3Pouyat R V, McDonnell M J. Heavy metal accumulations in forest soils along an urban-rural gradient in southeastern New York, USA[J]. Water, Air & Soil Pollution, 1991,(57-58): 797-807.
4Chen T B, Wong J W C, Zhou H Y, et al. Assessment of trace metal distribution and contamination in surface soils of Hong Kong[J]. Environmental Pollution, 1997, 96 (1): 61-68.
5Ma L Q, Rao G N. Chemical fractionation of cadmium, copper, nickel and zinc in contaminated soils[J]. Journal of Environmental Quality, 1997, 26(2): 259-264.
6Wilcke W, Lilienfein J, Lima S D C, et al. Contamination of highly weathered urban soils in Uberlndia, Brazil[J]. J. Plant Nutr. Soil Sci., 1999, 162(3): 539-548.
7Lu Y, Gong Z T, Zhang G L, et al. Concentrations and chemical speciations of Cu, Zn, Pb and Cr of urban soils in Nanjing, China[J]. Geoderma, 2003, 115(1-2): 101-111.
8Li X D, Poon C S, Liu P S. Heavy metal contamination of urban soils and street dusts in Hong Kong[J]. Applied Geochemistry, 2001, 16(11-12): 1361-1368.
9Ge Y, Murry P, Hendershot W H. Trace metal speciation and bioavailability in urban soils[J]. Environmental Pollution, 2000, 107(1): 137-144.
10Ruby M V. Advances in evaluation the oral bioavailability using a physiological based extraction test[J]. Environmental Science and Technology, 1999, 33: 3697-3705.
