Algicidal effects of four Chinese herb extracts on bloom-forming Microcystis aeruginosa and Chlorella pyrenoidosa

Extracts from four Chinese herbs, Phellodendri chinensis cortex, Artemisia annua L., Scutellaria baicalensis G. and Citrus reticulate peel were tested for their algicidal effects on Microcystis aeruginosa and Chlorella pyrenoidosa. The results showed that M. aeruginosa was more susceptible than C. pyrenoidosa. The growth of M. aeruginosa was significantly inhibited (p < 0.05) by the four herb extracts. Among the four herbs, P. chinensis cortex and S. baicalensis had the greatest inhibitory effects on M. aeruginosa, followed by C reticulate peel and A. annua. The 50% effective concentrations (EC50) of S. baicalensis, P chinensis cortex, C. reticulate peel and A. annua were 0.87, 0.88, 5.27 and 1 1.16 gherb L-1, respectively. The growth of C. pyrenoidosa was moderately inhibited by the herb extracts individually. The EC5o concentrations for S. baicalensis, P. chinensis cortex, C. reticulate peel andA. annua were 8.67, 11.67, 12.81 and 12.44 g herb L-1', respectively. Extract from S. baicalensis displayed stronger algicidal effects on C. pyrenoidosa than the other three herbs, although no lethal effect on C. pyrenoidosa was observed during the cultivation period. Compared with corresponding individual extract at the same dosage, the binary mixtures of the four herb extracts enhanced the algicidal effects on M. aeruginosa. The maximum inhibitory rates of all binary mixtures of the four herb extracts were all above 92% during the 10-day incubation. The results demonstrate that Chinese herbs, such as P. chinensis cortex or S. baicalensis and their combinations, could offer an effective alternative for mitigating outbreaks of harmful algal blooms in water bodies.