| This study is divided into two experiments of paddy field and soil culture,to explore the time-effectiveness of limestone+sepiolite(LS)for the treatment in mildly Cd contaminated paddy fields and whether it is suitable for the treatment of Cd and As contaminated paddy fields.In field experiment,three consecutive seasons of rice were planted in a single application of LS at 0,0.5,1.0,and 2.0 g·kg-1,and an in-situ passivation repair test was performed on a mildly Cd contaminated paddy field in Ningxiang,Hunan.When third season of rice planting,each application sample was divided into two,corresponding to additional experiment of supplementary applicatons of LS at 0.25,0.5 and 1.0 g·kg-1.In soil cultivation experiment,LS and its combination were used as amendment and applied to soil which contaminated by Cd and As for 30 days of cultivation.The main research results are as follow:(1)After the application of LS could increase soil pH value in three seasons,but with the increase of planting seasons,the improvement effect of each season in the experimental group was weakened than that in the control group.After the application of LS could significantly reduce the contents of acid-extractable Cd and CaCl2-extracted Cd of soil in three seasons,but had no significant effect on the contents of TCLP-extracted Cd.Compared with the control group,the content of acid-extractable Cd and CaCl2-extractable Cd in three season rice planting soil decreased by 18.2%-36.4%,17.7%-33.5%,9.6%-17.6%and 40.6%-68.8%,respectively.(2)Application of 0.5-2.0 g·kg-1 LS can effectively reduce the Cd contents in all tissus of rice in three seasons.The contents of Cd in brown rice in the three seasons decreased by 26.1%-65.2%,3.0%-42.4%and 13.0%-26.1%,respectively.On the whole,the contents of Cd in brown rice through three rice planting seasons under 0.2%LS treatment were lower than the national food contaminate limit standard,which indicated that the application of 2.0 g·kg-1 LS could ensure the safe production of rice and had good time-effectiveness.(3)Compared with the experiment group without LS supplementation in third season,the treatments with supplemented LS could increased significantly the pH value of the soil,could significantly reduce the content of acid-extractable Cd and CaCl2 extractable Cd,and the content of Cd in all tissue of rice showed a decreasing trend.In addition,the content of Cd in brown rice in supplementated LS experiment group was lower than the national food contaminant limit standard of 0.2 mg·kg-1,which indicated that LS had a good passivation effect on mildly contaminated paddy fields.(4)From the comprehensive effect and economic indicators,in the actual application of LS for the treatment of paddy fields with mildly Cd contaminated,it is suggested to apply the combined amendment of 300 kg·mu-1 in the first season and supplementary the application of 37.5-150 kg·mu-1 before rice planting in the third season,which can more effectively guarantee the safe production of rice.(5)LS is suitable for the treatment of Cd and As compound contaminated paddy field with Cd contamination degree greater than As contamination degree.LSA1 is suitable for the treatment of Cd and As compound contaminated paddy field with As contamination degree greater than Cd contamination degree,but it has certain limitations due to cost reasons. |
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