The Toxic Effects Of Two Kinds Of Polybrominated Diphenyl Ethers (PBDEs) On Four Species Of Marine Microalgae

As a new type of persistent organic pollutants (POPs), Polybrominated DiphenylEthers (PBDEs) has attracted scientists’ attention especially in a decade. PBDEs islipid soluble and can be accumulated in lipid and proteins. The bio-accumulation ofPBDEs indicates a potential damage to organisms. Phytoplankton is the first trophiclevel of marine food web and plays the key role in matter cycle and energy flux inmarine environment. The damage or negative effects on marine microalgae wouldultimately affect the equilibrium and sustainability of marine ecology. However, littleis known about the toxic effect of PBDEs on marine microalgae, especially on theinter-and intra-specific interactions between different species. We thus conduct thisresearch, aiming at eluminating the possible effects of different kinds of PBDEs onthe growth of different species of microalgae and on the interactions amongthem.Four species of marine microalgae: Platymonas helgolandica(Chlorophyta),Karenia Mikimotoi(Dinophyta),Heterosigma akashiwo(Rhaphidophyta) andIsochrysis Galbana Parke8701(Chrysophyta). The toxic effects of BDE-47andBDE-209on these microalgae are analyzed under controlled laboratory conditions,and results show that:Ⅰ.Acute toxic effects researchAcute toxic effects of BDE-47and BDE-209on four species of microalgae(1) The growth of K. Mikimotoi was stimulated by BDE-209（5mg/L）with lowconcentration and at the same time H. akashiwo was stimulated by BDE-209（0.5mg/L）, while the growth of target microalgae were inhibited by BDE-47;(2) The96h-EC50values of BDE-209for P. helgolandica, K. Mikimotoi, H.akashiwo and I. Galbana Parke8701are30.29mg/L、18.1mg/L、1.8mg/L、0.79mg/L,and the96h-EC50values of BDE-209were2.0mg/L、0.25mg/L、 0.046mg/L、0.016mg/L, respectively. Similar sensitivity was presented to the strss ofBDE-209and BDE-47, that was I. Galbana> H. akashiwo> K. Mikimotoi> P.helgolandica, and I. Galbana was the most sensitive one.Ⅱ.Subacute toxic effects research1. The effects of BDE-209and BDE-47on the ultra structure of K. Mikimotoiby TEM(1) The cell wall of K. Mikimotoi was thicken and cytoplasm vacuoles wereobserved when exposed to BDE-209and BDE-47, and plasmolysis occurred whenstressed by BDE-47. In the BDE-209stress group, thylakoids in chromatoplasts weredisconnected or destroyed, but the membranes of chromatoplasts were notdamaged;Both number and size of mitochondria increased, and some cristae ofmitochondria were dissolved; Pyrenoid became smaller, and sheathes diappeared. Inthe BDE-47strss group,no clearly structured thylakoids were found, and membranessystem of K. Mikimotoi were almost destroyed;Both the chromatoplast andmitochondria were damaged significantly in terms of decreased number ofmitochondria, dissolved cristae and broken membranes;Pyrenoids were not found inmicroalgal cells.(2) Different degree of damage was observed in groups when exposed to BDE-47orto BDE-209, and more serious damaged was presented the former one. And cellularorgans showed different sensitivity to the stress, and mitocondria and chloroplast weremore sensitive and nucleus was comparatively stable as compared to the others.2.Mechanisms of how BDE-209and BDE-47on the antioxidantenzyme(s)affecting target microalgae.(1) Four kinds of antioxidant enzymes relating to the microalgal detoxificationwere analyzed in K. Mikimotoi when exposed to sub-lethal concentration of BDE-209and BDE-47. Results showed that The activities of (gluthione peroxidase)GPx,(glutathione S-transferase) GST,(glutathione reductase)GR were stimulated firstlyand inhibited thereafter when exposed to during the experiment,but BDE-47restrained the activity of GPx, GST,GR and the concentration of（glutathione）GSHthrought out the whole experiment. (2) GSH in K. Mikimotoi was greatly inhibited by either BDE-209or BDE-47,and its change was more sensitive as compared to the other three index, inferring thatit be considered as the biological indicator to detect PBDEs pollution in marineecosystem.3. Effects of BDE-47and BDE-209on the population growth of K. Mikimotoiand H. akashiwo.(1) The population variations of K. Mikimotoi and H. akashiwo were regressed bylogistic equation. In mono-cultured conditions, the time of growth phase andstationary phase, population intrinsic growth rate (r) and environment carryingcapacity (K) varied from different initial densities of K. Mikimotoi and H. akashiw.With the increase of initial densities, the time of growth phase and stationary phasewas shortened.(2) The initial biomass ratio of K. Mikimotoi and H. akashiwo (H: K) influencedthe competition between them in co-culture. When H: K=4:1and1:1, H. akashiwosurpassed the growth of K. Mikimotoi and played the dominant role, and K. Mikimotoichanged to be dominant in the co-culture when H:K=1:4in the co-culture.(3) When exposed to BDE-47and BDE-209stress, the interactions between K.Mikimotoi and H. akashiwo differed greatly to that in the control without pollutants’addition. Both of the microalgae were stimulated when exposed to BDE-209stress ascompared to the control. In groups of BDE-47exposure, low concentration ofBDE-47stimulated both the microalgal when H:K was1:4, but significantly negativeeffects were observed on them when H:K were1:1and1:4.