Phytoremediation: a technology using green plants to remove contaminants from polluted areas

Research progress on remediation of organochlorine pesticide contamination in soil

Deteriorated soil pollution has grown into a worldwide environmental concern over the years. Organochlorine pesticide (OCP) residues, featured with ubiquity, persistence and refractoriness, are one of the main pollution sources, causing soil degradation, fertility decline and nutritional imbalance, and severely impacting soil ecology. Furthermore, residual OCPs in soil may enter the human body along with food chain accumulation and pose a serious health threat. To date, many remediation technologies including physicochemical and biological ways for organochlorine pollution have been developed at home and abroad, but none of them is a panacea suitable for all occasions. Rational selection and scientific decision-making are grounded in in-depth knowledge of various restoration techniques. However, soil pollution treatment often encounters the interference of multiple factors (climate, soil properties, cost, restoration efficiency, etc.) in complex environments, and there is still a lack of systematic summary and comparative analysis of different soil OCP removal methods. Thus, to better guide the remediation of contaminated soil, this review summarized the most commonly used strategies for OCP removal, evaluated their merits and limitations and discussed the application scenarios of different methods. It will facilitate the development of efficient, inexpensive and environmentally friendly soil remediation strategies for sustainable agricultural and ecological development.

Intercropping of kenaf and soybean affects plant growth, antioxidant capacity, and uptake of cadmium and lead in contaminated mining soil

Intercropping is considered a sustainable agricultural practice that can reduce the environmental impacts on agriculture. Our study investigated the morphology, physiology, and cadmium (Cd) and lead (Pb) uptake of kenaf (Hibiscus cannabinus L.) and soybean (Glycine max L.) under intercropping in mining soil. Results showed that mutual intercropping is conducive to the growth and biomass accumulation of kenaf and soybean, compared to their respective monoculture. Intercropping increased the relative chlorophyll index in kenaf, while that in soybean had no significant effect. Furthermore, intercropping increased the antioxidant enzyme activity of kenaf, while that of soybean reduced or had no significant effect. The content of malondialdehyde (MDA) was decreased in both of the species. Compared to their respective monoculture, Cd content was increased in kenaf leaves and reduced in soybean roots. Moreover, intercropping decreased the Pb content in tissues of both the species, except that Pb content of kenaf roots was increased. At the same time, root, leaf, or stem bioconcentration factors also performed the same trend, and TF was less than 1. These results indicated that intercropping can increase the plant growth and decrease the metal content in plant tissues. Present findings could provide support for future research on kenaf and soybean cultivation in contaminated lands. In addition, the present study strengthens our understanding about the effectiveness of intercropping system on heavy metal-contaminated lands for sustainable agricultural production.

Phytoremediation as a way to clean technogenically polluted areas of Kazakhstan

One of the most serious problems worldwide is heavy metal (HM) pollution. HMs can have a toxic effect on human health and thus cause serious diseases. To date, several methods have been used to clean environments contaminated by HMs, but most of them are expensive, and it is difficult to achieve the desired result. Phytoremediation is currently an effective and affordable processing solution used to clean and remove HMs from the environment. This review article discusses in detail the technology of phytoremediation and mechanisms of HM absorption. In addition, methods are described using genetic engineering of various plants to enhance the resistance and accumulation of HMs. Thus, phytoremediation technology can become an additional aid to traditional methods of purification.

Evaluation of trace metal accumulation in six vegetable crops intercropped with phytostabilizing plant species, in a French urban wasteland

The extensive development of agriculture in urban and peri-urban wastelands polluted with several trace elements (TE) poses risks to human health through contaminated food products. The objective was to explore the accumulation of TE in the various parts of vegetable crop plants (tomato, French bean, radish, potato, spinach, and leek) intercropped with phytostabilizing plant species (ryegrass and white clover, respectively). Field studies were conducted in a multicontaminated French urban wasteland with Cd, Cu, Pb and Zn, and an alkaline soil pH. Analyses of the respective non-edible parts of monocultured vegetable crops showed accumulation of all TE, mostly Zn, then Pb and Cu, and finally Cd. The corresponding TE accumulation factors (soil to plant) were all below 0.25. In the edible parts, average concentrations for TE were above the limit values, according to European and Chinese standards. TE contents in the phytostabilizing species chosen were in the same orders of magnitude and the same ranking as described for vegetable crops and most accumulation was in the roots. Unexpectedly, the presence of the phytostabilizing plants had a very strong positive impact on the soil to plant accumulation factor. Moreover, the edible plant parts were poorly impacted by the co-cropping with phytostabilizing plants.

Antimony induced structural and ultrastructural changes in Trapa natans

Antimony (Sb) is considered as a priority toxic metalloid in the earth crust having no known biological function. The current study was carried out in a hydroponic experiment to study the accumulation of ecotoxic Sb in subcellular level, and to find out the ultrastructural damage caused by Sb in different vegetative parts of Trapa natans. Sb-induced structural and ultrastructural changes of T. natans were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). Experimental plants were exposed to different Sb(III) treatments: SbT1 (1.5 μmol/L), SbT2 (40 μmol/L) and SbT3 (60 μmol/L). Calculated bioconcentration factor (BCF) and translocation factor (TF) showed that at higher concentration (SbT2, SbT3), T. natans is a potent phytoexcluder whereas it can translocate a substantial amount of Sb to the aerial parts at lower concentration (SbT1). SEM analysis revealed Sb-mediated structural changes in the size of stomatal aperture, intercellular spaces and vascular bundles of different vegetative tissues of T. natans. TEM results showed subcellular compartmentalization of Sb in vacuole and cell wall as electron dense deposition. This is considered as a part of strategy of T. natans to detoxify the deleterious effects under Sb stress conditions. Fourier transform infrared spectroscopy (FTIR) study of plant biomass revealed possible metabolites of T. natans which can bind Sb.

Cadmium uptake and transfer by Sedum plumbizincicola using EDTA, tea saponin, and citric acid as activators

Sedum plumbizincicola (S. plumbizincicola) is known as a sufficient plant for phytoremediation of cadmium (Cd) polluted soils. This study aimed to investigate the effects of ethylene diamine tetraacetic acid (EDTA), tea saponin (TS), and citric acid (CA) on Cd uptake and translocation by S. plumbizincicola. To do so, using a pot experiment, we set four concentration levels of activators (1, 3, 5, and 10 mmol L^-1) and a control (CK). Results showed that none of the applied activators had significant impact on soil pH. Except for CA-10, the concentration of available Cd in Cd polluted soils increased by 65.8-72.9% compared with CK. The EDTA-1, CA-1, and TS-5 treatments caused significant increases of 52.3, 67.2, and 38.4%, respectively, in the biomass of aerial parts of S. plumbizincicola (p < 0.05) compared with CK. Except for CA-3, activators increased Cd accumulation in the aerial parts of plants by 47-124% compared with CK. Of all activators, EDTA-3 caused the highest Cd accumulation of 6.64 g pot^-1 in the aerial plant tissues followed by CA-10 (6.25 g pot^-1) and TS-1 (5.48 g pot^-1). Finally, our results suggested that the application of S. plumbizincicola together with different activators sufficiently reduced soil total Cd by 4.64-48.4% compared with CK. These findings suggest that appropriate application of EDTA, TS, and CA can promote phytoremediation of Cd contaminated soils by hyper-accumulators. In particular, the combined use of EDTA and S. plumbizincicola is an affordable and promising strategy for remediation of Cd contaminated soil.Novelty statement: Sedum plumbizincicola (S. plumbizincicola) is a well-known hyper-accumulator plant for remediation of cadmium (Cd) and zinc (Zn) contaminated soils. In addition, low molecular rganic acids and macromolecular chelating agents can improve the solubility and leaching of soil heavy metals. In the present work, we examined the combined effects of three activators (EDTA, tea saponin, and citric acid) with S. plumbizincicola to remediate a Cd contaminated soil in Anhui Province, East China. Our results indicated the effectiveness of these activators to increase soil available Cd, as well as improving the biomass of S. plumbizincicola and its Cd uptake. We believe that this study provides an efficient approach to increase the uptake of Cd by S. plumbizincicola, restoring Cd contaminated soils. Nevertheless, excessive activators may have adverse effects on soil aggregates and soil microorganisms. Therefore, it is necessary to control the amount of chelating agents and subsequently the deterioration of soil quality.

Physiological and Transcriptomic Response of Grey Poplar (Populus ×canescens Aiton Sm.) to Cadmium Stress

(1) Background: Populus ×canescens (Aiton) Sm. is a fast-growing woody plant belonging to the family Salicaceae. Two poplar genotypes characterized by unique phenotypic traits (TP11 and TP20) were chosen to be characterized and tested for a physiological and transcriptomic response to Cd stress. (2) Methods: A comparative analysis of the effects of exposure to high cadmium (Cd) concentrations (10 µM and 100 µM) of TP11 and TP20 was performed. (3) Results: Neither of the tested Cd concentration negatively affected plant growth; however, the chlorophyll content significantly decreased. The potassium (K) content was higher in the shoots than in the roots. The magnesium concentrations were only slightly affected by Cd treatment. The zinc content in the shoots of TP20 was lower than that in the shoots of TP11. Cd accumulation was higher in the roots than in the shoots. After 10 days of exposure, 10 µM Cd resulted in comparable amounts of Cd in the roots and shoots of TP20. The most significant change in transcript amount was observed in endochitinase 2, 12-oxophytodienoate reductase 1 and phi classglutathione S-transferase. (4) Conclusions: Our study provided new insights for effective assessing the ability of different poplar genotypes to tolerate Cd stress and underlying Cd tolerance.

Phytoremediation and Bioremediation of Pesticide-Contaminated Soil

Management and destruction of obsolete pesticides and the remediation of pesticide-contaminated soil are significant global issues with importance in agriculture, environmental health and quality of life. Pesticide use and management have a history of problems because of insufficient knowledge of proper planning, storage, and use. This manuscript reviews recent literature with an emphasis on the management of obsolete pesticides and remediation of pesticide-contaminated soil. The rhizosphere of plants is a zone of active remediation. Plants also take up contaminated water and remove pesticides from soil. The beneficial effects of growing plants in pesticide-contaminated soil include pesticide transformation by both plant and microbial enzymes. This review addresses recent advances in the remediation of pesticide-contaminated soil with an emphasis on processes that are simple and can be applied widely in any country.

Biomass and phytoextraction potential of three ornamental shrub species tested over three years on a large-scale experimental site in Shanghai, China

Issues related to environmental degradation are of increasing concern worldwide. In urban Shanghai, many plant species used for ornamental purposes grow under harsh conditions yet show good resistance to pollution. Twelve shrub species were tested in a previous study to evaluate their capacity to tolerate and absorb inorganic contaminants. Among these, Hibiscus mutabilis and H. hamabo and Senna corymbosa, presented good performance and were tested over three growing seasons in a large experimental design (2000 m²) where the soil was spiked with salts of Cu, Pb, or Zn. Each year of the study, all plants were cut and biomass was harvested and analyzed. Despite the relatively high concentration of metals in plots, no signs of toxicity were observed. Concentrations of metals in root tissues were generally much higher than those found in aerial parts. The bioconcentration factor values were generally very low, but the high biomass yield produced by H. mutabilis led to significant removal of Cu and Zn. No difference in the quantity of Pb extracted was found between species. As these plants respond well to coppicing, it may be possible to gradually eliminate contaminants from soils. Their use can also embellish the landscape while generating many other ecological services.

From cells highly tolerant to Zn and Pb to fully fertile plants - Selection of tolerant lines with in vitro culture

Viola arvensis cells were selected after treatment with Zn or Pb and regenerated into plants likely to have higher tolerance levels than the initial plant. The surviving cells in the suspension treated with 2000 μM of Zn, 2000 μM of Pb or 0 μM for 72 h were maintained on a solidified half-strength MS medium supplemented with 0.5 mg L^-1 TDZ to induce divisions and organogenesis. The adventitious shoots obtained were rooted on a half-strength MS medium with 1 mg L^-1 IBA. Regenerants derived from the Zn- and Pb-treated cells were vigorous and fully fertile. The in vitro conditions and metal impact generated a low genome alteration and overall low genetic diversity of regenerants compared to the initial plant and plants from the natural population. The cells of regenerants obtained after Pb treatment represented an approximately 12% higher tolerance level to Pb than the cells of the initial plant. This is the first report of plant regeneration from highly tolerant cells selected by heavy metal treatment. Regenerants successfully obtained in vitro could be considered as a source material for the recultivation of areas polluted with heavy metals.

Monitoring soil biological properties during the restoration of a phosphate mine under different tree species and plantation types

Open-pit mining activities for minerals and metals have left an international legacy of highly polluted soils and degraded landscapes. Reforestation is usually supposed to restore soil fertility and ecosystem services, and therefore to remediate and recover polluted sites. However, our understanding of the effects of tree species and recovery time on the restoration of abiotic and biotic soil properties remains scarce. In this study, the effects of a series of restoration chronosequence (unrestored control, 10-year, 20-year, and natural forest) and plantation types (nitrogen-fixing broad-leaved Alnus nepalensis and coniferous Cupressus torulosa monocultures, as well as their mixed plantation) on soil physicochemical and biological properties were explored in a phosphate mine. Our results showed that soil quality index (SQI), which integrates important soil physical, chemical, and biological parameters including bulk density, soil organic carbon and microbial biomass, could provide valuable information about soil health. The average SQI values of 20-year plantations were 1.55 times of 10-year plantations, and the mixed plantation was 1.13 and 1.27 times of A. nepalensis and C. torulosa monoculture, respectively. Thus, recovery time, as well as plantation type, were the main determinants of the alterations in key soil conditions during the phosphate mining restoration. At the beginning restoration (10 years), A. nepalensis monoculture performed better than C. torulosa, providing an efficient restoration strategy for early revegetation. The mixed plantation of C. torulosa and A. nepalensis showed the higher moisture and soil organic carbon than did the monocultures, especially after 20 years of revegetation. Hence, our findings address a helpful guideline for selection of tree species and plantation practices, thereby aiding in long-term success of restoration.

Long-term responses of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) to the contamination of light soils with diesel oil

Research into trees plays a very important role in evaluations of soil contamination with diesel oil. Trees are ideal for reclaiming contaminated soils because their large biomass renders them more resistant to higher concentrations of pollutants. In the literature, there is a general scarcity of long-term studies performed on trees, in particular European beeches. The aim of this study was to evaluate the responses of Scots pines and European beeches grown for 8 years on soil contaminated with diesel oil. Selected morphological and physiological parameters of trees were analyzed. The biomass yield of Scots pines was not significantly correlated with increasing concentrations of diesel oil, but it was more than 700% higher than in European beeches. Scots pines were taller and had a larger stem diameter than European beeches during the 8-year study. The diameter of trees grown on the most contaminated soil was reduced 1.5-fold in Scots pines and more than twofold in European beeches. The length of Scots pine needles from the most contaminated treatment decreased by 50% relative to control needles. The shortest needles were heaviest. The fluctuating asymmetry (FA) of needle length was highest in Scots pines grown on the most contaminated soil, whereas the reverse was noted in the FA of needle weight. Diesel oil decreased the concentrations of chlorophylls a and b, total chlorophyll, and carotenoids. The Fv/Fm ratio of needles and leaves was influenced by the tested concentrations of diesel oil. The results of the study indicate that the Scots pine better adapts (grows more rapidly and produces higher biomass) to long-term soil contamination with diesel oil than the European beech. In European beeches, growth inhibition and leaf discoloration (a decrease in chlorophyll content) were observed already after the first year of the experiment, which indicates that 1-year-old seedlings of European beech are robust bioindicators of soil contamination with diesel oil.

Licorice Root Extract Boosts <i>Capsicum annuum</i> L. Production and Reduces Fruit Contamination on a Heavy Metals-Contaminated Saline Soil

Natural supplementations are used in agriculture nowadays not only for improving plant performance but also for reducing the contamination of plant edible parts. Two field trials were conducted to study the potential effects of licorice root extract (LRE; 0.5%) on performance, physio-biochemical components, antioxidant defense system, and contaminants concentrations of Capsicum annuum L. plants grown on a saline soil contaminated with heavy metals. LRE was applied in single (i.e., as rhizosphere application with drip irrigation water; -RA or as foliar spray; -FA) or in integration (i.e., LRE-RA + LRE-FA) treatment. The results showed that both single or integrative treatments significantly increased plant growth and yield, leaf concentrations of photosynthetic pigments, free proline, total soluble sugars, N, P, and K+, ratio of K+/Na+, and activities of CAT, POX, APX, SOD and GR, while significantly reduced contaminants; Na+, Cd, Cu, Pb and Ni concentrations in plant leaves and fruits on heavy metals-contaminated saline soil compared to the control (without LRE). Additionally, the integrative LRE-RA + LRE-FA treatment significantly exceeded both single treatments in this concern, which had been recommended for maximizing pepper plant performances with minimizing heavy metals in fruits on contaminated saline soils.

Licorice Root Extract Boosts <i>Capsicum annuum</i> L. Production and Reduces Fruit Contamination on a Heavy Metals-Contaminated Saline Soil

Natural supplementations are used in agriculture nowadays not only for improving plant performance but also for reducing the contamination of plant edible parts. Two field trials were conducted to study the potential effects of licorice root extract (LRE; 0.5%) on performance, physio-biochemical components, antioxidant defense system, and contaminants concentrations ofCapsicum annuumL. plants grown on a saline soil contaminated with heavy metals. LRE was applied in single (i.e., as rhizosphere application with drip irrigation water; -RA or as foliar spray; -FA) or in integration (i.e., LRE-RA + LRE-FA) treatment. The results showed that both single or integrative treatments significantly increased plant growth and yield, leaf concentrations of photosynthetic pigments, free proline, total soluble sugars, N, P, and K+, ratio of K+/Na+, and activities of CAT, POX, APX, SOD and GR, while significantly reduced contaminants; Na+, Cd, Cu, Pb and Ni concentrations in plant leaves and fruits on heavy metals-contaminated saline soil compared to the control (without LRE). Additionally, the integrative LRE-RA + LRE-FA treatment significantly exceeded both single treatments in this concern, which had been recommended for maximizing pepper plant performances with minimizing heavy metals in fruits on contaminated saline soils.

Roles of reactive oxygen species and antioxidant enzymes on formaldehyde removal from air by plants

The roles of enzymatic reactions and redox reactions caused by reactive oxygen species (ROS) in formaldehyde metabolism in tomatoes and wheat seedlings and the changes in peroxidase (POD) and catalase (CAT) activities in plants were investigated. Differences in the breakdown of added formaldehyde between fresh and boiled plant extracts were determined to calculate the contributions of different removal mechanisms. Two plant seedlings efficiently removed formaldehyde from air when its level varied from 0.65 to 1.91 mg m^-3; meanwhile, the maximum rate at which tomato seedlings transported formaldehyde from air to the rhizosphere solution reached 182.26 µg h^-1 kg^-1 FW (fresh weight). Metabolism in plants was mainly responsible for the formaldehyde dissipation. The enzymatic contribution to formaldehyde dissipation decreased with increasing shoot exposure time or air formaldehyde level, while the redox contribution increased in importance because of an increasing level of ROS. The different enzymatic antioxidant activities of plants resulted in different levels of ROS and hence different tolerance and removal efficiencies toward formaldehyde. The self-enhancing ability of plants to remove formaldehyde via redox reactions suggested that the formaldehyde removal efficiency could be enhanced by plant adaptation to environmental stress.

Lead, zinc, and cadmium uptake, accumulation, and phytoremediation by plants growing around Tang-e Douzan lead-zinc mine, Iran

In the current study, soils of Tang-e Douzan mine, located in Isfahan, Iran, were collected and analyzed for soluble, exchangeable, and total amounts of Pb, Zn, Cd, Ca, and Mg. The maximum Pb, Zn, Cd, Ca, and Mg concentrations in soils were 2500, 1100, 59, 43,800, and 1320 mg/kg for total metals, 86, 83, 6.3, 4650, and 48 mg/kg for their exchangeable fractions, and 59, 3.7, 0.53, 430, and 6.4 mg/kg for their soluble fractions, respectively. All specimens collected, including 69 plant species, were analyzed for Pb, Zn, and Cd. Moreover, their phytoremediation potential was investigated by calculating bioconcentration factors (BCF), translocation factors (TF), and extraction factors (EF) for each heavy metal. Analysis of the leaves for heavy metals showed no metal hyperaccumulation. The highest shoot concentrations of Pb (298 mg/kg) and Zn (740 mg/kg) were found in Roemeria hybrida subsp. dodecandra and Cd (43 mg/kg) in Chenopodium foliosum. Plants having BCFs and TFs > 1 are capable of phytoextraction. Among the analyzed species, four had both TFs and BCFs > 1 for Zn, 13 for Cd, and none for Pb. R. hybrida, Bromus squarrosus, Descurainia sophia, and Poa bulbosa seem to be the best choices for phytoextraction of Zn. Aegilops columnaris, Allium ampeloprasum subsp. iranicum, B. squarrosus, and Cousinia piptocephala are the best choices for phytoextraction of Cd. Plants with BCF > 1 and TF < 1, including Cerastium dichotomum and Muscari neglectum for Pb, Ceratocephala falcata, M. neglectum, Ornithogalum orthophyllum, and Ranunculus arvensis for Zn and C. falcata, M. neglectum, O. orthophyllum, and R. hybrida subsp. dodecandra for Cd, are proposed to be the most efficient species for metal phytostabilization.

Plasmid-Mediated Bioaugmentation for the Bioremediation of Contaminated Soils

Bioaugmentation, or the inoculation of microorganisms (e.g., bacteria harboring the required catabolic genes) into soil to enhance the rate of contaminant degradation, has great potential for the bioremediation of soils contaminated with organic compounds. Regrettably, cell bioaugmentation frequently turns into an unsuccessful initiative, owing to the rapid decrease of bacterial viability and abundance after inoculation, as well as the limited dispersal of the inoculated bacteria in the soil matrix. Genes that encode the degradation of organic compounds are often located on plasmids and, consequently, they can be spread by horizontal gene transfer into well-established, ecologically competitive, indigenous bacterial populations. Plasmid-mediated bioaugmentation aims to stimulate the spread of contaminant degradation genes among indigenous soil bacteria by the introduction of plasmids, located in donor cells, harboring such genes. But the acquisition of plasmids by recipient cells can affect the host’s fitness, a crucial aspect for the success of plasmid-mediated bioaugmentation. Besides, environmental factors (e.g., soil moisture, temperature, organic matter content) can play important roles for the transfer efficiency of catabolic plasmids, the expression of horizontally acquired genes and, finally, the contaminant degradation activity. For plasmid-mediated bioaugmentation to be reproducible, much more research is needed for a better selection of donor bacterial strains and accompanying plasmids, together with an in-depth understanding of indigenous soil bacterial populations and the environmental conditions that affect plasmid acquisition and the expression and functioning of the catabolic genes of interest.

Evaluation of air pollution tolerance index and anticipated performance index of plants and their application in development of green space along the urban areas

Air pollution due to vehicular emissions has become one of the most serious problems in the whole world and has resulted in huge threat to both the environment and the health of living organisms (plants, humans, animals, microorganisms). Plants growing along the roadsides get affected at the maximum as they are the primary recipients to different air pollutants and show varied levels of tolerance and sensitivity. Taking this into account, the present work was based on assessment of seasonal variation in air pollution tolerance index (APTI) and anticipated performance index (API) of four roadside plants, namely, Alstonia scholaris, Nerium oleander, Tabernaemontana coronaria, and Thevetia peruviana belonging to family Apocynaceae. APTI was calculated by the determination of four important biochemical parameters, viz., pH, relative water content (RWC), total chlorophyll (TChl), and ascorbic acid (AsA) content of leaves. The leaf samples were collected from plants growing at seven different sites of Amritsar (Punjab), India, for pre-monsoon and post-monsoon seasons. Highest APTI (82.14) was reported in N. oleander during the pre-monsoon season while the lowest was recorded in T. coronaria (18.59) in the post-monsoon season. On the basis of API score, A. scholaris was anticipated to be an excellent performer during the pre-monsoon and post-monsoon seasons followed by N. oleander, T. coronaria, and T. peruviana. Linear regression analysis and Pearson's correlation coefficient depicted significant positive correlation between APTI and ascorbic acid content during the pre-monsoon and post-monsoon seasons.

Partition uptake of a brominated diphenyl ether by the edible plant root of white radish (Raphanus sativus L.)

Polybrominated diphenyl ethers (PBDEs) are of a class of emerging contaminants. In this study, the accumulation of 4-bromodiphenyl ether (BDE-3) by different parts of a live white radish was investigated. Different cultural media (hydroponics, silica sand, and soil) were used to sustain the radish plant during its uptake and in-plant translocation of BDE-3. The results showed that BDE-3 can be translocated from the roots to the aboveground organs and the accumulated levels of BDE-3 in different parts of the white radish followed the order for the three types of cultivation: fibrous roots > peels > main roots > leaves. The results were analyzed by the aid of the partition-limited model for the plant uptake. The relevant partition coefficients (K_OC and K_d) and uptake parameters of BDE-3 with plant components (K_pt and K_lip) were obtained for analyzing the BDE-3 distribution. The partition-limited model offers a significant insight into the uptakes of BDE-3 by the various components of live white radishes. The types of cultivation affected the total sorption level, translocation factors (TFs), extent to equilibrium (α_pt), and root concentration factors (RCFs).

A microcosm investigation of fe (iron) removal using macrophytes of ramsar lake: A phytoremediation approach

The present study deals with the microcosm study of Fe (Iron) phytoremediation using Eichhornia crassipes, Lemna minor, Pistia stratiotes and Salvinia cucullata species collected from the Loktak Lake, a Ramsar Site which exists in north-eastern India (an Indo-Burma hotspot region). Efficiency of these four macrophytes was compared using different Fe concentrations of 1 mg L(-1), 3 mg L(-1) and 5 mg L(-1) for 4 days, 8 days and 12 days, respectively. E. crassipes was the most efficient macrophyte whereas L. minor was the least efficient. E. crassipes removed the highest percentage of Fe, i.e. 89% from 1 mg L(-1), 81.3% from 3 mg L(-1) and 73.2% from 5 mg L(-1) in 12-day experiment.

Accumulation and partitioning of biomass, nutrients, and trace elements in switchgrass for phytoremediation of municipal biosolids

In situ phytoremediation of municipal biosolids is a promising alternative to the land spreading and landfilling of biosolids from end-of-life municipal lagoons. Accumulation and partitioning of dry matter, nitrogen (N), phosphorus (P), and trace elements were determined in aboveground biomass (AGB) and belowground biomass (BGB) of switchgrass (Panicum virgatum L.) to determine the harvest stage that maximizes phytoextraction of contaminants from municipal biosolids. Seedlings were transplanted into 15-L plastic pails containing 3.9 kg (dry wt.) biosolids. Biomass yield components and contaminant concentrations were assessed every 14 days for up to 161 days. Logistic model fits to biomass yield data indicated no significant differences in asymptotic yield between AGB and BGB. Switchgrass partitioned significantly more N and P to AGB than to BGB. Maximum uptake occurred 86 days after transplanting (DAT) for N and 102 DAT for P. Harvesting at peak aboveground element accumulation removed 5% of N, 1.6% of P, 0.2% of Zn, 0.05% of Cd, and 0.1% of Cr initially present in the biosolids. These results will contribute toward identification of the harvest stage that will optimize contaminant uptake and enhance in situ phytoremediation of biosolids using switchgrass.

Use of Energy Crop (Ricinus communis L.) for Phytoextraction of Heavy Metals Assisted with Citric Acid

Ricinus communis L. is a bioenergetic crop with high-biomass production and tolerance to cadmium (Cd) and lead (Pb), thus, the plant is a candidate crop for phytoremediation. Pot experiments were performed to study the effects of citric acid in enhancing phytoextraction of Cd/Pb by Ricinus communis L. Citric acid increased Cd and Pb contents in plant shoots in all treatments by about 78% and 18-45%, respectively, at the dosage of 10 mM kg(-1) soil without affecting aboveground biomass production. Addition of citric acid reduced CEC, weakened soil adsorption of heavy metals and activated Cd and Pb in soil solutions. The acid-exchangeable fraction (BCR-1) of Pb remained lower than 7% and significantly increased with citric acid amendment. Respective increases in soil evaluation index induces by 14% and 19% under the Cd1Pb50 and Cd1Pb250 treatments upon addition of citric acid resulted in soil quality improvement. Ricinus communis L. has great potential in citric acid-assisted phytoextraction for Cd and Pb remediation.

Phytoremediation of lead (Pb) and arsenic (As) by Melastoma malabathricum L. from contaminated soil in separate exposure

This study was conducted to investigate the uptake of lead (Pb) and arsenic (As) from contaminated soil using Melastoma malabathricum L. species. The cultivated plants were exposed to As and Pb in separate soils for an observation period of 70 days. From the results of the analysis, M. malabathricum accumulated relatively high range of As concentration in its roots, up to a maximum of 2800 mg/kg. The highest accumulation of As in stems and leaves was 570 mg/kg of plant. For Pb treatment, the highest concentration (13,800 mg/kg) was accumulated in the roots of plants. The maximum accumulation in stems was 880 mg/kg while maximum accumulation in leaves was 2,200 mg/kg. Only small amounts of Pb were translocated from roots to above ground plant parts (TF < 1). However, a wider range of TF values (0.01-23) for As treated plants proved that the translocation of As from root to above ground parts was greater. However, the high capacity of roots to take up Pb and As (BF > 1) is indicative this plants is a good bioaccumulator for these metals. Therefore, phytostabilisation is the mechanism at work in M. malabathricum's uptake of Pb, while phytoextraction is the dominant mechanism with As.

Plant-bacteria partnerships for the remediation of hydrocarbon contaminated soils

Plant-bacteria partnerships have been extensively studied and applied to improve crop yield. In addition to their application in agriculture, a promising field to exploit plant-bacteria partnerships is the remediation of soil and water polluted with hydrocarbons. Application of effective plant-bacteria partnerships for the remediation of hydrocarbons depend mainly on the presence and metabolic activities of plant associated rhizo- and endophytic bacteria possessing specific genes required for the degradation of hydrocarbon pollutants. Plants and their associated bacteria interact with each other whereby plant supplies the bacteria with a special carbon source that stimulates the bacteria to degrade organic contaminants in the soil. In return, plant associated-bacteria can support their host plant to overcome contaminated-induced stress responses, and improve plant growth and development. In addition, plants further get benefits from their associated-bacteria possessing hydrocarbon-degradation potential, leading to enhanced hydrocarbon mineralization and lowering of both phytotoxicity and evapotranspiration of volatile hydrocarbons. A better understanding of plant-bacteria partnerships could be exploited to enhance the remediation of hydrocarbon contaminated soils in conjunction with sustainable production of non-food crops for biomass and biofuel production.

Modeling the plant-soil interaction in presence of heavy metal pollution and acidity variations

On a mathematical interaction model, developed to model metal uptake by plants and the effects on their growth, we introduce a modification which considers also effects on variations of acidity in soil. The model relates the dynamics of the uptake of metals from soil to plants and also variations of uptake according to the acidity level. Two types of relationships are considered: total and available metal content. We suppose simple mathematical assumptions in order to get as simple as possible expressions with the aim of being easily tested in experimental problems. This work introduces modifications to two versions of the model: on the one hand, the expression of the relationship between the metal in soil and the concentration of the metal in plants and, on the other hand, the relationship between the metal in the soil and total amount of the metal in plants. The fine difference of both versions is fundamental at the moment to consider the tolerance and capacity of accumulation of pollutants in the biomass from the soil.

A study on the waste metal remediation using floriculture at East Calcutta Wetlands, a Ramsar site in India

Use of specific plant species in remediation of heavy metal-contaminated soil and water was a promising eco-friendly technology. The present study indicated the possibilities of phytoremediation of metal-contaminated (namely Ca, Cr, Mn, Fe, Cu, Zn, and Pb) soil by using plant species important for floriculture of East Calcutta Wetlands, a Ramsar site at the eastern fringe of Calcutta city. Plant species like sunflower (Helianthus annuus), marigold (Tagetes patula), and cock's comb (Celocia cristata) grew on soil contaminated by industrial sludge and irrigated regularly with wastewater accumulated different metals in different plant parts in varied concentrations. Pot culture study in the laboratory setup was also done to ascertain the efficiency of these plants for ameliorating contaminated soil. It was found that general accumulation patterns of metals concerned in different plant parts were root > leaf > stem > flower. This work indicated the importance of cultivation of economically important, non-edible, ornamental plant species as an alternative cost-effective practice to remediate heavily contaminated farmlands of East Calcutta Wetlands.

Accumulation of cadmium, zinc, and copper by Helianthus annuus L.: impact on plant growth and uptake of nutritional elements

We investigated the effects on physiological response, trace elements and nutrients accumulation of sunflower plants grown in soil contaminated with: 5 mg kg(-1) of Cd; 5 and 300 mg kg(-1) of Cd and Zn, respectively; 5, 300, and 400 mg kg(-1) of Cd, Zn, and Cu, respectively. Contaminants applied did not produce large effects on growth, except in Cd-Zn-Cu treatment in which leaf area and total dry matter were reduced, by 15%. The contamination with Cd alone did not affect neither growth nor physiological parameters, despite considerable amounts of Cd accumulated in roots and older leaves, with a high bioconcentration factor from soil to plant. By adding Zn and then Cu to Cd in soil, significant were the toxic effects on chlorophyll content and water relations due to greater accumulation of trace elements in tissues, with imbalances in nutrients uptake. Highly significant was the interaction between shoot elements concentration (Cd, Zn, Cu, Fe, Mg, K, Ca) and treatments. Heavy metals concentrations in roots always exceeded those in stem and leaves, with a lower translocation from roots to shoots, suggesting a strategy of sunflower to compartmentalise the potentially toxic elements in physiologically less active parts in order to preserve younger tissues.

Development of a model to select plants with optimum metal phytoextraction potential

PURPOSE

The aim of the present study is to propose a nonlinear model which provides an indicator for the maximum phytoextraction of metals to help in the decision-making process. Research into different species and strategies plays an important role in the application of phytoextraction techniques to the remediation of contaminated soil. Also, the convenience of species according to their biomass and pollutant accumulation capacities has gained important space in discussions regarding remediation strategies, whether to choose species with low accumulation capacities and high biomass or high accumulation capacities with low biomass.

METHODS

The effects of heavy metals in soil on plant growth are studied by means of a nonlinear interaction model which relates the dynamics of the uptake of heavy metals by plants to heavy metal deposed in soil.

RESULTS

The model, presented theoretically, provides an indicator for the maximum phytoextraction of metals which depends on adjustable parameters of both the plant and the environmental conditions. Finally, in order to clarify its applicability, a series of experimental results found in the literature are presented to show how the model performs consistently with real data.

CONCLUSIONS

The inhibition of plant growth due to heavy metal concentration can be predicted by a simple kinetic model. The model proposed in this study makes it possible to characterize the nonlinear behaviour of the soil-plant interaction with heavy metal pollution in order to establish maximum uptake values for heavy metals in the harvestable part of plants.

A study on the phytoaccumulation of waste elements in wetland plants of a Ramsar site in India

Some wetland plant species are adapted to growing in the areas of higher metal concentrations. Use of such vegetation in remediation of soil and water contaminated with heavy metals is a promising cost-effective alternative to the more established treatment methods. Throughout the year, composite industrial effluents bringing various kinds of heavy metals contaminate our study site, the East Calcutta Wetlands, a Ramsar site at the eastern fringe of Kolkata city (formerly Calcutta), India. In the present study, possible measures for remediation of contaminated soil and water (with elements namely, Ca, Cr, Cu, Pb, Zn, Mn, and Fe) of the ecosystem had been investigated. Ten common regional wetland plant species were selected to study their efficiency and diversity in metal uptake and accumulation. Results showed that Bermuda grass (Cynodon dactylon) had the highest total Cr concentration (6,601 ± 33 mg kg( -1) dw). The extent of accumulation of various elements in ten common wetland plants of the study sites was: Pb (4.4-57 mg kg( -1) dw), Cu (6.2-39 mg kg( -1) dw), Zn (59-364 mg kg( -1) dw), Mn (87-376 mg kg( -1) dw), Fe (188-8,625 mg kg( -1) dw), Ca (969-3,756 mg kg( -1) dw), and Cr (27-660 mg kg( -1) dw) indicating an uptake gradient of elements by plants as Ca>Fe>Mn>Cr>Zn>Cu>Pb. The present study indicates the importance of identification and efficiency of metal uptake and accumulation capabilities by plants in relation to their applications in remediation of a contaminated East Calcutta Wetland ecosystem.

Effects of IDSA, EDDS and EDTA on heavy metals accumulation in hydroponically grown maize (Zea mays, L.)

Heavy metals contamination of soil is a widespread global problem. Chelant assisted phytoextraction has been proposed to improve the efficiency of phytoextraction which involves three subsequent levels: transfer of metals from the bulk soil to the root surfaces, uptake into the roots and translocation to the shoots. However, most studies focused on the first level. A hydroponic experiment, which addresses the latter two levels, was conducted to study the effects of EDTA, EDDS and IDSA on the uptake and the distribution of Pb, Zn, Cu and Cd in the apoplast and the symplast of roots of maize (Zea mays, L.). The concentrations of the metals (with exception of Zn) in the shoots were increased significantly by addition of all the chelants. EDTA was most effective for Pb uptake and IDSA was interestingly most effective for Cd uptake. Pb in the roots with EDTA was mostly distributed in the apoplast, while Zn, especially with IDSA, was mostly located in the symplast. The results indicated that, the capacity of chelant to enhance the nonselective apoplastic transport of metal may be most important for chelant enhanced phytoextraction.

Phytostabilization of metal contaminated soils

The contamination of soils with heavy metals represents a worldwide environmental problem of great concern. Traditional methods for the remediation of metal contaminated soils are usually very expensive and frequently induce adverse effects on soil properties and biological activity. Consequently, biological methods of soil remediation like phytoremediation (the use of green plants to clean up contaminated sites) are currently receiving a great deal of attention. In particular, chemophytostabilization of metal contaminated soils (the use of metal tolerant plants together with different amendments like organic materials, liming agents, or phosphorus compounds and such) to reduce metal mobility and bioavailability in soils appears most promising for sites contaminated with high levels of several metals when phytoextraction is not a feasible option. During chemophytostabilization processes, one must at all times be cautious with a possible future reversal of soil metal immobilization, with concomitant adverse environmental consequences.

Jatropha curcas: a potential crop for phytoremediation of coal fly ash

A greenhouse pot experiment was conducted to test the heavy metal phytoremediation capacity of Jatropha curcas from fly ash. Both natural accumulation by J. curcas and chemically enhanced phytoextraction was investigated. Plants were grown on FA and FA amended with fertile garden soil, in presence and absence of chemical chelating agent EDTA at 0.1 g kg(-1) and 0.3 g kg(-1) of soil. EDTA enhanced the uptake of all five elements (Fe, Al, Cr, Cu and Mn) tested. Fe and Mn were retained more in roots while Cu, Al and Cr were translocated more to the shoot. Metal accumulation index indicates that the effect of EDTA at 0.3 g kg(-1) was more pronounced than EDTA at 0.1 g kg(-1) in terms of metal accumulation. Biomass was enhanced up to 37% when FA was amended with GS. Heavy metal uptake was enhanced by 117% in root, 62% in stem, 86% in leaves when EDTA was applied at 0.3 g kg(-1) to FA amended with GS. Study suggest that J. curcas has potential of establishing itself on FA when provided with basic plant nutrients and can also accumulate heavy metals many folds from FA without attenuating plant growth.

Effects of inoculation with arbuscular mycorrhizal fungi on maize grown in multi-metal contaminated soils

Pot culture experiments were established to determine the effects of colonization by arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. sp) on maize (Zea mays L.) grown in Pb, Zn, and Cd complex contaminated soils. AMF and non-AMF inoculated maize were grown in sterilized substrates and subjected to different soil heavy metal (Pb, Zn, Cd) concentrations. The root and shoot biomasses of inoculated maize were significantly higher than those of non-inoculated maize. Pb, Zn, and Cd concentrations in roots were significantly higher than those in shoots in both the inoculated and non-inoculated maize, indicating the heavy metals mostly accumulated in the roots of maize. The translocation rates of Pb, Zn, and Cd from roots to shoots were not significantly difference between inoculated and non-inoculated maize. However, at high soil heavy metal concentrations, Pb, Zn, and Cd in the shoots and Pb in the roots of inoculated maize were significantly reduced by about 50% compared to the non-inoculated maize. These results indicated that AMF could promote maize growth and decrease the uptake of these heavy metals at higher soil concentrations, thus protecting their hosts from the toxicity of heavy metals in Pb, Zn, and Cd complex contaminated soils.

Comparison of EDTA- and citric acid-enhanced phytoextraction of heavy metals in artificially metal contaminated soil by Typha angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.

Reclamation of tannery polluted soil through phytoremediation

The huge volume of sludge emanating from the tannery effluent treatment plants poses a serious environmental problem. Phytoremediation is an emerging technology in which the plants are employed to reclamate the contaminated soil strewn with heavy metals (metalloids) and toxic compounds. This work focuses the impact of application of tannery sludge on biochemical properties of 6 months old tree saplings of Azadirachta indica A. Juss. (Neem), Melia azedarach Linn. (Wild Neem) and Leucaena leucocephala (Lam) de Wit (Subabool) raised over the tannery sludge in an attempt to use these plants for phytoremediation. The plants raised over the garden soil served as the control. The porosity and water holding capacity of the tannery sludge were higher. The plant growth supporting elements such as Ca, total N2, NO3 and Mg were higher in the sludge. The plants raised over the sludge were found to be dark green with increased morphometric parameters. Electrophoretic profile revealed amplification of a few polypeptides (100, 105, 49 and 55 KDa). The levels of biomolecules and the CO2 absorption increased in 6 months old plants. There was a significant uptake and transport of chromium in all the three tree species suggesting that these plants could be employed in phytoremediation of soils contaminated with heavy metals.

Dendroremediation of heavy metal polluted soils

Heavy metals are among the most common and harmful pollutants reaching the soil ecosystem all over the world. Phytoextraction is an effective, non-intrusive, inexpensive, aesthetically pleasing, socially accepted, highly promising phytotechnology for the remediation of soils polluted with heavy metals. To overcome the so-called 'Achilles' heel' of phytoextraction, namely, the long time needed for effective remediation, this phytotechnology should be combined with other profit-making activities such as forestry or bioenergy production. Dendroremediation, or the use of trees to clean up polluted soil and water, appears of great potential for metal phytoextraction, especially when using fast-growing tree species, for example, willows (Salix sp. pl.) and poplars (Populus sp. pl.). Most important, the ecologic and environmental risks of dispersing heavy metals into the ecosystems by dendroremediation strategies should be minimized by selecting the right tree species, properly managing/disposing the polluted plant material, or a combination of both options.

Gene manipulation of a heavy metal hyperaccumulator species Thlaspi caerulescens L. via Agrobacterium-mediated transformation

Thlaspi caerulescens L. is well known as a Zn/Cd hyperaccumulator. The genetic manipulation of T. caerulescens through transgenic technology can modify plant features for use in phytoremediation. Here, we describe the efficient transformation of T. caerulescens using Agrobacterium tumefaciens strain EHA105 harboring a binary vector pBI121 with the nptII gene as a selectable marker, the gus gene as a reporter and a foreign catalase gene. Based on the optimal concentration of growth regulators, the shoot cluster regeneration system via callus phase provided the basis of the genetic transformation in T. caerulescens. The key variables in transformation were examined, such as co-cultivation period and bacterial suspension density. Optimizing factors for T-DNA delivery resulted in kanamycin-resistant transgenic shoots with transformation efficiency more than 20%, proven by histochemical GUS assay and PCR analysis. Southern analysis of nptII and RT-PCR of catalase gene demonstrated that the foreign genes were integrated in the genome of transformed plantlets. Moreover, the activity of catalase enzyme in transgenic plants was obviously higher than in wild-type plants. This method offers new prospects for the genetic engineering of this important hyperaccumulator species.

Identification of lead-regulated genes by suppression subtractive hybridization in the heavy metal accumulator Sesbania drummondii

Heavy metal contamination of soils is of widespread occurrence as a result of human, agricultural and industrial activities. Among heavy metals, lead is a potential pollutant that readily accumulates in soils and sediments. Although lead is not an essential element for plants, it gets easily absorbed and accumulated in Sesbania drummondii, which exhibits a significant level of tolerance to lead. The response of a metal tolerant plant to heavy metal stress involves a number of biochemical and physiological pathways. To investigate the overall molecular response of a metal-tolerant plant to lead exposure, suppression subtractive hybridization (SSH) was used to construct a cDNA library enriched in lead induced mRNA transcripts from lead-tolerant Sesbania. Screening the library by reverse Northern analysis revealed that between 20 and 25% of clones selected from the library were differentially regulated in lead treated plants. After differential screening, we isolated several differentially expressed cDNA clones, including a type 2 metallothionein (MT) gene which is involved in detoxification and homeostasis and shown to be differentially regulated in lead treated plants. The data from the reverse Northern analysis was further confirmed with conventional Northern analysis of a select group of genes including MT, ACC synthase/oxidase, cold-, water stress-, and other abiotic stress-induced genes, which are up-regulated rapidly in response to lead treatment. The mRNA levels of MT increased substantially after lead treatment indicating a potential role for it under lead stress in Sesbania. The present results show that SSH can serve as an effective tool for isolating genes induced in response to lead heavy metal tolerance in Sesbania. A better understanding of lead induced gene expression in Sesbania should help select candidates associated with remediation of heavy metal toxicity. The possible link between this result and the heavy-metal response of plants is discussed.

Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils

Heavy metal pollution of soil is a significant environmental problem and has its negative impact on human health and agriculture. Rhizosphere, as an important interface of soil and plant, plays a significant role in phytoremediation of contaminated soil by heavy metals, in which, microbial populations are known to affect heavy metal mobility and availability to the plant through release of chelating agents, acidification, phosphate solubilization and redox changes, and therefore, have potential to enhance phytoremediation processes. Phytoremediation strategies with appropriate heavy metal-adapted rhizobacteria have received more and more attention. This article paper reviews some recent advances in effect and significance of rhizobacteria in phytoremediation of heavy metal contaminated soils. There is also a need to improve our understanding of the mechanisms involved in the transfer and mobilization of heavy metals by rhizobacteria and to conduct research on the selection of microbial isolates from rhizosphere of plants growing on heavy metal contaminated soils for specific restoration programmes.