Fraction Distributions And Analysis Of Bioavailabilities Of Heavy Metals In Three Contaminated Soils Before And After Extracted With EDTA Solution

Three types of soil samples were collected at Pb-Zn mining area located in Chenzhou City, southern Hunan Province (southern China). The batch experiment of the fraction distributions of Pb, Cd, Cu and Zn in the three contaminated soils and effect on the fractions distribution of Pb, Cd, Cu and Zn in the contaminated soils before and after treated with an EDTA solution were carried out. The Tessier's five sequential extraction procedures and Leleyter's eight sequential extraction procedures were applied to extract the different fractions of heavy metals, respectively. The results were given as the follows.The total quantities of heavy metals Pb, Cd, Cu, and Zn in tailing contaminated soil were 1267.36 mg·kg-1, 9.97 mg·kg-1, 165.93 mg·kg-1 and 1332.08 mg·kg-1, and in soil irrigated with waste water were 1122.75mg·kg-1, 11.90 mg·kg-1, 93.80 mg·kg-1, and 950.50 mg·kg-1, and in tailing were 6153.50 mg·kg-1, 35.35 mg·kg-1, 267.25 mg·kg-1 and 6603.58 mg·kg-1, respectively. And the concentrations of these four heavy metals were far beyond that recommended in soil standard (GB15618-1995) more or less.Two extraction procedures could extract heavy metals Pb, Cd, Cu and Zn effectively from the three contaminated soils. But the sums of different fractions of heavy metals analyzed by Leleyter's sequential extraction procedures were more than those of Tessier's sequential extraction procedures, and the results of Leleyter's method were close to the total contents of heavy metals in contaminated soils.There were different fraction distributions of Pb, Cd, Cu and Zn, and the proportions of residual fractions of heavy metals were more than those of other fractions in tested soils, and the proportions of exchangeable and water-soluble were least fractions. The residual fractions of Pb (42.99-60.68%), Cd (32.33-50.43%), Cu (33.45-37.27%), and Zn (54.24-54.89%) more than bound to organic matter, and bound to Fe-Mn oxides in tailings contaminated soils, and the residual fractions of Pb (51.68-58.16%), Cd (40.42-59.18%), Cu (40.25-53.37%), and Zn (27.64-46.92%) were more than bound to organic matter, and bound to Fe-Mn oxides in soil irrigated with waste water, and the residual fractions of Pb (12.26-38.42%), Cd (32.58-39.56%), Cu (53.18-60.91%), Zn (48.99-59.11%) were more than bound to organic matter, bound to Fe-Mn oxides and bound to carbonates in the tailings.EDTA solution had strong chelating ability for heavy metals at solution-to-soil ratio of 10:1. Laboratory studies showed that EDTA is effective in removing Pb, Cd, Cu, and Zn from contaminated soils, although extraction efficiency depended on many factors such as lability of heavy metals in soils. The quantities of heavy metals such as Pb 483.98 mg·kg-1, Cd 2.27 mg·kg-1,...