Remediation of Cr(VI)-Contaminated Soil by Nano-Zero-Valent Iron in Combination with Biochar or Humic Acid and the Consequences for Plant Performance.

Yuhuan Sun,Wenjie Wang,Shuwu Zhang,Fangyuan Zheng,Fayuan Wang

doi:10.3390/toxics8020026

Abstract

Nano-scale zero-valent iron (nZVI) is among the most common nanoparticles widely used for the treatment of various environmental contaminants. However, little is known about the combined effects of nano-zero-valent iron (nZVI) and other soil amendments on soil remediation and plant performance. For the first time, we studied the remediation of Cr(VI)-contaminated soil using bare nZVI (B-nZVI) and starch-supported nZVI (S-nZVI) in combination with either biochar (BC) or humic acid (HA), and the consequent effects on plant growth and Cr accumulation. Both S-nZVI and B-nZVI decreased the contents of Cr(VI) and available Cr in soil, but increased available Fe content, with S-nZVI generally showing more pronounced effects at a higher dose (1000 mg/kg). B-nZVI exerted no inhibition and even stimulation on plant growth, but 1000 mg/kg S-nZVI produced significant phytotoxicity, resulting in decreased plant growth, low chlorophyll content in leaves, and excessive accumulation of Fe in roots. Each nZVI decreased shoot and root Cr concentrations. BC and HA produced synergistic effects with nZVI on Cr(VI) removal from soil, but HA decreased soil pH and increased the availability of Cr and Fe, implying a potential environmental risk. Addition of BC or HA did not alter the effects of either nZVI on plant growth. In conclusion, combined application of 100 mg/kg nZVI and BC could be an ideal strategy for the remediation of soil contaminated with Cr(VI), whereas high-dose S-nZVI and HA are not recommended in the remediation of agricultural soils for crop production or in the phytostabilization of Cr(VI).

Highlights

Chromium (Cr) can enter the environment via a variety of human activities, including mining, smelting, and electroplating, leading to potential contamination to soil, surface water, or groundwater [1,2,3]
Our present study found that soil pH was slightly decreased by both Nano-scale zero-valent iron (nZVI)
supported nZVI (S-nZVI) may induce nutrient deficiency and interfere with the biosynthesis and subsequent photosynthesis of chlorophyll, resulting in plant growth reduction. This is the first study evaluating nZVI remediation of Cr(VI)-contaminated soil assisted by BC or humic acid (HA) and the consequent phytotoxicity

Summary

Introduction

Chromium (Cr) can enter the environment via a variety of human activities, including mining, smelting, and electroplating, leading to potential contamination to soil, surface water, or groundwater [1,2,3]. Among several redox states of Cr, Cr(III) and Cr(VI) represent the most stable and common forms. Oxidative Cr(VI) has higher toxicity to organisms than reductive Cr(III). Cr(VI) has been classified as a class I carcinogen to humans by the International Agency for Research on Cancer (IARC) and is listed as one of the priority contaminants [4]. Cr(VI) may migrate in soil and accumulate in plants (especially crops), posing a health risk to human and animals [5]. For this reason, various technologies have been developed for the remediation of Cr(VI)-contaminated

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Conclusion