383-5 Reducing Bioaccessibility of Lead and Arsenic in a Contaminated Urban Garden Soil.

See more from this Division: S02 Soil Chemistry
See more from this Session: Metal and Radionuclide Contaminants: Partitioning, Sequestration and Availability: I
Wednesday, October 24, 2012: 2:00 PM
Duke Energy Convention Center, Room 202, Level 2
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Phillip Defoe, Kansas State University, Manhattan, KS and Ganga Hettiarachchi, Agronomy, Kansas State University, Manhattan, KS
Elevated levels of environmental contaminants such as lead (Pb) and arsenic (As) in urban soils, pose a significant problem to gardeners concerned about soil-plant-human transfer. Chemical sorbents containing high phosphorus (P) and iron oxy/hydroxides have been used to bind these contaminants rendering them immobile in the soil, and not available for plant root uptake. We investigated the effectiveness of a class A biosolid amendment (Tagro mix) and an iron oxyhydroxide (2 line-ferrihydrite) on reducing the bioaccessibility of Pb and As. An incubation study was conducted on a moderately acidic loamy sand surface soil (0-15cm) contaminated with Pb (166-172 mg/kg) and As (82-86 mg/kg), collected from an urban garden in Tacoma, WA. The experimental design was a completely randomized design with two factors [Tagro mix: 10% and 20%; Ferrihydrite (1%)] with three replication. A 200 g soil amendment adjusted to a pH of about 6.8-7.5 with calcium oxide and moistened with deionized water to 60% water holding capacity (WHC). The amendments were placed in 8 oz high density polyethylene containers, covered with clear plastic wrap and incubated for 30, 90 and 180 days in a precision low temperature incubator at 25 C. Lead bioaccessibility was determined by a physiologically based extraction test (PBET), using a gastric solution (pH: 2.5). A two-step sequential extraction procedure (SEP) targeting the non-specifically bound and specifically bound As fractions was conducted on the soils. Preliminary results indicated that pH decreased slightly with increasing incubation time. Extractable As concentrations in Tagro (20%) + ferrihydrite amended soils were as low as 3.2 mg/kg. PBET extractable Pb was the lowest (2.95 mg/kg) for the Tagro (20%) + ferrihydrite amendments as compared to the unamended control (9.45 mg/kg).
See more from this Division: S02 Soil Chemistry
See more from this Session: Metal and Radionuclide Contaminants: Partitioning, Sequestration and Availability: I