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

Christoph Noller,Markus Puschenreiter,Wolfgang Friesl-Hanl,Rebecca Hood-Nowotny,Andrea Watzinger

doi:10.1007/s11270-021-05356-0

Christoph Noller, Markus Puschenreiter + Show 3 more

Open Access

https://doi.org/10.1007/s11270-021-05356-0

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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.

Highlights

Soils exposed to potentially toxic metal (PTM) immissions present a direct sink for those pollutants, since metals do not decompose and accumulate via atmospheric deposition (Adriano et al, 2004)
The results of two pot experiments showed that traces of EDTA will form complexes with Pb due to their favorable formation constant leading to high plant uptake even at low total soil concentration
1 3 residual EDTA complexes and successfully reduced PTM plant concentrations to substantially lower levels compared to the contaminated soil but failed to match national regulation thresholds

Summary

Introduction

Soils exposed to potentially toxic metal (PTM) immissions present a direct sink for those pollutants, since metals do not decompose and accumulate via atmospheric deposition (Adriano et al, 2004). Soil contamination can be found all over the world, mostly stemming from mining activities. To remediate such contaminated sites, a large variety of technologies has been developed, among them soil excavation, washing, phytoremediation, or metal stabilization. Immobilization approaches are generally effective and incur low costs, but the longterm stability of a system has to be monitored constantly to prevent future environmental risks (Lwin et al, 2018). Traditional dig and dump approaches, as well as physical separation, are still widely used

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