulin, hormones, and ROS-signaling. The toxicity of As may significantly be reduced through various remediation techniques. Among them, the microbial-assisted remediation technique is cost-effective and eco-friendly. It breaks down the metalloid into less harmful species through various processes viz. biovolatilization, biomethylation, and transformation. Moreover, the adaptation strategies towards As toxicity are vacuolar sequestration, involvement of plant defense mechanism, and restricting its uptake from plant roots to above-ground parts. The speciation, uptake, transport, metabolism, ion dynamics, signaling pathways, crosstalk with phytohormones and gaseous molecules, as well as harmful impacts of the As on physiological processes, overall development of plants and remediation techniques are summarized in this review.

Are Grasses Really Useful for the Phytoremediation of Potentially Toxic Trace Elements? A Review

The pollution of soil, water, and air by potentially toxic trace elements poses risks to environmental and human health. For this reason, many chemical, physical, and biological processes of remediation have been developed to reduce the (available) trace element concentrations in the environment. Among those technologies, phytoremediation is an environmentally friendly in situ and cost-effective approach to remediate sites with low-to-moderate pollution with trace elements. However, not all species have the potential to be used for phytoremediation of trace element-polluted sites due to their morpho-physiological characteristics and low tolerance to toxicity induced by the trace elements. Grasses are prospective candidates due to their high biomass yields, fast growth, adaptations to infertile soils, and successive shoot regrowth after harvest. A large number of studies evaluating the processes related to the uptake, transport, accumulation, and toxicity of trace elements in grasses assessed for phytoremediation have been conducted. The aim of this review is (i) to synthesize the available information on the mechanisms involved in uptake, transport, accumulation, toxicity, and tolerance to trace elements in grasses; (ii) to identify suitable grasses for trace element phytoextraction, phytostabilization, and phytofiltration; (iii) to describe the main strategies used to improve trace element phytoremediation efficiency by grasses; and (iv) to point out the advantages, disadvantages, and perspectives for the use of grasses for phytoremediation of trace element-polluted soils.

Targeting redox metabolism of the maize-Azospirillum brasilense interaction exposed to arsenic-affected groundwater

Arsenic in groundwater constitutes an agronomic problem due to its potential accumulation in the food chain. Among the agro-sustainable tools to reduce metal(oid)s toxicity, the use of plant growth-promoting bacteria (PGPB) becomes important. For that, and based on previous results in which significant differences of As translocation were observed when inoculating maize plants with Az39 or CD Azospirillum strains, we decided to decipher the redox metabolism changes and the antioxidant system response of maize plants inoculated when exposed to a realistic arsenate (As^V ) dose. Results showed that As^V caused morphological changes in the root exodermis. Photosynthetic pigments decreased only in CD inoculated plants, while oxidative stress evidence was detected throughout the plant, regardless of the assayed strain. The antioxidant response was strain-differential since only CD inoculated plants showed an increase in superoxide dismutase, glutathione S-transferase (GST), and glutathione reductase (GR) activities while other enzymes showed the same behavior irrespective of the inoculated strain. Gene expression assays reported that only GST23 transcript level was upregulated by arsenate, regardless of the inoculated strain. As^V diminished the glutathione (GSH) content of roots inoculated with the Az39 strain, and CD inoculated plants showed a decrease of oxidized GSH (GSSG) levels. We suggest a model in which the antioxidant response of the maize-diazotrophs system is modulated by the strain and that GSH plays a central role acting mainly as a substrate for GST. These findings generate knowledge for a suitable PGPB selection, and its scaling to an effective bioinoculant formulation for maize crops exposed to adverse environmental conditions.

Vicia villosa Roth: a cover crop to phytoremediate arsenic polluted environments

Vicia villosa Roth is a legume species with a growing application in Argentina as a cover crop (CC), a practice that favors the sustainable development of agricultural systems. However, several areas where the use of this CC provides numerous advantages are affected by high concentrations of arsenic (As). Thus, in the present work we studied hairy vetch ability to cope with arsenate [As(V)], arsenite [As(III)], and the mixture of both along with oxidative stress indexes [chlorophyll content, malondialdehyde (MDA) equivalents] as well as anatomical and histological changes in the root structure. The results obtained suggested a different behavior of hairy vetch depending on its growth stage and on metal(oid) concentration. The roots treated with the contaminant showed less turgidity, thickening of the epidermal and subepidermal parenchymal outer layers, and the presence of dark deposits. The morpho-anatomic parameters (cortex length, vascular cylinder diameter, total diameter, and vascular cylinder area) were altered in plants treated with As(V) and As(V)/As(III) whereas the roots of plants treated with As(III) did not show significant differences respect to the control. Moreover V. villosa could tolerate and remove As from soil, thus the use of this legume species seems an attractive approach to remediate As while protecting contaminated soils.

Abandoned Mine Lands Reclamation by Plant Remediation Technologies

Abandoned mine lands (AMLs), which are considered some of the most dangerous anthropogenic activities in the world, are a source of hazards relating to potentially toxic elements (PTEs). Traditional reclamation techniques, which are expensive, time-consuming and not well accepted by the general public, cannot be used on a large scale. However, plant-based techniques have gained acceptance as an environmentally friendly alternative over the last 20 years. Plants can be used in AMLs for PTE phytoextraction, phytostabilization, and phytovolatilization. We reviewed these phytoremediation techniques, paying particular attention to the selection of appropriate plants in each case. In order to assess the suitability of plants for phytoremediation purposes, the accumulation capacity and tolerance mechanisms of PTEs was described. We also compiled a collection of interesting actual examples of AML phytoremediation. On-site studies have shown positive results in terms of soil quality improvement, reduced PTE bioavailability, and increased biodiversity. However, phytoremediation strategies need to better characterize potential plant candidates in order to improve PTE extraction and to reduce the negative impact on AMLs.

Melatonin application differentially modulates the enzymes associated with antioxidative machinery and ascorbate-glutathione cycle during arsenate exposure in indica rice varieties

Arsenic (As) contamination and accumulation in rice is a serious concern causing severe oxidative damage. Melatonin acts as a protective agent in plant defence against multiple abiotic stresses. The mechanism of antioxidant function of melatonin during As stress in rice genotypes is less studied. In this study, hydroponically-grown As-susceptible (Khitish) and As-tolerant (Muktashri) rice cultivars, subjected to 150 µm arsenate stress, were supplemented with exogenously applied melatonin (20 µm) to examine the plant defence mechanism. Melatonin (Mel) increased root and shoot length, fresh and dry weight, chlorophyll a and b content and activated reducing power and free radical scavenging capacity in both rice cultivars. The role of Mel in the sensitive variety appeared to be more prominent with respect to reduced water saturation deficit by reducing endogenous As and H₂ O₂ accumulation, and enhancing overall antioxidant capacity by imposing reduced requirement of catalase for ROS detoxification, and restoring As-inhibited activity of glutathione-S-transferase, glutathione peroxidase and dehydroascorbate reductase. In contrast, melatonin treatment in the tolerant cultivar required reduced involvement of ascorbate peroxidase to deal with As toxicity, and complemented the stress-mediated inhibition of guaiacol peroxidase activity. Isozyme profiling also established extensive varietal differences with regard to induction of new isoform(s) by Mel during As treatment. This study provides clear insights into mechanistic details of the regulation of antioxidative enzymes by melatonin in contrasting rice genotypes, which may prove helpful in generating As tolerance in susceptible rice varieties grown in marginalized soils, thereby improving crop yield and productivity.

Arsenic uptake and toxicity in wheat (Triticum aestivum L.): A review of multi-omics approaches to identify tolerance mechanisms

Arsenic (As) due to its widespread has become a primary concern for sustainable food production, especially in Southeast Asian countries. In that context, the present review presented a comprehensive detail of the available literature marking an assortment of As-induced impacts on wheat. The conclusive findings of past research suggest that As tends to grossly affect the germination, elongation, biomass, grain yield, and induce oxidative stress. Several human studies are suggestive of higher cancer risks (>1 × 10^-6) due to the ingestion of wheat grains. However, the body of proof is limited and the scarcity of information limited understanding about tolerance mechanism in wheat against As. Therefore, the paper provided a reference from tolerance mechanism based studies in other crops like rice and maize. The generated knowledge of arsenomics would pave the way for plant breeders to develop resistant varieties for As to ensure sustainable food production.

Phytoextraction of arsenic using a weed plant Calotropis procera from contaminated water and soil: growth and biochemical response

Developing effective and environment-friendly alternatives to remove arsenic (As) from soil and water systems is of great importance and phytoremediation may be a promising alternative in this direction. Weeds have wide geographical distribution, not a part of food chain, well adapted to adverse conditions and reported to grow at various heavy metal contaminated sites. The present work delineates potential of a weed plant Calotropis procera L. for the remediation and translocation of As from water and soil and this plant has been found efficient in remediating significant quantities of As after 15 and 30 d when exposed to a range of concentrations. Moreover, As accumulation was found more in shoots than the roots when exposed to higher As levels for 30d having translocation factor >1 and make this plant suitable for phytoextraction of As. Effect of As on plant growth, photosynthetic pigments and lipid peroxidation in response to As is also presented here. The activities of antioxidant enzymes, superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase and catalase were found to increase in response to As stress. High As accumulation and tolerance potential of C. procera from artificially As contaminated water and soil coupled with good growth and its phytoextraction ability suggests the feasibility of this plant for the phytoremediation of As from contaminated water and soils.

Artificial Floating Island with Vetiver for Treatment of Arsenic-Contaminated Water: A Real Scale Study in High-Andean Reservoir

Arsenic found in agriculture water reservoirs represents a threat to water security and safe agricultural products in developing countries. Small farms do not implement traditional water treatments due to the high cost; hence, a nature-based solution is an alternative to tackling this challenge. This paper investigated the potential of artificial floating island with Vetiver (AFIV) for the geogenic arsenic removal present in the reservoir of the Ilinizas páramo in Ecuador. We constructed two AFIV systems using PVC pipes in a reservoir batch type with a 3.6 m3 treatment capacity. Arsenic and iron were analyzed in duplicated every 30 days at the affluent and effluent through 120 days. The average remediation of arsenic was recorded as 97% in water and 84% in sediment, while the average remediation of iron was 87% in sediment. The survival rate of macrophytes was 92%; they accumulated arsenic in its roots that acted as a barrier against the translocation. The research demonstrated that the use of AFIV has the potential to rehabilitate reservoirs contaminated with arsenic under adverse climatic conditions such as the páramo ecosystem.

Unraveling the impact of arsenic on the redox response of peanut plants inoculated with two different Bradyrhizobium sp. strains

Arsenic (As) can be present naturally in groundwater from peanut fields, constituting a serious problem, as roots can accumulate and mobilize the metalloid to their edible parts. Understanding the redox changes in the legume exposed to As may help to detect potential risks to human health and recognize tolerance mechanisms. Thirty-days old peanut plants inoculated with Bradyrhizobium sp. strains (SEMIA6144 or C-145) were exposed to a realistic arsenate concentration, in order to unravel the redox response and characterize the oxidative stress indexes. Thus, root anatomy, reactive oxygen species detection by fluorescence microscopy and, ROS histochemical staining along with the NADPH oxidase activity were analyzed. Besides, photosynthetic pigments and damage to lipids and proteins were determined as oxidative stress indicators. Results showed that at 3 μM As^V, the cross-section areas of peanut roots were augmented; NADPH oxidase activity was significantly increased and O₂˙¯and H₂O₂ accumulated in leaves and roots. Likewise, an increase in the lipid peroxidation and protein carbonyls was also observed throughout the plant regardless the inoculated strain, while chlorophylls and carotenes were increased only in those inoculated with Bradyrhizobium sp. C-145. Interestingly, the oxidative burst, mainly induced by the NADPH oxidase activity, and the consequent oxidative stress was strain-dependent and organ-differential. Additionally, As modifies the root anatomy, acting as a possibly first defense mechanism against the metalloid entry. All these findings allowed us to conclude that the redox response of peanut is conditioned by the rhizobial strain, which contributes to the importance of effectively formulating bioinoculants for this crop.

Differential distribution of and similar biochemical responses to different species of arsenic and antimony in Vetiveria zizanioides

Vetiver grass (Vetiveria zizanioides L. Nash) has a great application potential to the phytoremediation of heavy metals pollution. However, few studies explored the bioavailability and distribution of different speciations of As and Sb in V. zizanioides. This study aimed to clarify the allocation and accumulation of two inorganic species arsenic (As(III) and As(V)) and antimony (Sb(III) and Sb(V)) in V. zizanioides, to understand the self-defense mechanisms of V. zizanioides to these metal(loids) elements. Thus, an experiment was conducted under greenhouse conditions to identify distribution of As and Sb in plant roots and shoots. Antioxidant enzymes (superoxide dismutase, SOD) and changes of subcellular structures were tested to evaluate metal(loids) tolerance capacities of V. zizanioides. This study demonstrated that V. zizanioides had higher capacity to accumulate Sb than As. For Sb absorption, Sb(III) content is significantly higher than Sb(V) in tissues of V. zizanioides under all concentration levels, despite the oxidation of Sb(III) on the nutrient solution surface. Additional Sb was mainly accumulated in plant roots due to Sb immobilization by transforming it into precipitates. As was more easily transferred to aerial tissues and had low accumulation rates, probably due to its restricted uptake rather than restricted transport. In many cases, two inorganic species of As and Sb showed almost same biotoxicity to V. zizanioides estimated from its biomass, SOD activity, and MDA content as well as functional groups. In summary, the results of this study provide new insights into understanding allocation, accumulation and phytotoxicity effects of arsenic and antimony in V. zizanioides. Schematic diagram of distribution of and biochemical responses to As(III), As(V), Sb(III), and Sb(V) in tissue of V. zizanioides.

Potential of Vetiver grass for the phytoremediation of a real multi-contaminated soil, assisted by electrokinetic

Phytoremediation assisted by electrokinetic is a potential technology for remediation of contaminated soil, but little is known about its application on real contaminated soils. This study aims to evaluate the Vetiver grass application on the electro-phytoremediation of a real contaminated soil around a metal smelter factory. Different types of the electric field (AC-DC), voltage gradient (1-2V/cm), saturation and unsaturation condition, and Eh-pH variation were investigated for Vetiver electro-phytoremediation performance. Vetiver grass had been grown for 21 days. Then three different voltage gradients (1, 2DCV/cm and 2ACV/cm) were applied for 8 h/d across the soil domain for the next 21 days in comparison with a control cell without electric field (PR). The results showed that despite the AC current application which induced small changes, the application of DC current significantly changed the Eh-pH values. The maximum accumulation of extractable metals in Vetiver grass occurred in 2DCV/cm that shows approximately 50% increase in comparison with the AC and PR cells. The presence of contaminants poisons the Vetiver in all cells and all plants under 2DCV/cm dried out at the end of the experiment. Despite the significant reduction of heavy metals, there was no noticeable phytoextraction due to the application of DC current. Therefore, DC current can be used for phytoremediation through phytostabilization. However, the overall metals uptake in plants shoots under AC treatment with BCF>1 was much higher than the PR and DC treatment. Considering the translocation rate and plants health, if the AC current is applied in a long treatment time, it could have better results in electro-phytoremediation of the Vetiver grass through phytoextraction process. However, the maximum removal of heavy metals was in the cathode part of the cell under 2DCV/cm that shows 65% improvement in comparison with the PR cell.

Mixed plantation of wheat and accumulators in arsenic contaminated plots: A novel way to reduce the uptake of arsenic in wheat and load on antioxidative defence of plant

Wheat (W) and accumulators (A) were planted in plots (arsenic amended soil and without arsenic) designed with ecotoxicological concern for arsenic safe-grains. For the study sixteen plots of 2 × 2 × 0.5 m (l × b × h) size were prepared. Arsenic (As) in the form of sodium arsenate was applied at 50 mg/kg in plots. Out of these sixteen plots eight plots had arsenic amended soil and rest 8 without any arsenic (C). Accumulator's viz. Pteris vittata (PV), Phragmites australis (PA) and Vetiveria zizanioides (VZ) were planted along with wheat in combination (W + PV, W + PA and W + VZ) in twelve plots (6 AWAs plots and 6 AWC plots). In the rest 4 plots (2 WAs plots and 2 WC plots), only wheat was planted. The study was conducted for two cropping seasons, where accumulators were left in the plots between the cropping seasons except that before 2nd cropping accumulators were properly pruned and extra tillers were removed. The germination % of wheat in WAs in 1st and the 2nd cropping season was found to be 55 and 57%, while in AWAs and AWC plots it was between 86 and 92% (W + VZ, 56 and 73%). The physiological activity was found to be reduced in WAs plots compared to AWAs (except for vetiver combination) and AWC plots in both cropping seasons. The antioxidant activity was enhanced in WAs compared with AWAs. The arsenic concentration in grains of wheat was within the permissible limit set by WHO and GOI in AWAs plots while it exceeded the limit in W + VZ (in 1st cropping) and WAs in both cropings.

Application of phytoremediation technology in decontamination of a fish culture pond fed with coal mine effluent using three aquatic macrophytes

In the present study, three aquatic macrophytes, Eichhornia crassipes, Salvinia molesta, and Pistia stratiotes were used to assess their relative efficacies in decontamination of a fish culture pond, regularly fed with coal mine effluent (CME). The level of metals like Fe, Mn, Ni, Zn, Cu, Pb, Cr, and Cd were much higher in CME-fed pond water than their recommended limits in drinking water set by the Bureau of Indian standards and in effluents by the Environmental Protection Agency. The levels of metal were lowered substantially in CME-fed pond water after exposure of the above plants to such water, however, metal levels in the plants increased tremendously. The increased metal levels in plants severely damaged their physiological and biochemical processes. The contents of chlorophyll a, b and carotenoid were reduced by 63.2, 64.2, and 46.3%, respectively, in E. crassipes, 41, 57.4, and 57.8% in S. molesta, and 42, 62, and 61% in P. stratiotes. The accumulating metals also generated oxidative stress in plants, as evident from the increased superoxide dismutase and catalase activities and enhanced malondialdehyde content. The E. crassipes was the most potent in absorbing the metals from the CME-fed pond water, followed by S. molesta and P. stratiotes.

Suitability of aromatic plants for phytoremediation of heavy metal contaminated areas: a review

This review briefly elucidates the research undertaken and benefits of using aromatic plants for remediation of heavy metal polluted sites. A sustainable approach to mitigate heavy metal contamination of environment is need of the hour. Phytoremediation has emerged to be one of the most preferable choices for combating the metal pollution problem. Aromatic plants can be used for remediation of contaminated sites as they are non-food crops thus minimizing the risk of food chain contamination. Most promising aromatic plants for phytoremediation of heavy metal contaminated sites have been identified from families - Poaceae, Lamiaceae, Asteraceae, and Geraniaceae. They act as potential phytostabilisers, hyper accumulators, bio-monitors, and facultative metallophytes. Being high value economic crops, monetary benefits can be obtained by growing them in tainted areas instead of food crops. It has been observed that heavy metal stress enhances the essential oil percentage of certain aromatic crops. Research conducted on some major aromatic plants in this context has been highlighted in the present review which suggests that aromatic plants hold a great potential for phytoremediation. It has been reported that essential oil from aromatic crops is not contaminated by heavy metals significantly. Thus, aromatic plants are emerging as an ideal candidate for phytoremediation. Highlights • Aromatic plants hold a great potential for phytoremediation of heavy metal contaminated sites. • Being high value economic crops, monetary benefits can be obtained by growing them in contaminated areas instead of food crops. • Research done on some major aromatic plants in this context has been highlighted in the present review.

Arsenic forms in phytoextraction of this metalloid in organs of 2-year-old Acer platanoides seedlings

The aim of the study was to estimate the significance of the role of arsenite (As(III)), arsenate (As(V)), and dimethylarsinic acid (DMA) presence in modified Knop medium in the efficiency of phytoextraction of arsenic (As) in Acer platanoides root, stem, and leaves. The addition of particular As forms in single, double, and triple experimental systems was associated with a lower increase of seedling biomass compared to control plants (system free of As forms addition). Depending on As forms and their concentration in solution, negative symptoms from slight visible changes (inorganic forms separately or jointly), through smaller and discolored leaves (after DMA addition), and finally to their withering (after high DMA addition) were observed. Changes of color and shape for root systems exposed to particular As forms separately or jointly were also observed, in spite of the fact that there were no significant changes in biomass of seedlings growing in all experimental systems. The highest mean concentrations of As in root, stem, and leaves (590, 70, and 140 mg kg^-1 dry weight (DW), respectively) were observed in plants growing under different experimental systems. The highest bioconcentration factor values were 10.8 for plants exposed to 0.06 mM of As(III) and DMA, while the highest translocation factor (1.0) was recorded for plants growing under the same As forms (0.6 and 0.06 mM, respectively). The obtained results indicate that the presence of particular As forms not only determines As phytoextraction and transport of this metalloid form but also has a decisive influence on plant morphology and survivability. As regards the practical aspects of phytoremediation, the kind of As forms present in substrate are more important than their total concentration.

Uptake of Heavy Metals from Industrial Wastewater Using In Vitro Plant Cultures

The plant species Bacopa monnieri has been observed to reduce the heavy metal concentrations in its vicinity. The present study is a comparison of in vitro culture and soil-grown plants of B. monnieri to remove Cr and Cd, from synthetic solution and effluent obtained from industrial area. Results were obtained at every half hour interval upto 180 min. Samples were observed for light absorption using UV-Visible spectrophotometer. Statistically, both systems reclaimed Cr and Cd from polluted water. In vitro cultures showed 67% and 93% removal of Cr and Cd from industrial wastewater whereas soil-grown plants showed 64% and 83% Cr and Cd removal. However, reduction rate was significantly higher for in vitro culture as compared to soil-grown plants. Besides other advantages, in vitro plant cultures proved to be more potent to detoxify pollutants in less time. This approach can be used for the removal of heavy metals at large scale.