Attapulgite and processed oyster shell powder effectively reduce cadmium accumulation in grains of rice growing in a contaminated acidic paddy field

https://doi.org/10.1016/j.ecoenv.2020.111840Get rights and content
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Highlights

  • Attapulgite (AT) & processed oyster shell powder (POS) are cost-effective passivators.

  • AT and POS decrease Cd bioavailability in soil and accumulation in rice grains.

  • AT and POS immobilize Cd through ion exchange, precipitation and complexation.

  • Cadmium accumulation in grains correlated positively with bioavailable Cd in soil.

Abstract

Heavy-metal contamination is widespread in agricultural soils worldwide, especially paddy soils contaminated by Cd. Amendment-induced immobilization of heavy metals is an attractive and effective technique, provided that cost-effective materials are used. This field experiment compared three alkaline passivators (attapulgite, processed oyster shell powder, and mixed soil conditioner) at a rate of 2.25 t ha−1 for their effectiveness in decreasing Cd bioavailability in soils and accumulation in rice plants in a paddy field contaminated by Cd (0.38 Cd mg kg−1). The utilization of attapulgite and processed oyster shell powder decreased labile fractions but increased stable fractions of Cd in soils through ion exchange, precipitation and complexation. The addition of attapulgite decreased the concentration of bioavailable Cd in both bulk and rhizosphere soils, whereas the amendment of processed oyster shell powder decreased it only in bulk soil. The Cd accumulation in rice plants correlated significantly with acid-soluble and residual Cd fractions in the rhizosphere soil but not in the bulk soil. The addition of attapulgite and processed oyster shell powder decreased Cd accumulation in rice grains from 0.26 mg kg−1 to 0.14 and 0.19 mg kg−1, respectively, meeting the National Food Safety Standard (< 0.20 mg kg−1). However, the mixed soil conditioner did not decrease the Cd accumulation in rice shoots or grains. This study demonstrated that attapulgite and processed oyster shell powder were economic agents in reducing Cd accumulation in rice grains.

Keywords

Attapulgite
Cadmium contamination
Calcareous material
Immobilization
Plant uptake

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