| With the increase of human industrial and agricultural activities, organic pollution problem of fresh water was getting worse. Polycyclic aromatic hydrocarbons (PAHs) were one class of persistent organic pollutants (POPs) being ubiquitous in water. PAHs were easily accumulated in living organisms, and affected the aquatic organisms. These could lead to eutrophication of water bodies, thereby causing algal bloom and affected aquatic ecosystem and water safety. Therefore, the eutrophication of water bodies caused by PAHs cannot be ignored.In this study, naphthalene, phenanthrene and pyrene were selected as the representive for PAHs, and Microcystis aeruginosa was selected as research material to reveal the effects of PAHs on the growth of Microcystis. The study was focused on the cell growth, photosynthesis and antioxidant systems of Microcystis. Some useful research results were listed as below:1. Fostering M.aeruginosa in the lab was adopted to investigate the effects of naphthalene, phenanthrene and pyrene on the growth and photosynthesis of Microcystis under single and combined conditions. When exposed to single PAH pollution system, the cell density of M.aeruginosa. was reduced with PAHs concentration increaseing. It showed that PAHs had significant inhibitory effects on the growth of M.aeruginosa. The inhibitory effect of phenanthrene was stronger than those of naphthalene and pyrene, and the effects were enhanced by phenanthrene concentration increasing. The growth inhibition rate of M.aeruginosa rised from 26.1% to 84.8% with phenanthrene concentration increased from 0.486 mg·L-1 to 5.24 mg·L-1. Compared with the control group, chlorophyll-a content and photosynthetic rate reduced from 18.2 fg per cell and 0.51 to 9.4 fg per cell and 0.17, respectively. Low doses of naphthalene (0.05 mg·L-1) and pyrene (0.0015 mg·L-1) had promoted the growth of M.aeruginosa, which inferred that low concentration of naphthalene or pyrene would stimulate the growth of M.aeruginosa. Different types of PAHs showed different toxicity to the Microcystis. The damaging effects of phenanthrene in high concentration were irreversible. However, as the time went by, the Microcystis could recover to multiply from the toxicity of naphthalene and pyrene. The compound contamination of naphthalene, phenanthrene and pyrene had much more toxicity than the single one, and enhanced with the increase of concentration. The inhibition ratio of the specific growth rate, chlorophyll-a content and photosynthetic rate in compound contamination were up to 115.3%,74.2% and 85.7%, respectively, all stronger than the single one.2. The effects of PAHs on the competitive growth of M.aeruginosa and Chlorella pyrenoidosa were investigated with the method of mixed culture in the lab. In the system of single PAH contamination, M.aeruginosa showed competitive advantage in competition with C. pyrenoidosa. Cell density and specific growth rate of M.aeruginosa were all higher than C. pyrenoidosa. The toxicity of PAHs to the Microcystis in the mixed culture was lower than that in the single culture. In mixed culture, the effects of high concentration of naphthalene and pyrene on M.aeruginosa changed from growth inhibition to growth stimulation. Compared with the control group, the cell densities increased by 32.4% and 14.2% with the naphthalene and pyrene concentration at 4.05 mg·L-1, respectively. Under the exposure to phenanthrene, specific growth rate of M.aeruginos in the mixed culture had the similar rule to the single one, which decreased to the lowest with the phenanthrene concentration at 5.24 mg·L-1 whose growth inhibition rate was only 22.8%, which was much lower than that of single culture. The cell growth of M.aeruginos was not inhibited completely.3. The effects of three kinds of PAHs on the antioxidant enzyme system activity of M.aeruginos were also investigated in the test. Under the exposure to phenanthrene, SOD and CAT enzyme activities decreased with phenanthrene concentration increaseing, while MDA content increased. The activities of SOD and CAT decreased from 8.71 U·10-8 cells and 27.02 U·10-10cells to 3.05 U·10-8cells and 16.24 U·10-10cells with phenanthrene concentration increased from 0 to 5.24 mg·L-1, respectively, meanwhile MDA content increased from 4.81 nmol·10-10cells to 7.27 nmol·10-10cells. The Microcystis cells were suffered from serious oxidative damage, and the cell function was significantly inhibited. Compared with the control group, the SOD and CAT activities were significantly stimulated when exposed to low doses of naphthalene and pyrene, and there were no significant difference in MDA contents, indicating no obvious oxidative damage to the cells. It was futher suggested that phenanthrene was more toxic to the Microcystis than naphthalene and pyrene. The oxidative damage of Microcystis cells was lighter when exposure to naphthalene and pyrene, as the time went by the cells could recover from naphthalene and pyrene toxicity. |
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