Gianniantonio Petruzzelli

HEAVY METAL DISTRIBUTION BETWEEN CONTAMINATED SOIL AND PAULOWNIA TOMENTOSA, IN A PILOT-SCALE ASSISTED PHYTOREMEDIATION STUDY: INFLUENCE OF DIFFERENT COMPLEXING AGENTS

The distribution of Cd, Cu, Pb and Zn between a contaminated soil and the tree species Paulownia tomentosa was investigated in a pilot-scale assisted phytoremediation study. The influence of the addition of EDTA, tartrate and glutamate at 1, 5 and 10mM concentrations on metal accumulation by the plant and on metal mobilization in soil was evaluated. Root/shoot metal concentration ratios were in the range of 3-5 for Zn, 7-17 for Cu, 9-18 for Cd and 11-39 for Pb, depending on the type and concentration of complexing agent. A significant enhancement of metal uptake in response to complexing agent application was mainly obtained in roots for Pb (i.e. 359 mg kg(-1) for EDTA 10mM and 128 mg kg(-1) for the control), Cu (i.e. 594 mg kg(-1) for glutamate 10mM and 146 mg kg(-1) for the control) and, with the exception of glutamate, also for Zn (i.e. 670 mg kg(-1) for tartrate 10mM and 237 mg kg(-1) for the control). Despite its higher metal mobilization capacity, EDTA produced a metal accumulation in plants quite similar to those obtained with tartrate and glutamate. Consequently the concentration gradient between soil pore water and plant tissues does not seem to be the predominant mechanism for metal accumulation in Paulownia tomentosa and a role of the plant should be invoked in the selection of the chemical species taken up. Metal bioavailability in soil at the end of the experiment was higher in the trials treated with EDTA than in those treated with tartrate and glutamate, the latter not being significantly different from the control. These findings indicated the persistence of a leaching risk associated to the use of this chelator, while an increase of the environmental impact is not expected when glutamate and tartrate are applied.

POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) SLURRY PHASE BIOREMEDIATION OF A MANUFACTURING GAS PLANT (MGP) SITE AGED SOIL

Bench scale tests have been carried out in order to investigatebioremediation feasibility of a Manufacturing Gas Plant site(Bovisa Gasometri – MI – I) aged soil, highly contaminated bypolyaromatic hydrocarbons (PAHs) and mineral oils. Biodegradationstudies were carried out at 22 °C in a slurry system reactor, with a solid to liquid ratio of 10% w/w. Three testswere performed, over a period of 23, 24 and 91 days respectively.In the first test, only soil and water were put into the system.In the second test, microbial activity was inhibited to evaluatethe amount of abiotic losses. In the third test, macronutrientswere added to the reactor; bioaugmentation was also carried outby an inoculum of autochthonous PAH-degrading microorganisms. Saturated hydrocarbons, PAHs, transformation products, heterotropic and PAH-degrading bacteria and fungi were monitored.Tests showed that high removal efficiency could be obtained following 23 days of treatment for all PAHs, including high molecular weight compounds. Abiotic losses were an importantprocess contributing to concentration abatement in soil, especially in the first phase of the treatment. Lag time lackfor all polyaromatic hydrocarbons revealed that autochthonousmicroorganisms were well adapted to these contaminants; bioaugmentation did not seem to speed up the process. The higherremoval rate and efficiency for high molecular weight PAHs obtained in the third test suggested that nutrient addition could play an important role in the biodegradation process ofthese compounds, whereas it did not significantly modify total(abiotic + biotic) removal of light compounds.

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.

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.

Influence of the Application Renewal of Glutamate and Tartrate on Cd, Cu, Pb and Zn Distribution Between Contaminated Soil and Paulownia Tomentosa in a Pilot-Scale Assisted Phytoremediation Study

The influence of repeated applications of tartrate (TAR) and glutamate (GLU) at 50-mmol kg−1 of soil on Cd, Cu, Pb, and Zn distribution between a contaminated soil and Paulownia tomentosa was investigated. TAR and GLU were applied by a single or a double dosage, the latter carried out with an interval between the two applications of thirty days. The comparison of the differences in mean amounts of metals accumulated in the whole plant at the end of single and double TAR and GLU application experiments indicated the positive effect of repeated GLU applications on the accumulation of Cu, Pb, and Zn by Paulownia tomentosa as compared to untreated controls. A similar effect was not observed for the TAR treatments. When soil treated with either TAR or GLU was compared with untreated controls, no significant effect on heavy-metal concentrations in the soil solution was observed 30 days after treatment, suggesting the absence of an increase of the long-term leaching risk of heavy metals in aquifers and surface waters due to the ligand application. A cost analysis of the treatment is also reported.

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.

Green remediation strategies to improve the quality of contaminated soils

Soil contamination has been identified as an important issue requiring action for soil protection in Europe. New approaches to remediation will be required if soils are to perform their essential functions. There is a need to find new strategies of remediation which, to date, have involved rather drastic technologies or landfill disposal. The US EPA is promoting strategies (green remediation) that restore contaminated sites to productive use with great attention paid to global environmental quality, including the preservation of soil functionality. As an example of this approach, a case study is reported in which phytoremediation as a ‘green remediation strategy’ has been selected to clean-up sites contaminated by polycyclic aromatic hydrocarbons (PAHs). Lupinus albus and Zea mays were tested and the efficiency of the remediation was determined comparing the decrease in PAH concentration in soil with and without plants growing (32 and 22%, respectively). This is a consequence of the presence of plants that stimulated the microbial biomass involved in PAH degradation. As an index of soil quality at the end of the phytoremediation test, soil stability structure was evaluated by means of wet aggregate stability (WAS). This parameter sharply increased from 35 to 60% after cultivating selected plants.

The Bioavailability Processes as a Key to Evaluate Phytoremediation Efficiency

Bioavailability is the key to understanding the risks from pollution and to defining remediation strategies, since organisms only respond to the fraction that is biologically available. Plants are able to uptake the substances only if present in available forms in the soil environment; this means that bioavailability is the key to evaluating the feasibility of phytoextraction as a remediation technology.

Phytoremediation Towards the Future: Focus on Bioavailable Contaminants

The hypothesis that one of the possible future trends of phytoextraction should be the removal of the bioavailable contaminants has recently received renewed and increasing interest. This fraction is the most hazardous to the environment and human health. The evaluation of contaminant bioavailability is essential for the appropriate application of the technology. Before selecting a phytoextraction process, it is necessary to consider the specific characteristics of the soil at the contaminated site in order to evaluate how the soil properties will influence the final result of remediation in the field. With this approach based on the concept of bioavailable contaminant stripping (BCS), an evaluation of the hazards of the residual fraction not removed by plants is left to a risk assessment procedure. This approach can be safely applied, if the soil ability to replenish the bioavailable pools in the long term is considered. This problem can be overcome by enhanced bioavailable contaminant stripping (EBCS) which evaluates this amount through the combined use of chemical extraction with a mobilizing agent, specific for each metal, and pot experiments in which successive growing cycles must confirm the absence of the bioavailable fractions. Phytoextraction can be selected as “green remediation” to minimize the mobile and bioavailable fractions of contaminants, while improving soil quality.