Assessment of phytoextraction using Sedum plumbizincicola and rice production in Cd-polluted acid paddy soils of south China: A field study

Soil cadmium (Cd) contamination threatens the quality of agricultural products and human health and the situation is particularly serious in acid paddy soils in south China. Phytoextraction is an in-situ and environmentally friendly technique but it is still a challenge to complete remediation in the short term and resume rice production safely. A field experiment on a total area of one hectare was conducted to evaluate the Cd removal efficiency from a contaminated acid paddy soil (pH 5.0, Cd 0.6 mg kg(-1)) by repeated phytoextraction using the hyperaccumulator Sedum plumbizincicola from October to next June every year. The plant grew well with a shoot dry biomass of 1.8-5.9 t ha(-1) and a Cd concentration of 51.4-94.9 mg kg(-1) and Cd accumulation of 169-353 g ha(-1). The Cd removal rate from rooting depth (the top 15 cm) of the arable soil ranged from 13.8 to 34.7% each season with an average of 21.8%. In plot 1 the soil total Cd concentration decreased from 0.64 to 0.29 mg kg(-1) after two seasons of phytoextraction. The soil Cd concentration decreased mainly within the depth range 2-10 cm which corresponded with the root distribution pattern of S. plumbizincicola. Subsequent rice Cd risk assessment shows that grain Cd concentrations in phytoextracted soil decreased significantly compared to non-phytoextracted soil. Brown rice Cd in lower accumulating rice cultivars MY12085 and MY12086 was< 0.2 mg kg(-1) (Chinese standard), while additional immobilization was needed in the case of higher accumulating cultivars. This field study strongly indicates that phytoextraction of slightly contaminated acid soils using S. plumbizincicola is feasible to depress the total Cd concentration to meet the statutory limit within a relatively short time. Appropriate utilization of rice cultivars and soil amendments in the phytoextracted soils may further contribute to safe agricultural production.