APPLICATION OF EXTRACTION METHODS TO PREDICT BIOAVAILABILITY OF HEAVY METALS IN POLLUTED AGRICULTURAL SOILS IN THE MINING AREAS

Human exposure to toxic heavy metals via dietary intake is of increasing concern. Mining activities concentrate heavy metals, making them the major contaminants in agricultural soil in mining areas. Heavy-metal pollution of the soil-crops production system can pose a threat to human health. It was necessary to develop a suitable extraction procedure which would represent the content of metal available to the crop plant.

Three single extraction methods(extracting agents, 0.05mol/L EDTA, 0.43mol/L HOAC, 0.1mol/L HCl) and two sequential extraction ones (Tessier’s and BRC) were tested to evaluate the bioavailability of heavy metals (Cu, Pb, Zn and Cd) from agricultural soils contaminated to sweet potato, which is the main crop in the Pb-Zn mining areas, southwest of China. Based on the 14 soil samples and 14 sweet potato samples correspondingly from the contaminated soil, the correlation analysis between metals extracted with different extractants/methords and concentrations of the metals in sweet potato showed that the greatest values of correlation coefficients are different for the metals: Cu vs HAC(63%), Pb vs T1+T2(72%), Zn vs EDTA(88%), Cd vs BRC(83%) (table1).

Table1 Correlation between bioacceccible fraction of metal contents in the soils and contents in Sweet potato

Metal	EDTA	HCl	HAC	T1+T2	B1
Cu	0.00	0.20	0.63	0.45	0.56
Pb	-0.29	0.59	0.68	0.72	0.69
Zn	0.88	0.71	0.81	0.79	0.81
Cd	0.69	0.73	0.75	0.79	0.83

Notice: T1 +T2 for the water soluble fran + exchangeable fraction of Tessier’s; B1 for Acid-soluble fraction

This demonstrates that HAC , EDTA, T1+T2 and BRC are the most suitable extractants for predicting bioavailability of Cu, Pb, Zn and Cd respectively in the polluted soil to sweet potato in the areas studied. The results suggested that the different extractants are suitable different metals for prediction bioavailability of the metals in the polluted soil to the same plant and in the same quality soil.

Acknowledgements Support by State Key Lab. of Environmental Geochemistry, China (SKLEG50)