Effect of Chelant-Based Soil Washing and Post-Treatment on Pb, Cd, and Zn Bioavailability and Plant Uptake

Abstract

The remediation of Pb, Cd, and Zn contaminated soil by ex situ EDTA washing was investigated in two pot experiments. We tested the influence of (i) 0, 0.5, 1.0, and 1.5%wt zero-valent iron (ZVI) and (ii) a combination of 5%wt vermicompost, 2%wt biochar, and 1%wt ZVI on the metal availability in EDTA-washed soil using different soil extracts (Aqua regia, NH₄NO₃) and plant concentrations. We found that EDTA soil washing significantly reduced the total concentration of Pb, Cd, and Zn and significantly reduced the Cd and Zn plant uptake. Residual EDTA was detected in water extracts causing the formation of highly available Pb-EDTA complexes. While organic amendments had no significant effect on Pb behavior in washed soils, an amendment of ≥ 1%wt ZVI successfully reduced EDTA concentrations, Pb bioavailability, and plant uptake. Our results suggest that Pb-EDTA complexes adsorb to a Fe oxyhydroxide layer, quickly developing on the ZVI surface. The increase in ZVI application strongly decreases Zn concentrations in plant tissue, whereas the uptake of Cd was not reduced, but even slightly increased. Soil washing did not affect plant productivity and organic amendments improved biomass production.

Supplementary information: The online version contains supplementary material available at 10.1007/s11270-021-05356-0.

Keywords: Biochar; Remediation; Soil pollution; Toxic metals; Vermicompost; Zero-valent iron.

Fig. 1

Metal concentrations per dry weight in the leaf tissues of radish plants. C contaminated soil, ZVI0/0.5/1.0/1.5 washed soil amended with 0, 0.5, 1.0, 1.5%wt ZVI. Lower case letters represent statistically homogenous groups

Fig. 2

Metal concentrations per dry weight in the leaf tissues of radish plants. C contaminated soil, CA contaminated amended with 5%wt vermicompost and 2%wt biochar. W washed soil, WA washed soil amended with 5%wt vermicompost and 2%wt biochar. WZ washed soil amended with 1%wt ZVI, WZA washed soil amended with 1%wt ZVI, amended with 5%wt vermicompost and 2%wt biochar. Lower case letters represent statistically homogenous groups

Fig. 3

The figures show data from the 1^st experiment. a–c Show the linear dependence of PTM concentrations in radish leave tissue and ZVI soil amendment. d–f Show the linear relation between the plant uptake of single PTMs into radish leave tissue. The Spearman correlation coefficient (ρ) and the statistical significance (p) are indicated

Fig. 4

Biomass data from the EDTA stabilization experiment (left, n = 3) and the revitalization experiment (right, n = 4). The error bars represent the mean ± standard deviation. C contaminated soil, ZVI.0/0.5/1.0/1.5 washed soil amended with 0, 0.5, 1.0, 1.5%wt ZVI. C contaminated soil, W washed soil, WZ washed soil amended with 1%wt ZVI, A amended with 5%wt vermicompost and 2%wt biochar. Lower case letters represent statistically homogenous groups, separately tested for leaf and root data