Research Of Effects Of Microcystins On Aquatic Plant Iris Pseudacorus L. And Its Degradation Characteristics

Cyanobacterial blooms not only poses a serious harm to the ecosystem,but also adversely affects the growth and development of aquatic animals and plants.And human health can be threatened by cyanobacterial toxins through food chain.Emergent plants,such as Phragmites australias Trin.,Iris pseudacorus L.?calamus?and Canna indica L.are often directly contacted with water and their growth and survival are threatened by algal toxins.Therefore,it is of great significance to study the effects of microcystins on aquatic plants and the degradation of microcystins.In this paper,the effect of Microcystis aeruginosa crude extract which contains various toxins and cell substances on the germination of aquatic plant calamus was studied firstly.The 3D-fluorescence spectrum displayed that the crude extract mainly containing fulvic acid like and humic like organic compounds and some exopolysaccharides,as well as a little cellular metabolites with carboxyl.The crude extract had significant inhibitory effect on seed germination.The germination rate was only 10%after being treated by 221?g/L microcystin-LR?MC-LR?.It also could inhibit the increase of fresh weight of and growth of root and leaf,and showed obvious dosage effect.During the germination stage,the crude extract could cause excessive accumulation of H₂O₂?22.9 mmol/g-prot?and resulted in oxidative stress on plants.Then seedlings enhanced activities of catalase?CAT?,peroxidase?POD?and superoxide dismutase?SOD?to resist this stress.Toxicity exposure test of MC-LR on calamus seedlings showed that MC-LR could obviously inhibit the elongation of leaf length and the increase of leaf area.MC-LR damaged the integrity of cell system and resulted in an increase of leaf conductivity.And it also inhibited the synthesis of leaf pigments.Low concentrations of MC-LR made plants form defense mechanism and elongate root and enhance root activity to absorb nutrients for their normal growth.But high concentrations of MC-LR exceeded the tolerance of plants and inhibited the growth of roots.The presence of MC-LR also affected the ability of calamus to remove nitrogen and phosphorus in water.As the main source of nitrogen,the removal rate of NO₃^--N was 63.53%in the presence of100?g/L MC-LR,which led to the increase of pH,and indirectly inhibited the growth of plants.Four kinds of advanced oxidation processes?UV?UV/H₂O₂?O₃ and O₃/H₂O₂?were used for MC-LR degradation tests.The removal efficiency of UV on MC-LR was remarkable,and the addition of H₂O₂ could significantly reduce the UV dosage required for the reaction.MC-LR could be completely removed through the synergistic effect of these two processes within 15 min,but the biotoxicity of the products was greatly improved after degradation because of the production of small molecular organic compounds which were more sensitive to luminescent bacteria.The degradation of MC-LR by O₃ was a transient reaction.60%MC-LR could be removed by 0.125 mg/L O₃ in 2 min and the biotoxicity of the products decreased.The degradation of MC-LR by O₃ was a transient reaction.60%MC-LR could be removed by 0.125 mg/L O₃ in 2 min and the biotoxicity of the products decreased.The removal efficiency of MC-LR by O₃/H₂O₂ system increased with the increase of O₃ dosage.However,the addition of H₂O₂ caused an increase of biotoxicity.Among the four processes,O₃/H₂O₂ was the most efficient.Moreover,The removal efficiency of UV/H₂O₂ on MC-LR which in the crude extract was only related to UV irradiation dosage.And UV/H₂O₂ could effectively remove other components of the crude extracts so then reduce the whole biotoxicity of the solution.