Remediation effect of Cd polluted paddy soil evaluated by grain Cd reduction rate and marginal efficiency

Abstract: Cadmium (Cd) pollution in paddy soil is becoming an increasingly serious issue in China. A nationwide survey in China revealed that Cd is the most frequently detected heavy metal in soil and 7% of the investigated site soil is contaminated by Cd. Cadmium is accumulated in plants more readily than most other metals, and can be translocated into the edible parts (cereal grains) and causes health risk through the food chain. Numerous efforts have been paid for remediation of heavy metal polluted soil in China in past decades. In present, development of high efficiency and low cost remediation materials and keeping the consistency of pot and field experiments results are still the technical difficulties for in-situ remediation of heavy metal polluted soils. In this study, two rice cultivars characterized with Cd-sensitive cultivar (JH212) and Cd-enrichment cultivar (XS09) were used, and the red earth from Hunan province and paddy soil from Zhejiang province polluted by Cd were also collected for pot experiment, while the field validation experiment were simultaneously conducted to investigate the remediation efficiency of different amendments (including: amendment from rock foundation FS, clay mineral AT and humus WG) on Cd polluted soils, the remediation efficiency was evaluated by rice grain Cd reduction rate (%), the DTPA-extracted fraction of Cd in soil and remediation marginal cost. The results indicated that the Cd uptake and translocation by the rice cultivars were significantly (P<0.05) reduced by the soil amendment applications. For the pot experiment, compared with control (CK), the maximum Cd reduction rate of rice grain for the tested rice cultivars reached 65.3% and 61.4% for red earth from Hunan province and paddy soil from Zhejiang province, respectively. In field condition, the maximum Cd reduction rate of rice grain for the tested rice cultivars reached 61.8% and 60.1%, respectively for the above two type of polluted soils. In terms of the Cd-sensitive rice cultivars, higher remediation efficiency was generally observed for Cd-enrichment cultivar (XS09) than that for Cd-sensitive cultivar (JH212) for both soil types and culture condition (i.e. pot experiment and field validation experiment). In general, the rice grain Cd reduction rate reached 41.6%-65.3% for the two rice cultivars compared with the control after amendments, and the rice grain Cd reduction rate for Cd-enrichment cultivar (XS09) were generally higher than that for Cd-sensitive cultivar (JH212), and the rice grain Cd reduction efficiency for red earth were generally higher (P<0.05) than that for paddy soil among the treatments. The remediation efficiency followed the order of AT>WG≈FS based on rice grain Cd reduction efficiency. The remediation marginal efficiency (RME) (defined as rice grain Cd reduction rate based on 1 500 yuan cost per hectare) for the tested soils ranged from 9.10% to 15.4%. The highest RME was observed with AT, followed with WG and FS treatment. By considering the rice grain Cd reduction rate and remediation marginal efficiency, the remediation effect of Cd polluted soil for different amendments ordered as AT>WG>FS.