This study presents the results from laboratory investigations of the capacity of kaolinite to adsorb heavy metals including copper, nickel, cadmium, and lead. Kaolinite is a clay commonly found in suspended solids and sediments in natural water systems. The purpose of the study was to evaluate the validity of the competitive adsorption equation presented by weber in describing metal adsorption on kaolinite. This equation describes adsorption competition among the components of a mixture of solutes. Adsorption studies were conducted for single and mixed metal systems. Controlling factors considered include solution pH, clay dosage, and cation competition. The investigation demonstrated that the competitive adsorption equation is a valid and useful equation for describing the adsorption of mixed metal systems on kaolinite. The equation may be used to predict equilibrium metal concentrations in mixed metal systems. The results of the study also indicated that the rate of adsorption of the metals on kaolinite was very rapid. Equilibrium was complete within thirty minutes of the addition of the metals to the clay. / Master of Science

Hydrophobic organic contaminants released into the subsurface can become sorbed to the soil matrix. The sorbed compounds may slowly leach into the groundwater, providing a long-term source of contamination. Bioremediation has been cited as a potential clean-up strategy for residual organics in soils. At present, factors which control biological utilization and retention of organic contaminants in the subsurface are poorly understood. The purpose of this study was to investigate how the adsorption/desorption and biodegradation processes interact to control the distribution and biological fate of subsurface contaminants. Batch soil microcosms were used to evaluate the sorption of a chlorinated aromatic compound [2,4,6-trichlorophenol (TCP)] to mineral soils, organic soils, and dissolved macromolecules (humic acid). Microbial utilization of 2,4,6-TCP was then evaluated after addition of a bacterial culture previously acclimated to the substrate. Biodegradation was evaluated by production of ¹⁴CO₂ and disappearance of 2,4,6-TCP from the sorbed and solution phases. Size exclusion chromatography was used to distinguish between free 2,4,6-TCP in solution and 2,4,6-TCP bound to humic acid in solution. Sorption of 2,4,6-TCP to mineral surfaces was rapid but sorption to organic soils varied with contact time. Most 2,4,6-TCP sorption to organic soils occurred during the first few days of contact with the soil. However, the sorption rate gradually decreased with time and 2,4,6-TCP continued to sorb for weeks at a reduced rate. The amount of 2,4,6-TCP which sorbed at the slower rate was dependent upon the organic matter content of the soil. Desorption of 2,4,6-TCP from organic soils was similar to adsorption; however, it appeared that slow desorption took longer than slow adsorption. Humic acid in solution formed an additional phase to which 2,4,6-TCP sorbed. The sorption capacity of dissolved humic acid was a function of the humic acid concentration. Higher concentrations of humic acid had lower sorption capacities when normalized for total organic carbon content. The mineralization rate of 2,4,6-TCP by Pseudomonas aeruginosa was dependent upon the initial substrate concentration. Total mineralization of 2,4,6-TCP by P. aeruginosa decreased in the presence of organic soils. However, mineralization rates were elevated in organic soils compared to mineral soils after 5 days of incubation. This was attributed to an influx of substrate into solution from an initially sorbed state. Total mineralization of 2,4,6-TCP in humic-containing solutions was reduced by 5-10 % over humic-free solutions. The bioavailability of 2,4,6-TCP was greatly reduced in the sorbed state. Biodegradation of unbound 2,4,6-TCP in solution was very rapid while biodegradation of 2,4,6-TCP sorbed to organic soil or to dissolved humic acid was much reduced. Desorption of most 2,4,6-TCP from soil was rapid, thereby becoming available to acclimated bacteria. However, a small quantity of 2,4,6-TCP desorbed from organic soil and dissolved humic acid very slowly and became available for biodegradation at a rate limited by desorption. / Ph. D.

Thesis (M.S.)--Oregon State University, 1996. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Graduation date: 1994

An infiltration-wetting agent study, using the wetting agent "WATER-IN", was conducted in the ponderosa pine forest type of east central Arizona, near McNary, Arizona. An application rate of 10 gallons of wetting agent per surface acre was used both on bare mineral soil and on ponderosa pine litter. The infiltration rate was measured by a modified North Fork infiltrometer. It was found that "WATER-IN" significantly increased water runoff, when applied to litter, but when applied to bare mineral soil, "WATER-IN" caused a significant increase in water infiltration. The wetting agent did not significantly affect antecedent moisture, soil particle distribution, litter water holding capacity, or litter bulk density. It is presently hypothesized that the increase in water infiltration on treated bare mineral soil is due to a decrease in the average bulk density of the surface inch of soil. The data strongly suggests this hypothesis to be correct. The increase in runoff when litter is treated is probably due to an interaction, either physical, chemical, or both, between the humus layer and "WATER-IN", creating a hydrophobic condition where one did not exist before.

No description available.

It was found that Azotobacter vinelandii grown in a dialyzed soil medium did not fix nitrogen and had a much lower rate of respiration than when grown in Burk's nitrogen-free medium. When para-hydroxybenzoic acid served as the added oxidizable organic carbon source in dialyzed soil medium, the azotobacter grown in it were found to be unable to fix nitrogen. On the other hand, A. vinelandii fixed nitrogen when grown in soil supplemented with glucose. It was concluded that natural conditions in the soil are not conducive to nitrogen fixation by A. vinelandii.

Call number: LD2668 .T4 1986 L39 / Master of Science / Agronomy

No description available.

Long-term low-level ingestion of cadmium (Cd) causes human health problems, and in Australia, vegetables supply ~40% of the Cd in the typical diet. Plants take up Cd from the soil; however, the uptake is poorly predicted by simple soil tests, such as the total concentration of Cd (Cdt). Therefore, a greater understanding of Cd behaviour in soils is needed to improve the prediction of Cd uptake by plants and open a new path to minimise the risks for human health. The objectives of the research in this thesis were to: identify key soil properties affecting Cd behaviour, identify/develop selective methods to measure them, and to formulate a conceptual model of Cd partitioning. These objectives were based on the hypothesis that empirical modelling informed by a better understanding of Cd chemistry would accurately describe Cd partitioning in soil. To test the hypothesis, the key properties were measured on soils from the peri-urban fringe of Greater Sydney (n = 41) and a series of models of increasing complexity were fitted to the data. A model with three explanatory variables— log10 Cdt, pH and log10 ECEC (effective cation exchange capacity)—explained 94.6% of variation in log10 CdCa (the concentration of Cd in solution in a suspension of soil in 10 mM CaCl2), which strongly supported the hypothesis. The study also indicated that the explanatory variables, Cdt, pH and ECEC, may describe Cd behaviour in many soils, and that for these general models, partition coefficients, such as log10 (Cdt/CdCa), are unsuitable dependent variables. The preceding model used Cdt as an explanatory variable, notwithstanding that labile Cd (CdE) was mechanistically preferable. However, CdE can only be measured using isotopic techniques: a requirement that has constrained the evaluation of CdE as an index of Cd behaviour and bioavailability. Therefore, a simple proxy measure of CdE was investigated. The literature indicated that solutions of chloride salts might selectively extract CdE, and Cd extracted into 1 M NH4Cl (CdNH4Cl) was compared with CdE measured by stable isotope dilution ICPMS. For 23 soils from the partitioning study, 1 M NH4Cl failed to completely extract CdE, unless the pH was less than 5. The cause(s) of this effect will be investigated with the aim of developing a universally applicable measure of CdE that does not require isotopic measurements. All models of Cd uptake by plants rely on soil properties measured on homogenised samples, although the distribution and bioavailability of Cd vary spatially in the field. Were such variability to increase at the micro-scale, its effects could erode the accuracy with which models could predict Cd behaviour and uptake. Consequently, I tested whether the distribution of Cd could be mapped by using synchrotron micro-x-ray fluorescence spectroscopy (micro- XRFS): the most sensitive method of observation. The soils examined contained 0.3–6.4 mg Cd/kg, i.e. were typical agricultural soils, and one was spiked to ~100 mg Cd/kg. Micro-XRFS mapped the Cd in the spiked soil, and in one particle in the other soils. For typical agricultural soils, the sensitivity realised in this study would have been sufficient to characterise the average Cd binding site, but fell at least 10-fold below that needed to map the Cd distribution in them. The research satisfied the objectives, advanced knowledge of Cd behaviour in soils, and provided new research leads. These leads include the possibility of developing general models of Cd partitioning in soils, derivatives of which may predict Cd uptake by plants. The accuracy of these models may be strengthened by the use of CdE as an explanatory variable, but may be weakened by the effects of in situ variation in the distribution of Cd. The benefits to human health of agricultural practices that decrease dietary Cd justify continuation of research to develop models that accurately predict Cd uptake by plants. / Doctor of Philosophy (PhD)