Location: Poisonous Plant ResearchTitle: Selenium geochemistry in reclaimed phosphate mine soils and its relationship with plant bioavailability
|FAVORITO, JESSICA - Virginia Polytechnic Institution & State University|
|EICK, MATTHEW - Virginia Polytechnic Institution & State University|
|GROSSL, PAUL - Utah State University|
|Davis, Thomas - Zane|
Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2017
Publication Date: 6/23/2017
Citation: Favorito, J.E., Eick, M.J., Grossl, P.R., Davis, T.Z. 2017. Selenium geochemistry in reclaimed phosphate mine soils and its relationship with plant bioavailability. Plant and Soil. 418(1-2):541-555. https://doi.org/10.1007/s11104-017-3299-5.
Interpretive Summary: Selenium (Se) is a trace element, with concentrations in natural soils ranging from 0.01 to 2.0 mg Se kg-1. Elevated levels of Se can result from a variety of anthropogenic processes, such as those associated with phosphate mining in southeast Idaho, where it is not uncommon to find soil Se levels 100 times greater than normal background levels. To date, there have been over a thousand reported grazing deaths due to livestock ingesting plants growing on these contaminated soils. Western aster (Symphyotrichum ascendens) is the plant responsible for the vast majority of these deaths in Southeastern Idaho, with toxicity linked to its Se content, which can be up to 13,000 mg Se kg-1DM. Deaths from grazing on this plant in Southeastern Idaho occurred on lands reclaimed prior to 1996, where Se-laden shale overburden was used as topsoil medium. Land reclaimed after 1996 used the original salvaged topsoil as the topsoil medium. This change in practice was established in accordance with the Bureau of Land Management and the Clean Water Act in 1996. Plant tissue Se concentrations were reflective of soil Se concentrations. High levels of Se were found in Se accumulating and hyperaccumulating vegetation sampled from sites which were reclaimed before 1996, with lower levels noted for plants sampled from sites reclaimed post-1996. This was especially true for S. ascendens. Regression data suggests that a strong relationship exists for water-soluble and PO4-extractable Se with increasing plant uptake. Simple water extractions could be beneficial tools, as indicated by the relationship between the water-soluble fraction and selenate fraction and the water-soluble fraction and aster plant Se. This work identifies a method for quick assessment of Se bioavailability in soils and for relating this information to Se accumulation in S. ascendens found in problematic locations.
Technical Abstract: Background and Aims Selenium contamination and accumulation in vegetation have resulted in Se toxicity in livestock and wildlife in reclaimed phosphate mine soils in Southeastern Idaho. Methods Plant and soil samples were collected from five study sites near phosphate mines. Soil physiochemical properties, Se speciation, and Se distribution from a sequential extraction procedure (SEP) were examined in relation to Se bioavailability. Results Chemical analyses revealed that Western Aster contained Se exceeding 6,000 mg Se kg-1 (dry weight). Soil speciation results indicated that selenite (SeO32-) was the dominant species with lower quantities of selenate (SeO42-) present. This was expanded using an SEP that accounted for six fractions. Highly significant relationships were determined for Aster Se and water-soluble, phosphate extractable, and carbonate-associated SEP fractions (R2 > 0.80). This relationship decreased once fractions related to amorphous iron oxides, organic, and residual Se were factored into the regression analysis. A highly significant relationship between selenate and water-soluble Se fraction was also observed (R2 = 0.83). Conclusions Soluble and ligand exchangeable Se were determined to be “bioavailable fractions” for Se-hyperaccumulators. Thus, simple water extractions can be used as a quick assessment for Se bioavailability to Aster and provide a means to identify potential hazardous areas for grazing livestock.