Assessing long-term stability of arsenic immobilization by iron-impregnated biochar under simulated irrigation and...

Arsenic (As) contamination in agricultural soils poses significant risks to food safety and human health, particularly in regions relying on As-contaminated groundwater for irrigation. This study evaluates the efficacy of iron-impregnated biochar (Fe/TBC) in mitigating As leaching and enhancing long-term immobilization in two contrasting soils (sandy loam PP1 and sandy U43) under simulated irrigation and accelerated aging conditions. Statistical analyses including ANOVA and MANOVA revealed that Fe/TBC significantly improved As retention (up to 88%) and reduced post-aging As remobilization (to 31% and 27% in PP1 and U43, respectively). Sequential extraction with Tukey HSD tests showed that Fe/TBC and HA@Fe/TBC treatments notably increased stable As fraction. But the retention efficacy in PP1 decreased to 65% after the addition of humic acid (HA@Fe/TBC). Microbial enumeration indicated enhanced culturable bacterial abundance in Fe/TBC-amended soils, indicating reduced As bioavailability. Conversely, the addition of HA suppressed microbial activity in U43 soil. These findings highlight Fe/TBC as a robust amendment for As immobilization, while also underscoring the potential context-dependent risks associated with organic additives such as HA, particularly in clay-rich soils.