Effect of Liming with Various Water Regimes on Both Immobilization of Cadmium and Improvement of Bacterial Communities in Contaminated Paddy: A Field Experiment.

Lei Shi,Hongzhen Ran,Fang Liang,Chi Peng,Peng Zeng,Zhaohui Guo,Xiyuan Xiao,Wenli Feng

doi:10.3390/ijerph16030498

Abstract

Cadmium (Cd) in paddy soil is one of the most harmful potentially toxic elements threatening human health. In order to study the effect of lime combined with intermittent and flooding conditions on the soil pH, Cd availability and its accumulation in tissues at the tillering, filling and maturity stages of rice, as well as enzyme activity and the microbial community in contaminated soil, a field experiment was conducted. The results showed that liming under flooding conditions is a more suitable strategy for in situ remediation of Cd-contaminated paddy soil than intermittent conditions. The availability of Cd in soils was closely related to the duration of flooding. Liming was an effective way at reducing available Cd in flooding soil because it promotes the transformation of Cd in soil from acid-extractable to reducible fraction or residual fraction during the reproductive growth period of rice. Compared with control, after liming, the concentration of Cd in brown rice was reduced by 34.9% under intermittent condition while reduced by 55.8% under flooding condition. Meanwhile, phosphatase, urease, and invertase activities in soil increased by 116.7%, 61.4% and 28.8%, and 41.3%, 46.5% and 20.8%, respectively. The high urease activity in tested soils could be used to assess soil recovery with liming for the remediation of contaminated soil. Soil microbial diversity was determined by the activities of soil acid phosphatase, urease and available Cd by redundancy analysis (RDA). The results indicated that the problem of Cd-contaminated paddy soil could achieve risk control of agricultural planting by chemical treatment such as lime, combined with various water regimes.

Highlights

Contamination of paddy soils with potentially toxic elements has become a worldwide environmental problem with the extensive development of industrial activities [1,2,3], over-fertilization [4], and irrigation with water contaminated with toxic elements [5,6]
The yield of the rice grain is lower under flooding condition than that under intermittent condition
At the filling stage of rice, compared to control, the Cd concentration in root was significantly decreased by 33.3% in the intermittent combined with lime treatment (IL), while the corresponding figure was 30.3% in the flooding combined with lime treatment(FL)

Summary

Introduction

Contamination of paddy soils with potentially toxic elements has become a worldwide environmental problem with the extensive development of industrial activities [1,2,3], over-fertilization [4], and irrigation with water contaminated with toxic elements [5,6]. They can accumulate in the edible parts of crops, enter the human body through the food chain and threaten human health [7,8,9,10,11]. Rice is considered as a major source for Cadmium (Cd) in the

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