Tesis sobre el tema "Chromium Environmental aspects"

Due to increasing awareness of potential Cr toxicity, there is a pressing need to establish sensitive and robust Cr fractionation and speciation methodologies that will be enable separation of the two redox Cr species (CrIII and CrVI) from different environmental phases and their quantification. The intention of this work was to assess the behaviour of Cr species, especially CrVI, in soils and the factors controlling Cr solubility, fractionation, redox transformation rates and uptake by plants. The analysis methods relied on alkaline extraction in TMAH, liquid chromatography (LC) to separate the chromium species and inductively couple plasma mass spectrometry (ICP-MS) for quantification of chromium. The interference of 40Ar12C+ background peak at mass 52 was reduced by using the CCT-KED facility of the ICP-MS. A solution of 50 mM TRIS buffer, 40 mM NH4NO3, 10-5 M ammonium-EDTA at pH 7.0 was used as the chromatographic eluent. The method developed is suitable for determining CrVI in soil, following alkaline extraction in TMAH, but not for CrIII due to poor recovery, redox transformation and strong binding of CrIII with humic acid despite attempts to preserve the trivalent species using EDTA and heating. The extraction method was applied to assessing Cr speciation and fractionation in a wide range of soil ecosystems collected from urban sites in Wolverhampton, Nottingham, London and a historical sewage sludge disposal farm in Nottinghamshire. To predict soil CrVI content the use of TMAH-extractable Cr (CrTMAH) was better (R=0.911) compared to total soil Cr content (Crtotal; R=0.554). The same analytical approaches were also applied to the development of a method to determine isotopically exchangeable CrVI in soils. This employed isotopically enriched 50CrVI as a ‘spike’ isotope added to soils suspended in varying concentrations of TMAH in an attempt to resolve a consistent fraction of isotopically exchangeable, or ‘labile’, CrVIO42- in soil. It was apparent that, because of the slow exchange kinetics of CrVI in soils, it was difficult to determine a consistent isotopically exchangeable fraction. Nevertheless, the investigation did suggest a refinement of the simple TMAH extraction protocol could enable direct determination of labile soil CrVI. The kinetics of CrVI interaction with a geocolloid (humic acid) was assessed and humic acid was found capable of both reducing CrVI and binding with the resulting CrIII species. Finally, Cr uptake by maize grown on a historical sewage sludge disposal farm was assessed with several approaches to finding a correlation between Cr in soil and Cr uptake by plants. The concentration of CrVI in soil, and its solubility, could be reasonably well predicted from Crtotal or CrTMAH and soil properties. However, restricted uptake of CrVI by the maize plants, and probably reduction of CrVI to CrIII in the root system, made it impossible to predict Cr transfer to shoots or the speciation of the Cr in maize shoots. Overall, due mainly to the apparent ability of the maize plants to control uptake and speciation of CrVI, the produce was considered safe to be consumed by ruminants as regards CrVI content.

A standard methodology was developed for performing avoidance-preference tests, using Rainbow Trout (Salmo gairdneri) as the test organism. Experiments were conducted in a hydraulic channel, 9.15 m long by 0.30 m wide, partly divided along its length, and at a flow depth of 0.30 m. The design combined steep and shallow gradient characteristics. The toxicants investigated included Cu(II), Cr(III) and Cr(VI). The lowest avoidance threshold values were established at 2.1 $ mu$g/l for Cu(II) and 0.0026 mg/l and 0.026 mg/l for Cr(III) and Cr(VI) respectively while avoidance reactions increased with levels of toxicant in the channel. Similar experiments were performed with rainbow trout which were pre-exposed at sublethal levels to the toxicant, in order to assess the influence of toxic pre-exposure to the subsequent fish avoidance response. The length of pre-exposure varied between 7-20 weeks. Avoidance threshold values were correlated with safe levels of toxicant exposure.
Pre-exposed fish exhibited decreasing avoidance reactions compared to non-exposed populations. Increased tolerance to the toxicant, was suggested by the increase in avoidance threshold values with pre-exposure levels. Fish exposed to test concentrations matching their pre-exposure levels, clearly preferred this same concentration over the adjacent lower or higher test concentration.
A two mechanism avoidance model was proposed independent of toxicant used or level of pre-exposure. The toxicant concentration where the second mechanism begins to dominate was referred to as avoidance breakpoint, and was correlated to a MATC level for the toxicant in question. Olfactory responses were proposed to be associated with fish avoidance responses below the avoidance breakpoint, while hypoxic stress along with osmo- and iono regulatory stress appeared to be responsible for driving fish avoidance reactions beyond the avoidance breakpoint.
A clearance period of 7 days was sufficient to allow fish to recover normal avoidance behaviour following pre-exposure to Cr(VI) below the avoidance breakpoint.

Bibliography: leaves 166-180. Determines the effect of chromium on the soil microbial community and its activity, the biotic-abiotic mechanisms involved in chromium oxidation, and phytostabilization of chromium using plants and organic amendment in tannery-waste contaminated soil.

Research efforts in aquatic toxicology have historically centered on the chemical analyses and toxic effects of waters to aquatic organisms. More recently, sediment-source toxicity has been explored, with efforts concentrated on establishing sensitive and accurate methodologies. This study focused on the toxicity of trivalent chromium, hexavalent chromium, and fluoranthene to Pimephales promelas, Ictalurus punctatus, and Lepomis macrochirus. Test fish were exposed to both water-borne and sediment-source toxicants for 96 hours (h) and 30 days (d). A 96-h and 30-d LC50 (mg/L Cr, ug/L Fluoranthene) was determined for each fish species exposed to aqueous toxicants. In addition, 96-h and 30-d LC50s were determined for each fish species from sediment chromium concentrations (mg/kg) and sediment fluoranthene concentrations (ug/kg). Although lethality endpoints were used throughout this research, acute effects other than mortality were determined for Lepomis macrochirus exposed to hexavalent chromium. Lethal toxicity values (96-h and 30-d LC50 and their 95% confidence limits) for trivalent chromium could not be determined since trivalent chromium concentations above 6.0 mg/L could not be obtained at water pHs compatible with these fish species. Trivalent chromium addition to test waters at pHs compatible with fish survival resulted in a chromium precipitate that was not lethal to test fish. In contrast, fathead minnows, channel catfish, and bluegill sunfish exposed to hexavalent chromium in water and sediments experienced mortality. Fathead minnows exposed to fluoranthene in water for 96h demonstrated a maximum mortality of 69%, while 100% mortality was achieved with channel catfish in similar tests. Sediment tests with fluoranthene resulted in 100% mortality with both fathead minnows and channel catfish.

M. Tech. Chemistry.
The aim of this study was to develop and evaluate an analytical method for the determination of Cr(VI) in ferrochrome dusts and to apply the method in the analysis of environmental samples (grass, soil and tree bark) for Cr(VI) content (that might be caused by dust emissions originating from the smelter). Both the public and Xstrata Wonderkop ferrochrome plant will benefit from data of Cr(VI) determination generated from the study. The information can potentially be incorporated into health risk assessments of the affected geographical areas. The results of the investigation showed that ferrochrome smelter dust emissions were the source of contamination of the environment with Cr(VI). With time, Cr(VI) could accumulate in soil to unacceptable levels, thereby endangering both plants and animals.

Corrigenda inside front cover.
Includes bibliographical references (leaves 205-232)
xii, 232, [27] leaves : ill., plates ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2002

Bibliography: leaves 166-180.
180, [4] leaves : ill. (chiefly col.) ; 30 cm.
Determines the effect of chromium on the soil microbial community and its activity, the biotic-abiotic mechanisms involved in chromium oxidation, and phytostabilization of chromium using plants and organic amendment in tannery-waste contaminated soil.
Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2002

Chromium hydroxide sludge is the end product of the aluminum phosphate coating process used by a truck manufacturer in the Pacific Northwest. This sludge is listed as an (F019) hazardous waste by the Environmental Protection Agency, and must be landfilled in a hazardous waste landfill site. The purpose of this thesis is to evaluate the characteristics of this sludge, and to then recommend suitable methods for handling and disposal. The chemical analysis of the sludge found total chromium to be 5.4% by weight. Industrial hygiene monitoring found the highest concentrations of 0.002 mg/m3 total chromium and 0.00006 mg/m3 hexavalent chromium at the waste treatment plant. The eight hour permissible exposure limit for total chromium is 0.5 mg/m3 and 0.05 mg/m3 for hexavalent chromium. Given the chemical analysis and industrial hygiene monitoring, a management plan is proposed for this truck manufacturer that discusses possible options for handling the (F019) waste, and provides a cost analysis for each of the options. The options that were investigated were onsite treatment, recycling, no change, and delisting. Onsite treatment was not required since the sludge passed the TCLP extraction test. Recycling costs were determined by contacting four recycling firms. Costs were found to be $600/ton and above, which exceeded the current disposal costs of $466/ton. Delisting the sludge from the hazardous waste listing was determined to be the most feasible from a management, cost, and environmental standpoint. Delisting would reduce the costs of handling the waste, would allow a reduction in landfilling costs, and reduce recycling costs. A literature survey provides background information on industrial uses of chromium, health problems associated with chromium, and discusses the regulations that govern disposal of these chromium sludges.
Graduation date: 1991

The overall efficiency of plants to remediate soils contaminated by metals depends on their growth ability especially on soils with low-fertility. For twelve weeks, the ability of Psoralea pinnata to grow well and remove chromium and iron from artificially contaminated soil was tested. The concentrations of chromium and iron in two soils obtained from different sources namely, University of South Africa premises (US) and commercial potting soil (PS) were 80 ppm, 130ppm, 180ppm, 230ppm, 280ppm, 330ppm, 380pp, 430ppm and 480ppm. Psoralea pinnata was transplanted into the contaminated soils and the experiments were watered daily to maintain 70% moisture at field capacity in a greenhouse. Shoot height and root length of Psoralea pinnata before and after planting were measured. Other parameters that were measured were number of leaves, wet shoot and dry weights, and wet root and dry weights. The growth of Psoralea pinnata, after 12 weeks of experimentation was noticeably affected by the concentrations of chromium and iron in the soil. The percentage increases in shoot height of Psoralea pinnata in the PS Soil (C-PS, 48cm from initial shoot height of 12.6cm) treatments were generally higher than the increases in the US Soil (C-US, 45.2cm from initial shoot height of 12.8cm) treatments. Psoralea pinnata in the (US) treatments accumulated Fe (50.02 ppm) from the soil more than Cr (32.38ppm). In the (PS) treatments, Psoralea pinnata also accumulated more Fe (60.57 ppm) than Cr (38.34 ppm). In the experiments containing both Fe and Cr, the US treatments with 40 ppm each of Cr and Fe, chromium was initially mostly accumulated by Psoralea pinnata (68%). At higher concentrations (320 ppm) of the combined metals (Cr and Fe) treatment, more Fe (55%) was accumulated in Psoralea pinnata. This study however showed that Psoralea pinnata may not be an efficient phytoextraction plant for hyperaccumulation.
Environmental Sciences
M. Sc. (Environmental Management)

Soil column studies were performed on a chromium contaminated soil from the United Chrome Products Superfund Site currently undergoing a pump-and-treat cleanup process. The goal of the research was to provide insight into the feasibility of chemically changing the injection fluid of the pump-and-treat system to enhance hexavalent chromium (Cr(VI)) mobility. The parameters tested were pH, ionic strength, and competitive anion type and concentration. Ionic strength effects were investigated by adjusting the NaCl concentration of the extracting solution and by observing the influence of varying anion concentrations on desorption (bicarbonate, sulfate, and phosphate). The results indicated that high ionic strength solutions slow the rate of Cr(VI) desorption. This possibly indicates most of the Cr(VI) was in pore water solution and was adsorbing, slowing the removal process. Cr(VI) desorption was fastest for distilled water solution followed by competitive anion/distilled water solutions. The high ionic strength extracting solutions, 0.05 M and 0.10 M NaCl, had the slowest Cr(VI) desorption rates. Effluent pHs dropped as the ionic strength was increased (increasing NaCl concentrations) which was attributed to a Na-H exchange. Increased concentrations of bicarbonate, sulfate, and phosphate resulted in only small pH differences in the effluent of less than 0.5 pH units. The effect of pH was investigated by varying the pH of the 0.01 M NaCl solution with strong acid and base and by varying the pH of phosphate competitive anion solutions. The effects of changing 0.01 M NaCl solution pH were inconclusive. Differences between Cr(VI) desorption rates for the soil columns with adjusted influent pHs were small. Cr(VI) desorption curves and column effluent pH values for phosphate solutions of varying influent pH values were nearly identical, indicating that soil buffering and effluent pH are more important factors than influent pH in achieving Cr(VI) desorption. Nitrate, bicarbonate, sulfate, and phosphate were investigated to determine the effect of various competitive anions on Cr(VI) desorption. The effectiveness of each anion at extracting Cr(VI) from soil appeared to follow the order of adsorption affinity to the soil.
Graduation date: 1992

The mixed metal compound, Chromated Copper Arsenate, or CCA, has been widely used as a wood preservative. The metal ions in CCA, CrO��������, Cu�����, and AsO��������, have been found in contaminated surface and subsurface soils and groundwater nearby some wood preservative facilities and nearby wood structures. Iron oxides are a ubiquitous soil-coating constituent and are believed to be a main factor in controlling the transport and fate of many metals in the soil solution. In this research, iron-oxide-coated sand (IOCS) is used as a surrogate soil to investigate the adsorption and transport behavior of the mixed metals solution, copper, chromate, and arsenate, in the subsurface environment. Copper adsorption increases with increasing pH. The presence of arsenate in the solution slightly increases, while chromate has minimal effect, on the amount of copper adsorbed. Chromate adsorption decreases with increasing pH. With arsenate present in solution, chromate adsorption is significantly suppressed over the pH range studied. In contrast, the presence of copper slightly increases chromate adsorption. Similar to chromate, arsenate adsorption decreases with increasing pH. The presence of chromate or copper does not affect the amount of arsenate adsorbed over the range of concentrations studied. Two surface complexation models, the triple layer model (TLM) and the electrostatic implicit model (EIM), were used to simulate equilibrium adsorption in both single-metal and multi-metal systems. Simulations using the specific surface complexation equilibrium constants derived from either the single-metal or the multi-metal systems with both the TLM and the EIM were successful in fitting the adsorption data in that respective single or multi-metal system. The local equilibrium assumption using batch-derived sorption isotherm parameters from the EIM failed to predict the copper and arsenate transport, while it adequately described chromate transport. The breakthrough curves of all three metals were asymmetrical and showed long-tailing behavior. This nonideal behavior is caused by nonlinear sorption and/or non-equilibrium conditions during transport. The two-site chemical non-equilibrium model, which accounts for the kinetically controlled adsorption sites, was able to fit the observed breakthrough curves for all three metals in single-metal systems. However, the model was partially successful in predicting transport in multi-metal systems.
Graduation date: 2002

The presence of heavy metal ions in waste streams is one of the most pervasive environmental issues of present times. A rotating biological contactor (RBC) was used to investigate the potential capacity of microbial biofilms in remediation of the metal ion species from a mixed metal contaminated effluent solution containing Cr+3 , Pb+2 and Cu+2 , each at a concentration of 200 mg r1 • In the first part of this study the effectiveness of various support materials for the development of microbial biofilms capable of removing heavy metals from a synthetic effluent was investigated. EDX analysis showed that none of the support matrices investigated, viz. gravel, polyester batting and sand, adsorbed metal ions on their surfaces; hence, metal adsorption was due purely to microbial activities. The biofilms attached more firmly and uniformly to polyester batting than to gravel and sand. The characteristics of polyester batting which made it a superior support matrix were its surface roughness and porous hydrophilic nature, which provided a larger surface area for the adhesion of microorganisms and attraction of nutrients during the biofilm development process. The selective accumulation of metal ion specIes by various microbial populations grown as biofilm using polyester batting as support matrix in separate compartments of a single-stage RBC bioreactor was examined. Lead ions were readily accumulated by almost all the microbial biofilms tested. Fungus-dominated biofilms selectively accumulated chromium ions whereas biofilms comprising mainly bacteria more readily accumulated copper ions from the mixed metal contaminated effluent solution. However, where interactions between the bacterial and fungal components were encouraged the mechanical stability of the biofilms was enhanced so that large amounts of all three metal ion species were removed by this biofilm. The combined effect of a series of bench-scale columns containing liquid humic acid and a three stage RBC bioreactor on the removal of metal ion species from a mixed metal contaminated effluent was investigated. After seven days of treatment the combined system had removed approximately 99% of the Cr+3, 98% of the Pb+2 and 90% of the Cu+2 ions from the mixed metal contaminated synthetic effluent. Complexation of the metal ions with humic acid was the predominant factor accounting for approximately 68-86% Cr+3 , 70-86% Pb+2 and 53-73% Cu+2 removal levels within the columns. A large proportion of the remaining Cr+3 and Pb+2, but not of the Cu+2, was removed in compartment 1 of the RBC. This suggested that the presence of the former two metals in solution might have reduced the removal of the Cu+2 ions from the system. The removal of substantially large amounts of the competing ions chromium and lead during the initial stages of the treatment process meant that copper was successfully taken up in the second and third RBC compartments. Hence, the economy of the treatment process was improved as larger quantities of the metal ions were removed in a shorter period of time than was possible when using the individual treatments (humic acid-metal complexation and biofilm adsorption) separately. More than 75%,92% and 86% of the adsorbed Cr+3 , Pb+2 and Cu+2 ions, respectively, were recovered from the three RBC bioreactor compartments following repeated washing of the biofilms with 0.1 M HCI. This relatively easy desorption suggested that the metal ions were simply adsorbed onto the surfaces of the biofilm cells rather than being taken into the cytoplasm of the cells.
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Most developing countries are faced with drinking water problems, with conditions becoming more severe due to water pollution. Meeting the growing demands for clean water in most countries, there are difficult challenges as the availability and supply of drinkable water are diminishing. Due to economic and environmental concerns, development of additional physical means for the removal of organic compounds from wastewater using permanent magnets, electromagnetic coils, electrodes and ultrasonic pretreatment is desirable. Improving the adsorption and separation process, magnetic field exposure method has progressively drawn consideration. Magnetic field exposure method has demonstrated its capacity for increasing the adsorptive elimination of contaminants from water as static magnetization is suitable, simple and cost-effective. The polypyrrole magnetic nanocomposite use for adsorption experiments influenced by exter-nal magnetic field was prepared using the in-situ polymerization method, which was charac-terized using TEM, SEM, EDX, XRD, BET, FTIR, VSM, and ESR spectrophotometers. The magnetic nanocomposite (PPy/Fe3O4) was observed to have an average particle size of 10 nm with the elementary composition of carbon, oxygen, nitrogen, chloride and iron. The magnetic nanocomposite had a crystalline structure of face-centred cubic lattice of Fe3O4, an adsorption-desorption isotherm shape indicating a typical type-IV mesoporous material with a surface area of 28.77 m2/g. Characteristic peaks of Fe3O4 and PPy were also observed using FTIR spectro-photometer. From the VSM and ESR characterization, the synthesized superparamagnetic ma-terial was shown to have a saturation magnetization of 23 emu/g and an effective g-value of 2.25 g which was attributed to Fe3+ spin interaction. An enhanced removal of Cr(VI), fluoride and congo red dye were observed under the influence of magnetic field, with parameters like pH, adsorbent dosage, the initial concentration of ad-sorbate, magnetic field and magnetic exposure time been varied. The enhanced adsorption of contaminants using magnetic field is attributed to the increase in the magnetic field induced on the particles over a magnetic exposure time, resulting in the rotating particles forming aggre-gates due to the increased magnetic force and torque on the particles from the PSV results. This leads to increase in the chain collision and area of particle interaction with the aqueous solution of hexavalent chromium, fluoride and congo red dye.
Physics
Ph. D. (Physics)