Study On Environment-Benign HABs-Inhibitors Based On Allelopathy

Nowadays,harmful algae blooms(HABs) is a worldwide phenomenon that has led to the deterioration of aquatic environments,prejudicing the many uses to which the water is put,and the development and application of algicides has been considered as one of the potential methods to control HABs availably.Based on the allelopathy and using algicidal test and ecological safety analysis of some natural plant materials, seven HABs-inhibitors showing strong algal inhibition and low risk for aquatic environment were developed,and the effects of environmental conditions and sorbents on the algicides were studied.Meanwhile,the mechanisms of algal inhibition have been studied by means of the research to the algal physiology and biochemistry. The dissertation provides the basic knowledge for further application of these algicides.The main results of this study were as follow:1.According to the allelopathy relationship,several materials with strong algal inhibition have been screened out from fifteen species of familiar vegetation according to the inhibitory rates(IR),the inhibitory time,the effective inhibitory concentrations and so on.As for a red-tide causing alga-Alexandrium tamarense strain DH01,the most effectual inhibitory materials were found to be Fructus Mume, Rhizoma Coptidis,Radix et Rhizoma Rhei,green tea,Semen Arecae,Folium Isatidis, with the 1 d IR at concentration 1 g L^-1 from 90.13%to 100%;followed by red tea, Radix Isatidis,Radix Sophorae Flavescentis,Herba Houttuyniae and Fructus Carpesiim,which 1 d IR was more than 70%(74.77 - 88.31);moreover,the high IR (90 - 100%) could last at least 5 days.However,Fructus Quisqualis couldn't inhibit ATDH01.The algal inhibition test showed that herb combinations such as Radix Isatidis + Radix Sophorae Flavescentis,Radix Isatidis + Herba Houttuyniae,Herba Houttuyniae + Radix Sophorae Flavescentis and so on inhibited algae more effectively than that these herbs individual.In addition,the residua of green tea dunked many times, having still good algicidal effect,should be paid attention to because it may be a cheap resource of algicides. The inhibition of six familiar red-tide causing algae by garlic solution were researched,and the results showed that garlic solution can strongly inhibit A.tamarense strain DH01,Scrippsiella trochoidea strain XM01,A.catenella strain DH01and A.satoanum strain DH01 with an effective concentration 0.04%,but it endows no inhibition to A.minutum strain TW01 and Chaetoceros muelleri.Moreover, diallyl trisulfide was also found the inhibition to ATDH01 and the effective concentration was 1 mg L^-1.Both garlic solution and diallyl trisulfide can inhibit algae fast,generally,the algal inhibitory rate were more than 90%after 3 hours experiment at the effective concentrations.2.The mechanisms of garlic algicide were also clarified.A.tamarense strain DH01 was used as the model alga to study the effect of garlic solution and diallyl trisulfide on the algal physiology and biochemistry.The results showed that both garlic solution and diallyl trisulfide at the concentrations tested could decrease the relative contents of key components in algae such as protein,chlorophyll and carotenoids.With the increase of the concentrations of garlic solution or diallyl trisulfide,the activity of algal catalase increased also.By contrary,the activities of superoxide dismutase and anti-superoxide anion free radical in the algae of test groups were mostly lower than the control with a fluctuation.In general,garlic solution and diallyl trisulfide could significantly decrease the photosynthetic rate and increase the respiratory rate.It can be inferred that garlic solution and diallyl trisulfide can inhibit algal mobility and even bring to death by changing the components of cells and making the algal metabolism abnormal.In addition,the algicidal effect of garlic solution was steady;it reduced a little even if garlic solution was boiled in 100℃for one hour.Indeed no significant difference of IR values was found among times or temperatures for garlic solution store.3.The ecological safety of these algicidal materials has been assessed using 24-h LC₅₀ values obtained in the growth tests of three familiar species of algae,the toxicity tests for three species of zooplanktons,two species of juvenile prawns and two species of juvenile fish.The results showed that the growth of Chlorella sp.,Isochrysis galbana and Chaetoceros muelleri were not affected by diallyl trisulfide in 96 hours,even the concentration was 10 mg L^-1;and likewise,the garlic solution(0.32%) couldn't inhibit Chaetoceros muelleri.The toxicity of garlic solution on the aquatic organisms can be ranked from weak to strong as the population of Brachionus plicatilis, Pagrosomus major juveniles,Moina mongolica daday,Plectorhinchus cinctus juveniles,Brachionus plicatilis(same age),5-day Artemia parthenogenetica,Penaeus monodon juveniles,Litopenaeus vannamei juveniles;and the rank for diaUyltrisulfide was Pagrosomus major juveniles,Moina mongolica daday,Brachionus plicatilis (same age),Plectorhinchus cinctus juveniles,the population of Brachionus plicatilis, 5-day Artemia parthenogenetica,Penaeus monodon juveniles,Litopenaeus vannamei juveniles.Otherwise,the resistance of Litopenaeus vannamei juveniles to the algicides can be ranked from strong to weak as green tea,Semen Arecae,Rhizoma Coptidis, diallyl trisulfide;and the rank for Penaeus monodon juveniles was Cortex Fraxini, Herba Houttuyniae,Semen Arecae,Rhizoma Coptidis,green tea,Fructus Carpesii, Semen Torreyae,Radix Isatidis,Fructus Mume,Radix Sophorae Flavescentis,Radix et Rhizoma Rhei,diallyl trisulfide.The ratio of efficiency to safety(RES),an integrative issue used first time in the paper considering the inhibitory effect,toxicology and cost of algicides,can help for the choice of cheap safe algicides.On the whole,the seven materials - green tea, garlic solution,diallyl trisulfide,Cortex Fraxini,Herba Houttuyniae,Semen Arecae and Rhizoma Coptidis - were good algicides with low risk for the aquatic environment.4.The usages of algicides have been elucidated according to the algicidal effects of various shapes such as water extract,dry powder and freeze-dried powder,the effects of sorbents and carriers on the algicides and the algicidal cost.Several algicides have been made and applied to control the algal bloom simulated in laboratory. Furthermore,the reasonable methods and conditions for the application of algicides were suggested.Firstly,the crude extract of Chinese herbs could inhibit algae a little faster than the dry powder,but the latter's inhibitory effect lasted longer than the former.The herb inhibitors using the powder of aloe(Aloe vera L.var.chinensis (Haw.) Berg.) or kelp(Laminaria japonica) as the sorbents have high IR values because they can suspend long.Secondly,the garlic algicides using pumice or gauze as the carriers had as much as the IR value of the garlic solution,but showed lower IR value using pottery granule.Although freeze-dried powder of garlic algicides have higher IR value than the fresh garlic solution(about 10%more),fresh garlic solution was still considered as much more practicable one with its low cost and short time of production.Finally,it could inhibit algae fast and expediently by pulling the bag filled with garlic algicide through the water,as the bags made of gauze,filtration mesh or no woven fabric.