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Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/1/2005 Publication Date: 11/1/2006 Citation: Banuelos, G.S. 2006. Phytoproducts may be essential for sustainability and implementation of phytoremediation. Environmental Pollution, Vol 144, Issue 1, pgs 19-23. Interpretive Summary: Interest in selenium pollution and remediation technology has escalated during the past two decades. Although not known to be essential for plants, selenium is both essential and toxic for humans and animals, depending on its concentrations. A major selenium controversy in the 1980’s emerged in California when the general public and scientific community became aware of selenium’s potential as an environmental contaminant. After extensive research on several strategies to reduce loads of mobile Se for entering the agricultural ecosystem a plant-based technology, defined as ‘phytoremediation’ received increasing recognition, as a low-cost environmentally friendly approach for managing soluble Se in the soil and water environment. Successful long-term field remediation of Se by plants is, however, dependent upon acceptance and widespread use by growers, who are also concerned about potential commercial value from using the plant-based technology. Obtaining products with economic value from plants used in the cleanup of soil would certainly be an additional benefit to phytoremediation, which could help sustain its long-term use. In this regard, new phyto-products were developed from plants used in the field phytoremediation of Se in central California. These included; Se-enriched broccoli, Se-enriched animal meal, Se-enriched organic fertilizer, and canola oil for use as a blend with diesel fuel in the production of biofuel. This paper will discuss the production of these alternative phyto-products from plants grown for remediation of Se under field conditions. Technical Abstract: Multi-year field phytoremediation studies were conducted with plants at different locations in the Westside of central California known to have high concentrations in their soils and/or waters used of irrigation. Some of the plant species include: canola (Brassica napus), broccoli (Brassica oleracea), and sunflower (Helianthus annus). Generally the soils (Oxalis silty clay form) and the waters have sodium sulfate dominated salinity between 6-10 dS m-1, pH of 7.9, and concentrations of water extractable Se and B ranging from 0.13-0.50 mg L-1 and 5-10 mg L-1, respectively. Broccoli is harvested for its edible florets, and canola and sunflower are harvested primarily for their seed. Typical floret yields for broccoli were 8 metric tons ha-1, and canola and sunflower seed yields were 3 to 3.5 metric tons ha-1, respectively. Selenium concentrations did not exceed 3.5 mg kg-1 DM for broccoli. Harvested seed was processed onsite for its oil by an “oil press” and “extruder”, which utilize high pressure and temperature for maximizing oil extraction.. Generally 40% and 30% oil can be extracted from canola and sunflower seeds, respectively. Due to the inefficiency of oil extraction at this time under field conditions, we were extracting only 25% of the available oil. This percentage represented approximately 1500-2000 liters oil per hectare for each respective crop. Presently, we are blending canola oil with diesel fuel at 20% by weight. The resulting biofuel (approximately 6000-8000 liter of biofuel per hectare) is being used on the farm site to operate diesel driven equipment. Nutritional analyses of the seed byproduct (after oil extraction) is probably the most valuable commodity of the two. Results show that nutrient concentrations, except Ca, are more than adequate for the meal when compared to other reported values for grass and or legume forage. Importantly, the Se concentration in the meal was less than 2 mg kg -1 DM..The ADF (13%) and NDF (23%) values are lower than typical values for good quality legume, grass and legume grass hays and silages. However the CP (27%) and CF (CF%) values are slightly better than legume hays. The low glucosinolate content in the meal of 20µ mol/g is an important quality of the seed meal. The Se-enriched meal is presently being fed to local dairy and sheep industries. Both bio-based products produced from plants used for phytoremediation can encourage growers to utilize oil-producing plants for managing soluble Se in poor quality soils and waters of the westside San Joaquin Valley. |
