Interactive impact of biochar, selenium and water management on rice plants and soil microbial diversity in a cadmium-contaminated soil and assessment of health risk

Global soil cadmium (Cd) contamination demands practical, low-cost solutions to ensure safe food production. This study presents findings from a pot experiment designed to examine the interactive effects of biochar (BC) (B1: 0 %, B2: 1 %, B3: 2 % w/w), foliar selenium (Se) (S1: 0, S2: 0.25 mM, S3: 0.50 mM), and water management (WM) (W1: 70 % water holding capacity, W2: continuous flooding) on Cd effects on rice plants and microbial communities in a Cd-contaminated soil (0.92 mg/kg total Cd) and the associated health risk. The results indicated that the main effects of BC and WM significantly influenced pH and SPAD during the tillering and milk stage, with B2 and B3, and W2 increasing these values compared to B1 and W1. At the milk stage, the B3W2 interaction was significant for SPAD, increasing by 7.40 % compared to B1W1. The measured yield parameters were significantly affected by the main effects of BC, Se, and WM, with B2 and B3, S2 and S3, and W2 showing increased values over B1, S1, and W1. Similar results were observed for bioavailable Cd content; however, Se showed no significant effect. The B3S3W2 interaction significantly increased SOD by 91.56 %, while the B2S3W2 interaction exhibited the highest reductions in MDA (28.35 %) and H₂O₂ (57.61 %) relative to B1S1W1. Furthermore, the B2S3W2 interaction resulted in a 95.32 % reduction in grain Cd content compared to B1S1W1 and enhanced the bacterial ACE, Chao1, and Shannon indices, and the fungal ACE and Chao1 indices. Lastly, the B1S1W1 interaction had the highest daily intake (DI) (1.66E-04) and health risk index (HRI) (0.166), while the B2S3W2 interaction had the lowest DI (8.10E-06) and HRI (0.008). Our results suggest that the application of B2S3W2 can significantly inhibit Cd absorption and concentration in rice, mitigate the resulting health consequences, and enhance the soil microbial environment.