Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Veterinary Physiology, Pharmacology, and Toxicology (Veterinary Medical Sciences)

First Advisor

Jay C. Means


Several methods of separating the dissolved 4+ and 6+ oxidation states of selenium were investigated. The use of Dowex 1 anion exchange resin in packed columns was not satisfactory as quantitative separation was not obtained. The determination of selenite after formation of a fluorescent complex with 2,4-diaminonaphthalene was quantitative but the procedure was too involved for routine work. Separation was achieved by co-precipitating the selenite from solution with ferric hydroxide precipitate formed between pH 5 and 6. The co-precipitation technique is effective from 4 to 50 degrees centigrade and is unaffected by salinity although phosphates interfere at high concentrations. The co-precipitation technique was also successfully employed to remove selenate from complex matrices after reduction to selenite by boiling the solution 5 minutes after acidification to 4M in hydrochloric acid. A pre-formed ferric hydroxide precipitate maintained submerged in water for 112 days was also effective at quantitatively removing selenite from solution. The speciation technique was utilized in determining the dissolved selenium speciation in water samples collected from the Mississippi River at Baton Rouge, Louisiana between January 1994 and July 1995 and in samples collected at various points along the Mississippi River from Winfield, Missouri to Belle chasse, Louisiana, in January 1995. The technique was also employed in assessing the selenium speciation in a laboratory microcosm bioaccumulation study involving oysters and aqueous oil refinery effluent. Attempts were made to determine the rate of transformation between the selenite and selenate forms in aqueous solution. The rate of the abiotic conversion was not determined as it was not detected in 324 hours and in an aerated solution at pH 9. The biotic reduction of selenate to selenite could be induced by the addition of seawater or estuarine sediment to a solution containing selenates. The reduction would cycle up to three times with a period of approximately 36 hours.