Browsing by Author "Grossl, Paul R."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- An Investigation into Selenium Geochemistry in Phosphate Mine SoilsFavorito, Jessica Elizabeth (Virginia Tech, 2017-06-07)In the western United States, elevated selenium (Se) levels in soil have resulted in documented cases of ruminant fatalities. This is due to the ingestion of Se-hyperaccumulating vegetation growing on previously reclaimed phosphate mine soils. A field-scale analysis was first conducted to examine Se bioavailability to plants. Soil and plant samples were collected from transects from five study locations in Soda Springs, Idaho. Soils were analyzed for Se speciation and geochemical phases using a sequential extraction procedure (SEP). Additionally, speciation, SEP results, and Se bioavailability in the hyperaccumulator, western aster (Symphyotrichum ascendens (Lindl.)), were related using simple linear regression. Soil speciation and the validity of this SEP were then evaluated using synchrotron-sourced X-ray absorption fine structure (XAFS) spectroscopy for both whole and a sequence of extracted soils. Lastly, competitive adsorption of Se with two dissolved organic carbon (DOC) species, citric and salicylic acid, was examined on an amorphous iron oxide mineral surface. A strong relationship was identified for western aster Se and the first two combined SEP fractions, water-soluble and PO43--extractable Se (R2 = 0.85; P = <0.0001). Results also indicated a strong relationship between selenate and water-soluble Se (R2 = 0.83; P = 0.0002). This suggests that water extracts could be useful Se bioavailability assessment tools in highly contaminated systems. XAFS analyses indicated that elemental and organic Se were the most predominant phases overall in whole soils. The dominant oxidized species present was selenite sorbed onto iron oxides and calcite. Critical SEP evaluations using XAFS also indicate that oxidized Se species were underestimated by the SEP and elemental Se was overestimated. In extracted soils, XAFS results indicated partial recovery of carbonate, iron oxide and organic Se occurred. Therefore, it is suggested that researchers exert caution when employing SEPs. Additionally, sorption analyses demonstrated the highly competitive behavior of citric acid with both selenite (pH 5-8) and selenate (pH 5-6). Little competition was observed in the presence of salicylic acid for both Se species. Competition and subsequent desorption of both sorbed species in the presence of citric acid suggest a possible mechanism for Se solubilization and bioavailability in seleniferous environments.
- Selenium geochemistry in reclaimed phosphate mine soils and its relationship with plant bioavailabilityFavorito, Jessica E.; Eick, Matthew J.; Grossl, Paul R.; Davis, Thomas Z. (2017-09)Selenium accumulation in vegetation has resulted in toxicity in livestock grazing on phosphate mine soils in Southeastern Idaho. Plant and soil samples were collected from sites located near phosphate mines. Soil physicochemical properties, Se speciation, and Se distribution from a sequential extraction procedure (SEP) were examined in relation to bioavailability in the Se-hyperaccumulator, western aster (Symphyotrichum ascendens Lindl.). Selenium-hyperaccumulators are plants that can absorb over 1000 mg Se kg(-1) (DM) (Dry Matter). Chemical analyses revealed that western aster contained Se exceeding 6000 mg kg(-1) (DM). Soil speciation results indicated that selenite (SeO3 (2-)) was dominant with lower levels of selenate (SeO4 (2-)) present. This was expanded using an SEP that accounted for six fractions. Regression analyses indicated a strong relationship for western aster Se and the water-soluble and phosphate-extractable SEP fractions combined (R (2) = 0.85). Once carbonate, amorphous Fe-oxide, organic, and residual Se fractions were factored into the analysis, the relationship decreased. A strong relationship between selenate and the water-soluble Se fraction was also observed (R-2 = 0.83). Soluble and phosphate-extractable Se were determined to be "bioavailable fractions" for western aster. Thus, simple water extractions can be used for quick assessment of Se bioavailability and provide a means to identify potentially hazardous areas locations.