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Document Type

Thesis - University Access Only

Award Date

2013

Degree Name

Master of Science (MS)

Department / School

Chemistry and Biochemistry

First Advisor

Jihong Cole-Dai

Abstract

Perchlorate, a nonvolatile, highly polarizable anion, has been found in ground water and soil. Human exposure to perchlorate through food and water constitutes a human health threat because perchlorate inhibits iodide intake needed by the thyroid gland for proper central nervous system development in infants and for regulating metabolism in adults. The perchlorate in the environment today likely comes from both natural and anthropogenic sources. To reduce the threat posed by environmental perchlorate, it is necessary to know the contribution from anthropogenic sources and that from natural sources. The contribution from natural sources can be estimated from perchlorate measurement of polar snow preserved from time periods when human impact on the environment was minimal. Therefore, a perchlorate record from ice cores will be valuable to our decision to reduce perchlorate from human activities. To measure ultra-trace perchlorate concentrations in ice cores, a method has been developed using IC-MS/MS with a detection limit of 0.1 ppt. The method (run time <16 min) analyzes an ice sample as-is without any additional sample preparation such as preconcentration. Using this method, perchlorate concentrations in a Greenland ice core were measured yielding a perchlorate record covering the last 300 years. This record is used to assess the anthropogenic contribution to perchlorate in the current environment by comparing the amount of perchlorate in the environment before the Industrial Revolution and to the amount present today. The average natural level was found to be 0.7 ppt with a standard deviation of 0.3 ppt from a time period before the Industrial Revolution. In comparison, perchlorate concentrations in a recent time period (1950 to present) average about 1.4 ppt, a 100% increase over the natural level. This data indicates that anthropogenic sources contribute about 50% to the total perchlorate found in the current environment. In addition, a correlation between volcanic events and perchlorate formation is discussed.

Description

Includes bibliographical references (pages 32-36)

Format

application/pdf

Number of Pages

46

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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