Transfer of heavy metals from the polluted rhizosphere soil to Celosia argentea L. in copper mine tailings

Abstract

Copper mine tailings are often contaminated by a range of heavy metals, which can restrict plant growth. The aim of this study was to investigate the degree of soil contamination by copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), chromium (Cr), and manganese (Mn) in a deserted copper mine tailings site, as well as the translocation of these heavy metals into the rhizosphere soil and the root, fibril and shoot tissues of a tolerant plant, Celosia argentea. In order of concentration, the heavy metal concentrations in the soils were Cu ≥ Mn > Zn ≥ Cr > Pb > Cd, and the mean concentrations of Cu, Zn, Pb, and Cd in the rhizosphere were 1.8, 1.6, 1.5, and 1.2 times greaterthanin the non-rhizosphere soil, respectively. The concentrations of all examined heavy metals except for Pb were higher than the second-level criterion of the Chinese soil environmental quality standard (CSES) (GB15618-1995) in both soil samples. The pollution load indexes of Cu, Zn, Pb, Cd, and Cr in the rhizosphere were 28.13, 1.69, 0.148, 8.67, and 1.49, respectively, using the CSES. Cu and Cr were mainly stored in the roots of C. argentea, whileCd, Mn, and Zn accumulated in the shoots. The translocation factors of Zn, Cd, and Mn were greater than 1, and the Cd enrichment factor of the C. argentea shoots was close to 1. This indicates that C. argentea is a hyperaccumulator of Cd, and could be used in the phytoremediation of Cd-contaminated soils.