Effects of combined amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on contaminated paddy soil.

Stabilization of heavy metals in situ was investigated. Two combined amendments (LS, limestone+sepiolite; HZ, hydroxyhistidine+zeolite) were applied at ratios of 0.2%, 0.4%, and 0.8% (w/w) to paddy soil with multi-metal (Pb, Cd, Cu, and Zn) contamination. The effects of these two combined amendments on heavy metal bioavailability in soil, and on uptake and accumulation of heavy metals in rice plants were investigated. Application of LS and HZ significantly increased soil pH values and cation exchange capacity contents, and resulted in a reduction in exchangeable fraction of metals and in extract metal concentrations of amended soils through toxicity characteristic leaching procedure (TCLP). LS and HZ obviously inhibited uptake and accumulation of Pb, Cd, Cu, and Zn in rice plants. Compared with the control soil, concentrations of Pb, Cd, Cu, and Zn in brown rice were decreased by 10.6-31.8%, 16.7-25.5%, 11.5-22.1%, and 11.7-16.3%, respectively, as a result of 0.2% to 0.8% addition of LS, and decreased by 5.1-40.8%, 16.7-20.0%, 8.1-16.2%, and 13.3-21.7%, respectively, as a result of 0.2-0.8% addition of HZ. Significant positive linear correlations were found between heavy metal concentrations in TCLP extracts and those in rice tissues except for Pb. Extracting heavy metals with TCLP was a more suitable method for estimating heavy metal bioavailability concentrations of amended soil than exchangeable fraction of heavy metals, because the latter underestimated heavy metal bioavailability. These results demonstrate that LS and HZ could be effective in reducing heavy metal bioavailability and accumulation in rice grown on multi-metal-contaminated soils.

[Effects of group matching curing agent on exchangeable Pb, Cd, Zn contents in the potted soils and their accumulation in rice plants].

A pot experiment was conducted to study the effects of a group matching curing agent (limestone plus sepiolite) with different concentrations (0, 1.0, 2.0, 4.0, 8.0, 16.0 g x kg(-1)) on the exchangeable Pb, Cd, and Zn contents in the potted soil collected from a mining area in southern China and their cumulative distribution in rice plants. The results showed that: (1) Exchangeable Pb, Cd, and Zn contents in the potted soils decreased obviously with the increase in the amounts of group matching curing agent by 15.3%-99.9%, 9.2%-99.9%, and 7.0%-99.9%, respectively, compared with the CK, indicating that the addition of limestone plus sepiolite effectively inhibited the uptake of Pb, Cd, Zn from soils into rice plants. (2) Growth conditions of rice plants were improved, and the heights of rice plants increased with the increase in the amounts of group matching curing agent. The rice yield reached the optimal level and was increased by 60.4% compared with the CK, when the amount of limestone plus sepiolite was 1.0 g x kg(-1). The uptake of heavy metals in different organs of rice plants decreased obviously with the increasing amounts of the group matching curing agent, and the Pb, Cd, and Zn contents of rice grains decreased by 2.2%-13.1%, 29.3%-79.3%, 19.5%-43.3% with different concentrations (1.0-16.0 g x kg(-1)) of the group matching curing agent, respectively, compared with the CK.