<p><i>Bacillus thuringiensis</i> (Bt) protein released from transgenic crops and their subsequent complexation with heavy metals pose potential ecological risks that remain inadequately assessed. Understanding the interfacial behavior of these complexes is essential for predicting their mobility and bioavailability in soils. Thus, this study investigated the co-adsorption of Bt protein (Cry1Ac) with Zn²⁺ and Cd²⁺ onto soil minerals (SiO₂ and Al₂O₃) using dissipative quartz crystal microbalance (QCM-D). Results showed that the adsorption capacity reached a maximum at pH 6. The increased ionic strength suppressed adsorption on the negatively charged SiO₂ surface, but enhanced adsorption on the positively charged Al₂O₃ surface. Furthermore, the maximum equilibrium sorption capacity, determined from isotherm analysis, was significantly higher for the Cry1Ac-Zn²⁺ (2.957 × 10^–3&#xa0;mg·cm⁻²) than for the Cry1Ac-Cd²⁺ complex (7.250 × 10^–4&#xa0;mg·cm⁻²) the Al₂O₃ surface. However, the opposite trend was observed on the SiO₂ surface. The analysis of the adsorption mechanism revealed that the primary driving force was electrostatic interaction between mineral surfaces and Cry1Ac-Cd²⁺/Zn²⁺. Furthermore, the formation of complexes between the metal ions and the protein, potentially leading to metal ion bridging and subsequent bilayer adsorption, constituted a significant secondary mechanism contributing to the overall adsorption capacity and layer structure. These findings highlight the critical role of mineral surfaces in modulating the transport and potential bioavailability of heavy metals in the presence of Bt proteins. The study provides key parameters for improving risk assessment of heavy metal mobility in areas cultivated with transgenic Bt crops, supporting more accurate evaluation and mitigation of associated ecological impacts.</p> Graphical Abstract <p></p>