Remediation of Cadmium-contaminated Paddy Soils by Washing with Ferric Chloride (FeCl3): Effect of Soil Washing on the Cadmium Concentration in Soil Solution and Spinach

We evaluated the effects of soil washing with ferric chloride (FeCl3) on cadmium (Cd) concentrations in soil solutions and Cd absorption by two spinach cultivars in pot experiments. Soil samples were collected from washed and unwashed plots of rice paddy fields in Fukuoka and Toyama, Japan. Spinach pot cultivation was performed with the above mentioned soil under oxidative conditions. Before and after spinach cultivation, the Cd content in washed soils was always lower than that in unwashed soils. Soil washing with FeCl3 affected the exchangeable cations (i.e. calcium increased and magnesium decreased). The Cd concentration in the soil solution from washed plot was lower than that in the solution from the unwashed plot throughout the spinach growth period, which was attributed to the exchangeable Cd content in both soils, because the fraction equilibrated with the Cd concentration in the soil solution. The exchangeable cation composition was affected by soil washing, but no significant difference in spinach yield was observed between the washed and unwashed plots. The leaf Cd concentration in the two spinach cultivars was up to 70% lower in the washed soils. This study suggested that soil washing in rice paddy fields with FeCl3 was effective for controlling the Cd absorption risk of upland crops such as spinach. However, some risks remain to clear the CODEX standard (0.2 mg kg) in the Cd content of leaf such as spinach, which has a high Cd absorptive capacity. Discipline: Agricultural environment Additional key words: chemical washing, heavy metal, leaf vegetable, pot experiment, remediation technology