Translocation Of Heavy Metals Research Articles

Amendment of vanadium-contaminated soil with soil conditioners: A study based on pot experiments with canola plants (Brassica campestris L.)

ABSTRACTWe performed pot experiments with canola plants (Brassica campestris L.) to evaluate the effect of eight soil conditioners on the amendment of vanadium (V)-contaminated soil based on analysis of the growth of canola plants and the uptake, bioaccumulation, and translocation of heavy metals. Tested soil conditioners included polyacrylamide (PAM), sepiolite, humic acid (HAC), peat, sludge compost (SC), bentonite, lime, and fly ash. Results from the analysis of the growth of canola plants and the analysis of variance showed that the best soil conditioners for V-contaminated soil were 0.05–0.1 wt% PAM, 1 wt% peat, 1 wt% HAC, and 1 wt% SC; moderately effective soil conditioners included sepiolite and lime. The best combination of soil conditioners was 0.1 wt% PAM, 1 wt% HAC, and 0.15 wt% lime, in addition of 1% ZVI, which increased the biomass and height of canola plants by 1.18-fold and 59.49%, respectively. We conclude that the best combination of soil conditioners determined from this study is promising for mitigating V contamination in soil.

Assessment of plant growth attributes, bioaccumulation, enrichment, and translocation of heavy metals in water lettuce (Pistia stratiotes L.) grown in sugar mill effluent

ABSTRACTThis study was conducted to assess the pollutant uptake capability of water lettuce (Pistia stratiotes L.) in terms of bioaccumulation, enrichment, and translocation of heavy metals grown in sugar mill effluent. Results showed that the maximum fresh weight (328.48 ± 2.04 gm kg−1), total chlorophyll content (2.13 ± 2.03 mg g−1 fwt), and relative growth rate, RGR (11.89 gg−1 d−1) of P. stratiotes were observed at 75% concentration of the sugar mill effluent after 60 days of phytoremediation experiment. The bioaccumulation factor (BF) of different heavy metals was greater than 1 with 50% and 75% concentrations of sugar mill effluent and this indicated that P. stratiotes was hyperaccumulator or phytoremediator of these metals. The enrichment factor (EF < 2 for Cu, Fe, Cr, Pb, Zn, and Mn) and (EF > 2 for Cd) indicated that P. stratiotes mineral enrichment deficient and it moderately enriched the different heavy metals. Moreover, translocation factor (TF) was less than 1 which indicated the low mobility of metals in different parts (root and leaves) of P. stratiotes after phytoremediation. Therefore, P. stratiotes can be used for phytotreatment of sugar mill effluent up to 50% to 75% concentrations and considered as hyperaccumulator aquatic plant for different heavy metals and other pollutants from the contaminated effluents.

Metal accumulation in populations of Calamagrostis epigejos (L.) Roth from diverse anthropogenically degraded sites (SE Europe, Serbia)

Heavy metal accumulation is recognized as a very important global pollution problem in the last decades. Plant species have been recognized as natural bioindicators of environmental pollution, especially the amount of heavy metals in soils. Moreover, only a limited number of plant species can survive in highly contaminated soils. It is also known that metal accumulation can vary greatly among different populations of the same species. This study examines the chemical composition and accumulation potential of the expansive clonal grass Calamagrostis epigejos at five localities exposed to different levels of anthropogenic pressure. Considerable differences were observed between uptake, translocation, and accumulation of total and available heavy metals, such differences corresponding to soil physico-chemical characteristics and the level of site pollution. The results indicate that Calamagrostis epigejos uptakes a significant portion of the available fraction of heavy metals in the soil and stores it in the roots, thereby exhibiting a certain potential for metal phytostabilization.

Accumulation and Translocation of Heavy Metals in Eggplant (&amp;lt;i&amp;gt;Solanum melongena L.&amp;lt;/i&amp;gt;) Grown in a Contaminated Soil

A pot experiment was conducted to investigate the effects of the rock phosphate application on accumulation and translocation of heavy metals from the soil to the roots, shoots and fruits of eggplant (<i>Solanum melongena</i> L.) grown in a sewage sludge amended soil contaminated with Cd, Pb and Ni were 30, 30 and 60 mgkg^-1, respectively. The obtained results demonstrated that the sewage sludge application caused a significance accumulation of metals in the fruits of eggplant. The concentrations of these metals in the fruits were in the order of: Pb > Cd > Ni. The fruits of eggplant were not safe for the human consumption, because the levels of heavy metals exceeded the permissible limits. These, heavy metals in different parts of eggplant can be ranked in the order of: roots > shoots > fruits, were (mgkg^-1). The soil-plant transfer factor (TF) showed that the order of uptake of metals by eggplant was: Cd > Ni > Pb. This calls for concern especially in the case of Pb and Cd which are highly toxic and of no known biological use. Therefore, Eggplant should not be cultivated in the farms and fields which use sewage sludge contaminated with heavy metals as an amendment.

Effects of Industrial Effluents Polluting the Ismailia Water Canal on Growth and Metabolic Responses of Pisum sativum Seedlings

THE AIM of this work was to evaluate the impact of sources of waste water pollution on Ismailia canal and irrigated plants. The industrial sources along Ismailia canal produce large wastes that disturb the environmental balance. This study was based on investigating the growth and biochemical characteristics of Pisum sativum seedlings irrigated with industrial waste water collected from three selected stations of Ismailia canal. Results revealed an enrichment of organic matter and heavy metals in polluted water. Irrigation of plants using waste water affected germination, physiological, biochemical and growth characteristics of Pisum sativum. Irrigation with polluted water reduced photosynthetic pigments, total nitrogen and proteins in plant. Uptake and translocation of heavy metals and metal ions were higher in the polluted Pisum sativum which produced more metabolites to combat metal toxicity. High activity of antioxidant enzymes (Catalase, peroxidase and polyphenol oxidase), the contents of soluble sugars, anthocyanine, proline and new protein bands were induced.

Surfactant and heavy metal interaction in poplar: a focus on SDS and Zn uptake.

Surfactants are widely used detergent ingredients and, thanks to their chemical properties, they are applied for remediation of sites polluted by heavy metals and organic contaminants, both in soil flushing and in phytoremediation. However, their direct effects on tree physiology especially in consociation with heavy metal pollution, as well as their possible absorption by plants, have not been appropriately investigated. In order to evaluate plant uptake/translocation of the surfactant sodium dodecyl sulfate (SDS) and the heavy metal zinc (Zn) in Populus alba L. Villafranca clone, SDS was applied alone (0.5 mM) or in combination with Zn (1 mM). Physiological effects on plant growth and photosynthetic performance were investigated. An increasing trend of Zn translocation towards basal leaves as a consequence of SDS co-treatment (1 mM Zn + 0.5 mM SDS; P = 0.03) was observed, proving the ability of SDS to improve heavy metals translocation. However, SDS exposure (both in 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS treated plants) resulted in the appearance of foliar necrosis that expanded with an acropetal trend and finally led to leaf abscission. This phenotype may be caused by the emergence of an additional stress during the experimental trial, which could be related to the dissociation of sodium (Na) ions from the dodecyl sulfate molecules in the hydroponic system. In fact, while liquid chromatography-tandem mass spectrometry measurements revealed that dodecyl sulfate is mainly retained at root levels, Na is translocated to the aerial parts of the plant.

Evaluation of the Sagittaria montevidensis Cham. &amp; Schltdl. as a bioindicator and phytoextractor of toxic metals

This study evaluated the bioindication and phytoremediation capacity of the aquatic macrophyte Sagittaria montevidensis by using it to assess the bioconcentration and translocation of heavy metals. A simple sampling was conducted at four sites in the region of Pelotas, southern Brazil, where plants, water and sediments were collected. The plants were subjected to nitric-perchloric acid digestion and the sediments underwent pseudo-total acid digestion. The determination of the elements Cr, Cu, Pb, Ni and Zn in the extracts was performed by flame atomic absorption spectrometry. Physicochemical tests were also carried out on water samples, including pH, electrical conductivity, chlorides, alkalinity, hardness and organic matter, and in sediment samples, moisture and organic matter content. The macrophyte study indicated a Bioconcentration Factor (BCF) and a Translocation Factor (TF), especially for Ni. The results showed that the aquatic macrophyte species S. montevidensis has a phytoextraction capacity, mainly for Ni, and potentially for bioindication of Cu, Ni and Zn.

Assisted phytoremediation of heavy metal contaminated soil from a mined site with Typha latifolia and Chrysopogon zizanioides

Chemically assisted phytoremediation is fast gaining attention as a biotechnology to accelerate heavy metal removal from contaminated substrates, but how different chemical amendments affect the process remains an important research question. Here, bioaccumulation factor (BAF), translocation factor (TF), removal efficiency (RE) and uptake of Hg, As, Pb, Cu and Zn by cattail (Typha latifolia) and vetiver (Chrysopogon zizanioides) were quantified in a potted experiment to determine the effects of amendments on the phytoremediation success. Baseline concentrations of heavy metals within the studied mined site were determined. The experiment involved three soil treatments (each comprising 16 samples amended with 0.05mol/L ethylene di-aminetetraacetic acid (EDTA), 3g of aluminum sulfate [Al2(SO4)3], and unamended control) transplanted with equal numbers of vetiver and cattail. Growth performance (height) of plant species was monitored every two weeks. Sixteen weeks after transplanting, heavy metal levels in plant and soil samples were quantified following standard protocols, and the biomass and root length measured for each plant species. Results indicated strong negative impact of mining activities on heavy metal levels of soil in the study area. Soil amendment considerably enhanced the BAF, TF, RE and uptake but the effect varied with plant species and heavy metal in question. The amendment also stimulated strong positive correlation between RE and BAF, TF and metal uptake, and generally did not show any negative effects on plant growth performance. In general, soil amendment aided the accumulation and translocation of heavy metals in the plant species studied, and could be explored for cleaning up contaminated sites.

Soil amendments: a tool to reduce heavy metal uptake in crops for production of safe food

Population explosion, urbanization, crunch of resources, changes in social outlook and improper distribution of food has elicited a situation where every one in nine people are deprived of sufficient food. To increase the production and attain food security, many malpractices like cultivation on contaminated land and irrigation with wastewater are being carried out. These practices lead to the transfer of heavy metals from soil to food crops and thus food chain. Translocation of heavy metals can be reduced by decreasing the mobility of heavy metals. Amending the soil with suitable substrates helps in immobilization of heavy metals and thus reducing the uptake by plants. There is need to identify suitable soil amendments which can reduce heavy metal uptake and enhance crop yield. The present review summarizes various inorganic and organic amendments which can immobilize heavy metals and thus can be used for soil remediation.

Uptake and translocation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by maize from soil irrigated with wastewater

By investigating the uptake of 16 priority polycyclic aromatic hydrocarbons (PAHs) and five heavy metals from soils to maize at the farmlands with industrial wastewater irrigation, this study revealed the effects of heavy metals on PAHs uptake in terms of co-contamination. The results of 15 investigated soils showed medium contamination level and the vertical PAHs distribution in soils indicated that 2–3 rings PAHs with low octanol-water partition coefficient (log Kow < 4.5) were easier to transport in soils, causing a great potential risk immigrating to the groundwater. The 3-ring PAHs were most likely to be taken up by maize roots whereas 2- and 4–6 ring PAHs had the lower likelihood. The translocation of PAHs in maize tissues has positive relationship with log Kow less than 4.5, while negatively correlated otherwise. Redundancy analysis indicated the unexpected results that, except for soil PAHs concentration, the PAHs translocation by maize was reduced by Pb uptake, but not significantly affected by soil organic matters, pH or the other four heavy metals (Cr, Cu, Ni and Zn). This study for the first time provides the restricted factors of PAHs and heavy metal acropetal translocation by maize when they co-exist at wastewater irrigation sites.

Assessment of Heavy Metal Pollution and Health Risks in the Soil-Plant-Human System in the Yangtze River Delta, China.

Heavy metal (HM) contamination and accumulation is a serious problem around the world due to the toxicity, abundant sources, non-biodegradable properties, and accumulative behaviour of HMs. The degree of soil HM contamination in China, especially in the Yangtze River Delta, is prominent. In this study, 1822 pairs of soil and crop samples at corresponding locations were collected from the southern Yangtze River Delta of China, and the contents of Ni, Cr, Zn, Cd, As, Cu, Hg, and Pb were measured. The single pollution index in soil (SPI) and Nemerow composite pollution index (NCPI) were used to assess the degree of HM pollution in soil, and the crop pollution index (CPI) was used to explore the degree of HM accumulation in crops. The bioaccumulation factor (BAF) was used to investigate the translocation of heavy metals in the soil-crop system. The health risks caused by HMs were calculated based on the model released by the U.S. Environmental Protection Agency. The SPIs of all elements were at the unpolluted level. The mean NCPI was at the alert level. The mean CPIs were in the following decreasing order: Ni (1.007) > Cr (0.483) > Zn (0.335) > Cd (0.314) > As (0.232) > Cu (0.187) > Hg (0.118) > Pb (0.105). Only the mean content of Ni in the crops exceeded the national standard value. The standard exceeding rates were used to represent the percentage of samples whose heavy metal content is higher than the corresponding national standard values. The standard exceeding rates of Cu, Hg, and Cd in soil were significantly higher than corresponding values in crops. Meanwhile, the standard exceeding rates of Ni, As, and Cr in crops were significantly higher than corresponding values in soil. The chronic daily intake (CDI) of children (13.8 × 10−3) was the largest among three age groups, followed by adults (6.998 × 10−4) and seniors (5.488 × 10−4). The bioaccumulation factors (BAFs) of all crops followed the order Cd (0.249) > Zn (0.133) > As (0.076) > Cu (0.064) > Ni (0.018) > Hg (0.011) > Cr (0.010) > Pb (0.001). Therefore, Cd was most easily absorbed by crops, and different crops had different capacities to absorb HMs. The hazard quotient (HQ) represents the potential non-carcinogenic risk for an individual HM and it is an estimation of daily exposure to the human population that is not likely to represent an appreciable risk of deleterious effects during a lifetime. All the HQs of the HMs for the different age groups were significantly less than the alert value of 1.0 and were at a safe level. This indicated that citizens in the study area face low potential non-carcinogenic risk caused by HMs. The total carcinogens risks (TCRs) for children, adults, and seniors were 5.24 × 10−5, 2.65 × 10−5, and 2.08 × 10−5, respectively, all of which were less than the guideline value but at the alert level. Ingestion was the main pathway of carcinogen risk to human health.

Bioaccumulation and Translocation of Heavy Metals from Coastal Soil by Wild Halophytes

In the present study, six native halophytes were collected from soil of northern Nile Delta to evaluate their phytoremediation potential of heavy metals. For this purpose, soil, the aboveground parts and roots of the samples were analyzed for total concentrations of Fe, Pb, Ni, Co and Cd using atomic absorption spectrometer. The concentrations of different heavy metals in soils have the sequence of Fe>Ni>Pb>Co>Cd. The pollution quantification for each metal in the study area indicated that, the extremely high enrichment value for Cd; very high enrichment values for Pb and Co and low enrichment values for Ni and Fe; The contamination factor has very high for Cd; moderate for Pb and Co and low for Ni and Fe, while the contamination degree (CD) indicates that the study area is considered to be coast with low to moderate contamination degree (2.74 and 10.29). In the study area, the concentrations of heavy metals in plant species have the order of Fe>Pb> Ni>Cd >Co. Most plant species had a TF1, while the BAF values for Fe, Pb, Ni, Co and Cd were A. halimus, L. pruinosum and S. pruinosa were >1. The highest BAF shoot and root values was observed in Atriplex halimus, while the lowest was for Suaeda maritima. Similarly, the highest TF values were observed for Z. aegyptium, S. pruinosa and L. monopetalum, while the lowest was for S. pruinosa. Results suggest that these plants could be suitable for use in the phytoremediation of contaminated soil sites.

Heavy metal bioaccumulation in mangrove ecosystem at the coral triangle ecoregion, Southeast Sulawesi, Indonesia

This study aimed to determine the role of mangroves as a biofilter of heavy metals. The concentrations of heavy metals, namely copper, mercury, cadmium, zinc, and lead, in the mangroves Rhizophora apiculata, Ceriops tagal, Bruguiera gymnorrhiza, Lumnitzera racemosa, Xylocarpus granatum, Sonneratia alba, and Bruguiera parviflora at RAWN Park were determined using a Flame atomic absorption spectrophotometer. High concentrations of Cu (83.85μgg−1) and Hg (0.52μgg−1) were found in the tissues of L. racemosa, while high concentrations of Cd (10.81μgg−1), Zn (70.41μgg−1), and Pb (1.36μgg−1) were found in the tissues of B. gymnorrhiza, B. parviflora and C. tagal, respectively. The translocation and bioaccumulation factors of heavy metals by mangroves showed a variety of trends, which indicated the different partitioning and uptake capability of heavy metals in the tissues of various mangrove species. Thus, maintaining high diversity of mangroves is crucial to ensure the health and productivity of coastal zones.

Phytoremediation assessment of native plants growing on Pb–Zn mine site in Northern Tunisia

Pollution by heavy metals presents an environmental concern, and their toxicity threats soil, water, animals and human health. Phytoremediation can be used as a solution to remediate contaminated soils. The aim of this study was to identify native plants collected from tailings: material of Pb–Zn mine sites of Fedj Lahdoum and Jebel Ressas (two abandoned mines located, respectively, in the northwest of Tunisia and in the south of Tunis City). The tolerance of plant to heavy metals (lead, zinc and cadmium) is evaluated. Soil samples were collected and analyzed for Pb, Zn and Cd concentration. The total soil Pb, Zn and Cd are, respectively, reached 6132 mg kg−1, 11,052 mg kg−1 and it doesn’t exceed 479 mg kg−1 for Cd. The highest content of Zn in plants was detected in shoots of Rumex bucephalophorus (1048 mg kg−1), and the highest Pb concentration was detected in roots of Chrysopogon zizanioides (381 mg kg−1), while for Cd Silene colorata it accumulated the highest content in roots (51 mg kg−1). From all plants, only 12 have a translocation factor for Pb which is higher than one. Among all plants, only 17 have a translocation factor that is higher than one for Zn, while for Cd only 13 plants indicate TF > 1. As for the biological absorption coefficient, all samples indicate a rate which is lower than one. These plants can be primarily hyper accumulators and useful in remediation of lead- and zinc-contaminated soils after further biochemistry researches in mechanism of accumulation and translocation of heavy metals in plants.

Translocation of heavy metals from soils into floral organs and rewards of Cucurbita pepo: Implications for plant reproductive fitness

Metals and metalloids in soil could be transferred into reproductive organs and floral rewards of hyperaccumulator plants and influence their reproductive success, yet little is known whether non-hyperaccumulator plants can translocate heavy metals from soil into their floral organs and rewards (i.e., nectar and pollen) and, if so, whether plant reproduction will be affected. In our studies, summer squash (Cucurbita pepo L. cv. Golden Apple) was exposed to heavy-metal treatments during bud stage to investigate the translocation of soil-supplemented zinc, copper, nickel and lead into its floral organs (pistil, anther and nectary) and rewards (nectar and pollen) as well as floral metal accumulation effects on its reproduction. The results showed that metals taken up by squash did translocate into its floral organs and rewards, although metal accumulation varied depending on different metal types and concentrations as well as floral organ/reward types. Mean foraging time of honey bees to each male and female flower of squash grown in metal-supplemented soils was shorter relative to that of plants grown in control soils, although the visitation rate of honeybees to both male and female flowers was not affected by metal treatments. Pollen viability, pollen removal and deposition as well as mean mass per seed produced by metal-treated squash that received pollen from plants grown in control soils decreased with elevated soil-supplemented metal concentrations. The fact that squash could translocate soil-supplemented heavy metals into floral organs and rewards indicated possible reproductive consequences caused either directly (i.e., decreasing pollen viability or seed mass) or indirectly (i.e., affecting pollinators’ visitation behavior to flowers) to plant fitness.

The influence of bioavailable heavy metals and microbial parameters of soil on the metal accumulation in rice grain

A field-based study was undertaken to analyze the effects of soil bioavailable heavy metals determined by a sequential extraction procedure, and soil microbial parameters on the heavy metal accumulation in rice grain. The results showed that Cd, Cr, Cu, Ni, Pb and Zn concentrations in rice grain decreases by 65.9%, 78.9%, 32.6%, 80.5%, 61.0% and 15.7%, respectively in the sites 3 (far-away), compared with those in sites 1 (close-to). Redundancy analysis (RDA) indicated that soil catalase activity, the MBC/MBN ratio, along with bioavailable Cd, Cr and Ni could explain 68.9% of the total eigenvalue, indicating that these parameters have a great impact on the heavy metal accumulation in rice grain. The soil bioavailable heavy metals have a dominant impact on their accumulation in rice grain, with a variance contribution of 60.1%, while the MBC/MBN has a regulatory effect, with a variance contribution of 4.1%. Stepwise regression analysis showed that the MBC/MBN, urease and catalase activities are the key microbial parameters that affect the heavy metal accumulation in rice by influencing the soil bioavailable heavy metals or the translocation of heavy metals in rice. RDA showed an interactive effect between Cu, Pb and Zn in rice grain and the soil bioavailable Cd, Cr and Ni. The heavy metals in rice grain, with the exception of Pb, could be predicted by their respective soil bioavailable heavy metals. The results suggested that Pb accumulation in rice grain was mainly influenced by the multi-metal interactive effects, and less affected by soil bioavailable Pb.

Tolerance and translocation of heavy metals in young grapevine (Vitis vinifera) grown in sandy acidic soil with interaction of high doses of copper and zinc

Vineyard soils may have high levels of copper due to frequent applications of Bordeaux mixture for the control of fungal diseases. Therefore, many winegrowers have used zinc-based fungicides instead of copper-based fungicides, resulting in high levels of Cu and Zn in vineyard soils. The aim of the study was to evaluate the tolerance of young grapevines grown in soil with interaction of high contents of Cu and Zn, and the translocation of these heavy metals from roots to shoots. We collected soil of a natural field of Rio Grande do Sul, the southernmost state of Brazil. Soil treatments were addition of 0, 30, and 60mg Cu kg−1, and addition of 0, 15, 30, 60, 120, and 180mg Zn kg−1 for each copper dose. A seedling of grapevine per pot was grown for 60days. After that, we measured root and shoot dry matter, Cu and Zn content in roots and shoots, chlorophyll a fluorescence, photosynthetic pigments, and peroxidase and superoxide dismutase activity. Young grapevines showed tolerance mechanisms to high concentrations of Cu and Zn by retaining these metals in the roots, decreasing translocation to the shoots. However, at the highest doses of Cu and Zn, we observed decrease in plant growth and in photochemical efficiency associated with the decrease in photosynthetic pigment content. Furthermore, the activity of antioxidant enzymes increased in intermediate doses of Zn, which indicates activation of the antioxidant system. However, the stress condition in treatments with high levels of Cu and Zn was not reversed.

Heavy metals translocation and accumulation from the rhizosphere soils to the edible parts of the medicinal plant Fengdan (Paeonia ostii) grown on a metal mining area, China

Fengdan (Paeonia ostii) is one of Chinese 34 famous medicinal materials. This study investigated the concentrations of Arsenic (As), Chromium (Cr), Cadmium (Cd), Copper (Cu), Lead (Pb), Iron (Fe), Manganese (Mn), and Zinc (Zn) in rhizosphere soils, cortex mouton and seeds of Fengdan planted in a metal mining area, China. The mean concentrations of As, Cd, Cu, and Zn in the rhizosphere soils were above the limits set by the Chinese Soil Environmental Quality Standard (GB 15618-1995). The contamination factor (CF) of Cd was >5, while it was >2for As, Cu, Pb, and Zn in all the soils. The integrated pollution index for all the soils was >3 and ˂ 5. Metal concentrations in the edible parts of Fengdan were in the following decreasing order: Mn>Fe>Zn>Cu>Pb>As>Cr≥Cd. The transfer factor mean values for As, Cu, Cd and Fe in the cortex moutan of old Fengdan (over 6 years) were significantly higher than in young Fengdan. Available metal concentrations, pH and soil organic matter content influenced the metal concentrations of the cortex moutan. The results indicated that mining and smelting operations have led to heavy metals contamination of soils and medicinal parts of Fengdan. The major metal pollutants were elemental Cd, Cu, Pb, and Zn. Heavy metals mainly accumulated in the cortex moutan of Fengdan. The mean concentrations of Cd, Cu, and Pb in the old cortex moutan (over 6 years) were above those of the Chinese Green Trade Standards for Medicinal Plants and Preparations in Foreign Trade (WM/T2-2004).

Contrasting effects of engineered carbon nanotubes on plants: a review.

Rapid surge of interest for carbon nanotube (CNT) in the last decade has made it an imperative member of nanomaterial family. Because of the distinctive physicochemical properties, CNTs are widely used in a number of scientific applications including plant sciences. This review mainly describes the role of CNT in plant sciences. Contradictory effects of CNT on plants physiology are reported. CNT can act as plant growth inducer causing enhanced plant dry biomass and root/shoot lengths. At the same time, CNT can cause negative effects on plants by forming reactive oxygen species in plant tissues, consequently leading to cell death. Enhanced seed germination with CNT is related to the water uptake process. CNT can be positioned as micro-tubes inside the plant body to enhance the water uptake efficiency. Due to its ability to act as a slow-release fertilizer and plant growth promoter, CNT is transpiring as a novel nano-carbon fertilizer in the field of agricultural sciences. On the other hand, accumulation of CNT in soil can cause deleterious effects on soil microbial diversity, composition and population. It can further modify the balance between plant-toxic metals in soil, thereby enhancing the translocation of heavy metal(loids) into the plant system. The research gaps that need careful attention have been identified in this review.

Analysis of zntA gene in environmental Escherichia coli and additional implications on its role in zinc translocation

Escherichia coli strains from sewage sample were screened for the presence and expression of heavy metal-translocating zntA gene by PCR and RT-PCR analysis with type culture of K-12 as standard strain. The strain which showed high level of gene expression (SBVP1) was chosen to further study the growth and heavy metal translocation. This superior strain was grown in the presence of ZnSO4, Pb (CH3COO)2 and mixture of ZnSO4, Pb(CH3COO)2 metal salts and the growth was observed at different time points. The cell pellet fraction was found to have more of zinc than lead as determined by atomic absorption spectroscopy indicating the translocation of these metals from media to the cells. However, the intracellular translocation of zinc is affected by the presence of lead in the media. Expression of the zntA gene in bacteria grown in the presence of ZnSO4 was also studied and the molecular analysis results correlate with spectroscopic observations.