Submitted to: Book Chapter
Publication Type: Book / chapter
Publication Acceptance Date: 8/3/2005
Publication Date: 10/20/2005
Citation: Banuelos, G.S., Ayars, J.E. 2005. Application of Field Phytoremediation Under High Saline and Boron Conditions. Plant Nutrition Colloquium Proceedings. pp 642-643, In: Plant nutrition for food security, human health and environmental protection. Tsinghua University Press, Beijing, China. Interpretive Summary: The phytoremediation technology has been recognized as an inexpensive, environmentally friendly method for managing soluble 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. For this paper, we will report on field experiences using phytoextraction and biovolatilization on a natural contaminant – selenium (Se). For a number of years we tested typical agronomic crops, e.g., canola, sunflower, salt-tolerant crops, e.g., salt grass, salado grass, and trees, e.g. poplars, for their ability to survive and manage soluble Se in Westside soils and waters of central California. We found in our multi-year studies 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 becomes an even more important process of phytoremediation of Se. The gaseous forms of Se are dispersed and diluted to such an extent that they do not pose a threat. Harvesting Se-enriched crops produces products of potential economic importance for the grower, because Se is an essential trace element for normal nutrition. Our animal studies demonstrated elevated levels in body tissues, blood, as well as in excreta, after feeding sheep, dairy cows, and rabbits Se-enriched plant material. Successful management of Se by phytoremediation requires time, a multi-disciplinary approach, and selection of salt and B tolerant crops for the specific site.
Technical Abstract: The excessive bioaccumulation of soluble Se originating from irrigated agriculture soils led to a well-publicized environmental disaster in central California. 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 phytoremediation 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 in canola and generally ranged from 2-4 mg/kg for the perennial crops. Canola was the most effective species in managing soluble Se concentrations in soil. 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 not only increased blood Se concentrations to adequate levels for each respective animal, but also provides growers with a potential disposal option for their phytoremediation crop. Lastly, analyzing insects and dove eggs collected from field sites did not show Se concentrations greater than 1.15 mg/kg. Sustainable field phytoremediation of Se requires using salt and B tolerant crops in conjunction with a multi-disciplinary approach for managing soluble in soil and in poor quality waters.