Phytoavailability control based management for paddy soil contaminated with Cd and Pb: Implications for safer rice production

Abstract

A metal phytoavailability control based management protocol for a metal contaminated paddy soil was investigated as an alternative to conventional engineering-based remediation methods such as 'clean soil cover' for safer rice crop production. The accumulation of Cd and Pb in rice was monitored following application of three pH change-induced immobilizing agents (dolomite, steel slag, and agricultural lime) and two sorption agents (zeolite and compost) to a Cd and Pb contaminated paddy soil. Changes in the phytoavailable pool of Cd and Pb in soils following the application of each immobilizing agents were also determined using 1 M NH4NO3 extraction. Among the immobilizing agents considered, pH change-induced immobilizers were more effective than sorption agents; exhibiting more significant decreases (p < 0.001) in phytoavailable Cd and Pb concentrations. The phytoavailable pool of these metals was even lower than those measured in the 'clean soil cover' where the total metal concentrations of the plow layer were reduced via capping the surface with uncontaminated soil. Consequently, the decline in the phytoavailable pool of Cd and Pb in soil induced by immobilizing agents resulted in significantly lower accumulation of these metals in the rice grain (0.02-0.03 mg kg(-1) for Cd and 0.11-0.16 mg kg(-1) for Pb) compared to those measured in the rice cultivated in the control (unammended) soil (0.16-0.23 mg kg(-1) for Cd and 0.19-0.30 mg kg(-1) for Pb). This indicated that immobilization using pH-change induced immobilizing agents was a feasible approach for safe rice crop production in Cd and Pb contaminated paddy soils. (C) 2015 Elsevier B.V. All rights reserved.