Efficiency and surface characterization of different plant derived biochar for cadmium (Cd) mobility, bioaccessibility and bioavailability to Chinese cabbage in highly contaminated soil.

Cadmium (Cd) contamination in red soil has become a serious environmental concern due to its toxic effects on organisms and the food chain. Possible eco-friendly solutions for Cd immobilization were required to reduce its mobility through biochar. This study evaluated the comparative efficiency of rice straw (RSB), rice hull (RHB) and maize stover (MSB) derived biochar (BC) on Cd mobility and its accumulation in Chinese cabbage (Brassica chinensis L.), which is highly Cd accumulating crop. Results showed that the soil chemical properties (pH, organic carbon and nutrients) significantly increased with increasing the biochar application rate from 1.5% to 3%. Concentration of Cd decreased in CaCl2 extract by 58.6, 39.7 and 46.49% and in toxicity characteristics leaching test (TCLP) by 42.9, 32.7 and 36.7% for RSB, RHB and MSB, respectively at 3% application rate. The simple bioaccessibility extraction test (SBET) techniques showed a significant decrease in Cd by 30.5, 20.6 and 27.5% for RSB, RHB and MSB, respectively at the 3% application rate. Moreover, the Cd contents in the cabbage shoots decreased by 25, 21.3 and 23.1% for RSB, RHB and MSB at a 3% application rate and in the roots by 31.3, 23.9 and 26.5% for RSB, RHB and MSB at a 3% application rate, respectively. Bioaccumulation (BCF) and translocation factors (TF) were significantly decreased upto 26.5% and 11%, respectively among all biochar types. Overall, RSB demonstrated positive results as soil amendments for Cd immobilization and thereby, reducing its bioavailability in the Cd contaminated soil to mitigate food security risks.