Submitted to: Conservation Research Report
Publication Type: Other
Publication Acceptance Date: July 31, 2004
Publication Date: August 6, 2004
Citation: Banuelos, G.S. 2004. Salt-tolerant plants may provide means for reducing soil selenium. Conservation Research Report. california Agr. Research Initiative Report #00-2-004. 5 pp. Interpretive Summary: The use of phytoremediation was evaluated for managing selenium (Se) levels in drainage sediment that resides in portions of the San Luis Drain in the westside of the San Joaquin Valley. In this regard, the WMRU initially evaluated the ability of salt and boron tolerant plants to tolerate and take up selenium when grown in different blends of sediment and soil under greenhouse conditions. The results showed that all plants grew best when sediment was blended with soil, and that wild-type canola accumulated the highest conentration of Se among the tested plants. Based upon these results, a multi-year field study was conducted with the same plant species, e.g. canola, salado grass, cordgrass, tall fescue, elephant grass, whereby drainage sediment was applied to a 0.5 ha field plot. Selenium accumulation and volatilization, and biomass yields were evaluated in plants that were grown on 30 x 1 m beds. Total and soluble Se were evaluated throughout soil profile. The wild-type canola accumulated and volatilized the greatest amount of Se compared to other plant species. Importantly, total Se concentrations were lower in the soil after 2 years, however, soluble Se concentrations increased with depth. The observations indicate that strict monitoring of the movement of soluble Se to deeper depths is necessary when using phytoremediation for managing Se in field-applied drainage sediment.
Technical Abstract: The objective of this study was to determine role of vegetation in managing Se levels in land-applied drainage sediment by plant uptake and volatilization. Selenium concentrations were greatest in wild-type canola at 42 ppm, but generally Se concentrations ranged from 10-15 ppm for other plant species. Volatilization measurements of Se showed that wild-type canola volatilized as much as 120 ppb Se/m2/day compared to a mean of 25 ppb Se/m2/day for the other plant species. Soil samples collected to a depth of 90 cm showed increases of soluble Se to concentrations as high as 1 to 2 mg/L for the vegetated plots vs less than 50 mg/L for non-irrigated unvegetated plots. The transformation of insoluble Se to mobile forms and water application likely contributed to the downward movement of Se. The movement of soluble Se to deeper depths is a serious concern and must be strictly monitored when considering phytoremediation for managing Se levels in drainage sediment.