title: Bioaccessibility of As and Pb in orchard and urban soils amended with phosphate, Fe oxide and organic matter.
abstract: Soils historically contaminated in urban and orchard environments by Pb and As were amended separately with organic matter, soluble Ca phosphate, and Fe oxide to determine whether these materials could lower Pb or As bioaccessibility. After 5 years of equilibration in the laboratory, the amended soils and control were tested for bioaccessibility using the standard physiologically based extraction test (PBET). Bioaccessibilities of Pb and As were not substantially reduced relative to the unamended controls after the 5-year period by any of the soil amendments. Gastric bioaccessibility (GB) of Pb was in all cases much greater than gastrointestinal bioaccessibility (GIB) regardless of soil treatment, whereas GB and GIB of As were similar in magnitude for all soils. Both GB and GIB of Pb were greater in the orchard than the urban soil. Electron microprobe investigations identified discrete particulate forms of Pb in the soils by elemental mapping, and energy dispersive spectrometry (EDS) revealed a frequent spatial association of Pb-rich particles with phosphorus. It is suggested that Pb-rich particles in anthropogenically contaminated soils resist chemical transformation into less labile forms despite thermodynamic favorability because of their low surface area and low solubility. This kinetic effect could explain the observed ineffectiveness of amendments in reducing metal bioaccessibility.
authors.affiliation: National Key Laboratory of Water Environmental Simulation and Pollution Control & Guangdong Key Laboratory of Water and Air Pollution Control, South China Institute of Environmental Sciences, Ministry of Environmental Protection of the People's Republic of China, Guangzhou 510655, China.
authors.forename: Meifang
authors.initials: M
authors.lastname: Cai
authors.affiliation: Section of Soil and Crop Sciences, School of Integrative Plant Sciences, Cornell University, Ithaca, NY 14853, USA. Electronic address: mbm7@cornell.edu.
authors.forename: Murray B
authors.initials: MB
authors.lastname: McBride
authors.affiliation: National Key Laboratory of Water Environmental Simulation and Pollution Control & Guangdong Key Laboratory of Water and Air Pollution Control, South China Institute of Environmental Sciences, Ministry of Environmental Protection of the People's Republic of China, Guangzhou 510655, China.
authors.forename: Kaiming
authors.initials: K
authors.lastname: Li
authors.affiliation: Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.
authors.forename: Zhian
authors.initials: Z
authors.lastname: Li
mesh_terms: D001151:Arsenic / Q000032:analysis*; D004784:Environmental Monitoring; D005290:Ferric Compounds / Q000737:chemistry*; D051639:Gardening; D007854:Lead / Q000032:analysis*; D009930:Organic Chemicals / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D005290:Ferric Compounds; D009930:Organic Chemicals; D010087:Oxides; D012987:Soil; D012989:Soil Pollutants; C000499:ferric oxide; D010758:Phosphorus; D007854:Lead; D001151:Arsenic
keywords: Metal bioaccessibility; Orchard soil; Soil amendments; Urban soil