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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-1 micro particle hydroxyapatite with 20 g·kg-1 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-1 micro particle hydroxyapatite with 20 g·kg-1 humic acid may be an efficient method to remediate Pb, Cd, and Zn in heavy metals-contaminated soil. [ABSTRACT FROM AUTHOR]

The effects of nanoscale particle hydroxyapatite (nHAP) on biomass, Cd uptake, the level of chlorophyll, vitamin C, malondialdehyde (MDA), and the activities of antioxidant enzymes, including SOD, CAT, and POD in pakchoi in Cd-contaminated soil, were evaluated by conducting pot experiment. Results showed that, by application of the 5 g·kg-1, 10g·kg-1, 20g·kg-1, and 30g·kg-1 nHAP in 10mg·kg-1 Cd-contaminated soil, the biomass of plant increased by 7.97%, 13.21%, 19.53%, and 20.23%, respectively. In addition, the reduction of Cd in shoots was 27.12%, 44.20%, 50.91%, and 62.36% compared to control samples. It was found that the supplement of the nHAP can increase the level of chlorophyll and vitamin C and decrease the level of MDA in plant shoots. Furthermore, the increment activities of SOD, CAT, and PODcan be observed after addition of nHAP in Cd-contaminated soil.The results confirmed that nHAPcanbe applied to reduce theplant uptake of Cd andresist theCd stress in theplant inCd-contaminated soil. [ABSTRACT FROM AUTHOR]

It was believed that when hydroxyapatite (HAP) was used to remediate heavy metal-contaminated soils, its effectiveness seemed likely to be affected by its particle size. In this study, a pot trial was conducted to evaluate the efficiency of two particle sizes of HAP: nanometer particle size ofHAP (nHAP) and micrometer particle size ofHAP (mHAP) induced metal immobilization in soils. Both mHAP and nHAP were assessed for their ability to reduce lead (Pb), zinc (Zn), copper (Cu), and chromium (Cr) bioavailability in an artificially metal-contaminated soil. The pakchoi (Brassica chinensis L.) uptake and soil sequential extraction method were used to determine the immobilization and bioavailability of Pb, Zn, Cu, and Cr. The results indicated that both mHAP and nHAP had significant effect on reducing the uptake of Pb, Zn, Cu, and Cr by pakchoi. Furthermore, both mHAP and nHAP were efficient in covering Pb, Zn, Cu, and Cr from nonresidual into residual forms. However, mHAP was superior to nHAP in immobilization of Pb, Zn, Cu, and Cr in metal-contaminated soil and reducing the Pb, Zn, Cu, and Cr utilized by pakchoi. The results suggested that mHAP had the better effect on remediation multiple metal-contaminated soils than nHAP and was more suitable for applying in in situ remediation technology. [ABSTRACT FROM AUTHOR]