Reduction of antimony bioavailability with the application of stable exogenous organic matter: a comparative study between rice straw and manure compost.

Considering the widespread use of organic amendments to improve soil quality and enhance soil carbon sequestration, it is crucial to understand their impact on the bioavailability of metalloids in soils. Antimony (Sb), a priority pollutant, is particularly impacted by organic matter, yet the effects of different organic amendments-varying in stability and composition-on Sb bioavailability remain unclear. This study investigates the influence of different organic amendments, rice straw and compost, on Sb bioavailability in the rice-soil system, with rice ingestion being a major Sb exposure pathway in humans. Results show that while both amendments increased dissolved organic carbon in soil solution, their effects on Sb bioavailability differed markedly. Rice straw increased C-Sb by 13.24 %-66.63 %, whereas compost decreased C-Sb by 32.47 %-43.51 %. These differences were also reflected in Sb accumulation in rice shoots, where compost application resulted in lower Sb content. This reduction may be attributed to increased microbial genera such as Ramlibacter and Sphingomonas, which are associated with Sb oxidation. Conversely, organic matter with low stability, prone to rapid degradation, could promote reducing soil conditions, thereby increasing Sb concentrations. Our findings suggest that stable exogenous organic matter, such as pre-decomposed compost, is preferable for managing Sb-contaminated soils.