Dual pH responsive azoxystrobin controlled release microspheres constructed from porous calcium carbonate and its biosecurity

Stimuli-responsive pesticide controlled release systems provide a powerful strategy for improving pesticide utilization efficiency and reducing environmental pollution. In this study, based on the preparation of porous calcium carbonate microspheres (CaCO₃) by co-precipitation method, porous calcium carbonate microspheres loaded with pyrimethanil (Az) (Az/CaCO₃) were obtained by impregnation and adsorption method, and the surface of the composite microspheres was further encapsulated with a tannic acid (TA)-Cu²⁺ complex, which constructed a pyrimethanil controlled-release system with dual pH-responsiveness (Az/CaCO₃@TA-Cu). Physicochemical performance studies showed successful preparation of Az/CaCO₃@TA-Cu microspheres with 16.42% drug loading. The results of simulated release studies showed that Az/CaCO₃@TA-Cu had good pH-controlled release properties, with a cumulative release rate of 36.99% in phosphate buffer solution at pH=7 for 96 h, whereas the cumulative release rates at pH=5 and pH=9 were 74.32% and 58.79%, respectively. Mycelial growth rate experiments showed that Az/CaCO₃@TA-Cu had a better inhibitory effect on the growth of Fusarium graminearum, with median inhibitory concentrations of 6.58 and 3.28 times that of pure Az and Az/CaCO₃. In addition, wheat germination and zebrafish survival statistics showed that Az/CaCO₃@TA-Cu exhibited superior biosafety relative to Az/CaCO₃ and pure Az.