Toxic Metal(loid) Lability in Response to Phytostabilization: A Mesocosm Study
Selective Sequential Extraction
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PublisherThe University of Arizona.
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AbstractPrevious studies have shown that application of phytostabilization at the Iron King Superfund site resulted in large reductions in fugitive toxic dust emissions as well as a shifting mine tailing biogeochemical regime. In this study, the impact of this shifting biogeochemical regime on contaminant speciation and mobility were investigated throughout the phytostabilization process on the mesocosm scale. Selective sequential extractions coupled with X-ray spectroscopic and scattering characterization were utilized to monitor contaminant speciation in this study. Planting buffalo grass into compost amended tailings as a phytostabilization treatment resulted in minor enrichments of jarosite and ferrihydrite in the upper section of the tailings profile. Development of these host phases also enriched their bound fractions of As and Pb. Water soluble zinc was almost entirely flushed out of the tailings following this treatment, indicating acidic conditions in the tailings throughout the phytostabilization. The quail bush treatment resulted in extensive weathering of Fe in the tailings throughout the profile. Along with enriched ferrihydrite and jarosite, inner sphere complexed As was enriched throughout most of the tailing profile, increasing the bioaccessibility risk of these tailings. Zinc leaching, on the other hand, was limited by this treatment through the sequestration of water soluble zinc. Indicating more basic pH conditions in the tailings, despite further Fe weathering. The Risk Assessment Code, or RAC, was used in this study to quantify bioavailable metal(loid) species. Tailings treated with irrigation only, composting and irrigation, and buffalo grass phytostabilization resulted in decreased or similar RAC values for As in the untreated tailings. The quail bush plant treatment resulted in a roughly 2%-3% increase in this value. The phytostabilization treatments were successful for fugitive dust emission reduction, but this work indicates that irrigation, composting, and the two plant treatments impact metal(loid) lability and ultimately the bioaccessibility of toxic metal(loid)s in these tailings.
Degree ProgramGraduate College
Soil, Water & Environmental Science