Utilization of environmental waste cyanobacteria as a pesticide carrier: studies on controlled release and photostability of avermectin.

Cyanobacteria (Cyb), an environment waste, was first utilized as a carrier for controlled release of avermectin (Av) and improvement of pesticide photostability. Microalgae powder prepared from Cyb blooms was characterized by elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), optical microscopy, and scanning electron microscopy (SEM). The globular morphology and the size (~3.5μm) of Cyb do not change significantly, with increase of roughness, after Av adsorption and Carbopol coating. Av manifests considerable binding affinity to Cyb in isopropanol and adsorption decreases in more polar solvents at 25°C. An extended release of Av from Cyb-Av in ethanol/water (v/v, 4:1) mixture was obtained and the release was further controlled by the Carbopol resin coated on Cyb-Av. Thicker Carbopol coating results in larger lag time (t(0)), slower release rate, and less total release amount. The release process was found to be controlled by a diffusion mechanism, but was strongly affected by polymer matrix-Av interaction and polymer relaxation. Finally, adsorbed Av on Cyb exhibits much greater UV-stability than free Av.