Impact of citric acid on cadmium immobilization in soil amended with biochar

Cadmium (Cd) contamination in agricultural soils poses severe threats to human health and ecosystem integrity. While biochar is recognized for its ability to immobilize heavy metals, the impact of plant-derived low molecular weight organic acids (LMWOAs), such as citric acid (CA), on this process remains unclear. This study shows that CA and biochar synergistically immobilize Cd in alkaline soil from extensively polluted southeastern Hubei, China. Soils were amended with maize stover biochar at rates of 0, 0.5 %, 1 %, and 2 % (W/W), with or without CA addition (1 mmol/L), and incubated for 80 days. Results show that biochar significantly reduced bioavailable Cd, with a 2 % application decreasing extractable Cd by 26.84 %. Unexpectedly, CA alone increased Cd…