Phytoremediation of metals using lemongrass (Cymbopogon citratus (D.C.) Stapf.) grown under different levels of red mud in soil amended with biowastes

Emilia fosbergii Nicolson, a novel and effective accumulator for phytoremediation of mercury-contaminated soils

Soil contamination by toxic metals threatens global public health, highlighting the need for cost-effective and ecologically sound site remediation. In this study, we assessed phytoremediation of Hg-contaminated soils by Emilia fosbergii Nicolson (Asteraceae). Pot experiment was conducted using a substrate of sand and vermiculite (1:1 volume ratio), treatments consisted of five Hg concentrations (0, 1, 3, 5, and 7 mg kg-1). Metal transfer rates were calculated, including accumulation (BAF), translocation (TF) and bioconcentration (BCF) factors. E. fosbergii roots exhibited greater Hg accumulation than other tissues, but biomass production and plant health were not significantly affected at the concentrations tested, as indicated by elongation factors and tolerance index. The results revealed BAF values between 2.18 and 7.14, TF values ranged between 0.15 and 0.52, and the BCF index varied between 8.97 and 26.58. Treatments with Hg content of 5 mg kg-1 and 7 mg kg-1 recorded the highest total Hg concentrations of 66 mg kg-1 and 65.53 mg kg-1 (roots), and 9.18 mg kg-1 and 33.88 mg kg-1 (aerial), respectively. E. fosbergii demonstrated promise for Hg phytoremediation due to its high accumulation capacity, indicated by regular TF and high BCF and BAF indexes, thus classifying it as a high Hg accumulator.

Roles and significance of chelating agents for potentially toxic elements (PTEs) phytoremediation in soil: A review

Phytoremediation is a biological remediation technique known for low-cost technology and environmentally friendly approach, which employs plants to extract, stabilise, and transform various compounds, such as potentially toxic elements (PTEs), in the soil or water. Recent developments in utilising chelating agents soil remediation have led to a renewed interest in chelate-induced phytoremediation. This review article summarises the roles of various chelating agents and the mechanisms of chelate-induced phytoremediation. This paper also discusses the recent findings on the impacts of chelating agents on PTEs uptake and plant growth and development in phytoremediation. It was found that the chelating agents have increased the rate of metal absorption and translocation up to 45% from roots to the aboveground plant parts during PTEs phytoremediation. Besides, it was also explored that the plants may experience some phytotoxicity after adding chelating agents to the soil. However, due to the leaching potential of synthetic chelating agents, the use of organic chelants have been explored to be used in PTEs phytoremediation. Finally, this paper also presents comprehensive insights on the significance of using chelating agents through SWOT analysis to discuss the advantages and limitations of chelate-induced phytoremediation.

Zinc (Zn) mitigates copper (Cu) toxicity and retrieves yield and quality of lettuce irrigated with Cu and Zn-contaminated simulated wastewater

Owing to a competitive interaction, zinc (Zn) contained in highly Cu-contained wastewater was hypothesized to mitigate Cu toxicity-induced negative effects on the growth and quality of lettuce. Thus, growth, metal accumulation and biochemical responses of lettuce irrigated with simulated wastewater (SW, control), Cu-contaminated SW (CuSW, 20 mg Cu L-1), Zn-contaminated SW (ZnSW, 100 mg Zn L-1) and both Cu- and Zn-contaminated SW (CuZnSW, 20 mg Cu and 100 mg Zn L-1) were evaluated. Results revealed that irrigation with CuSW negatively affected growth (dry matters, root length and plant height) and quality (low mineral concentrations) of lettuce, which were associated with higher Cu uptake. Irrigation with Zn + Cu-contaminated SW retrieved Cu toxicity and improved root and shoot dry matters and root length by 13.5%, 46% and 19%, respectively compared to that with alone Cu-contaminated SW. Moreover, CuZnSW improved lettuce leaf quality compared to CuSW and increased concentrations of Mg (30%), P (15%), Ca (41%), Mn (24%) and Fe (23%). Moreover, compared to CuSW, CuZnSW improved flavonoids (54%), total polyphenolic compounds (1.8-fold), polyphenolic acids (77%) and antiradical activities (16.6%). Most importantly, Zn addition boosted up lettuce Cu tolerance index by 18% under Cu-contaminated SW treatment. Pearson's correlation analysis among various growth and mineral parameters demonstrated that shoot Zn concentration was positively related to elemental concentrations, phytochemical contents and antioxidant activity under Cu-contaminated environment. Thus, it is concluded that Zn supplementation retrieves negative effects of Cu toxicity to lettuce grown with Cu-contaminated wastewater.

Effect of chromium stress on metal accumulation and cell wall fractions in Cosmos bipinnatus

As one of the major pollutants in the environment, chromium (Cr), a heavy metal, poses a serious threat to urban green spaces and human life and health. Cosmos bipinnatus is considered a potential accumulator of Cr, and the differences in cellular Cr distribution and compartmentalization may uncover the mechanisms involved in its tolerance to Cr. To elucidate the effects of Cr stress on C. bipinnatus and determine the mechanism of Cr tolerance in C. bipinnatus, we investigated the physiological indicators, subcellular distribution and chemical forms, cell wall fractions and their Cr contents, uronic acid content in the cell wall fractions, and Fourier transform infrared spectroscopy (FTIR) of the cell wall. The results showed that the antioxidant enzyme activities in C. bipinnatus under Cr stress and most of the Cr were fixed in the cell wall. Notably, changes in the content of pectin fractions in the cell wall affected the accumulation of Cr in the cell wall of C. bipinnatus and the stability of negatively charged groups. In addition, the carboxyl and hydroxyl groups played a role in fixing metal in various parts of the C. bipinnatus cell wall.

Rhizobium induced modulation of growth and photosynthetic efficiency of Lens culinaris Medik. grown on fly ash amended soil by antioxidants regulation

Rhizobium leguminosarum is a rhizospheres' nitrogen fixing microbe that improves plant growth and productivity by releasing sufficient nutrient sources from the root, by biological nitrogen fixation, solubilization of phosphorous, acquisition of iron, and enhancement of antioxidant activity in plants. On this account, a greenhouse experiment was carried out to assess the feasibility of growing lentil (Lens culinaris Medik.) on fly ash (FA) amended soil (0%, 10%, 20%, and 30%) in combination with R. leguminosarum inoculation. The data was recorded at 45 day after sowing to evaluate the plant growth characteristics, photosynthetic variables (total chlorophyll and carotenoid pigments, carbonic anhydrase activity, nitrate reductase activity), damage markers (ROS, MDA, and cell viability), and defensive factors (proline and antioxidants). Among the FA-proportions tested, 20% proved most favorable in all the mentioned attributes while 30% concentration had negative repercussions on all the variables. Rhizobium inoculation had synergistic effect on all the concentrations being maximum on 20% FA. Thus, Rhizobium and 20% FA caused a significant increase on growth characteristics, photosynthetic pigments; stomatal behavior (aperture shape, size, and frequency of stomata); and activity of CA and NR, and cell viability. Application of Rhizobium on 20% FA was corroborated with decline in MDA and ROS contents and a coordinated enhancement of the activity of SOD, CAT, and POX. Therefore, 20% FA with fly ash-tolerant strain of Rhizobium in Lens culinaris may be utilized as an integrated approach towards sustainable agriculture and an impulse of management of fly-ash.

Individual and combined effects of chromium and ultraviolet-B radiation on defense system, ultrastructural changes, and production of secondary metabolite psoralen in a medicinal plant Psoralea corylifolia L

The present study focuses on the effects of individual and combined stress of chromium (Cr) and ultraviolet-B (UV-B) radiation on Psoralea corylifolia L. The experiment comprised four sets: (i) control, (ii) eUV-B (elevated UV-B i.e., ambient + 7.2 kJ m^-2 day^-1 UV-B), (iii) Cr (chromium; 30 mg kg^-1 soil), and (iv) Cr + eUV-B (chromium and elevated UV-B; Cr 30 mg kg^-1 and ambient + 7.2 kJ m^-2 day^-1 UV-B). The eUV-B and Cr individually and in combination showed the variable responses on ultrastructure, physiology and biomass however, the impact was more prominent under individual Cr treatment followed by Cr + eUV-B and eUV-B. Higher bioconcentration factor and the lowered translocation factor consequently led to a higher reduction in the below ground biomass and the lesser reduction in above ground biomass under Cr + eUV-B treatment as compared to individual Cr treatment. In addition, higher induction in the enzymatic (glutathione reductase, ascorbate peroxidase, superoxide dismutase, and glutathione-S-transferase) and non-enzymatic antioxidants (glutathione reduced) were found to be responsible for efficient scavenging of hydrogen peroxide and superoxide radical leading to lowered MDA content under combined treatment as compared to Cr treatment. Deposition of Cr as electron dense granules in the cytoplasm, vacuoles, and cell wall under Cr and Cr + eUV-B is contemplated as one of the cellular mechanisms of P. corylifolia against the toxicity of Cr. Psoralen increased under all treatments with a maximum increase under Cr + eUV-B treatment. Taken together our results accentuated that P. corylifolia can be grown in an area contaminated with Cr and has a higher influx of UV-B for the attainment of psoralen considering its pharmaceutical perspectives.

Chromium phytoextraction using Phyllostachys pubescens (Moso Bamboo)

In this study, a bamboo species, the Phyllostachys pubescens - Moso Bamboo (MB) -, was selected for its heavy metals accumulation and translocation potential to restore Chromium (Cr)-contaminated soil. In order to evaluate the MB Chromium growth, tolerance and the potential for phytoremediation using MB to restore Cr-contaminated soil, pot experiments were carried out in simulated Mediterranean conditions in a laboratory, in a controlled environment, at a temperature of 20 °C. The results showed that MB growth rate was 4.28 cm/week on average, with an irrigation flow of 1.644 mm/d. MB tolerance was tested over a 12-week irrigation period with the addition of Cr-contaminated water. Cr removal from soil was 43% starting from a Cr content of approx. 200 mg/kg dry weight (dw) and the quantity of Cr per gram of root and rhizome was equal to 1.31 mg/g dw, while the quantity of Cr per gram of stem and leaves was equal to 0.86 mg/g dw, after 12 weeks. Pot experiments confirm that phytoremediation using plants such as MB provides an alternative approach for handling Cr-contaminated soil.

The Effect of Immobilizing Agents on Zn and Cu Availability for Plants in Relation to Their Potential Health Risks

Soil contamination with heavy metals is one of the most important threats to the environment because they are easily incorporated into the food chain, threatening the health of plants, animals, and humans. In this study, the effectiveness of the introduced substances (compost and fly ash) was assessed in terms of its influence on the content of Cu and Zn in the soil, potential accumulation of these metals in the cultivated plants (camelina and oat), and thus in food products prepared from these plants. Therefore, the following indicators were used: bioconcentration factors calculated for the total amount (BCFT) and bioavailable amount of metals (BCFB) as well as gender-estimated daily intake (EDI) and health risk index (HRI). Regardless of gender, the EDI values ranged from 0.31 µg·kg−1 to 0.49 µg·kg−1 for Cu and from 0.9 µg·kg−1 to 1.8 µg·kg−1 for Zn in oat. For camelina, the calculated values were as follows: 4.1–8.5 µg·kg−1 for Cu and 7.1–12.1 µg·kg−1 for Zn. The HRI values were very low (in general 0.03–0.2), indicating no health risk connected with potential consumption of oat or camelina food products. The amounts of Cu and Zn in the crops grown on the soil amended with compost or fly ash were significantly lower (by 21–37% for oat and 14–34% for camelina) compared to the content of these metals in the control plants. Moreover, the levels of bioavailable metals decreased in soil as a result of the applied immobilizing agents. The study showed that the immobilization efficiency of compost and fly ash was comparable, and therefore the choice of either of these substances for the chemical remediation of soil contaminated with heavy metals is justified.

Stabilization of metals in sludge-amended soil using red mud and its effects on yield and oil quality of Brassica juncea cultivar Kranti

Prolonged application of sewage-sludge may cause excessive accumulation of metal(oid)s in soil, leading to phytotoxic effects. Spread of contaminants in soil can probably be hindered by using an effective metal(oid) stabilizer. Pot experiment in open field conditions was conducted for five months to evaluate the metal(oid) (Al, Cu, Zn, Cd and Cr) stabilization potential of red mud (RM) in sludge-amended soil and its effects on growth, yield, oil quality parameters and metal(oid) accumulations in Brassica juncea cultivar Kranti. The test plant was grown at different RM concentrations (0, 5, 10 and 15% w/w) in sludge-amended soil (soil/sludge: 2:1 w/w). As the total and phytoavailable metal(oid) concentrations in sludge were high, its application increased their concentrations in soil compared to the control (no RM and sludge). Increasing RM concentrations in sludge-amended soil effectively stabilized Cd followed by Cr, Cu, Zn and Al, leading to their reduced contents in plants coupled with enhanced growth performance and yield. Maximum plant (root and shoot) biomass (14.9%) and seed yield (40.4%) were found in 10% RM treatment, whereas oil content showed substantial increase with increasing RM treatments in sludge-amended soil. Mustard oil showed low rancidification, high long-chain fatty acids, saturated and polyunsaturated (ω-3 and ω-6) fatty acids within FAO ranges for edible oils under varying RM treatments compared to sludge-amended soil. Furthermore, high oleic and low erucic acid contents in mustard oil indicated a better oil quality under different RM treatments. Metal(oid) contents in seeds under different red mud treatments were within FAO/WHO limits for consumption. Thus, RM applications preferably 5 and 10% (w/w) in sludge-amended soil might be effective in stabilization of metal(oid)s using B. juncea cultivar Kranti coupled with better yield, improved oil quality and metal(oid)s within limits for human consumption.

Growth, biochemical, and antioxidant response of pot marigold (Calendula officinalis L.) grown in fly ash amended soil

The present study was carried out to determine the impact of FA application on growth performance, biochemical parameters, and antioxidant defense activity of Calendula officinalis. The results revealed that under a low dose of FA (40%) amended soil, the plant growth performance and metal tolerance index (MTI) were increased compared to control plants and further decreased with increased FA application (60%, 80%, and 100% FA). In addition, the incorporation of 40% FA in soil not only improved the physicochemical properties of soil but also increased the biochemical parameters in the Calendula plant, however, these parameters declined under high FA applications. It was also observed that antioxidant enzyme activity (SOD, CAT, POD, and APX) in leaves of Calendula officinalis increased at high FA application (100% FA) to combat heavy metal stress from FA. The overall study suggests that 40% FA amended soil is the best suitable dose for growing Calendula officinalis and can be considered as metal tolerant species for phytoremediation of 40% FA amended soil.Novelty statement: Fly ash (FA) management is a major problem nowadays. The present study was carried out for FA utilization and to determine the impact of FA amended soil on growth performance, antioxidant properties, and biochemical attributes of Calendula officinalis. This is a sustainable approach in which waste (FA) utilization was done simultaneously with the enhancement in response of the medicinally potent Calendula species. The novelty of this study also suggests that Calendula has phytoremediation potential for remediation of heavy metal polluted soil. Further, the relationship between the growth, biochemical parameters, and antioxidant defense mechanism of Calendula grown on FA amended soil was studied which has not been studied so far. It was found that Calendula is a hyperaccumulator that can adapt to heavy metal stress from FA due to its ability to mitigate oxidative damage. Statistical analysis (ANOVA, Duncan's multiple range test, and PCA) was done for the results obtained using SPSS (11.5) and Origin 8 Pro software.

Modeling the Carbon Sequestration Potential of Multifunctional Agroforestry-Based Phytoremediation (MAP) Systems in Chinandega, Nicaragua

Global sustainability challenges associated with increasing resource demands from a growing population call for resource-efficient land-use strategies that address multiple sustainability issues. Multifunctional agroforestry-based phytoremediation (MAP) is one such strategy that can simultaneously capture carbon, decontaminate soils, and provide diverse incomes for local farmers. Chinandega, Nicaragua, is a densely populated agricultural region with heavily polluted soils. Four different MAP systems scenarios relevant to Chinandega were created and carbon sequestration potentials were calculated using CO2FIX. All scenarios showed the potential to store significantly more carbon than conventional farming practices, ranging from 2.5 to 8.0 Mg CO2eq ha−1 yr−1. Overall, carbon sequestration in crops is relatively small, but results in increased soil organic carbon (SOC), especially in perennials, and the combination of crops and trees provide higher carbon sequestration rates than monoculture. Changes in SOC are crucial for long-term carbon sequestration, here ranging between 0.4 and 0.9 Mg C ha−1 yr−1, with the most given in scenario 4, an alley cropping system with pollarded trees with prunings used as green mulch. The adoption rate of multifunctional strategies providing both commodity and non-commodity outputs, such as carbon sequestration, would likely increase if phytoremediation is included. Well-designed MAP systems could help reduce land-use conflicts, provide healthier soil, act as climate change mitigation, and have positive impacts on local health and economies.

Ascorbate glutathione antioxidant system alleviates fly ash stress by modulating growth physiology and biochemical responses in Solanum lycopersicum

Tomato plants (Solanum lycopersicum L.) were developed in soils with different fly ash (FA) amendments (25, 50, 75, 100% FA) to measure the effects of FA on metal accumulation, chlorophyll pigments, chlorophyll fluorescence, growth, biomass, gas exchange parameters, and the ascorbate glutathione pathway (AsA-GSH). The metal concentration was much higher in FA compared to the garden soil/(control). The observed metal translocation was higher in roots than shoots. Plants raised in soils treated with 50% or more FA showed significant decreases in growth, biomass, gas exchange parameters, protein, chlorophyll pigments, and fluorescence parameters. Additionally, a significant increase in antioxidants under higher FA-amended soils were observed. Our results showed that the ability of Solanum lycopersicum plants to effectively synchronize the actions of antioxidant enzymes associated in reactive oxygen species (ROS) scavenging - notably superoxidase dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) - with good maintenance of the AsA/DHA ratio, that could be connected to FA stress tolerance. The toxic metals present in FA caused oxidative stress in Solanum lycopersicum, as evident from the increase in electrolyte leakage (EL), lipid peroxidation (MDA), and ROS levels. Furthermore, the AsA-GSH cycle plays a key role in alleviating oxidative damage caused by FA application.

Development of phytoremediator screening strategy and exploration of Pennisetum aided chromium phytoremediation mechanisms in soil

Screening of chromium (Cr) phytoremediators (i.e., hyperaccumulator plants and accumulation plants) is essential for the phytoremediation of Cr-contaminated soils but less tackled previously. In this study, we proposed a stepwise strategy for screening Cr phytoremediators and explored tolerance mechanism of the screened species. To achieve effective screening of Cr phytoremediators, seed germination, hydroponic, and pot experiment were performed sequentially, and an improved indicator system was established accordingly. Pennisetum was selected from nine plants, with its high growth rate and Cr remediation efficiency successfully demonstrated in the field. Antioxidant enzymes (i.e., superoxide dismutase (SOD) and catalase (CAT)) and photosynthesis under Cr stress were monitored for tracking the tolerance mechanism. Results showed that the enhanced SOD and CAT contributed to the strong tolerance of Pennisetum to Cr. The SOD and CAT were positively correlated with net photosynthetic rate (Pn), resulting in a phenomenon that Cr had no significant effect on Pn of Pennisetum even at 400 mg kg^-1. The research findings helped obtain powerful Cr phytoremediators, deepen our understanding of the tolerance mechanisms associated with phytoremediation, and eventually facilitate effective Cr removal in soil.

Nickel and cadmium phytoextraction efficiencies of vetiver and lemongrass grown on Ni-Cd battery waste contaminated soil: A comparative study of linear and nonlinear models

A comparative assessment of the phytoremediation efficiency of two tolerant grass species viz. vetiver and lemongrass were performed in pots against simulated Ni-Cd battery electrolyte waste (EW) contaminated soil (EW1%, EW2% and EW4% w/w). Ni (μg g^-1) accumulation was higher in shoots (36.8) and roots (252.9) of vetiver than in lemongrass (12.5 and 79.7, respectively). While the same trend was true for Cd (μg g^-1) accumulation in vetiver and lemon grass roots (232.2 and 147.2, respectively), however, the accumulation in vetiver shoot (43.4) was less than in lemongrass (99.9). The bioaccumulation factor of metals in both grasses increased with EW contamination. Vetiver was tolerant towards EW toxicity than lemongrass, as it exhibited lesser decline in morphological parameters, lesser rise in TBARS against the doses of EW. The activities of SOD, APX, POD enzymes were higher in vetiver whereas, only GR in lemongrass. Multiple linear regression model show, pH had strong and positive influence over the Ni and Cd uptake by the plants whereas, phosphate, OM and bioavailable metals influenced negatively. The higher R² (>0.9) and Chi-square values ≤ 1 in sigmoid non-linear model demonstrates robustness of the model for predicting the Ni and Cd accumulation (M_HM) in both the grasses. Ni accumulation was higher than Cd, roots had greater accumulation of heavy metal and vetiver was a greater accumulator of Ni and Cd from EW the contaminated soil than lemongrass.

Comparing chromium phyto-assessment in Brachiaria mutica and Leptochloa fusca growing on chromium polluted soil

Industrial discharge of chromium (Cr) into environment puts serious threat on living beings due to its potent toxicity. Phytostabilization, a type of in-situ phytoremediation is aimed to immobilize and stabilize the toxic elements in soil using root system of metal resistant potential plants. To evaluate the phytostabilization potential of two grass species Brachiaria mutica and Leptochloa fusca, a pot study was conducted using soil spiked with different concentrations of Cr (control, 25, 50 and 100 mg kg^-1). Three plants were sown in each pot with three replications and arranged following completely randomized design. After three months of growth, the plants were harvested and above and below ground plant's parts were analyzed for various growth and physiological parameters. Data revealed that plant biomass, chlorophylls and carotenoids reduced substantially with increasing Cr concentration. Antioxidant enzymatic activity increased significantly in L. fusca as compared to B. mutica with increasing Cr levels (up to 50 mg kg^-1), then reduced at maximum Cr level (100 mg kg^-1) in both grasses. Leptochloa fusca performed better with maximum root Cr accumulation 93.7 μg plant^-1, shoot Cr accumulation 24.7 μg plant^-1, root bioconcentration factor (BCF) 2.0, shoot BCF 0.08, shoot TF 0.06 and MTI 87%. While B. mutica showed maximum root Cr accumulation 18.4 μg plant^-1, shoot Cr accumulation 7.6 μg plant^-1, shoot BCF 0.03, root BCF 1.28, shoot TF 0.04, and MTI 56%. These results showed that L. fusca possessed good potential with better Cr bioaccumulation, MTI, BCF and antioxidant activities compared to B. mutica. Hence L. fusca can be used as good phytostabilizing agent for the soils contaminated with lower to moderate levels of Cr.

Application potential of Chrysopogon zizanioides (L.) Roberty for the remediation of red mud-treated soil: an analysis via determining alterations in essential oil content and composition

The present study is of significant importance because phytoremediation of metals in red mud using essential oil-bearing plants such as Chrysopogon zizanioides (commonly known as vetiver) is a potential alternative for on-site management of the waste in most economical and sustainable way. Vetiver is a potential metal tolerant plant with high economic value; therefore the present study was accomplished to evaluate the impacts of metals in red mud on essential oil content and composition, used for remediation and stabilization of dumps. Novelty of the study is that, it aimed to utilize red mud along with sewage-sludge to cultivate vetiver which offers twin benefits, i.e. phytoremediation of metals in red mud coupled with improved quantity and quality of high valued essential oil without metal contamination.

Phytostabilization of coal mine overburden waste, exploiting the phytoremedial efficacy of lemongrass under varying level of cow dung manure

A pot study was performed to assess the phytoremedial potential of Cymbopogon citratus (D.C.) Staf. for reclamation of coal mine overburden dump wastes, emphasizing the outcome of amendment practices using cow dung manure (CM) and garden soil mixtures on the revegetation of over-burden wastes (OB). Wastes amendment with cow dung manure and garden soil resulted in a significant increase in soil health and nutrient status along with an increment in the phytoavailability of Zn and Cu which are usually considered as micronutrients, essential for plant growth. A significant increment in the total biomass of lemongrass by 38.6% under CM20 (OB: CM 80:20) was observed along with improved growth parameters under amended treatments as compared to OB (100% waste). Furthermore, the proportionate increases in the assimilative rate, water use efficiency, and chlorophyll fluorescence have been observed with the manure application rates. Lemongrass emerged out to be an efficient metal-tolerant herb species owing to its high metal-tolerance index (>100%). Additionally, lemongrass efficiently phytostablized Pb and Ni in the roots. Based on the strong plant performances, the present study highly encourages the cultivation of lemongrass in coal mining dumpsites for phytostabilization coupled with cow-dung manure application (20% w/w).

Growth Performance of Jatropha curcas Cultivated on Local Abandoned Bauxite Mine Soil

Lack of regulation in bauxite mining has caused land contamination in Malaysia. Land rehabilitation requires plants with excellent adaptability to adverse conditions. Inedible, economical viable crops with environmental co-benefits, like phytoremediation, are preferred. In this study, Jatropha curcas was evaluated for its growth performance in bauxite mine soil. Topsoil and exposed subsoil were sampled from a bauxite mine at Bukit Goh, Kuantan and used for growing J. curcas for 90 days under greenhouse conditions. The soil physicochemical properties, plant growth parameters (increase in number of leaves, plant height, and basal diameter), and oil yield were determined. The findings showed that the mine soils had lower nutrient status than unmined soil as reflected by the total C, N, P, and K values. Al, Fe, and Pb were relatively high in topsoil and subsoil. Plants grown in both mine soils recorded significantly lower increases in plant height and basal diameter but higher increases in number of leaves than that of nursery soil. Oil yield was significantly different between the plants grown in subsoil (46.54%) and topsoil (41.65%). The study demonstrated that J. curcas has the potential to be cultivated as an alternative crop in bauxite mine soil.

Invisible contaminants and food security in former coal mining areas of Santa Catarina, Southern Brazil

BACKGROUND

Mining activities have environmental impacts due to sediment movement and contamination of areas and may also pose risks to people's food security. In Brazil, the majority of coal mining activities are in the south, in the Santa Catarina carboniferous region. In this region, previously mined areas contaminated with heavy metals frequently occur nearby inhabited zones. Mining is part of the daily lives of local communities, and its environmental impacts are visible in the landscape; however, plants with medicinal and food use from these areas can be still consumed. Heavy metals are contaminants that do not have odor, color, or taste, and are therefore difficult to detect. We aimed to verify whether people use plants from contaminated mine areas, and understand which factors can influence the use of these resources, even from areas visibly impacted.

METHODS

We conducted 195 semi-structured interviews with residents from 14 areas nearby abandoned mines in the main municipalities of the Santa Catarina carboniferous region. We asked each interviewee about the length of time they lived in the region, their perception of the quality of the environment, and what plant species were used and for what purpose. We constructed generalized multivariate linear models to verify which variables can affect the group of species mentioned and generalized linear models to verify which variables can affect the total number of citations. We estimated the frequency of citing species collected using the Smith index.

RESULTS

From all interviewees, 127 (65%) reported collecting plants for medicinal and food use, directly from contaminated mine areas. Long-term residents, as well as those who noticed more environmental changes (positive and negative), cited more plants used and had more detailed knowledge of plant use in their communities. When asked if they were aware of the possible contamination of mined areas, 85% said they knew about it. However, only 10% associated negative health effects with the use of plant species collected in contaminated mined areas.

CONCLUSIONS

Our study demonstrates that people living nearby contaminated areas use and consume locally sourced plants, e.g., people know little about the danger of this contamination in their food and the risk of these contaminants to their health. These results also reveal a lack of information about contamination, as well as a lack of actions that include local communities in contaminated area restoration strategies. This situation poses a risk to the food security of the people living nearby former coal mining areas.

Growth and yield of lemongrass (Cymbopogon citratus) in fly ash with nutrient amendments and Mycorrhiza for three-ratoon period

Environmental and health concerns due to fly ash dumpsite could be prevented by phytostabilization using non-food crops that will prevent pollutants' migration and provide additional economic returns. The growth and yield of Cymbopogon citratus in the fly ash dumpsite were evaluated in a pot experiment for a three-ratoon period. Application of compost, mycorrhiza, and NPK fertilizer, singly or the combination compost + mycorrhiza, compost + NPK fertilizer, mycorrhiza + NPK fertilizer, and compost + mycorrhiza + NPK fertilizer had increased the dry matter yield and the total essential oil content compared to the control. NPK fertilization regardless of compost and mycorrhiza resulted in more than 5-fold yield over the control. Compost lowered the available heavy metals from fly ash and supplied some essential nutrients while mycorrhiza could have improved water and nutrients acquisition and uptake. However, the nutrients supplied by the compost cannot sustain the requirements for the three-ratoon period. NPK fertilization, compost, and mycorrhiza reduced the concentrations of Cr, Cu, Ni, and Pb in shoots and in essential oil. Overall, the combined application of compost, mycorrhiza, and NPK fertilization at the rate of 120-90-90 kg NPK/ha could enhance the phytostabilization potential of C. citratus in fly ash and produce a high amount of essential oil with a low concentration of heavy metals that could be safe for human use. Novelty Statement Phytostabilization using aromatic plants is a potential alternative for the on-site pollution mitigation strategy of fly ash dumpsite. In this report, the appropriateness of lemongrass as a phytostabilization agent for fly ash dumpsite of the Morupule Power Plant in Botswana was evaluated for a three-ratoon period. This is the first report from Botswana that considered the effect of soil amendments, mycorrhiza inoculation, and NPK fertilization on the growth and yield of lemongrass in fly ash as well as the heavy metal availability and uptake. The results from this study are very useful for identifying site-specific cultural management strategy of using lemongrass in the phytostabilization of fly ash dumpsite in Botswana and elsewhere.

Characterization of Trichoderma asperellum RM-28 for its sodic/saline-alkali tolerance and plant growth promoting activities to alleviate toxicity of red mud

Red mud (RM) is a highly alkaline, saline and sodic solid by-product released by alumina industries, which pose an economical and environmental problem and establishment of vegetation on these sites is a big challenge. In the present study, a fungus RM-28 exhibiting high tolerance to alkaline (pH 12), saline/sodic (NaCl 4%) was isolated from RM flooded rhizosphere soil of bermudagrass and tested its ability to reduce RM toxicity and promote the growth of sorghum-sudangrass seedlings. This fungus also exhibited high tolerance to heavy metal(loid)s (HMs) and desirable plant growth-promoting traits. This fungus was identified as Trichoderma asperellum based on its internal transcribed spacer (ITS) of rDNA and translation elongation factor-1α (TEF 1α) gene analysis. This fungus was effective in reducing the pH and solubilizing tricalcium phosphate under high alkaline and saline conditions in vitro. Further, RM-28 inoculation significantly lowered the pH and EC of the red mud from 11.8 to 8.2 and 2.23 to 1.42, respectively. Inoculation of RM-28 significantly improved the growth, chlorophyll content and reduced the oxidative stress of sorghum-sudangrass seedlings grown in red mud leachate. These observations suggest that T. asperellum RM-28 serves as potential source for the establishment of vegetation on red mud/red mud contaminated soils.

Screening of most potential candidate among different lemongrass varieties for phytoremediation of tannery sludge contaminated sites

One of the most sustainable approaches for reclamation of heavy metal contaminated sites is by phytoremediation. Cultivation of aromatic plants in such areas has been proposed by a number of researchers as it fulfills the purpose of phytoremediation alongside monetary benefits. A pot experiment was conducted to screen out most potential candidate among different lemongrass varieties which can be recommended to be grown in tannery effluent contaminated sites. Four consecutive harvests of nine varieties of lemongrass were tested. Translocation factor (TF) < 1 for chromium and cadmium whereas >1 for nickel and lead was observed in all varieties. Bioconcentration factor (BF) > 1 was observed for chromium in Suwarna variety. Photosynthetic pigments, growth parameters, antioxidants, oil content, and yield were highly correlated. Neighbor joining (NJ) cluster analysis was performed to predict the relationship between varieties according to their chromium uptake potential. Endurance of varieties towards metal stress was assessed using chlorophyll a fluorescence kinetics. Maximum reduction potential of chromium (70.07%), lead (85.29%), and cadmium (77.36%) was observed in Suwarna variety. Our study indicated that lemongrass acts as potential phytoextractor for nickel and lead. Suwarna variety appeared to be the best candidate among all the varieties tested owing to its higher biomass and metal uptake potential.

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.

The interactions of metal concentrations and soil properties on toxic metal accumulation of native plants in vanadium mining area

High demand of Vanadium (V) in high-strength steel and battery manufacturing industry led to extensive V mining activity in China, and caused multi-metal pollution of soil around V mining area. To understand the phytoremediation potentials of native plants grown in V mining area, and the effect of soil properties and soil metal concentrations on toxic metal accumulations of native plants. Setaria viridis, Kochia scoparia and Chenopodium album were sampled from different sites in V mining area, soil properties, soil metal concentrations and metal accumulation amount of investigated plants were measured, bioaccumulation (BAF) and translocation (TF) efficiencies were calculated. Soil pH, cation exchange capacity (CEC) and available phosphorous (P) can significantly affect V and copper (Cu) uptake in the shoots of Setaria viridis while soil metal contents were lower than the permissible limits. Soil pH can significantly affect V accumulations in the roots and shoots of Kochia scoparia grown in slightly V polluted soils. Setaria viridis exhibited TF > 1 for moderately V and slightly chromium (Cr) polluted soils, and BAF>1 for slightly Cu contaminated soils respectively. Kochia scoparia and Chenopodium album showed TF > 1 and BAF>1 for slightly V polluted soils, respectively. Setaria viridis was practical for in situ phytoextractions of moderately V and slightly Cr polluted soils, and phytostabilization of slightly Cu contaminated soils. Kochia scoparia and Chenopodium album could be used as phytoextractor and phytostablizer in slightly V polluted soils in V mining area. Metal uptake of native plants grown in slightly multi-metal contaminated sites in V mining area can be manipulated by altering soil properties.

Growth and physiological response of lemongrass (Cymbopogon citratus (D.C.) Stapf.) under different levels of fly ash-amended soil

Revegetation with metal tolerant plants for management of fly ash deposits is an important environmental perspective nowadays. Growth performance, photosynthesis, and antioxidant defense of lemongrass (Cymbopogon citratus (D.C.) Stapf.) were evaluated under various combination of fly ash amended with garden soil in order to assess its fly ash tolerance potential. Under low level of fly ash (25%) amended soil, the plant growth parameters such as shoot, root, and total plant biomass as well as metal tolerance index were increased compared to the control plants grown on garden soil, followed by decline under higher concentration of fly ash (50%, 75% and 100%). In addition, leaf photosynthetic rate, stomatal conductance, and photosystem (PS) II activity were not significantly changed under low level of fly ash (25%) amended soil compared to the garden soil but these parameters were significantly decreased further with increase of fly ash concentrations. Furthermore, increase of activities of some antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and guaiacol peroxidase over control were noticed in lemongrass under all fly ash treatments. Taken together, the study suggests that lemongrass can be used for phytoremediation of fly ash at 25% amended soil.

Toxic metal tolerance in native plant species grown in a vanadium mining area

Vanadium (V) has been extensively mined in China and caused soil pollution in mining area. It has toxic effects on plants, animals and humans, posing potential health risks to communities that farm and graze cattle adjacent to the mining area. To evaluate in situ phytoremediation potentials of native plants, V, chromium, copper and zinc concentrations in roots and shoots were measured and the bioaccumulation (BAF) and translocation (TF) efficiencies were calculated. The results showed that Setaria viridis accumulated greater than 1000 mg kg^-1 V in its shoots and exhibited TF > 1 for V, Cr, Zn and BAF > 1 for Cu. The V accumulation amount in the roots of Kochia scoparia also surpassed 1000 mg kg^-1 and showed TF > 1 for Zn. Chenopodium album had BAF > 1 for V and Zn and Daucus carota showed TF > 1 for Cu. Eleusine indica presented strong tolerance and high metal accumulations. S. viridis is practical for in situ phytoextractions of V, Cr and Zn and phytostabilisation of Cu in V mining area. Other species had low potential use as phytoremediation plant at multi-metal polluted sites, but showed relatively strong resistance to V, Cr, Cu and Zn toxicity, can be used to vegetate the contaminated soils and stabilise toxic metals in V mining area.