The values of dissolved oxygen (DO) and pH in the control and treatments had little change during the 48-hour experiment period, fluctuating from ÷ and ÷ mg L-1 , respectively, and they were still good conditions for growth. Finally, these results prove clearly that the ethyl acetate fraction is more toxic to the freshwater cladoceran than the ethanol extract. | Vietnam Journal of Science and Technology 56 (2C) (2018) 36-42 ACUTE TOXICITY OF THE ETHANOL EXTRACT AND ETHYL ACETATE FRACTION OF EUPATORIUM FORTUNEI TO DAPHNIA MAGNA Pham Thanh Nga1, 2, *, Dao Thanh Son3, Vo Thi My Chi3, Le Thi Phuong Quynh4, Nguyen Tien Dat5, Duong Thi Thuy6, Dang Dinh Kim6 1 2 Hanoi National University of Education, 136 Xuan Thuy, CauGiay, Ha Noi Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, CauGiay, Ha Noi 3 Ho Chi Minh City University of Technology, 268 Ly Thuong Kiet, , Ho Chi Minh City 4 5 Institute of Natural Products Chemistry, VAST, 18 Hoang Quoc Viet, CauGiay, Ha Noi Center for Research and Technology Transfer, VAST, 18 Hoang Quoc Viet, CauGiay, Ha Noi 6 Institute of Environmental Technology, VAST, 18 Hoang Quoc Viet, CauGiay, Ha Noi * Email: Received: 9 May 2018, Accepted for publication: 20 August 2018 ABSTRACT Previous studies have shown that the crude ethanol extract and its ethylacetate fraction of the plant Eupatorium fortunei Turcz strongly inhibited the growth of a harmful freshwater cyanobacterium Microcystis aeruginosa. However, the perspective of using these plant extracts as alternative algicides takes into account their potential risks to other species in aquatic ecosystems, including Daphnia magna. The current study presents the acute toxicity of the extracts to D. magna. The median lethal concentrations, immobilizing 50 % of D. magna, (LC50) after 24 and 48 h of the ethanol extract were 247 and 183 mg L-1, respectively. In the exposure to ethyl acetate fraction, the values of 24h-LC50 and 48h-LC50 were 47 and 13 mg L-1, respectively. The values of dissolved oxygen (DO) and pH in the control and treatments had little change during the 48-hour experiment period, fluctuating from ÷ and ÷ mg L-1, respectively, and they were still good conditions for growth. Finally, these results prove clearly that the ethyl acetate fraction
