Management of heavy metals in rice (Oryza sativa) soils by silicon rich biochar materials

Abstract

Multiple heavy metals have contaminated soils with a combination of ecological consequences that make soil remediation more challenging. An experiment was conducted during 2022–23 at University of Agriculture and Forestry, Hue University, Hue city, Vietnam to evaluate the potential of silicon rich biochar from rice (Oryza sativa L.) husk and peanut shell in the remediation of heavy metals (Cd, Pb, Cu and Zn) present in rice soils of central Vietnam. A total of 20 samples of rice soil were taken from two distinct locations, Quang Tho commune and Thuy Phuong ward, Thua Thien Hue province, Central Vietnam to measure the quantity of heavy metals and evaluate the level of pollution. Silicon is a beneficial element and its external application as fertilizer seems impractical. Therefore, in this study, the effects of different silicon-rich materials [rice husk biochar (RHB) and peanut shell biochar (PSB)] at 6 different rates (0, 1, 2, 3, 4 and 5%) were determined in reducing heavy metal (Cd and Pb). The mean concentrations of Cd, Pb, Cu and Zn in soil samples ranged between 0.56–22.14 mg/kg; 19.48–81.30 mg/kg; 23.26–48.54 mg/kg and 28.47–55.12 mg/kg, respectively. Cd and Pb toxicity in rice soil samples was greater in Thuy Phuong ward than the average shale values. Considering the pollution load index (PLI), a total of 6 sites in Thuy Phuong ward had values >1.0 indicating pollution load in the respective sites, and Cd, Pb were the major contaminants in soils of the study area. The addition of silicon-rich materials decreased the contents of Cd and Pb in rice soils with adsorption efficiency from 22.83–38.54% and 30.69–31.53% in rice husk biochar (RHB); 20.47–29.55% and 26.77–27.87% in peanut shell biochar (PSB), respectively. Thus, RHB could be more effective to remediate soils contaminated with heavy metals when compared to other silicon-rich materials.