Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2004
Publication Date: 12/15/2004
Citation: Banuelos, G.S., Lin, Z.Q. 2004. Phytoremediation management of selenium-laden drainage sediments in the san luis drain: a greenhouse feasibility study. Ecotoxicology and Environmental Safety. Vol. 62, pp 309-316. Interpretive Summary: Land disposal of selenium-enriched sediments from the San Luis Drain is an applicable option in the San Joaquin Valley, CA. The fate of the high levels of selenium (Se) must, however, be taken into full consideration. The WMRL is considering phytoremediation for reducing the selenium content by plant extraction. Hence, a greenhouse study was conducted to evaluate the feasibility of growing plants in different ratios of drainage sediment and non-sediment soil. Among the plants tested -- canola, tall fescue, salado grass, and cordgrass, cordgrass and salado grass tolerated the saline and boron-laden sediment to the greatest degree. However, plant Se concentrations were greatest in canola and in tall fescue. Although total Se concentrations in the soil were lower at postharvest compared to preplant concentrations for all plant species, the concentrations of the mobile form of Se were at least three times greater at postharvest. Moreover, leaching of Se occurred in bare pots (without plants) irrigated with water for the duration of the study. Because higher concentrations of soluble Se and hence leachable Se were produced over time in the potted soils, it may be more prudent to consider growing salado and cordgrass directly into the drainage canal, if phytoremediation is to be considered for removing Se from drainage sediment.
Technical Abstract: An estimated 100,000 m3 selenium-laden drainage sediment resides in the San Luis Drain (SLD) in the westside of the 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 total Se (50-75 mg/kg) in the sediment, precautionary strategies for managing the mobility of Se from the sediment onto the disposal site must be considered. Hence, a greenhouse study was initiated to evaluate phytoremediation as a strategy to manage the high levels of Se in the sediment by plant uptake. Canola, tall fescue, salado grass, and cordgrass were grown in different ratios of sediment to soil; only non-sediment soil (control; 0:3), 1/3 sediment and 2/3 non-sediment soil (1:2); 2/3 sediment and 1/3 non-sediment; and 3/3 sediment and no non-sediment soil (3:0). Increased ratios of sediment:soil resulted in decreased dry matter yields for all tested plant species, especially for canola and tall fescue. Plant Se concentrations (mg/kg)were as follows for the tested plants: in canola (51-72), tall fescue (16-36), and cordgrass and salado grass (9-14) for all ratios of sediment:soil. Total soil Se concentrations significantly decreased by at least 20% for all plant species at postharvest for all ratios of sediment:soil. In contrast, concentrations of extractable soil Se were at least three times greater at postharvest for all plant species for all ratios of sediment:soil. Moreover, Irrigation of bare pots from each respective ratio of sediment:soil produced leachate with Se concentrations as high as 24 mg/L. The increased concentrations of extractable Se measured in soils at postharvest for all planted pots and the high concentrations of Se measured in the leachate demonstrate that mobile forms of Se were produced in the soil over time. If phytoremediation is to be considered for managing Se in drainage sediment, the data on soluble Se indicate that growing the plants directly in the SLD may be advisable for preventing downward migration of mobile Se.