Succinic acid, a low molecular weight dicarboxylic acid was used to leach out heavy metals from Willamette Valley soil (contaminated separately with lead, copper, and zinc) in form of water-soluble organo-metal complexes. The research tasks included developing synthetic contaminated soils representative of those found at Superfund sites and making heavy metal adsorption and desorption studies. Fixed amounts of single-metal contaminated soil were treated with succinic acid under varying conditions of pH and organic ligand concentration. Based on the total metal mobilized into the aqueous phase, the optimum values of pH and organic acid were established for each metal. Since the direct determination of all species solubilized by the organic acid solution was not possible, a computer speciation program called MICROQL was used to determine the concentration of metal species in solution containing several metals and potential ligands. The results indicate that succinic acid is capable of significantly altering the partitioning of metals between the soil and the aqueous phase. Higher concentrations of the organic acid resulted in higher removal of metal from the soil. In case of lead and copper, low pH (3.5) succinic acid flushing solution was found to be the most effective, while a pH range of 4.5-5.5 was deemed optimum for zinc. The results also established that the extent of removal of any metal depended not only upon the the stability constant of the organo-metal complex, but also on its mode of retention within the soil. / Graduation date: 1993

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 292-310). Available also in a digital version from Dissertation Abstracts.

Thesis (MTech. : Environmental Management.)--Tshwane University of Technology, 2010.

No description available.

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.

Many studies have been undertaken to determine the effects of soil and soil properties on migrating metal pollutants. Organic pollutants, however, in addition to their interactions with soil components , are also susceptible to degradation (catabolism) by microorganisms. Soil-microorganism-pollutant interactions have, traditionally, been studied in soil columns (microcosms). One of the shortcomings of column and in situ studies is that the identity and specific effect(s) of the soil component(s) affecting or influencing attenuation are not known and cannot readily be determined. Attenuation effects of the soil components are, therefore, difficult to interpret. ("Attenuation" in this context is the combined effects of both soil adsorption and microbial catabolism). Attenuation studies often only consider the physical conditions such as aeration, permeability, flow rate, temperature, etc. This approach assumes the soil to be a homogeneous matrix with no specific physico-chemical properties attributable to different components within the matrix. Soil physical factors suspected of influencing pollutant attenuation could be misleading without consideration of the physico-chemical interactions between soil components, microorganisms and pollutants. Adhesion of pollutants and microorganisms seems to be most important in this regard. The initial phase of this study was undertaken to examine the effects of three different soil materials on attenuation of key landfill leachate molecules. Examination of the effects of soil surface type on attenuation focused on adsorption / desorption of the pollutant molecules and microorganisms. These experiments sought to investigate the physico-chemical effects of soil, microorganism, pollutant interactions and were done as batch slurry experiments as well as in soil columns. Two soil horizons from the Inanda soil form (humic A and red apedal B) and the topsoil (vertic A) from a Rensburg soil form were used. The Inanda topsoil had a high organic matter content and both the topsoil and subsoil had a kaolinitic clay mineralogy; the Rensburg topsoil clay mineralogy was predominantly smectitic with a relatively low organic matter content. From the batch experiments, the adsorption of a hydrophobic molecule (naphthalene) and a heavy metal (cadmium) were found to be influenced to a significant extent by soil characteristics. Adsorption of naphthalene was due to the soil organic matter (SOM) content whereas cadmium adsorption was due to the cation exchange capacity (CEC) of the soil. Soil characteristics did not seem to have a significant influence on the adsorption of a water soluble compound such as phenol at the concentrations used. Attenuation of naphthalene was found to be affected by adsorption of the pollutant molecule (related to SOM) as well as the CEC of the soil. The attenuation of hydrophobic molecules can possibly be ascribed to the influence of CEC on the microbial population responsible for attenuation. This would seem to indicate interaction between the soil surfaces and the catabolizing microbial population. Desorption of the pollutant (and possibly also of the microbial population) was achieved by the addition of acetonitrile and methanol both of which reduced the polarity of the water. These solvents were also found to be toxic to the catabolizing microbial population at high concentrations. The toxicity thresholds of both solvents for catabolizing microorganisms differed significantly between soil- (> 15 %, v/v) and soil free (< 5 %, v/v) treatments. This discrepancy cannot be accounted for by adsorption and is ascribed to physico-chemical interaction between microorganisms and the soil surfaces. This interaction probably affords protection from, otherwise, toxic concentrations of solvents or metals. The important effects of soil surfaces on attenuation processes were thought to be due to the strong adsorption of naphthalene. Surface attachment of microorganisms was, however, also inferred from results obtained with phenol. This seemed to indicate that microbial attachment to soil surfaces was an important aspect in attenuation and did not occur only because of pollutant adsorption. Soil column experiments were made with both naphthalene and phenol. The naphthalene, which was adsorbed to the soil, did not leach from the columns to any appreciable extent. This was despite the addition of acetonitrile to some columns. This was probably due to greater microbial catabolism caused by desorption and, subsequent, increased soluble concentrations of the molecule. After extraction from the soil at the end of the experiment it was clear that the sterile controls held much higher concentrations of naphthalene than the experimental columns. The soil type and treatments showed little difference in the naphthalen concentration extracted from the soil columns. This did not reflect the differences found between soil materials in the batch experiments and was probably due to the masking effect of the soil physical factors on attenuation processes. Unlike naphthalene, phenol, because of its high solubility, was detected in the column leachates at relatively high concentrations. The phenol concentrations were much higher for the Inanda subsoil (approximately 4 mM) than the Inanda topsoil (approximately 2 mM) and Rensburg topsoil (< 1 mM). The Rensburg topsoil produced the lowest phenol concentrations in the leachate and this can probably be ascribed to the larger quantity of micropores in this soil. Thus, it seems that the soil physical features had a pronounced influence on attenuation. Whether this effect was directly on the studied molecule or indirectly, because of the effects on the microbial population, is not known. Inoculation of the columns with a phenol catabolizing population had only a slight increased effect on leachate phenol concentrations from all columns. This increased effect was, however, only prolonged in the case of the Inanda subsoil. The flow rate through the columns affected leachate phenol concentration which was lower with a slower flow rate and, thus, longer retention time. From the column experiments soil physical parameters were suspected of influencing, and possibly overriding, the soil surface effects on microbial activity (capacity to catabolize a organic molecule of interest). Soil porosity, as caused by different soil materials, was suspected of being the most important soil physical parameter influencing microbial activity. To investigate the potential effect of soil porosity, relatively homogeneous porous media i.e. chromatography packing material and acid washed sand were used. These materials had more defined and distinct porosities and were considered to be suitable for investigating the fundamental influence of porosity on microbial activity. Saturated continuous flow columns were used and three types of packing configurations were tested: chromatography packing (CHROM) material (porous particles); acid washed sand (non-porous) (AWS); and a 1: 1 (w/w) mixture of chromatography packing and acid washed sand (MIX). Only a single water soluble molecule, phenol, was used in this phase of the investigation. Bacterial filtration ("filtration" as a component of "attenuation'') was found to be highest for the CHROM and lowest for the AWS materials. This difference in microbial retention affected the phenol catabolism in response to increased column dilution rates. The CHROM and MIX materials had distinctly different porosities than that of the AWS, due to the internal porosity of the chromatography packing. This greater pore size distribution in the MIX and CHROM packing materials created pores with different effective pore dilution rates within the microcosms at similar overall flow rates. The greater pore size distribution in the MIX and CHROM packing materials facilitated pore colonization since some pores did not participate, or conduct, mass flow as occurred in macropores. This led to different microcolonization effects in the macro- vs micropores. Since the MIX and CHROM packing materials had more micropore colonization sites these packing materials showed a greater range of substrate affinities (i.e. Ks values) for the phenol substrate. The extent to which micropore colonization occurred could be detected by the effect it had on phenol breakthrough curves. In the MIX and CHROM materials, microbial colonization caused blocking of micropores with a subsequent effect on the phenol breakthrough curves. The AWS material, however, which had a low inherent microporosity, showed microbially induced microporosity probably due to biofilm development. The fact that the MIX and CHROM packing materials facilitated micropore colonization was also responsible for the greater resistance to, and the recovery from , potentially inhibitory cadmium concentrations. This effect was also apparent in the presence of acetonitrile, although this effect was not identical to that observed with cadmium. Finally, column pressure build up as a function of pore clogging was determined and was found to occur in the order AWS > MIX > CHROM. This was most likely due to fewer potential liquid flow paths with a higher blocking potential in the AWS. Extrapolation of the fundamentals of the above findings led to the conclusion that soil surface- and soil porosity effects are extremely important factors in determining the behavior of soils as bioreactors. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1995.

No description available.

There is an ever-increasing need to address problems associated with the creation and disposal of wastes which result from human activities. Pb and Cd contamination is a common problem at many abandoned and uncontrolled commercial and industrial sites. Phytoremediation is one technology that can be employed to remove metals such as Pb from the soil. This study investigated the effectiveness of several plant and soil treatments on the uptake and retention of Pb and Cd by vegetation from contaminated soil at a Superfund site. Field plots were established and plant treatments included a mixture of grasses including Festuca, Poa. and Phleum; red clover (Trifolium Pratense); and sunflower (Helianthus annuus). Soil treatments included a common NPK fertilizer, ethylenediaminetetraacetic acid (EDTA), dilute sulfuric acid (H2SO4), and a mixture of EDTA and H2SO4 (EDTA+H2SO4). Trifolium tissue contained a greater quantity of Pb (182 mg Pb/kg tissue) than that of Poa (65 mg Pb/kg tissue). Cadmium concentration was similar in Poa and Trifolium tissue. ranging from 7.2 to 10.6 mg/kg tissue. Different soil treatments affected Pb levels found in plant tissue in order of effectiveness: H2SO4>EDTA>NPK>EDTA+H2SO4 The effects of soil treatments on Cd levels were similar to those for Pb with a difference of 0.1 mg Cd/kg tissue between EDTA and NPK treatments. Soil amendments differentially influenced Pb bioavailability and uptake, with H2SO4 exhibiting the greatest positive influence on Pb and Cd concentration in tissue. There was no correlation between the quantity of Pb and Cd up taken by vegetation at the site. The current study demonstrated the capability of common native plant species to grow on toxic and infertile soils, and the ability to uptake Pb and Cd to a limited degree. Regardless of tissue concentrations of Pb or Cd, Poa coverage at the site was generally dense. demonstrating the ability of Poa to become established on toxic soils and prevent soil erosion. / Department of Natural Resources and Environmental Management

This project developed methodology for in vitro toxicity assessment of contaminated sites using the Promega?? MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay performed on human cells (HepG2 and Skin fibroblasts). The project included the development of a method for extracting contaminants from soil based on leaching and centrifugation. A number of solvents and surfactants were assessed for their suitability as extracting agents. The Zwitterionic surfactant CHAPS ({3[(3-Cholamidopropyl) dimethylammonio] propanesulphonic acid}), which is an irritant in vivo, was found suitable for in vitro toxicity assessment applications. CHAPS was found to be the least toxic surfactant in vitro when tested on skin fibroblasts (NOEC: 1800??577 ppm, IC50: 4000??577 ppm) and HepG2 cells (NOEC: 833??289 ppm, IC50: 5300??287 ppm). The chosen surfactant was used in three different methods for extraction of Toluene and Xylene spiked in 2 g and 10g soil. The combination comprising of 0.1% (s/w) CHAPS and cosolvent 1% (w/w) Isopropanol, at their respective NOEC (No Observed Effective Concentration) toxicity values, showed good recovery of the nonpolar organic compounds in comparison to the recovery by 0.1% CHAPS and 0.5% CHAPS. The study found additive interactions to be the most common form of toxicity for 16 concentration combinations of Formaldehyde (polar), Toluene and Xylene (nonpolar) when compared to predicted toxicity (R2=0.943, P&lt0.0001). When assessing the in vitro toxicity of unknown (blind) contaminated soil samples, the Hazard Index (HI) predicted from the chemical analyses results showed a relatively good correlation (R2&gt0.7062, n=26) when compared to the experimental toxicity results on HepG2 cells. Furthermore, the comparison of Australian Health Investigation Levels (HIL) with in vitro toxicity testing gave similar correlation (R2&gt0.6882, n=26) on HepG2 cells. The overall project suggests the potential application of the zwitterionic surfactant (CHAPS) in sampling contaminants from soils in an in vitro toxicity assessment. This study demonstrates the application of in vitro toxicity assessment using human cells for the prediction of toxic risk as a sentinel to human toxicity from a contaminated site.

Thesis (M.Sc.). / Written for the Dept. of Natural Resource Sciences. Title from title page of PDF (viewed 2008/07/30). Includes bibliographical references.