Temperature responsive sustained-release microsphere for harmful algal bloom control: preparation, algicidal activity...

Temperature is one of the most important factors driving cyanobacterial harmful algal blooms (CHABs). However, existing algicide designs rarely consider the influence of temperature on algal growth. Novel temperature-responsive sustained-release microspheres (T-SRMs) of anti-algal 5,4'-dihydroxyflavone (DHF) were designed using n-heptadecane as the temperature-responsive material, which can adjust DHF release behavior in response to temperature. Compared to DHF direct application, T-SRMs showed higher inhibition rates against Microcystis aeruginosa and sustained inhibitory activity at various temperatures (15-25 °C). The theoretical inhibition time of T-SRMs substantially exceeds that of conventional SRMs, with the potential to cover the entire CHABs outbreak period and extend the duration of validity. T-SRMs can accurately regulate DHF release rate based on water temperature. When the temperature is higher than the melting point of n-heptadecane (22 °C), the phase transition of heptadecane significantly promotes the DHF release rate. Moreover, salinity had no significant effect on the DHF release behavior, and the temperature-responsive materials can be adjusted to linearly regulate the release of DHF, which is favorable for the wide application of T-SRMs in freshwater, brackish and salt waters with flexible temperature windows. In addition, the T-SRMs had no apparent toxic effects on Chlorella vulgaris, Daphnia magna and Danio rerio. Our study has an important scientific significance to achieve a more intelligent, accurate and efficient control of CHABs.