Cuicui Tian

A sensitive method for the determination of total microcystins in water and sediment samples by liquid chromatography with fluorescence detection

Microcystins (MCs) are potent hepatotoxins that comprise a family of more than 90 different variants. MCs can bind to matrices, after which they cannot be completely extracted by the solvent. Currently, the MMPB (2-methyl-3-methoxy-4-phenylbutyric acid) method is the only effective way of determining total MCs without solvent extraction. In this study, a sensitive method to determine the total MCs in water and sediment was developed based on the MMPB method. Specifically, MCs were oxidized to MMPB with an improved oxidation reagent (20 mg mL−1 NaIO4, 4000 mg L−1 KMnO4, pH ∼ 9) and a stable MMPB yield of about 35% was obtained for both water and sediment samples. The minimum volume of the oxidation reagent could be determined by the organic content in the matrix. After being concentrated, the MMPB was derivatized with 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-p-toluenesulfonate (BDETS) and detected by liquid chromatography using a fluorescence detector. Quantification limits of MCs in water and sediment samples were 125 ng L−1 and 100 ng g−1 respectively. The method was successfully applied to Lake Dianchi and the soluble MC concentrations determined by this method were correlated well with those obtained by the enzyme-linked immunosorbent assay (ELISA).

Evaluation of the potential of anoxic biodegradation of intracellular and dissolved microcystins in lake sediments

The kinetics of the anoxic biodegradation of intracellular and dissolved microcystin (MCs) and the effects of soluble organic materials on the process were investigated via a series of well-controlled microcosm experiments. The potential for the removal of intracellular and dissolved MCs from lake sediment differed. The dissolved MCs could be degraded to below the detection limit at 20 °C within one to 3 days after a lag phase of 2-6 days under anoxic conditions. The levels of intracellular MCs were also significantly reduced in the sun-dried cyanobacterial samples but not rapidly reduced in fresh cyanobacterial samples until the cells were ruptured. The addition of soluble organic matter enhanced the anoxic biodegradation of MCs. These results indicate that the application of anoxic biodegradation via lake sediments is an effective method to remove dissolved and intracellular MCs and that this process exhibits significant bioremediation potential for the further treatment of cyanobacteria.

Vertical distribution of Fe and Fe(III)-reducing bacteria in the sediments of Lake Donghu, China

In lake sediments, iron (Fe) is the most versatile element, and the redox cycling of Fe has a wide influence on the biogeochemical cycling of organic and inorganic substances. The aim of the present study was to analyze the vertical distribution of Fe and Fe(III)-reducing bacteria (FeRB) in the surface sediment (30 cm) of Lake Donghu, China. At the 3 sites we surveyed, FeRB and Fe(II)-oxidizing bacteria (FeOB) coexisted in anoxic sediments. Geobacter-related FeRB accounted for 5%-31% of the total Bacteria, while Gallionella-related FeOB accounted for only 0.1%-1.3%. A significant correlation between the relative abundance of poorly crystalline Fe and Geobacter spp. suggested that poorly crystalline Fe favored microbial Fe(III) reduction. Poorly crystalline Fe and Geobacter spp. were significantly associated with solid-phase Fe(II) and total inorganic phosphorus levels. Pore water Fe(II) concentrations negatively correlated with NO3(-) at all sites. We concluded that Geobacter spp. were abundant in the sediments of Lake Donghu, and the redox of Fe might participate in the cycling of nitrogen and phosphorus in sediments. These observations provided insight into the roles of microbial Fe cycling in lake sediments.