Date of Award
Ph.D. in Chemistry
Chemistry and Biochemistry
James V Cizdziel
Clifford A. Ochs
Steven R. Davis
A novel method was developed to measure mercury (Hg) directly in environmental solids using inductively coupled plasma mass spectrometry (ICP-MS) with online sample ashing. The method combines a direct mercury analyzer (DMA) that is based on sample combustion, Hg pre-concentration by amalgamation with gold, and atomic absorption spectrometry (AAS), with a high resolution ICP-MS. Unlike AAS, the ICP-MS is capable of individual isotope measurements allowing for accurate quantitation by isotope dilution mass spectrometry (IDMS) and for isotope tracer experiments. The method was validated using certified reference materials including sediment (NIST 2709), leaves (NIST 1547), and fish-muscle (DORM-3), with recoveries within 8% of Hg certified values. The limit of detection was 0.37 pg, nearly two orders of magnitude lower than the DMA alone. For external calibration, precision was <7% relative standard deviation (RSD). For IDMS, precision was <4% RSD for both DORM-3 and NIST 2709, but higher for NIST 1547 (11% RSD). The method has several advantages over conventional methods including eliminating the need for time-consuming and error-prone sample preparation using acids.
The newly developed method, along with species-specific enriched stable isotope tracers, were used to investigate, for the first time, mercury transformations in an old growth cypress wetland (located at Sky Lake in the Mississippi Delta). Wetland sediments are of particular interest because they are known “hot-spots” for mercury methylation in ecosystems. Methylmercury is a particularly toxic form of Hg that bioaccumulates in the aquatic food chain. Mercury methylation rates in the sediments ranged from 0.012 to 0.054 day-1, with methylation rates generally higher in the summer and spring. Rates tended to be higher in the open water then in the swamp areas. There were also higher levels of organic matter and higher temperatures in the open water areas, suggesting higher microbial activity may have been a factor in this difference. Mercury methylation rates were also systematically studied after amending sediment with ∼5% (wt/wt) of select sorbent materials. Activated carbon and bio-char decreased Hg methylation rates by 83% and 89%, respectively. Humic material increased rates by 455%, presumably by providing nutrients to the methylating microorganisms and increasing their activity. Further work is needed to understand the associated mechanism(s) and to develop this potential method of remediation of highly contaminated sites.
Finally, this dissertation includes results from a large-scale study of trace metals and trace organic contaminants in the Mississippi River and its major tributaries (Missouri, Illinois, Ohio, Tennessee, and Arkansas Rivers). Trace metals and ancillary data were sufficiently different to distinguish the river waters using multivariate statistics. Thirteen trace organic contaminants, including several endocrine disrupting compounds, were detected at multiple sites in the river system, with particularly high levels downstream of wastewater treatment plants.
Bussan, Derek Davin, "Mercury methylation potentials in sediments an ancient cypress wetland using species-specific isotope dilution-GC-ICP-MS: Analytical method development and the effect of sorbent amendments" (2015). Electronic Theses and Dissertations. 1367.