Utilization of polarography in analyzing for lead and chromium in field and laboratory environmental studies
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Description
Polarography is an electroanalytical technique whose main strength lies in its ability to detect different valence states of the same element dissolved in an electrolyte. In this research, its value in environmentally related studies has been demonstrated in three separate investigations focusing upon two specific metals, lead and chromium. Lead is a well-documented toxicant associated with developmental disorders and other health hazards. Chromium is found in the environment in two oxidation states that much differently affect human health. The trivalent form is an essential trace element involved in glucose metabolism while the hexavalent form is a known carcinogen The first study used polarography to measure the concentration of lead and chromium in water, sediment, and bullfrog tissues obtained from a known polluted site. The second study examined the harmful effect lead has upon the development of tadpoles exposed to this metal originating from water and/or adsorbed onto a model sediment. It was shown that body weight and developmental stage decreased as body lead concentration increased in tadpoles exposed to increasing amounts of lead. Additionally, the uptake of lead was similar whether it was dissolved or adsorbed onto sediment, indicating both exposure paths are important routes of uptake in tadpoles. The third study capitalized upon polarography's ability to detect the different valence states of a metal dissolved in an electrolyte. Here, four extraction methods were studied to determine their effect upon the valence state of chromium when either trivalent or hexavalent chromium is dissolved in an aqueous solution and when adsorbed onto a model sediment. Two methods, an acid extraction and a H2SO4/KMnO 4 treatment, caused a valence state conversion. However, the other two, an alkaline and a phosphate buffer method, did not cause a valence state conversion while showing their utility in extracting hexavalent chromium. Next, two of the methods were combined to form a preliminary protocol able to determine both forms of chromium when present in a sample. The methodology used in the latter two investigations is adaptable to additional studies exploring uptake of contaminants from water and/or sediment and the speciation of metals subject to different extraction techniques, respectively