Assessment of heavy metal tolerance in native plant species from soils contaminated with electroplating effluent

Available heavy metals concentrations in agricultural soils: Relationship with soil properties and total heavy metals concentrations in different industries

Heavy metal (HM) pollution in agricultural soils has arisen sharply in recent years. However, the impact of main factors on available HMs concentrations in agricultural soils of the three main industries (smelting, chemical and mining industry) is unclear. Herein, soil properties (pH, cation exchange capacity (CEC) and texture (sand, slit, clay)), total and available concentrations were concluded based on the results of 165 research papers from 2000 to 2023 in Web of Science database. In the three industries, the correlation and redundancy analysis were used to study the correlation between main factors and available concentrations, and quantitatively analyzed the contribution of each factor to available concentrations with gradient boosting decision tree model. The results showed that different factors had varying degrees of impact on available metals in the three main industries, and the importance of same factors varied in each industry, as for soil pH, it was most important for available Pb and Zn in the chemical industry, but the total concentrations were most important in the smelting and mining industry. There was no significant correlation between total and available concentrations. Soil properties involved in this paper (especially soil pH) were negatively correlated with available concentrations. This study provides effective guidance for the formulation of soil pollution control and risk assessment standards based on industry classification in the three major industrial impact areas.

Bio-transfer and bioaccumulation patterns of heavy metals in mine site-inhabiting ants and grasshoppers, across mine site restoration chronosequence

Soil is known to serve as a significant sink for heavy metals in coal mine sites, thus also influence the plant and other organisms of that area. Hence, the presence of heavy metals in coal mine soil is of concern to land managers. Insects occupy different trophic positions in the food chains, thus many insect species accumulate large amounts of heavy metals in their bodies and this is a matter of concern. In the present study, we investigated biotransfer and bioaccumulation of heavy metals from soil, grass species Cynodon dactylon, Vetiveria zizanioides, grasshopper species Gastrimargus africanus, Choroedocus robustus, ant species Cataglyphis longipedem and Camponotus compressus in six different ages (2, 4, 6, 8, 10 and 12 year old) of coal mine sites. Our study revealed that at some extent the heavy metal content and BAF patterns of heavy metals along different pathways (from soil to grass, soil to grasshoppers and from grass to grasshoppers) were not consistent and did not reflect the soil pollution status for all the metals, related to the mine spoil dump age. However, in contrast, ants successfully reflected a consistent pattern in the bioaccumulation of heavy metals via soil, thereby indicating the pollution status of the soil along with the restoration age of mine spoil dumps. Our study showed that ant species can successfully forecast the presence of heavy metals of coal mine spoils along with their restoration.

Assessment of native plants for their potential to remove trace metals around Legadembi tailings dam, Southern Ethiopia

Native plant species growing on metal contaminated soil at the foot of the Legadembi tailings dam were selected to evaluate their phytoremediation potential. For this purpose, soil, aboveground tissues, and roots of plant samples were analyzed for the concentrations of Zn, Cu, Ni, Pb, and Cd. The bioaccumulation and transfer of metals were evaluated in terms of translocation factor (TF), bioconcentration factor (BCF), and biological accumulation coefficient (BAC). The results showed that most of the species were efficient to take up and translocate more than one trace element (TE) from roots to shoots. Argemone mexicana L., Rumex nepalensis Spreng., Cyperus alopecuroides Rottb., and Schoenoplectu sconfusus (N.E.Br.) Lye showed potential for phytoextraction of Cu, while R. nepalensis and C. alopecuroides can accumulate in their above-ground parts and are suitable for phytoextraction of Ni. Rumex nepalensis, C. alopecuroides, and Typha latifolia L. have the ability for phytostabilization of Zn metal. Findings suggest concentrations of some metals in plants' tissue showed above the normal range which suggests their potential use in phytoremediation.

Migration, accumulation, and risk assessment of potentially toxic elements in soil-plant (shrub and herbage) systems at typical polymetallic mines in Northwest China

In grassland systems of the semi-arid mining area, the migration, accumulation, and bioavailability of potentially toxic elements (PTEs) are important ecological and health risk issues. Thirty-eight pairs of topsoil (0-20 cm) and plant samples were collected around Baiyin City and in Dongdagou stream valley to investigate the migration of PTEs in soils, transfer of PTEs in soil-plant (shrub and herbage) systems, and assess the risk in soils and plants. The total concentrations of PTE (Hg, As, Cu, Zn, Cd, and Pb) were analyzed following digestion in mixture acid solution, and bioavailable PTE was extracted with a strong chelating agent (DTPA-TEA-CaCl₂). The transfer factor (TF) and bioaccumulation factor (BCF) were calculated to examine the migration of PTEs in soil-plant. Hazard quotient (HQ) and total hazard index (THI) were calculated to assess the risk and migration of PTEs in soils. The results showed that PTEs in soils and plants of study area exceeded the soil background value and Hygienic Standard for Feeds. Correlation among the total Hg, As, Cu, Zn, Cd, and Pb in soils of Dongdagou stream valley was significant at p < 0.01. A good correlation was exhibited between PTEs in root/aboveground parts of plants and DTPA-soil extractable. Difference of TF and BCF was existed between Dongdagou stream valley and around Baiyin City. Hg, Cu, Zn, Cd, and Pb were mainly accumulated in soils near the mining area. The calculated THI exceeded 1, and As and Pb were the major risk factors. The ability to absorb and transfer Hg, As, Cu, and Pb of plants was lower in more serious polluted area. As had a stronger migration capacity in study area. PTEs in soils had an adverse health effect for residents, and PTEs in plants may cause toxicity to cattle and sheep.

Resource utilization of hazardous Cr/Fe-rich sludge: synthesis of erdite flocculant to treat real electroplating wastewater

Cr/Fe-bearing sludge is a hazardous solid waste, produced at mass production in smelting, plating and surface finishing industries. Such waste is commonly treated by chemical detoxification and safety landfill, whereas only a few Cr-rich sludge is recycled as a tanning reagent. In this study, a novel route was developed to recycle Cr/Fe-bearing sludge as erdite-bearing flocculant for wastewater treatment. Results showed that two sludges were irregular aggregates, one of which contained 1.6 wt.% Cr (short for LS) and the other contained 4.2 wt.% Cr (HS). After hydrothermal treatment, stable Cr(III)/S-bearing product was formed from the Cr(VI) reduction in the sludges. Conversely, erdite was generated in nanorod form with diameter and length of 200 nm and 0.5-1 μm from LS, respectively, whereas grew radially to 1.5-2.5 μm for HS. The two erdite-bearing products were spontaneously hydrolysed to Fe/S-bearing flocs and showed similar performance in the treatment of real electroplating effluent with 91.55, 1.94 and 0.25 mg/L of Zn, Ni and Cr, respectively. For instance, by adding 1 g/L product of LS, the release of Cr from the products did not occur, and the residual Zn, Ni and Cr in the effluent was 0.25, 0.65 and 0.17 mg/L, respectively, which met the discharge standard of the electroplating industry. With the two converted products, the residual Zn/Ni/Cr concentrations were apparently lower than those of the raw sludges and other common reagents (e.g. polymeric ferric sulphate, activated carbon and diatomite). Thus, such erdite-bearing products could serve as a flocculant and then be applied in electroplating wastewater treatment.

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

Bioaugmentation, the addition of cultured microorganisms to enhance the currently existing microbial community, is an option to remediate contaminated areas. Several studies reported the success of the bioaugmentation method in treating heavy metal contaminated soil, but concerns related to the applicability of this method in real-scale application were raised. A comprehensive analysis of the mechanisms of heavy metal treatment by microbes (especially bacteria) and the concerns related to the possible application in the real scale were juxtaposed to show the weakness of the claim. This review proposes the use of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil. The performance of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil as well as the mechanisms of removal and interactions between plants and microbes are also discussed in detail. Bioaugmentation-assisted phytoremediation shows greater efficiencies and performs complete metal removal from soil compared with only bioaugmentation. Research related to selection of hyperaccumulator species, potential microbial species, analysis of interaction mechanisms, and potential usage of treating plant biomass after treatment are suggested as future research directions to enhance this currently proposed topic.

Concentrations and isotopic analysis for the sources and transfer of lead in an urban atmosphere-plant-soil system

Lead pollution has attracted significant attention over the years. However, research on the transfer of lead between urban atmospheric particles, soils, and plants remains rare. We measured lead concentrations and lead isotope ratios in total suspended particles (TSP), soil, and plants in an urban wetland in Beijing. The study period was September 2016-August 2017- covering all four seasons. The concentrations of lead in the atmospheric particles vary from 3.13 to 6.68 mg/m3. It is significantly higher in autumn than that in spring and summer (P < 0.05). There is also a significant difference between summer and winter (P < 0.05). The soil lead concentrations range from 57 to 114 mg/kg, with the highest concentration in spring, followed by summer, winter and autumn. The lead concentrations are 1.28-7.75 mg/kg in plants. The concentration was highest in spring and significantly higher than in summer. The bioaccumulation factor of Phragmites australis was 0.064 (<0.1), indicating that lead is not easily transferred to plants. Unlike the bioaccumulation factors, translocation factors have much higher values, indicating a higher transfer within the plants. Results also indicate an interesting seasonal pattern with almost 97% of lead in plants during spring being of atmospheric origin, whereas in autumn, soilborne sources contribute almost 94%. The isotopic compositions of lead in the urban atmosphere-soil-plant system show that lead pollution results from the mixing of geogenic and anthropogenic materials. Vehicle exhaust, crustal rocks and ore deposits are likely primary sources of lead pollution within the study domain.

Chromium Distribution, Leachability and Speciation in a Chrome Plating Site

Hexavalent chromium (Cr(VI)) waste produced by chrome plating activities pollutes the surrounding environment and harms human health. However, information about the chromium (Cr) pollution characteristics of actual electroplating sites is still lacking. In this study, the concentration, leachability and speciation of Cr in soils from a typical chrome plating site were analyzed. Our results showed that this site was severely contaminated by Cr (7.2 to 7735.2 mg/kg) and Cr(VI) reached the mean concentration of 138.7 mg/kg. The spatial distribution of Cr(VI) was related to the plating processes. Chrome plating and sewage treatment areas could be considered as the hot spots of contaminated sites. The vertical distribution of Cr(VI) was mainly affected by soil properties, where the loam layer retained and reduced a large amount of Cr(VI) due to its high content of iron minerals and finer particle fractions. Additionally, the chemical extraction results showed that Cr was mainly in non-residual fractions and the existence of Cr(VI) led to a high leaching toxicity based on the toxicity characteristic leaching procedure (TCLP) results. Moreover, X-ray photoelectron spectroscopy (XPS) results revealed the speciation of Cr in the long-term contaminated soils. A large amount of Cr(VI) was reduced into Cr(III) and mainly existed as Cr(OH)3 and Cr2O3. Furthermore, Cr(VI) tended to precipitate as CaCrO4 and persisted in soils. Therefore, it is necessary to find appropriate strategies to remediate these contaminated soils. Overall, these findings strengthen our understanding of Cr(VI) behaviors and lay a foundation for the future pollution investigation, ecological remediation and risk assessment of sites contaminated by electroplating.

Plasma membrane-localized protein BcHIPP16 promotes the uptake of copper and cadmium in planta

Cadmium (Cd) is one of the toxic heavy metals in soil, which not only suppresses crop production but also threatens human health. In this study, we aim to clarify the biological function of Cd-related gene BcHIPP16, so as to provide potential genetic solutions to decrease the Cd levels of pak choi. Tissue expression analysis showed that BcHIPP16 expressed in almost all the plant bodies. The transcriptional level of BcHIPP16 in roots was higher than that in shoots, which was significantly induced by copper (Cu) deficiency and Cd exposure conditions. Subcellular localization revealed that BcHIPP16 localized in plasma membrane. Expressing BcHIPP16 in yeast cells improved the sensitivity to Cu and Cd and improved their accumulation in yeast. Furthermore, the Cu and Cd content of Arabidopsis seedlings were increased and complemented, respectively when expressing BcHIPP16 in wild type (WT) and hip16 mutants. Non-invasive Micro-test Technology (NMT) was used to measure the real-time Cd²⁺ influx from the root surface of BcHIPP16 transgenic Arabidopsis lines, and the result demonstrated that BcHIPP16 promoted Cd²⁺ influx into Arabidopsis root cells. Taken together, our study showed that BcHIPP16 contributed to absorbing nutrient metal Cu and heavy metal Cd in planta.

Kinetics of Cu, Pb and Zn removal during soil flushing with washing agents derived from sewage sludge

This paper presents the first tests of Cu (7875 mg/kg), Pb (1414 mg/kg) and Zn (566 mg/kg) removal from contaminated soil with sewage-sludge-derived washing agents (SS_WAs) (dissolved organic matter, DOM; soluble humic-like substances, HLS; soluble humic substances, SHS) and Na₂EDTA (as a standard benchmark) in column experiments. Flow rates of 0.5 ml/min and 1 ml/min were used. Using a 1. order kinetic model, the kinetic constant (k), the maximum concentrations of each metal removed (C_max), and the initial rates of metal removal (r) were established. At both flow rates, stable flow velocity was maintained for approximately eight pore volumes, for flushing times of 8 h (1.0 ml/min) and 16 h (0.5 ml/min). Although the flow rate did not influence k, it influenced C_max: at 1 ml/min, C_max values were higher than at 0.5 ml/min. For Cu and Zn, but not Pb, k was about twofold higher with Na₂EDTA than with SS_WAs. Although Na₂EDTA gave the highest k_Cu, C_max,Cu was highest with DOM (Na₂EDTA, 66%; DOM 73%). For Pb removal, HLS was the most effective SS_WA (77%; Na₂EDTA was 80% effective). k_Zn was about twofold higher with Na₂EDTA than with SS_WAs. C_max,Zn was highest with HLS. The quick mobilization of Cu, Pb and Zn with most of the WAs corresponded to efficient metal removal from the exchangeable (F1) fraction.

Implications of the Phytoremediation of Heavy Metal Contamination of Soils and Wild Plants in the Industrial Area of Haina, Dominican Republic

The study evaluates pollution by Pb, Zn, and Cr, and a possible sustainable solution through phytoremediation technologies, in the surroundings of Haina, a very polluted area of the Dominican Republic. Soils and plants were analyzed at 11 sampling points. After sample processing, the elemental composition was analyzed by ICP-OES. Soil metal concentrations, contaminating factors, pollution load indexes, and the Nemerow pollution index were assessed. Soil metal concentrations showed Pb > Zn > Cr, resulting in very strong Pb pollution and medium-impact Zn pollution, with an anthropogenic origin in some sites. This means that some agricultural and residential restrictions must be applied. Accumulation levels in plant tissues, bioaccumulation factors in roots and shoots, and translocation factors were determined for Acalypha alopecuroidea, Achyranthes aspera, Amaranthus dubius, Bidenspilosa, Heliotropium angiospermum, Parthenium hysterophorus, and Sida rhombifolia. The vast majority of the plants showed very low levels of the potentially toxic elements studied, although it may be advisable to take precautions before consumption as they are all considered edible, fodder, and/or medicinal plants. Despite their low rate of bioaccumulation, most of the plants studied could be suitable for the application of phytoremediation of Zn in the field, although further studies are needed to assess their potential for this.

Tolerance and phytoremediation potential of grass species native to South American grasslands to copper-contaminated soils

Grass species native to South American can have mechanisms to tolerate copper (Cu) excess, which improves their use to phytoremediate Cu-contaminated soils . The aims of the present study are to assess the tolerance of grass species native to South American grasslands to copper-contaminated soils, as well as their adaptive responses under high Cu-stressed condition and to identify native grass species presenting the highest potential to be used for phytoremediation purposes. Soil samples were air-dried and their acidity, phosphorus and potassium levels were corrected, and the samples were incubated. Three Cu levels were used in the experiment: natural (Dose 0), with added of 40 mg kg^-1 of Cu and with added of 80 mg kg^-1 of Cu. Three Axonopus affinis, Paspalum notatum and Paspalum plicatulum seedlings were transferred to 5-L pots filled with soil in August and grown for 121 days. Soil solution was collected during cultivation with the aid of Rhizon lysimeters. Main concentrations of cations and anions, dissolved organic carbon and pH in the soil solution were analyzed and the ionic speciation was carried out. Cu toxicity impaired the growth of grass species native to South America, since Cu excess led to both changes in root morphology and nutritional unbalance. Among all assessed native species, Paspalum plicatulum was the one presenting the greatest potential to phytostabilize in Cu-contaminated soils, since it mainly accumulates Cu absorbed in the roots; therefore, its intercropping with grapevines is can be beneficial in Cu-contaminated soils.

Differential proteome analysis of the leaves of lead hyperaccumulator, Rhoeo discolor (L. Her.) Hance

The present study investigated Rhoeo discolor (L. Her.) Hance for its ability to accumulate Pb, which is of relevance to phytoremediation applications. Based on this analysis, plants were found to accumulate greater than 10 mg/g (0.1%) of dry weight Pb in the shoots, which classifies the plant a Pb hyperaccumulator. Further, changes in the leaf proteome profiles in response to Pb stress were investigated. Wild-type plants were subjected to a high concentration of Pb(NO3 )2 , and the levels of Pb that accumulated in different plant tissues were determined using atomic absorption spectrophotometry. Using 2D-difference gel electrophoresis, 181 protein spots were detected to be differentially abundant in response to Pb stress and selected spots exhibiting the strongest differential abundance suggested an impairment of the photosynthetic apparatus of the plant under Pb stress. Subsequently, a more extensive, proteome wide analysis utilizing label-free quantitation further identified a predominant decrease in protein levels and a significant effect on the nuclear proteome, as well as photosynthesis, carbon fixation and metabolism, providing insight into the Pb tolerance of this system in a potential phytoremediation context.

Effective recycling of Cu from electroplating wastewater effluent via the combined Fenton oxidation and hydrometallurgy route

Heavy metals, which commonly occur in complex forms, are difficult to remove in alkali electroplating wastewater effluent, and their resource recycling is rarely reported. Here, a Cu-bearing alkali wastewater effluent was effectively treated through Fenton oxidation, and the generated Fenton sludge was recycled into highly pure tenorite and hematite particles. The effluent contained 1.51 mg/L Cu and was subjected to Fenton oxidation, pH adjustment and coagulation. Amongst the three methods, Fenton oxidation showed superior efficiency to Cu removal, and the residual Cu in the effluent was 0.06 mg/L, thereby meeting the discharge standard for electroplating wastewater. However, Cu removal achieved less than 20% after pH adjustment and coagulation. Cu-bearing sludge, which was generated through the Fenton process, was dissolved in a mixture of hydrochloric and nitric acids. The dissolved solution contained 1.92 g/L Cu and 73.6 g/L Fe impurity. Impure Fe (67.4%) was removed as hematite aggregates after the solution was directly treated via a hydrometallurgy route, whilst 99.2% Cu was kept. When 0.5 mL of methanol was introduced to the hydrometallurgy system, nearly 100% Fe was removed as hematite nanoparticles with 94.8% purity, whilst more than 98% Cu was kept. The residual Cu was 1.88 g/L and precipitated as a tenorite block with a CuO content of 91.1% by adjusting the treated solution to pH 9. This study presented an environment-friendly method for enriching Cu from electroplating wastewater effluent without generating any waste.

New-Generation Washing Agents in Remediation of Metal-Polluted Soils and Methods for Washing Effluent Treatment: A Review

Soil quality is seriously reduced due to chemical pollution, including heavy metal (HM) pollution. To meet quality standards, polluted soils must be remediated. Soil washing/soil flushing offers efficient removal of heavy metals and decreases environmental risk in polluted areas. These goals can be obtained by using proper washing agents to remove HMs from soil. These washing agents should not pose unacceptable threats to humans and ecosystems, including soil composition. Currently, it is desirable to use more environmentally and economically attractive washing agents instead of synthetic, environmentally problematic chemicals (e.g., ethylenediaminetetraacetic acid (EDTA)). The usefulness of novel washing agents for treatment of heavy metal-contaminated soils is being intensively developed, in terms of the efficiency of HM removal and properties of washed soils. Despite the unquestionable effectiveness of soil washing/flushing, it should be remembered that both methods generate secondary fluid waste (spent washing solution), and the final stage of the process should be treatment of the contaminated spent washing solution. This paper reviews information on soil contamination with heavy metals. This review examines the principles and status of soil washing and soil flushing. The novel contribution of this review is a presentation of the sources and characteristics of novel washing agents and chemical substitutes for EDTA, with their potential for heavy metal removal. Methods for treating spent washing solution are discussed separately.

Improvement of water quality in the Pearl River Estuary, China: a long-term (2008-2017) case study of temporal-spatial variation, source identification and ecological risk of heavy metals in surface water of Guangzhou

A series of environmental protective policies have been taken recently in the Pearl River Estuary (PRE) to alleviate water pollution; however, their influence on the reduction of heavy metals in estuarine water has not been known. This study selected Guangzhou as a representative city in the PRE and collected estuarine water monthly from 2008 to 2017 to track the variation of As, Hg, Pb, Cd, Cu, Zn, and Se. During the last decade, the high time-resolved record showed that the concentration of Hg, Pb, Cd, Cu, and Zn in estuarine water reduced by 39.5%, 91.0%, 86.2%, 74.6%, and 97.3%, respectively. However, the concentration of As kept in a stable range (1.89-2.69 μg L^-1) and Se (0.17-0.65 μg L^-1) increased slightly. The principal component analysis (PCA) and absolute principal component scores-multiple linear regression (APCS-MLR) results suggested that the upstream industrial effluents were major sources for Hg (45.5-92.7%), Pb (47.3-100%), Cd (42.0-90.6%), Cu (85.5-100%), and Zn (100%) and the geogenic source was major origin for As (84.6-98.3%) and Se (0-67.5%). The risk quotient of Hg, Pb, Cd, Cu, and Zn to aquatic organisms largely decreased from 0.03, 0.59, 0.03, 2.06, and 0.26 in 2008 to 0.02, 0.05, 0.006, 0.52, and 0.007 in 2017, respectively. The effective control of heavy metal pollution in the study area can be primarily due to the relocation of hundreds of polluting factories during the last decade.

Potential of indigenous plant species for phytoremediation of metal(loid)-contaminated soil in the Baoshan mining area, China

A field survey was conducted to investigate metal(loid) concentration in soils and native plants in the Baoshan mining area for potential application in phytoremediation. Total concentrations of arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn) in soil varied from 125 to 6656, 5.10 to 1061, 568 to 49294, and 241 to 17296 mg kg^-1, respectively, showing severe contamination. Among 20 species native to this area, Pteris ensiformis accumulated 1091 mg kg^-1 As in the shoot, and its translocation factor (TF) was greater than 1, suggesting potential capacity for As phytoextraction. Boehmeria nivea, Aster prorerus, and Hydrocotyle sibthorpioides showed potential for phytoextraction of Cd due to their high accumulation of Cd in shoots (490.3, 175.4, and 128.5 mg kg^-1, respectively) and high TFs (92.0, 22.1, and 6.7, respectively). Eleusine indica and P. ensiformis were found to contain high concentrations of Pb (7474 mg kg^-1) and Zn (1662 mg kg^-1) in roots, but with low TFs for Pb (0.4) and Zn (0.2), suggesting potential capability for phytostabilization. There was a positive correlation (p < 0.01, N = 25) of TFs between the metal(loid)s, indicating a synergic interaction in the uptake of metal(loid)s by these plants. According to metal(loid) concentrations in shoots, bioconcentration factors (BFs), and TFs, as well as the botanical features such as wide occurrence, high biomass yield, and rapid growth of the plants, the five native species identified above have the potential for phytoremediation in the Baoshan mining area.

Toxicological potential of cobalt in forage for ruminants grown in polluted soil: a health risk assessment from trace metal pollution for livestock

The trace metal pollution in the environment is a highly concerned issue in these days. One of the important causes of trace metal pollution is the exhaust gases released from the vehicles on the roads. These dangerous gases pose life-threatening effects on the forage plants grown along the roadside as these plants are at direct risk to these trace metals. The aims of the present study were to determine the cobalt (Co) concentrations in soil, forages, and blood plasma of the buffaloes and to evaluate the Co deficiencies and toxicities in these samples. All samples were collected from six sites (Faisalabad roadside, Bhalwal roadside, Shaheenabad roadside, Mateela roadside, 50 Chak roadside, and Dera Saudi-control) of Sargodha city. The Co concentrations in these samples were determined by atomic absorption spectrophotometer (AA-6300 Shimadzu Japan). In soil samples, Co level ranged from 1.958 to 3.457 mg/kg in the six sampling sites. The highest Co level was observed at site 6 and the lowest at site 2. In forage samples, Co level ranged from 0.770 to 2.309 mg/kg in the six sampling sites. The highest Co level was observed at site 3 and the lowest at site 2. In blood plasma samples, Co level ranged from 2.644 to 4.927 mg/kg in the six sampling sites. The highest Co level was observed at site 1 and the lowest at site 3. The results showed higher Co values in the samples collected from the site IV while the bioconcentration factor for forage-soil was found highest in the samples collected from Site III. On the other hand, a correlation was found positively significant when soil and forage were correlated, and it was found negatively significant when blood and forage were correlated.

Accumulation of heavy metals in metallophytes from three mining sites (Southern Centre Morocco) and evaluation of their phytoremediation potential

The current study aims to perform a field survey of three abandoned mining sites in the southern centre of Morocco to assess the recent metal pollution in soils and accumulation potential of plant species. Native plants and soils were sampled at several sites in the studied mines and analysed for Cu, Zn, Pb and Cd concentrations. Soils in the investigated sites proved to be deficient in major macronutrients and to contain toxic levels of Cu, Zn, Pb and Cd. Botanical survey of the prospected sites showed the abundance of diverse plant communities (46 species and 19 families), with no obvious toxicity symptoms. Results showed that the concentrations of heavy metals were different in the same plant species and from plant species to another. Eight plants of 46 species namely Hirschfeldia incana (L.) Lagr.-Foss, Citrullus vulgaris (L.) Schradi, Portulaca oleracea L., Stipa capensis Thunb., Lactuca viminea (L.) J.Presl & C.Presl, Forsskaolea tenacissima L., Lycium intricatum Boiss. and Hammada scoparia (Pomel) Iljin were considered as the best-performing specimens due to their high ability to accumulate multiple metals in their shoots and roots without being affected by excessive metal contents. This was confirmed by the transfer factors generally higher than 1. Consequently, these tolerant and native plant species could be used as tools for an effective phytorestoration of metal-contaminated sites.

Intercropping of young grapevines with native grasses for phytoremediation of Cu-contaminated soils

Intercropping may be a strategy for phytoremediation of vineyard soils with high copper (Cu) content. The study aimed to evaluate the contribution of South American native grasses in limiting Cu availability and toxicity in soils grown with grapevines. The soil used in the experiment was collected in natural grassland with no history of cultivation. The samples were air-dried; acidity, P and K levels were corrected and samples were then incubated. We used three Cu levels - natural content (Dose 0) and the addition of 40 and 80 mg Cu kg^-1 of soil (Dose 40 and 80). At each Cu dose, grapevine was grown in three cropping treatments: monocropping, intercropping with Paspalum plicatulum and intercropping with Axonopus affinis. In intercropping, two grass seedlings were transplanted into each experimental unit 35 days prior to the transplanting of the grapevines. The soil solution was sampled and ionic speciation was carried out. At 70 days after planting, we sampled the grapevines to determine dry matter, morphological parameters and nutrient concentration in the roots and shoots. Intercropping young grapevines with Paspalum plicatulum and Axonopus affinis was efficient in promoting the growth of young grapevines at moderate and low levels of Cu contamination by reducing Cu bioavailability. This indicates that maintaining native grasses in young vineyards is an effective strategy for phytoremediating Cu-contaminated soils and obtaining a grape production system with reduced interventions in the native environment, in addition to contributing to soil protection and nutrient cycling.

Oxidative Stress and Heavy Metals in Plants

Oxidative stress is a pathological process related to not only animal kingdom but also plants. Regarding oxidative stress in plants, heavy metals are frequently discussed as causative stimuli with relevance to ecology. Because heavy metals have broad technological importance, they can easily contaminate the environment. Much of previous effort regarding the harmful impact of the heavy metals was given to their toxicology in the animals and humans. Their implication in plant pathogeneses is less known and remains underestimated.The current paper summarizes basic facts about heavy metals, their distribution in soil, mobility, accumulation by plants, and initiation of oxidative stress including the decline in basal metabolism. The both actual and frontier studies in the field are summarized and discussed. The major pathophysiological pathways are introduced as well and link between heavy metals toxicity and their ability to initiate an oxidative damage is provided. Mobility and bioaccessibility of the metals is also considered as key factors in their impact on oxidative stress development in the plant. The metals like lead, mercury, copper, cadmium, iron, zinc, nickel, vanadium are depicted in the text.Heavy metals appear to be significant contributors to pathological processes in the plants and oxidative stress is probably an important contributor to the effect. The most sensitive plant species are enlisted and discussed in this review. The facts presented here outline next effort to investigate pathological processes in the plants.

Cadmium tolerance and accumulation characteristics of wetland emergent plants under hydroponic conditions

For the purpose of screening a potential Cd-hyperaccumulator for Cd-contaminated soil in paddy fields, four kinds of wetland emergent plants (Iris sibirica L., Acorus calamus L., Typha orientalis Presl and Cyperus alternifolius L.) were investigated for their cadmium tolerance and accumulation characteristics under hydroponic conditions. The physiological responses of plants, Cd concentration in tissues, Cd accumulation, bioaccumulation factor (BCF) and translocation factor (TCF) were investigated to evaluate the abilities of wetland emergent plants to absorb and accumulate Cd. In comparison with the other selected emergent plants, Iris sibirica L. has the strongest Cd-tolerance for the absence of Cd toxic symptoms and a Cd concentration as high as 127.3 mg kg⁻¹ in shoots. Due to its large biomass, the Cd accumulation could reach up to 9.4 mg per plant in roots and 5.7 mg per plant in shoots, respectively. Iris sibirica L. possesses the highest TCF, and its BCF for Cd increased with increasing concentration of spiked Cd in the hydroponic solutions. The results indicate that Iris sibirica L. is a potential Cd-hyperaccumulator that may have a strong capacity for extracting Cd from Cd-contaminated paddy soils.

Four kinds of wetland emergent plants (Iris sibirica L., Acorus calamus L., Typha orientalis Presl and Cyperus alternifolius L.) were investigated for their cadmium tolerance and accumulation characteristics under hydroponic conditions.

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.

Physiological and biochemical characterization of two Amaranthus species under Cr(VI) stress differing in Cr(VI) tolerance

The present study was undertaken to evaluate Cr(VI) toxicity tolerance in two Amaranthus species viz. Amaranthus viridis and Amaranthus cruentus exposed to hexavalent chromium [Cr(VI)] stress. To ascertain this, both Amaranthus species were grown under various concentrations (0, 10 and 50 μM) of Cr(VI) in the hydroponic system. After 7 days of Cr(VI) treatment, various traits such as growth, Cr accumulation, photochemistry of photosystem II (PS II) (JIP-test), oxidative stress and antioxidant defense system were analyzed. Cr(VI) treatments caused inhibition in growth and PS II photochemistry, which was accompanied with increased accumulation of Cr that results into enhanced generation of reactive oxygen species (ROS): O₂^- and H₂O₂, which subsequently induced the peroxidation of lipids and leakage of electrolyte in both the Amaranthus species. Cr(VI) accumulation, lipid peroxidation and electrolyte leakage were more pronounced in A. viridis than in A. cruentus. On the other hand, A. cruentus seedlings showed higher activities of enzymatic antioxidants: SOD, POD, CAT and GST, and non-enzymatic antioxidants: cysteine and non-protein thiols (NP-SH) levels than A. viridis. The overall results suggest that A. cruentus is more tolerant than A. viridis due to its higher antioxidant defense system that protected seedlings under Cr(VI) stress.

Classification and identification of metal-accumulating plant species by cluster analysis

Identification and classification of metal-accumulating plant species is essential for phytoextraction. Cluster analysis is used for classifying individuals based on measured characteristics. In this study, classification of plant species for metal accumulation was conducted using cluster analysis based on a practical survey. Forty plant samples belonging to 21 species were collected from an ancient silver-mining site. Five groups such as hyperaccumulator, potential hyperaccumulator, accumulator, potential accumulator, and normal accumulating plant were graded. For Cd accumulation, the ancient silver-mining ecotype of Sedum alfredii was treated as a Cd hyperaccumulator, and the others were normal Cd-accumulating plants. For Zn accumulation, S. alfredii was considered as a potential Zn hyperaccumulator, Conyza canadensis and Artemisia lavandulaefolia were Zn accumulators, and the others were normal Zn-accumulating plants. For Pb accumulation, S. alfredii and Elatostema lineolatum were potential Pb hyperaccumulators, Rubus hunanensis, Ajuga decumbens, and Erigeron annuus were Pb accumulators, C. canadensis and A. lavandulaefolia were potential Pb accumulators, and the others were normal Pb-accumulating plants. Plant species with the potential for phytoextraction were identified such as S. alfredii for Cd and Zn, C. canadensis and A. lavandulaefolia for Zn and Pb, and E. lineolatum, R. hunanensis, A. decumbens, and E. annuus for Pb. Cluster analysis is effective in the classification of plant species for metal accumulation and identification of potential species for phytoextraction.

Metal accumulation strategies in plants spontaneously inhabiting Zn-Pb waste deposits

Metal (Zn, Pb, Cd, Cu, Ni, Cr) accumulation in shoots of 38 plant species spontaneously colonizing three Zn-Pb waste deposits in southern Poland was studied in order to find out if the age of the waste (30-130 years) or its type (slag or flotation residues) influence metal content in plants and to identify species potentially suitable for biomonitoring and phytoremediation. The total metal concentrations in the waste upper layers ranged from 7300 to 171,790 mg kg(-1) for Zn, from 1390 to 22,265 mg kg(-1) for Pb, and from 66 to 1,464 mg kg(-1) for Cd, whereas CaCl2-extracted fractions accounted for 0.034-0.11 %, 0.005-0.03 %, and 0.28-0.62 % of total Zn, Pb and Cd concentrations, respectively. The concentrations of Cu, Ni, and Cr in substrates and in plants were low and ranged within the background values. Metal accumulation in plant shoots was poorly correlated with both total and CaCl2-extracted forms of metals in the substrate and was highly variable among species and also specimens of the same species. The highest mean concentrations of Zn, Pb and Cd were found in Anthyllis vulneraria L. (901.5 mg kg(-1)), Echium vulgare L. (116.92 mg kg(-1)), and Hieracium piloselloides Vill. (26.86 mg kg(-1)), respectively. Besides Reseda lutea L., no species appeared to be a good indicator of polymetallic environment pollution based on chemical analysis of shoots; however, metal accumulation in the whole plant communities of a particular contaminated area might be an accurate tool for assessment of metal transfer to vegetation irrespective of the type or age of the waste. All the species studied developed a metal exclusion strategy, thus exhibiting potential for phytostabilization of metalliferous wastelands.

Bioaccumulation of zinc, lead, copper, and cadmium from contaminated sediments by native plant species and Acrida cinerea in South China

This research was conducted to search and identify spontaneously growing heavy metal-tolerant plant species that are potentially useful for phytoremediation in contaminated sediment. Five sites were selected for collection of plants growing on polluted shore (river bank) sediment of the Xiang River, China. The concentrations of Zn, Pb, Cu and Cd in plants, sediments, and grasshoppers were determined using flame atomic absorption spectrophotometer (AAS700, Perkin-Elmer, USA). Considering translocation factor and bioaccumulation factor, Rumex crispus (Polygonaceae), Rumex dentatus (Polygonaceae), and Lagopsis supina (Labiatae) could be potentially useful for phytostabilization of metals. R. crispus can be considered potentially useful for phytoextraction of Cd. In light of the biomagnification factors, grasshoppers are deconcentrators for Pb and Cd, microconcentrators for Zn and macroconcentrators for Cu to the plants, respectively. To the best of our knowledge, the present study is the first report on Zn, Pb, Cu and Cd accumulation in R. crispus and L. supina, providing a pioneer contribution to the very small volume of data available on the potential use of native plant species from contaminated sediments in phytostabilization and phytoremediation technologies.