Differential effect of metals/metalloids on the growth and element uptake of mesquite plants obtained from plants grown at a copper mine tailing and commercial seeds

Research on the role of bamboo species in the restoration of heavy metal-contaminated soil

Heavy metal contamination in the soil has become more serious due to the rapid development of the economy. Phytoremediation has evoked widespread curiosity in recent years due to its advantages in terms of being environmentally friendly and sustainable. However, there are few reports on the application of bamboo species in the field of phytoremediation, and a comprehensive overview of their potential for restoring contaminated soil by removing heavy metals is lacking. This paper incorporates existing research on bamboo species for the remediation of heavy metal-contaminated soils. It meticulously debates the physiological responses exhibited by bamboo species to heavy metal stress, encompassing growth and development responses, photosynthetic responses, and antioxidant system responses, among others. Furthermore, it elaborates on the capacity of bamboo for heavy metal accumulation and translocation, as well as their remarkable tolerance and detoxification mechanisms. This comprehensive analysis sheds light on the intricate interactions between bamboo and contaminated soil environments. Additionally, the paper summarizes various strategies for the remediation of heavy metal contamination using bamboo species. This review facilitates a more thorough exploration of the potential applications of bamboo species in the remediation of heavy metal-contaminated soils, offering a novel approach for soil environmental restoration.

Uptake of uranium into desert plants in an abandoned uranium mine and its implications for phytostabilization strategies

This research assessed a variety of native desert plant species for their ability to accumulate toxic elements in an abandoned uranium mine in the Sonoran Desert. Paired soil and plant samples were collected for six species of plants that had naturally re-colonized the mine. The mine soils had a median uranium concentration of 56.0 mg kg^-1 (range: MDL to 696) while the plant samples had concentrations of 3.7 mg kg^-1 (range: MDL to 20.0). The results showed uranium bioconcentration factors (BCFs) were between 0.051 and 0.234 with the longer-living, woody species having higher concentrations than short-lived herbaceous species. These BCF values were near the high end of values reported in the literature which implies that these desert species were either better at acquiring elements or they have fewer mechanisms to eliminate elements (e.g. litterfall). The life histories of the species were then evaluated on four criteria, namely uranium BCF, inedibility, longevity, and root depth, to assess which species would be best for phytostabilization, which is the use of plants to stabilize the soil to prevent water or wind erosion that might transport contaminants off site. The goal was to select a species that would stabilize the soil without accumulating uranium in the above ground biomass where it could enter the food web and be transported off site. Ultimately, brittlebush (Encelia farinosa A. Gray ex Torr.) was selected because of its low BCF, shallow roots and reasonable longevity.

Bamboo - An untapped plant resource for the phytoremediation of heavy metal contaminated soils

Phytoremediation is a green technology used for the remediation of heavy metal soils. However, up to now, very few plants are known to be both hyperaccumulators and fast-growers. In contrast, some non-hyperaccumulators, which possess lower extraction capacities than hyperaccumulators, are fast-growing species with much higher total biomass yields and are potential alternative phytoremediators. Bamboo is a taxonomic group comprised of 1439 species that are mostly distributed in the tropics and subtropics. Although limited studies on bamboo for phytoremediation, recent studies have shown that some bamboo species have high ability to adapt to metalliferous environments and a high capacity to absorb heavy metals. Bamboo tissues in the rhizome and culm can accumulate a large amount of heavy metals that mainly accumulate in the cell wall, vacuole, and cytoplasm. Certain bamboo species such as moso bamboo, Phyllostachys praecox, have been shown to have a high endurance in metal contaminated soils, enabling a considerable uptake and accumulation of heavy metals. However, excessive concentrations of heavy metals may cause oxidative stress and damage bamboo plants. Therefore, several management strategies have been developed to improve the phytoremediation ability of bamboo species, including the selection of tolerant bamboo species, intercropping with hyperaccumulators, fertilization applications, and employment of chelate in soil. This review demonstrates that bamboo species, which have high biomass productivity, short rotation, and high economic value, can be used for phytoremediation. However, the mechanisms of heavy metal uptake, transport, sequestration, and detoxification of different bamboo species require urgent investigation.

Variations of soil microbial communities accompanied by different vegetation restoration in an open-cut iron mining area

Overexploitation of iron mining in China has caused serious environmental pollution. Therefore, establishing a stable ecological restoration with vegetation in mining areas has gradually aroused people's awareness and obtained extensive concerns. This study aimed to evaluate vegetation restoration with Robinia pseudoacacia (RP), Acer mono (AM) and Pinus koraiensis (PK) in iron mining compared with unrestored area, to investigate the soil environment factors and microbial communities, and to better understand the correlations between soil environment factors and soil microbial communities. Vegetation restoration could reduce soil pH and alleviate soil alkaline, and remarkably increase soil nutrients, especially in RP site. Analysis of 16S rRNA and ITS rRNA gene sequences provided a total of 645,004 and 906, 276 valid sequences clustered into 7091 OTUs and 1689 OTUs at a 0.03 genetic distance for bacteria and fungi, respectively. The predominant bacterial and fungal phyla were Actinobacteria and Ascomycota in studied sites, respectively. Additionally, revegetation significantly increased the relative abundances of Proteobacteria, Gemmatimonadetes, Bacteroidetes and Patescibacteria, and decreased the relative abundance of Actinobacteria. Robinia pseudoacacia harbored the highest soil fungal community diversity, and bacterial Simpson index and Shannon index. Vegetation restoration with RP could clearly shifted soil communities compared to AM and PK. Along with the restoration of vegetation, the remarkable abiotic changes were the accumulation of total C, total N, total P, available P, available N and available K and the decreasing of soil pH, which were the most important factors affecting soil microbial communities. Our results addressed that Robinia pseudoacacia was the best preferable species than AM and PK in improving soil nutrients, soil community diversity and structure in Fe mining, providing a helpful guideline for selection of tree species.

Effect of irrigation water containing arsenic on elemental composition of bean and lettuce plants cultivated in calcareous sandy soil

Background

The uptake of arsenic by vegetables from soil irrigated with arsenic enriched groundwater poses a major health hazard. The edible portion of these vegetables transfer arsenic to the human beings. The uptake of arsenic was studied in bean (Phaseolus vulgaris L.) and lettuce (Lactuca sativa L.) in a controlled greenhouse pot culture with calcareous sandy soil as substrate. The plants were irrigated with water containing sodium arsenate at concentrations 0.1, 0.25 and 0.5 mg L− 1. The total arsenic concentration of the different plants parts was determined by ICP-MS, following microwave-assisted acid digestion. The change in plant biomass production and essential macroelements (Mg, P, K) and microelements concentration (Fe, Mn, Cu, Zn) was also studied.

Results

The As concentration in the bean was in the order: root>stem>leaf>bean fruit and in lettuce: root>leaves. At the highest dose (0.5 mg L− 1) the As concentration in the bean fruit and lettuce leaves was 22.1 μg kg− 1 and 1207.5 μg kg− 1 DW, respectively. Increasing As concentration in the irrigation water resulted in decreased edible biomass production in bean, while in lettuce the edible biomass production increased. Neither plant exhibited any visible toxicity symptoms. No significant change was observed in the macro and microelements concentration. The total and the water-soluble arsenic in soil amounted to 3.5 mg kg− 1 and 0.023 mg kg− 1, respectively. The transfer factor was found to increase with increase in the As treatment applied. The transfer factor range for bean from root to fruit was 0.003–0.005, and for lettuce from root to leaves was 0.14–0.24.

Conclusion

Considering the FAO-WHO recommended maximum tolerable daily intake (MTDI) limit of 2.1 μg kg− 1 body weight, and the biomass production, both plants should not be cultivated at As treatment level higher than 0.1 mg L− 1.

Graphical abstract

Comparison of heavy metal phytoremediation in monoculture and intercropping systems of Phyllostachys praecox and Sedum plumbizincicola in polluted soil

A bamboo species (Phyllostachys praecox) and a Cd/Zn hyperaccumulator (Sedum plumbizincicola) were tested under different planting systems to compare their heavy metal phytoremediation ability. P. praecox (MP), S. plumbizincicola (MS) and P. praecox × S. plumbizincicola (IPS) plantations were established in Cu, Zn, and Cd-contaminated soil. Soil properties and heavy metal contents in plants were determined and compared after four years of plantation establishment. The rankings of available and total metal contents in soil layers were MP > MS > IPS (0-20 cm) and MP > IPS > MS (20-40 cm, except for Cu), respectively. The Cu and Zn contents in mature bamboo tissues were significantly lower, but the Cd contents in bamboo tissues (except for leaves) higher, in the IPS than in the MP. The bioconcentration and the translocation factors in most of bamboo tissues showed an increasing trend from the MP to the IPS. Heavy metal distribution in plants is greatly affected by the planting patterns. The tested intercropping system of two plant species showed higher biomass productivity, implying more heavy metals can be removed from the soil through the harvesting of plants. Therefore, the IPS leads to significant improvement of soil phytoremediation.

Rhizoremediation of cadmium-contaminated soil associated with hydroxamate siderophores isolated from Cd-resistant plant growth-promoting Dietzia maris and Lysinibacillus strains

In search of multitrait plant growth-promoting (PGP) inoculants, we introduced two cadmium-resistant bacterial strains, C4 (PG), C5 (WB), and their consortium C6 (PG × WB) isolated from metal-contaminated industrial waste-fed canal near West Bengal. The test isolates were biochemically characterized and screened in vitro for siderophore production. The infrared spectra revealed the hydroxamate nature of the siderophore produced. Further in green house, siderophore-based seed inoculation with selected PGP isolates exhibited stimulatory effects on seed germination (up to 85.4%), chlorophyll index (22.9 spad unit), shoot and root length (70% and 62.7%), tiller numbers (38.82%), spikelet numbers (52.2%), straw yield (62.2%), grain yield (76.1%), total dry matter of root and shoot (55.56% and 64.4%, respectively), and grain yields (76.1%) of tested wheat cultivars. The 16S rRNA sequencing identified strain PG and WB as Dietzia maris and Lysinibacillus sp. strains. Furthermore, inoculation of C6 (consortium) in both cultivar UP-2565 and KS-227 showed maximum Cd sorption capacity in roots (38.3% and 67.1%) and shoots (68.4% and 67.5%), respectively. Both the strains and their consortium showed a great potential to increase the growth and yield of wheat cultivars, which can also be utilized for rhizoremediation process.

Impact of proline application on cadmium accumulation, mineral nutrition and enzymatic antioxidant defense system of Olea europaea L. cv Chemlali exposed to cadmium stress

Proline plays an important role in plant response to various environmental stresses. However, its involvement in mitigation of heavy metal stress in plants remains elusive. In this study, we examined the effectiveness of exogenous proline (10 and 20 mM) in alleviating cadmium induced inhibitory effects in young olive plants (Olea europaea L. cv. Chemlali) exposed to two Cd levels (10 and 30 mg CdCl2 kg(-1) soil). The Cd treatment induced substantial accumulation of Cd in both root and leaf tissues and a decrease in gas exchange, photosynthetic pigments contents, uptake of essential elements (Ca, Mg and K) and plant biomass. Furthermore, an elevation of antioxidant enzymes activities (superoxide dismutase, catalase, glutathione peroxydase) and proline content in association with relatively high amounts of hydrogen peroxide, thiobarbituric acid reactive substances and electrolyte leakage were observed. Interestingly, the application of exogenous proline alleviated the oxidative damage induced by Cd accumulation. In fact, Cd-stressed olive plants treated with proline showed an increase of antioxidant enzymes activities, photosynthetic activity, nutritional status, plant growth and oil content of olive fruit. Generally, it seems that proline supplementation alleviated the deleterious effects of young olive plants exposed to Cd stress.

Copper uptake by Eichhornia crassipes exposed at high level concentrations

The objective of this study was to assess the growth of water hyacinth (Eichhornia crassipes) and its ability to accumulate Cu from polluted water with high Cu concentrations and a mixture of other contaminants under short-term exposure, in order to use this species for the remediation of highly contaminated sites. Two hydroponic experiments were performed under greenhouse conditions for 7 days. One of them consisted of growing water hyacinth in Hoagland solution supplemented with 15 or 25 mg Cu/L and a control. The other one contained water hyacinth growing in polluted river water supplemented with 15 mg Cu/L and a control. Cu was accumulated principally in roots. The maximum Cu concentration was 23,387.2 mg/kg dw in the treatment of 25 mg Cu/L in Hoagland solution. Cu translocation from roots to leaves was low. The mixture of 15 mg Cu/L with polluted water did not appear to have toxic effects on the water hyacinth. This plant showed a remarkable uptake capacity under elevated Cu concentrations in a mixture of pollutants similar to pure industrial effluents in a short time of exposure. This result has not been reported before, to our knowledge. This species is suitable for phytoremediation of waters subject to discharge of mixed industrial effluents containing elevated Cu concentrations (≥15 mg Cu/L), as well as nutrient-rich domestic wastewaters.

Tolerance to cadmium of Agave lechuguilla (Agavaceae) seeds and seedlings from sites contaminated with heavy metals

We investigated if seeds of Agave lechuguilla from contaminated sites with heavy metals were more tolerant to Cd ions than seeds from noncontaminated sites. Seeds from a highly contaminated site (Villa de la Paz) and from a noncontaminated site (Villa de Zaragoza) were evaluated. We tested the effect of Cd concentrations on several ecophysiological, morphological, genetical, and anatomical responses. Seed viability, seed germination, seedling biomass, and radicle length were higher for the non-polluted site than for the contaminated one. The leaves of seedlings from the contaminated place had more cadmium and showed peaks attributed to chemical functional groups such as amines, amides, carboxyl, and alkenes that tended to disappear due to increasing the concentration of cadmium than those from Villa de Zaragoza. Malformed cells in the parenchyma surrounding the vascular bundles were found in seedlings grown with Cd from both sites. The leaves from the contaminated place showed a higher metallothioneins expression in seedlings from the control group than that of seedlings at different Cd concentrations. Most of our results fitted into the hypothesis that plants from metal-contaminated places do not tolerate more pollution, because of the accumulative effect that cadmium might have on them.

Mineral nutrition and enzymatic adaptation induced by arsenate and arsenite exposure in lettuce plants

Arsenate (As(V)) and arsenite (As(III)) contamination is able to interfere negatively on plant metabolism, promoting a reduction of nutrients uptake and transport and also an increase of reactive oxygen species (ROS) generation. However, some plants are considered tolerant against As exposure through the activation of defense mechanisms. Therefore, this study aimed to evaluate the effects of different As(V) and As(III) concentrations (0.0, 6.6, 13.2, 26.4 and 52.8 μmol L(-1)), on mineral nutrients concentration [calcium (Ca), magnesium (Mg), phosphorous (P), iron (Fe), manganese (Mg) and copper (Cu)], on membrane lipid peroxidation and also on the enzymes belonging to the antioxidant defense system [superoxide dismutase (SOD), total peroxidase (POX), catalase (CAT), glutathione reductase (GR) and ascorbate peroxidase (APX)] of plants of Lactuca sativa L. cv Hanson. As(V) and As(III), showed, in general, the same toxic effects in leaves and roots with significant changes in essential macro- and micronutrients concentration. Lipid peroxidation of cellular membranes was also observed in tested plants, probably resulted from an action of ROS generated by this metalloid. The increase of ROS generation and their scavenge were evident since an increase of SOD, POX, CAT and APX activity in leaves, and SOD, CAT and GR activity in roots were observed. Therefore, As(V) and As(III) exposure resulted in toxic effects in leaves and roots of lettuce plants; however, this plant species was able to attenuate these potential As damages through the activation of defense mechanisms, keeping its metabolism. Arsenic-tolerant plants are considered a great risk to the public health since it results in As insertion to the food chain.

Accumulation of arsenic, lead, copper, and zinc, and synthesis of phytochelatins by indigenous plants of a mining impacted area

Several native plants, able to grow in an unconfined mining impacted area that is now in close vicinity with urban areas, were evaluated for their ability to accumulate heavy metals. The main soil contaminants were As, Pb, Cu, and Zn. Sampling of the rhizospheric metal polluted soil showed that Euphorbia prostrata Aiton, Parthenium incanum Kunth, and Zinnia acerosa (DC.) A. Gray were able to grow in the presence of high amounts of mixtures of these elements. The plants accumulated the metals in the above ground parts and increased the synthesis of thiol molecules. E. prostrata showed the highest capacity for accumulation of the mixture of elements (588 μg g DW(-1)). Analysis of the thiol-molecules profile showed that these plants synthesized high amounts of long-chain phytochelatins, accompanied by low amounts of monothiol molecules, which may be related to their higher resistance to As and heavy metals. The three plants showed translocation factors from roots to leaves >1 for As, Pb, Cu, and Zn. Thus, by periodically removing aerial parts, these plants could be useful for the phytoremediation of semi-arid and arid mining impacted areas, in which metal hyper-accumulator plants are not able to grow.

Nopalea cochenillifera, a potential chromium (VI) hyperaccumulator plant

Hexavalant chromium [Cr(VI)] tolerance and accumulation in in vitro grown Nopalea cochenillifera Salm. Dyck. plants was investigated. A micropropagation protocol was establish for a rapid multiplication of N. cochenillifera and [Cr(VI)] tolerance and accumulation was studied in in vitro grown cultures. Cr concentration was estimated by atomic absorption spectroscopy in roots and shoots to confirm plant's hyperaccumulation capacity. Plants showed tolerance up to 100 μM K(2)Cr(2)O(7) without any significant changes in root growth after 16 days treatment; whereas, chlorophyll content in plants treated with 1 and 10 μM K(2)Cr(2)O(7) were not so different than the control plant. The levels of lipid peroxidation and protein oxidation increased significantly (p < 0.01) with increasing concentration of chromium. Exposures of N. cochenillifera to lower concentrations of K(2)Cr(2)O(7) (≤ 10 μM) induced catalase (CAT) and superoxide dismutase (SOD) significantly (p < 0.001) but higher concentrations of K(2)Cr(2)O(7) (>100 μM) inhibited the activities of CAT and SOD. Roots accumulated a maximum of 25,263.396 ± 1,722.672 mg Cr Kg(-1) dry weight (DW); while the highest concentration of Cr in N. cochenillifera shoots was 705.714 ± 32.324 mg Cr Kg(-1) DW. N. cochenillifera could be a prospective hyperaccumulator plant of Cr(VI) and a promising candidate for phytoremediation purposes.

Gold phytomining. A review of the relevance of this technology to mineral extraction in the 21st century

The precious metal gold can be found at high concentration in tailings dumps and waste rock piles at many mining locations around the world. Conventional technology is generally unable to economically recover this residual gold, and, as a result, the potential resource is wasted, presenting environmental risk to the wider ecosystem through particulate and dissolved metal leaching and erosion. For the past 14 years, the idea of gold phytomining to recover this gold resource has been researched by various scientific groups worldwide. A number of plant species have been tested under laboratory, greenhouse, and field conditions to determine their potential for use in the phytoextraction of gold. This paper presents a review of reported gold phytomining trials developed in the laboratory, the greenhouse under soil and hydroponic conditions, as well as in the field, between 1998 and 2011. A summary economic assessment for gold phytomining in Mexico is also presented. Mexico is an example of a developing country with a long history of gold mining that has a large resource of sites that might be suitable to gold phytomining. The technology remains limited by certain environmental and plant physiology factors. However, the increase in the market price for gold during the first decade of the 21st century and into 2011, and advances recorded for the gold concentration and biomass yield of a range of plant species, suggest that gold phytomining might be an economically viable technology.

Use of plasma-based spectroscopy and infrared microspectroscopy techniques to determine the uptake and effects of chromium(III) and chromium(VI) on Parkinsonia aculeata

Chromium uptake and tolerance by Mexican Palo Verde (Parkinsonia aculeata) (MPV) was studied in a six-month experiment with Cr(III) and Cr(VI) at 60 and 10 mg kg(-1), respectively. Chromium and nutrient uptake were determined by ICP-OES and changes in macromolecules were studied by infrared microspectroscopy (IMS). In the Cr(VI)-treated plants, chromium concentration increased in the roots only through the third month, while translocation to stems increased constantly throughout the six months. Cr(III) applications decreased the amount of Zn in leaves and stems (p < or = 0.05). Cr(VI) increased P and S in all plant tissues and increased Ca in roots, but decreased Ca in stems and leaves, and Mg in roots and stems. Cr(III) decreased P in stems and leaves, while both Cr ions decreased K in all MPV tissues. Relative to untreated plant tissue, the IMS revealed significant changes at 1730 cm(-1) and 845 cm(-1). Changes at 1730 cm(-1) indicated that the cortex and xylem of Cr-treated plants were more proteinaceous. Changes at 845 cm(-1) revealed higher lignifications in cortex. However, at the stem level, Cr(VI) decreased lignin deposition in xylem. The data showed that MPV could be useful in the phytoremediation of Cr in moderately impacted soils.

Prosopis laevigata a potential chromium (VI) and cadmium (II) hyperaccumulator desert plant

The bioaccumulation of Cr(VI) and Cd(II) in Prosopis laevigata and the effect of these heavy metals on plant growth were assessed. P. laevigata seeds were cultured during 50 days on modified Murashige-Skoog medium supplemented with four different concentrations of Cr(VI) (0-3.4mM) and Cd(II) (0-2.2mM), respectively. Heavy metals did not stop germination, but smaller plants with fewer leaves and secondary roots were produced. Seedlings showed an accumulation of 8176 and 21,437 mg Cd kg(-1) and of 5461 and 8090 mg Cr kg(-1) dry weight, in shoot and root, when cultured with 0.65 mM Cd(II) and 3.4mM Cr(VI), respectively. These results indicated that significant translocation from the roots unto aerial parts took place. A bioaccumulation factor greater than 100 for Cd and 24 for Cr was exhibited by the seedlings. P. laevigata can be considered as a potential hyperaccumulator of Cd(II) and Cr(VI) species and considered as a promising candidate for phytoremediation purposes.