Humic Acid Reduces the Available Cadmium, Copper, Lead, and Zinc in Soil and Their Uptake by Tobacco

Qun Rong,Xinyu Nong,Kai Zhong,Chuanzhang Li,He Huang,Chaolan Zhang

doi:10.3390/app10031077

Qun Rong, Xinyu Nong + Show 4 more

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https://doi.org/10.3390/app10031077

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Abstract

Tobacco (Nicotiana tabacum L.) is a crop that is able to accumulate metals. In this study, humic acid was selected as a Cd, Cu, Pb, and Zn passivator, and added to calcareous field soil in amounts of 6.4, 10.3, and 14.8 kg·ha−1. Its impact on the soil fractions of the metals in the soil was extracted by the Community Bureau of Reference (BCR) sequential extraction method, and their accumulation of the metals in tobacco leaves was investigated. Application of 14.8 kg·ha−1 humic acid decreased the DTPA-extracted concentrations of Pb, Cd, Zn, and Cu by 39%, 37%, 29%, and 18%, respectively, as compared with untreated soil. The fractions of Cd, Pb, Cu, and Zn in soil were extracted by the BCR sequential extraction method, and the relationship between the difference metal fractions in the soil and the metal contents in the plant materials were analyzed. The exchangeable fractions of Cd, Pb, Cu, and Zn and the reducible fractions of Pb and Cu are the main bioavailable fractions. Additionally, the reducible fractions of Cd and Zn, the oxidizable fractions of Pb, Cu, and Zn, and all residual fractions of metals were nonbioavailable fractions in the soil. The soils were treated with humic acid (HA) to shift bioavailable metals to stable phases that were less bioavailable. The available Cd, Pb, Cu, and Zn were strongly retained in the soil after the application of humic acid, which decreased the uptake in tobacco in the upper, middle, and lower leaves.

Highlights

Metal pollution in soils is a serious environmental problem with potentially harmful consequences for agriculture and human health
The HA10.8-amended soil presented lower concentrations of diethylene triamine pentaacetate acid (DTPA)-extracted metals than the other treated soils, with DTPA-extracted Cd, Pb, Cu, and Zn contents reduced by 37%, 39%, 18%, and 29%, respectively, as compared with those in CK
The reduction of the DTPA-extracted metal fraction was more significant for Cd and Pb than for

Summary

Introduction

Metal pollution in soils is a serious environmental problem with potentially harmful consequences for agriculture and human health. Modern agricultural practices and industrial activities have resulted in Cd, Cu, Pb, and Zn accumulation in soils [1]. The long-term use of phosphate fertilizers that contain these metals and the application of contaminated sewage sludge can further enrich agricultural soils with metals [5]. Because these trace elements can be found at relatively high concentrations in crops, their presence in plants is of concern for humans [6]

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