Isotopes of selenium as redox tracers of geochemical processes influencing the export and behavior of selenium contamination in coal mine watersheds
Stiegman, Matthew S
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/124565
Description
Title
Isotopes of selenium as redox tracers of geochemical processes influencing the export and behavior of selenium contamination in coal mine watersheds
Author(s)
Stiegman, Matthew S
Issue Date
2024-04-30
Director of Research (if dissertation) or Advisor (if thesis)
Johnson, Thomas M
Department of Study
Earth Sci & Environmental Chng
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Isotope Geochemistry
Selenium
Abstract
Selenium is a redox-active element that is necessary for life in small quantities but causes toxic effects for wildlife above 5 μg/L in water and for humans above 50 μg/L in drinking water. Se contamination is released by oxidative weathering of Se-bearing shales, and this contamination is often associated with mining activity. Selenium is most mobile and toxic in its oxidized Se(VI) form, less mobile as Se(IV), and immobile in the Se(0) or Se(-II) forms. Se isotope ratios have been developed to measure the presence and extent of geochemical processes affecting the mobility and environmental impact of Se. Se isotope systematics are well defined through laboratory experiments but have seldom been applied to real environments.
The leftover material from coal mines within the Appalachian region is constructed into valley fills along mountain slopes, which produce Se-laden effluents exceeding EPA regulations. The redox conditions within these watersheds are relatively unknown, and the behavior of Se is not well studied. Water samples collected from 3 valley fills and their respective watersheds were analyzed for Se concentration, Se speciation, and 82Se/76Se isotope ratios. A leaching experiment on shale to determine the Se(VI) isotopic composition before the Se(VI) undergoes redox reactions yielded a δ82/76Se = -0.46‰ for Se(VI). The δ82/76Se values of surface water samples observed at each site for Se(VI) were; Mary’s Fork (2.56 – 4.54‰), 4-Mile Site (3.38 – 3.86‰), and the T&M Site (3.53 – 4.35‰). The isotopically heavy values of Se(VI) suggest that reduction of Se(VI) occurs within the fills. A trend of increasingly heavy Se(VI) values further downstream is hypothesized to occur due to Se(VI) reduction in the hyporheic zone. The groundwater and isotope data suggest that the effluents leaving the toe are a mix of runoff from oxic and suboxic/anoxic portions of the fill, highlighting the heterogeneous structure and varying redox conditions within valley fills.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
