Effects of Combined Amendments on Growth and Heavy Metal Uptake by Pakchoi (Brassica chinensis L.) Planted in Contaminated Soil

Remediating soils with heavy metals contamination is a significant challenge. This study investigated the co-remediation effect when paired soil amendment mixtures were used to treat soil contaminated by Pb, Cd, and Zn. The three mixed amendments are: 1) micro particle hydroxyapatite (mHAP) and humic acid 2) nano particle hydroxyapatite (nHAP) and humic acid 3) sepiolite and humic acid. Co-remediation with these amendment pairs was compared with remediation using mHAP, nHAP, sepiolite, and humic acid on their own. Using pot experiments, the Pb, Cd, and Zn fractions of sequential extraction in the contaminated soil and the concentration of Pb, Cd, and Zn in shoots and roots of pakchoi were measured by the use of inductively coupled plasma optical emission spectrometry (ICP-OES). Mixed and single treatments were applied to investigate the differences in remediation effects for the three metals. Study results showed that the co-application of amendments more effectively reduced Pb, Cd, and Zn in pakchoi shoots and roots than with single amendments alone. Co-remediation with the amendment mixtures reduced non-residual fractions of Pb, Cd, and Zn in the contaminated soil more than single amendment supplements. Furthermore, the co-application of 30 g·kg micro particle hydroxyapatite with 20 g·kg humic acid was most effective in reducing the amount of Pb, Cd, and Zn absorbed by the pakchoi and the non-residual fraction of Pb, Cd, and Zn in the contaminated soil. Results suggest that co-remediation using 30 g·kg micro particle hydroxyapatite with 20 g·kg humic acid may be an efficient method to remediate Pb, Cd, and Zn in heavy metals-contami-