The main objective of this study was to confirm and estimate the algal inhibiting effects of the ethanol and ethyl acetate E. fortunei extracts at concentrations of 500 mg.L- in some natural water samples collected from Hoan Kiem and Lang Lakes. The results of this work may be useful for controlling the toxic cyanobacterium bloom in natural aquatic ecosystem.
HNUE JOURNAL OF SCIENCE Natural Sciences, 2020, Volume 65, Issue 4A, pp 11-20 This paper is available online at http://stdb.hnue.edu.vn EFFECT OF PLANT EXTRACTS FROM Eupatorium fortunei TURCZ ON THE GROWTH OF PHYTOPLANKTON COMMUNITIES IN NATURAL WATER SAMPLES COLLECTED FROM HOAN KIEM AND LANG LAKES Pham Thanh Nga1*, Le Thi Phuong Quynh2, Nguyen Tien Dat3 and Dang Dinh Kim4 Hanoi National University of Education Institute of Natural Products Chemistry, Vietnam Academy of Science and Technology Center for Research and Technology Transfer, Vietnam Academy of Science and Technology Institute of Environmental Technology, Vietnam Academy of Science and Technology Abstract This study presents the inhibited effect of these extracts on the growth of Microcystis and phytoplankton communities in natural water samples collected from Hoan Kiem and Lang Lakes in a 10-day experiment By using chlorophyll a concentration analysis, the ethyl acetate extract at 500 mg L-1 indicated the highest toxicity with inhibition efficiency (IE) reaching 49.90 - 58.83 in Hoan Kiem and Lang’s natural water samples, respectively; following by the CuSO 4-sample at mg L -1 with IE of 44.90 and 54.60% and the E-ethanol sample with IE of 34.70 and 48.42 % The maximum inhibition of Microcytis growth was observed for the ethyl acetate extract during the experiment However, by cell counting methods, the ethanol extracts showed selectively toxic to Microcystis in comparison with other phytoplankton communities in natural water samples collected from both lakes It had the IE values around 43.43 - 46.44% for Microcystis genus which was much higher than those for other species such as green algae and silica algae (27.67 - 34.68 %) The ethyl acetate extract and CuSO 4-samples did not indicate significant differences in the inhibition effects to the species in the communities with IE from 46.26 - 59.95% and 42.78 - 51.37%, respectively The results proved that the ethanol extract should be further investigated to use as an algaecide to control algal bloom in fresh water body Keywords: Eupatorium fortunei Turcz, Microcystis genus, phytoplankton communities, Hoan Kiem Lake, Lang Lake, inhibitory efficiency (IE) Introduction Eutrophication is a widespread problem in aquatic ecosystems around the world due to sewage and surface run-off increased significantly the amount of nutrients (mainly N and P) [1] It significantly affects water quality and induces off-flavor problem Moreover, cyanobacterial blooms usually break out along with release of cyanotoxins, which cause a series of adverse effects such as decreasing water quality and biodiversity, and illness in animals and humans [2, 3] The water blooming can produce hepatotoxin and neurotoxins which may lead to headache, fever, abdominal pain, nausea, vomiting and even cancer [1] Therefore, it is of great importance Received March 30, 2020 Revised May 8, 2020 Accepted May 12, 2020 Contact Pham Thanh Nga , e-mail address: phamthanhnga.russia@gmail.com 11 Pham Thanh Nga, Le Thi Phuong Quynh, Nguyen Tien Dat and Dang Dinh Kim to inhibit the growth of cyanobacteria, especially Microcystis genus in eutrophic waters Until now, about 100 species of freshwater cyanobacteria have been discovered in 40 genera of which Microcystis, Anabaena, Aphanizomenon, Oscillatoria, Nostoc and Cylindrospermopsis are the most frequently encountered in water blooms Microcystis genus is the most common cyanobacteria, it is toxic to humans, animals and other aquatic organisms [4] The discovery and use of natural compounds that feature selective toxicity towards phytoplankton communities and are nontoxic to other aquatic species, have been a significant advance in the management of aquatic ecosystems In recent years, the extracts of many plants have been reported to inhibit the growth of algae For example, barley straw has been reported for having algal-inhibiting properties by authors [5, 6] Other natural compounds have also been screened to control algal bloom, including extracts of banana and mandarin skin [7], and the family Papaveraceae [8] Of these methods, rice straw extract is the most widely applied and has shown positive results in laboratory testing [9] However, considerable management is required when using this product, and its long-term ecological effects have yet to be ascertained Recent laboratory and outdoor exposed tests by the present study’s research group such as Boylan D [10], Jancular [8], Ding YL [11], Zhou [12, 13] have also shown that the cyanobacteria bloom may be successfully repressed by using plant extracts Among the extracts, Eupatorium fortunei showed the strong anticyanobacteria properties at the concentration of 500 mg.L - with the inhibition efficiency (IE) of 95.5 % which were comparable with that of CuSO at mg.L- (IE of 81.7 %) and other plant extracts (Chromolaena odorata, Cyperus rotundus, Callisa fragrans, Garcinia mangostana, Morus alba) [14-16] Moreover, the extract was higher toxic to M aeruginosa (IC50 of 119.3 g L-1) than to other green algae such as Chlorella vulgaris (IC50 of 315.1 mg.L-) In another investigation, the toxicity of the extracts from E fortunei to duckweeds (Lemna minor and Spirodella polyrhiza) was tested as representatives of sensitive non-target aquatic organisms to evaluate environmental safety [17].The significant growth inhibition of the extract on M aeruginosa was reported at the 500 g.L- while L minor was slightly affected by the extracts at the same concentration with IE of 25 % and S polyrhiza was stimulated to about % through fresh weight determinations [17] Their tested potential risks to other species in aquatic ecosystems, including Daphnia magna showed that 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-, respectively In the exposure to ethyl acetate fraction, the values of 24h-LC50 and 48h-LC50 were 47 and 13 mg.L-, respectively [18] The results proved that the extracts from E fortunei indicated selectively the inhibition effects on Microcystis aeruginosa among other species The main objective of this study was to confirm and estimate the algal inhibiting effects of the ethanol and ethyl acetate E fortunei extracts at concentrations of 500 mg.L- in some natural water samples collected from Hoan Kiem and Lang Lakes The results of this work may be useful for controlling the toxic cyanobacterium bloom in natural aquatic ecosystem Content 2.1 Material and Method 2.1.1 Preparation of different extracts from E fortunei Experimental setup is similar to the experiment published by the authors (Pham Thanh Nga, 2018) The aerial parts (leaves and stem) of Eupatorium fortunei; collected in January 2016 from Hoa Binh province and Soc Son district, Ha Noi, Viet Nam; were used for the experiment The cleaned material was dried at room temperature to constant weight, cut into small pieces and then ground into powder Then, the powdered material was immersed separately in ethanol solvents 96 % (5L × times) and subsequently macerated for two days at room temperature (23 ± 25 0C) The combined extracts were concentrated under vacuum to 12 Effect of plant extracts from Eupatorium fortunei Turcz on the growth of phytoplankton communities… obtain the crude residue This extract was resuspended in distilled water (2 L) and successively partitioned in hexane (1 L × times) and ethyl acetate (1L × times) Ethanol, ethyl acetate and hexane solvents were products of Merck (Germany) The ethyl acetate organic layers were concentrated to give ethyl acetate fraction, respectively These extracts were kept at -5 0C for two weeks until use [16-18] 2.1.2 Preparation of different water samples Water samples of Hoan Kiem and Lang lakes were taken in March 2017 and September 2017 and transferred to the laboratory just before conducting experiments At the time of the experiment period, the outdoor temperature fluctuated about 27-28 0C, the lake surface was green- blue which was the signer of cyanobacteria bloom Examining these samples under the BX51 fluorescence electron microscope showed that the Microcystis species was clearly dominant in both samples After collecting samples, the samples were filtered through the net to remove garbage and suspended particles, then evenly poured 5L into glass jars for the laboratory scale Adding plant extracts and copper sulphate sample to the glass jar according to at the 500 mg.L- and mg.L- concentrations, respectively, then place these jars at room temperature under natural light for 10 days The experimental formulas studied include: the control samples (the sample contained only lake water), CuSO samples (the sample of lake water supplemented with CuSO at the concentration of mg L- ) and the plant extract samples like E-Ethanol-500 and E-Ethyl-500, added the ethanol and ethyl acetate extracts of Eupatorium fortunei at the concentration of 500 mg L- (from 2.1) Each experimental formula was repeated times, monitored for 10 consecutive days The samples were stirred times daily Chlorophyll a content analysis and cell density measurement for assessment of effect of plant extracts on natural phytoplankton assemblage The chlorophyll a content in samples was determined after 0, 3, and 10 days of the incubation according to Lorenzen (1967) which was similar to the experiment with plant extracts published by the authors [15-17] The cells fluorescence electron microscope at the beginning and last days of the experiment One milliliter of samples was loaded on a Sedgewick- Rafter (20 nm × 50 nm × nm) counting cell chamber and was counted under the BX51 electron microscope [19] 2.1.3 Statistical analysis 2.2 Results and discussion All experiments were done in triplicate and the data were calculated as mean ± SE (standard error) and drawn by the software GraphPad Prism Statistical significance was accepted at a level of p < 0.05 2.2.1 Effect of plant extracts on the growth of phytoplankton in water samples collected from Hoan Kiem Lake in the laboratory scale According to the analysis of chlorophyll a content, the value of the control sample at the beginning (T0) was 25.34 ± 1.15 µg L - and increased continuously during 10 days of the experiment, on the last day it was as high as 34.32 ± 2.15 µg L - In contrast, samples with added plant extracts and copper ingredient, phytoplankton biomass decreases gradually On the first day (T0) the values were recorded in the CuSO 4, E-Ethanol 500 and E-Ethyl 500 samples is 24.89 ± 2.75; 25,95 ± 1,58 and 26,16 ± 1,37 µg L - , respectively, while at the end of the experiment, the chlorophyll a contents decreased to 18,91 ± 1,80; 22.41 ± 1.15 and 17.19 ± 1.75 µg L -, respectively According to Park's formula of growth inhibition (IE) [9] the IE values determined by chlorophyll a concentration was the highest 13 Pham Thanh Nga, Le Thi Phuong Quynh, Nguyen Tien Dat and Dang Dinh Kim Chlorophyll a Concentration , µg/L to the E-Ethyl-500 treatment, 49,91%, following by CuSO 4-5 sample (IE of 44,90 %) and the E-Ethanol 500 sample (IE of 34,70 %) Control - HK E-Ethanol-500 40.00 35.00 CuSO4-5 E-Ethyl-500 30.00 25.00 20.00 15.00 10.00 5.00 0.00 T0 T3 Time (days) T6 T10 Cell Density x 105 TB/mL Figure Effect of plant extracts on the growth of phytoplankton in water samples collected from Hoan Kiem Lake determined by chlorophyll a content (Laboratory scale) 35.00 Microcystis sp sp Microcystis VKL khác Other cyanobacteria Tảo lục agla tảo& silic Green silic agla Nhóm TVN Phytoplanton 30.00 25.00 20.00 A 15.00 10.00 5.00 0.00 Control-HK CuSO4-5 Cell Density × 105 TB/mL 35.00 E-Ethanol-500 E-Ethyl-500 Microcystis sp sp Microcystis VKLOther kháccyanobacteria Tảo Green lục tảo aglasilic & silic agla Nhóm TVN Phytoplankton 30.00 25.00 B 20.00 15.00 10.00 5.00 0.00 Control - HK CuSO4-5 E-Ethanol - 500 E-Ethyl- 500 Figure Effect of plant extracts on the growth of phytoplankton in water samples collected from Hoan Kiem Lake determined by cell density (Laboratory Scale) T0- the beginning (A) and T10- the end (B) In fact, phytoplankton communities in aquatic ecosystems are abundant and diverse with many different species and different morphologies Analysis of species composition at the first day (T0) (Figure 1) indicated that in the natural phytoplankton assemblage of Hoan Kiem lake, the Microcystis genus dominated with the proportion of 90 - 95%, green algae, blue-green algae 14 Effect of plant extracts from Eupatorium fortunei Turcz on the growth of phytoplankton communities… Chlorophyll a,Concentration µg/L and silica algae accounted for only ± 5% During the treatment process, in the control sample all species grew gradually, especially Microcystis sps with increasing from (10.91 ± 0.37) × 10 cells.mL-1 at beginning to (21.16 ± 1.27) × 10 cells.mL-1 at the end of experiment While biomass of Microcystis sps in other treatments significantly decreased in comparison with the control Cell density of the CuSO4-5 sample was just (11.77 ± 1.24) x 10 cells.mL-1; of the EEthanol 500 sample was (13.16 ± 1.12) x10 cells/mL and of the E-Ethyl 500 (11.93 ± 1.14) × 106 cells.mL- with the IE values of 44.40; 37.82 and 43.61 %, respectively In the experimental sample of copper sulfate exposure, there was no difference in the growth inhibiting effect between Microcystis species and other species groups such as green algae, blue-green algae and silicon algae (p > 0.05) The growth inhibition (IE value) under the CuSO4-5 treatment is 49.04 % and 46.26 % for Microcystis, phytoplankton respectively Similar results were observed with the E-Ethyl 500 sample, when the difference in the growth inhibition effect was not significant for all studied species (p > 0.05), the IE ranged from 42.78 to 46.99 % This result demonstrated that, like the copper sulfate treatment, the ethyl acetate extract did not selectively inhibit between Microcystis species and the remaining species in the samples However, the ethanol extract showed different inhibitory effect between Microcystis, cyanobacteria (with IE of 37.81 and 38.21%, respectively), green algae, silica algae which were recorded lower the IE value, just being of 27.67 % Control Ethanol- 500 18.00 16.00 CuSO4-5 Ethyl - 500 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 T0 T3 T6 T10 Time (days) Figure Effect of plant extracts on the growth of phytoplankton in water samples collected from Lang Lake determined by chlorophyll a content (Laboratory scale) At the beginning (T0), the study revealed that the biomass of water samples in Lang lake had a much lower than that of Hoan Kiem Lake, the chlorophyll a content in all samples was fluctuated ranging from 10.42 to 11.68 µg.L- (Figure 3) During the 10-day period, the control sample gradually increased biomass, on the last day the value increased slightly to 14.89 ± 1.30 µg.L-, while the remaining treatments decreased, and the greatest decrease was observed in the E-Ethyl-500 sample was 6.13 ± 0.94 µg.L- corresponding to the IE of 58.83 %, followed by CuSO4-5 sample with 6.76 ± 0.38 µg.L - and IE 54.60 % The lowest one was E-Ethanol 500 sample with 7.68 ± 1.36 µg.L- cholorophyll a content and the IE of 48.42 % The growth inhibition effect of the experimental samples collected from Lang Lake was higher than that of the Hoan Kiem water samples (p < 0.05) 15 Cell Density × 105 TB/mL Pham Thanh Nga, Le Thi Phuong Quynh, Nguyen Tien Dat and Dang Dinh Kim 20.00 Microcystis sp sp Microcystis VKL khác cyanobacteria Other TảoGreen lục tảo silic agla & silic agla Nhóm TVN Phytoplankton 18.00 16.00 14.00 A 12.00 10.00 8.00 6.00 4.00 2.00 0.00 Control - HL CuSO4-5 Cell Density ×105 TB/mL 20.00 E-Ethanol-500 E-Ethyl-500 Microcystis Microcystis sp sp VKLOther khác cyanobacteria & silic agla TảoGreen lục & agla tảo silic Phytoplanton Nhóm TVN 18.00 16.00 14.00 B 12.00 10.00 8.00 6.00 4.00 2.00 0.00 Control-HL CuSO4-5 E-Ethanol-500 E-Ethyl-500 Figure Effect of plant extracts on the growth of phytoplankton in water samples collected from Lang Lake determined by cell density (Laboratory scale), T0- the beginning (A) and T10- the end (B) The result of cell counting in all water Lang samples showed that there was a great difference in composition and proportion of species compared to those in Hoan Kiem water samples (Figure 4) Obviously, algal biomass in all Lang water samples was consistently dominated by Microcystis genus (67-70 %), following by other cyanobacteria (15-20%) and green algae, blue-green algae, silica algae which were just 5-10% The total number of phytoplankton fluctuated on the first day from (8.43 ± 0.97) × 105 to (9.07 ± 1.03) × 10 cells mL- On the tenth day, the cells of the control sample increased to (15.67 ± 1.05) × 105 cells mL- while these in the CuSO4 samples, E-Ethanol 500; E-Ethyl 500 extract treatments were reduced to (6.53 ± 0.45) × 105, (8.83 ± 1.30) × 105 and (7.96 ± 0.93) × 105 cells mL -, corresponding to the inhibition of biomass of total phytoplankton (IE) 58.33; 43.65 and 49.20 %, respectively Similar to the analysis on Hoan Kiem Lake water samples, the sample test in Lang Lake showed the selective inhibition of E-thanol-500 extract on Microcystis sp in the community compared with the CuSO compound and ethyl acetate extract In the copper sulfate sample at the concentration of µg mL-, all species were inhibited with IE values ranging from 55.15 ÷ 59.95 %, which was similar to the sample added the ethyl acetate extract (IE of 48 12 ÷ 51.37 %) There was no big difference in inhibiting effect between Microcystis strains and other algae in the environment (p> 0.05) in both treatments While the E-Etanol-500 treatment noted the inhibition rate (IE) to Microcystis and cyanobacteria ranged from 43.43 ÷ 46.44 % which was much higher to green algae, blue16 Effect of plant extracts from Eupatorium fortunei Turcz on the growth of phytoplankton communities… green algae, silicon algae (IE of just 34.68 %) (p> 0.05) Although the E-Ethyl-500 extract was more effective in inhibiting Microcystis strains, cyanobacteria and total phytoplankton than the E-Ethanol extracts However, this extract also showed toxic to other species in the ecosystem such as green algae and silica algae In addition, the ethyl acetate extract was harm to the freshwater cladoceran (Daphnia magna) [18] This suggested that ethanol extract can be applied as an algaecide to control algal bloom with a strong specific algicide potential in comparison with ethyl acetate fraction The density and composition of phytoplankton community in the study water samples were the main reason leading to the difference in the efficiency of using different extracts to control the bloom of microalgae in fresh water Comparing the experimental results inverstigated in both water samples of Hoan Kiem and Lang Lakes, this study had reported that the higher the initial cell densities of species in the samples were, the lower the inhibitory effect (IE) on their growth under exposure of the extracts were observed For example, the density of phytoplankton in Lang water was ranged from (8.43 ữ 15.67) ì 105 cells mL-, which is the lower compared to that of Hoan Kiem lake water (10.91 ± 0.37) x 106 cells.mL-, and the results was recorded the effectiveness higher inhibition on the development of Microcystis, cyanobacteria and phytoplankton communities 43.43 ÷ 51.37 % These factors greatly affected the biological experiment efficiency of evaluating the activity of natural extracts on the growth of cyanobacteria [20, 21] Similar results had been found by other authors including Lirong's et al [12, 13] The initial density of the research sample was lower as × 106 cells mL-, the effect of growth inhibition of the extracts was obviously shown after 48 hours of exposure and achieved the highest after 72 hours However, when the cell density increased up to × 107 cells mL -, the slight inhibitory effect observed in 24 ÷ 48 hours and after 36 hours with no any inhibitory effects Over the last two decades, as an alternative to synthetic algicidal agents, natural compounds have been tested for controlling harmful algae in aquatic systems [20] The test of plant extracts to control bloom of toxic microalgae in natural water samples was also researched by many authors [8, 9, 12, 13] In 2007, Jancular et al [8] tested the ethanol extract from Chelidonium majus to control the bloom in eutrophic swamp water with the dominant density of cyanobacteria and eukaryotic algae, especially Actinastrum sp., Dictyosphaerium sp., Mougotia sp., Nitzschia sp., Planktothrix agardhii The extract was preferred which had the potential to kill toxic microalgae very effectively, but also shows low toxicity to non -target species such as green algae, crustaceans and duckweed The effective inhibition of C majus extract could be explained due to the containing Quaternary compounds benzo [C] phenanthridine alkaloids (QBA) such as Coptisine, Magnoflorine, Protopine, Sanguinarine, Cheleryhtrine, especially Sanguinarine, Magnoflorine taking up the large proportion of 1.37 and 0.35% dry weight of C Majus roots Then, Zhou (2012) applied the extract from black wattle Acacia mearnsii in water samples collected from Jinjiang River, in Chengdu, China at a small scale with a study volume of 200 mL under the laboratory conditions (natural light and stable adjusted temperature of 25 oC [12,13] Results were measured based on chlorophyll a concentration and cell density The effective inhibition (IE) by cell counting reached 59% after 11 days of exposure However, after 14 days, the inhibitory effect dropped against to 29% (P < 0.05), compared to the control sample due to the decomposition of the plant extracts in the natural environment Based on the biodegradation ratios, the wattle and black wattle extracts showed similar levels of biodegradability About 50% of both extracts were biodegraded after just week After two weeks of the experiment, about 80% of the extracts had been biodegraded to prove its environmental safety The extracts from Acacia mearnsii (black wattle) contains significant amounts of water-soluble components called "wattle 17 Pham Thanh Nga, Le Thi Phuong Quynh, Nguyen Tien Dat and Dang Dinh Kim tannin" which had the ability to inactivate α-amylase, lipase and glucosidase [23] or may be associated with extracellular substances, interfering with the process of carbon and nitrogen mineralization there by reducing the source of nutrition for cyanobacteria growth resulting in deterioration of biomass [24] Zhou also investigated the effect of Wattle Extract on the optimization of phytoplankton population structure with the dominant species such as Pseudanabaenaceae, Cyclotella…and zooplankton alanoida, Cladocera, Cyclops in eutrophic water sample After experiment a significant decrease was observed in the number of these species, especially the small-sized zooplankton (< 1mm) Meanwhile, the number of larger zooplankton began to increase with the dominant species shifting to Calanoida, which favors cleaner water bodies However, this change was not recorded in the control, in which the total abundance of zooplankton was higher than the treatments The changes was explained due to the addition of plant extracts to the environment, which leads to a decrease in the number of cyanobacteria or Microcystis species, which make small aquatic animals such as Alonella sp., Chydorus sp., Trichocerca sp Centropyxis sp reduced by due to limited food source, resulting in an increase in the density of large-sized animals such as Cladocera Sp Other natural plant extracts have also been observed as having good inhibitory effects on cyanobacteria For example, Ball et al (2001) showed that decomposed-barley straw has a strong inhibitory effect on the growth of Microcystis sp at low concentrations (0.005%), with chlorophyll-a levels being around 10-fold lower than in untreated flasks Then, Park et al (2009) reported that rice hull extract and its pure compounds inhibited the growth of low concentrations of colonial M aeruginosa by 66% and 80%, respectively The study of the effects of plant extracts on nontarget aquatic species that share the same environmental habitat with cyanobacteria or Microcystis genus had shown positive results The ethanol extract seems to have positive antialgal properties due to the outstanding advantages compared with ethyl acetate extract, such as its high Microcystis inhibition efficiency [16], less toxic to C vulgaris, Lemna minor, Spirodela polyrhiza [17] Daphnia Magna [18] Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei Turcz demonstrated the strong inhibition effects on the growth of Microcystis aeruginosa [25, 26] Conclusions The present work indicated that by cell counting methods and analysis of Chlorophyll a concentration the ethanol extract of Eupatorium fortunei Turcz at 500 µg/mL showed higher selective potential ability to inhibit the growth of Microcystis genus, Cyanobacteria (IE of 43.43-46.44 %) than some other phytoplankton community like green algae, blue-green algae, silicon algae (IE of 27.67-34.68) in both Hoan Kiem and Lang water samples The effect of the ethanol extract on the physical parameters (pH, conductivity, DO, salty) and chemical water parameters (Ammonium (NH4 +) and Phosphate (PO43-), nitrate (NO3-), nitrite (NO2-) in natural water samples should be further investigated in our near future studies REFERENCE [1] Paerl H W, Otten TG, 2013 Harmful cyanobacterial blooms: causes, consequences, and controls Microbial Ecology, 65(4), 995-1010 [2] Panpan M., Haiyan P., Wenrong H., Zhongde L., Xiuqing L., Hangzhou X, 2015 Allelopathic effects of Ailanthus altissima extracts on Microcystis aeruginosa growth, physiological changes and microcystins release Chemosphere, 141, 219-226 18 Effect of plant extracts from Eupatorium fortunei Turcz on the 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Effect of plant extracts on the growth of phytoplankton in water samples collected from Hoan Kiem Lake determined by cell density (Laboratory Scale) T0- the beginning (A) and T10- the end (B) In. .. difference in the efficiency of using different extracts to control the bloom of microalgae in fresh water Comparing the experimental results inverstigated in both water samples of Hoan Kiem and Lang Lakes, ... µg.L- cholorophyll a content and the IE of 48.42 % The growth inhibition effect of the experimental samples collected from Lang Lake was higher than that of the Hoan Kiem water samples (p < 0.05)