Eliana Tassi

Strategies to use phytoextraction in very acidic soil contaminated by heavy metals

In microcosm experiments, the use of inorganic and organic amendments has been studied as potential agents to reduce heavy metal bioavailability in an acidic soil highly contaminated by Cu, Zn and Ni, that has to be remediated by phytoremediation. The concentrations of heavy metals in the original soil (O-Soil) produced phytotoxic effects with a strong reduction in biomass yield that hinder the utilization of this technology. To overcome phytotoxicity the use of three immobilizing agents was evaluated. The results obtained showed that all the strategies decreased the mobile fractions of heavy metals in soil and increased the metal removal efficiency. In the case of Brassica juncea the best results for Zn and Ni were obtained after zeolites addition (Z-Soil) with an increase of about 6 times with respect to the value found in the O-Soil. In the case of Cu, the more efficient treatment was Ca(OH)(2) addition (Ca-Soil). The B. juncea plants accumulated Cu amounts 8 times greater than in the O-Soil. For this metal, relevant results were obtained also with compost, that increased the amount of Cu in the plants of 7 times with respect to the O-Soil. Similar results were obtained with Helianthus annuus the highest Zn and Ni accumulation was detected in the Z-Soil and compost-treated soils (C-Soil), with an increase of nearly 11 times with respect to the accumulation in the O-Soil. In the case of Cu the highest increase of total uptake was found in the C-Soil: 28 times higher than in the O-Soil. Total accumulation in Poa annua plants showed the highest removal efficiency in the Z-Soil for all metals. The values obtained increased of 4, 11 and 12 times for Cu, Zn and Ni, respectively.

Nitrogen fertilizer improves boron phytoextraction by Brassica juncea grown in contaminated sediments and alleviates plant stress

In this study we evaluated the effect of different fertilizer treatments on Brassica plants grown on boron-contaminated sediments. Experiments were conducted in the laboratory and on the lysimeter scale. At laboratory scale (microcosm), five different fertilizers were tested for a 35-d period. On the lysimeter scale, nitrogen fertilization was tested at three different doses and plants were allowed to grow until the end of the vegetative phase (70 d). Results showed that nitrogen application had effectively increased plant biomass production, while B uptake was not affected. Total B phytoextracted increased three-fold when the highest nitrogen dose was applied. Phytotoxicity on Brassica was evaluated by biochemical parameters. In plants grown in unfertilized B-contaminated sediments, the activity of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and pyrogallol peroxidase (PPX) increased, whereas catalase (CAT) decreased with respect to control plants. Addition of N progressively mitigated the alteration of enzymatic activity, thus suggesting that N can aid in alleviating B-induced oxidative stress. SOD activity was restored to control levels just at the lowest N treatment, whereas the CAT inhibition was partially restored only at the highest one. N application also lowered the B-induced increase in APX and PPX activities. Increased glutathione reductase activity indicated the need to restore the oxidative balance of glutathione. Data also suggest a role of glutathione and phytochelatins in B defense mechanisms. Results suggest that the nitrogen fertilizer was effective in improving B phytoextraction by increasing Brassica biomass and by alleviating B-induced oxidative stress.

Uptake of heavy metals by native species growing in a mining area in Sardinia, Italy: discovering native flora for phytoremediation.

This study assessed the distribution and availability of plant uptake of Zn, Pb, and Cd present in an abandoned mine at Ingurtosu, Sardinia (Italy). Geological matrix samples (sediments, tailings, and soil from a nearby pasture site) and samples of the predominant plant species growing on sediments and tailings were collected. Mean values of total Zn, Pb and Cd were respectively (mg kg−1) 7400, 1800, and 56 in tailings, 31000, 2900, and 100 in sediments, and 400, 200, and 8 in the pasture soil. The metal concentration values were high even in the mobile fractions evaluated by simplified sequential extraction (Zn 7485-103, Pb 1015-101, Cd 47-4 mg kg−1). Predominant native species were identified and analyzed for heavy metal content in various tissues. Among the plant species investigated Inula viscosa, Euphorbia dendroides, and Poa annua showed the highest metal concentration in aboveground biomass (mean average of Zn: 1680, 1020, 1400; Pb: 420, 240, 80; Cd: 28, 7, 19 mg kg−1, respectively). The above mentioned species and A. donax could be good candidates for a phytoextraction procedure. Cistus salvifolius and Helichrysum italicus generally showed behavior more suitable for a phytostabilizer.

Using a plant hormone and a thioligand to improve phytoremediation of Hg-contaminated soil from a petrochemical plant.

Mercury-contaminated soils from a petrochemical plant in southern Italy were investigated to assess the phytoextraction efficiency of crop plants treated with the phytohormone, cytokinine (CK foliar treatment), and with the thioligand, ammonium thiosulfate (TS, soil application). Plant biomass, evapotranspiration, Hg uptake and distribution in plant tissues following treatment were compared. Results indicate the effectiveness of CK in increasing plant biomass and the evapotranspiration rate while TS treatment promoted soil Hg solubility and availability. The simultaneous addition of CK and TS treatments increased Hg uptake and translocation in both tested plants with up to 248 and 232% in Brassica juncea (Indian mustard) and Helianthus annuus (sunflower) respectively. B. juncea was more effective in Hg uptake, whereas H. annuus gave better response regarding plant biomass production. The effectiveness of the treatments was confirmed by the calculation of Hg phytoextraction and evaluation of labile-Hg residue in the soil after plant growth. In one growing cycle the plants subject to simultaneous CK and TS treatment significantly reduced labile-Hg pools that were characterized by the soil sequential extraction, but did not significantly affect the pseudototal metal content in the soil. Results support the use of plant growth regulators in the assisted phytoextraction process for Hg-contaminated soils.

Remediation of a Mercury-Contaminated Industrial Soil Using Bioavailable Contaminant Stripping

Abstract The method to remove bioavailable amounts of heavy metals from a contaminated soil by using plants is defined as bioavailable contaminant stripping (BCS) and could safely be applied if the soils long-term ability to replenish the bioavailable pool is known. The aim of this study was to evaluate the ability of three common plant species selected, Brassica juncea, Poa annua, and Helianthus annus, to remove bioavailable amounts of mercury (Hg) from a contaminated industrial soil containing 15.1 mg kg−1 Hg. Trials were carried out under greenhouse conditions using pots (mesocosms). According to the precautionary principle, we modified the BCS remediation approach by adding a new step, in which mercury bioavailability was increased by the addition of a strong mobilizing agent, ammonium thiosulphate, (NH4)2S2O3, to obtain an estimate of the likely long-term bioavailable Hg pool. The modified BCS remediation approach was called enhanced bioavailable contaminant stripping (EBCS). After one growth cycle, nearly all the bioavailable mercury (95.7%) was removed and the metal remaining in the soil was considered inert since it was neither extractable by (NH4)2S2O3 nor taken up by plants during a second growth cycle. The results demonstrated that EBCS appeared promising since it removed the most dangerous metal forms while substantially shortening the cleanup time.

Exogenous Cytokinin Treatments of an NI Hyper-Accumulator, Alyssum Murale, Grown in a Serpentine Soil: Implications for Phytoextraction

Application of exogenous plant growth regulators was examined as a viable technique to increase the efficiency of plant metal extraction from contaminated soils. The aim of this study was to investigate the alteration of Ni phytoextraction by Alyssum murale, a Ni hyperaccumulator, following the application of cytokinins. The following parameters were investigated: Ni accumulation, plant growth, gas exchange, stomata behavior and the concentration of nonprotein thiols (glutathione, y-Glu-Cys, and phytochelatins). In a pot experiment, A. murale plants grown in a serpentine soil were treated with a mix of naturally occurring cytokinins. Results showed that Ni accumulation in plants ranged from 4000 to 7000 mg kg−1 confirming the hyper-accumulation ability from the soil used. Cytokinin treatments produced a significant increase in plant biomass and transpiration rate whereas no significant variation in Ni accumulation or the concentration of non-protein thiols was observed. The results suggest that A. murale is a plant species sensitive to cytokinin treatment and that cytokinin treatment is potentially useful in increasing the phytoextraction capability by increasing biomass. Moreover, for first time, evidence was obtained that the Ni hyperaccumulation mechanism is independent of water flux and transpiration rate.

Mercury Mobilization in a Contaminated Industrial Soil for Phytoremediation

The aim of this work was to investigate the possibility of using plants for mercury (Hg) removal from a contaminated industrial soil, increasing the metals bioaccessibility by using mobilizing agents: ammonium thiosulphate [(NH4)2S2O3] and potassium iodide (KI). The selected plant species were Brassica juncea and Poa annua. The addition of the mobilizing agents promoted Hg uptake by plants, with respect to controls. Treatments promoted Hg translocation to aerial parts. In the case of Poa annua, greater Hg uptake was found in plants after the 100 mM KI treatment, reaching values that were nearly 400 mg kg−1 in the aerial part. In contrast, Brassica juncea plants accumulated in their aerial part the greatest Hg quantities, about 100 mg kg−1, after treatment with 0.27 M (NH4)2S2O3. The ratio between the concentration of Hg in the shoots and the initial concentration in the soil support the potential for successfully applying Hg phytoextraction on this soil.

Field assessment of Pb in contaminated soils and in leaf mustard (Brassica juncea): the LIBS technique

Monitoring contaminated sites is faster and cheaper if portable analytical instruments are used rather than traditional laboratory analysis. We developed a transportable system based on the laser-induced breakdown spectroscopy (LIBS) technique for rapid on-site measurement of heavy metal concentrations. Portable instruments also offer great advantages for on-site remediation technology, where continuous monitoring is required. LIBS is especially useful when plants are used to remove or contain contaminants. Phytoremediation takes time to achieve its goals, and many analyses are required to evaluate its efficiency during the process. In this study, LIBS was used to measure Pb concentration in soils from three contaminated sites and in plant samples from phytoremediation experiments. Results obtained from LIBS show good correlation with data obtained with atomic absorption spectroscopy (AAS). In particular, in the case of contaminated site characterisation, LIBS permits delimitation of areas showing metal concentration over the legal limits, where further investigations are required. Speeding up the characterisation procedure decreases investigation costs and increases the number of analysed samples with a given economic budget, thus increasing the informational value of data. Thus reliable spatial information can be obtained, leading to lower remediation costs.

Modeling the Transport Phenomena of TiO2 Nanoparticles into Leachate of Municipal Waste Landfills

Several nanomaterials have been currently developed and new applications has became possible due to the special materials performance requirements. The TiO2 nanoparticles are of special interest due to the wide range of applications from cosmetics to paint and new applications have continuously been searched. However, the effect of these particles into the environment need detailed investigation since some deleterious effects on the ecosystems have been observed. This paper deals with the mechanism of nanoparticles absorption/desorption by soil landfills. A long term simulation of the nanoparticles motion and contamination plume is carried out in the Volta Redonda Municipal Waste landfill and main transport parameters are determined. The model is used to predict the concentration of TiO2 nanoparticles in suspension on the leachate of Municipal Waste landfills and the rate of particles dynamically attached into the soil particles

An integrated approach to highlight biological responses of Pisum sativum root to nano-TiO2 exposure in a biosolid-amended agricultural soil

This study focused on crop plant response to a simultaneous exposure to biosolid and TiO2 at micro- and nano-scale, being biosolid one of the major sink of TiO2 nanoparticles released into the soil environment. We settled an experimental design as much as possible realistic, at microcosm scale, using the crop Pisum sativum. This experimental design supported the hypotheses that the presence of biosolid in the farming soil might influence plant growth and metabolism and that, after TiO2 spiking, the different dimension and crystal forms of TiO2 might be otherwise bioavailable and differently interacting with the plant system. To test these hypotheses, we have considered different aspects of the response elicited by TiO2 and biosolid at cellular and organism level, focusing on the root system, with an integrative approach. In our experimental conditions, the presence of biosolid disturbed plant growth of P. sativum, causing cellular damages at root level, probably through mechanisms not only oxidative stress-dependent but also involving altered signalling processes. These disturbances could depend on non-humified compounds and/or on the presence of toxic elements and of nanoparticles in the biosolid-amended soil. The addition of TiO2 particles in the sludge-amended soil, further altered plant growth and induced oxidative and ultrastructural damages. Although non typical dose-effect response was detected, the most responsiveness treatments were found for the anatase crystal form, alone or mixed with rutile. Based on ultrastructural observations, we could hypothesise that the toxicity level of TiO2 nanoparticles may depend on the cell ability to isolate nanoparticles in subcellular compartments, avoiding their interaction with organelles and/or metabolic processes. The results of the present work suggest reflections on the promising practice of soil amendments and on the use of nanomaterials and their safety for food plants and living organisms.