Continuous-release beads of natural allelochemicals for the long-term control of cyanobacterial growth: Preparation, release dynamics and inhibitory effects

Abstract

The effects of allelochemicals on cyanobacterial blooms have been observed for more than 20 years; however, the use of these compounds, usually involving a "direct-added" mode, has clear disadvantages, such as a short activity period or temporarily excessive localized concentration. Here, a simulated-allelopathy mode to facilitate the application of allelochemicals was proposed and tested on Microcystis aeruginosa. The continuous-release beads of 5,4'-dihydroxyflavone (DHF) were constitutive of a polymer matrix and showed a high drug-loading rate (47.18%) and encapsulation efficiency (67.65%) with a theoretical release time of approximately 120 d. Cyanobacterial growth tests showed that the DHF beads had long-term inhibition effects (>30 d), whereas those of "direct-added" DHF to cells lasted a maximum of 10 d. The beads also continuously affected the superoxide dismutase, catalase, and lipid peroxidation of M. aeruginosa. The inhibitory effects of DHF beads on cyanobacterial growth increased as initial cell densities of M. aeruginosa decreased, suggesting that the beads inhibit cyanobacterial activity more effectively in the early bloom phase. Consequently, the anti-cyanobacterial beads represent a novel application mode of allelochemicals with long-term inhibitory effects on cyanobacterial growth. Our study demonstrates that the successful application of allelochemicals offers great potential to control harmful cyanobacterial blooms, especially at the initial stage of development.

Keywords: 5,4′-dihydroxyflavone; Allelochemical; Continuous-release bead; Cyanobacterial bloom control; Inhibition efficiency; Release kinetics.