Submitted to: International Journal of Phytoremediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2010
Publication Date: 12/1/2010
Citation: Banuelos, G.S., Dhillon, K. 2010. Developing a sustainable phytomanagement strategy for excessive selenium in western united states and India. International Journal of Phytoremediation. 13:208-222. Interpretive Summary: Selenium (Se) toxicity affects biological ecosystems in arid and semi-arid regions of the world with alkaline seleniferous soils derived from marine-type sediments. In central California, the bioaccumulation of soluble Se in the avian food chain and the resulting high mortality and reproduction failure in migratory aquatic birds led to a well-publicized environmental disaster. While in northwestern India consumption of Se-rich forage and grain crops grown on seleniferous soils resulted in serious health hazards to animals and humans. Irrespective of region, one inexpensive alternative method for managing high levels of soil Se may be a green technology known as phytoremediation. In its broadest sense, the strategy uses plants to manage contaminated water and/or soil by accumulation, extraction, volatilization, stabilization, filtration, and degradation. Effective phytoextraction requires that plants produce relatively large amounts of biomass and absorb appreciable amounts of Se from the soil. Once absorbed by plant roots, Se translocated to the shoot may be harvested and removed from the site. In addition to extracting Se from contaminated soils/waters and immobilizing Se in their tissues, plants also have the ability to metabolize Se into a non-toxic volatile gas. In this paper, we will discuss the field application of phytoremediation to manage Se from Se-laden soils and waters and in two different long-term case studies in California, USA and in Punjab, India and discuss the importance of developing new plant-based resources for increasing the sustainability of the phyto-strategy. Multi-year field phytomanagement studies were conducted with plants and trees from 1993-2009 at different sites in the Westside of central California, known to have pockets of high Se concentrations in their soils, in waters used for irrigation, and in drainage water produced from these areas. A large number of plants and trees were also evaluated for their ability of phytoremediation on Se-contaminated soils under greenhouse and field conditions from 1998-2008 at different locations in northwestern India. In California, high sulfate concentrations in the soils or waters used for irrigation by plants reduced the accumulation of soluble Se, while low sulfate concentrations in Punjab soils allowed the plants to accumulate high concentrations of Se. Phytoextraction of Se by plants not only removes Se from soils and waters by plant accumulation, but harvesting the Se-enriched crops produces food and feed products of potential economic importance for the grower. Moreover, sustained operation of this agronomic based system demonstrates the effectiveness of attempting to develop a holistic phytoremediation system for managing contaminants, e.g., Se, and transforming them into valuable biofortified products and byproducts.
Technical Abstract: The phytomanagement technology is recognized as an inexpensive and environmental friendly strategy for managing natural-occurring selenium (Se) in soils and in poor quality waters. Multi-year field and greenhouse studies were conducted with different plant species in California, USA and Punjab, India under high Se growing conditions. Some of the plant species included; canola (Brassica napus), mustard (B. juncea), broccoli (B.oleracea), menta (Menthe viridis) sugarcane (Saccharum officcinarum), guara (Cyam opsis tetragon oloba), wheat (Triticum aestivum) and poplar (Populous deltoides). California soils had a sodium-sulfate-dominated salinity between 6-10 dS m-1, while Indian soils had a calcium carbonate salinity less than 1 dS m-1. Results demonstrated that high sulfate conditions reduced plant Se accumulation more than 100x in Californian grown plants compared to Se accumulation in India grown plants. Tissue concentrations generally did not exceed 10 and 200 mg kg DM-1 in leaves of plants grown in California and India, respectively. Importantly, India-grown plants should not be directly consumed by animals or humans because the excessive plant tissue Se levels could lead to Se toxicity. At these plant concentrations, Se phytomanagement is more effective in Indian soils than in California soils. In northwestern India, the Brassica and poplar based cropping systems were highly suitable for managing Se-contaminated soils under low sulfate growing conditions. Results showed that irrespective of harvesting stage, total Se removed in the above-ground biomass of rapeseed based cropping sequences ranged between 740 and 1040 g Se ha-1 yr-1 between 500 and 760 g Se ha-1 yr-1 for poplar based farming systems. If this practice was adopted as a regular strategy in the seleniferous region of northwestern India, remediation of Se-contaminated soils is possible within a period of 20-35 years. The time needed for a near complete remediation (if possible) becomes less important if Se-rich biomass produced by the plant-based strategy is considered a resource of economic value. Successful management of Se by plants requires selecting crops or crop rotations that are tolerant for the soil condition and identifying and creating new viable Se-enriched products. Coupling phytomanagement of Se with the creation of new biofortified and byproducts, e.g., Se-enriched vegetables, animal feed, organic Se fertilizer, and even a byproduct like biofuel, may provide California and Indian growers unique opportunities to increase the environmental and economic sustainability of a plant Se-management system, while supporting the agriculture community in the respective region.