Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2005
Publication Date: 3/19/2005
Citation: Banuelos, G.S., Lin, Z.Q., Arroyo, I.S., Terry, N. 2005. Selenium volatilization in vegetated agricultural drainage sediment from the san luis drain, Central California. Chemosphere. Available on-line at: www.elsevier.com/locate/chemosphere. Vol 60(9): 1203-1213. Interpretive Summary: Land disposal of selenium-enriched sediments from the San Luis Drain is an applicable option in the San Joaquin Valley, CA. The WMRU is considering phytovolatilization for reducing the soluble selenium content in the drainage sediment. Hence, a field study was conducted to evaluate the ability of different salt-tolerant crops to volatilize selenium from drainage sediment disposed of on a field site. Volatilization of selenium was measured periodically over two years with the following plants: elephant grass, salado grass, cord grass, saltgrass-turf and forage, leucania, salado alfalfa, wild-type Brassica, and irrigated and non-irrigated bare plots. The vegetated plots, irrespective of plant species, always volatilized more selenium than bare plots. The wild-type Brassica volatilized the greatest amount of selenium among all tested species. The perennial plants were,however, considered low maintenance crops, that were repeatedly clipped, and produced a large amount of Se-enriched animal forage. Biological volatilization of Se represents an environmentally friendly strategy for gradually remediating Se-contaminated sediment, although volatilization does not appear to remove as much Se as plant extraction.
Technical Abstract: An estimated 100,000 m3 selenium-laden drainage sediment resides in the San Luis Drain in the westside of San Joaquin Valley. Dredging the sediment from the canal and disposing on land is an option that is currently under investigation. Due to the high levels of Se in the sediment (i.e., 50 mg/kg), phytoremediation may be a technology to consider for removing Se by biological volatilization and plant accumulation. In the multi-year field study the following plant species were planted on 0.5 ha field plot: elephant grass, leucania, salado grass, cord grass, saltgrass-turf and forage, and wild-type Brassica. The field beds (30 x 1m) were constructed with drainage sediment that had been applied to a depth of 25 cm and mixed with 10 cm of good quality sandy loam soil. In the beds, total Se concentrations ranged from 3.2 to 8.2 mg/kg, EC (electrical conductivity) ranged from 9.6 to 17.3 dS/m, and soluble B concentrations ranged from 9.6 to 14.6 mg/L. For two years, measurements for volatile Se were taken 4 to 8 times for the perennial plants during each 9-month growing season and up to 11 times each month for the one nine-month growing season for wild-type Brassica. Among the plant species, the mean daily rates of Se volatilization were as follows in ug Se/m2/day: wild-type Brassica (39) > saltgrass-turf (31) > cordgrass (27) > salado grass (21) > leucania (19) > salado alfalfa (14) > irrigated bare (11) > non-irrigated bare (3). The wild-type Brassica produced as much as 120 ug volative Se/m2/day. A preliminary estimation between plant accumulation and biological volatilization of Se suggests that plants remove more Se via plant extraction than plant volatilization. Although biological volatilization of Se needs to be enhanced under drainage sediment conditions, the process represents an environmentally friendly and safe mechanism that plants and presumably microbes use to transform inorganic Se to a non-toxic volatile form of Se.