Immobilization of Lead Migrating from Contaminated Soil in Rhizosphere Soil of Barley (Hordeum vulgare L.) and Hairy Vetch (Vicia villosa) Using Hydroxyapatite

Masahiko Katoh,Takeshi Sato,Elsya Risky

doi:10.3390/ijerph14101273

Abstract

This study conducted plant growth tests using a rhizobox system to quantitatively determine the distance of immobilization lead migrating from contaminated soil into uncontaminated rhizosphere soil, and to assess the lead phases accumulated in rhizosphere soil by sequential extraction. Without the hydroxyapatite, exchangeable lead fractions increased as the rhizosphere soil got closer to the contaminated soil. Exchangeable lead fractions were higher even in the rhizosphere soil that shares a boundary with the root surface than in the soil before being planted. Thus, plant growth of hairy vetch was lower in the soil without the hydroxyapatite than in the soil with the hydroxyapatite. The presence of hydroxyapatite may immobilize the majority of lead migrating from contaminated soil into the rhizosphere soil within 1 mm from the contaminated soil. The dominant lead fraction in the rhizosphere soil with the hydroxyapatite was residual. Thus, plant growth was not suppressed and the lead concentration of the plant shoot remained at the background level. These results indicate that the presence of hydroxyapatite in the rhizosphere soil at 5% wt may immobilize most of the lead migrating into the rhizosphere soil within 1 mm from the contaminated soil, resulting in the prevention of lead migration toward the root surface.

Highlights

Lead poses risks to humans and animals, as well as to plant growth; lead contamination in soil and water environments is a common and harmful worldwide concern
This study indicates that the presence of hydroxyapatite in the rhizosphere soil at 5% wt could immobilize the lead that migrated from the contaminated soil within 1-mm from the contaminated soil, resulting in the prevention of lead migration toward the root surface
In the rhizosphere soil of rhizosphere compartments (RCs) without the hydroxyapatite for both barley and hairy vetch, as the rhizosphere soil of RC got closer to the contaminated soil, the lead content and percentage in the exchangeable and carbonates fractions by the sequential extraction increased when compared with those in the soil before it was planted

Summary

Introduction

Lead poses risks to humans and animals, as well as to plant growth; lead contamination in soil and water environments is a common and harmful worldwide concern. Soil remediation techniques should be applied to such sites to protect environmental and public health from lead migration through the soil profile into groundwater and its uptake by root systems. In these areas, lead contamination is extensive and these areas have very low asset value. Phytostabilization, which stabilizes toxic metals in the root zone and prevents their leaching into groundwater [3,4], is one of the phytoremedial approaches [5]. Phytostabilization is an eco-friendly and cost-effective technique; it seems to be a suitable approach for heavily and extensively lead-contaminated soil.

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Discussion

Conclusion