Short- and Long-Term Biochar Cadmium and Lead Immobilization Mechanisms

Liqiang Cui,Yuming Liu,Jinlong Yan,Rongjun Bian,Hui Wang,Guixiang Quan,Lianqing Li,James A. Ippolito

doi:10.3390/environments7070053

Abstract

The mechanisms of soil Cd and Pb alterations and distribution following biochar (BC; 0 to 40 t ha−1) amendments applied (in either 2009 [long-term] or in 2016 [short-term]) to a contaminated rice paddy soil, and subsequent plant Cd and Pb tissue distribution over time was investigated. Water-soluble Cd and Pb concentrations decreased by 6.7–76.0% (short-term) and 10.3–88.1% (long-term) with biochar application compared to the control. The soil exchangeable metal fractions (i.e., considered more available) decreased, and the residual metal fractions (i.e., considered less available) increased with short- and long-term biochar amendments, the latter likely a function of biochar increasing pH and forcing Cd and Pb to form crystal mineral lattice associations. Biochar application reduced Cd (16.1–84.1%) and Pb (4.1–40.0%) transfer from root to rice grain, with rice Cd and Pb concentrations lowered to nearly Chinese national food safety standards. Concomitantly, soil organic matter (SOM), pH and soil water content increased by 3.9–49.3%, 0.05–0.35 pH units, and 3.8–77.4%, respectively, with increasing biochar application rate. Following biochar applications, soil microbial diversity (Shannon index) also increased (0.8–46.2%) and soil enzymatic activities were enhanced. Biochar appears to play a pivotal role in forcing Cd and Pb sequestration in contaminated paddy soils, reducing heavy metal transfer to rice grain, and potentially leading to reduced heavy metal consumption by humans.

Highlights

Soil heavy metal pollution is a worldwide problem, with accumulation leading to toxicity and environmental persistence; this is especially true for cadmium (Cd) and lead (Pb), both of which pose serious human and ecological health threats [1,2]
(2016), 15.7–82.4% (2017) and 10.3–46.2% (2018) (Figure S2A,C) with biochar applications compared to the control
S2B,D), respectively, with biochar applications compared to the control

Summary

Introduction

Soil heavy metal pollution is a worldwide problem, with accumulation leading to toxicity and environmental persistence; this is especially true for cadmium (Cd) and lead (Pb), both of which pose serious human and ecological health threats [1,2]. It is obvious that in order to protect human health and the environment, reducing heavy metal bioavailability is of paramount importance. Stabilization/immobilization has been considered practical with respect to short-term effectiveness when using different stabilizers, yet longer-term effectiveness does require more research, especially for the biochar [5]. Found that the biochar could stabilize Cd and Pb in the paddy soil and reduce the rice uptake in short term [7]. Finding a heavy metal stabilizing material that is effective both in the short- and long-term may be as simple as utilizing biochar [8]

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Methods

Results

Conclusion