The influence of four organic fertilizers (OF) (rapeseed dregs (RD), sesame dregs (SD), bean dregs (BD), and peanut dregs (PD)), two brassinosteroids (Br) (24-epibrassinolide (Br24), and 28-homobrassinolide (Br28)), and their combination (RD+Br and BD+Br) on the accumulation and uptake of arsenic (As) and cadmium (Cd) by rice plants grown in paddy soil spiked with 40 mg kg⁻¹ As and 5 Cd mg kg⁻¹ was performed under waterlogged conditions. The results showed that OF, Br, and their combination significantly decreased Cd contents in shoot and root, but increased As contents in shoot of rice seedling. Iron (Fe) concentration in shoot showed a significant negative correlation with Cd concentration in shoot, but a positive correlation with As concentration in shoot. There was a positive correlation between the Fe content and As or Cd content in plaque. The application of SD, BD, and BD+Br increased the amount of iron plaque, which promoted the adsorption of As, manganese (Mn), copper (Cu), and zinc (Zn) on root surface of rice plant. These findings suggested that the application of OF, Br, and their combination in As-Cd-contaminated paddy soil was an effective approach to decrease Cd uptake by rice plant, but not for As reduction. This is a preliminary study, which has the potential for further enhancing the understanding of uptake mechanisms of As and Cd in rice plant in paddy fields.

The co-contamination of arsenic (As) and cadmium (Cd) in paddy soils threatens rice safety, yet synergistic mitigation strategies using silicon (Si) and ferrous sulfate (FeSO₄) remain underexplored. This study integrated hydroponic and soil pot experiments to evaluate Si-FeSO₄ interactions on As/Cd accumulation and rice growth. Hydroponic trials employed 21-day-old rice seedlings exposed to 0.5 mg As(III)/Cd(II) L⁻¹ with/without 70 mg Si L⁻¹ and 30–70 mg Fe L⁻¹, followed by sequential harvesting at 14 and 21 days. Soil experiments utilized co-contaminated paddy soil (50 mg As kg⁻¹ and 1.2 mg Cd kg⁻¹) amended with Si (80 or 400 mg kg⁻¹) and Fe (100 or 1000 mg kg⁻¹), with pore water dynamics monitored over 120 days. Hydroponic results demonstrated that 70 mg Si L⁻¹ combined with 30 or 70 mg Fe L⁻¹ enhanced shoot biomass by 12–79% under As stress, while simultaneously reducing shoot As concentrations by 76–87% and Cd concentrations by 14–33%. Iron plaque induced by FeSO₄ exhibited contrasting adsorption behaviors: hydroponic roots immobilized both As and Cd (p < 0.01), whereas roots in soil primarily retained Cd (p < 0.05). In soil experiments, the optimal treatment of 100 mg Fe kg⁻¹ and 400 mg Si kg⁻¹ (Fe₁ + Si₂) increased grain biomass by 54%, while reducing As and Cd concentrations by 37% and 42%, respectively. However, a higher Fe dosage (Fe₂: 1000 mg kg⁻¹ Fe) paradoxically increased grain Cd concentrations. Mechanistically, Si amendment elevated soil pH (Δ + 0.72), facilitating Cd immobilization, while FeSO₄ lowered pH (Δ−0.07–0.53), increasing Cd mobility. A strong correlation between soluble Cd and plant uptake was observed (p < 0.01), while changes in As accumulation were unrelated to aqueous behavior. The optimized Si/Fe molar ratio of 7.95:1 effectively mitigated As and Cd co-accumulation, offering a dual-functional strategy for safe rice cultivation in contaminated soils.

Thallium (Tl) and cadmium (Cd) are highly toxic heavy metals that frequently co-occur in sulfide ores, posing a serious food safety risk through accumulation in rice. Although calcium-based (Ca-based) amendments have been widely applied to remediate heavy metal-contaminated soils, their effectiveness in Tl–Cd co-contaminated paddy soils remains unclear. A pot experiment was conducted to evaluate four Ca-based amendments—limestone powder, dolomite powder, hydrated lime, and oyster shell powder—on Tl and Cd bioavailability and uptake in paddy soil near a mining area. Ca-based amendments effectively reduced Tl and Cd bioavailability, with DTPA-Tl reducing by 11.2–17.2% and DTPA-Cd by 8.9–21.3%. These reductions were attributed to increased soil pH and decreased DOC, Fe, and Mn in the pore water. Additionally, Ca-based amendments shifted Tl and Cd from acid-extractable to residual fractions, reducing mobility. Additionally, Ca-based amendments promoted Fe/Mn plaque formation on rice roots, reducing Tl and Cd uptake. Consequently, Tl and Cd concentrations in brown rice decreased by over 14%, with the lowest levels observed under oyster shell powder. However, Cd concentrations still exceeded the maximum permissible limit, indicating that, although Ca-based amendments show considerable potential for in situ remediation of Tl–Cd co-contaminated paddy soils, further optimization and additional measures are required to achieve safe production.