PHYTOEXTRACTION OF METAL POLLUTED SOILS AROUND A Pb-Zn MINE BY CROP PLANTS

Abstract

In order to assess their practical capability for the absorption and accumulation of Pb, Zn, and Cu, five common crop plants, i.e. maize (Zea mays), sunflower (Helianthus annuus), canola (Brassica napus), barley (Hordeum vulgare) and White lupine (Lupinus albus) were tested in pot experiments using six soil samples taken from mine tailings, pasture and arable soils around an old Pb-Zn mine in Spain. Metal concentration ranges of the soils were 76.2–785 mg kg⁻¹, 127–1652 mg kg⁻¹, and 12.4–82.6 mg kg⁻¹ for Zn, Pb, and Cu, respectively. With the exception of the highest polluted sample, soil total metal concentration did not influence significantly biomass yields of each crop for the different growth substrates. The order found for the total metal accumulation rate (TMAR) in the crops was Zn>>Pb > Cu, with maize reaching the highest metal concentrations. Pb root concentrations were markedly higher than those of shoots for all the crops, while Zn and Cu were translocated to shoots more efficiently. Concentrations of metals extracted by EDTA and BCR sequential extraction were well correlated, in general, with both root metal content and TMAR. CaCl₂-extracted Zn was well correlated with root concentrations, TMAR and, in some cases, with shoot contents. Our study showed that the test crops were not feasible to remediate the heavily or moderately contaminated soils studied here in order to achieve the total metal soil concentrations required by the current European laws.

KEY WORDS:

• metal polluted soils
• phytoextraction
• lead
• copper
• zinc
• metal phytoavailability
• BCR sequential extraction

ACKNOWLEDGMENTS

This research has received financial support from the Spanish Ministry of Education and Science (Project REN2003–04788/ TECNO), the Spanish Ministry of Environment (Projects 1.2–089/2005/3-B and 097/20062–1.2) and the Government of Castilla-La Mancha (Project PREG-05–13). We thank all of them for their financial support.

Notes

^a EC, electrical conductivity

^b CEC, cation exchange capacity

^c OM, organic matter content.

*Reported values correspond to one replicate.

* n.d.: not detectable (<0.01 mg kg⁻¹)

** Reported values correspond to one replicate.

* n.d.: analysis not conducted for low amount of sample

** Reported values correspond to one replicate.

*n.d.: not detectable (<0.01 mg kg⁻¹).