The surface dust samples and soil samples were analyzed for Pb, Zn, Cu and Cd. About 0.5000g of the
bulk or sieved subsample was placed into precleaned erlenmeyer flask and digested on electrothermal
plate at a low temperature with 10ml concentrated hydrochloric acid until about 3ml, then10ml
concentrated nitric was added into the erlenmeyer flask and the erlenmeyer flask was heated at a middle
temperature until the liquid is thicken, the sides of the erlenmeyer flask were rinsed with deionized water
and gently heated until the residue was completely dissolved. After cooling, the solution was filtered into
50ml volumetric flask and diluted to volume with deionized water. Heavy metals concentrations were
determined by FAAS (flame atomic absorption spectrometry). Reagent blanks and replicate samples were
used for analytical process to assess pollution, precision and bias. The precision and bias in the analysis
were less than 10%.