Researches On The Methods Of Monitoring The Microcystins In The Sediment

Nowadays, water eutrophycation has become a global environmental problem. In the eutrophicated water, algae growing in an abnormal way usually forms algal bloom, which is generally poisonous. Among the toxins produced by algae bloom, microcystins found in Microcystis aeruginosa,Anabaena flos-aquae, Oscillatoria rubescens and so on, take a major part. Recent years, the reported illness and death caused by microcystins have drawn the public attention. Many researches have been done on microcystins, including category, structure, toxin producing mechanism, toxicity and so on.Up to now, no definite conclusion has been made on the decomposition approaches of microcystin, but most reseachers believe that dilution, photolysis and microorganisms contribute to the decrease of microcystins in water body. Sediment is often considered to be the pool of contamination in water body. Whether microcystins are accumulated in sediment and how much does sediment contribute to the decreaes of microcystin? Such problems still hang in doubt. Limited by detecting method, there is little research on the accumulation, distribution, transference and translation of microcystins in the sediment. So a method was established here to monitoring microcystins in the sediment of Lake Dianchi. The main results were obtained as follows: 1. Researches on detecting microcystins in sediment by SPE-HPLCmethod: Nowadays, HPLC method, which can characterize and quantitate microcystins, is widely used to detect microcystins in water body and algae. In such methods, microcystins are often extracted by some solvents and enriched by SPE (solid-phase extraction) method before detected by HPLC, as the concentration of microcystins are very low in the extracts and a lot of impurities also exist. In this part, microcystins were spiked in sediments, extracted and then detected by HPLC. Before detecting, the extracts were applied to SPE-Qg cartridge. The feasibility of SPE-HPLC method was estimated by the recoveries of microcystins. The factors such as the enriching ability of Qg cartridge of microcystins, different extracting methods, solvents and microcystin variants were considered. The results showed when the sample is neutral, microcystins-RR and LR were applied to the cartridge, washed out by 15mL methanol (containing 0.1% trifluoroacetic acid, TFA), and then detected by HPLC. The recoveries of those substances are 84.8% and 100%, respectively, which shows C18 cartridge of this kind has a good capacity of enriching and isolating microcystins. Then different extracting methods, solvents and microcystin variants were also examined. By solvent C and stirring repetitious, the recoveries of MC-RR and MC-LR in three sampling zones are 12.9%, 15.7% in Haigeng Bay, 33.8%, 26.4% in Macun Bay and 35.5%, 19.7% in Haidong Bayo Using this method, microcystins, whose concentration was close to the detection limit of HPLC method,were also detected in the sedment of Lake Dianchi.The results suggest, as no suitable solvent exist, SPE-HPLC method can not be used in detecting microcystins in sediments. So a suitable method should be built.2. Improvement of MMPB-GC method in detecting microcystins in solution: The solution containing KMnO4 and NaIO4 can oxidize microcystins quantitatively, forming MMPB at room temperature, as has been used to detect microcystins. One of the advantages the so-called MMPB method is that it can detect microcystins both in free state and covalent bound state. In this part, the influence factors on the recovery of MMPB, such as initial pH, temperature, reaction time and the initial concentration of KMnO4, were investigated. The results revealed that when microcystins oxidized by 0.0156mol/L KMnO4 at 2°C for 1 hour and then at 25°Cfor 2 hours under initial pH 9, the best recovery of MMPB, 93.55%±1%, will be gained and the detection limit was 0.0225/*g.3. Researches on monitoring microcystins in sediment using MMPB-GC method: Based on the method mentioned above, the oxidation of microcystins in sediments was studied in this part. Due to complicated composition of sediments, acidic oxidant, higher initial concentration of KMnO4, and longer reaction time could bring better recovery of MMPB in the oxidation of sediments. So samples were first oxidized by the solution (initial pH=2) containing 0.025mol/L KMnO4 at 2°C for 1 hourand then at 25°Cfor 5 hours. Added the same oxidant for the second time, samples were oxidized till the whole reaction time added up to 24 hours. The recovery of MMPB here was 85.4%±2% and the detection limit was O.ljug. Then the sediment samples from Lake Dianchi were detected, which proved the existence of microcystins in the sediment, ranging from 0.6—6/fg/g.4. The environmental action of microcystins in the sediment of Lake Dianchi: According to the unique natural condition of Lake Dianchi, the detection results demonstrated microcystins, existing in the surface layer of sediments in the north part of the lake and some places near the bank, is made up of two parts, mostly confined in the cells and small amount of absorbed by sediment. The microcystins absorbed by sediment is hardly to be released. But the release tendency of microcystins comfined in the cells will be influenced by the condition of the lake. The microcystin in the cells can exchange and transfer with water. Due to the protection of cells, it is hard to degrade and will be released, poisoning the water when the cells break. The microcystins absorbed by sediments will be degraded and can not contaminate the water again.