Mitigation of thallium risk in Brassica oleracea L. by phosphate-mediated natural mineral composite: Soil Tl stabilization and microbial community responses

Thallium (Tl) is a highly toxic metal, and its contamination in agricultural soils poses a serious risk to human health through the food chain. Despite evidence that mineral amendments can reduce soil Tl bioavailability, it remains unclear how phosphate-mediated mineral composites regulate Tl uptake in leafy vegetables with high Tl accumulation, such as green cabbage ( Brassica oleracea L.). Herein, we evaluated the mitigating effects of a phosphate-mediated natural mineral composite (PNMC; the I 1 M 1 C 1 treatment), consisting of natural iron oxide, montmorillonite, and calcium phosphate, on Tl stabilization in soils and Tl uptake by green cabbage in a pot experiment. Results showed that the application of PNMC considerably mitigated Tl accumulation in the edible tissues of green cabbage. Specifically, compared with the control, the 1.5% w/w I 1 M 1 C 1 treatment decreased leaf Tl content by over 60% while promoting plant growth. This mitigation was primarily attributable to PNMC-driven redistribution of soil Tl from bioavailable fractions (Aci-Tl, Red-Tl, Oxi-Tl) toward more stable solid-phase pools (Res-Tl), thereby reducing Tl bioavailability. Redundancy analysis further indicated that multiple geochemical factors were associated with Tl fraction redistribution, among which available phosphorus (AP) exhibited the highest explanatory power, whereas partial least-squares path modeling demonstrated that these fraction shifts contributed the most to the reduction in Tl accumulation in the edible tissues of green cabbage (total path coefficient: 0.629). In addition, PNMC increased bacterial diversity and enriched nutrient-cycling microbial communities, particularly Proteobacteria and Bacteroidota. Genus-level analyses further suggested that Pseudarthrobacter and Flavisolibacter were closely linked to Tl fraction dynamics. Overall, these findings highlight coupled geochemical–microbial responses associated with Tl fraction redistribution and plant uptake, supporting the potential application of phosphate-mediated natural mineral composites for Tl-contaminated agricultural soils.