Date of Award

August 2020

Degree Type

Thesis

Degree Name

Master of Science

Department

Chemistry

First Advisor

Joseph H Aldstadt III

Committee Members

Mark Dietz, Arsenio Pacheco

Abstract

The research herein will describe a novel method to better understand heavy metal contamination over long periods of time by studying soils for which the spatial and temporal dimensions are relatively well-defined. This work is based on the ability to pin-point the initial time and place of contamination on an American Civil War battlefield, where the firearms left distinctive chemical signatures (e.g., dropped and impacted bullets and percussion caps). The abundance and distribution of Copper and Mercury was measured in soil core samples collected at Manassas National Battlefield (Manassas, VA, USA) transecting the line occupied by an infantry regiment, a site where the study could be compared to recent archaeological studies as well as prior studies of Pb at this site.

This study developed, optimized, validated, and applied a novel Microwave-Assisted Extraction (MAE) method based on European Community Bureau of Reference (BCR) methodology for soil samples. Trace (low parts per billion) levels were quantified from soil cores by Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS), supported by isotopic studies using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to classify Cu, Hg, and Pb as: (a) mobile, (b) carbonate-bound, (c) metal oxide-bound, (d) organically complexed, and (e) refractory-bound. To optimize the method, key factors were studied including MAE conditions to improve upon the standard BCR methodology and AAS conditions including the use of a permanent modifier consisting of a mixture of W and Ru.

Significant concentrations of Cu, Pb, and Hg (> 100 parts per billion) were found in the battlefield transect. From this study of the Manassas soil cores, Cu, Pb, and Hg can be reliably quantified, and the depth at which the analytes were quantified coincides with deposition in 1862 where there is a clear correlation between the deposited toxic metals and historical accounts of unit positions. Trends in transport and fate were inferred for the physico-chemical speciation of Cu, Pb, and Hg through the transect of the battlefield revealing that each has a unique transport mechanism controlled by different factors. The Cu and Pb clearly migrated predominantly as metal oxide- and organic-bound species whereas Hg was migrating mainly as an ORG-complexed species that were found primarily in the shallow layers. First-order rate constants for the migration of three Cu species (carbonate-, metal oxide-, and organic-bound) were calculated and compared to those from previous studies with Pb. By utilizing the novel methodology developed in this study, regulatory organizations can more accurately evaluate the risk imposed by contaminated sites on surrounding communities.

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