Persistence of CaCl_2 washing effect for amelioration of a Cd-contaminated paddy field soil(Soil Chemistry)

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Soil washing is one of the methods used to remediate soil contaminated with heavy metals, and when the contaminated elements have been effectively removed the washed soil can be used for agriculture. Soil washing was conducted using 0.5mol L^<-1> CaCl_2 solution at pH 4 as an extracting agent to remediate a paddy field soil contaminated with Cd. Dolomite powder was applied to neutralize the soil to the original pH 6.2. After CaCl_2 washing, the content of Cd extractable in 0.1mol L^<-1> HCl decreased from 2.4 to 0.8mg kg^<-1>. Subsequently, a pot experiment was carried out to evaluate the effect of soil washing on Cd concentration in polished rice (Cd_<pr>) for three successive years. Using the washed soil, Cd_<pr> was &le 0.2mg kg^<-1> with and without a treatment that simulates midseason drainage, whereas it was>0.5mg kg^<-1> in the unwashed soil with the midseason drainage treatment. The reasons for low Cd_<pr> growth in the washed soil were the low content of exchangeable Cd in the soil and the resultant high soil pH (>7). To evaluate the effect of soil pH on Cd_<pr> in the fourth year, we adjusted soil pH to 5 with H_2SO_4 before transplanting rice seedlings. The Cd_<pr> in the washed soil with the midseason drainage treatment increased to 0.47mg kg^<-1>, whereas it was less than 0.2mg kg^<-1> under continuous flooding. Thus, high pH or whole season flooding are important to keep Cd_<pr> at ≤ 0.2mg kg^<-1> even after soil washing. With the application of dolomite and other ordinary fertilizers, soil properties were little affected by the present soil washing procedure because the difference in rice yield between the washed and unwashed plots was not significant within each year.
社団法人日本土壌肥料学会の論文

Persistence of CaCl_2 washing effect for amelioration of a Cd-contaminated paddy field soil(Soil Chemistry)

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