Submitted to: Journal of Forest Snow and Landscape Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2006
Publication Date: January 20, 2007
Citation: Banuelos, G.S. 2007. Multi-faceted considerations for sustainable phytoremediation under field conditions. Journal of Forest Snow and Landscape Research, Vol 80:234-245, 2006. Interpretive Summary: The phytoremediation technology has been recognized as an inexpensive, environmentally friendly method for managing soluble selenium (Se)in soils and in poor quality waters in Central California. There are various processes associated with phytoremediation e.g., accumulation, extraction, volatilization, stabilization, and degradation. This paper reports on field experiences using phytoextraction and volatilization of a natural contaminated-selenium. For a number of years, typical agronomic crops, e.g., canola, sunflower, salt-tolerant crops, e.g., salt grass, salado grass, and trees, e.g. poplars, were tested for their ability to survive and manage soluble Se in Westside soils and waters of central California. Our multi-year studies demonstrate that the high salt and boron levels reduce yields of many of the selected crops, and the high sulfate concentrations reduced the accumulation of Se by the plants and trees. For this reason, volatilization of Se became an even more important process for the phytoremediation of Se because the gaseous forms of Se are dispersed and diluted to such an extent that they do not pose a threat to the biological ecosystem. In addition, harvesting Se-enriched crops produced products of potential importance for animal producers. The research demonstrated that feeding sheep, dairy cows, and rabbits Se-enriched plant material increased Se levels in body tissues. Successful management of Se by phytoremediation requires a multi-disciplinary approach with a selection of salt and B tolerant crops for the specific site.
Technical Abstract: In central California, the excessive bioaccumulation of soluble Se originating from irrigated agriculture soils led to a well-publicized environmental disaster. Field research conducted by ARS scientists has demonstrated that a green technology (phytoremediation) may be an applicable method for managing high levels of Se in soils and in waters by plant intake and biological volatilization of Se. Multi-year field studies were conducted with plants and trees at different locations in the Westside of central California. Some of the plant species included: canola, broccoli, salt grass, Paulownia and poplar trees. Generally, soils and waters had a sodium sulfate-dominated salinity between 6-10 dS/m, pH of 7.9, and concentrations of soluble Se and B ranging from 0.13-0.50 mg/L and 5-10 mg/L, respectively. At each site, soil samples were collected from 0-90 cm, volatilization of Se was measured, and plant samples were collected and analyzed for Se. Results demonstrated that high salt and B reduced biomass yields, and high sulfate levels reduced the accumulation of Se. Under our experimental conditions, plant Se concentrations were as high as 12 mg/kg DM in canola and generally ranged from 2-4 mg/kg DM for the perennial crops. Volatilization of Se was greatest with pickleweed and Canola (as high as 155 and 170 ug Se/m2/day, respectively). Harvested Se-enriched plant material fed to sheep, dairy, and rabbits safely increased blood Se concentrations to adequate levels for each respective animal, and provided growers with a potential disposal option for their phytoremediation crop. Sustainable field phytoremediation of Se requires using salt and B tolerant crops in conjunction with a multi-disciplinary approach for managing soluble Se in soil and in poor quality waters.