Uptake of Lead and Arsenic By Vegetables Grown in a Contaminated Urban Soil Amended With Biosolids and An Iron (III) Oxyhydroxide.

Chemical sorbents containing high phosphorus (P) and iron oxyhydroxides have been shown as plausible remediation strategy for reducing lead (Pb) and arsenic (As) uptake in crops grown on contaminated urban soils. A greenhouse study was conducted using soils from an urban garden located within four miles from a former copper smelter in Tacoma, WA. The moderately acidic (pH of 5.6), loamy sand surface soil (0-15 cm), had average Pb and As concentrations of 163 ± 22 and 90 ± 11 mg kg^-1, respectively. We evaluated the effectiveness of a class A biosolids (Tagro: 50% biosolids, 25% sand, and 25% sawdust), and ferrihydrite added alone or in-combination to reduce Pb and As uptake in carrots (D. carota), lettuce (L. sativa), and beet (B. vulgaris). Treatment pots (1.8 kg) included a control, ferrihydrite 1%, Tagro 10%, and a ferrihydrite 1% & Tagro 10% mixture, all adjusted to ~ pH 7.3 using calcium oxide. Following harvest, the vegetables were thoroughly cleaned with 5 g/kg dodecyl sulfate solution and deionized water to remove adhering soil particles. All plants were dried at 65 °C, and ground prior to chemical analysis. Results to be presented will examine the treatment effects on reducing trace metal transfer of both contaminants simultaneously, soil Pb bioaccessibility determined by a physiologically based extraction technique (PBET), and the non-specifically bound soil As determined by a two-step sequential extraction procedure (SEP). X-ray absorption spectroscopy data will also be presented to discuss the influence of soil treatments on Pb and As speciation.

Keywords: greenhouse, urban soils, lead, arsenic, biosolids