Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2005
Publication Date: June 15, 2005
Citation: Codling, E.E., Ritchie, J.C. 2005. Eastern gamagrass uptake of lead and arsenic from lead arsenate contaminated soil amended with lime and phosphorus. Soil Science. 170(6):413-424.
Interpretive Summary: Even though eastern gamagrass produced a large amount of biomass on the Bagtown orchard soil, the lead and arsenic concentrations in the tissue were much lower than the 1000 mg kg-1 dry mass, which is used as a criterion for metal hyperaccumulation (Brooks et al., 1977; Reeves, 1992). On both contaminated soils, the shoot/root and shoot/soil ratios for both As and Pb were far below 1, which is the critical level above which a plant is identified as an accumulator (Reeves and Baker, 2000). Burch orchard soil, which had the highest concentrations of As and Pb, severely reduced gamagrass yield. Lime application reduced As uptake in the plants grown on the Bagtown soil but not the Burch soil. Lime and P have little effect on Pb uptake in plants grown on the Bagtown soil, but lime significantly reduced the Pb uptake for the plants grown on the Burch soil. Lime was effective in reducing As taken up by the roots of the plants grown on the Bagstown soil, but no effect on the plants grown on the Christiana and Burch soils. Root Pb concentrations was severely reduced with lime for all three soils. Eastern gamagrass did not meet any of the characteristics used to identify plants as metal accumulators: 1) ability to tolerate high levels of the element; 2) ability to translocate an element from root to shoot at high rate; and 3) rapid uptake rate of the element at levels that occur in soil solution. The extremely low levels of both As and Pb in the gamagrass shoot tissue make it a poor candidate for use in phytoremediation of soils contaminated with As and/or Pb.
Lead arsenate was used as an insecticide to control the apple codling moth (Cydia pomonella) in orchards from the 1930s to the 1960s. As a result, many orchard soils are contaminated with lead and arsenic, which may become an environmental problem when these lands are used for other purposes. Because soil removal is expensive, one alternative is to use plants to remove lead and arsenic from these soils (phytoremediation). Eastern gamagrass (Tripsacum dactyloides (L.) L.) has an extensive root system and is being used in soil remediation. The objective of this experiment was to determine uptake of lead and arsenic by eastern gamagrass from lead arsenate contaminated orchard soils. A non-contaminated soil from Maryland (Christiana) and orchard soils from Maryland (Bagtown) and Washington (Burch) with total (Aqua Regia extraction) Pb levels of 15, 574, and 943 mg kg-1 and As levels of 8, 113, and194 mg kg-1, respectively, were used. These three soils were treated with calcium carbonate and potassium phosphate and incubated for two weeks, after which the amended soils were planted with eastern gamagrass. There was a slight increase in eastern gamagrass dry matter yield with P application compared to the no phosphorus treatments. Yields were significantly reduced on the Burch orchard soil, which had the lowest level of organic carbon and highest levels of Pb and As. There was a slight but insignificant increase in tissue arsenic concentration and a reduction in Pb in plants grown on lime- and P- mended soils. Uptake of Pb was related to soil Pb concentration. Shoot As was related to soil As concentration, but there was no significant difference in root As level between the orchard soils. Eastern gamagrass did not remove substantial amounts of Pb and As from the soils, making this species a poor candidate for phytoremediation of lead arsenate contaminated soils.