Study On The Inhibitory Effect On Heterosigma Akashiwo Of Magnetic Chitosan Composite Microsphere

For the past few years, the harmful red tide frequently occurs on a global scale.In the occurrence of red tide, red tide organisms secrete toxic substances or consumethe dissolved oxygen in water, resulting in fish and other aquatic organisms to deathbecause of poisoning or suffocation, which has a serious impact on aquaculture andthe quality of aquatic products even threat to human health. Consequently, how tocontrol the red tide is extremely urgent.This research is designed to firstly study the preparation of three antialgal agentmaterials and their inhibitory effects to Heterosigma akashiwo. The antialgalperformance was evaluated by the lowest dosage, rare earth residues and recyclability,and the optimal antialgal material was confirmed as Magnetic Chitosan-Rareearth-Clay composite microsphere （It was abbreviated as MCRC）. Then thepreparation conditions and the best combination factors which affected the antialgaleffect were discussed by orthogonal experiments, and the MCRC was characterized.Finally, the inhibition mechanism was initially investigated via both measuring thechanges in the contents of chlorophyll a, soluble protein, soluble sugar, MDA, therelative conductivity, OD₂₆₀and the effects on the activities of antioxidant enzymesystem SOD, POD and CAT. The results are as follows:Through comparative studying, the antialgal percentage comes up to80%withthe MCRC dosage0.8g/L and in24hours. Lanthanum ion residue is77μg/L and otherrare earth ions are almost not residual, which shows that MCRC has the minimumsecondary pollution to the environment. MCRC is easy to recycle with its magneticproperty and the antialgal percentage of MCRC is still more than70%after beingreused for three times. So MCRC is determined as the optimal antialgal material.The optimum preparation conditions of MCRC are as follows: chitosan:clay:rareearth ratio of10:5:1, chitosan and rare earth ions in reaction pH7, clay and rare earthreaction time8h and the Fe₃O₄dosage30mL. The best combination factors which affected the antialgal effect on Heterosigma akashiwo are listed: the initialconcentration2×10⁶cells/mL, the algae solution pH7, the MCRC dosage0.8g/L andreaction time30h.The figure of FT-IR shows some aminos participate in the crosslinking reaction,some crosslinking reactions occurred with C₃-OH and epichlorohydrin, and chitosanis complexed with cerium ions. DSC thermogram revealed the thermal stability of theMCRC is less than the chitosan powder. XRD shows that the diffraction peaks aroundthe MCRC crystalline2θ angle at10°and20°are almost disappeared, which indicatesthat the crystallization degree of chitosan decreases after cross-linking reaction.MCRC has the characteristic diffraction peaks of the clay and Fe₃O₄while there aresome changes in the intensity of these diffraction peaks, which shows that thecrystallization structures of clay and Fe₃O₄are changed in the cross-linking reaction.The particle size analysis shows the particle size of MCRC is443μm in average. Thesaturation magnetization of MCRC is4.6585emu/g and there is superparamagnetismin MCRC.Under the low concentration （0.4g/L） of MCRC treatment, chlorophyll a andsoluble protein contents of algal cells is lower than the control group, while thesoluble sugar content is still higher than the control group. Under the higherconcentration （0.8g/L,1.2g/L） of MCRC treatment, chlorophyll a, soluble protein andsoluble sugar contents show the overall trend of increase and then decrease and theinhibition effect is strengthened with the extension of treatment time. MCRC indifferent concentrations makes the MDA content in the algal cells increased invarying degrees, Meanwhile, the relative conductivity and OD₂₆₀in the surroundingenvironment is also increased, which indicate the lipid peroxidation is observed in thecell membrane, further more the cell membrane permeability increases. In the MCRCtreatment, the activities of three enzymes SOD, POD, CAT were increasing at firstand then decreasing in general with the extension of treatment time, which shows thatthe three enzymes play a protective effect on the algal cells, but increasingconcentration of MCRC and prolonging treatment time have bad influence on theincreasing algal cells, which beyond the limits of self-protection in the cellular defense system, so that the activities of three protected enzymes decrease eventually.This rearch aims to prepare a kind of magnetic composite microspheres with thecombination of chitosan, clay and rare earth. It has excellent antialgal effect, lowpollution and better recycle, which takes advantages of both the power neutralizationand adsorption bridging of the organic and inorganic flocculants and the toxic effectsof rare earth on the algal cells. It will provide a theoretical basis for the chitosan tocontrol red tide and the development of new algecide, as well as the new ideasforcontrolling red tide.