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Weak organic acids and/or their salts were tested as soil washing or flushing agents for the ex- or in-situ remediation of soils polluted by heavy metals. Three soils naturally with heavy metals were used for the tea. / The three soils were characterized as a clay loam, loam and sandy clay loam. Their organic matter, pH, saturated hydraulic conductivity, cation exchange capacity, particle density and heavy metal contents were also characterized. The different retention forms of heavy metals in all 3 soils were studied by sequential extraction. The clay loam was contaminated with Cr, Hg, Mn and Pb while the loam and sandy clay loam were contaminated with Cd, Pb, Cu and Zn. Weak organic adds and/or their salts and chelating agents (EDTA and DTPA) were used at different pH, levels of concentration and leaching time in batch experiments to establish optimum conditions for maximum removal of heavy metals from the three soils. Citrate and tartarate were found to be quite effective, in leaching heavy metals from these soils. The rate of leaching of heavy metals from soils with citrate, tartarate and EDTA was modeled using two-reaction model at a constant pH and temperature. / Three contaminated soils of different textures were flushed in a column at optimum pH with a salt of weak organic acids, namely, citrate, tartarate, citrate+oxalate or a chelating agent such as EDTA and DTPA. The citrate and tartarate (ammonium salts) were found to be quite effective in removing heavy metals from the three contaminated soils while leaching little macronutrients and improving the soil's structure. An in-situ soil remediation simulation was also successfully tested using the sandy clay loam at large scale level in a tub (plastic container) using citrate as a flushing liquid. EDTA and DTPA were effective in removing the heavy metals except for Hg, but these strong chelating agents extracted important quantities of macronutrients from the soil. These chelating agents are also known to pollute the soil by being adsorbed on the soil particles. / A bioremediation process was developed using the fungus Aspergillus niger to produce weak organic acids (mainly citrate and partly oxalate depending on pH) for the leaching of heavy metals from contaminated soils. The fungus was cultivated on the surface of the three contaminated soils for 15 days at 30°C and a pH ≤ 4 to enhance the production of citric acid rather than oxalic acid which hinders Pb leaching. By extrapolating the result, the three contaminated soils were expected to be sufficiently remediated to meet the A category (Quebec clean up criteria for cleaning soils contaminated by heavy metals) after 20 to 25 days of leaching using this technique. / Finally, the leachate, collected following the soil remediation using weak organic acids and/or their salts, EDTA and DTPA was treated effectively using granular activated carbon.

A possible remediation strategy that involved washing with complexing reagents(s) [disodium ethylenediaminetetraacetate (Na2EDTA) alone or in combination with bis-(2-hydroxyethyl)dithiocarbamate (HEDC)] was evaluated with an urban soil that had been field contaminated with excesses of heavy metal (HMs). Heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) were targeted for removal. The aqueous solution that resulted from, washing was treated with zero-valent (ZV) magnesium (Mg0) or bimetallic mixture (Pd0/Mg 0 or Ag0/Mg0) to release the chelating reagent(s) from their heavy metal complexes. During this reaction, the heavy metals were precipitated from solution as hydroxides or became plated on to the surface of the excess ZV reagent. Thus, an appreciable fraction of the mobilized Pb and Cu and a portion of Zn became cemented to the surface of the ZV metal whereas most of the Fe and Mn were removed from solution as insoluble hydroxides. After filtration and pH re-adjustment, the demetallized solution was then returned to the soil to extract more heavy metals. After three washing cycles with the same reagent, it was observed that the sparing quantity of EDTA (10 mmoles) had mobilized 32--54% of the soil burden heavy metals (5 mmoles), but only 0.1% of the iron had been removed. / A 1:1 (mol/mol) mixture of EDTA and HEDC proved to be approximately equally efficient at HM extraction despite more than a three-fold reduction (3 mmoles) in the quantity of reagents. Three washing with the same reagent mobilized some 49% of the Pb, 18% of the Zn and 19% of the Mn but only 7% of the Cu and 1% of the Fe from the test soil.

Thesis (M. Tech.: Biotechnology)-Dept. of Biotechnology and Food Technology, Durban University of Technology, 2008. xiv, 103 leaves : ill. / Phytoremediation is an emerging technology where specially selected and engineered metal-accumulating plants are used for bioremediation. Amaranthus dubius (marog or wild spinach) is a popular nutritious leafy vegetable crop which is widespread especially in the continents of Africa, Asia and South America. Their rapid growth and great biomass makes them some of the highest yielding leafy crops which may be beneficial for phytoremediation. This study was undertaken to evaluate the potential of A. dubius for the phytoremediation of Chromium (Cr), Mercury (Hg), Arsenic (As), Lead (Pb), Copper (Cu) and Nickel (Ni). Locally gathered soil and plants of A. dubius were investigated for the metals from a regularly cultivated area, a landfill site and a sewage site. Metals were extracted from the samples using microwave-digestion and analyzed using Inductively Coupled Plasma – Mass Spectroscopy (ICP-MS). Further experiments were conducted with plants from locally collected seeds of A. dubius, in a tunnel house under controlled conditions. The mode of phytoremediation, the effect of the metals on the plants, the ability of the plant to extract metals from soil (Bioconcentration Factor - BCF), and the ability of the plants to move the metals to the aerial parts of the plants (Translocation Factor - TF) were evaluated for the different metals. Finally, A. dubius was micro-propagated in a tissue culture system with and without exposure to the metal, and the effect was studied by electron microscopy.

Heavy metal contamination of mangroves is of critical concern due to its accumulative and adverse effects in aquatic ecosystems. This study was undertaken to investigate the effects of mercury (Hg ), lead (Pb ), copper (Cu ) and zinc (Zn ) on plant responses, specifically growth and productivity, in Avicennia marina (Forssk.) Vierh. A. marina plants were grown for twelve months in pots contaminated with Hg +, Pb +, Cu2+ and Zn2+ at concentrations of 0, 40, 80, 120 and 160 ppm (1 ppm = 1 (agmf1). Accumulation and distribution of the heavy metals in shoot and root tissues were determined using atomic absorption spectroscopy (Perkin-Elmer Model 303) while secretion of the heavy metals from leaves was studied using scanning electron microscopy and energy dispersive X-ray microanalysis. I hypothesized that heavy metals have deleterious effects on plant growth and that they are absorbed by roots and secreted from salt glands present on the leaves. SEM X-ray microanalyses confirmed secretion of Cu + and Zn + ions as well as salt (NaCl) from glandular structures on both the adaxial and abaxial surfaces of leaves; however Hg2+ and Pb2+ were not detected in the secretion. Ion concentrations were significantly higher in plant roots than in shoots, particularly at 160 ligml"1 for all heavy metals. In addition, toxic levels of Hg and Pb were detected in the shoot tissue; however, Cu2+ and Zn2+ were within the normal ion concentration in the shoots. Plant height, number of leaves, biomass accumulation and chlorophyll content were significantly lower at 160 ugml" than the control values for all heavy metals. Carbon dioxide exchange, transpiration and leaf conductance generally decreased with increasing metal concentration. CO2 exchange at a concentration of 160 (J-gmf1 was significantly lower than the control for all metals. CO2 exchange at 160 ugml"1 for Hg2+, Pb2+, Cu2+ and Zn were 49.6 %, 55 %, 47.6 % and 63.6 % respectively lower than the control values. Photosystem II (PS II) quantum yield, photochemical efficiency of PSII (Fv/Fm) and electron transport rate (ETR) through PS II generally decreased with increasing concentration for all heavy metals. XV This study has shown that A. marina experiences dose-dependent stress responses to Cu2+, Zn2+, Hg2+ and Pb2+ in shoot and root tissue at a concentration of 160 lagmi"1, evidenced by decreases in growth and photosynthetic performance. The results also ~)A- "7-1- 9-1- "J-\-indicate that CuZT, Znz\ HgZT and PbZT are taken up by roots and transported to shoots. In addition, only Cu and Zn are secreted via the glands while Hg and Pb accumulate within the shoots. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2008.

The present project aimed at measuring plant heavy metal uptake as a function of transpiration rates and dissolved heavy metal level in the soil solution. Two experiment was conducted separately in two season (Spring and Fall 2000). In these two experiments, young wheat plants ( Triticum aestivum) were irrigated with nine different solutions containing Cd and Zn. The study was conducted in two chambers where relative humidity was controlled to obtain two different levels of transpiration rates. Each control chambers contained 27 pots filled with sand and seeded with wheat plants, each nine triplicated pots receiving a different treatment: three Cd treatments with levels of 0.01, 0.10, and 0.50 mg/L; one Zn treatment with level of 25mg/L and four treatment combinations of Cd/Zn with levels of 0.01 Cd/25Zn, 0.10Cd/25ZN, 0.50Cd/25Zn and 0.50Cd/50Zn mg/L. The transpiration rate of the plants was monitored over a period of 30 days, measured from the emergence of the plants by weighing the pots daily. On day 15 and 30, three plants were removed from each pot, to weigh their dry matter production and to analyze their heavy metal uptake. (Abstract shortened by UMI.)

Despite improved liner design, there are still reported incidences of landfill leachate, rich in heavy metals, percolating through to groundwater and threatening ecosystems. This thesis introduces the concept of segregating municipal solid wastes (MSW) according to their major heavy metals and their metal's adsorption compatibility. Each segregated portion can be disposed in a different landfill compartment to minimize leaching of these heavy metals with the greatest bioactive impact. The validity of the concept was evaluated by batch and column retention mobility studies using copper (Cu) alone or with either lead (Pb) or cadmium (Cd) in solutions bearing various pHs. This was supported by selective sequential extraction (SSE) to determine the affinity to specific liner fractions. The following summarizes the procedure used. / Beforehand, a soil column test using sand with 5 and 10% bentonite was conducted to develop an equation predicting liner permeability, k , under simulated field conditions. The column permeability test revealed that a liner with 5% bentonite resulted in a k value which respected the North American criteria of 10-5 m/s. / In the batch experiments, solutions with Cu alone or with Cd or Pb, adjusted to pH of 3.7, 5.5 or 7.5, were applied to sand liners with 0%, 5% or 10% bentonite, having CEC's of 2.0, 6.4, and 10.8 (cmol(+) kg-1 ), respectively. Bentonite, pH and Pb significantly affected Cu adsorption. Cu was adsorbed by the liners at pH <6.5 whereas Cu precipitated at pH >6.5. Cu retention was higher in the presence of Cd than in that of Pb, at all combinations of CEC and pH. Competition between metals was greater in liners with lower CEC and therefore fewer adsorption sites. Limiting Pb in a landfill compartment can improve Cu adsorption at pH's below the precipitating threshold. / In the SSE procedure, the liner samples were centrifuged, decanted from their solutions and each adsorption fraction analyzed for Cu content. Results indicated that the carbonate fraction adsorbed more Cu, and that Pb significantly increased the mobility of Cu due to competition for exchangeable sites. / In the final soil column test using a sand liner with 5% bentonite, the leachate had an initial pH of 3.7. The leaching test confirmed the compatibility of Cu with Cd. The leaching of Cu was greater in the presence of Pb. Total metals in leachate was greater for the Cu-Cd solutions than for the Cu-Pb, because of Cd's relatively high mobility. The sequential extraction results showed again that the carbonate fraction dominated metal adsorption. Total heavy metal leaching followed the order of Cu/Cd > Cu/Pb > Cu alone. / Thus, disposing MSW in landfill compartments based on their heavy metal compatibility can minimize migration of heavy metals.

Chemical treatment of contaminated soils (in-situ or ex-situ) is the current most practical option for remediation. The degree of metal complexation by organic acids depends on the type, concentration, metal type, pH and temperature. The influence of pH, temperature on the extraction efficiency of lead, zinc and copper was evaluated using Sodium citrate and sodium acetate buffers. Sodium citrate buffer was selected for the soil treatment. The soil was characterized for its pH, total metal content and the distribution of target heavy metals in soil fractions. Optimal conditions for Pb extraction with 0.5M citrate buffer was used to treat soil in batches and in columns, to evaluate their extraction efficiency and possible use for in-situ remediation. / Chitosan, a derivative of chitin is a versatile biopolymer with metal uptake capabilities. Due to the large amounts of chitosan required to treat heavily contaminated leachates, magnesium (Mg) and iron (Fe) metals granules were evaluated for stripping the heavy metals from solution before the use of chitosan at optimized conditions to effectively polish the soil washing. (Abstract shortened by UMI.)

The aim of this study was to examine the metal contributions to and from the lake Råsvalen, in northern Örebro County in Sweden, from incoming and outgoing streams.  The main questions were: what is the metal concentration in the streams? How large is the metal transport from the streams, do the concentrations imply a risk for the biota, and can any source be identified. Water was sampled at six locations at six occasions with two-week intervals. The water samples were analyzed for total metal concentrations. The results were compared to environmental quality standards; EQS and from Swedish environmental protection agency suggested class limits. The concentrations were also compared to deviations from background levels and estimations of risk for biological effects. Metal transport was calculated from the average measured concentrations and water flow data from SMHI. Data from sediment analysis in 1989 was included for information about temporal trends. Zn, Cu, and Pb had concentrations above the limits and therefore they could have an effect on biota in water. Zn had a maximum concentration of 39 µg/l in Storån, which is 12 times higher than limits. Pb was found in a maximum concentration of 4,3 µg/l in Hammarskogsån downstream, which is more than twice as high as EQS. Cu was found in concentration of 6,1 µg/l in Storån downstream. Comparison with estimations of biological effects showed no or little effects except for Pb in Hammarskogsån downstream and Storån showing moderate risk. The stream that contributes most to metal influx is Storån. The stream stands for &gt;80% of the total estimated metal transport. Possible sources could be historical mining, and higher levels upstream may contribute to the metal levels found in Storån.

Persistent organic pollutants and heavy metals are released into the environment through different anthropogenic processes. They are of concern because they tend to bioaccumulate in the food chain and show adverse health effects ranging from acute to chronic toxicity. These pollutants need therefore to be monitored to conserve the environment. Conventionally, samples are sent to a laboratory for analysis by standard techniques such as chromatography and spectroscopy. Although these conventional techniques display high accuracy and low detection limits, they are expensive, require the use of highly trained personnel and tedious sample preparation. In comparison, electrochemical methods such as biosensors are sensitive, low cost and simple to operate. In this thesis, the determination of selected persistent organic pollutants (polybrominated diphenyl ethers, polybrominated biphenyls and polychlorinated biphenyls) and heavy metals (Cd, Pb and Cu) was achieved by the use of amperometric inhibition biosensor based on horseradish peroxidase (HRP) immobilized on the surface of platinum-polyaniline modified electrode. Polyaniline (PANI) film was electrochemically deposited on the platinum electrode surface. The film was characterized by cyclic voltammetry and spectrometric techniques. The CV results proved that the PANI was electroactive and exhibited a fast reversible electrochemistry. Characteristic Ultraviolet–Visible and Fourier Transform Infrared features of the polymer film were identified. They revealed that PANI film synthesized in this study is the conductive emeraldine salt. Horseradish peroxidase based biosensor was constructed by electrostatic attachment of the enzyme onto Pt-PANI electrode surface. Spectrometric and cyclic voltammetric results indicated that the immobilized HRP retained its bioelectrocatalytic activity towards the reduction of hydrogen peroxide. The Pt/PANI/HRP biosensor showed a linear response over a concentration range of 0.05 to 3.17 mM with a detection limit of 36.8 nM. Apparent Michaelis- Menten constant ( app M K ) was calculated as 1.04 mM. This implied that the HRP biosensor had a high affinity for H2O2. Furthermore, the fabricated biosensor showed high sensitivity, good reproducibility, repeatability and long-term stability. The Pt/PANI/HRP biosensor was applied to the determination of selected persistent organic pollutants and heavy metals. The latter was found to inhibit the HRP enzyme’s activity. The percentage inhibition of the investigated persistent organic pollutants decreases in the following order: 2,2´4,4´,6-pentabrominated diphenyl ether> 2-brominated biphenyl> 2-chlorinated biphenyl> 2,2´,4,5,5´-pentachlorinated biphenyl> 2,4,4´-trichlorinated biphenyl. In the case of heavy metals, the degree of inhibition of heavy metals was highest for Cd2+, followed by Cu2+ and then Pb2+. Kinetic study for the amperometric response to H2O2, recorded in the absence and presence of persistent organic pollutants and heavy metals revealed that for polybrominated diphenyl ethers, the inhibition process corresponded to a competitive type whereas for polybrominated biphenyls, polychlorinated biphenyls and heavy metals, it corresponded to the on-competitive type. The biosensor exhibited high sensitivity towards the determination of the metals and persistent organic pollutants as pollutants in real water samples, namely tap water and landfill leachate samples. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.