Plants in Heavy Metal Soils

Arsenic and heavy metals at Japanese abandoned chemical weapons site in China: distribution characterization, source identification and contamination risk assessment

As-containing chemical weapons (CWs) and their degraded products pose a great threat to the environment and to human health. In this study, concentration and distribution characteristics, source identification, and health risk assessments were determined for As, Cr, Ni, Cu, Zn, Cd and Pb in environmental samples from Lianhuapao (LHP), a typical site of Japanese abandoned chemical weapons (JACWs) in China. The results show that the concentration levels of As, Cr and Ni in the LHP soils are abnormally high, with 69.57%, 83.33% and 91.67%, respectively, of the total sample exceeding the risk screening values for soil contamination of agricultural land. As levels in water samples were generally within safety limits, with the exception of perched water in the core contamination area. In the study area, none of the dominant plant species were enriched with As, except for the Pteris vittata L. Pentavalent arsenic was found to be the predominant arsenic species in the topsoil and water samples. Source identification using statistical approaches indicated that the concentrations of As, Pb, Cu, Cd and Zn are likely influenced by JACWs, while Cr and Ni levels may be related to the natural weathering process. The total concentrations of As, Cr and Ni showed a significant degree of contamination, but only As displayed high potential ecological risk. The calculated indexes of health risk evaluation strongly indicate an unacceptable carcinogenic risk (1E-04) to children, and higher non-carcinogenic risk, relative to that of adults. Our data indicate that the health risk from the resulting As contamination is still a cause for concern, although the JACWs were excavated decades ago from these soils.

Strategies of accumulation of potentially toxic elements in Minuartia recurva and M. bulgarica

The aim of this study was to determine the concentrations of potentially toxic elements in soil samples and plant tissues of Minuartia recurva and M. bulgarica, predominantly or exclusively calcifuge species. Biological concentration (BCs) and translocation factors (TFs) were used to evaluate their accumulation potential. Considerable differences were observed between M. recurva and M. bulgarica assessions in terms of accumulation strategies of potentially toxic elements (PTEs). In M. recurva, most of the elements analyzed (Mn, Cu, Zn, Cd, and Co) were transported to the shoot, whereas in M. bulgarica, these elements remained predominantly in the roots. The Cu concentrations in the shoot samples of M. recurva from an abandoned iron-copper mine at Mt. Kopaonik were clearly above the notional hyperaccumulation threshold, characterizing this species as a possible Cu hyperaccumulator. Additionally, strong accumulation potential for Cr, Ni, Zn, Pb, and Cd was observed in M. recurva assessions, but without significant accumulation due to the low concentrations of these elements in the soils. The strong accumulation capacity and the different strategies in tolerance to PTEs indicate a potential of the two species for an application in phytoremediation: M. recurva for phytoextraction and M. bulgarica for phytostabilization.

Storage and recycling of major and trace element in mangroves

The role of mangroves in sequestering metal and nutrients in sediment has been described in the past, but knowledge gaps still exist on storage capacity and recycling fluxes of elements in plant biomass, notably concerning their magnitude in root uptake and loss by litterfall. This study addresses the storage and transport pathways of 16 elements, classified as macro-nutrients (Ca, Mg, Na, K), micro-nutrients (Fe, Mn, Ni, Co, Cu, Cr, Zn, Mo), and potential toxicants (Al, Cd, Sn, Pb) in the world's largest mangroves, the Sundarbans. Elemental concentrations in plant organs were generally lower than in the sediment. The stock of macro and micro-nutrients in plant biomass varied from 60 to 2717 and 0.003 to 37.7 Mg ha^-1 respectively, with highest values observed for Na and lowest for Cd. The Avicennia species exhibited the maximal accumulation of all elements. Translocation of major elements to different plant organs increased with increasing their concentrations in the sediment. Elemental loss via litterfall indicated that Sundarbans mangrove could act as a source, particularly of Mn, to the Bay of Bengal. Moreover, belowground uptake of the 16 elements showed 2-3 fold higher fluxes than their loss via litterfall. There was a significant retention of some trace elements (notably Mo, Cd, and Sn) in plant biomass, which might allow one to use these mangroves for phytoremediation and restoration purposes. We conclude that mangroves efficiently store and remobilize major and trace elements from the sediments by root uptake and recycle back to sediment surface via litterfall.

Combining genotype, phenotype, and environmental data to delineate site-adjusted provenance strategies for ecological restoration

Despite the importance of climate-adjusted provenancing to mitigate the effects of environmental change, climatic considerations alone are insufficient when restoring highly degraded sites. Here we propose a comprehensive landscape genomic approach to assist the restoration of moderately disturbed and highly degraded sites. To illustrate it we employ genomic data sets comprising thousands of single nucleotide polymorphisms from two plant species suitable for the restoration of iron-rich Amazonian Savannas. We first use a subset of neutral loci to assess genetic structure and determine the genetic neighbourhood size. We then identify genotype-phenotype-environment associations, map adaptive genetic variation, and predict adaptive genotypes for restoration sites. Whereas local provenances were found optimal to restore a moderately disturbed site, a mixture of genotypes seemed the most promising strategy to recover a highly degraded mining site. We discuss how our results can help define site-adjusted provenancing strategies, and argue that our methods can be more broadly applied to assist other restoration initiatives.

Plant abiotic stress response and nutrient use efficiency

Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth, productivity and quality. Plants have evolved mechanisms to perceive these environmental challenges, transmit the stress signals within cells as well as between cells and tissues, and make appropriate adjustments in their growth and development in order to survive and reproduce. In recent years, significant progress has been made on many fronts of the stress signaling research, particularly in understanding the downstream signaling events that culminate at the activation of stress- and nutrient limitation-responsive genes, cellular ion homeostasis, and growth adjustment. However, the revelation of the early events of stress signaling, particularly the identification of primary stress sensors, still lags behind. In this review, we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies.

Copper-induced concomitant increases in photosynthesis, respiration, and C, N and S assimilation revealed by transcriptomic analyses in Ulva compressa (Chlorophyta)

BACKGROUND

The marine alga Ulva compressa is the dominant species in copper-polluted coastal areas in northern Chile. It has been shown that the alga tolerates micromolar concentrations of copper and accumulates copper at the intracellular level. Transcriptomic analyses were performed using total RNA of the alga cultivated with 10 μ M copper for 0, 1, 3 and 5 days using RNA-seq in order to identify processes involved in copper tolerance.

RESULTS

The levels of transcripts encoding proteins belonging to Light Harvesting Complex II (LHCII), photosystem II (PSII), cytochrome b6f, PSI, LHCI, ATP synthase and proteins involved in repair of PSII and protection of PSI were increased in the alga cultivated with copper. In addition, the level of transcripts encoding proteins of mitochondrial electron transport chain, ATP synthase, and enzymes involved in C, N and S assimilation were also enhanced. The higher percentages of increase in the level of transcripts were mainly observed at days 3 and 5. In contrast, transcripts involved protein synthesis and degradation, signal transduction, and replication and DNA repair, were decreased. In addition, net photosynthesis and respiration increased in the alga cultivated with copper, mainly at days 1 to 3. Furthermore, the activities of enzymes involved in C, N and S assimilation, rubisco, glutamine synthase and cysteine synthase, respectively, were also increased, mainly at days 1 and 3.

CONCLUSIONS

The marine alga U. compressa tolerates copper excess through a concomitant increase in expression of proteins involved in photosynthesis, respiration, and C, N and S assimilation, which represents an exceptional mechanism of copper tolerance.

A review on global metal accumulators-mechanism, enhancement, commercial application, and research trend

The biosphere is polluted with metals due to burning of fossil fuels, pesticides, fertilizers, and mining. The metals interfere with soil conservations such as contaminating aqueous waste streams and groundwater, and the evidence of this has been recorded since 1900. Heavy metals also impact human health; therefore, the emancipation of the environment from these environmental pollutants is critical. Traditionally, techniques to remove these metals include soil washing, removal, and excavation. Metal-accumulating plants could be utilized to remove these metal pollutants which would be an alternative option that would simultaneously benefit commercially and at the same time clean the environment from these pollutants. Commercial application of pollutant metals includes biofortification, phytomining, phytoremediation, and intercropping. This review discusses about the metal-accumulating plants, mechanism of metal accumulation, enhancement of metal accumulation, potential commercial applications, research trends, and research progress to enhance the metal accumulation, benefits, and limitations of metal accumulators. The review identified that the metal accumulator plants only survive in low or medium polluted environments with heavy metals. Also, more research is required about metal accumulators in terms of genetics, breeding potential, agronomics, and the disease spectrum. Moreover, metal accumulators' ability to uptake metals need to be optimized by enhancing metal transportation, transformation, tolerance to toxicity, and volatilization in the plant. This review would benefit the industries and environment management authorities as it provides up-to-date research information about the metal accumulators, limitation of the technology, and what could be done to improve the metal enhancement in the future.

High levels of heavy metals in Western Arabian Gulf mangrove soils

Major development along the Western Arabian Gulf coast has disturbed the marine environment, and led to increased concentrations of heavy metals in the coastal soils. The amount of 13 of these metals (Ag, Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, V and Zn) in Avicennia marina branches and leaves as well as in rhizosphere soil samples from two Bays 70 km apart (Tarut Bay; Saudi Arabia and Tubli Bay; Bahrain) was quantified. Heavy metal concentration in the two bays were similar and higher than those reported in other regions suggesting a generalized heavy metal pollution in the area. These concentrations are much higher than the international permissible limits of soil contaminations except for Iron and Manganese which were within the limits. The results indicate that marine environments in the area need recovery plans and monitoring.

Copper-induced increased expression of genes involved in photosynthesis, carotenoid synthesis and C assimilation in the marine alga Ulva compressa

Background

The marine alga Ulva compressa is the dominant species in coastal areas receiving effluents from copper mines. The alga can accumulate high amounts of copper and possesses a strong antioxidant system. Here, we performed short-term transcriptomic analyses using total RNA of the alga cultivated with 10 μM of copper for 0, 3, 6, 12 and 24 h by RNA-seq.

Results

De novo transcriptomes were assembled using the Trinity software, putative proteins were annotated and classified using Blast2GO. Differentially expressed transcripts were identified using edgeR. Transcript levels were compared by paired times 0 vs 3, 0 vs 6, 0 vs 12 and 0 vs 24 h at an FDR < 0.01 and Log2 Fold Change > 2. Up-regulated transcripts encode proteins belonging to photosystem II (PSII), Light Harvesting II Complex (LHCII), PSI and LHCI, proteins involved in assembly and repair of PSII, and assembly and protection of PSI. In addition, transcripts encoding enzymes leading to β-carotene synthesis and enzymes belonging to the Calvin-Benson cycle were also increased. We further analyzed photosynthesis and carotenoid levels in the alga cultivated with 10 μM of copper for 0 to 24 h. Photosynthesis was increased from 3 to 24 h as well as the level of total carotenoids. The increase in transcripts encoding enzymes of the Calvin-Benson cycle suggests that C assimilation may also be increased.

Conclusions

Thus, U. compressa displays a short-term response to copper stress enhancing the expression of genes encoding proteins involved in photosynthesis, enzymes involved carotenoids synthesis, as well as those belonging to the Calvin-Benson cycle, which may result in an increase in C assimilation.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5226-4) contains supplementary material, which is available to authorized users.

Glomeromycota communities survive extreme levels of metal toxicity in an orphan mining site

Abandoned tailing basins and waste heaps of orphan mining sites are of great concern since extreme metal contamination makes soil improper for any human activity and is a permanent threat for nearby surroundings. Although spontaneous revegetation can occur, the process is slow or unsuccessful and rhizostabilisation strategies to reduce dispersal of contaminated dust represent an option to rehabilitate such sites. This requires selection of plants tolerant to such conditions, and optimization of their fitness and growth. Arbuscular mycorrhizal fungi (AMF) can enhance metal tolerance in moderately polluted soils, but their ability to survive extreme levels of metal contamination has not been reported. This question was addressed in the tailing basin and nearby waste heaps of an orphan mining site in southern France, reaching in the tailing basin exceptionally high contents of zinc (ppm: 97,333 total) and lead (ppm: 31,333 total). In order to contribute to a better understanding of AMF ecology under severe abiotic stress and to identify AMF associated with plants growing under such conditions, that may be considered in future revegetation and rhizostabilisation of highly polluted areas, nine plant species were sampled at different growing seasons and AMF root colonization was determined. Glomeromycota diversity was monitored in mycorrhizal roots by sequencing of the ribosomal LSU. This first survey of AMF in such highly contaminated soils revealed the presence of several AMF ribotypes, belonging mainly to the Glomerales, with some examples from the Paraglomerales and Diversisporales. AMF diversity and root colonization in the tailing basin were lower than in the less-contaminated waste heaps. A Paraglomus species previously identified in a polish mining site was common in roots of different plants. Presence of active AMF in such an environment is an outstanding finding, which should be clearly considered for the design of efficient rhizostabilisation processes.

A tabulated review on distribution of heavy metals in various plants

Plants are a rich source of elements, and knowledge of their elemental composition determines their use for various purposes, especially for food and medicine. Therefore, it is necessary to create a database of the elemental composition of plants. The present review focuses on the concentration of various heavy metals as reported by various workers from time to time by using different sophisticated techniques. Cluster analysis was applied on the basis of mean values of heavy metals in plants. Co, Cu, and Cr have similar proximities. Cluster analysis was also applied to different families on the basis of their heavy metal contents. Elaeagnaceae, Adoxaceae, Thymelaeaceae, Cupressaceae, and Acoraceae had close proximities with each other. First three components of principal component analysis explained 95.7 % of the total variance. Factor analysis explained four underlying factors for heavy metal analysis. Factor 1 explained for 26.5 % of the total variance and had maximum loadings on Co, Cu, and Cr. Of the total variance, 21.7 % was explained by factor 2 and had maximum loadings on Zn and Cd. Factor 3 accounted for 19.2 % of the total variance and had maximum loadings on Ni and Pb. Mn had maximum loading on factor 4. The mean values of heavy metals as listed in this paper are Cu (18.7 μg/g dw), Mn (99.67 μg/g dw), Cr (22.9 μg/g dw), Co (19.7 μg/g dw), As (1.25 μg/g dw), Hg (0.17 μg/g dw), Zn (94.0 μg/g dw), Pb (6.93 μg/g dw), Cd (26.9 μg/g dw), Ni (19.9 μg/g dw), and Sb (0.25 μg/g dw).

Remediation of metalliferous mines, revegetation challenges and emerging prospects in semi-arid and arid conditions

Understanding plant behaviour in polluted soils is critical for the sustainable remediation of metal-polluted sites including abandoned mines. Post-operational and abandoned metal mines particularly in semi-arid and arid zones are one of the major sources of pollution by soil erosion or plant hyperaccumulation bringing ecological impacts. We have selected from the literature 157 species belonging to 50 families to present a global overview of 'plants under action' against heavy metal pollution. Generally, all species of plants that are drought, salt and metal tolerant are candidates of interest to deal with harsh environmental conditions, particularly at semi-arid and arid mine sites. Pioneer metallophytes namely Atriplex nummularia, Atriplex semibaccata, Salsola kali, Phragmites australis and Medicago sativa, representing the taxonomic orders Caryophyllales, Poales and Fabales are evaluated in terms of phytoremediation in this review. Phytoremediation processes, microbial and algal bioremediation, the use and implication of tissue culture and biotechnology are critically examined. Overall, an integration of available remediation plant-based technologies, referred to here as 'integrated remediation technology,' is proposed to be one of the possible ways ahead to effectively address problems of toxic heavy metal pollution. Graphical abstract Integrated remediation technology (IRT) in metal-contaminated semi-arid and arid conditions. The hexagonal red line represents an IRT concept based on remediation decisions by combination of plants and microbial processes.

Accumulation of heavy metals and antioxidant responses in Pinus sylvestris L. needles in polluted and non-polluted sites

The purpose of this study was to determine the concentrations of heavy metals (cadmium, iron, manganese, lead and zinc) in current-year, 1-year old and 2-year old needles of Pinus sylvestris L. Trees were from three heavily polluted (immediate vicinity of zinc smelter, iron smelter and power plant) and three relatively clean sites (nature reserve, ecologically clean site and unprotected natural forest community) in southern Poland. Analysis also concerned the antioxidant response and contents of protein, proline, total glutathione, non-protein thiols and activity of guaiacol peroxidase (GPX) in the needles. Generally, in pine needles from the polluted sites, the concentrations of the metals were higher and increased with the age of needles, and in most cases, antioxidant responses also were elevated. The highest levels of Cd, Pb and Zn were found in 2-year old pine needles collected near the polluted zinc smelter (respectively: 6.15, 256.49, 393.5 mg kg(-1)), Fe in 2-year old pine needles in the vicinity of the iron smelter (206.82 mg kg(-1)) and Mn in 2-year old needles at the ecologically clean site (180.32 mg kg(-1)). Positive correlations were found between Fe, Mn and Pb and the content of proteins and NPTs, between Cd and non-protein -SH groups, and between Zn and proline levels. The activity of GPX increased under the influence of Mn, while glutathione levels tended to decrease as Mn levels rose. The data obtained show that the levels of protein and non-protein -SH groups may be useful in biological monitoring, and that these ecophysiological parameters seem to be good evidence of elevated oxidative stress caused by heavy metals.

Mycorrhizal limonium sinuatum (L.) mill. Enhances accumulation of lead and cadmium

Heavy metals accumulation in soils poses a potential threat to ecosystems, which, in turn, threat human health through food chains. Therefore, remediating polluted sites is important to environment and humanity. In this investigation, statice (L. sinuatum) was exposed to Cd (0, 15, 30, 60 mg kg(-1) soil) or Pb (0, 100, 150, 300 mg kg(-1) soil) in a pot experiment to assess its tolerance to each metal and study its phytoaccumulation capability. The benefits of mycorrhization (mixture of Glomus mosseae and G. intraradices) were also studied simultaneously. Single exposure to Cd or Pb reduced the plant growth, but statice was still relatively tolerant to both metals. The plants accumulated both metals in their roots; little was translocated to the shoots. Total Pb and total Cd accumulated by the roots was approximately 2 and 3 times higher in mycorrhizal than non-mycorrhizal plants (49 versus 147 and 595 versus 956 μg plant(-1)) respectively; however, mycorrhization alleviated metal phytotoxicity. The results suggest that statice is a potential candidate to be used as an ornamental plant in lead and cadmium polluted sites, mainly inoculated with arbuscular mycorrhizae. Besides that, it would be useful as a Pb or Cd controlling agent by means of phytostabilization.

Use of extracts from oyster shell and soil for cultivation of Spirulina maxima

Calcium ion and trace metals play important roles in various metabolisms of photosynthetic organisms. In this study, simple methods were developed to extract calcium ion and micronutrients from oyster shell and common soil, and the prepared extracts were tested as a replacement of the corresponding chemicals that are essential for growth of microalgae. The oyster shell and soil were treated with 0.1 M sodium hydroxide or with 10 % hydrogen peroxide, respectively. The potential application of these natural sources to cultivation was investigated with Spirulina maxima. When compared to standard Zarrouk medium, the Spirulina maxima cultivated in a modified Zarrouk media with elements from oyster shell and soil extract exhibited increases in biomass, chlorophyll, and phycocyanin by 17, 16, and 64 %, respectively. These results indicate that the extracts of oyster shell and soil provide sufficient amounts of calcium and trace metals for successful cultivation of Spirulina maxima.

Heavy metal bioaccumulation and antioxidative responses in Cardaminopsis arenosa and Plantago lanceolata leaves from metalliferous and non-metalliferous sites: a field study

The purpose of this study was to determine the concentrations of heavy metals (cadmium, lead, zinc, copper, iron and manganese) in soil, their bioavailability and bioaccumulation in plants leaves. This study also examined their influences on the antioxidant response of the plants Cardaminopsis arenosa and Plantago lanceolata grown in metal-contaminated and non-contaminated soils. The activities of guaiacol peroxidase and superoxide dismutase and the levels of antioxidants such as glutathione, proline and non-protein thiols were measured. Concentrations of the examined metals were several to thousands of times lower in the potentially bioavailable fraction than in the acid-extracted fraction of the soil. Similar mode of antioxidant responses in plant leaves of metalliferous populations indicates the tolerance of plants towards heavy metals. However POD and GSHt had a particularly strong role in defense reactions, as their increase was the most common reaction to heavy metal contamination.The levels of Zn, Cd and Pb in the leaves of C. arenosa better reflected metal concentrations in the metalliferous and non-metalliferous soil than the determined metal concentrations in P. lanceolata. Bioaccumulated Zn, Cd and Pb concentrations were above or in the ranges mentioned as toxic for plant tissues and therefore the studied plants have potential for use in phytostabilization.