Using passivation materials to immobilize soil copper in a rape-rice rotation system

Abstract

Copper (Cu) contamination in agricultural soils is a serious concern and unposmg health risks to mdividuals through Cu soil-food chain transfer. Hence, soil Cu immobilization is essential to reduce its bioavailability in the soil system. Tliis two year (2016-2013) field experiment was conducted to investigate the impacts of nano-hydroxyapatite. quicklime, biochar. bio-organic fertilizer, and mesoporous ceramic functional nanomaterials amendments on Cu bioavailability and its uptake by rape and rice in an acidic soil (pH=5.04). Compared to control plots, passivation materials (PMs) application significantly (P < 0.05) improved soil pH and organic matter contents by 0.39-12.3% and 3.08-41.3%. respectively. Among them, quicklime was the best to increase soil pH while biochar had the greatest effect on increasing soil organic matter. Moreover, these materials reduced the soil available Cu (DTPA-extractable Cu) and Cu removal by rice and rape crops. After two years restoration. Cu contents in rape and brown-rice seeds ranged between 6.32 to 8.50 and 6.56 to 3.47 mg kg"1, respectively, lower than the National Standard of Pollutants in Food of China (GB 15199-1994. 10 mg kg-1). Nonetheless, these materials had slight effect on growth, yield and related traits of both crops. The results showed that the crop yields, plant height, diy weight (DW). 1000-grain weight with PMs were slightly influenced, hi conclusion, tliis two-year field study indicated that the rape-rice rotation combined with PMs application (quicklime and mesoporous ceramic functional nanomaterials in particular) can reduce Cu uptake by rice and rape crops, and therefore, improve their safety. From the perspective of food safety, rape is recommended for Cu-contaminated acidic soil because it had low Cu uptake ability compared with rice.